=head1 NAME
-perlguts - Perl's Internal Functions
+perlguts - Introduction to the Perl API
=head1 DESCRIPTION
-This document attempts to describe some of the internal functions of the
-Perl executable. It is far from complete and probably contains many errors.
-Please refer any questions or comments to the author below.
+This document attempts to describe how to use the Perl API, as well as
+containing some info on the basic workings of the Perl core. It is far
+from complete and probably contains many errors. Please refer any
+questions or comments to the author below.
-=head1 Datatypes
+=head1 Variables
+
+=head2 Datatypes
Perl has three typedefs that handle Perl's three main data types:
=head2 What is an "IV"?
-Perl uses a special typedef IV which is large enough to hold either an
-integer or a pointer.
+Perl uses a special typedef IV which is a simple signed integer type that is
+guaranteed to be large enough to hold a pointer (as well as an integer).
+Additionally, there is the UV, which is simply an unsigned IV.
Perl also uses two special typedefs, I32 and I16, which will always be at
-least 32-bits and 16-bits long, respectively.
+least 32-bits and 16-bits long, respectively. (Again, there are U32 and U16,
+as well.)
=head2 Working with SVs
An SV can be created and loaded with one command. There are four types of
-values that can be loaded: an integer value (IV), a double (NV), a string,
-(PV), and another scalar (SV).
+values that can be loaded: an integer value (IV), a double (NV),
+a string (PV), and another scalar (SV).
-The four routines are:
+The six routines are:
SV* newSViv(IV);
SV* newSVnv(double);
- SV* newSVpv(char*, int);
+ SV* newSVpv(const char*, int);
+ SV* newSVpvn(const char*, int);
+ SV* newSVpvf(const char*, ...);
SV* newSVsv(SV*);
-To change the value of an *already-existing* SV, there are five routines:
+To change the value of an *already-existing* SV, there are seven routines:
void sv_setiv(SV*, IV);
+ void sv_setuv(SV*, UV);
void sv_setnv(SV*, double);
- void sv_setpvn(SV*, char*, int)
- void sv_setpv(SV*, char*);
+ void sv_setpv(SV*, const char*);
+ void sv_setpvn(SV*, const char*, int)
+ void sv_setpvf(SV*, const char*, ...);
+ void sv_vsetpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
void sv_setsv(SV*, SV*);
Notice that you can choose to specify the length of the string to be
-assigned by using C<sv_setpvn> or C<newSVpv>, or you may allow Perl to
-calculate the length by using C<sv_setpv> or by specifying 0 as the second
-argument to C<newSVpv>. Be warned, though, that Perl will determine the
-string's length by using C<strlen>, which depends on the string terminating
-with a NUL character.
+assigned by using C<sv_setpvn>, C<newSVpvn>, or C<newSVpv>, or you may
+allow Perl to calculate the length by using C<sv_setpv> or by specifying
+0 as the second argument to C<newSVpv>. Be warned, though, that Perl will
+determine the string's length by using C<strlen>, which depends on the
+string terminating with a NUL character.
+
+The arguments of C<sv_setpvf> are processed like C<sprintf>, and the
+formatted output becomes the value.
+
+C<sv_vsetpvfn> is an analogue of C<vsprintf>, but it allows you to specify
+either a pointer to a variable argument list or the address and length of
+an array of SVs. The last argument points to a boolean; on return, if that
+boolean is true, then locale-specific information has been used to format
+the string, and the string's contents are therefore untrustworthy (see
+L<perlsec>). This pointer may be NULL if that information is not
+important. Note that this function requires you to specify the length of
+the format.
+
+STRLEN is an integer type (Size_t, usually defined as size_t in
+config.h) guaranteed to be large enough to represent the size of
+any string that perl can handle.
+
+The C<sv_set*()> functions are not generic enough to operate on values
+that have "magic". See L<Magic Virtual Tables> later in this document.
+
+All SVs that contain strings should be terminated with a NUL character.
+If it is not NUL-terminated there is a risk of
+core dumps and corruptions from code which passes the string to C
+functions or system calls which expect a NUL-terminated string.
+Perl's own functions typically add a trailing NUL for this reason.
+Nevertheless, you should be very careful when you pass a string stored
+in an SV to a C function or system call.
To access the actual value that an SV points to, you can use the macros:
SvIV(SV*)
+ SvUV(SV*)
SvNV(SV*)
SvPV(SV*, STRLEN len)
+ SvPV_nolen(SV*)
-which will automatically coerce the actual scalar type into an IV, double,
+which will automatically coerce the actual scalar type into an IV, UV, double,
or string.
In the C<SvPV> macro, the length of the string returned is placed into the
-variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
-care what the length of the data is, use the global variable C<na>. Remember,
-however, that Perl allows arbitrary strings of data that may both contain
-NULs and not be terminated by a NUL.
-
-If you simply want to know if the scalar value is TRUE, you can use:
+variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do
+not care what the length of the data is, use the C<SvPV_nolen> macro.
+Historically the C<SvPV> macro with the global variable C<PL_na> has been
+used in this case. But that can be quite inefficient because C<PL_na> must
+be accessed in thread-local storage in threaded Perl. In any case, remember
+that Perl allows arbitrary strings of data that may both contain NULs and
+might not be terminated by a NUL.
+
+Also remember that C doesn't allow you to safely say C<foo(SvPV(s, len),
+len);>. It might work with your compiler, but it won't work for everyone.
+Break this sort of statement up into separate assignments:
+
+ SV *s;
+ STRLEN len;
+ char * ptr;
+ ptr = SvPV(s, len);
+ foo(ptr, len);
+
+If you want to know if the scalar value is TRUE, you can use:
SvTRUE(SV*)
which will determine if more memory needs to be allocated. If so, it will
call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
-decrease, the allocated memory of an SV.
+decrease, the allocated memory of an SV and that it does not automatically
+add a byte for the a trailing NUL (perl's own string functions typically do
+C<SvGROW(sv, len + 1)>).
If you have an SV and want to know what kind of data Perl thinks is stored
in it, you can use the following macros to check the type of SV you have.
If you want to append something to the end of string stored in an C<SV*>,
you can use the following functions:
- void sv_catpv(SV*, char*);
- void sv_catpvn(SV*, char*, int);
+ void sv_catpv(SV*, const char*);
+ void sv_catpvn(SV*, const char*, STRLEN);
+ void sv_catpvf(SV*, const char*, ...);
+ void sv_vcatpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
void sv_catsv(SV*, SV*);
The first function calculates the length of the string to be appended by
using C<strlen>. In the second, you specify the length of the string
-yourself. The third function extends the string stored in the first SV
-with the string stored in the second SV. It also forces the second SV to
-be interpreted as a string.
+yourself. The third function processes its arguments like C<sprintf> and
+appends the formatted output. The fourth function works like C<vsprintf>.
+You can specify the address and length of an array of SVs instead of the
+va_list argument. The fifth function extends the string stored in the first
+SV with the string stored in the second SV. It also forces the second SV
+to be interpreted as a string.
+
+The C<sv_cat*()> functions are not generic enough to operate on values that
+have "magic". See L<Magic Virtual Tables> later in this document.
If you know the name of a scalar variable, you can get a pointer to its SV
by using the following:
- SV* perl_get_sv("varname", FALSE);
+ SV* get_sv("package::varname", FALSE);
This returns NULL if the variable does not exist.
SvOK(SV*)
-The scalar C<undef> value is stored in an SV instance called C<sv_undef>. Its
+The scalar C<undef> value is stored in an SV instance called C<PL_sv_undef>. Its
address can be used whenever an C<SV*> is needed.
-There are also the two values C<sv_yes> and C<sv_no>, which contain Boolean
-TRUE and FALSE values, respectively. Like C<sv_undef>, their addresses can
+There are also the two values C<PL_sv_yes> and C<PL_sv_no>, which contain Boolean
+TRUE and FALSE values, respectively. Like C<PL_sv_undef>, their addresses can
be used whenever an C<SV*> is needed.
-Do not be fooled into thinking that C<(SV *) 0> is the same as C<&sv_undef>.
+Do not be fooled into thinking that C<(SV *) 0> is the same as C<&PL_sv_undef>.
Take this code:
SV* sv = (SV*) 0;
sv_setsv(ST(0), sv);
This code tries to return a new SV (which contains the value 42) if it should
-return a real value, or undef otherwise. Instead it has returned a null
+return a real value, or undef otherwise. Instead it has returned a NULL
pointer which, somewhere down the line, will cause a segmentation violation,
-bus error, or just plain weird results. Change the zero to C<&sv_undef> in
-the first line and all will be well.
+bus error, or just weird results. Change the zero to C<&PL_sv_undef> in the first
+line and all will be well.
To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
-call is not necessary. See the section on L<Mortality>.
+call is not necessary (see L<Reference Counts and Mortality>).
+
+=head2 Offsets
+
+Perl provides the function C<sv_chop> to efficiently remove characters
+from the beginning of a string; you give it an SV and a pointer to
+somewhere inside the PV, and it discards everything before the
+pointer. The efficiency comes by means of a little hack: instead of
+actually removing the characters, C<sv_chop> sets the flag C<OOK>
+(offset OK) to signal to other functions that the offset hack is in
+effect, and it puts the number of bytes chopped off into the IV field
+of the SV. It then moves the PV pointer (called C<SvPVX>) forward that
+many bytes, and adjusts C<SvCUR> and C<SvLEN>.
+
+Hence, at this point, the start of the buffer that we allocated lives
+at C<SvPVX(sv) - SvIV(sv)> in memory and the PV pointer is pointing
+into the middle of this allocated storage.
+
+This is best demonstrated by example:
+
+ % ./perl -Ilib -MDevel::Peek -le '$a="12345"; $a=~s/.//; Dump($a)'
+ SV = PVIV(0x8128450) at 0x81340f0
+ REFCNT = 1
+ FLAGS = (POK,OOK,pPOK)
+ IV = 1 (OFFSET)
+ PV = 0x8135781 ( "1" . ) "2345"\0
+ CUR = 4
+ LEN = 5
+
+Here the number of bytes chopped off (1) is put into IV, and
+C<Devel::Peek::Dump> helpfully reminds us that this is an offset. The
+portion of the string between the "real" and the "fake" beginnings is
+shown in parentheses, and the values of C<SvCUR> and C<SvLEN> reflect
+the fake beginning, not the real one.
+
+Something similar to the offset hack is performed on AVs to enable
+efficient shifting and splicing off the beginning of the array; while
+C<AvARRAY> points to the first element in the array that is visible from
+Perl, C<AvALLOC> points to the real start of the C array. These are
+usually the same, but a C<shift> operation can be carried out by
+increasing C<AvARRAY> by one and decreasing C<AvFILL> and C<AvLEN>.
+Again, the location of the real start of the C array only comes into
+play when freeing the array. See C<av_shift> in F<av.c>.
=head2 What's Really Stored in an SV?
Recall that the usual method of determining the type of scalar you have is
-to use C<Sv*OK> macros. Since a scalar can be both a number and a string,
+to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
usually these macros will always return TRUE and calling the C<Sv*V>
macros will do the appropriate conversion of string to integer/double or
integer/double to string.
These will tell you if you truly have an integer, double, or string pointer
stored in your SV. The "p" stands for private.
-In general, though, it's best to just use the C<Sv*V> macros.
+The are various ways in which the private and public flags may differ.
+For example, a tied SV may have a valid underlying value in the IV slot
+(so SvIOKp is true), but the data should be accessed via the FETCH
+routine rather than directly, so SvIOK is false. Another is when
+numeric conversion has occured and precision has been lost: only the
+private flag is set on 'lossy' values. So when an NV is converted to an
+IV with loss, SvIOKp, SvNOKp and SvNOK will be set, while SvIOK wont be.
+
+In general, though, it's best to use the C<Sv*V> macros.
=head2 Working with AVs
-There are two ways to create and load an AV. The first method just creates
-an empty AV:
+There are two ways to create and load an AV. The first method creates an
+empty AV:
AV* newAV();
AV* av_make(I32 num, SV **ptr);
-The second argument points to an array containing C<num> C<SV*>s. Once the
+The second argument points to an array containing C<num> C<SV*>'s. Once the
AV has been created, the SVs can be destroyed, if so desired.
Once the AV has been created, the following operations are possible on AVs:
Here are some other functions:
- I32 av_len(AV*); /* Returns highest index value in array */
-
+ I32 av_len(AV*);
SV** av_fetch(AV*, I32 key, I32 lval);
- /* Fetches value at key offset, but it stores an undef value
- at the offset if lval is non-zero */
SV** av_store(AV*, I32 key, SV* val);
- /* Stores val at offset key */
-Take note that C<av_fetch> and C<av_store> return C<SV**>s, not C<SV*>s.
+The C<av_len> function returns the highest index value in array (just
+like $#array in Perl). If the array is empty, -1 is returned. The
+C<av_fetch> function returns the value at index C<key>, but if C<lval>
+is non-zero, then C<av_fetch> will store an undef value at that index.
+The C<av_store> function stores the value C<val> at index C<key>, and does
+not increment the reference count of C<val>. Thus the caller is responsible
+for taking care of that, and if C<av_store> returns NULL, the caller will
+have to decrement the reference count to avoid a memory leak. Note that
+C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s as their
+return value.
void av_clear(AV*);
- /* Clear out all elements, but leave the array */
void av_undef(AV*);
- /* Undefines the array, removing all elements */
void av_extend(AV*, I32 key);
- /* Extend the array to a total of key elements */
+
+The C<av_clear> function deletes all the elements in the AV* array, but
+does not actually delete the array itself. The C<av_undef> function will
+delete all the elements in the array plus the array itself. The
+C<av_extend> function extends the array so that it contains at least C<key+1>
+elements. If C<key+1> is less than the currently allocated length of the array,
+then nothing is done.
If you know the name of an array variable, you can get a pointer to its AV
by using the following:
- AV* perl_get_av("varname", FALSE);
+ AV* get_av("package::varname", FALSE);
This returns NULL if the variable does not exist.
+See L<Understanding the Magic of Tied Hashes and Arrays> for more
+information on how to use the array access functions on tied arrays.
+
=head2 Working with HVs
To create an HV, you use the following routine:
Once the HV has been created, the following operations are possible on HVs:
- SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
- SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
+ SV** hv_store(HV*, const char* key, U32 klen, SV* val, U32 hash);
+ SV** hv_fetch(HV*, const char* key, U32 klen, I32 lval);
-The C<klen> parameter is the length of the key being passed in. The C<val>
-argument contains the SV pointer to the scalar being stored, and C<hash> is
-the pre-computed hash value (zero if you want C<hv_store> to calculate it
-for you). The C<lval> parameter indicates whether this fetch is actually a
-part of a store operation.
+The C<klen> parameter is the length of the key being passed in (Note that
+you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
+length of the key). The C<val> argument contains the SV pointer to the
+scalar being stored, and C<hash> is the precomputed hash value (zero if
+you want C<hv_store> to calculate it for you). The C<lval> parameter
+indicates whether this fetch is actually a part of a store operation, in
+which case a new undefined value will be added to the HV with the supplied
+key and C<hv_fetch> will return as if the value had already existed.
-Remember that C<hv_store> and C<hv_fetch> return C<SV**>s and not just
-C<SV*>. In order to access the scalar value, you must first dereference
-the return value. However, you should check to make sure that the return
-value is not NULL before dereferencing it.
+Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
+C<SV*>. To access the scalar value, you must first dereference the return
+value. However, you should check to make sure that the return value is
+not NULL before dereferencing it.
These two functions check if a hash table entry exists, and deletes it.
- bool hv_exists(HV*, char* key, U32 klen);
- SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
+ bool hv_exists(HV*, const char* key, U32 klen);
+ SV* hv_delete(HV*, const char* key, U32 klen, I32 flags);
+
+If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
+create and return a mortal copy of the deleted value.
And more miscellaneous functions:
void hv_clear(HV*);
- /* Clears all entries in hash table */
void hv_undef(HV*);
- /* Undefines the hash table */
+
+Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
+table but does not actually delete the hash table. The C<hv_undef> deletes
+both the entries and the hash table itself.
Perl keeps the actual data in linked list of structures with a typedef of HE.
These contain the actual key and value pointers (plus extra administrative
/* Get the key from an HE structure and also return
the length of the key string */
SV* hv_iterval(HV*, HE* entry);
- /* Return a SV pointer to the value of the HE
+ /* Return an SV pointer to the value of the HE
structure */
SV* hv_iternextsv(HV*, char** key, I32* retlen);
/* This convenience routine combines hv_iternext,
If you know the name of a hash variable, you can get a pointer to its HV
by using the following:
- HV* perl_get_hv("varname", FALSE);
+ HV* get_hv("package::varname", FALSE);
This returns NULL if the variable does not exist.
-The hash algorithm, for those who are interested, is:
+The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
- i = klen;
hash = 0;
- s = key;
- while (i--)
- hash = hash * 33 + *s++;
+ while (klen--)
+ hash = (hash * 33) + *key++;
+ hash = hash + (hash >> 5); /* after 5.6 */
+
+The last step was added in version 5.6 to improve distribution of
+lower bits in the resulting hash value.
+
+See L<Understanding the Magic of Tied Hashes and Arrays> for more
+information on how to use the hash access functions on tied hashes.
+
+=head2 Hash API Extensions
+
+Beginning with version 5.004, the following functions are also supported:
+
+ HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
+ HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
+
+ bool hv_exists_ent (HV* tb, SV* key, U32 hash);
+ SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
+
+ SV* hv_iterkeysv (HE* entry);
+
+Note that these functions take C<SV*> keys, which simplifies writing
+of extension code that deals with hash structures. These functions
+also allow passing of C<SV*> keys to C<tie> functions without forcing
+you to stringify the keys (unlike the previous set of functions).
+
+They also return and accept whole hash entries (C<HE*>), making their
+use more efficient (since the hash number for a particular string
+doesn't have to be recomputed every time). See L<perlapi> for detailed
+descriptions.
+
+The following macros must always be used to access the contents of hash
+entries. Note that the arguments to these macros must be simple
+variables, since they may get evaluated more than once. See
+L<perlapi> for detailed descriptions of these macros.
+
+ HePV(HE* he, STRLEN len)
+ HeVAL(HE* he)
+ HeHASH(HE* he)
+ HeSVKEY(HE* he)
+ HeSVKEY_force(HE* he)
+ HeSVKEY_set(HE* he, SV* sv)
+
+These two lower level macros are defined, but must only be used when
+dealing with keys that are not C<SV*>s:
+
+ HeKEY(HE* he)
+ HeKLEN(HE* he)
+
+Note that both C<hv_store> and C<hv_store_ent> do not increment the
+reference count of the stored C<val>, which is the caller's responsibility.
+If these functions return a NULL value, the caller will usually have to
+decrement the reference count of C<val> to avoid a memory leak.
=head2 References
References are a special type of scalar that point to other data types
(including references).
-To create a reference, use the following command:
+To create a reference, use either of the following functions:
+
+ SV* newRV_inc((SV*) thing);
+ SV* newRV_noinc((SV*) thing);
- SV* newRV((SV*) thing);
+The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
+functions are identical except that C<newRV_inc> increments the reference
+count of the C<thing>, while C<newRV_noinc> does not. For historical
+reasons, C<newRV> is a synonym for C<newRV_inc>.
-The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. Once
-you have a reference, you can use the following macro to dereference the
-reference:
+Once you have a reference, you can use the following macro to dereference
+the reference:
SvRV(SV*)
SvROK(SV*)
-To actually discover what the reference refers to, you must use the following
-macro and then check the value returned.
+To discover what type of value the reference refers to, use the following
+macro and then check the return value.
SvTYPE(SvRV(SV*))
SVt_IV Scalar
SVt_NV Scalar
SVt_PV Scalar
+ SVt_RV Scalar
SVt_PVAV Array
SVt_PVHV Hash
SVt_PVCV Code
- SVt_PVMG Blessed Scalar
+ SVt_PVGV Glob (possible a file handle)
+ SVt_PVMG Blessed or Magical Scalar
+
+ See the sv.h header file for more details.
=head2 Blessed References and Class Objects
SV* sv_bless(SV* sv, HV* stash);
The C<sv> argument must be a reference. The C<stash> argument specifies
-which class the reference will belong to. See the section on L<Stashes>
-for information on converting class names into stashes.
+which class the reference will belong to. See
+L<Stashes and Globs> for information on converting class names into stashes.
/* Still under construction */
Upgrades rv to reference if not already one. Creates new SV for rv to
-point to.
-If classname is non-null, the SV is blessed into the specified class.
-SV is returned.
-
- SV* newSVrv(SV* rv, char* classname);
-
-Copies integer or double into an SV whose reference is rv. SV is blessed
-if classname is non-null.
-
- SV* sv_setref_iv(SV* rv, char* classname, IV iv);
- SV* sv_setref_nv(SV* rv, char* classname, NV iv);
-
-Copies pointer (I<not a string!>) into an SV whose reference is rv.
-SV is blessed if classname is non-null.
-
- SV* sv_setref_pv(SV* rv, char* classname, PV iv);
-
-Copies string into an SV whose reference is rv.
-Set length to 0 to let Perl calculate the string length.
-SV is blessed if classname is non-null.
-
- SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
-
- int sv_isa(SV* sv, char* name);
- int sv_isobject(SV* sv);
-
-=head1 Creating New Variables
-
-To create a new Perl variable, which can be accessed from your Perl script,
-use the following routines, depending on the variable type.
-
- SV* perl_get_sv("varname", TRUE);
- AV* perl_get_av("varname", TRUE);
- HV* perl_get_hv("varname", TRUE);
-
-Notice the use of TRUE as the second parameter. The new variable can now
-be set, using the routines appropriate to the data type.
-
-There are additional bits that may be OR'ed with the TRUE argument to enable
-certain extra features. Those bits are:
-
- 0x02 Marks the variable as multiply defined, thus preventing the
- "Identifier <varname> used only once: possible typo" warning.
- 0x04 Issues a "Had to create <varname> unexpectedly" warning if
- the variable didn't actually exist. This is useful if
- you expected the variable to already exist and want to propagate
- this warning back to the user.
-
-If the C<varname> argument does not contain a package specifier, it is
-created in the current package.
-
-=head1 XSUBs and the Argument Stack
-
-The XSUB mechanism is a simple way for Perl programs to access C subroutines.
-An XSUB routine will have a stack that contains the arguments from the Perl
-program, and a way to map from the Perl data structures to a C equivalent.
-
-The stack arguments are accessible through the C<ST(n)> macro, which returns
-the C<n>'th stack argument. Argument 0 is the first argument passed in the
-Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
-an C<SV*> is used.
-
-Most of the time, output from the C routine can be handled through use of
-the RETVAL and OUTPUT directives. However, there are some cases where the
-argument stack is not already long enough to handle all the return values.
-An example is the POSIX tzname() call, which takes no arguments, but returns
-two, the local timezone's standard and summer time abbreviations.
-
-To handle this situation, the PPCODE directive is used and the stack is
-extended using the macro:
-
- EXTEND(sp, num);
-
-where C<sp> is the stack pointer, and C<num> is the number of elements the
-stack should be extended by.
-
-Now that there is room on the stack, values can be pushed on it using the
-macros to push IVs, doubles, strings, and SV pointers respectively:
-
- PUSHi(IV)
- PUSHn(double)
- PUSHp(char*, I32)
- PUSHs(SV*)
-
-And now the Perl program calling C<tzname>, the two values will be assigned
-as in:
-
- ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
-
-An alternate (and possibly simpler) method to pushing values on the stack is
-to use the macros:
-
- XPUSHi(IV)
- XPUSHn(double)
- XPUSHp(char*, I32)
- XPUSHs(SV*)
-
-These macros automatically adjust the stack for you, if needed. Thus, you
-do not need to call C<EXTEND> to extend the stack.
-
-For more information, consult L<perlxs>.
-
-=head1 Localizing Changes
-
-Perl has a very handy construction
-
- {
- local $var = 2;
- ...
- }
-
-This construction is I<approximately> equivalent to
-
- {
- my $oldvar = $var;
- $var = 2;
- ...
- $var = $oldvar;
- }
-
-The biggest difference is that the first construction would would
-reinstate the initial value of $var, irrespective of how control exits
-the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
-more efficient as well.
-
-There is a way to achieve a similar task from C via Perl API: create a
-I<pseudo-block>, and arrange for some changes to be automatically
-undone at the end of it, either explicit, or via a non-local exit (via
-die()). A I<block>-like construct is created by a pair of
-C<ENTER>/C<LEAVE> macros (see L<perlcall/EXAMPLE/"Returning a
-Scalar">). Such a construct may be created specially for some
-important localized task, or an existing one (like boundaries of
-enclosing Perl subroutine/block, or an existing pair for freeing TMPs)
-may be used. (In the second case the overhead of additional
-localization must be almost negligible.) Note that any XSUB is
-automatically enclosed in an C<ENTER>/C<LEAVE> pair.
-
-Inside such a I<pseudo-block> the following service is available:
-
-=over
-
-=item C<SAVEINT(int i)>
-
-=item C<SAVEIV(IV i)>
-
-=item C<SAVEI16(I16 i)>
-
-=item C<SAVEI32(I32 i)>
-
-=item C<SAVELONG(long i)>
-
-These macros arrange things to restore the value of integer variable
-C<i> at the end of enclosing I<pseudo-block>.
-
-=item C<SAVESPTR(p)>
-
-=item C<SAVEPPTR(s)>
-
-These macros arrange things to restore the value of pointers C<s> and
-C<p>. C<p> must be a pointer of a type which survives conversion to
-C<SV*> and back, C<s> should be able to survive conversion to C<char*>
-and back.
-
-=item C<SAVEFREESV(SV *sv)>
-
-The refcount of C<sv> would be decremented at the end of
-I<pseudo-block>. This is similar to C<sv_2mortal>, which should (?) be
-used instead.
-
-=item C<SAVEFREEOP(OP *op)>
+point to. If C<classname> is non-null, the SV is blessed into the specified
+class. SV is returned.
-The C<OP *> is op_free()ed at the end of I<pseudo-block>.
-
-=item C<SAVEFREEPV(p)>
-
-The chunk of memory which is pointed to by C<p> is Safefree()ed at the
-end of I<pseudo-block>.
-
-=item C<SAVECLEARSV(SV *sv)>
-
-Clears a slot in the current scratchpad which corresponds to C<sv> at
-the end of I<pseudo-block>.
-
-=item C<SAVEDELETE(HV *hv, char *key, I32 length)>
-
-The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
-string pointed to by C<key> is Safefree()ed. If one has a I<key> in
-short-lived storage, the corresponding string may be reallocated like
-this:
-
- SAVEDELETE(defstash, savepv(tmpbuf), strlen(tmpbuf));
-
-=item C<SAVEDESTRUCTOR(f,p)>
-
-At the end of I<pseudo-block> the function C<f> is called with the
-only argument (of type C<void*>) C<p>.
-
-=item C<SAVESTACK_POS()>
+ SV* newSVrv(SV* rv, const char* classname);
-The current offset on the Perl internal stack (cf. C<SP>) is restored
-at the end of I<pseudo-block>.
+Copies integer, unsigned integer or double into an SV whose reference is C<rv>. SV is blessed
+if C<classname> is non-null.
-=back
+ SV* sv_setref_iv(SV* rv, const char* classname, IV iv);
+ SV* sv_setref_uv(SV* rv, const char* classname, UV uv);
+ SV* sv_setref_nv(SV* rv, const char* classname, NV iv);
-The following API list contains functions, thus one needs to
-provide pointers to the modifiable data explicitly (either C pointers,
-or Perlish C<GV *>s):
+Copies the pointer value (I<the address, not the string!>) into an SV whose
+reference is rv. SV is blessed if C<classname> is non-null.
-=over
+ SV* sv_setref_pv(SV* rv, const char* classname, PV iv);
-=item C<SV* save_scalar(GV *gv)>
+Copies string into an SV whose reference is C<rv>. Set length to 0 to let
+Perl calculate the string length. SV is blessed if C<classname> is non-null.
-Equivalent to Perl code C<local $gv>.
+ SV* sv_setref_pvn(SV* rv, const char* classname, PV iv, STRLEN length);
-=item C<AV* save_ary(GV *gv)>
+Tests whether the SV is blessed into the specified class. It does not
+check inheritance relationships.
-=item C<HV* save_hash(GV *gv)>
+ int sv_isa(SV* sv, const char* name);
-Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
+Tests whether the SV is a reference to a blessed object.
-=item C<void save_item(SV *item)>
+ int sv_isobject(SV* sv);
-Duplicates the current value of C<SV>, on the exit from the current
-C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
-using the stored value.
+Tests whether the SV is derived from the specified class. SV can be either
+a reference to a blessed object or a string containing a class name. This
+is the function implementing the C<UNIVERSAL::isa> functionality.
-=item C<void save_list(SV **sarg, I32 maxsarg)>
+ bool sv_derived_from(SV* sv, const char* name);
-A variant of C<save_item> which takes multiple arguments via an array
-C<sarg> of C<SV*> of length C<maxsarg>.
+To check if you've got an object derived from a specific class you have
+to write:
-=item C<SV* save_svref(SV **sptr)>
+ if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... }
-Similar to C<save_scalar>, but will reinstate a C<SV *>.
+=head2 Creating New Variables
-=item C<void save_aptr(AV **aptr)>
+To create a new Perl variable with an undef value which can be accessed from
+your Perl script, use the following routines, depending on the variable type.
-=item C<void save_hptr(HV **hptr)>
+ SV* get_sv("package::varname", TRUE);
+ AV* get_av("package::varname", TRUE);
+ HV* get_hv("package::varname", TRUE);
-Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
+Notice the use of TRUE as the second parameter. The new variable can now
+be set, using the routines appropriate to the data type.
-=item C<void save_nogv(GV *gv)>
+There are additional macros whose values may be bitwise OR'ed with the
+C<TRUE> argument to enable certain extra features. Those bits are:
-Will postpone destruction of a I<stub> glob.
+ GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
+ "Name <varname> used only once: possible typo" warning.
+ GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
+ the variable did not exist before the function was called.
-=back
+If you do not specify a package name, the variable is created in the current
+package.
-=head1 Mortality
+=head2 Reference Counts and Mortality
-Perl uses an reference count-driven garbage collection mechanism. SV's,
-AV's, or HV's (xV for short in the following) start their life with a
+Perl uses a reference count-driven garbage collection mechanism. SVs,
+AVs, or HVs (xV for short in the following) start their life with a
reference count of 1. If the reference count of an xV ever drops to 0,
-then they will be destroyed and their memory made available for reuse.
+then it will be destroyed and its memory made available for reuse.
This normally doesn't happen at the Perl level unless a variable is
-undef'ed. At the internal level, however, reference counts can be
+undef'ed or the last variable holding a reference to it is changed or
+overwritten. At the internal level, however, reference counts can be
manipulated with the following macros:
int SvREFCNT(SV* sv);
- void SvREFCNT_inc(SV* sv);
+ SV* SvREFCNT_inc(SV* sv);
void SvREFCNT_dec(SV* sv);
However, there is one other function which manipulates the reference
-count of its argument. The C<newRV> function, as you should recall,
-creates a reference to the specified argument. As a side effect, it
-increments the argument's reference count, which is ok in most
-circumstances. But imagine you want to return a reference from an XS
-function. You create a new SV which initially has a reference count
-of 1. Then you call C<newRV>, passing the just-created SV. This returns
-the reference as a new SV, but the reference count of the SV you passed
-to C<newRV> has been incremented to 2. Now you return the reference and
-forget about the SV. But Perl hasn't! Whenever the returned reference
-is destroyed, the reference count of the original SV is decreased to 1
-and nothing happens. The SV will hang around without any way to access
-it until Perl itself terminates. This is a memory leak.
-
-The correct procedure, then, is to call C<SvREFCNT_dec> on the SV after
-C<newRV> has returned. Then, if and when the reference is destroyed,
-the reference count of the SV will go to 0 and also be destroyed, stopping
-any memory leak.
-
-There are some convenience functions available that can help with this
-process. These functions introduce the concept of "mortality". An xV
-that is mortal has had its reference count marked to be decremented,
-but not actually decremented, until the "current context" is left.
-Generally the "current context" means a single Perl statement, such as
-a call to an XSUB function.
+count of its argument. The C<newRV_inc> function, you will recall,
+creates a reference to the specified argument. As a side effect,
+it increments the argument's reference count. If this is not what
+you want, use C<newRV_noinc> instead.
+
+For example, imagine you want to return a reference from an XSUB function.
+Inside the XSUB routine, you create an SV which initially has a reference
+count of one. Then you call C<newRV_inc>, passing it the just-created SV.
+This returns the reference as a new SV, but the reference count of the
+SV you passed to C<newRV_inc> has been incremented to two. Now you
+return the reference from the XSUB routine and forget about the SV.
+But Perl hasn't! Whenever the returned reference is destroyed, the
+reference count of the original SV is decreased to one and nothing happens.
+The SV will hang around without any way to access it until Perl itself
+terminates. This is a memory leak.
+
+The correct procedure, then, is to use C<newRV_noinc> instead of
+C<newRV_inc>. Then, if and when the last reference is destroyed,
+the reference count of the SV will go to zero and it will be destroyed,
+stopping any memory leak.
+
+There are some convenience functions available that can help with the
+destruction of xVs. These functions introduce the concept of "mortality".
+An xV that is mortal has had its reference count marked to be decremented,
+but not actually decremented, until "a short time later". Generally the
+term "short time later" means a single Perl statement, such as a call to
+an XSUB function. The actual determinant for when mortal xVs have their
+reference count decremented depends on two macros, SAVETMPS and FREETMPS.
+See L<perlcall> and L<perlxs> for more details on these macros.
"Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
However, if you mortalize a variable twice, the reference count will
later be decremented twice.
-You should be careful about creating mortal variables. Strange things
-can happen if you make the same value mortal within multiple contexts,
-or if you make a variable mortal multiple times. Doing the latter can
-cause a variable to become invalid prematurely.
+"Mortal" SVs are mainly used for SVs that are placed on perl's stack.
+For example an SV which is created just to pass a number to a called sub
+is made mortal to have it cleaned up automatically when stack is popped.
+Similarly results returned by XSUBs (which go in the stack) are often
+made mortal.
To create a mortal variable, use the functions:
SV* sv_2mortal(SV*)
SV* sv_mortalcopy(SV*)
-The first call creates a mortal SV, the second converts an existing SV to
-a mortal SV, the third creates a mortal copy of an existing SV (possibly
-destroying it in the process).
+The first call creates a mortal SV (with no value), the second converts an existing
+SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
+third creates a mortal copy of an existing SV.
+Because C<sv_newmortal> gives the new SV no value,it must normally be given one
+via C<sv_setpv>, C<sv_setiv> etc. :
-The mortal routines are not just for SVs -- AVs and HVs can be made mortal
-by passing their address (and casting them to C<SV*>) to the C<sv_2mortal> or
-C<sv_mortalcopy> routines.
+ SV *tmp = sv_newmortal();
+ sv_setiv(tmp, an_integer);
-I<From Ilya:>
-Beware that the sv_2mortal() call is eventually equivalent to
-svREFCNT_dec(). A value can happily be mortal in two different contexts,
-and it will be svREFCNT_dec()ed twice, once on exit from these
-contexts. It can also be mortal twice in the same context. This means
-that you should be very careful to make a value mortal exactly as many
-times as it is needed. The value that go to the Perl stack I<should>
-be mortal.
+As that is multiple C statements it is quite common so see this idiom instead:
+ SV *tmp = sv_2mortal(newSViv(an_integer));
-=head1 Stashes
-A stash is a hash table (associative array) that contains all of the
-different objects that are contained within a package. Each key of the
-stash is a symbol name (shared by all the different types of objects
-that have the same name), and each value in the hash table is called a
-GV (for Glob Value). This GV in turn contains references to the various
-objects of that name, including (but not limited to) the following:
+You should be careful about creating mortal variables. Strange things
+can happen if you make the same value mortal within multiple contexts,
+or if you make a variable mortal multiple times. Thinking of "Mortalization"
+as deferred C<SvREFCNT_dec> should help to minimize such problems.
+For example if you are passing an SV which you I<know> has high enough REFCNT
+to survive its use on the stack you need not do any mortalization.
+If you are not sure then doing an C<SvREFCNT_inc> and C<sv_2mortal>, or
+making a C<sv_mortalcopy> is safer.
+
+The mortal routines are not just for SVs -- AVs and HVs can be
+made mortal by passing their address (type-casted to C<SV*>) to the
+C<sv_2mortal> or C<sv_mortalcopy> routines.
+
+=head2 Stashes and Globs
+
+A "stash" is a hash that contains all of the different objects that
+are contained within a package. Each key of the stash is a symbol
+name (shared by all the different types of objects that have the same
+name), and each value in the hash table is a GV (Glob Value). This GV
+in turn contains references to the various objects of that name,
+including (but not limited to) the following:
Scalar Value
Array Value
Hash Value
- File Handle
- Directory Handle
+ I/O Handle
Format
Subroutine
-Perl stores various stashes in a separate GV structure (for global
-variable) but represents them with an HV structure. The keys in this
-larger GV are the various package names; the values are the C<GV*>s
-which are stashes. It may help to think of a stash purely as an HV,
-and that the term "GV" means the global variable hash.
+There is a single stash called "PL_defstash" that holds the items that exist
+in the "main" package. To get at the items in other packages, append the
+string "::" to the package name. The items in the "Foo" package are in
+the stash "Foo::" in PL_defstash. The items in the "Bar::Baz" package are
+in the stash "Baz::" in "Bar::"'s stash.
To get the stash pointer for a particular package, use the function:
- HV* gv_stashpv(char* name, I32 create)
+ HV* gv_stashpv(const char* name, I32 create)
HV* gv_stashsv(SV*, I32 create)
The first function takes a literal string, the second uses the string stored
char* HvNAME(HV* stash);
-If you need to return a blessed value to your Perl script, you can use the
-following function:
+If you need to bless or re-bless an object you can use the following
+function:
SV* sv_bless(SV*, HV* stash)
For more information on references and blessings, consult L<perlref>.
-=head1 Magic
+=head2 Double-Typed SVs
+
+Scalar variables normally contain only one type of value, an integer,
+double, pointer, or reference. Perl will automatically convert the
+actual scalar data from the stored type into the requested type.
+
+Some scalar variables contain more than one type of scalar data. For
+example, the variable C<$!> contains either the numeric value of C<errno>
+or its string equivalent from either C<strerror> or C<sys_errlist[]>.
+
+To force multiple data values into an SV, you must do two things: use the
+C<sv_set*v> routines to add the additional scalar type, then set a flag
+so that Perl will believe it contains more than one type of data. The
+four macros to set the flags are:
+
+ SvIOK_on
+ SvNOK_on
+ SvPOK_on
+ SvROK_on
+
+The particular macro you must use depends on which C<sv_set*v> routine
+you called first. This is because every C<sv_set*v> routine turns on
+only the bit for the particular type of data being set, and turns off
+all the rest.
+
+For example, to create a new Perl variable called "dberror" that contains
+both the numeric and descriptive string error values, you could use the
+following code:
+
+ extern int dberror;
+ extern char *dberror_list;
+
+ SV* sv = get_sv("dberror", TRUE);
+ sv_setiv(sv, (IV) dberror);
+ sv_setpv(sv, dberror_list[dberror]);
+ SvIOK_on(sv);
+
+If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
+macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
+
+=head2 Magic Variables
[This section still under construction. Ignore everything here. Post no
bills. Everything not permitted is forbidden.]
Any SV may be magical, that is, it has special features that a normal
SV does not have. These features are stored in the SV structure in a
-linked list of C<struct magic>s, typedef'ed to C<MAGIC>.
+linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
struct magic {
MAGIC* mg_moremagic;
Perl adds magic to an SV using the sv_magic function:
- void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
+ void sv_magic(SV* sv, SV* obj, int how, const char* name, I32 namlen);
The C<sv> argument is a pointer to the SV that is to acquire a new magical
feature.
If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
-set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
-it to the beginning of the linked list of magical features. Any prior
-entry of the same type of magic is deleted. Note that this can be
-overridden, and multiple instances of the same type of magic can be
-associated with an SV.
-
-The C<name> and C<namlem> arguments are used to associate a string with
-the magic, typically the name of a variable. C<namlem> is stored in the
-C<mg_len> field and if C<name> is non-null and C<namlem> >= 0 a malloc'd
+convert C<sv> to type C<SVt_PVMG>. Perl then continues by adding new magic
+to the beginning of the linked list of magical features. Any prior entry
+of the same type of magic is deleted. Note that this can be overridden,
+and multiple instances of the same type of magic can be associated with an
+SV.
+
+The C<name> and C<namlen> arguments are used to associate a string with
+the magic, typically the name of a variable. C<namlen> is stored in the
+C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
copy of the name is stored in C<mg_ptr> field.
The sv_magic function uses C<how> to determine which, if any, predefined
"Magic Virtual Table" should be assigned to the C<mg_virtual> field.
See the "Magic Virtual Table" section below. The C<how> argument is also
-stored in the C<mg_type> field.
+stored in the C<mg_type> field. The value of C<how> should be chosen
+from the set of macros C<PERL_MAGIC_foo> found perl.h. Note that before
+these macros were added, Perl internals used to directly use character
+literals, so you may occasionally come across old code or documentation
+referrring to 'U' magic rather than C<PERL_MAGIC_uvar> for example.
The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
structure. If it is not the same as the C<sv> argument, the reference
count of the C<obj> object is incremented. If it is the same, or if
-the C<how> argument is "#", or if it is a null pointer, then C<obj> is
-merely stored, without the reference count being incremented.
+the C<how> argument is C<PERL_MAGIC_arylen>, or if it is a NULL pointer,
+then C<obj> is merely stored, without the reference count being incremented.
There is also a function to add magic to an C<HV>:
=head2 Magic Virtual Tables
-The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
+The C<mg_virtual> field in the C<MAGIC> structure is a pointer to an
C<MGVTBL>, which is a structure of function pointers and stands for
"Magic Virtual Table" to handle the various operations that might be
applied to that variable.
svt_free Free any extra storage associated with the SV.
For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
-to an C<mg_type> of '\0') contains:
+to an C<mg_type> of C<PERL_MAGIC_sv>) contains:
{ magic_get, magic_set, magic_len, 0, 0 }
-Thus, when an SV is determined to be magical and of type '\0', if a get
-operation is being performed, the routine C<magic_get> is called. All
-the various routines for the various magical types begin with C<magic_>.
+Thus, when an SV is determined to be magical and of type C<PERL_MAGIC_sv>,
+if a get operation is being performed, the routine C<magic_get> is
+called. All the various routines for the various magical types begin
+with C<magic_>. NOTE: the magic routines are not considered part of
+the Perl API, and may not be exported by the Perl library.
The current kinds of Magic Virtual Tables are:
- mg_type MGVTBL Type of magicalness
- ------- ------ -------------------
- \0 vtbl_sv Regexp???
- A vtbl_amagic Operator Overloading
- a vtbl_amagicelem Operator Overloading
- c 0 Used in Operator Overloading
- B vtbl_bm Boyer-Moore???
- E vtbl_env %ENV hash
- e vtbl_envelem %ENV hash element
- g vtbl_mglob Regexp /g flag???
- I vtbl_isa @ISA array
- i vtbl_isaelem @ISA array element
- L 0 (but sets RMAGICAL) Perl Module/Debugger???
- l vtbl_dbline Debugger?
- o vtbl_collxfrm Locale Collation
- P vtbl_pack Tied Array or Hash
- p vtbl_packelem Tied Array or Hash element
- q vtbl_packelem Tied Scalar or Handle
- S vtbl_sig Signal Hash
- s vtbl_sigelem Signal Hash element
- t vtbl_taint Taintedness
- U vtbl_uvar ???
- v vtbl_vec Vector
- x vtbl_substr Substring???
- * vtbl_glob GV???
- # vtbl_arylen Array Length
- . vtbl_pos $. scalar variable
- ~ Reserved for extensions, but multiple extensions may clash
-
-When an upper-case and lower-case letter both exist in the table, then the
-upper-case letter is used to represent some kind of composite type (a list
-or a hash), and the lower-case letter is used to represent an element of
-that composite type.
+ mg_type
+ (old-style char and macro) MGVTBL Type of magic
+ -------------------------- ------ ----------------------------
+ \0 PERL_MAGIC_sv vtbl_sv Special scalar variable
+ A PERL_MAGIC_overload vtbl_amagic %OVERLOAD hash
+ a PERL_MAGIC_overload_elem vtbl_amagicelem %OVERLOAD hash element
+ c PERL_MAGIC_overload_table (none) Holds overload table (AMT)
+ on stash
+ B PERL_MAGIC_bm vtbl_bm Boyer-Moore (fast string search)
+ D PERL_MAGIC_regdata vtbl_regdata Regex match position data
+ (@+ and @- vars)
+ d PERL_MAGIC_regdatum vtbl_regdatum Regex match position data
+ element
+ E PERL_MAGIC_env vtbl_env %ENV hash
+ e PERL_MAGIC_envelem vtbl_envelem %ENV hash element
+ f PERL_MAGIC_fm vtbl_fm Formline ('compiled' format)
+ g PERL_MAGIC_regex_global vtbl_mglob m//g target / study()ed string
+ I PERL_MAGIC_isa vtbl_isa @ISA array
+ i PERL_MAGIC_isaelem vtbl_isaelem @ISA array element
+ k PERL_MAGIC_nkeys vtbl_nkeys scalar(keys()) lvalue
+ L PERL_MAGIC_dbfile (none) Debugger %_<filename
+ l PERL_MAGIC_dbline vtbl_dbline Debugger %_<filename element
+ m PERL_MAGIC_mutex vtbl_mutex ???
+ o PERL_MAGIC_collxfrm vtbl_collxfrm Locale collate transformation
+ P PERL_MAGIC_tied vtbl_pack Tied array or hash
+ p PERL_MAGIC_tiedelem vtbl_packelem Tied array or hash element
+ q PERL_MAGIC_tiedscalar vtbl_packelem Tied scalar or handle
+ r PERL_MAGIC_qr vtbl_qr precompiled qr// regex
+ S PERL_MAGIC_sig vtbl_sig %SIG hash
+ s PERL_MAGIC_sigelem vtbl_sigelem %SIG hash element
+ t PERL_MAGIC_taint vtbl_taint Taintedness
+ U PERL_MAGIC_uvar vtbl_uvar Available for use by extensions
+ v PERL_MAGIC_vec vtbl_vec vec() lvalue
+ x PERL_MAGIC_substr vtbl_substr substr() lvalue
+ y PERL_MAGIC_defelem vtbl_defelem Shadow "foreach" iterator
+ variable / smart parameter
+ vivification
+ * PERL_MAGIC_glob vtbl_glob GV (typeglob)
+ # PERL_MAGIC_arylen vtbl_arylen Array length ($#ary)
+ . PERL_MAGIC_pos vtbl_pos pos() lvalue
+ < PERL_MAGIC_backref vtbl_backref ???
+ ~ PERL_MAGIC_ext (none) Available for use by extensions
+
+When an uppercase and lowercase letter both exist in the table, then the
+uppercase letter is used to represent some kind of composite type (a list
+or a hash), and the lowercase letter is used to represent an element of
+that composite type. Some internals code makes use of this case
+relationship.
+
+The C<PERL_MAGIC_ext> and C<PERL_MAGIC_uvar> magic types are defined
+specifically for use by extensions and will not be used by perl itself.
+Extensions can use C<PERL_MAGIC_ext> magic to 'attach' private information
+to variables (typically objects). This is especially useful because
+there is no way for normal perl code to corrupt this private information
+(unlike using extra elements of a hash object).
+
+Similarly, C<PERL_MAGIC_uvar> magic can be used much like tie() to call a
+C function any time a scalar's value is used or changed. The C<MAGIC>'s
+C<mg_ptr> field points to a C<ufuncs> structure:
+
+ struct ufuncs {
+ I32 (*uf_val)(pTHX_ IV, SV*);
+ I32 (*uf_set)(pTHX_ IV, SV*);
+ IV uf_index;
+ };
+
+When the SV is read from or written to, the C<uf_val> or C<uf_set>
+function will be called with C<uf_index> as the first arg and a pointer to
+the SV as the second. A simple example of how to add C<PERL_MAGIC_uvar>
+magic is shown below. Note that the ufuncs structure is copied by
+sv_magic, so you can safely allocate it on the stack.
+
+ void
+ Umagic(sv)
+ SV *sv;
+ PREINIT:
+ struct ufuncs uf;
+ CODE:
+ uf.uf_val = &my_get_fn;
+ uf.uf_set = &my_set_fn;
+ uf.uf_index = 0;
+ sv_magic(sv, 0, PERL_MAGIC_uvar, (char*)&uf, sizeof(uf));
+
+Note that because multiple extensions may be using C<PERL_MAGIC_ext>
+or C<PERL_MAGIC_uvar> magic, it is important for extensions to take
+extra care to avoid conflict. Typically only using the magic on
+objects blessed into the same class as the extension is sufficient.
+For C<PERL_MAGIC_ext> magic, it may also be appropriate to add an I32
+'signature' at the top of the private data area and check that.
+
+Also note that the C<sv_set*()> and C<sv_cat*()> functions described
+earlier do B<not> invoke 'set' magic on their targets. This must
+be done by the user either by calling the C<SvSETMAGIC()> macro after
+calling these functions, or by using one of the C<sv_set*_mg()> or
+C<sv_cat*_mg()> functions. Similarly, generic C code must call the
+C<SvGETMAGIC()> macro to invoke any 'get' magic if they use an SV
+obtained from external sources in functions that don't handle magic.
+See L<perlapi> for a description of these functions.
+For example, calls to the C<sv_cat*()> functions typically need to be
+followed by C<SvSETMAGIC()>, but they don't need a prior C<SvGETMAGIC()>
+since their implementation handles 'get' magic.
=head2 Finding Magic
This routine returns a pointer to the C<MAGIC> structure stored in the SV.
If the SV does not have that magical feature, C<NULL> is returned. Also,
-if the SV is not of type SVt_PVMG, Perl may core-dump.
+if the SV is not of type SVt_PVMG, Perl may core dump.
- int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
+ int mg_copy(SV* sv, SV* nsv, const char* key, STRLEN klen);
This routine checks to see what types of magic C<sv> has. If the mg_type
-field is an upper-case letter, then the mg_obj is copied to C<nsv>, but
-the mg_type field is changed to be the lower-case letter.
+field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
+the mg_type field is changed to be the lowercase letter.
+
+=head2 Understanding the Magic of Tied Hashes and Arrays
+
+Tied hashes and arrays are magical beasts of the C<PERL_MAGIC_tied>
+magic type.
+
+WARNING: As of the 5.004 release, proper usage of the array and hash
+access functions requires understanding a few caveats. Some
+of these caveats are actually considered bugs in the API, to be fixed
+in later releases, and are bracketed with [MAYCHANGE] below. If
+you find yourself actually applying such information in this section, be
+aware that the behavior may change in the future, umm, without warning.
+
+The perl tie function associates a variable with an object that implements
+the various GET, SET etc methods. To perform the equivalent of the perl
+tie function from an XSUB, you must mimic this behaviour. The code below
+carries out the necessary steps - firstly it creates a new hash, and then
+creates a second hash which it blesses into the class which will implement
+the tie methods. Lastly it ties the two hashes together, and returns a
+reference to the new tied hash. Note that the code below does NOT call the
+TIEHASH method in the MyTie class -
+see L<Calling Perl Routines from within C Programs> for details on how
+to do this.
+
+ SV*
+ mytie()
+ PREINIT:
+ HV *hash;
+ HV *stash;
+ SV *tie;
+ CODE:
+ hash = newHV();
+ tie = newRV_noinc((SV*)newHV());
+ stash = gv_stashpv("MyTie", TRUE);
+ sv_bless(tie, stash);
+ hv_magic(hash, (GV*)tie, PERL_MAGIC_tied);
+ RETVAL = newRV_noinc(hash);
+ OUTPUT:
+ RETVAL
+
+The C<av_store> function, when given a tied array argument, merely
+copies the magic of the array onto the value to be "stored", using
+C<mg_copy>. It may also return NULL, indicating that the value did not
+actually need to be stored in the array. [MAYCHANGE] After a call to
+C<av_store> on a tied array, the caller will usually need to call
+C<mg_set(val)> to actually invoke the perl level "STORE" method on the
+TIEARRAY object. If C<av_store> did return NULL, a call to
+C<SvREFCNT_dec(val)> will also be usually necessary to avoid a memory
+leak. [/MAYCHANGE]
+
+The previous paragraph is applicable verbatim to tied hash access using the
+C<hv_store> and C<hv_store_ent> functions as well.
+
+C<av_fetch> and the corresponding hash functions C<hv_fetch> and
+C<hv_fetch_ent> actually return an undefined mortal value whose magic
+has been initialized using C<mg_copy>. Note the value so returned does not
+need to be deallocated, as it is already mortal. [MAYCHANGE] But you will
+need to call C<mg_get()> on the returned value in order to actually invoke
+the perl level "FETCH" method on the underlying TIE object. Similarly,
+you may also call C<mg_set()> on the return value after possibly assigning
+a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
+method on the TIE object. [/MAYCHANGE]
+
+[MAYCHANGE]
+In other words, the array or hash fetch/store functions don't really
+fetch and store actual values in the case of tied arrays and hashes. They
+merely call C<mg_copy> to attach magic to the values that were meant to be
+"stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
+do the job of invoking the TIE methods on the underlying objects. Thus
+the magic mechanism currently implements a kind of lazy access to arrays
+and hashes.
+
+Currently (as of perl version 5.004), use of the hash and array access
+functions requires the user to be aware of whether they are operating on
+"normal" hashes and arrays, or on their tied variants. The API may be
+changed to provide more transparent access to both tied and normal data
+types in future versions.
+[/MAYCHANGE]
+
+You would do well to understand that the TIEARRAY and TIEHASH interfaces
+are mere sugar to invoke some perl method calls while using the uniform hash
+and array syntax. The use of this sugar imposes some overhead (typically
+about two to four extra opcodes per FETCH/STORE operation, in addition to
+the creation of all the mortal variables required to invoke the methods).
+This overhead will be comparatively small if the TIE methods are themselves
+substantial, but if they are only a few statements long, the overhead
+will not be insignificant.
+
+=head2 Localizing changes
-=head1 Double-Typed SVs
-
-Scalar variables normally contain only one type of value, an integer,
-double, pointer, or reference. Perl will automatically convert the
-actual scalar data from the stored type into the requested type.
+Perl has a very handy construction
-Some scalar variables contain more than one type of scalar data. For
-example, the variable C<$!> contains either the numeric value of C<errno>
-or its string equivalent from either C<strerror> or C<sys_errlist[]>.
+ {
+ local $var = 2;
+ ...
+ }
-To force multiple data values into an SV, you must do two things: use the
-C<sv_set*v> routines to add the additional scalar type, then set a flag
-so that Perl will believe it contains more than one type of data. The
-four macros to set the flags are:
+This construction is I<approximately> equivalent to
- SvIOK_on
- SvNOK_on
- SvPOK_on
- SvROK_on
+ {
+ my $oldvar = $var;
+ $var = 2;
+ ...
+ $var = $oldvar;
+ }
-The particular macro you must use depends on which C<sv_set*v> routine
-you called first. This is because every C<sv_set*v> routine turns on
-only the bit for the particular type of data being set, and turns off
-all the rest.
+The biggest difference is that the first construction would
+reinstate the initial value of $var, irrespective of how control exits
+the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
+more efficient as well.
-For example, to create a new Perl variable called "dberror" that contains
-both the numeric and descriptive string error values, you could use the
-following code:
-
- extern int dberror;
- extern char *dberror_list;
-
- SV* sv = perl_get_sv("dberror", TRUE);
- sv_setiv(sv, (IV) dberror);
- sv_setpv(sv, dberror_list[dberror]);
- SvIOK_on(sv);
-
-If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
-macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
-
-=head1 Calling Perl Routines from within C Programs
-
-There are four routines that can be used to call a Perl subroutine from
-within a C program. These four are:
-
- I32 perl_call_sv(SV*, I32);
- I32 perl_call_pv(char*, I32);
- I32 perl_call_method(char*, I32);
- I32 perl_call_argv(char*, I32, register char**);
-
-The routine most often used is C<perl_call_sv>. The C<SV*> argument
-contains either the name of the Perl subroutine to be called, or a
-reference to the subroutine. The second argument consists of flags
-that control the context in which the subroutine is called, whether
-or not the subroutine is being passed arguments, how errors should be
-trapped, and how to treat return values.
-
-All four routines return the number of arguments that the subroutine returned
-on the Perl stack.
-
-When using any of these routines (except C<perl_call_argv>), the programmer
-must manipulate the Perl stack. These include the following macros and
-functions:
-
- dSP
- PUSHMARK()
- PUTBACK
- SPAGAIN
- ENTER
- SAVETMPS
- FREETMPS
- LEAVE
- XPUSH*()
- POP*()
-
-For more information, consult L<perlcall>.
-
-=head1 Memory Allocation
-
-It is strongly suggested that you use the version of malloc that is distributed
-with Perl. It keeps pools of various sizes of unallocated memory in order to
-more quickly satisfy allocation requests.
-However, on some platforms, it may cause spurious malloc or free errors.
-
- New(x, pointer, number, type);
- Newc(x, pointer, number, type, cast);
- Newz(x, pointer, number, type);
-
-These three macros are used to initially allocate memory. The first argument
-C<x> was a "magic cookie" that was used to keep track of who called the macro,
-to help when debugging memory problems. However, the current code makes no
-use of this feature (Larry has switched to using a run-time memory checker),
-so this argument can be any number.
-
-The second argument C<pointer> will point to the newly allocated memory.
-The third and fourth arguments C<number> and C<type> specify how many of
-the specified type of data structure should be allocated. The argument
-C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
-should be used if the C<pointer> argument is different from the C<type>
-argument.
-
-Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
-to zero out all the newly allocated memory.
-
- Renew(pointer, number, type);
- Renewc(pointer, number, type, cast);
- Safefree(pointer)
-
-These three macros are used to change a memory buffer size or to free a
-piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
-match those of C<New> and C<Newc> with the exception of not needing the
-"magic cookie" argument.
-
- Move(source, dest, number, type);
- Copy(source, dest, number, type);
- Zero(dest, number, type);
-
-These three macros are used to move, copy, or zero out previously allocated
-memory. The C<source> and C<dest> arguments point to the source and
-destination starting points. Perl will move, copy, or zero out C<number>
-instances of the size of the C<type> data structure (using the C<sizeof>
-function).
-
-=head1 API LISTING
-
-This is a listing of functions, macros, flags, and variables that may be
-useful to extension writers or that may be found while reading other
-extensions.
-
-=over 8
-
-=item AvFILL
-
-See C<av_len>.
-
-=item av_clear
-
-Clears an array, making it empty.
-
- void av_clear _((AV* ar));
-
-=item av_extend
-
-Pre-extend an array. The C<key> is the index to which the array should be
-extended.
-
- void av_extend _((AV* ar, I32 key));
-
-=item av_fetch
-
-Returns the SV at the specified index in the array. The C<key> is the
-index. If C<lval> is set then the fetch will be part of a store. Check
-that the return value is non-null before dereferencing it to a C<SV*>.
-
- SV** av_fetch _((AV* ar, I32 key, I32 lval));
-
-=item av_len
-
-Returns the highest index in the array. Returns -1 if the array is empty.
-
- I32 av_len _((AV* ar));
-
-=item av_make
-
-Creates a new AV and populates it with a list of SVs. The SVs are copied
-into the array, so they may be freed after the call to av_make. The new AV
-will have a refcount of 1.
-
- AV* av_make _((I32 size, SV** svp));
-
-=item av_pop
-
-Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
-empty.
-
- SV* av_pop _((AV* ar));
-
-=item av_push
-
-Pushes an SV onto the end of the array. The array will grow automatically
-to accommodate the addition.
-
- void av_push _((AV* ar, SV* val));
-
-=item av_shift
-
-Shifts an SV off the beginning of the array.
-
- SV* av_shift _((AV* ar));
-
-=item av_store
-
-Stores an SV in an array. The array index is specified as C<key>. The
-return value will be null if the operation failed, otherwise it can be
-dereferenced to get the original C<SV*>.
-
- SV** av_store _((AV* ar, I32 key, SV* val));
-
-=item av_undef
-
-Undefines the array.
-
- void av_undef _((AV* ar));
-
-=item av_unshift
-
-Unshift an SV onto the beginning of the array. The array will grow
-automatically to accommodate the addition.
-
- void av_unshift _((AV* ar, I32 num));
-
-=item CLASS
-
-Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
-constructor. This is always a C<char*>. See C<THIS> and
-L<perlxs/"Using XS With C++">.
-
-=item Copy
-
-The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
-source, C<d> is the destination, C<n> is the number of items, and C<t> is
-the type.
-
- (void) Copy( s, d, n, t );
-
-=item croak
-
-This is the XSUB-writer's interface to Perl's C<die> function. Use this
-function the same way you use the C C<printf> function. See C<warn>.
-
-=item CvSTASH
-
-Returns the stash of the CV.
-
- HV * CvSTASH( SV* sv )
-
-=item DBsingle
-
-When Perl is run in debugging mode, with the B<-d> switch, this SV is a
-boolean which indicates whether subs are being single-stepped.
-Single-stepping is automatically turned on after every step. This is the C
-variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
-
-=item DBsub
-
-When Perl is run in debugging mode, with the B<-d> switch, this GV contains
-the SV which holds the name of the sub being debugged. This is the C
-variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
-The sub name can be found by
-
- SvPV( GvSV( DBsub ), na )
-
-=item DBtrace
-
-Trace variable used when Perl is run in debugging mode, with the B<-d>
-switch. This is the C variable which corresponds to Perl's $DB::trace
-variable. See C<DBsingle>.
-
-=item dMARK
-
-Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
-C<dORIGMARK>.
-
-=item dORIGMARK
-
-Saves the original stack mark for the XSUB. See C<ORIGMARK>.
-
-=item dowarn
-
-The C variable which corresponds to Perl's $^W warning variable.
-
-=item dSP
-
-Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
-
-=item dXSARGS
-
-Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
-usually handled automatically by C<xsubpp>. Declares the C<items> variable
-to indicate the number of items on the stack.
-
-=item dXSI32
-
-Sets up the C<ix> variable for an XSUB which has aliases. This is usually
-handled automatically by C<xsubpp>.
-
-=item dXSI32
-
-Sets up the C<ix> variable for an XSUB which has aliases. This is usually
-handled automatically by C<xsubpp>.
-
-=item ENTER
-
-Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
-
- ENTER;
-
-=item EXTEND
-
-Used to extend the argument stack for an XSUB's return values.
-
- EXTEND( sp, int x );
-
-=item FREETMPS
-
-Closing bracket for temporaries on a callback. See C<SAVETMPS> and
-L<perlcall>.
-
- FREETMPS;
-
-=item G_ARRAY
-
-Used to indicate array context. See C<GIMME> and L<perlcall>.
-
-=item G_DISCARD
-
-Indicates that arguments returned from a callback should be discarded. See
-L<perlcall>.
-
-=item G_EVAL
-
-Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
-
-=item GIMME
-
-The XSUB-writer's equivalent to Perl's C<wantarray>. Returns C<G_SCALAR> or
-C<G_ARRAY> for scalar or array context.
-
-=item G_NOARGS
-
-Indicates that no arguments are being sent to a callback. See L<perlcall>.
-
-=item G_SCALAR
-
-Used to indicate scalar context. See C<GIMME> and L<perlcall>.
-
-=item gv_stashpv
-
-Returns a pointer to the stash for a specified package. If C<create> is set
-then the package will be created if it does not already exist. If C<create>
-is not set and the package does not exist then NULL is returned.
-
- HV* gv_stashpv _((char* name, I32 create));
-
-=item gv_stashsv
-
-Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
-
- HV* gv_stashsv _((SV* sv, I32 create));
-
-=item GvSV
-
-Return the SV from the GV.
-
-=item he_free
-
-Releases a hash entry from an iterator. See C<hv_iternext>.
-
-=item hv_clear
-
-Clears a hash, making it empty.
-
- void hv_clear _((HV* tb));
-
-=item hv_delete
-
-Deletes a key/value pair in the hash. The value SV is removed from the hash
-and returned to the caller. The C<klen> is the length of the key. The
-C<flags> value will normally be zero; if set to G_DISCARD then null will be
-returned.
-
- SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
-
-=item hv_exists
-
-Returns a boolean indicating whether the specified hash key exists. The
-C<klen> is the length of the key.
-
- bool hv_exists _((HV* tb, char* key, U32 klen));
-
-=item hv_fetch
-
-Returns the SV which corresponds to the specified key in the hash. The
-C<klen> is the length of the key. If C<lval> is set then the fetch will be
-part of a store. Check that the return value is non-null before
-dereferencing it to a C<SV*>.
-
- SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
-
-=item hv_iterinit
-
-Prepares a starting point to traverse a hash table.
-
- I32 hv_iterinit _((HV* tb));
-
-=item hv_iterkey
-
-Returns the key from the current position of the hash iterator. See
-C<hv_iterinit>.
-
- char* hv_iterkey _((HE* entry, I32* retlen));
-
-=item hv_iternext
-
-Returns entries from a hash iterator. See C<hv_iterinit>.
-
- HE* hv_iternext _((HV* tb));
-
-=item hv_iternextsv
-
-Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
-operation.
-
- SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
-
-=item hv_iterval
-
-Returns the value from the current position of the hash iterator. See
-C<hv_iterkey>.
-
- SV* hv_iterval _((HV* tb, HE* entry));
-
-=item hv_magic
-
-Adds magic to a hash. See C<sv_magic>.
-
- void hv_magic _((HV* hv, GV* gv, int how));
-
-=item HvNAME
-
-Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
-
- char *HvNAME (HV* stash)
-
-=item hv_store
-
-Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
-the length of the key. The C<hash> parameter is the pre-computed hash
-value; if it is zero then Perl will compute it. The return value will be
-null if the operation failed, otherwise it can be dereferenced to get the
-original C<SV*>.
-
- SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
-
-=item hv_undef
-
-Undefines the hash.
-
- void hv_undef _((HV* tb));
-
-=item isALNUM
-
-Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
-character.
-
- int isALNUM (char c)
-
-=item isALPHA
-
-Returns a boolean indicating whether the C C<char> is an ascii alphabetic
-character.
-
- int isALPHA (char c)
-
-=item isDIGIT
-
-Returns a boolean indicating whether the C C<char> is an ascii digit.
-
- int isDIGIT (char c)
-
-=item isLOWER
-
-Returns a boolean indicating whether the C C<char> is a lowercase character.
-
- int isLOWER (char c)
-
-=item isSPACE
-
-Returns a boolean indicating whether the C C<char> is whitespace.
-
- int isSPACE (char c)
-
-=item isUPPER
-
-Returns a boolean indicating whether the C C<char> is an uppercase character.
-
- int isUPPER (char c)
-
-=item items
-
-Variable which is setup by C<xsubpp> to indicate the number of items on the
-stack. See L<perlxs/"Variable-length Parameter Lists">.
-
-=item ix
-
-Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
-was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
-
-=item LEAVE
-
-Closing bracket on a callback. See C<ENTER> and L<perlcall>.
-
- LEAVE;
-
-=item MARK
-
-Stack marker variable for the XSUB. See C<dMARK>.
-
-=item mg_clear
-
-Clear something magical that the SV represents. See C<sv_magic>.
-
- int mg_clear _((SV* sv));
-
-=item mg_copy
-
-Copies the magic from one SV to another. See C<sv_magic>.
-
- int mg_copy _((SV *, SV *, char *, STRLEN));
-
-=item mg_find
-
-Finds the magic pointer for type matching the SV. See C<sv_magic>.
-
- MAGIC* mg_find _((SV* sv, int type));
-
-=item mg_free
-
-Free any magic storage used by the SV. See C<sv_magic>.
-
- int mg_free _((SV* sv));
-
-=item mg_get
-
-Do magic after a value is retrieved from the SV. See C<sv_magic>.
-
- int mg_get _((SV* sv));
-
-=item mg_len
-
-Report on the SV's length. See C<sv_magic>.
-
- U32 mg_len _((SV* sv));
-
-=item mg_magical
-
-Turns on the magical status of an SV. See C<sv_magic>.
-
- void mg_magical _((SV* sv));
-
-=item mg_set
-
-Do magic after a value is assigned to the SV. See C<sv_magic>.
-
- int mg_set _((SV* sv));
-
-=item Move
-
-The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
-source, C<d> is the destination, C<n> is the number of items, and C<t> is
-the type.
-
- (void) Move( s, d, n, t );
-
-=item na
-
-A variable which may be used with C<SvPV> to tell Perl to calculate the
-string length.
-
-=item New
-
-The XSUB-writer's interface to the C C<malloc> function.
-
- void * New( x, void *ptr, int size, type )
-
-=item Newc
-
-The XSUB-writer's interface to the C C<malloc> function, with cast.
-
- void * Newc( x, void *ptr, int size, type, cast )
-
-=item Newz
-
-The XSUB-writer's interface to the C C<malloc> function. The allocated
-memory is zeroed with C<memzero>.
-
- void * Newz( x, void *ptr, int size, type )
-
-=item newAV
-
-Creates a new AV. The refcount is set to 1.
-
- AV* newAV _((void));
-
-=item newHV
-
-Creates a new HV. The refcount is set to 1.
-
- HV* newHV _((void));
-
-=item newRV
-
-Creates an RV wrapper for an SV. The refcount for the original SV is
-incremented.
-
- SV* newRV _((SV* ref));
-
-=item newSV
-
-Creates a new SV. The C<len> parameter indicates the number of bytes of
-pre-allocated string space the SV should have. The refcount for the new SV
-is set to 1.
-
- SV* newSV _((STRLEN len));
-
-=item newSViv
-
-Creates a new SV and copies an integer into it. The refcount for the SV is
-set to 1.
-
- SV* newSViv _((IV i));
-
-=item newSVnv
-
-Creates a new SV and copies a double into it. The refcount for the SV is
-set to 1.
-
- SV* newSVnv _((NV i));
-
-=item newSVpv
-
-Creates a new SV and copies a string into it. The refcount for the SV is
-set to 1. If C<len> is zero then Perl will compute the length.
-
- SV* newSVpv _((char* s, STRLEN len));
-
-=item newSVrv
-
-Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
-it will be upgraded to one. If C<classname> is non-null then the new SV will
-be blessed in the specified package. The new SV is returned and its
-refcount is 1.
-
- SV* newSVrv _((SV* rv, char* classname));
-
-=item newSVsv
-
-Creates a new SV which is an exact duplicate of the original SV.
-
- SV* newSVsv _((SV* old));
-
-=item newXS
-
-Used by C<xsubpp> to hook up XSUBs as Perl subs.
-
-=item newXSproto
-
-Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
-the subs.
-
-=item Nullav
-
-Null AV pointer.
-
-=item Nullch
-
-Null character pointer.
-
-=item Nullcv
-
-Null CV pointer.
-
-=item Nullhv
-
-Null HV pointer.
-
-=item Nullsv
-
-Null SV pointer.
-
-=item ORIGMARK
-
-The original stack mark for the XSUB. See C<dORIGMARK>.
-
-=item perl_alloc
-
-Allocates a new Perl interpreter. See L<perlembed>.
-
-=item perl_call_argv
-
-Performs a callback to the specified Perl sub. See L<perlcall>.
-
- I32 perl_call_argv _((char* subname, I32 flags, char** argv));
-
-=item perl_call_method
-
-Performs a callback to the specified Perl method. The blessed object must
-be on the stack. See L<perlcall>.
-
- I32 perl_call_method _((char* methname, I32 flags));
-
-=item perl_call_pv
-
-Performs a callback to the specified Perl sub. See L<perlcall>.
-
- I32 perl_call_pv _((char* subname, I32 flags));
-
-=item perl_call_sv
-
-Performs a callback to the Perl sub whose name is in the SV. See
-L<perlcall>.
-
- I32 perl_call_sv _((SV* sv, I32 flags));
-
-=item perl_construct
-
-Initializes a new Perl interpreter. See L<perlembed>.
-
-=item perl_destruct
-
-Shuts down a Perl interpreter. See L<perlembed>.
-
-=item perl_eval_sv
-
-Tells Perl to C<eval> the string in the SV.
-
- I32 perl_eval_sv _((SV* sv, I32 flags));
-
-=item perl_free
-
-Releases a Perl interpreter. See L<perlembed>.
-
-=item perl_get_av
-
-Returns the AV of the specified Perl array. If C<create> is set and the
-Perl variable does not exist then it will be created. If C<create> is not
-set and the variable does not exist then null is returned.
-
- AV* perl_get_av _((char* name, I32 create));
-
-=item perl_get_cv
-
-Returns the CV of the specified Perl sub. If C<create> is set and the Perl
-variable does not exist then it will be created. If C<create> is not
-set and the variable does not exist then null is returned.
-
- CV* perl_get_cv _((char* name, I32 create));
-
-=item perl_get_hv
-
-Returns the HV of the specified Perl hash. If C<create> is set and the Perl
-variable does not exist then it will be created. If C<create> is not
-set and the variable does not exist then null is returned.
-
- HV* perl_get_hv _((char* name, I32 create));
-
-=item perl_get_sv
-
-Returns the SV of the specified Perl scalar. If C<create> is set and the
-Perl variable does not exist then it will be created. If C<create> is not
-set and the variable does not exist then null is returned.
-
- SV* perl_get_sv _((char* name, I32 create));
-
-=item perl_parse
-
-Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
-
-=item perl_require_pv
-
-Tells Perl to C<require> a module.
-
- void perl_require_pv _((char* pv));
-
-=item perl_run
-
-Tells a Perl interpreter to run. See L<perlembed>.
-
-=item POPi
-
-Pops an integer off the stack.
-
- int POPi();
-
-=item POPl
-
-Pops a long off the stack.
-
- long POPl();
-
-=item POPp
-
-Pops a string off the stack.
-
- char * POPp();
-
-=item POPn
-
-Pops a double off the stack.
-
- double POPn();
-
-=item POPs
-
-Pops an SV off the stack.
-
- SV* POPs();
-
-=item PUSHMARK
-
-Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
-
- PUSHMARK(p)
-
-=item PUSHi
-
-Push an integer onto the stack. The stack must have room for this element.
-See C<XPUSHi>.
-
- PUSHi(int d)
-
-=item PUSHn
-
-Push a double onto the stack. The stack must have room for this element.
-See C<XPUSHn>.
-
- PUSHn(double d)
-
-=item PUSHp
-
-Push a string onto the stack. The stack must have room for this element.
-The C<len> indicates the length of the string. See C<XPUSHp>.
-
- PUSHp(char *c, int len )
-
-=item PUSHs
-
-Push an SV onto the stack. The stack must have room for this element. See
-C<XPUSHs>.
-
- PUSHs(sv)
-
-=item PUTBACK
-
-Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
-See C<PUSHMARK> and L<perlcall> for other uses.
-
- PUTBACK;
-
-=item Renew
-
-The XSUB-writer's interface to the C C<realloc> function.
-
- void * Renew( void *ptr, int size, type )
-
-=item Renewc
-
-The XSUB-writer's interface to the C C<realloc> function, with cast.
-
- void * Renewc( void *ptr, int size, type, cast )
-
-=item RETVAL
-
-Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
-This is always the proper type for the XSUB.
-See L<perlxs/"The RETVAL Variable">.
-
-=item safefree
-
-The XSUB-writer's interface to the C C<free> function.
-
-=item safemalloc
-
-The XSUB-writer's interface to the C C<malloc> function.
-
-=item saferealloc
-
-The XSUB-writer's interface to the C C<realloc> function.
-
-=item savepv
-
-Copy a string to a safe spot. This does not use an SV.
-
- char* savepv _((char* sv));
-
-=item savepvn
-
-Copy a string to a safe spot. The C<len> indicates number of bytes to
-copy. This does not use an SV.
-
- char* savepvn _((char* sv, I32 len));
-
-=item SAVETMPS
-
-Opening bracket for temporaries on a callback. See C<FREETMPS> and
-L<perlcall>.
-
- SAVETMPS;
-
-=item SP
-
-Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
-C<SPAGAIN>.
-
-=item SPAGAIN
-
-Refetch the stack pointer. Used after a callback. See L<perlcall>.
-
- SPAGAIN;
-
-=item ST
-
-Used to access elements on the XSUB's stack.
-
- SV* ST(int x)
-
-=item strEQ
-
-Test two strings to see if they are equal. Returns true or false.
-
- int strEQ( char *s1, char *s2 )
-
-=item strGE
-
-Test two strings to see if the first, C<s1>, is greater than or equal to the
-second, C<s2>. Returns true or false.
-
- int strGE( char *s1, char *s2 )
-
-=item strGT
-
-Test two strings to see if the first, C<s1>, is greater than the second,
-C<s2>. Returns true or false.
-
- int strGT( char *s1, char *s2 )
-
-=item strLE
-
-Test two strings to see if the first, C<s1>, is less than or equal to the
-second, C<s2>. Returns true or false.
-
- int strLE( char *s1, char *s2 )
-
-=item strLT
-
-Test two strings to see if the first, C<s1>, is less than the second,
-C<s2>. Returns true or false.
-
- int strLT( char *s1, char *s2 )
-
-=item strNE
-
-Test two strings to see if they are different. Returns true or false.
-
- int strNE( char *s1, char *s2 )
-
-=item strnEQ
-
-Test two strings to see if they are equal. The C<len> parameter indicates
-the number of bytes to compare. Returns true or false.
-
- int strnEQ( char *s1, char *s2 )
-
-=item strnNE
-
-Test two strings to see if they are different. The C<len> parameter
-indicates the number of bytes to compare. Returns true or false.
-
- int strnNE( char *s1, char *s2, int len )
-
-=item sv_2mortal
-
-Marks an SV as mortal. The SV will be destroyed when the current context
-ends.
-
- SV* sv_2mortal _((SV* sv));
-
-=item sv_bless
-
-Blesses an SV into a specified package. The SV must be an RV. The package
-must be designated by its stash (see C<gv_stashpv()>). The refcount of the
-SV is unaffected.
-
- SV* sv_bless _((SV* sv, HV* stash));
-
-=item sv_catpv
-
-Concatenates the string onto the end of the string which is in the SV.
-
- void sv_catpv _((SV* sv, char* ptr));
-
-=item sv_catpvn
-
-Concatenates the string onto the end of the string which is in the SV. The
-C<len> indicates number of bytes to copy.
-
- void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
-
-=item sv_catsv
-
-Concatenates the string from SV C<ssv> onto the end of the string in SV
-C<dsv>.
-
- void sv_catsv _((SV* dsv, SV* ssv));
-
-=item sv_cmp
-
-Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
-string in C<sv1> is less than, equal to, or greater than the string in
-C<sv2>.
-
- I32 sv_cmp _((SV* sv1, SV* sv2));
-
-=item sv_cmp
-
-Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
-string in C<sv1> is less than, equal to, or greater than the string in
-C<sv2>.
-
- I32 sv_cmp _((SV* sv1, SV* sv2));
-
-=item SvCUR
-
-Returns the length of the string which is in the SV. See C<SvLEN>.
-
- int SvCUR (SV* sv)
-
-=item SvCUR_set
-
-Set the length of the string which is in the SV. See C<SvCUR>.
-
- SvCUR_set (SV* sv, int val )
-
-=item sv_dec
-
-Autodecrement of the value in the SV.
-
- void sv_dec _((SV* sv));
-
-=item sv_dec
-
-Autodecrement of the value in the SV.
-
- void sv_dec _((SV* sv));
-
-=item SvEND
-
-Returns a pointer to the last character in the string which is in the SV.
-See C<SvCUR>. Access the character as
-
- *SvEND(sv)
-
-=item sv_eq
-
-Returns a boolean indicating whether the strings in the two SVs are
-identical.
-
- I32 sv_eq _((SV* sv1, SV* sv2));
-
-=item SvGROW
-
-Expands the character buffer in the SV. Calls C<sv_grow> to perform the
-expansion if necessary. Returns a pointer to the character buffer.
-
- char * SvGROW( SV* sv, int len )
-
-=item sv_grow
-
-Expands the character buffer in the SV. This will use C<sv_unref> and will
-upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
-Use C<SvGROW>.
-
-=item sv_inc
-
-Autoincrement of the value in the SV.
-
- void sv_inc _((SV* sv));
-
-=item SvIOK
-
-Returns a boolean indicating whether the SV contains an integer.
-
- int SvIOK (SV* SV)
-
-=item SvIOK_off
-
-Unsets the IV status of an SV.
-
- SvIOK_off (SV* sv)
-
-=item SvIOK_on
-
-Tells an SV that it is an integer.
-
- SvIOK_on (SV* sv)
-
-=item SvIOK_only
-
-Tells an SV that it is an integer and disables all other OK bits.
-
- SvIOK_on (SV* sv)
-
-=item SvIOK_only
-
-Tells an SV that it is an integer and disables all other OK bits.
-
- SvIOK_on (SV* sv)
-
-=item SvIOKp
-
-Returns a boolean indicating whether the SV contains an integer. Checks the
-B<private> setting. Use C<SvIOK>.
-
- int SvIOKp (SV* SV)
-
-=item sv_isa
-
-Returns a boolean indicating whether the SV is blessed into the specified
-class. This does not know how to check for subtype, so it doesn't work in
-an inheritance relationship.
+There is a way to achieve a similar task from C via Perl API: create a
+I<pseudo-block>, and arrange for some changes to be automatically
+undone at the end of it, either explicit, or via a non-local exit (via
+die()). A I<block>-like construct is created by a pair of
+C<ENTER>/C<LEAVE> macros (see L<perlcall/"Returning a Scalar">).
+Such a construct may be created specially for some important localized
+task, or an existing one (like boundaries of enclosing Perl
+subroutine/block, or an existing pair for freeing TMPs) may be
+used. (In the second case the overhead of additional localization must
+be almost negligible.) Note that any XSUB is automatically enclosed in
+an C<ENTER>/C<LEAVE> pair.
- int sv_isa _((SV* sv, char* name));
+Inside such a I<pseudo-block> the following service is available:
-=item SvIV
+=over 4
-Returns the integer which is in the SV.
+=item C<SAVEINT(int i)>
- int SvIV (SV* sv)
+=item C<SAVEIV(IV i)>
-=item sv_isobject
+=item C<SAVEI32(I32 i)>
-Returns a boolean indicating whether the SV is an RV pointing to a blessed
-object. If the SV is not an RV, or if the object is not blessed, then this
-will return false.
+=item C<SAVELONG(long i)>
- int sv_isobject _((SV* sv));
+These macros arrange things to restore the value of integer variable
+C<i> at the end of enclosing I<pseudo-block>.
-=item SvIVX
+=item C<SAVESPTR(s)>
-Returns the integer which is stored in the SV.
+=item C<SAVEPPTR(p)>
- int SvIVX (SV* sv);
+These macros arrange things to restore the value of pointers C<s> and
+C<p>. C<s> must be a pointer of a type which survives conversion to
+C<SV*> and back, C<p> should be able to survive conversion to C<char*>
+and back.
-=item SvLEN
+=item C<SAVEFREESV(SV *sv)>
-Returns the size of the string buffer in the SV. See C<SvCUR>.
+The refcount of C<sv> would be decremented at the end of
+I<pseudo-block>. This is similar to C<sv_2mortal> in that it is also a
+mechanism for doing a delayed C<SvREFCNT_dec>. However, while C<sv_2mortal>
+extends the lifetime of C<sv> until the beginning of the next statement,
+C<SAVEFREESV> extends it until the end of the enclosing scope. These
+lifetimes can be wildly different.
- int SvLEN (SV* sv)
+Also compare C<SAVEMORTALIZESV>.
-=item sv_len
+=item C<SAVEMORTALIZESV(SV *sv)>
-Returns the length of the string in the SV. Use C<SvCUR>.
+Just like C<SAVEFREESV>, but mortalizes C<sv> at the end of the current
+scope instead of decrementing its reference count. This usually has the
+effect of keeping C<sv> alive until the statement that called the currently
+live scope has finished executing.
- STRLEN sv_len _((SV* sv));
+=item C<SAVEFREEOP(OP *op)>
-=item sv_len
+The C<OP *> is op_free()ed at the end of I<pseudo-block>.
-Returns the length of the string in the SV. Use C<SvCUR>.
+=item C<SAVEFREEPV(p)>
- STRLEN sv_len _((SV* sv));
+The chunk of memory which is pointed to by C<p> is Safefree()ed at the
+end of I<pseudo-block>.
-=item sv_magic
+=item C<SAVECLEARSV(SV *sv)>
-Adds magic to an SV.
+Clears a slot in the current scratchpad which corresponds to C<sv> at
+the end of I<pseudo-block>.
- void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
+=item C<SAVEDELETE(HV *hv, char *key, I32 length)>
-=item sv_mortalcopy
+The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
+string pointed to by C<key> is Safefree()ed. If one has a I<key> in
+short-lived storage, the corresponding string may be reallocated like
+this:
-Creates a new SV which is a copy of the original SV. The new SV is marked
-as mortal. The old SV may become invalid if it was marked as a temporary.
+ SAVEDELETE(PL_defstash, savepv(tmpbuf), strlen(tmpbuf));
- SV* sv_mortalcopy _((SV* oldsv));
+=item C<SAVEDESTRUCTOR(DESTRUCTORFUNC_NOCONTEXT_t f, void *p)>
-=item SvOK
+At the end of I<pseudo-block> the function C<f> is called with the
+only argument C<p>.
-Returns a boolean indicating whether the value is an SV.
+=item C<SAVEDESTRUCTOR_X(DESTRUCTORFUNC_t f, void *p)>
- int SvOK (SV* sv)
+At the end of I<pseudo-block> the function C<f> is called with the
+implicit context argument (if any), and C<p>.
-=item sv_newmortal
+=item C<SAVESTACK_POS()>
-Creates a new SV which is mortal. The refcount of the SV is set to 1.
+The current offset on the Perl internal stack (cf. C<SP>) is restored
+at the end of I<pseudo-block>.
- SV* sv_newmortal _((void));
+=back
-=item sv_no
+The following API list contains functions, thus one needs to
+provide pointers to the modifiable data explicitly (either C pointers,
+or Perlish C<GV *>s). Where the above macros take C<int>, a similar
+function takes C<int *>.
-This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
+=over 4
-=item SvNIOK
+=item C<SV* save_scalar(GV *gv)>
-Returns a boolean indicating whether the SV contains a number, integer or
-double.
+Equivalent to Perl code C<local $gv>.
- int SvNIOK (SV* SV)
+=item C<AV* save_ary(GV *gv)>
-=item SvNIOK_off
+=item C<HV* save_hash(GV *gv)>
-Unsets the NV/IV status of an SV.
+Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
- SvNIOK_off (SV* sv)
+=item C<void save_item(SV *item)>
-=item SvNIOKp
+Duplicates the current value of C<SV>, on the exit from the current
+C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
+using the stored value.
-Returns a boolean indicating whether the SV contains a number, integer or
-double. Checks the B<private> setting. Use C<SvNIOK>.
+=item C<void save_list(SV **sarg, I32 maxsarg)>
- int SvNIOKp (SV* SV)
+A variant of C<save_item> which takes multiple arguments via an array
+C<sarg> of C<SV*> of length C<maxsarg>.
-=item SvNOK
+=item C<SV* save_svref(SV **sptr)>
-Returns a boolean indicating whether the SV contains a double.
+Similar to C<save_scalar>, but will reinstate an C<SV *>.
- int SvNOK (SV* SV)
+=item C<void save_aptr(AV **aptr)>
-=item SvNOK_off
+=item C<void save_hptr(HV **hptr)>
-Unsets the NV status of an SV.
+Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
- SvNOK_off (SV* sv)
+=back
-=item SvNOK_on
+The C<Alias> module implements localization of the basic types within the
+I<caller's scope>. People who are interested in how to localize things in
+the containing scope should take a look there too.
-Tells an SV that it is a double.
+=head1 Subroutines
- SvNOK_on (SV* sv)
+=head2 XSUBs and the Argument Stack
-=item SvNOK_only
+The XSUB mechanism is a simple way for Perl programs to access C subroutines.
+An XSUB routine will have a stack that contains the arguments from the Perl
+program, and a way to map from the Perl data structures to a C equivalent.
-Tells an SV that it is a double and disables all other OK bits.
+The stack arguments are accessible through the C<ST(n)> macro, which returns
+the C<n>'th stack argument. Argument 0 is the first argument passed in the
+Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
+an C<SV*> is used.
- SvNOK_on (SV* sv)
+Most of the time, output from the C routine can be handled through use of
+the RETVAL and OUTPUT directives. However, there are some cases where the
+argument stack is not already long enough to handle all the return values.
+An example is the POSIX tzname() call, which takes no arguments, but returns
+two, the local time zone's standard and summer time abbreviations.
-=item SvNOK_only
+To handle this situation, the PPCODE directive is used and the stack is
+extended using the macro:
-Tells an SV that it is a double and disables all other OK bits.
+ EXTEND(SP, num);
- SvNOK_on (SV* sv)
+where C<SP> is the macro that represents the local copy of the stack pointer,
+and C<num> is the number of elements the stack should be extended by.
-=item SvNOKp
+Now that there is room on the stack, values can be pushed on it using C<PUSHs>
+macro. The values pushed will often need to be "mortal" (See L</Reference Counts and Mortality>).
-Returns a boolean indicating whether the SV contains a double. Checks the
-B<private> setting. Use C<SvNOK>.
+ PUSHs(sv_2mortal(newSViv(an_integer)))
+ PUSHs(sv_2mortal(newSVpv("Some String",0)))
+ PUSHs(sv_2mortal(newSVnv(3.141592)))
- int SvNOKp (SV* SV)
+And now the Perl program calling C<tzname>, the two values will be assigned
+as in:
-=item SvNV
+ ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
-Returns the double which is stored in the SV.
+An alternate (and possibly simpler) method to pushing values on the stack is
+to use the macro:
- double SvNV (SV* sv);
+ XPUSHs(SV*)
-=item SvNVX
+This macro automatically adjust the stack for you, if needed. Thus, you
+do not need to call C<EXTEND> to extend the stack.
-Returns the double which is stored in the SV.
+Despite their suggestions in earlier versions of this document the macros
+C<PUSHi>, C<PUSHn> and C<PUSHp> are I<not> suited to XSUBs which return
+multiple results, see L</Putting a C value on Perl stack>.
- double SvNVX (SV* sv);
+For more information, consult L<perlxs> and L<perlxstut>.
-=item SvPOK
+=head2 Calling Perl Routines from within C Programs
-Returns a boolean indicating whether the SV contains a character string.
+There are four routines that can be used to call a Perl subroutine from
+within a C program. These four are:
- int SvPOK (SV* SV)
+ I32 call_sv(SV*, I32);
+ I32 call_pv(const char*, I32);
+ I32 call_method(const char*, I32);
+ I32 call_argv(const char*, I32, register char**);
-=item SvPOK_off
+The routine most often used is C<call_sv>. The C<SV*> argument
+contains either the name of the Perl subroutine to be called, or a
+reference to the subroutine. The second argument consists of flags
+that control the context in which the subroutine is called, whether
+or not the subroutine is being passed arguments, how errors should be
+trapped, and how to treat return values.
-Unsets the PV status of an SV.
+All four routines return the number of arguments that the subroutine returned
+on the Perl stack.
- SvPOK_off (SV* sv)
+These routines used to be called C<perl_call_sv> etc., before Perl v5.6.0,
+but those names are now deprecated; macros of the same name are provided for
+compatibility.
-=item SvPOK_on
+When using any of these routines (except C<call_argv>), the programmer
+must manipulate the Perl stack. These include the following macros and
+functions:
-Tells an SV that it is a string.
+ dSP
+ SP
+ PUSHMARK()
+ PUTBACK
+ SPAGAIN
+ ENTER
+ SAVETMPS
+ FREETMPS
+ LEAVE
+ XPUSH*()
+ POP*()
- SvPOK_on (SV* sv)
+For a detailed description of calling conventions from C to Perl,
+consult L<perlcall>.
-=item SvPOK_only
+=head2 Memory Allocation
-Tells an SV that it is a string and disables all other OK bits.
+All memory meant to be used with the Perl API functions should be manipulated
+using the macros described in this section. The macros provide the necessary
+transparency between differences in the actual malloc implementation that is
+used within perl.
- SvPOK_on (SV* sv)
+It is suggested that you enable the version of malloc that is distributed
+with Perl. It keeps pools of various sizes of unallocated memory in
+order to satisfy allocation requests more quickly. However, on some
+platforms, it may cause spurious malloc or free errors.
-=item SvPOK_only
+ New(x, pointer, number, type);
+ Newc(x, pointer, number, type, cast);
+ Newz(x, pointer, number, type);
-Tells an SV that it is a string and disables all other OK bits.
+These three macros are used to initially allocate memory.
- SvPOK_on (SV* sv)
+The first argument C<x> was a "magic cookie" that was used to keep track
+of who called the macro, to help when debugging memory problems. However,
+the current code makes no use of this feature (most Perl developers now
+use run-time memory checkers), so this argument can be any number.
-=item SvPOKp
+The second argument C<pointer> should be the name of a variable that will
+point to the newly allocated memory.
-Returns a boolean indicating whether the SV contains a character string.
-Checks the B<private> setting. Use C<SvPOK>.
+The third and fourth arguments C<number> and C<type> specify how many of
+the specified type of data structure should be allocated. The argument
+C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
+should be used if the C<pointer> argument is different from the C<type>
+argument.
- int SvPOKp (SV* SV)
+Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
+to zero out all the newly allocated memory.
-=item SvPV
+ Renew(pointer, number, type);
+ Renewc(pointer, number, type, cast);
+ Safefree(pointer)
-Returns a pointer to the string in the SV, or a stringified form of the SV
-if the SV does not contain a string. If C<len> is C<na> then Perl will
-handle the length on its own.
+These three macros are used to change a memory buffer size or to free a
+piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
+match those of C<New> and C<Newc> with the exception of not needing the
+"magic cookie" argument.
- char * SvPV (SV* sv, int len )
+ Move(source, dest, number, type);
+ Copy(source, dest, number, type);
+ Zero(dest, number, type);
-=item SvPVX
+These three macros are used to move, copy, or zero out previously allocated
+memory. The C<source> and C<dest> arguments point to the source and
+destination starting points. Perl will move, copy, or zero out C<number>
+instances of the size of the C<type> data structure (using the C<sizeof>
+function).
-Returns a pointer to the string in the SV. The SV must contain a string.
+=head2 PerlIO
- char * SvPVX (SV* sv)
+The most recent development releases of Perl has been experimenting with
+removing Perl's dependency on the "normal" standard I/O suite and allowing
+other stdio implementations to be used. This involves creating a new
+abstraction layer that then calls whichever implementation of stdio Perl
+was compiled with. All XSUBs should now use the functions in the PerlIO
+abstraction layer and not make any assumptions about what kind of stdio
+is being used.
-=item SvREFCNT
+For a complete description of the PerlIO abstraction, consult L<perlapio>.
-Returns the value of the object's refcount.
+=head2 Putting a C value on Perl stack
- int SvREFCNT (SV* sv);
+A lot of opcodes (this is an elementary operation in the internal perl
+stack machine) put an SV* on the stack. However, as an optimization
+the corresponding SV is (usually) not recreated each time. The opcodes
+reuse specially assigned SVs (I<target>s) which are (as a corollary)
+not constantly freed/created.
-=item SvREFCNT_dec
+Each of the targets is created only once (but see
+L<Scratchpads and recursion> below), and when an opcode needs to put
+an integer, a double, or a string on stack, it just sets the
+corresponding parts of its I<target> and puts the I<target> on stack.
-Decrements the refcount of the given SV.
+The macro to put this target on stack is C<PUSHTARG>, and it is
+directly used in some opcodes, as well as indirectly in zillions of
+others, which use it via C<(X)PUSH[pni]>.
- void SvREFCNT_dec (SV* sv)
+Because the target is reused, you must be careful when pushing multiple
+values on the stack. The following code will not do what you think:
-=item SvREFCNT_inc
+ XPUSHi(10);
+ XPUSHi(20);
-Increments the refcount of the given SV.
+This translates as "set C<TARG> to 10, push a pointer to C<TARG> onto
+the stack; set C<TARG> to 20, push a pointer to C<TARG> onto the stack".
+At the end of the operation, the stack does not contain the values 10
+and 20, but actually contains two pointers to C<TARG>, which we have set
+to 20. If you need to push multiple different values, use C<XPUSHs>,
+which bypasses C<TARG>.
- void SvREFCNT_inc (SV* sv)
+On a related note, if you do use C<(X)PUSH[npi]>, then you're going to
+need a C<dTARG> in your variable declarations so that the C<*PUSH*>
+macros can make use of the local variable C<TARG>.
-=item SvROK
+=head2 Scratchpads
-Tests if the SV is an RV.
+The question remains on when the SVs which are I<target>s for opcodes
+are created. The answer is that they are created when the current unit --
+a subroutine or a file (for opcodes for statements outside of
+subroutines) -- is compiled. During this time a special anonymous Perl
+array is created, which is called a scratchpad for the current
+unit.
- int SvROK (SV* sv)
+A scratchpad keeps SVs which are lexicals for the current unit and are
+targets for opcodes. One can deduce that an SV lives on a scratchpad
+by looking on its flags: lexicals have C<SVs_PADMY> set, and
+I<target>s have C<SVs_PADTMP> set.
-=item SvROK_off
+The correspondence between OPs and I<target>s is not 1-to-1. Different
+OPs in the compile tree of the unit can use the same target, if this
+would not conflict with the expected life of the temporary.
-Unsets the RV status of an SV.
+=head2 Scratchpads and recursion
- SvROK_off (SV* sv)
+In fact it is not 100% true that a compiled unit contains a pointer to
+the scratchpad AV. In fact it contains a pointer to an AV of
+(initially) one element, and this element is the scratchpad AV. Why do
+we need an extra level of indirection?
-=item SvROK_on
+The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
+these can create several execution pointers going into the same
+subroutine. For the subroutine-child not write over the temporaries
+for the subroutine-parent (lifespan of which covers the call to the
+child), the parent and the child should have different
+scratchpads. (I<And> the lexicals should be separate anyway!)
-Tells an SV that it is an RV.
+So each subroutine is born with an array of scratchpads (of length 1).
+On each entry to the subroutine it is checked that the current
+depth of the recursion is not more than the length of this array, and
+if it is, new scratchpad is created and pushed into the array.
- SvROK_on (SV* sv)
+The I<target>s on this scratchpad are C<undef>s, but they are already
+marked with correct flags.
-=item SvRV
+=head1 Compiled code
-Dereferences an RV to return the SV.
+=head2 Code tree
- SV* SvRV (SV* sv);
+Here we describe the internal form your code is converted to by
+Perl. Start with a simple example:
-=item sv_setiv
+ $a = $b + $c;
-Copies an integer into the given SV.
+This is converted to a tree similar to this one:
- void sv_setiv _((SV* sv, IV num));
+ assign-to
+ / \
+ + $a
+ / \
+ $b $c
+
+(but slightly more complicated). This tree reflects the way Perl
+parsed your code, but has nothing to do with the execution order.
+There is an additional "thread" going through the nodes of the tree
+which shows the order of execution of the nodes. In our simplified
+example above it looks like:
-=item sv_setnv
+ $b ---> $c ---> + ---> $a ---> assign-to
-Copies a double into the given SV.
+But with the actual compile tree for C<$a = $b + $c> it is different:
+some nodes I<optimized away>. As a corollary, though the actual tree
+contains more nodes than our simplified example, the execution order
+is the same as in our example.
- void sv_setnv _((SV* sv, double num));
+=head2 Examining the tree
-=item sv_setpv
+If you have your perl compiled for debugging (usually done with C<-D
+optimize=-g> on C<Configure> command line), you may examine the
+compiled tree by specifying C<-Dx> on the Perl command line. The
+output takes several lines per node, and for C<$b+$c> it looks like
+this:
-Copies a string into an SV. The string must be null-terminated.
+ 5 TYPE = add ===> 6
+ TARG = 1
+ FLAGS = (SCALAR,KIDS)
+ {
+ TYPE = null ===> (4)
+ (was rv2sv)
+ FLAGS = (SCALAR,KIDS)
+ {
+ 3 TYPE = gvsv ===> 4
+ FLAGS = (SCALAR)
+ GV = main::b
+ }
+ }
+ {
+ TYPE = null ===> (5)
+ (was rv2sv)
+ FLAGS = (SCALAR,KIDS)
+ {
+ 4 TYPE = gvsv ===> 5
+ FLAGS = (SCALAR)
+ GV = main::c
+ }
+ }
+
+This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
+not optimized away (one per number in the left column). The immediate
+children of the given node correspond to C<{}> pairs on the same level
+of indentation, thus this listing corresponds to the tree:
+
+ add
+ / \
+ null null
+ | |
+ gvsv gvsv
+
+The execution order is indicated by C<===E<gt>> marks, thus it is C<3
+4 5 6> (node C<6> is not included into above listing), i.e.,
+C<gvsv gvsv add whatever>.
+
+Each of these nodes represents an op, a fundamental operation inside the
+Perl core. The code which implements each operation can be found in the
+F<pp*.c> files; the function which implements the op with type C<gvsv>
+is C<pp_gvsv>, and so on. As the tree above shows, different ops have
+different numbers of children: C<add> is a binary operator, as one would
+expect, and so has two children. To accommodate the various different
+numbers of children, there are various types of op data structure, and
+they link together in different ways.
+
+The simplest type of op structure is C<OP>: this has no children. Unary
+operators, C<UNOP>s, have one child, and this is pointed to by the
+C<op_first> field. Binary operators (C<BINOP>s) have not only an
+C<op_first> field but also an C<op_last> field. The most complex type of
+op is a C<LISTOP>, which has any number of children. In this case, the
+first child is pointed to by C<op_first> and the last child by
+C<op_last>. The children in between can be found by iteratively
+following the C<op_sibling> pointer from the first child to the last.
+
+There are also two other op types: a C<PMOP> holds a regular expression,
+and has no children, and a C<LOOP> may or may not have children. If the
+C<op_children> field is non-zero, it behaves like a C<LISTOP>. To
+complicate matters, if a C<UNOP> is actually a C<null> op after
+optimization (see L</Compile pass 2: context propagation>) it will still
+have children in accordance with its former type.
+
+=head2 Compile pass 1: check routines
+
+The tree is created by the compiler while I<yacc> code feeds it
+the constructions it recognizes. Since I<yacc> works bottom-up, so does
+the first pass of perl compilation.
+
+What makes this pass interesting for perl developers is that some
+optimization may be performed on this pass. This is optimization by
+so-called "check routines". The correspondence between node names
+and corresponding check routines is described in F<opcode.pl> (do not
+forget to run C<make regen_headers> if you modify this file).
+
+A check routine is called when the node is fully constructed except
+for the execution-order thread. Since at this time there are no
+back-links to the currently constructed node, one can do most any
+operation to the top-level node, including freeing it and/or creating
+new nodes above/below it.
+
+The check routine returns the node which should be inserted into the
+tree (if the top-level node was not modified, check routine returns
+its argument).
+
+By convention, check routines have names C<ck_*>. They are usually
+called from C<new*OP> subroutines (or C<convert>) (which in turn are
+called from F<perly.y>).
+
+=head2 Compile pass 1a: constant folding
+
+Immediately after the check routine is called the returned node is
+checked for being compile-time executable. If it is (the value is
+judged to be constant) it is immediately executed, and a I<constant>
+node with the "return value" of the corresponding subtree is
+substituted instead. The subtree is deleted.
+
+If constant folding was not performed, the execution-order thread is
+created.
+
+=head2 Compile pass 2: context propagation
+
+When a context for a part of compile tree is known, it is propagated
+down through the tree. At this time the context can have 5 values
+(instead of 2 for runtime context): void, boolean, scalar, list, and
+lvalue. In contrast with the pass 1 this pass is processed from top
+to bottom: a node's context determines the context for its children.
+
+Additional context-dependent optimizations are performed at this time.
+Since at this moment the compile tree contains back-references (via
+"thread" pointers), nodes cannot be free()d now. To allow
+optimized-away nodes at this stage, such nodes are null()ified instead
+of free()ing (i.e. their type is changed to OP_NULL).
+
+=head2 Compile pass 3: peephole optimization
+
+After the compile tree for a subroutine (or for an C<eval> or a file)
+is created, an additional pass over the code is performed. This pass
+is neither top-down or bottom-up, but in the execution order (with
+additional complications for conditionals). These optimizations are
+done in the subroutine peep(). Optimizations performed at this stage
+are subject to the same restrictions as in the pass 2.
+
+=head2 Pluggable runops
+
+The compile tree is executed in a runops function. There are two runops
+functions in F<run.c>. C<Perl_runops_debug> is used with DEBUGGING and
+C<Perl_runops_standard> is used otherwise. For fine control over the
+execution of the compile tree it is possible to provide your own runops
+function.
+
+It's probably best to copy one of the existing runops functions and
+change it to suit your needs. Then, in the BOOT section of your XS
+file, add the line:
+
+ PL_runops = my_runops;
+
+This function should be as efficient as possible to keep your programs
+running as fast as possible.
+
+=head1 Examining internal data structures with the C<dump> functions
+
+To aid debugging, the source file F<dump.c> contains a number of
+functions which produce formatted output of internal data structures.
+
+The most commonly used of these functions is C<Perl_sv_dump>; it's used
+for dumping SVs, AVs, HVs, and CVs. The C<Devel::Peek> module calls
+C<sv_dump> to produce debugging output from Perl-space, so users of that
+module should already be familiar with its format.
+
+C<Perl_op_dump> can be used to dump an C<OP> structure or any of its
+derivatives, and produces output similar to C<perl -Dx>; in fact,
+C<Perl_dump_eval> will dump the main root of the code being evaluated,
+exactly like C<-Dx>.
+
+Other useful functions are C<Perl_dump_sub>, which turns a C<GV> into an
+op tree, C<Perl_dump_packsubs> which calls C<Perl_dump_sub> on all the
+subroutines in a package like so: (Thankfully, these are all xsubs, so
+there is no op tree)
+
+ (gdb) print Perl_dump_packsubs(PL_defstash)
+
+ SUB attributes::bootstrap = (xsub 0x811fedc 0)
+
+ SUB UNIVERSAL::can = (xsub 0x811f50c 0)
+
+ SUB UNIVERSAL::isa = (xsub 0x811f304 0)
+
+ SUB UNIVERSAL::VERSION = (xsub 0x811f7ac 0)
+
+ SUB DynaLoader::boot_DynaLoader = (xsub 0x805b188 0)
+
+and C<Perl_dump_all>, which dumps all the subroutines in the stash and
+the op tree of the main root.
+
+=head1 How multiple interpreters and concurrency are supported
+
+=head2 Background and PERL_IMPLICIT_CONTEXT
+
+The Perl interpreter can be regarded as a closed box: it has an API
+for feeding it code or otherwise making it do things, but it also has
+functions for its own use. This smells a lot like an object, and
+there are ways for you to build Perl so that you can have multiple
+interpreters, with one interpreter represented either as a C structure,
+or inside a thread-specific structure. These structures contain all
+the context, the state of that interpreter.
+
+Three macros control the major Perl build flavors: MULTIPLICITY, and
+USE_5005THREADS. The MULTIPLICITY build has a C structure
+that packages all the interpreter state, and there is a similar thread-specific
+data structure under USE_5005THREADS. In both cases,
+PERL_IMPLICIT_CONTEXT is also normally defined, and enables the
+support for passing in a "hidden" first argument that represents all three
+data structures.
+
+All this obviously requires a way for the Perl internal functions to be
+either subroutines taking some kind of structure as the first
+argument, or subroutines taking nothing as the first argument. To
+enable these two very different ways of building the interpreter,
+the Perl source (as it does in so many other situations) makes heavy
+use of macros and subroutine naming conventions.
+
+First problem: deciding which functions will be public API functions and
+which will be private. All functions whose names begin C<S_> are private
+(think "S" for "secret" or "static"). All other functions begin with
+"Perl_", but just because a function begins with "Perl_" does not mean it is
+part of the API. (See L</Internal Functions>.) The easiest way to be B<sure> a
+function is part of the API is to find its entry in L<perlapi>.
+If it exists in L<perlapi>, it's part of the API. If it doesn't, and you
+think it should be (i.e., you need it for your extension), send mail via
+L<perlbug> explaining why you think it should be.
- void sv_setpv _((SV* sv, char* ptr));
+Second problem: there must be a syntax so that the same subroutine
+declarations and calls can pass a structure as their first argument,
+or pass nothing. To solve this, the subroutines are named and
+declared in a particular way. Here's a typical start of a static
+function used within the Perl guts:
-=item sv_setpvn
+ STATIC void
+ S_incline(pTHX_ char *s)
-Copies a string into an SV. The C<len> parameter indicates the number of
-bytes to be copied.
+STATIC becomes "static" in C, and may be #define'd to nothing in some
+configurations in future.
- void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
+A public function (i.e. part of the internal API, but not necessarily
+sanctioned for use in extensions) begins like this:
-=item sv_setref_iv
+ void
+ Perl_sv_setsv(pTHX_ SV* dsv, SV* ssv)
-Copies an integer into a new SV, optionally blessing the SV. The C<rv>
-argument will be upgraded to an RV. That RV will be modified to point to
-the new SV. The C<classname> argument indicates the package for the
-blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
-will be returned and will have a refcount of 1.
+C<pTHX_> is one of a number of macros (in perl.h) that hide the
+details of the interpreter's context. THX stands for "thread", "this",
+or "thingy", as the case may be. (And no, George Lucas is not involved. :-)
+The first character could be 'p' for a B<p>rototype, 'a' for B<a>rgument,
+or 'd' for B<d>eclaration, so we have C<pTHX>, C<aTHX> and C<dTHX>, and
+their variants.
- SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
+When Perl is built without options that set PERL_IMPLICIT_CONTEXT, there is no
+first argument containing the interpreter's context. The trailing underscore
+in the pTHX_ macro indicates that the macro expansion needs a comma
+after the context argument because other arguments follow it. If
+PERL_IMPLICIT_CONTEXT is not defined, pTHX_ will be ignored, and the
+subroutine is not prototyped to take the extra argument. The form of the
+macro without the trailing underscore is used when there are no additional
+explicit arguments.
+
+When a core function calls another, it must pass the context. This
+is normally hidden via macros. Consider C<sv_setsv>. It expands into
+something like this:
-=item sv_setref_nv
+ ifdef PERL_IMPLICIT_CONTEXT
+ define sv_setsv(a,b) Perl_sv_setsv(aTHX_ a, b)
+ /* can't do this for vararg functions, see below */
+ else
+ define sv_setsv Perl_sv_setsv
+ endif
+
+This works well, and means that XS authors can gleefully write:
-Copies a double into a new SV, optionally blessing the SV. The C<rv>
-argument will be upgraded to an RV. That RV will be modified to point to
-the new SV. The C<classname> argument indicates the package for the
-blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
-will be returned and will have a refcount of 1.
+ sv_setsv(foo, bar);
- SV* sv_setref_nv _((SV *rv, char *classname, double nv));
+and still have it work under all the modes Perl could have been
+compiled with.
+
+This doesn't work so cleanly for varargs functions, though, as macros
+imply that the number of arguments is known in advance. Instead we
+either need to spell them out fully, passing C<aTHX_> as the first
+argument (the Perl core tends to do this with functions like
+Perl_warner), or use a context-free version.
+
+The context-free version of Perl_warner is called
+Perl_warner_nocontext, and does not take the extra argument. Instead
+it does dTHX; to get the context from thread-local storage. We
+C<#define warner Perl_warner_nocontext> so that extensions get source
+compatibility at the expense of performance. (Passing an arg is
+cheaper than grabbing it from thread-local storage.)
+
+You can ignore [pad]THXx when browsing the Perl headers/sources.
+Those are strictly for use within the core. Extensions and embedders
+need only be aware of [pad]THX.
+
+=head2 So what happened to dTHR?
+
+C<dTHR> was introduced in perl 5.005 to support the older thread model.
+The older thread model now uses the C<THX> mechanism to pass context
+pointers around, so C<dTHR> is not useful any more. Perl 5.6.0 and
+later still have it for backward source compatibility, but it is defined
+to be a no-op.
+
+=head2 How do I use all this in extensions?
+
+When Perl is built with PERL_IMPLICIT_CONTEXT, extensions that call
+any functions in the Perl API will need to pass the initial context
+argument somehow. The kicker is that you will need to write it in
+such a way that the extension still compiles when Perl hasn't been
+built with PERL_IMPLICIT_CONTEXT enabled.
+
+There are three ways to do this. First, the easy but inefficient way,
+which is also the default, in order to maintain source compatibility
+with extensions: whenever XSUB.h is #included, it redefines the aTHX
+and aTHX_ macros to call a function that will return the context.
+Thus, something like:
+
+ sv_setsv(asv, bsv);
+
+in your extension will translate to this when PERL_IMPLICIT_CONTEXT is
+in effect:
+
+ Perl_sv_setsv(Perl_get_context(), asv, bsv);
+
+or to this otherwise:
-=item sv_setref_pv
+ Perl_sv_setsv(asv, bsv);
-Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
-argument will be upgraded to an RV. That RV will be modified to point to
-the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
-into the SV. The C<classname> argument indicates the package for the
-blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
-will be returned and will have a refcount of 1.
+You have to do nothing new in your extension to get this; since
+the Perl library provides Perl_get_context(), it will all just
+work.
- SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
+The second, more efficient way is to use the following template for
+your Foo.xs:
-Do not use with integral Perl types such as HV, AV, SV, CV, because those
-objects will become corrupted by the pointer copy process.
+ #define PERL_NO_GET_CONTEXT /* we want efficiency */
+ #include "EXTERN.h"
+ #include "perl.h"
+ #include "XSUB.h"
-Note that C<sv_setref_pvn> copies the string while this copies the pointer.
+ static my_private_function(int arg1, int arg2);
+
+ static SV *
+ my_private_function(int arg1, int arg2)
+ {
+ dTHX; /* fetch context */
+ ... call many Perl API functions ...
+ }
+
+ [... etc ...]
+
+ MODULE = Foo PACKAGE = Foo
+
+ /* typical XSUB */
-=item sv_setref_pvn
+ void
+ my_xsub(arg)
+ int arg
+ CODE:
+ my_private_function(arg, 10);
-Copies a string into a new SV, optionally blessing the SV. The length of the
-string must be specified with C<n>. The C<rv> argument will be upgraded to
-an RV. That RV will be modified to point to the new SV. The C<classname>
-argument indicates the package for the blessing. Set C<classname> to
-C<Nullch> to avoid the blessing. The new SV will be returned and will have
-a refcount of 1.
+Note that the only two changes from the normal way of writing an
+extension is the addition of a C<#define PERL_NO_GET_CONTEXT> before
+including the Perl headers, followed by a C<dTHX;> declaration at
+the start of every function that will call the Perl API. (You'll
+know which functions need this, because the C compiler will complain
+that there's an undeclared identifier in those functions.) No changes
+are needed for the XSUBs themselves, because the XS() macro is
+correctly defined to pass in the implicit context if needed.
- SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
+The third, even more efficient way is to ape how it is done within
+the Perl guts:
-Note that C<sv_setref_pv> copies the pointer while this copies the string.
-=item sv_setsv
+ #define PERL_NO_GET_CONTEXT /* we want efficiency */
+ #include "EXTERN.h"
+ #include "perl.h"
+ #include "XSUB.h"
-Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
-The source SV may be destroyed if it is mortal or temporary.
+ /* pTHX_ only needed for functions that call Perl API */
+ static my_private_function(pTHX_ int arg1, int arg2);
- void sv_setsv _((SV* dsv, SV* ssv));
+ static SV *
+ my_private_function(pTHX_ int arg1, int arg2)
+ {
+ /* dTHX; not needed here, because THX is an argument */
+ ... call Perl API functions ...
+ }
-=item SvSetSV
+ [... etc ...]
-A wrapper around C<sv_setsv>. Safe even if C<dst==ssv>.
+ MODULE = Foo PACKAGE = Foo
-=item SvSTASH
+ /* typical XSUB */
-Returns the stash of the SV.
+ void
+ my_xsub(arg)
+ int arg
+ CODE:
+ my_private_function(aTHX_ arg, 10);
- HV * SvSTASH (SV* sv)
+This implementation never has to fetch the context using a function
+call, since it is always passed as an extra argument. Depending on
+your needs for simplicity or efficiency, you may mix the previous
+two approaches freely.
-=item SVt_IV
+Never add a comma after C<pTHX> yourself--always use the form of the
+macro with the underscore for functions that take explicit arguments,
+or the form without the argument for functions with no explicit arguments.
-Integer type flag for scalars. See C<svtype>.
+=head2 Should I do anything special if I call perl from multiple threads?
-=item SVt_PV
+If you create interpreters in one thread and then proceed to call them in
+another, you need to make sure perl's own Thread Local Storage (TLS) slot is
+initialized correctly in each of those threads.
-Pointer type flag for scalars. See C<svtype>.
+The C<perl_alloc> and C<perl_clone> API functions will automatically set
+the TLS slot to the interpreter they created, so that there is no need to do
+anything special if the interpreter is always accessed in the same thread that
+created it, and that thread did not create or call any other interpreters
+afterwards. If that is not the case, you have to set the TLS slot of the
+thread before calling any functions in the Perl API on that particular
+interpreter. This is done by calling the C<PERL_SET_CONTEXT> macro in that
+thread as the first thing you do:
-=item SVt_PVAV
+ /* do this before doing anything else with some_perl */
+ PERL_SET_CONTEXT(some_perl);
-Type flag for arrays. See C<svtype>.
+ ... other Perl API calls on some_perl go here ...
-=item SVt_PVCV
+=head2 Future Plans and PERL_IMPLICIT_SYS
-Type flag for code refs. See C<svtype>.
+Just as PERL_IMPLICIT_CONTEXT provides a way to bundle up everything
+that the interpreter knows about itself and pass it around, so too are
+there plans to allow the interpreter to bundle up everything it knows
+about the environment it's running on. This is enabled with the
+PERL_IMPLICIT_SYS macro. Currently it only works with USE_ITHREADS
+and USE_5005THREADS on Windows (see inside iperlsys.h).
-=item SVt_PVHV
+This allows the ability to provide an extra pointer (called the "host"
+environment) for all the system calls. This makes it possible for
+all the system stuff to maintain their own state, broken down into
+seven C structures. These are thin wrappers around the usual system
+calls (see win32/perllib.c) for the default perl executable, but for a
+more ambitious host (like the one that would do fork() emulation) all
+the extra work needed to pretend that different interpreters are
+actually different "processes", would be done here.
-Type flag for hashes. See C<svtype>.
+The Perl engine/interpreter and the host are orthogonal entities.
+There could be one or more interpreters in a process, and one or
+more "hosts", with free association between them.
-=item SVt_PVMG
+=head1 Internal Functions
-Type flag for blessed scalars. See C<svtype>.
+All of Perl's internal functions which will be exposed to the outside
+world are be prefixed by C<Perl_> so that they will not conflict with XS
+functions or functions used in a program in which Perl is embedded.
+Similarly, all global variables begin with C<PL_>. (By convention,
+static functions start with C<S_>)
-=item SVt_NV
+Inside the Perl core, you can get at the functions either with or
+without the C<Perl_> prefix, thanks to a bunch of defines that live in
+F<embed.h>. This header file is generated automatically from
+F<embed.pl>. F<embed.pl> also creates the prototyping header files for
+the internal functions, generates the documentation and a lot of other
+bits and pieces. It's important that when you add a new function to the
+core or change an existing one, you change the data in the table at the
+end of F<embed.pl> as well. Here's a sample entry from that table:
-Double type flag for scalars. See C<svtype>.
+ Apd |SV** |av_fetch |AV* ar|I32 key|I32 lval
-=item SvTRUE
+The second column is the return type, the third column the name. Columns
+after that are the arguments. The first column is a set of flags:
-Returns a boolean indicating whether Perl would evaluate the SV as true or
-false, defined or undefined.
+=over 3
- int SvTRUE (SV* sv)
+=item A
-=item SvTYPE
+This function is a part of the public API.
-Returns the type of the SV. See C<svtype>.
+=item p
- svtype SvTYPE (SV* sv)
+This function has a C<Perl_> prefix; ie, it is defined as C<Perl_av_fetch>
-=item svtype
+=item d
-An enum of flags for Perl types. These are found in the file B<sv.h> in the
-C<svtype> enum. Test these flags with the C<SvTYPE> macro.
+This function has documentation using the C<apidoc> feature which we'll
+look at in a second.
-=item SvUPGRADE
+=back
-Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
-the upgrade if necessary. See C<svtype>.
+Other available flags are:
- bool SvUPGRADE _((SV* sv, svtype mt));
+=over 3
-=item sv_upgrade
+=item s
-Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
+This is a static function and is defined as C<S_whatever>, and usually
+called within the sources as C<whatever(...)>.
-=item sv_undef
+=item n
-This is the C<undef> SV. Always refer to this as C<&sv_undef>.
+This does not use C<aTHX_> and C<pTHX> to pass interpreter context. (See
+L<perlguts/Background and PERL_IMPLICIT_CONTEXT>.)
-=item sv_unref
+=item r
-Unsets the RV status of the SV, and decrements the refcount of whatever was
-being referenced by the RV. This can almost be thought of as a reversal of
-C<newSVrv>. See C<SvROK_off>.
+This function never returns; C<croak>, C<exit> and friends.
- void sv_unref _((SV* sv));
+=item f
-=item sv_usepvn
+This function takes a variable number of arguments, C<printf> style.
+The argument list should end with C<...>, like this:
-Tells an SV to use C<ptr> to find its string value. Normally the string is
-stored inside the SV but sv_usepvn allows the SV to use an outside string.
-The C<ptr> should point to memory that was allocated by C<malloc>. The
-string length, C<len>, must be supplied. This function will realloc the
-memory pointed to by C<ptr>, so that pointer should not be freed or used by
-the programmer after giving it to sv_usepvn.
+ Afprd |void |croak |const char* pat|...
- void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
+=item M
-=item sv_yes
+This function is part of the experimental development API, and may change
+or disappear without notice.
-This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
+=item o
-=item THIS
+This function should not have a compatibility macro to define, say,
+C<Perl_parse> to C<parse>. It must be called as C<Perl_parse>.
-Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
-This is always the proper type for the C++ object. See C<CLASS> and
-L<perlxs/"Using XS With C++">.
+=item j
-=item toLOWER
+This function is not a member of C<CPerlObj>. If you don't know
+what this means, don't use it.
-Converts the specified character to lowercase.
+=item x
- int toLOWER (char c)
+This function isn't exported out of the Perl core.
-=item toUPPER
+=back
-Converts the specified character to uppercase.
+If you edit F<embed.pl>, you will need to run C<make regen_headers> to
+force a rebuild of F<embed.h> and other auto-generated files.
- int toUPPER (char c)
+=head2 Formatted Printing of IVs, UVs, and NVs
-=item warn
+If you are printing IVs, UVs, or NVS instead of the stdio(3) style
+formatting codes like C<%d>, C<%ld>, C<%f>, you should use the
+following macros for portability
-This is the XSUB-writer's interface to Perl's C<warn> function. Use this
-function the same way you use the C C<printf> function. See C<croak()>.
+ IVdf IV in decimal
+ UVuf UV in decimal
+ UVof UV in octal
+ UVxf UV in hexadecimal
+ NVef NV %e-like
+ NVff NV %f-like
+ NVgf NV %g-like
-=item XPUSHi
+These will take care of 64-bit integers and long doubles.
+For example:
-Push an integer onto the stack, extending the stack if necessary. See
-C<PUSHi>.
+ printf("IV is %"IVdf"\n", iv);
- XPUSHi(int d)
+The IVdf will expand to whatever is the correct format for the IVs.
-=item XPUSHn
+If you are printing addresses of pointers, use UVxf combined
+with PTR2UV(), do not use %lx or %p.
-Push a double onto the stack, extending the stack if necessary. See
-C<PUSHn>.
+=head2 Pointer-To-Integer and Integer-To-Pointer
- XPUSHn(double d)
+Because pointer size does not necessarily equal integer size,
+use the follow macros to do it right.
-=item XPUSHp
+ PTR2UV(pointer)
+ PTR2IV(pointer)
+ PTR2NV(pointer)
+ INT2PTR(pointertotype, integer)
-Push a string onto the stack, extending the stack if necessary. The C<len>
-indicates the length of the string. See C<PUSHp>.
+For example:
- XPUSHp(char *c, int len)
+ IV iv = ...;
+ SV *sv = INT2PTR(SV*, iv);
-=item XPUSHs
+and
-Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
+ AV *av = ...;
+ UV uv = PTR2UV(av);
- XPUSHs(sv)
+=head2 Source Documentation
-=item XS
+There's an effort going on to document the internal functions and
+automatically produce reference manuals from them - L<perlapi> is one
+such manual which details all the functions which are available to XS
+writers. L<perlintern> is the autogenerated manual for the functions
+which are not part of the API and are supposedly for internal use only.
-Macro to declare an XSUB and its C parameter list. This is handled by
-C<xsubpp>.
+Source documentation is created by putting POD comments into the C
+source, like this:
-=item XSRETURN
+ /*
+ =for apidoc sv_setiv
-Return from XSUB, indicating number of items on the stack. This is usually
-handled by C<xsubpp>.
+ Copies an integer into the given SV. Does not handle 'set' magic. See
+ C<sv_setiv_mg>.
- XSRETURN(int x);
+ =cut
+ */
-=item XSRETURN_EMPTY
+Please try and supply some documentation if you add functions to the
+Perl core.
-Return an empty list from an XSUB immediately.
+=head1 Unicode Support
- XSRETURN_EMPTY;
+Perl 5.6.0 introduced Unicode support. It's important for porters and XS
+writers to understand this support and make sure that the code they
+write does not corrupt Unicode data.
-=item XSRETURN_IV
+=head2 What B<is> Unicode, anyway?
-Return an integer from an XSUB immediately. Uses C<XST_mIV>.
+In the olden, less enlightened times, we all used to use ASCII. Most of
+us did, anyway. The big problem with ASCII is that it's American. Well,
+no, that's not actually the problem; the problem is that it's not
+particularly useful for people who don't use the Roman alphabet. What
+used to happen was that particular languages would stick their own
+alphabet in the upper range of the sequence, between 128 and 255. Of
+course, we then ended up with plenty of variants that weren't quite
+ASCII, and the whole point of it being a standard was lost.
- XSRETURN_IV(IV v);
+Worse still, if you've got a language like Chinese or
+Japanese that has hundreds or thousands of characters, then you really
+can't fit them into a mere 256, so they had to forget about ASCII
+altogether, and build their own systems using pairs of numbers to refer
+to one character.
-=item XSRETURN_NO
+To fix this, some people formed Unicode, Inc. and
+produced a new character set containing all the characters you can
+possibly think of and more. There are several ways of representing these
+characters, and the one Perl uses is called UTF8. UTF8 uses
+a variable number of bytes to represent a character, instead of just
+one. You can learn more about Unicode at http://www.unicode.org/
-Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
+=head2 How can I recognise a UTF8 string?
- XSRETURN_NO;
+You can't. This is because UTF8 data is stored in bytes just like
+non-UTF8 data. The Unicode character 200, (C<0xC8> for you hex types)
+capital E with a grave accent, is represented by the two bytes
+C<v196.172>. Unfortunately, the non-Unicode string C<chr(196).chr(172)>
+has that byte sequence as well. So you can't tell just by looking - this
+is what makes Unicode input an interesting problem.
-=item XSRETURN_NV
+The API function C<is_utf8_string> can help; it'll tell you if a string
+contains only valid UTF8 characters. However, it can't do the work for
+you. On a character-by-character basis, C<is_utf8_char> will tell you
+whether the current character in a string is valid UTF8.
-Return an double from an XSUB immediately. Uses C<XST_mNV>.
+=head2 How does UTF8 represent Unicode characters?
- XSRETURN_NV(NV v);
+As mentioned above, UTF8 uses a variable number of bytes to store a
+character. Characters with values 1...128 are stored in one byte, just
+like good ol' ASCII. Character 129 is stored as C<v194.129>; this
+continues up to character 191, which is C<v194.191>. Now we've run out of
+bits (191 is binary C<10111111>) so we move on; 192 is C<v195.128>. And
+so it goes on, moving to three bytes at character 2048.
-=item XSRETURN_PV
+Assuming you know you're dealing with a UTF8 string, you can find out
+how long the first character in it is with the C<UTF8SKIP> macro:
-Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
+ char *utf = "\305\233\340\240\201";
+ I32 len;
- XSRETURN_PV(char *v);
+ len = UTF8SKIP(utf); /* len is 2 here */
+ utf += len;
+ len = UTF8SKIP(utf); /* len is 3 here */
+
+Another way to skip over characters in a UTF8 string is to use
+C<utf8_hop>, which takes a string and a number of characters to skip
+over. You're on your own about bounds checking, though, so don't use it
+lightly.
+
+All bytes in a multi-byte UTF8 character will have the high bit set, so
+you can test if you need to do something special with this character
+like this:
+
+ UV uv;
+
+ if (utf & 0x80)
+ /* Must treat this as UTF8 */
+ uv = utf8_to_uv(utf);
+ else
+ /* OK to treat this character as a byte */
+ uv = *utf;
+
+You can also see in that example that we use C<utf8_to_uv> to get the
+value of the character; the inverse function C<uv_to_utf8> is available
+for putting a UV into UTF8:
-=item XSRETURN_UNDEF
+ if (uv > 0x80)
+ /* Must treat this as UTF8 */
+ utf8 = uv_to_utf8(utf8, uv);
+ else
+ /* OK to treat this character as a byte */
+ *utf8++ = uv;
-Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
+You B<must> convert characters to UVs using the above functions if
+you're ever in a situation where you have to match UTF8 and non-UTF8
+characters. You may not skip over UTF8 characters in this case. If you
+do this, you'll lose the ability to match hi-bit non-UTF8 characters;
+for instance, if your UTF8 string contains C<v196.172>, and you skip
+that character, you can never match a C<chr(200)> in a non-UTF8 string.
+So don't do that!
- XSRETURN_UNDEF;
+=head2 How does Perl store UTF8 strings?
-=item XSRETURN_YES
+Currently, Perl deals with Unicode strings and non-Unicode strings
+slightly differently. If a string has been identified as being UTF-8
+encoded, Perl will set a flag in the SV, C<SVf_UTF8>. You can check and
+manipulate this flag with the following macros:
-Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
+ SvUTF8(sv)
+ SvUTF8_on(sv)
+ SvUTF8_off(sv)
- XSRETURN_YES;
+This flag has an important effect on Perl's treatment of the string: if
+Unicode data is not properly distinguished, regular expressions,
+C<length>, C<substr> and other string handling operations will have
+undesirable results.
-=item XST_mIV
+The problem comes when you have, for instance, a string that isn't
+flagged is UTF8, and contains a byte sequence that could be UTF8 -
+especially when combining non-UTF8 and UTF8 strings.
-Place an integer into the specified position C<i> on the stack. The value is
-stored in a new mortal SV.
+Never forget that the C<SVf_UTF8> flag is separate to the PV value; you
+need be sure you don't accidentally knock it off while you're
+manipulating SVs. More specifically, you cannot expect to do this:
- XST_mIV( int i, IV v );
+ SV *sv;
+ SV *nsv;
+ STRLEN len;
+ char *p;
-=item XST_mNV
+ p = SvPV(sv, len);
+ frobnicate(p);
+ nsv = newSVpvn(p, len);
-Place a double into the specified position C<i> on the stack. The value is
-stored in a new mortal SV.
+The C<char*> string does not tell you the whole story, and you can't
+copy or reconstruct an SV just by copying the string value. Check if the
+old SV has the UTF8 flag set, and act accordingly:
- XST_mNV( int i, NV v );
+ p = SvPV(sv, len);
+ frobnicate(p);
+ nsv = newSVpvn(p, len);
+ if (SvUTF8(sv))
+ SvUTF8_on(nsv);
-=item XST_mNO
+In fact, your C<frobnicate> function should be made aware of whether or
+not it's dealing with UTF8 data, so that it can handle the string
+appropriately.
-Place C<&sv_no> into the specified position C<i> on the stack.
+=head2 How do I convert a string to UTF8?
- XST_mNO( int i );
+If you're mixing UTF8 and non-UTF8 strings, you might find it necessary
+to upgrade one of the strings to UTF8. If you've got an SV, the easiest
+way to do this is:
-=item XST_mPV
+ sv_utf8_upgrade(sv);
-Place a copy of a string into the specified position C<i> on the stack. The
-value is stored in a new mortal SV.
+However, you must not do this, for example:
- XST_mPV( int i, char *v );
+ if (!SvUTF8(left))
+ sv_utf8_upgrade(left);
-=item XST_mUNDEF
+If you do this in a binary operator, you will actually change one of the
+strings that came into the operator, and, while it shouldn't be noticeable
+by the end user, it can cause problems.
-Place C<&sv_undef> into the specified position C<i> on the stack.
+Instead, C<bytes_to_utf8> will give you a UTF8-encoded B<copy> of its
+string argument. This is useful for having the data available for
+comparisons and so on, without harming the original SV. There's also
+C<utf8_to_bytes> to go the other way, but naturally, this will fail if
+the string contains any characters above 255 that can't be represented
+in a single byte.
- XST_mUNDEF( int i );
+=head2 Is there anything else I need to know?
-=item XST_mYES
+Not really. Just remember these things:
-Place C<&sv_yes> into the specified position C<i> on the stack.
+=over 3
- XST_mYES( int i );
+=item *
-=item XS_VERSION
+There's no way to tell if a string is UTF8 or not. You can tell if an SV
+is UTF8 by looking at is C<SvUTF8> flag. Don't forget to set the flag if
+something should be UTF8. Treat the flag as part of the PV, even though
+it's not - if you pass on the PV to somewhere, pass on the flag too.
-The version identifier for an XS module. This is usually handled
-automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
+=item *
-=item XS_VERSION_BOOTCHECK
+If a string is UTF8, B<always> use C<utf8_to_uv> to get at the value,
+unless C<!(*s & 0x80)> in which case you can use C<*s>.
-Macro to verify that a PM module's $VERSION variable matches the XS module's
-C<XS_VERSION> variable. This is usually handled automatically by
-C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
+=item *
-=item Zero
+When writing to a UTF8 string, B<always> use C<uv_to_utf8>, unless
+C<uv < 0x80> in which case you can use C<*s = uv>.
-The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
-destination, C<n> is the number of items, and C<t> is the type.
+=item *
- (void) Zero( d, n, t );
+Mixing UTF8 and non-UTF8 strings is tricky. Use C<bytes_to_utf8> to get
+a new string which is UTF8 encoded. There are tricks you can use to
+delay deciding whether you need to use a UTF8 string until you get to a
+high character - C<HALF_UPGRADE> is one of those.
=back
-=head1 AUTHOR
-
-Jeff Okamoto <okamoto@corp.hp.com>
+=head1 Custom Operators
+
+Custom operator support is a new experimental feature that allows you do
+define your own ops. This is primarily to allow the building of
+interpreters for other languages in the Perl core, but it also allows
+optimizations through the creation of "macro-ops" (ops which perform the
+functions of multiple ops which are usually executed together, such as
+C<gvsv, gvsv, add>.)
+
+This feature is implemented as a new op type, C<OP_CUSTOM>. The Perl
+core does not "know" anything special about this op type, and so it will
+not be involved in any optimizations. This also means that you can
+define your custom ops to be any op structure - unary, binary, list and
+so on - you like.
+
+It's important to know what custom operators won't do for you. They
+won't let you add new syntax to Perl, directly. They won't even let you
+add new keywords, directly. In fact, they won't change the way Perl
+compiles a program at all. You have to do those changes yourself, after
+Perl has compiled the program. You do this either by manipulating the op
+tree using a C<CHECK> block and the C<B::Generate> module, or by adding
+a custom peephole optimizer with the C<optimize> module.
+
+When you do this, you replace ordinary Perl ops with custom ops by
+creating ops with the type C<OP_CUSTOM> and the C<pp_addr> of your own
+PP function. This should be defined in XS code, and should look like
+the PP ops in C<pp_*.c>. You are responsible for ensuring that your op
+takes the appropriate number of values from the stack, and you are
+responsible for adding stack marks if necessary.
+
+You should also "register" your op with the Perl interpreter so that it
+can produce sensible error and warning messages. Since it is possible to
+have multiple custom ops within the one "logical" op type C<OP_CUSTOM>,
+Perl uses the value of C<< o->op_ppaddr >> as a key into the
+C<PL_custom_op_descs> and C<PL_custom_op_names> hashes. This means you
+need to enter a name and description for your op at the appropriate
+place in the C<PL_custom_op_names> and C<PL_custom_op_descs> hashes.
+
+Forthcoming versions of C<B::Generate> (version 1.0 and above) should
+directly support the creation of custom ops by name; C<Opcodes::Custom>
+will provide functions which make it trivial to "register" custom ops to
+the Perl interpreter.
+
+=head1 AUTHORS
+
+Until May 1997, this document was maintained by Jeff Okamoto
+<okamoto@corp.hp.com>. It is now maintained as part of Perl itself
+by the Perl 5 Porters <perl5-porters@perl.org>.
With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
-Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
+Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
+Stephen McCamant, and Gurusamy Sarathy.
+
+API Listing originally by Dean Roehrich <roehrich@cray.com>.
-API Listing by Dean Roehrich <roehrich@cray.com>.
+Modifications to autogenerate the API listing (L<perlapi>) by Benjamin
+Stuhl.
-=head1 DATE
+=head1 SEE ALSO
-Version 23.1: 1996/10/19
+perlapi(1), perlintern(1), perlxs(1), perlembed(1)
https://perl5.git.perl.org / perl5.git / blobdiff