=head1 DESCRIPTION
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
+to provide 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.
SV* newSViv(IV);
SV* newSVuv(UV);
SV* newSVnv(double);
- SV* newSVpv(const char*, int);
- SV* newSVpvn(const char*, int);
+ SV* newSVpv(const char*, STRLEN);
+ SV* newSVpvn(const char*, STRLEN);
SV* newSVpvf(const char*, ...);
SV* newSVsv(SV*);
-If you require more complex initialisation you can create an empty SV with
-newSV(len). If C<len> is 0 an empty SV of type NULL is returned, else an
-SV of type PV is returned with len + 1 (for the NUL) bytes of storage
-allocated, accessible via SvPVX. In both cases the SV has value undef.
+C<STRLEN> is an integer type (Size_t, usually defined as size_t in
+F<config.h>) guaranteed to be large enough to represent the size of
+any string that perl can handle.
+
+In the unlikely case of a SV requiring more complex initialisation, you
+can create an empty SV with newSV(len). If C<len> is 0 an empty SV of
+type NULL is returned, else an SV of type PV is returned with len + 1 (for
+the NUL) bytes of storage allocated, accessible via SvPVX. In both cases
+the SV has value undef.
- SV* newSV(0); /* no storage allocated */
- SV* newSV(10); /* 10 (+1) bytes of uninitialised storage allocated */
+ SV *sv = newSV(0); /* no storage allocated */
+ SV *sv = newSV(10); /* 10 (+1) bytes of uninitialised storage allocated */
-To change the value of an *already-existing* SV, there are eight routines:
+To change the value of an I<already-existing> SV, there are eight routines:
void sv_setiv(SV*, IV);
void sv_setuv(SV*, UV);
void sv_setnv(SV*, double);
void sv_setpv(SV*, const char*);
- void sv_setpvn(SV*, const char*, int)
+ void sv_setpvn(SV*, const char*, STRLEN)
void sv_setpvf(SV*, const char*, ...);
void sv_vsetpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool *);
void sv_setsv(SV*, SV*);
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.
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);
+ 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:
SvOK(SV*)
-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.
+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. Make sure that
+you don't try to compare a random sv with C<&PL_sv_undef>. For example
+when interfacing Perl code, it'll work correctly for:
+
+ foo(undef);
+
+But won't work when called as:
+
+ $x = undef;
+ foo($x);
+
+So to repeat always use SvOK() to check whether an sv is defined.
+
+Also you have to be careful when using C<&PL_sv_undef> as a value in
+AVs or HVs (see L<AVs, HVs and undefined values>).
-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.
+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<&PL_sv_undef>.
Take this code:
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
pointer which, somewhere down the line, will cause a segmentation violation,
-bus error, or just weird results. Change the zero to C<&PL_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 L<Reference Counts and Mortality>).
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
+numeric conversion has occurred 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.
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 AVs, HVs and undefined values
+
+Sometimes you have to store undefined values in AVs or HVs. Although
+this may be a rare case, it can be tricky. That's because you're
+used to using C<&PL_sv_undef> if you need an undefined SV.
+
+For example, intuition tells you that this XS code:
+
+ AV *av = newAV();
+ av_store( av, 0, &PL_sv_undef );
+
+is equivalent to this Perl code:
+
+ my @av;
+ $av[0] = undef;
+
+Unfortunately, this isn't true. AVs use C<&PL_sv_undef> as a marker
+for indicating that an array element has not yet been initialized.
+Thus, C<exists $av[0]> would be true for the above Perl code, but
+false for the array generated by the XS code.
+
+Other problems can occur when storing C<&PL_sv_undef> in HVs:
+
+ hv_store( hv, "key", 3, &PL_sv_undef, 0 );
+
+This will indeed make the value C<undef>, but if you try to modify
+the value of C<key>, you'll get the following error:
+
+ Modification of non-creatable hash value attempted
+
+In perl 5.8.0, C<&PL_sv_undef> was also used to mark placeholders
+in restricted hashes. This caused such hash entries not to appear
+when iterating over the hash or when checking for the keys
+with the C<hv_exists> function.
+
+You can run into similar problems when you store C<&PL_sv_true> or
+C<&PL_sv_false> into AVs or HVs. Trying to modify such elements
+will give you the following error:
+
+ Modification of a read-only value attempted
+
+To make a long story short, you can use the special variables
+C<&PL_sv_undef>, C<&PL_sv_true> and C<&PL_sv_false> with AVs and
+HVs, but you have to make sure you know what you're doing.
+
+Generally, if you want to store an undefined value in an AV
+or HV, you should not use C<&PL_sv_undef>, but rather create a
+new undefined value using the C<newSV> function, for example:
+
+ av_store( av, 42, newSV(0) );
+ hv_store( hv, "foo", 3, newSV(0), 0 );
+
=head2 References
References are a special type of scalar that point to other data types
=head2 Blessed References and Class Objects
-References are also used to support object-oriented programming. In the
+References are also used to support object-oriented programming. In perl's
OO lexicon, an object is simply a reference that has been blessed into a
package (or class). Once blessed, the programmer may now use the reference
to access the various methods in the class.
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 C<sv> argument must be a reference value. The C<stash> argument
+specifies which class the reference will belong to. See
L<Stashes and Globs> for information on converting class names into stashes.
/* Still under construction */
"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.
+is made mortal to have it cleaned up automatically when it's popped off
+the stack. Similarly, results returned by XSUBs (which are pushed on the
+stack) are often made mortal.
To create a mortal variable, use the functions:
=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
+A B<stash> is a hash that contains all variables that are defined
+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,
Format
Subroutine
-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.
+There is a single stash called C<PL_defstash> that holds the items that exist
+in the C<main> package. To get at the items in other packages, append the
+string "::" to the package name. The items in the C<Foo> package are in
+the stash C<Foo::> in PL_defstash. The items in the C<Bar::Baz> package are
+in the stash C<Baz::> in C<Bar::>'s stash.
To get the stash pointer for a particular package, use the function:
- HV* gv_stashpv(const char* name, I32 create)
- HV* gv_stashsv(SV*, I32 create)
+ HV* gv_stashpv(const char* name, I32 flags)
+ HV* gv_stashsv(SV*, I32 flags)
The first function takes a literal string, the second uses the string stored
in the SV. Remember that a stash is just a hash table, so you get back an
-C<HV*>. The C<create> flag will create a new package if it is set.
+C<HV*>. The C<flags> flag will create a new package if it is set to GV_ADD.
The name that C<gv_stash*v> wants is the name of the package whose symbol table
you want. The default package is called C<main>. If you have multiply nested
U16 mg_private;
char mg_type;
U8 mg_flags;
+ I32 mg_len;
SV* mg_obj;
char* mg_ptr;
- I32 mg_len;
};
Note this is current as of patchlevel 0, and could change at any time.
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> E<gt>= 0 a malloc'd
-copy of the name is stored in C<mg_ptr> field.
+C<mg_len> field and if C<name> is non-null then either a C<savepvn> copy of
+C<name> or C<name> itself is stored in the C<mg_ptr> field, depending on
+whether C<namlen> is greater than zero or equal to zero respectively. As a
+special case, if C<(name && namlen == HEf_SVKEY)> then C<name> is assumed
+to contain an C<SV*> and is stored as-is with its REFCNT incremented.
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
+See the L<Magic Virtual Tables> section below. The C<how> argument is also
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
+from the set of macros C<PERL_MAGIC_foo> found in F<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
referring to 'U' magic rather than C<PERL_MAGIC_uvar> for example.
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.
+See also C<sv_magicext> in L<perlapi> for a more flexible way to add magic
+to an SV.
+
There is also a function to add magic to an C<HV>:
void hv_magic(HV *hv, GV *gv, int how);
"Magic Virtual Table" to handle the various operations that might be
applied to that variable.
-The C<MGVTBL> has five pointers to the following routine types:
+The C<MGVTBL> has five (or sometimes eight) pointers to the following
+routine types:
int (*svt_get)(SV* sv, MAGIC* mg);
int (*svt_set)(SV* sv, MAGIC* mg);
int (*svt_clear)(SV* sv, MAGIC* mg);
int (*svt_free)(SV* sv, MAGIC* mg);
-This MGVTBL structure is set at compile-time in C<perl.h> and there are
+ int (*svt_copy)(SV *sv, MAGIC* mg, SV *nsv, const char *name, int namlen);
+ int (*svt_dup)(MAGIC *mg, CLONE_PARAMS *param);
+ int (*svt_local)(SV *nsv, MAGIC *mg);
+
+
+This MGVTBL structure is set at compile-time in F<perl.h> and there are
currently 19 types (or 21 with overloading turned on). These different
structures contain pointers to various routines that perform additional
actions depending on which function is being called.
svt_get Do something before the value of the SV is retrieved.
svt_set Do something after the SV is assigned a value.
svt_len Report on the SV's length.
- svt_clear Clear something the SV represents.
+ svt_clear Clear something the SV represents.
svt_free Free any extra storage associated with the SV.
+ svt_copy copy tied variable magic to a tied element
+ svt_dup duplicate a magic structure during thread cloning
+ svt_local copy magic to local value during 'local'
+
For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
to an C<mg_type> of C<PERL_MAGIC_sv>) contains:
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 last three slots are a recent addition, and for source code
+compatibility they are only checked for if one of the three flags
+MGf_COPY, MGf_DUP or MGf_LOCAL is set in mg_flags. This means that most
+code can continue declaring a vtable as a 5-element value. These three are
+currently used exclusively by the threading code, and are highly subject
+to change.
+
The current kinds of Magic Virtual Tables are:
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
+ (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
- V PERL_MAGIC_vstring (none) v-string scalars
- w PERL_MAGIC_utf8 vtbl_utf8 UTF-8 length+offset cache
- 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
+ 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
+ H PERL_MAGIC_hints vtbl_sig %^H hash
+ h PERL_MAGIC_hintselem vtbl_hintselem %^H hash element
+ 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
+ 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
+ V PERL_MAGIC_vstring (none) v-string scalars
+ w PERL_MAGIC_utf8 vtbl_utf8 UTF-8 length+offset cache
+ x PERL_MAGIC_substr vtbl_substr substr() lvalue
+ y PERL_MAGIC_defelem vtbl_defelem Shadow "foreach" iterator
+ variable / smart parameter
+ vivification
+ # PERL_MAGIC_arylen vtbl_arylen Array length ($#ary)
+ . PERL_MAGIC_pos vtbl_pos pos() lvalue
+ < PERL_MAGIC_backref vtbl_backref back pointer to a weak ref
+ ~ PERL_MAGIC_ext (none) Available for use by extensions
+ : PERL_MAGIC_symtab (none) hash used as symbol table
+ % PERL_MAGIC_rhash (none) hash used as restricted hash
+ @ PERL_MAGIC_arylen_p vtbl_arylen_p pointer to $#a from @a
+
When an uppercase and lowercase letter both exist in the table, then the
uppercase letter is typically used to represent some kind of composite type
uf.uf_index = 0;
sv_magic(sv, 0, PERL_MAGIC_uvar, (char*)&uf, sizeof(uf));
+Attaching C<PERL_MAGIC_uvar> to arrays is permissible but has no effect.
+
+For hashes there is a specialized hook that gives control over hash
+keys (but not values). This hook calls C<PERL_MAGIC_uvar> 'get' magic
+if the "set" function in the C<ufuncs> structure is NULL. The hook
+is activated whenever the hash is accessed with a key specified as
+an C<SV> through the functions C<hv_store_ent>, C<hv_fetch_ent>,
+C<hv_delete_ent>, and C<hv_exists_ent>. Accessing the key as a string
+through the functions without the C<..._ent> suffix circumvents the
+hook. See L<Hash::Util::Fieldhash/Guts> for a detailed description.
+
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
CODE:
hash = newHV();
tie = newRV_noinc((SV*)newHV());
- stash = gv_stashpv("MyTie", TRUE);
+ stash = gv_stashpv("MyTie", GV_ADD);
sv_bless(tie, stash);
hv_magic(hash, (GV*)tie, PERL_MAGIC_tied);
RETVAL = newRV_noinc(hash);
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.
+using the stored value. It doesn't handle magic. Use C<save_scalar> if
+magic is affected.
=item C<void save_list(SV **sarg, I32 maxsarg)>
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 C<PUSHs>
-macro. The values pushed will often need to be "mortal" (See L</Reference Counts and Mortality>).
+macro. The pushed values will often need to be "mortal" (See
+L</Reference Counts and Mortality>):
PUSHs(sv_2mortal(newSViv(an_integer)))
+ PUSHs(sv_2mortal(newSVuv(an_unsigned_integer)))
+ PUSHs(sv_2mortal(newSVnv(a_double)))
PUSHs(sv_2mortal(newSVpv("Some String",0)))
- PUSHs(sv_2mortal(newSVnv(3.141592)))
And now the Perl program calling C<tzname>, the two values will be assigned
as in:
do not need to call C<EXTEND> to extend the stack.
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>.
+C<(X)PUSH[iunp]> are I<not> suited to XSUBs which return multiple results.
+For that, either stick to the C<(X)PUSHs> macros shown above, or use the new
+C<m(X)PUSH[iunp]> macros instead; see L</Putting a C value on Perl stack>.
For more information, consult L<perlxs> and L<perlxstut>.
=head2 Memory Allocation
+=head3 Allocation
+
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
order to satisfy allocation requests more quickly. 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 following 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 (most Perl developers now
-use run-time memory checkers), so this argument can be any number.
+ Newx(pointer, number, type);
+ Newxc(pointer, number, type, cast);
+ Newxz(pointer, number, type);
-The
second argument C<pointer> should be the name of a variable that will
+The
first argument C<pointer> should be the name of a variable that will
point to the newly allocated memory.
-The third and fourth arguments C<number> and C<type> specify how many of
+The second and third 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>,
+C<type> is passed to C<sizeof>. The final argument to C<Newxc>, 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>
+Unlike the C<Newx> and C<Newxc> macros, the C<Newxz> macro calls C<memzero>
to zero out all the newly allocated memory.
+=head3 Reallocation
+
Renew(pointer, number, type);
Renewc(pointer, number, type, cast);
Safefree(pointer)
match those of C<New> and C<Newc> with the exception of not needing the
"magic cookie" argument.
+=head3 Moving
+
Move(source, dest, number, type);
Copy(source, dest, number, type);
Zero(dest, number, type);
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]>.
+others, which use it via C<(X)PUSH[iunp]>.
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:
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>.
+to 20.
-On a related note, if you do use C<(X)PUSH[npi]>, then you're going to
+If you need to push multiple different values then you should either use
+the C<(X)PUSHs> macros, or else use the new C<m(X)PUSH[iunp]> macros,
+none of which make use of C<TARG>. The C<(X)PUSHs> macros simply push an
+SV* on the stack, which, as noted under L</XSUBs and the Argument Stack>,
+will often need to be "mortal". The new C<m(X)PUSH[iunp]> macros make
+this a little easier to achieve by creating a new mortal for you (via
+C<(X)PUSHmortal>), pushing that onto the stack (extending it if necessary
+in the case of the C<mXPUSH[iunp]> macros), and then setting its value.
+Thus, instead of writing this to "fix" the example above:
+
+ XPUSHs(sv_2mortal(newSViv(10)))
+ XPUSHs(sv_2mortal(newSViv(20)))
+
+you can simply write:
+
+ mXPUSHi(10)
+ mXPUSHi(20)
+
+On a related note, if you do use C<(X)PUSH[iunp]>, 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>.
+macros can make use of the local variable C<TARG>. See also C<dTARGET>
+and C<dXSTARG>.
=head2 Scratchpads
=head2 Examining the tree
-If you have your perl compiled for debugging (usually done with C<-D
-optimize=-g> on C<Configure> command line), you may examine the
+If you have your perl compiled for debugging (usually done with
+C<-DDEBUGGING> on the 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:
optimization (see L</Compile pass 2: context propagation>) it will still
have children in accordance with its former type.
+Another way to examine the tree is to use a compiler back-end module, such
+as L<B::Concise>.
+
=head2 Compile pass 1: check routines
The tree is created by the compiler while I<yacc> code feeds it
=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.
+functions, in F<run.c> and in F<dump.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
or inside a thread-specific structure. These structures contain all
the context, the state of that interpreter.
-Two 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.
+One macro controls the major Perl build flavor: MULTIPLICITY. The
+MULTIPLICITY build has a C structure that packages all the interpreter
+state. With multiplicity-enabled perls, PERL_IMPLICIT_CONTEXT is also
+normally defined, and enables the support for passing in a "hidden" first
+argument that represents all three data structures. MULTIPLICITY makes
+mutli-threaded perls possible (with the ithreads threading model, related
+to the macro USE_ITHREADS.)
+
+Two other "encapsulation" macros are the PERL_GLOBAL_STRUCT and
+PERL_GLOBAL_STRUCT_PRIVATE (the latter turns on the former, and the
+former turns on MULTIPLICITY.) The PERL_GLOBAL_STRUCT causes all the
+internal variables of Perl to be wrapped inside a single global struct,
+struct perl_vars, accessible as (globals) &PL_Vars or PL_VarsPtr or
+the function Perl_GetVars(). The PERL_GLOBAL_STRUCT_PRIVATE goes
+one step further, there is still a single struct (allocated in main()
+either from heap or from stack) but there are no global data symbols
+pointing to it. In either case the global struct should be initialised
+as the very first thing in main() using Perl_init_global_struct() and
+correspondingly tear it down after perl_free() using Perl_free_global_struct(),
+please see F<miniperlmain.c> for usage details. You may also need
+to use C<dVAR> in your coding to "declare the global variables"
+when you are using them. dTHX does this for you automatically.
+
+To see whether you have non-const data you can use a BSD-compatible C<nm>:
+
+ nm libperl.a | grep -v ' [TURtr] '
+
+If this displays any C<D> or C<d> symbols, you have non-const data.
+
+For backward compatibility reasons defining just PERL_GLOBAL_STRUCT
+doesn't actually hide all symbols inside a big global struct: some
+PerlIO_xxx vtables are left visible. The PERL_GLOBAL_STRUCT_PRIVATE
+then hides everything (see how the PERLIO_FUNCS_DECL is used).
All this obviously requires a way for the Perl internal functions to be
either subroutines taking some kind of structure as the first
sanctioned for use in extensions) begins like this:
void
- Perl_sv_setsv(pTHX_ SV* dsv, SV* ssv)
+ Perl_sv_setiv(pTHX_ SV* dsv, IV num)
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",
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
+is normally hidden via macros. Consider C<sv_setiv>. It expands into
something like this:
- ifdef PERL_IMPLICIT_CONTEXT
- define sv_setsv(a,b) Perl_sv_setsv(aTHX_ a, b)
+ #ifdef PERL_IMPLICIT_CONTEXT
+ #define sv_setiv(a,b) Perl_sv_setiv(aTHX_ a, b)
/* can't do this for vararg functions, see below */
- else
- define sv_setsv Perl_sv_setsv
- endif
+ #else
+ #define sv_setiv Perl_sv_setiv
+ #endif
This works well, and means that XS authors can gleefully write:
- sv_setsv(foo, bar);
+ sv_setiv(foo, bar);
and still have it work under all the modes Perl could have been
compiled with.
and aTHX_ macros to call a function that will return the context.
Thus, something like:
- sv_setsv(asv, bsv);
+ sv_setiv(sv, num);
in your extension will translate to this when PERL_IMPLICIT_CONTEXT is
in effect:
- Perl_sv_setsv(Perl_get_context(), asv, bsv);
+ Perl_sv_setiv(Perl_get_context(), sv, num);
or to this otherwise:
- Perl_sv_setsv(asv, bsv);
+ Perl_sv_setiv(sv, num);
You have to do nothing new in your extension to get this; since
the Perl library provides Perl_get_context(), it will all just
#include "perl.h"
#include "XSUB.h"
- static my_private_function(int arg1, int arg2);
+ STATIC void my_private_function(int arg1, int arg2);
- static SV *
+ STATIC void
my_private_function(int arg1, int arg2)
{
dTHX; /* fetch context */
#include "XSUB.h"
/* pTHX_ only needed for functions that call Perl API */
- static my_private_function(pTHX_ int arg1, int arg2);
+ STATIC void my_private_function(pTHX_ int arg1, int arg2);
- static SV *
+ STATIC void
my_private_function(pTHX_ int arg1, int arg2)
{
/* dTHX; not needed here, because THX is an argument */
macro with the underscore for functions that take explicit arguments,
or the form without the argument for functions with no explicit arguments.
+If one is compiling Perl with the C<-DPERL_GLOBAL_STRUCT> the C<dVAR>
+definition is needed if the Perl global variables (see F<perlvars.h>
+or F<globvar.sym>) are accessed in the function and C<dTHX> is not
+used (the C<dTHX> includes the C<dVAR> if necessary). One notices
+the need for C<dVAR> only with the said compile-time define, because
+otherwise the Perl global variables are visible as-is.
+
=head2 Should I do anything special if I call perl from multiple threads?
If you create interpreters in one thread and then proceed to call them in
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).
+PERL_IMPLICIT_SYS macro. Currently it only works with USE_ITHREADS on
+Windows.
This allows the ability to provide an extra pointer (called the "host"
environment) for all the system calls. This makes it possible for
=head1 Internal Functions
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
+world are 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_>)
+static functions start with C<S_>.)
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:
+F<embed.pl> and F<embed.fnc>. 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 in F<embed.fnc> as well. Here's a sample entry from
+that table:
Apd |SV** |av_fetch |AV* ar|I32 key|I32 lval
=item A
-This function is a part of the public API.
+This function is a part of the public API. All such functions should also
+have 'd', very few do not.
=item p
-This function has a C<Perl_> prefix; ie, it is defined as C<Perl_av_fetch>
+This function has a C<Perl_> prefix; i.e. it is defined as
+C<Perl_av_fetch>.
=item d
This function has documentation using the C<apidoc> feature which we'll
-look at in a second.
+look at in a second. Some functions have 'd' but not 'A'; docs are good.
=back
=item s
-This is a static function and is defined as C<S_whatever>, and usually
-called within the sources as C<whatever(...)>.
+This is a static function and is defined as C<STATIC S_whatever>, and
+usually called within the sources as C<whatever(...)>.
=item n
-This does not use C<aTHX_> and C<pTHX> to pass interpreter context. (See
+This does not need a interpreter context, so the definition has no
+C<pTHX>, and it follows that callers don't use C<aTHX>. (See
L<perlguts/Background and PERL_IMPLICIT_CONTEXT>.)
=item r
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>.
-=item j
-
-This function is not a member of C<CPerlObj>. If you don't know
-what this means, don't use it.
-
=item x
This function isn't exported out of the Perl core.
+=item m
+
+This is implemented as a macro.
+
+=item X
+
+This function is explicitly exported.
+
+=item E
+
+This function is visible to extensions included in the Perl core.
+
+=item b
+
+Binary backward compatibility; this function is a macro but also has
+a C<Perl_> implementation (which is exported).
+
+=item others
+
+See the comments at the top of C<embed.fnc> for others.
+
=back
-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.
+If you edit F<embed.pl> or F<embed.fnc>, you will need to run
+C<make regen_headers> to force a rebuild of F<embed.h> and other
+auto-generated files.
=head2 Formatted Printing of IVs, UVs, and NVs
AV *av = ...;
UV uv = PTR2UV(av);
+=head2 Exception Handling
+
+There are a couple of macros to do very basic exception handling in XS
+modules. You have to define C<NO_XSLOCKS> before including F<XSUB.h> to
+be able to use these macros:
+
+ #define NO_XSLOCKS
+ #include "XSUB.h"
+
+You can use these macros if you call code that may croak, but you need
+to do some cleanup before giving control back to Perl. For example:
+
+ dXCPT; /* set up necessary variables */
+
+ XCPT_TRY_START {
+ code_that_may_croak();
+ } XCPT_TRY_END
+
+ XCPT_CATCH
+ {
+ /* do cleanup here */
+ XCPT_RETHROW;
+ }
+
+Note that you always have to rethrow an exception that has been
+caught. Using these macros, it is not possible to just catch the
+exception and ignore it. If you have to ignore the exception, you
+have to use the C<call_*> function.
+
+The advantage of using the above macros is that you don't have
+to setup an extra function for C<call_*>, and that using these
+macros is faster than using C<call_*>.
+
=head2 Source Documentation
There's an effort going on to document the internal functions and
Please try and supply some documentation if you add functions to the
Perl core.
+=head2 Backwards compatibility
+
+The Perl API changes over time. New functions are added or the interfaces
+of existing functions are changed. The C<Devel::PPPort> module tries to
+provide compatibility code for some of these changes, so XS writers don't
+have to code it themselves when supporting multiple versions of Perl.
+
+C<Devel::PPPort> generates a C header file F<ppport.h> that can also
+be run as a Perl script. To generate F<ppport.h>, run:
+
+ perl -MDevel::PPPort -eDevel::PPPort::WriteFile
+
+Besides checking existing XS code, the script can also be used to retrieve
+compatibility information for various API calls using the C<--api-info>
+command line switch. For example:
+
+ % perl ppport.h --api-info=sv_magicext
+
+For details, see C<perldoc ppport.h>.
+
=head1 Unicode Support
Perl 5.6.0 introduced Unicode support. It's important for porters and XS
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/
+characters, and the one Perl uses is called UTF-8. UTF-8 uses
+a variable number of bytes to represent a character. You can learn more
+about Unicode and Perl's Unicode model in L<perlunicode>.
-=head2 How can I recognise a UTF8 string?
+=head2 How can I recognise a UTF-8 string?
-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)
+You can't. This is because UTF-8 data is stored in bytes just like
+non-UTF-8 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.
-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.
+In general, you either have to know what you're dealing with, or you
+have to guess. The API function C<is_utf8_string> can help; it'll tell
+you if a string contains only valid UTF-8 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 UTF-8.
-=head2 How does UTF8 represent Unicode characters?
+=head2 How does UTF-8 represent Unicode characters?
-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
+As mentioned above, UTF-8 uses a variable number of bytes to store a
+character. Characters with values 0...127 are stored in one byte, just
+like good ol' ASCII. Character 128 is stored as C<v194.128>; 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.
-Assuming you know you're dealing with a UTF8 string, you can find out
+Assuming you know you're dealing with a UTF-8 string, you can find out
how long the first character in it is with the C<UTF8SKIP> macro:
char *utf = "\305\233\340\240\201";
utf += len;
len = UTF8SKIP(utf); /* len is 3 here */
-Another way to skip over characters in a UTF8 string is to use
+Another way to skip over characters in a UTF-8 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,
+All bytes in a multi-byte UTF-8 character will have the high bit set,
so you can test if you need to do something special with this
character like this (the UTF8_IS_INVARIANT() is a macro that tests
whether the byte can be encoded as a single byte even in UTF-8):
UV uv; /* Note: a UV, not a U8, not a char */
if (!UTF8_IS_INVARIANT(*utf))
- /* Must treat this as UTF8 */
+ /* Must treat this as UTF-8 */
uv = utf8_to_uv(utf);
else
/* OK to treat this character as a byte */
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:
+for putting a UV into UTF-8:
if (!UTF8_IS_INVARIANT(uv))
/* Must treat this as UTF8 */
*utf8++ = uv;
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.
+you're ever in a situation where you have to match UTF-8 and non-UTF-8
+characters. You may not skip over UTF-8 characters in this case. If you
+do this, you'll lose the ability to match hi-bit non-UTF-8 characters;
+for instance, if your UTF-8 string contains C<v196.172>, and you skip
+that character, you can never match a C<chr(200)> in a non-UTF-8 string.
So don't do that!
-=head2 How does Perl store UTF8 strings?
+=head2 How does Perl store UTF-8 strings?
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:
+slightly differently. A flag in the SV, C<SVf_UTF8>, indicates that the
+string is internally encoded as UTF-8. Without it, the byte value is the
+codepoint number and vice versa (in other words, the string is encoded
+as iso-8859-1). You can check and manipulate this flag with the
+following macros:
SvUTF8(sv)
SvUTF8_on(sv)
undesirable results.
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.
+flagged as UTF-8, and contains a byte sequence that could be UTF-8 -
+especially when combining non-UTF-8 and UTF-8 strings.
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
SvUTF8_on(nsv);
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
+not it's dealing with UTF-8 data, so that it can handle the string
appropriately.
Since just passing an SV to an XS function and copying the data of
the SV is not enough to copy the UTF8 flags, even less right is just
passing a C<char *> to an XS function.
-=head2 How do I convert a string to UTF8?
+=head2 How do I convert a string to UTF-8?
-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:
+If you're mixing UTF-8 and non-UTF-8 strings, it is necessary to upgrade
+one of the strings to UTF-8. If you've got an SV, the easiest way to do
+this is:
sv_utf8_upgrade(sv);
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.
+by the end user, it can cause problems in deficient code.
-Instead, C<bytes_to_utf8> will give you a UTF8-encoded B<copy> of its
+Instead, C<bytes_to_utf8> will give you a UTF-8-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
=item *
-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
+There's no way to tell if a string is UTF-8 or not. You can tell if an SV
+is UTF-8 by looking at is C<SvUTF8> flag. Don't forget to set the flag if
+something should be UTF-8. 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.
=item *
-If a string is UTF8, B<always> use C<utf8_to_uv> to get at the value,
+If a string is UTF
-8, B<always> use C<utf8_to_uv> to get at the value,
unless C<UTF8_IS_INVARIANT(*s)> in which case you can use C<*s>.
=item *
-When writing a character C<uv> to a UTF8 string, B<always> use
+When writing a character C<uv> to a UTF
-8 string, B<always> use
C<uv_to_utf8>, unless C<UTF8_IS_INVARIANT(uv))> in which case
you can use C<*s = uv>.
=item *
-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
+Mixing UTF-8 and non-UTF-8 strings is tricky. Use C<bytes_to_utf8> to get
+a new string which is UTF-8 encoded. There are tricks you can use to
+delay deciding whether you need to use a UTF-8 string until you get to a
high character - C<HALF_UPGRADE> is one of those.
=back
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>.)
+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
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.
+directly support the creation of custom ops by name.
=head1 AUTHORS
Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
Stephen McCamant, and Gurusamy Sarathy.
-API Listing originally by Dean Roehrich E<lt>roehrich@cray.comE<gt>.
-
-Modifications to autogenerate the API listing (L<perlapi>) by Benjamin
-Stuhl.
-
=head1 SEE ALSO
perlapi(1), perlintern(1), perlxs(1), perlembed(1)
https://perl5.git.perl.org / perl5.git / blobdiff