An SV can be created and loaded with one command. There are five types of
values that can be loaded: an integer value (IV), an unsigned integer
value (UV), a double (NV), a string (PV), and another scalar (SV).
+("PV" stands for "Pointer Value". You might think that it is misnamed
+because it is described as pointing only to strings. However, it is
+possible to have it point to other things. For example, inversion
+lists, used in regular expression data structures, are scalars, each
+consisting of an array of UVs which are accessed through PVs. But,
+using it for non-strings requires care, as the underlying assumption of
+much of the internals is that PVs are just for strings. Often, for
+example, a trailing NUL is tacked on automatically. The non-string use
+is documented only in this paragraph.)
The seven routines are:
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.
+the SV has the undef value.
SV *sv = newSV(0); /* no storage allocated */
- SV *sv = newSV(10); /* 10 (+1) bytes of uninitialised storage allocated */
+ SV *sv = newSV(10); /* 10 (+1) bytes of uninitialised storage
+ * allocated */
To change the value of an I<already-existing> SV, there are eight routines:
void sv_setpv(SV*, const char*);
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_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
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.
+string terminating with a NUL character, and not otherwise containing
+NULs.
The arguments of C<sv_setpvf> are processed like C<sprintf>, and the
formatted output becomes the value.
SV *s;
STRLEN len;
- char * ptr;
+ char *ptr;
ptr = SvPV(s, len);
foo(ptr, len);
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 and that it does not automatically
-add a byte for the a trailing NUL (perl's own string functions typically do
+add space for the trailing NUL byte (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
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_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
If you know the name of a scalar variable, you can get a pointer to its SV
by using the following:
- SV* get_sv("package::varname", FALSE);
+ SV* get_sv("package::varname", 0);
This returns NULL if the variable does not exist.
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>.
+increasing C<AvARRAY> by one and decreasing C<AvFILL> and C<AvMAX>.
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>.
These will tell you if you truly have an integer, double, or string pointer
stored in your SV. The "p" stands for private.
-The are various ways in which the private and public flags may differ.
+There 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
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:
+Once the AV has been created, the following operations are possible on it:
void av_push(AV*, SV*);
SV* av_pop(AV*);
SV** av_fetch(AV*, I32 key, I32 lval);
SV** av_store(AV*, I32 key, SV* val);
-The C<av_len> function returns the highest index value in array (just
+The C<av_len> function returns the highest index value in an 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.
C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s as their
return value.
+A few more:
+
void av_clear(AV*);
void av_undef(AV*);
void av_extend(AV*, I32 key);
If you know the name of an array variable, you can get a pointer to its AV
by using the following:
- AV* get_av("package::varname", FALSE);
+ AV* get_av("package::varname", 0);
This returns NULL if the variable does not exist.
HV* newHV();
-Once the HV has been created, the following operations are possible on HVs:
+Once the HV has been created, the following operations are possible on it:
SV** hv_store(HV*, const char* key, U32 klen, SV* val, U32 hash);
SV** hv_fetch(HV*, const char* key, U32 klen, I32 lval);
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.
+The first of these two functions checks if a hash table entry exists, and the
+second deletes it.
bool hv_exists(HV*, const char* key, U32 klen);
SV* hv_delete(HV*, const char* key, U32 klen, I32 flags);
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.
+Perl keeps the actual data in a linked list of structures with a typedef of HE.
These contain the actual key and value pointers (plus extra administrative
overhead). The key is a string pointer; the value is an C<SV*>. However,
once you have an C<HE*>, to get the actual key and value, use the routines
If you know the name of a hash variable, you can get a pointer to its HV
by using the following:
- HV* get_hv("package::varname", FALSE);
+ HV* get_hv("package::varname", 0);
This returns NULL if the variable does not exist.
-The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
+The hash algorithm is defined in the C<PERL_HASH> macro:
- hash = 0;
- while (klen--)
- hash = (hash * 33) + *key++;
- hash = hash + (hash >> 5); /* after 5.6 */
+ PERL_HASH(hash, key, klen)
-The last step was added in version 5.6 to improve distribution of
-lower bits in the resulting hash value.
+The exact implementation of this macro varies by architecture and version
+of perl, and the return value may change per invocation, so the value
+is only valid for the duration of a single perl process.
See L<Understanding the Magic of Tied Hashes and Arrays> for more
information on how to use the hash access functions on tied hashes.
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
+You can run into similar problems when you store C<&PL_sv_yes> or
+C<&PL_sv_no> 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
+C<&PL_sv_undef>, C<&PL_sv_yes> and C<&PL_sv_no> 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
=head2 References
References are a special type of scalar that point to other data types
-(including references).
+(including other references).
To create a reference, use either of the following functions:
The most useful types that will be returned are:
- SVt_IV Scalar
- SVt_NV Scalar
- SVt_PV Scalar
- SVt_RV Scalar
- SVt_PVAV Array
- SVt_PVHV Hash
- SVt_PVCV Code
- SVt_PVGV Glob (possible a file handle)
- SVt_PVMG Blessed or Magical Scalar
+ < SVt_PVAV Scalar
+ SVt_PVAV Array
+ SVt_PVHV Hash
+ SVt_PVCV Code
+ SVt_PVGV Glob (possibly a file handle)
- See the sv.h header file for more details.
+See L<perlapi/svtype> for more details.
=head2 Blessed References and Class Objects
/* Still under construction */
-Upgrades rv to reference if not already one. Creates new SV for rv to
-point to. If C<classname> is non-null, the SV is blessed into the specified
-class. SV is returned.
+The following function upgrades rv to reference if not already one.
+Creates a new SV for rv to point to. If C<classname> is non-null, the SV
+is blessed into the specified class. SV is returned.
SV* newSVrv(SV* rv, const char* classname);
-Copies integer, unsigned integer or double into an SV whose reference is C<rv>. SV is blessed
-if C<classname> is non-null.
+The following three functions copy integer, unsigned integer or double
+into an SV whose reference is C<rv>. SV is blessed if C<classname> is
+non-null.
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);
-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.
+The following function 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.
- SV* sv_setref_pv(SV* rv, const char* classname, PV iv);
+ SV* sv_setref_pv(SV* rv, const char* classname, void* pv);
-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.
+The following function copies a 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.
- SV* sv_setref_pvn(SV* rv, const char* classname, PV iv, STRLEN length);
+ SV* sv_setref_pvn(SV* rv, const char* classname, char* pv,
+ STRLEN length);
-Tests whether the SV is blessed into the specified class. It does not
-check inheritance relationships.
+The following function tests whether the SV is blessed into the specified
+class. It does not check inheritance relationships.
int sv_isa(SV* sv, const char* name);
-Tests whether the SV is a reference to a blessed object.
+The following function tests whether the SV is a reference to a blessed object.
int sv_isobject(SV* sv);
-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.
+The following function 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.
bool sv_derived_from(SV* sv, const char* name);
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.
- SV* get_sv("package::varname", TRUE);
- AV* get_av("package::varname", TRUE);
- HV* get_hv("package::varname", TRUE);
+ SV* get_sv("package::varname", GV_ADD);
+ AV* get_av("package::varname", GV_ADD);
+ HV* get_hv("package::varname", GV_ADD);
-Notice the use of TRUE as the second parameter. The new variable can now
+Notice the use of GV_ADD as the second parameter. The new variable can now
be set, using the routines appropriate to the data type.
There are additional macros whose values may be bitwise OR'ed with the
-C<TRUE> argument to enable certain extra features. Those bits are:
+C<GV_ADD> argument to enable certain extra features. Those bits are:
=over
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
+Because C<sv_newmortal> gives the new SV no value, it must normally be given one
via C<sv_setpv>, C<sv_setiv>, etc. :
SV *tmp = sv_newmortal();
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
+For example if you are passing an SV which you I<know> has a 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
+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.
extern int dberror;
extern char *dberror_list;
- SV* sv = get_sv("dberror", TRUE);
+ SV* sv = get_sv("dberror", GV_ADD);
sv_setiv(sv, (IV) dberror);
sv_setpv(sv, dberror_list[dberror]);
SvIOK_on(sv);
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.
Perl adds magic to an SV using the sv_magic function:
- void sv_magic(SV* sv, SV* obj, int how, const 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.
To remove the magic from an SV, call the function sv_unmagic:
- void sv_unmagic(SV *sv, int type);
+ int sv_unmagic(SV *sv, int type);
The C<type> argument should be equal to the C<how> value when the C<SV>
was initially made magical.
+However, note that C<sv_unmagic> removes all magic of a certain C<type> from the
+C<SV>. If you want to remove only certain magic of a C<type> based on the magic
+virtual table, use C<sv_unmagicext> instead:
+
+ int sv_unmagicext(SV *sv, int type, MGVTBL *vtbl);
+
=head2 Magic Virtual Tables
The C<mg_virtual> field in the C<MAGIC> structure is a pointer to an
int (*svt_clear)(SV* sv, MAGIC* mg);
int (*svt_free)(SV* sv, MAGIC* mg);
- int (*svt_copy)(SV *sv, MAGIC* mg, SV *nsv, const char *name, int namlen);
+ int (*svt_copy)(SV *sv, MAGIC* mg, SV *nsv,
+ const char *name, I32 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.
-
- Function pointer Action taken
- ---------------- ------------
- 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_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'
+currently 32 types. These different structures contain pointers to various
+routines that perform additional actions depending on which function is
+being called.
+
+ Function pointer Action taken
+ ---------------- ------------
+ 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_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:
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
- 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
- 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
- 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_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 $#a from @a
-
+=for comment
+This table is generated by regen/mg_vtable.pl. Any changes made here
+will be lost.
+
+=for mg_vtable.pl begin
+
+ mg_type
+ (old-style char and macro) MGVTBL Type of magic
+ -------------------------- ------ -------------
+ \0 PERL_MAGIC_sv vtbl_sv Special scalar variable
+ # PERL_MAGIC_arylen vtbl_arylen Array length ($#ary)
+ % PERL_MAGIC_rhash (none) extra data for restricted
+ hashes
+ & PERL_MAGIC_proto (none) my sub prototype CV
+ . PERL_MAGIC_pos vtbl_pos pos() lvalue
+ : PERL_MAGIC_symtab (none) extra data for symbol
+ tables
+ < PERL_MAGIC_backref vtbl_backref for weak ref data
+ @ PERL_MAGIC_arylen_p (none) to move arylen out of XPVAV
+ B PERL_MAGIC_bm vtbl_regexp Boyer-Moore
+ (fast string search)
+ c PERL_MAGIC_overload_table vtbl_ovrld Holds overload table
+ (AMT) on stash
+ 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_regexp Formline
+ ('compiled' format)
+ g PERL_MAGIC_regex_global vtbl_mglob m//g target
+ H PERL_MAGIC_hints vtbl_hints %^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
+ N PERL_MAGIC_shared (none) Shared between threads
+ n PERL_MAGIC_shared_scalar (none) Shared between threads
+ o PERL_MAGIC_collxfrm vtbl_collxfrm Locale 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_regexp precompiled qr// regex
+ S PERL_MAGIC_sig (none) %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
+ u PERL_MAGIC_uvar_elem (none) Reserved for use by
+ extensions
+ V PERL_MAGIC_vstring (none) SV was vstring literal
+ v PERL_MAGIC_vec vtbl_vec vec() lvalue
+ w PERL_MAGIC_utf8 vtbl_utf8 Cached UTF-8 information
+ x PERL_MAGIC_substr vtbl_substr substr() lvalue
+ y PERL_MAGIC_defelem vtbl_defelem Shadow "foreach" iterator
+ variable / smart parameter
+ vivification
+ ] PERL_MAGIC_checkcall vtbl_checkcall inlining/mutation of call
+ to this CV
+ ~ PERL_MAGIC_ext (none) Available for use by
+ extensions
+
+=for mg_vtable.pl end
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
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.
+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
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.
+For C<PERL_MAGIC_ext> magic, it is usually a good idea to define an
+C<MGVTBL>, even if all its fields will be C<0>, so that individual
+C<MAGIC> pointers can be identified as a particular kind of magic
+using their magic virtual table. C<mg_findext> provides an easy way
+to do that:
+
+ STATIC MGVTBL my_vtbl = { 0, 0, 0, 0, 0, 0, 0, 0 };
+
+ MAGIC *mg;
+ if ((mg = mg_findext(sv, PERL_MAGIC_ext, &my_vtbl))) {
+ /* this is really ours, not another module's PERL_MAGIC_ext */
+ my_priv_data_t *priv = (my_priv_data_t *)mg->mg_ptr;
+ ...
+ }
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
=head2 Finding Magic
- MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
+ MAGIC *mg_find(SV *sv, int type); /* Finds the magic pointer of that
+ * type */
+
+This routine returns a pointer to a C<MAGIC> structure stored in the SV.
+If the SV does not have that magical feature, C<NULL> is returned. If the
+SV has multiple instances of that magical feature, the first one will be
+returned. C<mg_findext> can be used to find a C<MAGIC> structure of an SV
+based on both its magic type and its magic virtual table:
+
+ MAGIC *mg_findext(SV *sv, int type, MGVTBL *vtbl);
-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.
+Also, if the SV passed to C<mg_find> or C<mg_findext> is not of type
+SVt_PVMG, Perl may core dump.
int mg_copy(SV* sv, SV* nsv, const char* key, STRLEN klen);
PUSHs(sv_2mortal(newSVuv(an_unsigned_integer)))
PUSHs(sv_2mortal(newSVnv(a_double)))
PUSHs(sv_2mortal(newSVpv("Some String",0)))
+ /* Although the last example is better written as the more
+ * efficient: */
+ PUSHs(newSVpvs_flags("Some String", SVs_TEMP))
And now the Perl program calling C<tzname>, the two values will be assigned
as in:
XPUSHs(SV*)
-This macro automatically adjust the stack for you, if needed. Thus, you
+This macro automatically adjusts the stack for you, if needed. Thus, you
do not need to call C<EXTEND> to extend the stack.
Despite their suggestions in earlier versions of this document the macros
For more information, consult L<perlxs> and L<perlxstut>.
+=head2 Autoloading with XSUBs
+
+If an AUTOLOAD routine is an XSUB, as with Perl subroutines, Perl puts the
+fully-qualified name of the autoloaded subroutine in the $AUTOLOAD variable
+of the XSUB's package.
+
+But it also puts the same information in certain fields of the XSUB itself:
+
+ HV *stash = CvSTASH(cv);
+ const char *subname = SvPVX(cv);
+ STRLEN name_length = SvCUR(cv); /* in bytes */
+ U32 is_utf8 = SvUTF8(cv);
+
+C<SvPVX(cv)> contains just the sub name itself, not including the package.
+For an AUTOLOAD routine in UNIVERSAL or one of its superclasses,
+C<CvSTASH(cv)> returns NULL during a method call on a nonexistent package.
+
+B<Note>: Setting $AUTOLOAD stopped working in 5.6.1, which did not support
+XS AUTOLOAD subs at all. Perl 5.8.0 introduced the use of fields in the
+XSUB itself. Perl 5.16.0 restored the setting of $AUTOLOAD. If you need
+to support 5.8-5.14, use the XSUB's fields.
+
=head2 Calling Perl Routines from within C Programs
There are four routines that can be used to call a Perl subroutine from
=head2 PerlIO
-The most recent development releases of Perl has been experimenting with
+The most recent development releases of Perl have 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
=head2 Scratchpads
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.
+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.
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
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.
+additional complications for conditionals). Optimizations performed
+at this stage are subject to the same restrictions as in the pass 2.
+
+Peephole optimizations are done by calling the function pointed to
+by the global variable C<PL_peepp>. By default, C<PL_peepp> just
+calls the function pointed to by the global variable C<PL_rpeepp>.
+By default, that performs some basic op fixups and optimisations along
+the execution-order op chain, and recursively calls C<PL_rpeepp> for
+each side chain of ops (resulting from conditionals). Extensions may
+provide additional optimisations or fixups, hooking into either the
+per-subroutine or recursive stage, like this:
+
+ static peep_t prev_peepp;
+ static void my_peep(pTHX_ OP *o)
+ {
+ /* custom per-subroutine optimisation goes here */
+ prev_peepp(o);
+ /* custom per-subroutine optimisation may also go here */
+ }
+ BOOT:
+ prev_peepp = PL_peepp;
+ PL_peepp = my_peep;
+
+ static peep_t prev_rpeepp;
+ static void my_rpeep(pTHX_ OP *o)
+ {
+ OP *orig_o = o;
+ for(; o; o = o->op_next) {
+ /* custom per-op optimisation goes here */
+ }
+ prev_rpeepp(orig_o);
+ }
+ BOOT:
+ prev_rpeepp = PL_rpeepp;
+ PL_rpeepp = my_rpeep;
=head2 Pluggable runops
This function should be as efficient as possible to keep your programs
running as fast as possible.
+=head2 Compile-time scope hooks
+
+As of perl 5.14 it is possible to hook into the compile-time lexical
+scope mechanism using C<Perl_blockhook_register>. This is used like
+this:
+
+ STATIC void my_start_hook(pTHX_ int full);
+ STATIC BHK my_hooks;
+
+ BOOT:
+ BhkENTRY_set(&my_hooks, bhk_start, my_start_hook);
+ Perl_blockhook_register(aTHX_ &my_hooks);
+
+This will arrange to have C<my_start_hook> called at the start of
+compiling every lexical scope. The available hooks are:
+
+=over 4
+
+=item C<void bhk_start(pTHX_ int full)>
+
+This is called just after starting a new lexical scope. Note that Perl
+code like
+
+ if ($x) { ... }
+
+creates two scopes: the first starts at the C<(> and has C<full == 1>,
+the second starts at the C<{> and has C<full == 0>. Both end at the
+C<}>, so calls to C<start> and C<pre/post_end> will match. Anything
+pushed onto the save stack by this hook will be popped just before the
+scope ends (between the C<pre_> and C<post_end> hooks, in fact).
+
+=item C<void bhk_pre_end(pTHX_ OP **o)>
+
+This is called at the end of a lexical scope, just before unwinding the
+stack. I<o> is the root of the optree representing the scope; it is a
+double pointer so you can replace the OP if you need to.
+
+=item C<void bhk_post_end(pTHX_ OP **o)>
+
+This is called at the end of a lexical scope, just after unwinding the
+stack. I<o> is as above. Note that it is possible for calls to C<pre_>
+and C<post_end> to nest, if there is something on the save stack that
+calls string eval.
+
+=item C<void bhk_eval(pTHX_ OP *const o)>
+
+This is called just before starting to compile an C<eval STRING>, C<do
+FILE>, C<require> or C<use>, after the eval has been set up. I<o> is the
+OP that requested the eval, and will normally be an C<OP_ENTEREVAL>,
+C<OP_DOFILE> or C<OP_REQUIRE>.
+
+=back
+
+Once you have your hook functions, you need a C<BHK> structure to put
+them in. It's best to allocate it statically, since there is no way to
+free it once it's registered. The function pointers should be inserted
+into this structure using the C<BhkENTRY_set> macro, which will also set
+flags indicating which entries are valid. If you do need to allocate
+your C<BHK> dynamically for some reason, be sure to zero it before you
+start.
+
+Once registered, there is no mechanism to switch these hooks off, so if
+that is necessary you will need to do this yourself. An entry in C<%^H>
+is probably the best way, so the effect is lexically scoped; however it
+is also possible to use the C<BhkDISABLE> and C<BhkENABLE> macros to
+temporarily switch entries on and off. You should also be aware that
+generally speaking at least one scope will have opened before your
+extension is loaded, so you will see some C<pre/post_end> pairs that
+didn't have a matching C<start>.
+
=head1 Examining internal data structures with the C<dump> functions
To aid debugging, the source file F<dump.c> contains a number of
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
+multi-threaded perls possible (with the ithreads threading model, related
to the macro USE_ITHREADS.)
Two other "encapsulation" macros are the PERL_GLOBAL_STRUCT and
S_incline(pTHX_ char *s)
STATIC becomes "static" in C, and may be #define'd to nothing in some
-configurations in future.
+configurations in the future.
A public function (i.e. part of the internal API, but not necessarily
sanctioned for use in extensions) begins like this:
void
Perl_sv_setiv(pTHX_ SV* dsv, IV num)
-C<pTHX_> is one of a number of macros (in perl.h) that hide the
+C<pTHX_> is one of a number of macros (in F<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,
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
+with extensions: whenever F<XSUB.h> is #included, it redefines the aTHX
and aTHX_ macros to call a function that will return the context.
Thus, something like:
Perl_sv_setiv(sv, num);
-You have to do nothing new in your extension to get this; since
+You don't have to do anything new in your extension to get this; since
the Perl library provides Perl_get_context(), it will all just
work.
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
+calls (see F<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.
Similarly, all global variables begin with C<PL_>. (By convention,
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
+Inside the Perl core (C<PERL_CORE> defined), 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>. Note that extension code should I<not> set
+C<PERL_CORE>; this exposes the full perl internals, and is likely to cause
+breakage of the XS in each new perl release.
+
+The file F<embed.h> is generated automatically from
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
=item n
-This does not need a interpreter context, so the definition has no
+This does not need an 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>.)
+L</Background and PERL_IMPLICIT_CONTEXT>.)
=item r
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>
+do the work for you. On a character-by-character basis,
+C<is_utf8_char_buf>
will tell you whether the current character in a string is valid UTF-8.
=head2 How does UTF-8 represent Unicode characters?
whether the byte can be encoded as a single byte even in UTF-8):
U8 *utf;
+ U8 *utf_end; /* 1 beyond buffer pointed to by utf */
UV uv; /* Note: a UV, not a U8, not a char */
+ STRLEN len; /* length of character in bytes */
if (!UTF8_IS_INVARIANT(*utf))
/* Must treat this as UTF-8 */
- uv = utf8_to_uv(utf);
+ uv = utf8_to_uvchr_buf(utf, utf_end, &len);
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
+You can also see in that example that we use C<utf8_to_uvchr_buf> to get the
+value of the character; the inverse function C<uvchr_to_utf8> is available
for putting a UV into UTF-8:
if (!UTF8_IS_INVARIANT(uv))
/* Must treat this as UTF8 */
- utf8 = uv_to_utf8(utf8, uv);
+ utf8 = uvchr_to_utf8(utf8, uv);
else
/* OK to treat this character as a byte */
*utf8++ = uv;
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
+as iso-8859-1, but C<use feature 'unicode_strings'> is needed to get iso-8859-1
+semantics). You can check and manipulate this flag with the
following macros:
SvUTF8(sv)
=item *
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
+is UTF-8 by looking at its 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 UTF-8, B<always> use C<utf8_to_uv> to get at the value,
+If a string is UTF-8, B<always> use C<utf8_to_uvchr_buf> 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 UTF-8 string, B<always> use
-C<uv_to_utf8>, unless C<UTF8_IS_INVARIANT(uv))> in which case
+C<uvchr_to_utf8>, unless C<UTF8_IS_INVARIANT(uv))> in which case
you can use C<*s = uv>.
=item *
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.
+a new string which is UTF-8 encoded, and then combine them.
=back
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.
+Perl uses the value of C<< o->op_ppaddr >> to determine which custom op
+it is dealing with. You should create an C<XOP> structure for each
+ppaddr you use, set the properties of the custom op with
+C<XopENTRY_set>, and register the structure against the ppaddr using
+C<Perl_custom_op_register>. A trivial example might look like:
+
+ static XOP my_xop;
+ static OP *my_pp(pTHX);
+
+ BOOT:
+ XopENTRY_set(&my_xop, xop_name, "myxop");
+ XopENTRY_set(&my_xop, xop_desc, "Useless custom op");
+ Perl_custom_op_register(aTHX_ my_pp, &my_xop);
+
+The available fields in the structure are:
+
+=over 4
+
+=item xop_name
+
+A short name for your op. This will be included in some error messages,
+and will also be returned as C<< $op->name >> by the L<B|B> module, so
+it will appear in the output of module like L<B::Concise|B::Concise>.
+
+=item xop_desc
+
+A short description of the function of the op.
+
+=item xop_class
+
+Which of the various C<*OP> structures this op uses. This should be one of
+the C<OA_*> constants from F<op.h>, namely
+
+=over 4
+
+=item OA_BASEOP
+
+=item OA_UNOP
+
+=item OA_BINOP
+
+=item OA_LOGOP
+
+=item OA_LISTOP
+
+=item OA_PMOP
+
+=item OA_SVOP
+
+=item OA_PADOP
+
+=item OA_PVOP_OR_SVOP
+
+This should be interpreted as 'C<PVOP>' only. The C<_OR_SVOP> is because
+the only core C<PVOP>, C<OP_TRANS>, can sometimes be a C<SVOP> instead.
+
+=item OA_LOOP
+
+=item OA_COP
+
+=back
+
+The other C<OA_*> constants should not be used.
+
+=item xop_peep
+
+This member is of type C<Perl_cpeep_t>, which expands to C<void
+(*Perl_cpeep_t)(aTHX_ OP *o, OP *oldop)>. If it is set, this function
+will be called from C<Perl_rpeep> when ops of this type are encountered
+by the peephole optimizer. I<o> is the OP that needs optimizing;
+I<oldop> is the previous OP optimized, whose C<op_next> points to I<o>.
+
+=back
-Forthcoming versions of C<B::Generate> (version 1.0 and above) should
-directly support the creation of custom ops by name.
+C<B::Generate> directly supports the creation of custom ops by name.
=head1 AUTHORS
=head1 SEE ALSO
-perlapi(1), perlintern(1), perlxs(1), perlembed(1)
+L<perlapi>, L<perlintern>, L<perlxs>, L<perlembed>
https://perl5.git.perl.org / perl5.git / blobdiff