3 perlguts - Perl's Internal Functions
7 This document attempts to describe some of the internal functions of the
8 Perl executable. It is far from complete and probably contains many errors.
9 Please refer any questions or comments to the author below.
15 Perl has three typedefs that handle Perl's three main data types:
21 Each typedef has specific routines that manipulate the various data types.
23 =head2 What is an "IV"?
25 Perl uses a special typedef IV which is a simple integer type that is
26 guaranteed to be large enough to hold a pointer (as well as an integer).
28 Perl also uses two special typedefs, I32 and I16, which will always be at
29 least 32-bits and 16-bits long, respectively.
31 =head2 Working with SVs
33 An SV can be created and loaded with one command. There are four types of
34 values that can be loaded: an integer value (IV), a double (NV), a string,
35 (PV), and another scalar (SV).
41 SV* newSVpv(char*, int);
42 SV* newSVpvn(char*, int);
43 SV* newSVpvf(const char*, ...);
46 To change the value of an *already-existing* SV, there are seven routines:
48 void sv_setiv(SV*, IV);
49 void sv_setuv(SV*, UV);
50 void sv_setnv(SV*, double);
51 void sv_setpv(SV*, char*);
52 void sv_setpvn(SV*, char*, int)
53 void sv_setpvf(SV*, const char*, ...);
54 void sv_setsv(SV*, SV*);
56 Notice that you can choose to specify the length of the string to be
57 assigned by using C<sv_setpvn>, C<newSVpvn>, or C<newSVpv>, or you may
58 allow Perl to calculate the length by using C<sv_setpv> or by specifying
59 0 as the second argument to C<newSVpv>. Be warned, though, that Perl will
60 determine the string's length by using C<strlen>, which depends on the
61 string terminating with a NUL character. The arguments of C<sv_setpvf>
62 are processed like C<sprintf>, and the formatted output becomes the value.
63 The C<sv_set*()> functions are not generic enough to operate on values
64 that have "magic". See L<Magic Virtual Tables> later in this document.
66 All SVs that will contain strings should, but need not, be terminated
67 with a NUL character. If it is not NUL-terminated there is a risk of
68 core dumps and corruptions from code which passes the string to C
69 functions or system calls which expect a NUL-terminated string.
70 Perl's own functions typically add a trailing NUL for this reason.
71 Nevertheless, you should be very careful when you pass a string stored
72 in an SV to a C function or system call.
74 To access the actual value that an SV points to, you can use the macros:
80 which will automatically coerce the actual scalar type into an IV, double,
83 In the C<SvPV> macro, the length of the string returned is placed into the
84 variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
85 care what the length of the data is, use the global variable C<na>. Remember,
86 however, that Perl allows arbitrary strings of data that may both contain
87 NULs and might not be terminated by a NUL.
89 If you want to know if the scalar value is TRUE, you can use:
93 Although Perl will automatically grow strings for you, if you need to force
94 Perl to allocate more memory for your SV, you can use the macro
96 SvGROW(SV*, STRLEN newlen)
98 which will determine if more memory needs to be allocated. If so, it will
99 call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
100 decrease, the allocated memory of an SV and that it does not automatically
101 add a byte for the a trailing NUL (perl's own string functions typically do
102 C<SvGROW(sv, len + 1)>).
104 If you have an SV and want to know what kind of data Perl thinks is stored
105 in it, you can use the following macros to check the type of SV you have.
111 You can get and set the current length of the string stored in an SV with
112 the following macros:
115 SvCUR_set(SV*, I32 val)
117 You can also get a pointer to the end of the string stored in the SV
122 But note that these last three macros are valid only if C<SvPOK()> is true.
124 If you want to append something to the end of string stored in an C<SV*>,
125 you can use the following functions:
127 void sv_catpv(SV*, char*);
128 void sv_catpvn(SV*, char*, int);
129 void sv_catpvf(SV*, const char*, ...);
130 void sv_catsv(SV*, SV*);
132 The first function calculates the length of the string to be appended by
133 using C<strlen>. In the second, you specify the length of the string
134 yourself. The third function processes its arguments like C<sprintf> and
135 appends the formatted output. The fourth function extends the string
136 stored in the first SV with the string stored in the second SV. It also
137 forces the second SV to be interpreted as a string. The C<sv_cat*()>
138 functions are not generic enough to operate on values that have "magic".
139 See L<Magic Virtual Tables> later in this document.
141 If you know the name of a scalar variable, you can get a pointer to its SV
142 by using the following:
144 SV* perl_get_sv("package::varname", FALSE);
146 This returns NULL if the variable does not exist.
148 If you want to know if this variable (or any other SV) is actually C<defined>,
153 The scalar C<undef> value is stored in an SV instance called C<sv_undef>. Its
154 address can be used whenever an C<SV*> is needed.
156 There are also the two values C<sv_yes> and C<sv_no>, which contain Boolean
157 TRUE and FALSE values, respectively. Like C<sv_undef>, their addresses can
158 be used whenever an C<SV*> is needed.
160 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&sv_undef>.
164 if (I-am-to-return-a-real-value) {
165 sv = sv_2mortal(newSViv(42));
169 This code tries to return a new SV (which contains the value 42) if it should
170 return a real value, or undef otherwise. Instead it has returned a NULL
171 pointer which, somewhere down the line, will cause a segmentation violation,
172 bus error, or just weird results. Change the zero to C<&sv_undef> in the first
173 line and all will be well.
175 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
176 call is not necessary (see L<Reference Counts and Mortality>).
178 =head2 What's Really Stored in an SV?
180 Recall that the usual method of determining the type of scalar you have is
181 to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
182 usually these macros will always return TRUE and calling the C<Sv*V>
183 macros will do the appropriate conversion of string to integer/double or
184 integer/double to string.
186 If you I<really> need to know if you have an integer, double, or string
187 pointer in an SV, you can use the following three macros instead:
193 These will tell you if you truly have an integer, double, or string pointer
194 stored in your SV. The "p" stands for private.
196 In general, though, it's best to use the C<Sv*V> macros.
198 =head2 Working with AVs
200 There are two ways to create and load an AV. The first method creates an
205 The second method both creates the AV and initially populates it with SVs:
207 AV* av_make(I32 num, SV **ptr);
209 The second argument points to an array containing C<num> C<SV*>'s. Once the
210 AV has been created, the SVs can be destroyed, if so desired.
212 Once the AV has been created, the following operations are possible on AVs:
214 void av_push(AV*, SV*);
217 void av_unshift(AV*, I32 num);
219 These should be familiar operations, with the exception of C<av_unshift>.
220 This routine adds C<num> elements at the front of the array with the C<undef>
221 value. You must then use C<av_store> (described below) to assign values
222 to these new elements.
224 Here are some other functions:
227 SV** av_fetch(AV*, I32 key, I32 lval);
228 SV** av_store(AV*, I32 key, SV* val);
230 The C<av_len> function returns the highest index value in array (just
231 like $#array in Perl). If the array is empty, -1 is returned. The
232 C<av_fetch> function returns the value at index C<key>, but if C<lval>
233 is non-zero, then C<av_fetch> will store an undef value at that index.
234 The C<av_store> function stores the value C<val> at index C<key>, and does
235 not increment the reference count of C<val>. Thus the caller is responsible
236 for taking care of that, and if C<av_store> returns NULL, the caller will
237 have to decrement the reference count to avoid a memory leak. Note that
238 C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s as their
243 void av_extend(AV*, I32 key);
245 The C<av_clear> function deletes all the elements in the AV* array, but
246 does not actually delete the array itself. The C<av_undef> function will
247 delete all the elements in the array plus the array itself. The
248 C<av_extend> function extends the array so that it contains C<key>
249 elements. If C<key> is less than the current length of the array, then
252 If you know the name of an array variable, you can get a pointer to its AV
253 by using the following:
255 AV* perl_get_av("package::varname", FALSE);
257 This returns NULL if the variable does not exist.
259 See L<Understanding the Magic of Tied Hashes and Arrays> for more
260 information on how to use the array access functions on tied arrays.
262 =head2 Working with HVs
264 To create an HV, you use the following routine:
268 Once the HV has been created, the following operations are possible on HVs:
270 SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
271 SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
273 The C<klen> parameter is the length of the key being passed in (Note that
274 you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
275 length of the key). The C<val> argument contains the SV pointer to the
276 scalar being stored, and C<hash> is the precomputed hash value (zero if
277 you want C<hv_store> to calculate it for you). The C<lval> parameter
278 indicates whether this fetch is actually a part of a store operation, in
279 which case a new undefined value will be added to the HV with the supplied
280 key and C<hv_fetch> will return as if the value had already existed.
282 Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
283 C<SV*>. To access the scalar value, you must first dereference the return
284 value. However, you should check to make sure that the return value is
285 not NULL before dereferencing it.
287 These two functions check if a hash table entry exists, and deletes it.
289 bool hv_exists(HV*, char* key, U32 klen);
290 SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
292 If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
293 create and return a mortal copy of the deleted value.
295 And more miscellaneous functions:
300 Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
301 table but does not actually delete the hash table. The C<hv_undef> deletes
302 both the entries and the hash table itself.
304 Perl keeps the actual data in linked list of structures with a typedef of HE.
305 These contain the actual key and value pointers (plus extra administrative
306 overhead). The key is a string pointer; the value is an C<SV*>. However,
307 once you have an C<HE*>, to get the actual key and value, use the routines
310 I32 hv_iterinit(HV*);
311 /* Prepares starting point to traverse hash table */
312 HE* hv_iternext(HV*);
313 /* Get the next entry, and return a pointer to a
314 structure that has both the key and value */
315 char* hv_iterkey(HE* entry, I32* retlen);
316 /* Get the key from an HE structure and also return
317 the length of the key string */
318 SV* hv_iterval(HV*, HE* entry);
319 /* Return a SV pointer to the value of the HE
321 SV* hv_iternextsv(HV*, char** key, I32* retlen);
322 /* This convenience routine combines hv_iternext,
323 hv_iterkey, and hv_iterval. The key and retlen
324 arguments are return values for the key and its
325 length. The value is returned in the SV* argument */
327 If you know the name of a hash variable, you can get a pointer to its HV
328 by using the following:
330 HV* perl_get_hv("package::varname", FALSE);
332 This returns NULL if the variable does not exist.
334 The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
340 hash = hash * 33 + *s++;
342 See L<Understanding the Magic of Tied Hashes and Arrays> for more
343 information on how to use the hash access functions on tied hashes.
345 =head2 Hash API Extensions
347 Beginning with version 5.004, the following functions are also supported:
349 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
350 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
352 bool hv_exists_ent (HV* tb, SV* key, U32 hash);
353 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
355 SV* hv_iterkeysv (HE* entry);
357 Note that these functions take C<SV*> keys, which simplifies writing
358 of extension code that deals with hash structures. These functions
359 also allow passing of C<SV*> keys to C<tie> functions without forcing
360 you to stringify the keys (unlike the previous set of functions).
362 They also return and accept whole hash entries (C<HE*>), making their
363 use more efficient (since the hash number for a particular string
364 doesn't have to be recomputed every time). See L<API LISTING> later in
365 this document for detailed descriptions.
367 The following macros must always be used to access the contents of hash
368 entries. Note that the arguments to these macros must be simple
369 variables, since they may get evaluated more than once. See
370 L<API LISTING> later in this document for detailed descriptions of these
373 HePV(HE* he, STRLEN len)
377 HeSVKEY_force(HE* he)
378 HeSVKEY_set(HE* he, SV* sv)
380 These two lower level macros are defined, but must only be used when
381 dealing with keys that are not C<SV*>s:
386 Note that both C<hv_store> and C<hv_store_ent> do not increment the
387 reference count of the stored C<val>, which is the caller's responsibility.
388 If these functions return a NULL value, the caller will usually have to
389 decrement the reference count of C<val> to avoid a memory leak.
393 References are a special type of scalar that point to other data types
394 (including references).
396 To create a reference, use either of the following functions:
398 SV* newRV_inc((SV*) thing);
399 SV* newRV_noinc((SV*) thing);
401 The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
402 functions are identical except that C<newRV_inc> increments the reference
403 count of the C<thing>, while C<newRV_noinc> does not. For historical
404 reasons, C<newRV> is a synonym for C<newRV_inc>.
406 Once you have a reference, you can use the following macro to dereference
411 then call the appropriate routines, casting the returned C<SV*> to either an
412 C<AV*> or C<HV*>, if required.
414 To determine if an SV is a reference, you can use the following macro:
418 To discover what type of value the reference refers to, use the following
419 macro and then check the return value.
423 The most useful types that will be returned are:
432 SVt_PVGV Glob (possible a file handle)
433 SVt_PVMG Blessed or Magical Scalar
435 See the sv.h header file for more details.
437 =head2 Blessed References and Class Objects
439 References are also used to support object-oriented programming. In the
440 OO lexicon, an object is simply a reference that has been blessed into a
441 package (or class). Once blessed, the programmer may now use the reference
442 to access the various methods in the class.
444 A reference can be blessed into a package with the following function:
446 SV* sv_bless(SV* sv, HV* stash);
448 The C<sv> argument must be a reference. The C<stash> argument specifies
449 which class the reference will belong to. See
450 L<Stashes and Globs> for information on converting class names into stashes.
452 /* Still under construction */
454 Upgrades rv to reference if not already one. Creates new SV for rv to
455 point to. If C<classname> is non-null, the SV is blessed into the specified
456 class. SV is returned.
458 SV* newSVrv(SV* rv, char* classname);
460 Copies integer or double into an SV whose reference is C<rv>. SV is blessed
461 if C<classname> is non-null.
463 SV* sv_setref_iv(SV* rv, char* classname, IV iv);
464 SV* sv_setref_nv(SV* rv, char* classname, NV iv);
466 Copies the pointer value (I<the address, not the string!>) into an SV whose
467 reference is rv. SV is blessed if C<classname> is non-null.
469 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
471 Copies string into an SV whose reference is C<rv>. Set length to 0 to let
472 Perl calculate the string length. SV is blessed if C<classname> is non-null.
474 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
476 int sv_isa(SV* sv, char* name);
477 int sv_isobject(SV* sv);
479 =head2 Creating New Variables
481 To create a new Perl variable with an undef value which can be accessed from
482 your Perl script, use the following routines, depending on the variable type.
484 SV* perl_get_sv("package::varname", TRUE);
485 AV* perl_get_av("package::varname", TRUE);
486 HV* perl_get_hv("package::varname", TRUE);
488 Notice the use of TRUE as the second parameter. The new variable can now
489 be set, using the routines appropriate to the data type.
491 There are additional macros whose values may be bitwise OR'ed with the
492 C<TRUE> argument to enable certain extra features. Those bits are:
494 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
495 "Name <varname> used only once: possible typo" warning.
496 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
497 the variable did not exist before the function was called.
499 If you do not specify a package name, the variable is created in the current
502 =head2 Reference Counts and Mortality
504 Perl uses an reference count-driven garbage collection mechanism. SVs,
505 AVs, or HVs (xV for short in the following) start their life with a
506 reference count of 1. If the reference count of an xV ever drops to 0,
507 then it will be destroyed and its memory made available for reuse.
509 This normally doesn't happen at the Perl level unless a variable is
510 undef'ed or the last variable holding a reference to it is changed or
511 overwritten. At the internal level, however, reference counts can be
512 manipulated with the following macros:
514 int SvREFCNT(SV* sv);
515 SV* SvREFCNT_inc(SV* sv);
516 void SvREFCNT_dec(SV* sv);
518 However, there is one other function which manipulates the reference
519 count of its argument. The C<newRV_inc> function, you will recall,
520 creates a reference to the specified argument. As a side effect,
521 it increments the argument's reference count. If this is not what
522 you want, use C<newRV_noinc> instead.
524 For example, imagine you want to return a reference from an XSUB function.
525 Inside the XSUB routine, you create an SV which initially has a reference
526 count of one. Then you call C<newRV_inc>, passing it the just-created SV.
527 This returns the reference as a new SV, but the reference count of the
528 SV you passed to C<newRV_inc> has been incremented to two. Now you
529 return the reference from the XSUB routine and forget about the SV.
530 But Perl hasn't! Whenever the returned reference is destroyed, the
531 reference count of the original SV is decreased to one and nothing happens.
532 The SV will hang around without any way to access it until Perl itself
533 terminates. This is a memory leak.
535 The correct procedure, then, is to use C<newRV_noinc> instead of
536 C<newRV_inc>. Then, if and when the last reference is destroyed,
537 the reference count of the SV will go to zero and it will be destroyed,
538 stopping any memory leak.
540 There are some convenience functions available that can help with the
541 destruction of xVs. These functions introduce the concept of "mortality".
542 An xV that is mortal has had its reference count marked to be decremented,
543 but not actually decremented, until "a short time later". Generally the
544 term "short time later" means a single Perl statement, such as a call to
545 an XSUB function. The actual determinant for when mortal xVs have their
546 reference count decremented depends on two macros, SAVETMPS and FREETMPS.
547 See L<perlcall> and L<perlxs> for more details on these macros.
549 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
550 However, if you mortalize a variable twice, the reference count will
551 later be decremented twice.
553 You should be careful about creating mortal variables. Strange things
554 can happen if you make the same value mortal within multiple contexts,
555 or if you make a variable mortal multiple times.
557 To create a mortal variable, use the functions:
561 SV* sv_mortalcopy(SV*)
563 The first call creates a mortal SV, the second converts an existing
564 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
565 third creates a mortal copy of an existing SV.
567 The mortal routines are not just for SVs -- AVs and HVs can be
568 made mortal by passing their address (type-casted to C<SV*>) to the
569 C<sv_2mortal> or C<sv_mortalcopy> routines.
571 =head2 Stashes and Globs
573 A "stash" is a hash that contains all of the different objects that
574 are contained within a package. Each key of the stash is a symbol
575 name (shared by all the different types of objects that have the same
576 name), and each value in the hash table is a GV (Glob Value). This GV
577 in turn contains references to the various objects of that name,
578 including (but not limited to) the following:
588 There is a single stash called "defstash" that holds the items that exist
589 in the "main" package. To get at the items in other packages, append the
590 string "::" to the package name. The items in the "Foo" package are in
591 the stash "Foo::" in defstash. The items in the "Bar::Baz" package are
592 in the stash "Baz::" in "Bar::"'s stash.
594 To get the stash pointer for a particular package, use the function:
596 HV* gv_stashpv(char* name, I32 create)
597 HV* gv_stashsv(SV*, I32 create)
599 The first function takes a literal string, the second uses the string stored
600 in the SV. Remember that a stash is just a hash table, so you get back an
601 C<HV*>. The C<create> flag will create a new package if it is set.
603 The name that C<gv_stash*v> wants is the name of the package whose symbol table
604 you want. The default package is called C<main>. If you have multiply nested
605 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
608 Alternately, if you have an SV that is a blessed reference, you can find
609 out the stash pointer by using:
611 HV* SvSTASH(SvRV(SV*));
613 then use the following to get the package name itself:
615 char* HvNAME(HV* stash);
617 If you need to bless or re-bless an object you can use the following
620 SV* sv_bless(SV*, HV* stash)
622 where the first argument, an C<SV*>, must be a reference, and the second
623 argument is a stash. The returned C<SV*> can now be used in the same way
626 For more information on references and blessings, consult L<perlref>.
628 =head2 Double-Typed SVs
630 Scalar variables normally contain only one type of value, an integer,
631 double, pointer, or reference. Perl will automatically convert the
632 actual scalar data from the stored type into the requested type.
634 Some scalar variables contain more than one type of scalar data. For
635 example, the variable C<$!> contains either the numeric value of C<errno>
636 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
638 To force multiple data values into an SV, you must do two things: use the
639 C<sv_set*v> routines to add the additional scalar type, then set a flag
640 so that Perl will believe it contains more than one type of data. The
641 four macros to set the flags are:
648 The particular macro you must use depends on which C<sv_set*v> routine
649 you called first. This is because every C<sv_set*v> routine turns on
650 only the bit for the particular type of data being set, and turns off
653 For example, to create a new Perl variable called "dberror" that contains
654 both the numeric and descriptive string error values, you could use the
658 extern char *dberror_list;
660 SV* sv = perl_get_sv("dberror", TRUE);
661 sv_setiv(sv, (IV) dberror);
662 sv_setpv(sv, dberror_list[dberror]);
665 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
666 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
668 =head2 Magic Variables
670 [This section still under construction. Ignore everything here. Post no
671 bills. Everything not permitted is forbidden.]
673 Any SV may be magical, that is, it has special features that a normal
674 SV does not have. These features are stored in the SV structure in a
675 linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
688 Note this is current as of patchlevel 0, and could change at any time.
690 =head2 Assigning Magic
692 Perl adds magic to an SV using the sv_magic function:
694 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
696 The C<sv> argument is a pointer to the SV that is to acquire a new magical
699 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
700 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
701 it to the beginning of the linked list of magical features. Any prior
702 entry of the same type of magic is deleted. Note that this can be
703 overridden, and multiple instances of the same type of magic can be
704 associated with an SV.
706 The C<name> and C<namlen> arguments are used to associate a string with
707 the magic, typically the name of a variable. C<namlen> is stored in the
708 C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
709 copy of the name is stored in C<mg_ptr> field.
711 The sv_magic function uses C<how> to determine which, if any, predefined
712 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
713 See the "Magic Virtual Table" section below. The C<how> argument is also
714 stored in the C<mg_type> field.
716 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
717 structure. If it is not the same as the C<sv> argument, the reference
718 count of the C<obj> object is incremented. If it is the same, or if
719 the C<how> argument is "#", or if it is a NULL pointer, then C<obj> is
720 merely stored, without the reference count being incremented.
722 There is also a function to add magic to an C<HV>:
724 void hv_magic(HV *hv, GV *gv, int how);
726 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
728 To remove the magic from an SV, call the function sv_unmagic:
730 void sv_unmagic(SV *sv, int type);
732 The C<type> argument should be equal to the C<how> value when the C<SV>
733 was initially made magical.
735 =head2 Magic Virtual Tables
737 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
738 C<MGVTBL>, which is a structure of function pointers and stands for
739 "Magic Virtual Table" to handle the various operations that might be
740 applied to that variable.
742 The C<MGVTBL> has five pointers to the following routine types:
744 int (*svt_get)(SV* sv, MAGIC* mg);
745 int (*svt_set)(SV* sv, MAGIC* mg);
746 U32 (*svt_len)(SV* sv, MAGIC* mg);
747 int (*svt_clear)(SV* sv, MAGIC* mg);
748 int (*svt_free)(SV* sv, MAGIC* mg);
750 This MGVTBL structure is set at compile-time in C<perl.h> and there are
751 currently 19 types (or 21 with overloading turned on). These different
752 structures contain pointers to various routines that perform additional
753 actions depending on which function is being called.
755 Function pointer Action taken
756 ---------------- ------------
757 svt_get Do something after the value of the SV is retrieved.
758 svt_set Do something after the SV is assigned a value.
759 svt_len Report on the SV's length.
760 svt_clear Clear something the SV represents.
761 svt_free Free any extra storage associated with the SV.
763 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
764 to an C<mg_type> of '\0') contains:
766 { magic_get, magic_set, magic_len, 0, 0 }
768 Thus, when an SV is determined to be magical and of type '\0', if a get
769 operation is being performed, the routine C<magic_get> is called. All
770 the various routines for the various magical types begin with C<magic_>.
772 The current kinds of Magic Virtual Tables are:
774 mg_type MGVTBL Type of magic
775 ------- ------ ----------------------------
776 \0 vtbl_sv Special scalar variable
777 A vtbl_amagic %OVERLOAD hash
778 a vtbl_amagicelem %OVERLOAD hash element
779 c (none) Holds overload table (AMT) on stash
780 B vtbl_bm Boyer-Moore (fast string search)
782 e vtbl_envelem %ENV hash element
783 f vtbl_fm Formline ('compiled' format)
784 g vtbl_mglob m//g target / study()ed string
785 I vtbl_isa @ISA array
786 i vtbl_isaelem @ISA array element
787 k vtbl_nkeys scalar(keys()) lvalue
788 L (none) Debugger %_<filename
789 l vtbl_dbline Debugger %_<filename element
790 o vtbl_collxfrm Locale transformation
791 P vtbl_pack Tied array or hash
792 p vtbl_packelem Tied array or hash element
793 q vtbl_packelem Tied scalar or handle
795 s vtbl_sigelem %SIG hash element
796 t vtbl_taint Taintedness
797 U vtbl_uvar Available for use by extensions
798 v vtbl_vec vec() lvalue
799 x vtbl_substr substr() lvalue
800 y vtbl_defelem Shadow "foreach" iterator variable /
801 smart parameter vivification
802 * vtbl_glob GV (typeglob)
803 # vtbl_arylen Array length ($#ary)
804 . vtbl_pos pos() lvalue
805 ~ (none) Available for use by extensions
807 When an uppercase and lowercase letter both exist in the table, then the
808 uppercase letter is used to represent some kind of composite type (a list
809 or a hash), and the lowercase letter is used to represent an element of
812 The '~' and 'U' magic types are defined specifically for use by
813 extensions and will not be used by perl itself. Extensions can use
814 '~' magic to 'attach' private information to variables (typically
815 objects). This is especially useful because there is no way for
816 normal perl code to corrupt this private information (unlike using
817 extra elements of a hash object).
819 Similarly, 'U' magic can be used much like tie() to call a C function
820 any time a scalar's value is used or changed. The C<MAGIC>'s
821 C<mg_ptr> field points to a C<ufuncs> structure:
824 I32 (*uf_val)(IV, SV*);
825 I32 (*uf_set)(IV, SV*);
829 When the SV is read from or written to, the C<uf_val> or C<uf_set>
830 function will be called with C<uf_index> as the first arg and a
831 pointer to the SV as the second.
833 Note that because multiple extensions may be using '~' or 'U' magic,
834 it is important for extensions to take extra care to avoid conflict.
835 Typically only using the magic on objects blessed into the same class
836 as the extension is sufficient. For '~' magic, it may also be
837 appropriate to add an I32 'signature' at the top of the private data
840 Also note that the C<sv_set*()> and C<sv_cat*()> functions described
841 earlier do B<not> invoke 'set' magic on their targets. This must
842 be done by the user either by calling the C<SvSETMAGIC()> macro after
843 calling these functions, or by using one of the C<sv_set*_mg()> or
844 C<sv_cat*_mg()> functions. Similarly, generic C code must call the
845 C<SvGETMAGIC()> macro to invoke any 'get' magic if they use an SV
846 obtained from external sources in functions that don't handle magic.
847 L<API LISTING> later in this document identifies such functions.
848 For example, calls to the C<sv_cat*()> functions typically need to be
849 followed by C<SvSETMAGIC()>, but they don't need a prior C<SvGETMAGIC()>
850 since their implementation handles 'get' magic.
854 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
856 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
857 If the SV does not have that magical feature, C<NULL> is returned. Also,
858 if the SV is not of type SVt_PVMG, Perl may core dump.
860 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
862 This routine checks to see what types of magic C<sv> has. If the mg_type
863 field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
864 the mg_type field is changed to be the lowercase letter.
866 =head2 Understanding the Magic of Tied Hashes and Arrays
868 Tied hashes and arrays are magical beasts of the 'P' magic type.
870 WARNING: As of the 5.004 release, proper usage of the array and hash
871 access functions requires understanding a few caveats. Some
872 of these caveats are actually considered bugs in the API, to be fixed
873 in later releases, and are bracketed with [MAYCHANGE] below. If
874 you find yourself actually applying such information in this section, be
875 aware that the behavior may change in the future, umm, without warning.
877 The C<av_store> function, when given a tied array argument, merely
878 copies the magic of the array onto the value to be "stored", using
879 C<mg_copy>. It may also return NULL, indicating that the value did not
880 actually need to be stored in the array. [MAYCHANGE] After a call to
881 C<av_store> on a tied array, the caller will usually need to call
882 C<mg_set(val)> to actually invoke the perl level "STORE" method on the
883 TIEARRAY object. If C<av_store> did return NULL, a call to
884 C<SvREFCNT_dec(val)> will also be usually necessary to avoid a memory
887 The previous paragraph is applicable verbatim to tied hash access using the
888 C<hv_store> and C<hv_store_ent> functions as well.
890 C<av_fetch> and the corresponding hash functions C<hv_fetch> and
891 C<hv_fetch_ent> actually return an undefined mortal value whose magic
892 has been initialized using C<mg_copy>. Note the value so returned does not
893 need to be deallocated, as it is already mortal. [MAYCHANGE] But you will
894 need to call C<mg_get()> on the returned value in order to actually invoke
895 the perl level "FETCH" method on the underlying TIE object. Similarly,
896 you may also call C<mg_set()> on the return value after possibly assigning
897 a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
898 method on the TIE object. [/MAYCHANGE]
901 In other words, the array or hash fetch/store functions don't really
902 fetch and store actual values in the case of tied arrays and hashes. They
903 merely call C<mg_copy> to attach magic to the values that were meant to be
904 "stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
905 do the job of invoking the TIE methods on the underlying objects. Thus
906 the magic mechanism currently implements a kind of lazy access to arrays
909 Currently (as of perl version 5.004), use of the hash and array access
910 functions requires the user to be aware of whether they are operating on
911 "normal" hashes and arrays, or on their tied variants. The API may be
912 changed to provide more transparent access to both tied and normal data
913 types in future versions.
916 You would do well to understand that the TIEARRAY and TIEHASH interfaces
917 are mere sugar to invoke some perl method calls while using the uniform hash
918 and array syntax. The use of this sugar imposes some overhead (typically
919 about two to four extra opcodes per FETCH/STORE operation, in addition to
920 the creation of all the mortal variables required to invoke the methods).
921 This overhead will be comparatively small if the TIE methods are themselves
922 substantial, but if they are only a few statements long, the overhead
923 will not be insignificant.
925 =head2 Localizing changes
927 Perl has a very handy construction
934 This construction is I<approximately> equivalent to
943 The biggest difference is that the first construction would
944 reinstate the initial value of $var, irrespective of how control exits
945 the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
946 more efficient as well.
948 There is a way to achieve a similar task from C via Perl API: create a
949 I<pseudo-block>, and arrange for some changes to be automatically
950 undone at the end of it, either explicit, or via a non-local exit (via
951 die()). A I<block>-like construct is created by a pair of
952 C<ENTER>/C<LEAVE> macros (see L<perlcall/EXAMPLE/"Returning a
953 Scalar">). Such a construct may be created specially for some
954 important localized task, or an existing one (like boundaries of
955 enclosing Perl subroutine/block, or an existing pair for freeing TMPs)
956 may be used. (In the second case the overhead of additional
957 localization must be almost negligible.) Note that any XSUB is
958 automatically enclosed in an C<ENTER>/C<LEAVE> pair.
960 Inside such a I<pseudo-block> the following service is available:
964 =item C<SAVEINT(int i)>
966 =item C<SAVEIV(IV i)>
968 =item C<SAVEI32(I32 i)>
970 =item C<SAVELONG(long i)>
972 These macros arrange things to restore the value of integer variable
973 C<i> at the end of enclosing I<pseudo-block>.
979 These macros arrange things to restore the value of pointers C<s> and
980 C<p>. C<s> must be a pointer of a type which survives conversion to
981 C<SV*> and back, C<p> should be able to survive conversion to C<char*>
984 =item C<SAVEFREESV(SV *sv)>
986 The refcount of C<sv> would be decremented at the end of
987 I<pseudo-block>. This is similar to C<sv_2mortal>, which should (?) be
990 =item C<SAVEFREEOP(OP *op)>
992 The C<OP *> is op_free()ed at the end of I<pseudo-block>.
994 =item C<SAVEFREEPV(p)>
996 The chunk of memory which is pointed to by C<p> is Safefree()ed at the
997 end of I<pseudo-block>.
999 =item C<SAVECLEARSV(SV *sv)>
1001 Clears a slot in the current scratchpad which corresponds to C<sv> at
1002 the end of I<pseudo-block>.
1004 =item C<SAVEDELETE(HV *hv, char *key, I32 length)>
1006 The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
1007 string pointed to by C<key> is Safefree()ed. If one has a I<key> in
1008 short-lived storage, the corresponding string may be reallocated like
1011 SAVEDELETE(defstash, savepv(tmpbuf), strlen(tmpbuf));
1013 =item C<SAVEDESTRUCTOR(f,p)>
1015 At the end of I<pseudo-block> the function C<f> is called with the
1016 only argument (of type C<void*>) C<p>.
1018 =item C<SAVESTACK_POS()>
1020 The current offset on the Perl internal stack (cf. C<SP>) is restored
1021 at the end of I<pseudo-block>.
1025 The following API list contains functions, thus one needs to
1026 provide pointers to the modifiable data explicitly (either C pointers,
1027 or Perlish C<GV *>s). Where the above macros take C<int>, a similar
1028 function takes C<int *>.
1032 =item C<SV* save_scalar(GV *gv)>
1034 Equivalent to Perl code C<local $gv>.
1036 =item C<AV* save_ary(GV *gv)>
1038 =item C<HV* save_hash(GV *gv)>
1040 Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
1042 =item C<void save_item(SV *item)>
1044 Duplicates the current value of C<SV>, on the exit from the current
1045 C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
1046 using the stored value.
1048 =item C<void save_list(SV **sarg, I32 maxsarg)>
1050 A variant of C<save_item> which takes multiple arguments via an array
1051 C<sarg> of C<SV*> of length C<maxsarg>.
1053 =item C<SV* save_svref(SV **sptr)>
1055 Similar to C<save_scalar>, but will reinstate a C<SV *>.
1057 =item C<void save_aptr(AV **aptr)>
1059 =item C<void save_hptr(HV **hptr)>
1061 Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
1065 The C<Alias> module implements localization of the basic types within the
1066 I<caller's scope>. People who are interested in how to localize things in
1067 the containing scope should take a look there too.
1071 =head2 XSUBs and the Argument Stack
1073 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
1074 An XSUB routine will have a stack that contains the arguments from the Perl
1075 program, and a way to map from the Perl data structures to a C equivalent.
1077 The stack arguments are accessible through the C<ST(n)> macro, which returns
1078 the C<n>'th stack argument. Argument 0 is the first argument passed in the
1079 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
1082 Most of the time, output from the C routine can be handled through use of
1083 the RETVAL and OUTPUT directives. However, there are some cases where the
1084 argument stack is not already long enough to handle all the return values.
1085 An example is the POSIX tzname() call, which takes no arguments, but returns
1086 two, the local time zone's standard and summer time abbreviations.
1088 To handle this situation, the PPCODE directive is used and the stack is
1089 extended using the macro:
1093 where C<SP> is the macro that represents the local copy of the stack pointer,
1094 and C<num> is the number of elements the stack should be extended by.
1096 Now that there is room on the stack, values can be pushed on it using the
1097 macros to push IVs, doubles, strings, and SV pointers respectively:
1104 And now the Perl program calling C<tzname>, the two values will be assigned
1107 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
1109 An alternate (and possibly simpler) method to pushing values on the stack is
1117 These macros automatically adjust the stack for you, if needed. Thus, you
1118 do not need to call C<EXTEND> to extend the stack.
1120 For more information, consult L<perlxs> and L<perlxstut>.
1122 =head2 Calling Perl Routines from within C Programs
1124 There are four routines that can be used to call a Perl subroutine from
1125 within a C program. These four are:
1127 I32 perl_call_sv(SV*, I32);
1128 I32 perl_call_pv(char*, I32);
1129 I32 perl_call_method(char*, I32);
1130 I32 perl_call_argv(char*, I32, register char**);
1132 The routine most often used is C<perl_call_sv>. The C<SV*> argument
1133 contains either the name of the Perl subroutine to be called, or a
1134 reference to the subroutine. The second argument consists of flags
1135 that control the context in which the subroutine is called, whether
1136 or not the subroutine is being passed arguments, how errors should be
1137 trapped, and how to treat return values.
1139 All four routines return the number of arguments that the subroutine returned
1142 When using any of these routines (except C<perl_call_argv>), the programmer
1143 must manipulate the Perl stack. These include the following macros and
1158 For a detailed description of calling conventions from C to Perl,
1159 consult L<perlcall>.
1161 =head2 Memory Allocation
1163 It is suggested that you use the version of malloc that is distributed
1164 with Perl. It keeps pools of various sizes of unallocated memory in
1165 order to satisfy allocation requests more quickly. However, on some
1166 platforms, it may cause spurious malloc or free errors.
1168 New(x, pointer, number, type);
1169 Newc(x, pointer, number, type, cast);
1170 Newz(x, pointer, number, type);
1172 These three macros are used to initially allocate memory.
1174 The first argument C<x> was a "magic cookie" that was used to keep track
1175 of who called the macro, to help when debugging memory problems. However,
1176 the current code makes no use of this feature (most Perl developers now
1177 use run-time memory checkers), so this argument can be any number.
1179 The second argument C<pointer> should be the name of a variable that will
1180 point to the newly allocated memory.
1182 The third and fourth arguments C<number> and C<type> specify how many of
1183 the specified type of data structure should be allocated. The argument
1184 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
1185 should be used if the C<pointer> argument is different from the C<type>
1188 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
1189 to zero out all the newly allocated memory.
1191 Renew(pointer, number, type);
1192 Renewc(pointer, number, type, cast);
1195 These three macros are used to change a memory buffer size or to free a
1196 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1197 match those of C<New> and C<Newc> with the exception of not needing the
1198 "magic cookie" argument.
1200 Move(source, dest, number, type);
1201 Copy(source, dest, number, type);
1202 Zero(dest, number, type);
1204 These three macros are used to move, copy, or zero out previously allocated
1205 memory. The C<source> and C<dest> arguments point to the source and
1206 destination starting points. Perl will move, copy, or zero out C<number>
1207 instances of the size of the C<type> data structure (using the C<sizeof>
1212 The most recent development releases of Perl has been experimenting with
1213 removing Perl's dependency on the "normal" standard I/O suite and allowing
1214 other stdio implementations to be used. This involves creating a new
1215 abstraction layer that then calls whichever implementation of stdio Perl
1216 was compiled with. All XSUBs should now use the functions in the PerlIO
1217 abstraction layer and not make any assumptions about what kind of stdio
1220 For a complete description of the PerlIO abstraction, consult L<perlapio>.
1222 =head2 Putting a C value on Perl stack
1224 A lot of opcodes (this is an elementary operation in the internal perl
1225 stack machine) put an SV* on the stack. However, as an optimization
1226 the corresponding SV is (usually) not recreated each time. The opcodes
1227 reuse specially assigned SVs (I<target>s) which are (as a corollary)
1228 not constantly freed/created.
1230 Each of the targets is created only once (but see
1231 L<Scratchpads and recursion> below), and when an opcode needs to put
1232 an integer, a double, or a string on stack, it just sets the
1233 corresponding parts of its I<target> and puts the I<target> on stack.
1235 The macro to put this target on stack is C<PUSHTARG>, and it is
1236 directly used in some opcodes, as well as indirectly in zillions of
1237 others, which use it via C<(X)PUSH[pni]>.
1241 The question remains on when the SVs which are I<target>s for opcodes
1242 are created. The answer is that they are created when the current unit --
1243 a subroutine or a file (for opcodes for statements outside of
1244 subroutines) -- is compiled. During this time a special anonymous Perl
1245 array is created, which is called a scratchpad for the current
1248 A scratchpad keeps SVs which are lexicals for the current unit and are
1249 targets for opcodes. One can deduce that an SV lives on a scratchpad
1250 by looking on its flags: lexicals have C<SVs_PADMY> set, and
1251 I<target>s have C<SVs_PADTMP> set.
1253 The correspondence between OPs and I<target>s is not 1-to-1. Different
1254 OPs in the compile tree of the unit can use the same target, if this
1255 would not conflict with the expected life of the temporary.
1257 =head2 Scratchpads and recursion
1259 In fact it is not 100% true that a compiled unit contains a pointer to
1260 the scratchpad AV. In fact it contains a pointer to an AV of
1261 (initially) one element, and this element is the scratchpad AV. Why do
1262 we need an extra level of indirection?
1264 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1265 these can create several execution pointers going into the same
1266 subroutine. For the subroutine-child not write over the temporaries
1267 for the subroutine-parent (lifespan of which covers the call to the
1268 child), the parent and the child should have different
1269 scratchpads. (I<And> the lexicals should be separate anyway!)
1271 So each subroutine is born with an array of scratchpads (of length 1).
1272 On each entry to the subroutine it is checked that the current
1273 depth of the recursion is not more than the length of this array, and
1274 if it is, new scratchpad is created and pushed into the array.
1276 The I<target>s on this scratchpad are C<undef>s, but they are already
1277 marked with correct flags.
1279 =head1 Compiled code
1283 Here we describe the internal form your code is converted to by
1284 Perl. Start with a simple example:
1288 This is converted to a tree similar to this one:
1296 (but slightly more complicated). This tree reflect the way Perl
1297 parsed your code, but has nothing to do with the execution order.
1298 There is an additional "thread" going through the nodes of the tree
1299 which shows the order of execution of the nodes. In our simplified
1300 example above it looks like:
1302 $b ---> $c ---> + ---> $a ---> assign-to
1304 But with the actual compile tree for C<$a = $b + $c> it is different:
1305 some nodes I<optimized away>. As a corollary, though the actual tree
1306 contains more nodes than our simplified example, the execution order
1307 is the same as in our example.
1309 =head2 Examining the tree
1311 If you have your perl compiled for debugging (usually done with C<-D
1312 optimize=-g> on C<Configure> command line), you may examine the
1313 compiled tree by specifying C<-Dx> on the Perl command line. The
1314 output takes several lines per node, and for C<$b+$c> it looks like
1319 FLAGS = (SCALAR,KIDS)
1321 TYPE = null ===> (4)
1323 FLAGS = (SCALAR,KIDS)
1325 3 TYPE = gvsv ===> 4
1331 TYPE = null ===> (5)
1333 FLAGS = (SCALAR,KIDS)
1335 4 TYPE = gvsv ===> 5
1341 This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1342 not optimized away (one per number in the left column). The immediate
1343 children of the given node correspond to C<{}> pairs on the same level
1344 of indentation, thus this listing corresponds to the tree:
1352 The execution order is indicated by C<===E<gt>> marks, thus it is C<3
1353 4 5 6> (node C<6> is not included into above listing), i.e.,
1354 C<gvsv gvsv add whatever>.
1356 =head2 Compile pass 1: check routines
1358 The tree is created by the I<pseudo-compiler> while yacc code feeds it
1359 the constructions it recognizes. Since yacc works bottom-up, so does
1360 the first pass of perl compilation.
1362 What makes this pass interesting for perl developers is that some
1363 optimization may be performed on this pass. This is optimization by
1364 so-called I<check routines>. The correspondence between node names
1365 and corresponding check routines is described in F<opcode.pl> (do not
1366 forget to run C<make regen_headers> if you modify this file).
1368 A check routine is called when the node is fully constructed except
1369 for the execution-order thread. Since at this time there is no
1370 back-links to the currently constructed node, one can do most any
1371 operation to the top-level node, including freeing it and/or creating
1372 new nodes above/below it.
1374 The check routine returns the node which should be inserted into the
1375 tree (if the top-level node was not modified, check routine returns
1378 By convention, check routines have names C<ck_*>. They are usually
1379 called from C<new*OP> subroutines (or C<convert>) (which in turn are
1380 called from F<perly.y>).
1382 =head2 Compile pass 1a: constant folding
1384 Immediately after the check routine is called the returned node is
1385 checked for being compile-time executable. If it is (the value is
1386 judged to be constant) it is immediately executed, and a I<constant>
1387 node with the "return value" of the corresponding subtree is
1388 substituted instead. The subtree is deleted.
1390 If constant folding was not performed, the execution-order thread is
1393 =head2 Compile pass 2: context propagation
1395 When a context for a part of compile tree is known, it is propagated
1396 down through the tree. Aat this time the context can have 5 values
1397 (instead of 2 for runtime context): void, boolean, scalar, list, and
1398 lvalue. In contrast with the pass 1 this pass is processed from top
1399 to bottom: a node's context determines the context for its children.
1401 Additional context-dependent optimizations are performed at this time.
1402 Since at this moment the compile tree contains back-references (via
1403 "thread" pointers), nodes cannot be free()d now. To allow
1404 optimized-away nodes at this stage, such nodes are null()ified instead
1405 of free()ing (i.e. their type is changed to OP_NULL).
1407 =head2 Compile pass 3: peephole optimization
1409 After the compile tree for a subroutine (or for an C<eval> or a file)
1410 is created, an additional pass over the code is performed. This pass
1411 is neither top-down or bottom-up, but in the execution order (with
1412 additional compilications for conditionals). These optimizations are
1413 done in the subroutine peep(). Optimizations performed at this stage
1414 are subject to the same restrictions as in the pass 2.
1418 This is a listing of functions, macros, flags, and variables that may be
1419 useful to extension writers or that may be found while reading other
1421 The sort order of the listing is case insensitive, with any
1422 occurrences of '_' ignored for the the purpose of sorting.
1428 Clears an array, making it empty. Does not free the memory used by the
1431 void av_clear (AV* ar)
1435 Pre-extend an array. The C<key> is the index to which the array should be
1438 void av_extend (AV* ar, I32 key)
1442 Returns the SV at the specified index in the array. The C<key> is the
1443 index. If C<lval> is set then the fetch will be part of a store. Check
1444 that the return value is non-null before dereferencing it to a C<SV*>.
1446 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1447 information on how to use this function on tied arrays.
1449 SV** av_fetch (AV* ar, I32 key, I32 lval)
1457 Returns the highest index in the array. Returns -1 if the array is empty.
1463 Creates a new AV and populates it with a list of SVs. The SVs are copied
1464 into the array, so they may be freed after the call to av_make. The new AV
1465 will have a reference count of 1.
1467 AV* av_make (I32 size, SV** svp)
1471 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1478 Pushes an SV onto the end of the array. The array will grow automatically
1479 to accommodate the addition.
1481 void av_push (AV* ar, SV* val)
1485 Shifts an SV off the beginning of the array.
1487 SV* av_shift (AV* ar)
1491 Stores an SV in an array. The array index is specified as C<key>. The
1492 return value will be NULL if the operation failed or if the value did not
1493 need to be actually stored within the array (as in the case of tied arrays).
1494 Otherwise it can be dereferenced to get the original C<SV*>. Note that the
1495 caller is responsible for suitably incrementing the reference count of C<val>
1496 before the call, and decrementing it if the function returned NULL.
1498 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1499 information on how to use this function on tied arrays.
1501 SV** av_store (AV* ar, I32 key, SV* val)
1505 Undefines the array. Frees the memory used by the array itself.
1507 void av_undef (AV* ar)
1511 Unshift the given number of C<undef> values onto the beginning of the
1512 array. The array will grow automatically to accommodate the addition.
1513 You must then use C<av_store> to assign values to these new elements.
1515 void av_unshift (AV* ar, I32 num)
1519 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1520 constructor. This is always a C<char*>. See C<THIS> and
1521 L<perlxs/"Using XS With C++">.
1525 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1526 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1527 the type. May fail on overlapping copies. See also C<Move>.
1529 void Copy( s, d, n, t )
1533 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1534 function the same way you use the C C<printf> function. See C<warn>.
1538 Returns the stash of the CV.
1540 HV* CvSTASH( SV* sv )
1544 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1545 boolean which indicates whether subs are being single-stepped.
1546 Single-stepping is automatically turned on after every step. This is the C
1547 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1551 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1552 the SV which holds the name of the sub being debugged. This is the C
1553 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1554 The sub name can be found by
1556 SvPV( GvSV( DBsub ), na )
1560 Trace variable used when Perl is run in debugging mode, with the B<-d>
1561 switch. This is the C variable which corresponds to Perl's $DB::trace
1562 variable. See C<DBsingle>.
1566 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1571 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1575 The C variable which corresponds to Perl's $^W warning variable.
1579 Declares a local copy of perl's stack pointer for the XSUB, available via
1580 the C<SP> macro. See C<SP>.
1584 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1585 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1586 to indicate the number of items on the stack.
1590 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1591 handled automatically by C<xsubpp>.
1595 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1601 Used to extend the argument stack for an XSUB's return values.
1607 Analyses the string in order to make fast searches on it using fbm_instr() --
1608 the Boyer-Moore algorithm.
1610 void fbm_compile(SV* sv)
1614 Returns the location of the SV in the string delimited by C<str> and
1615 C<strend>. It returns C<Nullch> if the string can't be found. The
1616 C<sv> does not have to be fbm_compiled, but the search will not be as
1619 char* fbm_instr(char *str, char *strend, SV *sv)
1623 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1630 Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
1634 Indicates that arguments returned from a callback should be discarded. See
1639 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1643 A backward-compatible version of C<GIMME_V> which can only return
1644 C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
1648 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
1649 C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
1650 context, respectively.
1654 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1658 Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
1662 Returns the glob with the given C<name> and a defined subroutine or
1663 C<NULL>. The glob lives in the given C<stash>, or in the stashes
1664 accessable via @ISA and @<UNIVERSAL>.
1666 The argument C<level> should be either 0 or -1. If C<level==0>, as a
1667 side-effect creates a glob with the given C<name> in the given
1668 C<stash> which in the case of success contains an alias for the
1669 subroutine, and sets up caching info for this glob. Similarly for all
1670 the searched stashes.
1672 This function grants C<"SUPER"> token as a postfix of the stash name.
1674 The GV returned from C<gv_fetchmeth> may be a method cache entry,
1675 which is not visible to Perl code. So when calling C<perl_call_sv>,
1676 you should not use the GV directly; instead, you should use the
1677 method's CV, which can be obtained from the GV with the C<GvCV> macro.
1679 GV* gv_fetchmeth (HV* stash, char* name, STRLEN len, I32 level)
1681 =item gv_fetchmethod
1683 =item gv_fetchmethod_autoload
1685 Returns the glob which contains the subroutine to call to invoke the
1686 method on the C<stash>. In fact in the presense of autoloading this may
1687 be the glob for "AUTOLOAD". In this case the corresponding variable
1688 $AUTOLOAD is already setup.
1690 The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
1691 lookup is performed if the given method is not present: non-zero means
1692 yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
1693 C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
1694 non-zero C<autoload> parameter.
1696 These functions grant C<"SUPER"> token as a prefix of the method name.
1698 Note that if you want to keep the returned glob for a long time, you
1699 need to check for it being "AUTOLOAD", since at the later time the call
1700 may load a different subroutine due to $AUTOLOAD changing its value.
1701 Use the glob created via a side effect to do this.
1703 These functions have the same side-effects and as C<gv_fetchmeth> with
1704 C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
1705 The warning against passing the GV returned by C<gv_fetchmeth> to
1706 C<perl_call_sv> apply equally to these functions.
1708 GV* gv_fetchmethod (HV* stash, char* name)
1709 GV* gv_fetchmethod_autoload (HV* stash, char* name, I32 autoload)
1713 Used to indicate void context. See C<GIMME_V> and L<perlcall>.
1717 Returns a pointer to the stash for a specified package. If C<create> is set
1718 then the package will be created if it does not already exist. If C<create>
1719 is not set and the package does not exist then NULL is returned.
1721 HV* gv_stashpv (char* name, I32 create)
1725 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1727 HV* gv_stashsv (SV* sv, I32 create)
1731 Return the SV from the GV.
1735 This flag, used in the length slot of hash entries and magic
1736 structures, specifies the structure contains a C<SV*> pointer where a
1737 C<char*> pointer is to be expected. (For information only--not to be used).
1741 Returns the computed hash stored in the hash entry.
1747 Returns the actual pointer stored in the key slot of the hash entry.
1748 The pointer may be either C<char*> or C<SV*>, depending on the value of
1749 C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
1750 are usually preferable for finding the value of a key.
1756 If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
1757 holds an C<SV*> key. Otherwise, holds the actual length of the key.
1758 Can be assigned to. The C<HePV()> macro is usually preferable for finding
1765 Returns the key slot of the hash entry as a C<char*> value, doing any
1766 necessary dereferencing of possibly C<SV*> keys. The length of
1767 the string is placed in C<len> (this is a macro, so do I<not> use
1768 C<&len>). If you do not care about what the length of the key is,
1769 you may use the global variable C<na>. Remember though, that hash
1770 keys in perl are free to contain embedded nulls, so using C<strlen()>
1771 or similar is not a good way to find the length of hash keys.
1772 This is very similar to the C<SvPV()> macro described elsewhere in
1775 char* HePV(HE* he, STRLEN len)
1779 Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
1780 does not contain an C<SV*> key.
1786 Returns the key as an C<SV*>. Will create and return a temporary
1787 mortal C<SV*> if the hash entry contains only a C<char*> key.
1789 HeSVKEY_force(HE* he)
1793 Sets the key to a given C<SV*>, taking care to set the appropriate flags
1794 to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
1796 HeSVKEY_set(HE* he, SV* sv)
1800 Returns the value slot (type C<SV*>) stored in the hash entry.
1806 Clears a hash, making it empty.
1808 void hv_clear (HV* tb)
1810 =item hv_delayfree_ent
1812 Releases a hash entry, such as while iterating though the hash, but
1813 delays actual freeing of key and value until the end of the current
1814 statement (or thereabouts) with C<sv_2mortal>. See C<hv_iternext>
1817 void hv_delayfree_ent (HV* hv, HE* entry)
1821 Deletes a key/value pair in the hash. The value SV is removed from the hash
1822 and returned to the caller. The C<klen> is the length of the key. The
1823 C<flags> value will normally be zero; if set to G_DISCARD then NULL will be
1826 SV* hv_delete (HV* tb, char* key, U32 klen, I32 flags)
1830 Deletes a key/value pair in the hash. The value SV is removed from the hash
1831 and returned to the caller. The C<flags> value will normally be zero; if set
1832 to G_DISCARD then NULL will be returned. C<hash> can be a valid precomputed
1833 hash value, or 0 to ask for it to be computed.
1835 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash)
1839 Returns a boolean indicating whether the specified hash key exists. The
1840 C<klen> is the length of the key.
1842 bool hv_exists (HV* tb, char* key, U32 klen)
1846 Returns a boolean indicating whether the specified hash key exists. C<hash>
1847 can be a valid precomputed hash value, or 0 to ask for it to be computed.
1849 bool hv_exists_ent (HV* tb, SV* key, U32 hash)
1853 Returns the SV which corresponds to the specified key in the hash. The
1854 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1855 part of a store. Check that the return value is non-null before
1856 dereferencing it to a C<SV*>.
1858 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1859 information on how to use this function on tied hashes.
1861 SV** hv_fetch (HV* tb, char* key, U32 klen, I32 lval)
1865 Returns the hash entry which corresponds to the specified key in the hash.
1866 C<hash> must be a valid precomputed hash number for the given C<key>, or
1867 0 if you want the function to compute it. IF C<lval> is set then the
1868 fetch will be part of a store. Make sure the return value is non-null
1869 before accessing it. The return value when C<tb> is a tied hash
1870 is a pointer to a static location, so be sure to make a copy of the
1871 structure if you need to store it somewhere.
1873 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1874 information on how to use this function on tied hashes.
1876 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash)
1880 Releases a hash entry, such as while iterating though the hash. See
1881 C<hv_iternext> and C<hv_delayfree_ent>.
1883 void hv_free_ent (HV* hv, HE* entry)
1887 Prepares a starting point to traverse a hash table.
1889 I32 hv_iterinit (HV* tb)
1891 Returns the number of keys in the hash (i.e. the same as C<HvKEYS(tb)>).
1892 The return value is currently only meaningful for hashes without tie
1895 NOTE: Before version 5.004_65, C<hv_iterinit> used to return the number
1896 of hash buckets that happen to be in use. If you still need that
1897 esoteric value, you can get it through the macro C<HvFILL(tb)>.
1901 Returns the key from the current position of the hash iterator. See
1904 char* hv_iterkey (HE* entry, I32* retlen)
1908 Returns the key as an C<SV*> from the current position of the hash
1909 iterator. The return value will always be a mortal copy of the
1910 key. Also see C<hv_iterinit>.
1912 SV* hv_iterkeysv (HE* entry)
1916 Returns entries from a hash iterator. See C<hv_iterinit>.
1918 HE* hv_iternext (HV* tb)
1922 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1925 SV* hv_iternextsv (HV* hv, char** key, I32* retlen)
1929 Returns the value from the current position of the hash iterator. See
1932 SV* hv_iterval (HV* tb, HE* entry)
1936 Adds magic to a hash. See C<sv_magic>.
1938 void hv_magic (HV* hv, GV* gv, int how)
1942 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1944 char* HvNAME (HV* stash)
1948 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1949 the length of the key. The C<hash> parameter is the precomputed hash
1950 value; if it is zero then Perl will compute it. The return value will be
1951 NULL if the operation failed or if the value did not need to be actually
1952 stored within the hash (as in the case of tied hashes). Otherwise it can
1953 be dereferenced to get the original C<SV*>. Note that the caller is
1954 responsible for suitably incrementing the reference count of C<val>
1955 before the call, and decrementing it if the function returned NULL.
1957 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1958 information on how to use this function on tied hashes.
1960 SV** hv_store (HV* tb, char* key, U32 klen, SV* val, U32 hash)
1964 Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
1965 parameter is the precomputed hash value; if it is zero then Perl will
1966 compute it. The return value is the new hash entry so created. It will be
1967 NULL if the operation failed or if the value did not need to be actually
1968 stored within the hash (as in the case of tied hashes). Otherwise the
1969 contents of the return value can be accessed using the C<He???> macros
1970 described here. Note that the caller is responsible for suitably
1971 incrementing the reference count of C<val> before the call, and decrementing
1972 it if the function returned NULL.
1974 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1975 information on how to use this function on tied hashes.
1977 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash)
1983 void hv_undef (HV* tb)
1987 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
1990 int isALNUM (char c)
1994 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
1997 int isALPHA (char c)
2001 Returns a boolean indicating whether the C C<char> is an ascii digit.
2003 int isDIGIT (char c)
2007 Returns a boolean indicating whether the C C<char> is a lowercase character.
2009 int isLOWER (char c)
2013 Returns a boolean indicating whether the C C<char> is whitespace.
2015 int isSPACE (char c)
2019 Returns a boolean indicating whether the C C<char> is an uppercase character.
2021 int isUPPER (char c)
2025 Variable which is setup by C<xsubpp> to indicate the number of items on the
2026 stack. See L<perlxs/"Variable-length Parameter Lists">.
2030 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
2031 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
2035 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
2039 =item looks_like_number
2041 Test if an the content of an SV looks like a number (or is a number).
2043 int looks_like_number(SV*)
2048 Stack marker variable for the XSUB. See C<dMARK>.
2052 Clear something magical that the SV represents. See C<sv_magic>.
2054 int mg_clear (SV* sv)
2058 Copies the magic from one SV to another. See C<sv_magic>.
2060 int mg_copy (SV *, SV *, char *, STRLEN)
2064 Finds the magic pointer for type matching the SV. See C<sv_magic>.
2066 MAGIC* mg_find (SV* sv, int type)
2070 Free any magic storage used by the SV. See C<sv_magic>.
2072 int mg_free (SV* sv)
2076 Do magic after a value is retrieved from the SV. See C<sv_magic>.
2082 Report on the SV's length. See C<sv_magic>.
2088 Turns on the magical status of an SV. See C<sv_magic>.
2090 void mg_magical (SV* sv)
2094 Do magic after a value is assigned to the SV. See C<sv_magic>.
2100 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
2101 source, C<d> is the destination, C<n> is the number of items, and C<t> is
2102 the type. Can do overlapping moves. See also C<Copy>.
2104 void Move( s, d, n, t )
2108 A variable which may be used with C<SvPV> to tell Perl to calculate the
2113 The XSUB-writer's interface to the C C<malloc> function.
2115 void* New( x, void *ptr, int size, type )
2119 Creates a new AV. The reference count is set to 1.
2125 The XSUB-writer's interface to the C C<malloc> function, with cast.
2127 void* Newc( x, void *ptr, int size, type, cast )
2131 Creates a constant sub equivalent to Perl C<sub FOO () { 123 }>
2132 which is eligible for inlining at compile-time.
2134 void newCONSTSUB(HV* stash, char* name, SV* sv)
2138 Creates a new HV. The reference count is set to 1.
2144 Creates an RV wrapper for an SV. The reference count for the original SV is
2147 SV* newRV_inc (SV* ref)
2149 For historical reasons, "newRV" is a synonym for "newRV_inc".
2153 Creates an RV wrapper for an SV. The reference count for the original
2154 SV is B<not> incremented.
2156 SV* newRV_noinc (SV* ref)
2160 Creates a new SV. A non-zero C<len> parameter indicates the number of
2161 bytes of preallocated string space the SV should have. An extra byte
2162 for a tailing NUL is also reserved. (SvPOK is not set for the SV even
2163 if string space is allocated.) The reference count for the new SV is
2164 set to 1. C<id> is an integer id between 0 and 1299 (used to identify
2167 SV* NEWSV (int id, STRLEN len)
2171 Creates a new SV and copies an integer into it. The reference count for the
2178 Creates a new SV and copies a double into it. The reference count for the
2185 Creates a new SV and copies a string into it. The reference count for the
2186 SV is set to 1. If C<len> is zero then Perl will compute the length.
2188 SV* newSVpv (char* s, STRLEN len)
2192 Creates a new SV an initialize it with the string formatted like
2195 SV* newSVpvf(const char* pat, ...);
2199 Creates a new SV and copies a string into it. The reference count for the
2200 SV is set to 1. If C<len> is zero then Perl will create a zero length
2203 SV* newSVpvn (char* s, STRLEN len)
2207 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
2208 it will be upgraded to one. If C<classname> is non-null then the new SV will
2209 be blessed in the specified package. The new SV is returned and its
2210 reference count is 1.
2212 SV* newSVrv (SV* rv, char* classname)
2216 Creates a new SV which is an exact duplicate of the original SV.
2218 SV* newSVsv (SV* old)
2222 Used by C<xsubpp> to hook up XSUBs as Perl subs.
2226 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
2231 The XSUB-writer's interface to the C C<malloc> function. The allocated
2232 memory is zeroed with C<memzero>.
2234 void* Newz( x, void *ptr, int size, type )
2242 Null character pointer.
2258 The original stack mark for the XSUB. See C<dORIGMARK>.
2262 Allocates a new Perl interpreter. See L<perlembed>.
2264 =item perl_call_argv
2266 Performs a callback to the specified Perl sub. See L<perlcall>.
2268 I32 perl_call_argv (char* subname, I32 flags, char** argv)
2270 =item perl_call_method
2272 Performs a callback to the specified Perl method. The blessed object must
2273 be on the stack. See L<perlcall>.
2275 I32 perl_call_method (char* methname, I32 flags)
2279 Performs a callback to the specified Perl sub. See L<perlcall>.
2281 I32 perl_call_pv (char* subname, I32 flags)
2285 Performs a callback to the Perl sub whose name is in the SV. See
2288 I32 perl_call_sv (SV* sv, I32 flags)
2290 =item perl_construct
2292 Initializes a new Perl interpreter. See L<perlembed>.
2296 Shuts down a Perl interpreter. See L<perlembed>.
2300 Tells Perl to C<eval> the string in the SV.
2302 I32 perl_eval_sv (SV* sv, I32 flags)
2306 Tells Perl to C<eval> the given string and return an SV* result.
2308 SV* perl_eval_pv (char* p, I32 croak_on_error)
2312 Releases a Perl interpreter. See L<perlembed>.
2316 Returns the AV of the specified Perl array. If C<create> is set and the
2317 Perl variable does not exist then it will be created. If C<create> is not
2318 set and the variable does not exist then NULL is returned.
2320 AV* perl_get_av (char* name, I32 create)
2324 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
2325 variable does not exist then it will be created. If C<create> is not
2326 set and the variable does not exist then NULL is returned.
2328 CV* perl_get_cv (char* name, I32 create)
2332 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
2333 variable does not exist then it will be created. If C<create> is not
2334 set and the variable does not exist then NULL is returned.
2336 HV* perl_get_hv (char* name, I32 create)
2340 Returns the SV of the specified Perl scalar. If C<create> is set and the
2341 Perl variable does not exist then it will be created. If C<create> is not
2342 set and the variable does not exist then NULL is returned.
2344 SV* perl_get_sv (char* name, I32 create)
2348 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
2350 =item perl_require_pv
2352 Tells Perl to C<require> a module.
2354 void perl_require_pv (char* pv)
2358 Tells a Perl interpreter to run. See L<perlembed>.
2362 Pops an integer off the stack.
2368 Pops a long off the stack.
2374 Pops a string off the stack.
2380 Pops a double off the stack.
2386 Pops an SV off the stack.
2392 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2398 Push an integer onto the stack. The stack must have room for this element.
2399 Handles 'set' magic. See C<XPUSHi>.
2405 Push a double onto the stack. The stack must have room for this element.
2406 Handles 'set' magic. See C<XPUSHn>.
2408 void PUSHn(double d)
2412 Push a string onto the stack. The stack must have room for this element.
2413 The C<len> indicates the length of the string. Handles 'set' magic. See
2416 void PUSHp(char *c, int len )
2420 Push an SV onto the stack. The stack must have room for this element. Does
2421 not handle 'set' magic. See C<XPUSHs>.
2427 Push an unsigned integer onto the stack. The stack must have room for
2428 this element. See C<XPUSHu>.
2430 void PUSHu(unsigned int d)
2435 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2436 See C<PUSHMARK> and L<perlcall> for other uses.
2442 The XSUB-writer's interface to the C C<realloc> function.
2444 void* Renew( void *ptr, int size, type )
2448 The XSUB-writer's interface to the C C<realloc> function, with cast.
2450 void* Renewc( void *ptr, int size, type, cast )
2454 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
2455 This is always the proper type for the XSUB.
2456 See L<perlxs/"The RETVAL Variable">.
2460 The XSUB-writer's interface to the C C<free> function.
2464 The XSUB-writer's interface to the C C<malloc> function.
2468 The XSUB-writer's interface to the C C<realloc> function.
2472 Copy a string to a safe spot. This does not use an SV.
2474 char* savepv (char* sv)
2478 Copy a string to a safe spot. The C<len> indicates number of bytes to
2479 copy. This does not use an SV.
2481 char* savepvn (char* sv, I32 len)
2485 Opening bracket for temporaries on a callback. See C<FREETMPS> and
2492 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2497 Refetch the stack pointer. Used after a callback. See L<perlcall>.
2503 Used to access elements on the XSUB's stack.
2509 Test two strings to see if they are equal. Returns true or false.
2511 int strEQ( char *s1, char *s2 )
2515 Test two strings to see if the first, C<s1>, is greater than or equal to the
2516 second, C<s2>. Returns true or false.
2518 int strGE( char *s1, char *s2 )
2522 Test two strings to see if the first, C<s1>, is greater than the second,
2523 C<s2>. Returns true or false.
2525 int strGT( char *s1, char *s2 )
2529 Test two strings to see if the first, C<s1>, is less than or equal to the
2530 second, C<s2>. Returns true or false.
2532 int strLE( char *s1, char *s2 )
2536 Test two strings to see if the first, C<s1>, is less than the second,
2537 C<s2>. Returns true or false.
2539 int strLT( char *s1, char *s2 )
2543 Test two strings to see if they are different. Returns true or false.
2545 int strNE( char *s1, char *s2 )
2549 Test two strings to see if they are equal. The C<len> parameter indicates
2550 the number of bytes to compare. Returns true or false.
2552 int strnEQ( char *s1, char *s2 )
2556 Test two strings to see if they are different. The C<len> parameter
2557 indicates the number of bytes to compare. Returns true or false.
2559 int strnNE( char *s1, char *s2, int len )
2563 Marks an SV as mortal. The SV will be destroyed when the current context
2566 SV* sv_2mortal (SV* sv)
2570 Blesses an SV into a specified package. The SV must be an RV. The package
2571 must be designated by its stash (see C<gv_stashpv()>). The reference count
2572 of the SV is unaffected.
2574 SV* sv_bless (SV* sv, HV* stash)
2578 Concatenates the string onto the end of the string which is in the SV.
2579 Handles 'get' magic, but not 'set' magic. See C<sv_catpv_mg>.
2581 void sv_catpv (SV* sv, char* ptr)
2585 Like C<sv_catpv>, but also handles 'set' magic.
2587 void sv_catpvn (SV* sv, char* ptr)
2591 Concatenates the string onto the end of the string which is in the SV. The
2592 C<len> indicates number of bytes to copy. Handles 'get' magic, but not
2593 'set' magic. See C<sv_catpvn_mg>.
2595 void sv_catpvn (SV* sv, char* ptr, STRLEN len)
2599 Like C<sv_catpvn>, but also handles 'set' magic.
2601 void sv_catpvn_mg (SV* sv, char* ptr, STRLEN len)
2605 Processes its arguments like C<sprintf> and appends the formatted output
2606 to an SV. Handles 'get' magic, but not 'set' magic. C<SvSETMAGIC()> must
2607 typically be called after calling this function to handle 'set' magic.
2609 void sv_catpvf (SV* sv, const char* pat, ...)
2613 Like C<sv_catpvf>, but also handles 'set' magic.
2615 void sv_catpvf_mg (SV* sv, const char* pat, ...)
2619 Concatenates the string from SV C<ssv> onto the end of the string in SV
2620 C<dsv>. Handles 'get' magic, but not 'set' magic. See C<sv_catsv_mg>.
2622 void sv_catsv (SV* dsv, SV* ssv)
2626 Like C<sv_catsv>, but also handles 'set' magic.
2628 void sv_catsv_mg (SV* dsv, SV* ssv)
2632 Efficient removal of characters from the beginning of the string
2633 buffer. SvPOK(sv) must be true and the C<ptr> must be a pointer to
2634 somewhere inside the string buffer. The C<ptr> becomes the first
2635 character of the adjusted string.
2637 void sv_chop(SV* sv, char *ptr)
2642 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2643 string in C<sv1> is less than, equal to, or greater than the string in
2646 I32 sv_cmp (SV* sv1, SV* sv2)
2650 Returns the length of the string which is in the SV. See C<SvLEN>.
2656 Set the length of the string which is in the SV. See C<SvCUR>.
2658 void SvCUR_set (SV* sv, int val )
2662 Auto-decrement of the value in the SV.
2664 void sv_dec (SV* sv)
2666 =item sv_derived_from
2668 Returns a boolean indicating whether the SV is a subclass of the
2671 int sv_derived_from(SV* sv, char* class)
2675 Returns a pointer to the last character in the string which is in the SV.
2676 See C<SvCUR>. Access the character as
2682 Returns a boolean indicating whether the strings in the two SVs are
2685 I32 sv_eq (SV* sv1, SV* sv2)
2689 Invokes C<mg_get> on an SV if it has 'get' magic. This macro evaluates
2690 its argument more than once.
2692 void SvGETMAGIC( SV *sv )
2696 Expands the character buffer in the SV so that it has room for the
2697 indicated number of bytes (remember to reserve space for an extra
2698 trailing NUL character). Calls C<sv_grow> to perform the expansion if
2699 necessary. Returns a pointer to the character buffer.
2701 char* SvGROW( SV* sv, int len )
2705 Expands the character buffer in the SV. This will use C<sv_unref> and will
2706 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2711 Auto-increment of the value in the SV.
2713 void sv_inc (SV* sv)
2717 Inserts a string at the specified offset/length within the SV.
2718 Similar to the Perl substr() function.
2720 void sv_insert(SV *sv, STRLEN offset, STRLEN len,
2721 char *str, STRLEN strlen)
2725 Returns a boolean indicating whether the SV contains an integer.
2731 Unsets the IV status of an SV.
2733 void SvIOK_off (SV* sv)
2737 Tells an SV that it is an integer.
2739 void SvIOK_on (SV* sv)
2743 Tells an SV that it is an integer and disables all other OK bits.
2745 void SvIOK_only (SV* sv)
2749 Returns a boolean indicating whether the SV contains an integer. Checks the
2750 B<private> setting. Use C<SvIOK>.
2756 Returns a boolean indicating whether the SV is blessed into the specified
2757 class. This does not know how to check for subtype, so it doesn't work in
2758 an inheritance relationship.
2760 int sv_isa (SV* sv, char* name)
2764 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2765 object. If the SV is not an RV, or if the object is not blessed, then this
2768 int sv_isobject (SV* sv)
2772 Returns the integer which is in the SV.
2778 Returns the integer which is stored in the SV.
2784 Returns the size of the string buffer in the SV. See C<SvCUR>.
2790 Returns the length of the string in the SV. Use C<SvCUR>.
2792 STRLEN sv_len (SV* sv)
2796 Adds magic to an SV.
2798 void sv_magic (SV* sv, SV* obj, int how, char* name, I32 namlen)
2802 Creates a new SV which is a copy of the original SV. The new SV is marked
2805 SV* sv_mortalcopy (SV* oldsv)
2809 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2811 SV* sv_newmortal (void)
2815 Returns a boolean indicating whether the SV contains a number, integer or
2822 Unsets the NV/IV status of an SV.
2824 void SvNIOK_off (SV* sv)
2828 Returns a boolean indicating whether the SV contains a number, integer or
2829 double. Checks the B<private> setting. Use C<SvNIOK>.
2831 int SvNIOKp (SV* SV)
2835 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2839 Returns a boolean indicating whether the SV contains a double.
2845 Unsets the NV status of an SV.
2847 void SvNOK_off (SV* sv)
2851 Tells an SV that it is a double.
2853 void SvNOK_on (SV* sv)
2857 Tells an SV that it is a double and disables all other OK bits.
2859 void SvNOK_only (SV* sv)
2863 Returns a boolean indicating whether the SV contains a double. Checks the
2864 B<private> setting. Use C<SvNOK>.
2870 Returns the double which is stored in the SV.
2872 double SvNV (SV* sv)
2876 Returns the double which is stored in the SV.
2878 double SvNVX (SV* sv)
2882 Returns a boolean indicating whether the value is an SV.
2888 Returns a boolean indicating whether the SvIVX is a valid offset value
2889 for the SvPVX. This hack is used internally to speed up removal of
2890 characters from the beginning of a SvPV. When SvOOK is true, then the
2891 start of the allocated string buffer is really (SvPVX - SvIVX).
2897 Returns a boolean indicating whether the SV contains a character string.
2903 Unsets the PV status of an SV.
2905 void SvPOK_off (SV* sv)
2909 Tells an SV that it is a string.
2911 void SvPOK_on (SV* sv)
2915 Tells an SV that it is a string and disables all other OK bits.
2917 void SvPOK_only (SV* sv)
2921 Returns a boolean indicating whether the SV contains a character string.
2922 Checks the B<private> setting. Use C<SvPOK>.
2928 Returns a pointer to the string in the SV, or a stringified form of the SV
2929 if the SV does not contain a string. If C<len> is C<na> then Perl will
2930 handle the length on its own. Handles 'get' magic.
2932 char* SvPV (SV* sv, int len )
2936 Like <SvPV> but will force the SV into becoming a string (SvPOK). You
2937 want force if you are going to update the SvPVX directly.
2939 char* SvPV_force(SV* sv, int len)
2944 Returns a pointer to the string in the SV. The SV must contain a string.
2946 char* SvPVX (SV* sv)
2950 Returns the value of the object's reference count.
2952 int SvREFCNT (SV* sv)
2956 Decrements the reference count of the given SV.
2958 void SvREFCNT_dec (SV* sv)
2962 Increments the reference count of the given SV.
2964 void SvREFCNT_inc (SV* sv)
2968 Tests if the SV is an RV.
2974 Unsets the RV status of an SV.
2976 void SvROK_off (SV* sv)
2980 Tells an SV that it is an RV.
2982 void SvROK_on (SV* sv)
2986 Dereferences an RV to return the SV.
2992 Invokes C<mg_set> on an SV if it has 'set' magic. This macro evaluates
2993 its argument more than once.
2995 void SvSETMAGIC( SV *sv )
2999 Copies an integer into the given SV. Does not handle 'set' magic.
3002 void sv_setiv (SV* sv, IV num)
3006 Like C<sv_setiv>, but also handles 'set' magic.
3008 void sv_setiv_mg (SV* sv, IV num)
3012 Copies a double into the given SV. Does not handle 'set' magic.
3015 void sv_setnv (SV* sv, double num)
3019 Like C<sv_setnv>, but also handles 'set' magic.
3021 void sv_setnv_mg (SV* sv, double num)
3025 Copies a string into an SV. The string must be null-terminated.
3026 Does not handle 'set' magic. See C<sv_setpv_mg>.
3028 void sv_setpv (SV* sv, char* ptr)
3032 Like C<sv_setpv>, but also handles 'set' magic.
3034 void sv_setpv_mg (SV* sv, char* ptr)
3038 Copies an integer into the given SV, also updating its string value.
3039 Does not handle 'set' magic. See C<sv_setpviv_mg>.
3041 void sv_setpviv (SV* sv, IV num)
3045 Like C<sv_setpviv>, but also handles 'set' magic.
3047 void sv_setpviv_mg (SV* sv, IV num)
3051 Copies a string into an SV. The C<len> parameter indicates the number of
3052 bytes to be copied. Does not handle 'set' magic. See C<sv_setpvn_mg>.
3054 void sv_setpvn (SV* sv, char* ptr, STRLEN len)
3058 Like C<sv_setpvn>, but also handles 'set' magic.
3060 void sv_setpvn_mg (SV* sv, char* ptr, STRLEN len)
3064 Processes its arguments like C<sprintf> and sets an SV to the formatted
3065 output. Does not handle 'set' magic. See C<sv_setpvf_mg>.
3067 void sv_setpvf (SV* sv, const char* pat, ...)
3071 Like C<sv_setpvf>, but also handles 'set' magic.
3073 void sv_setpvf_mg (SV* sv, const char* pat, ...)
3077 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
3078 argument will be upgraded to an RV. That RV will be modified to point to
3079 the new SV. The C<classname> argument indicates the package for the
3080 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3081 will be returned and will have a reference count of 1.
3083 SV* sv_setref_iv (SV *rv, char *classname, IV iv)
3087 Copies a double into a new SV, optionally blessing the SV. The C<rv>
3088 argument will be upgraded to an RV. That RV will be modified to point to
3089 the new SV. The C<classname> argument indicates the package for the
3090 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3091 will be returned and will have a reference count of 1.
3093 SV* sv_setref_nv (SV *rv, char *classname, double nv)
3097 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
3098 argument will be upgraded to an RV. That RV will be modified to point to
3099 the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
3100 into the SV. The C<classname> argument indicates the package for the
3101 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3102 will be returned and will have a reference count of 1.
3104 SV* sv_setref_pv (SV *rv, char *classname, void* pv)
3106 Do not use with integral Perl types such as HV, AV, SV, CV, because those
3107 objects will become corrupted by the pointer copy process.
3109 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
3113 Copies a string into a new SV, optionally blessing the SV. The length of the
3114 string must be specified with C<n>. The C<rv> argument will be upgraded to
3115 an RV. That RV will be modified to point to the new SV. The C<classname>
3116 argument indicates the package for the blessing. Set C<classname> to
3117 C<Nullch> to avoid the blessing. The new SV will be returned and will have
3118 a reference count of 1.
3120 SV* sv_setref_pvn (SV *rv, char *classname, char* pv, I32 n)
3122 Note that C<sv_setref_pv> copies the pointer while this copies the string.
3126 Calls C<sv_setsv> if dsv is not the same as ssv. May evaluate arguments
3129 void SvSetSV (SV* dsv, SV* ssv)
3131 =item SvSetSV_nosteal
3133 Calls a non-destructive version of C<sv_setsv> if dsv is not the same as ssv.
3134 May evaluate arguments more than once.
3136 void SvSetSV_nosteal (SV* dsv, SV* ssv)
3140 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
3141 The source SV may be destroyed if it is mortal. Does not handle 'set' magic.
3142 See the macro forms C<SvSetSV>, C<SvSetSV_nosteal> and C<sv_setsv_mg>.
3144 void sv_setsv (SV* dsv, SV* ssv)
3148 Like C<sv_setsv>, but also handles 'set' magic.
3150 void sv_setsv_mg (SV* dsv, SV* ssv)
3154 Copies an unsigned integer into the given SV. Does not handle 'set' magic.
3157 void sv_setuv (SV* sv, UV num)
3161 Like C<sv_setuv>, but also handles 'set' magic.
3163 void sv_setuv_mg (SV* sv, UV num)
3167 Returns the stash of the SV.
3169 HV* SvSTASH (SV* sv)
3173 Taints an SV if tainting is enabled
3175 void SvTAINT (SV* sv)
3179 Checks to see if an SV is tainted. Returns TRUE if it is, FALSE if not.
3181 int SvTAINTED (SV* sv)
3185 Untaints an SV. Be I<very> careful with this routine, as it short-circuits
3186 some of Perl's fundamental security features. XS module authors should
3187 not use this function unless they fully understand all the implications
3188 of unconditionally untainting the value. Untainting should be done in
3189 the standard perl fashion, via a carefully crafted regexp, rather than
3190 directly untainting variables.
3192 void SvTAINTED_off (SV* sv)
3196 Marks an SV as tainted.
3198 void SvTAINTED_on (SV* sv)
3202 Integer type flag for scalars. See C<svtype>.
3206 Pointer type flag for scalars. See C<svtype>.
3210 Type flag for arrays. See C<svtype>.
3214 Type flag for code refs. See C<svtype>.
3218 Type flag for hashes. See C<svtype>.
3222 Type flag for blessed scalars. See C<svtype>.
3226 Double type flag for scalars. See C<svtype>.
3230 Returns a boolean indicating whether Perl would evaluate the SV as true or
3231 false, defined or undefined. Does not handle 'get' magic.
3237 Returns the type of the SV. See C<svtype>.
3239 svtype SvTYPE (SV* sv)
3243 An enum of flags for Perl types. These are found in the file B<sv.h> in the
3244 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
3248 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
3252 Unsets the RV status of the SV, and decrements the reference count of
3253 whatever was being referenced by the RV. This can almost be thought of
3254 as a reversal of C<newSVrv>. See C<SvROK_off>.
3256 void sv_unref (SV* sv)
3260 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
3261 the upgrade if necessary. See C<svtype>.
3263 bool SvUPGRADE (SV* sv, svtype mt)
3267 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
3271 Tells an SV to use C<ptr> to find its string value. Normally the string is
3272 stored inside the SV but sv_usepvn allows the SV to use an outside string.
3273 The C<ptr> should point to memory that was allocated by C<malloc>. The
3274 string length, C<len>, must be supplied. This function will realloc the
3275 memory pointed to by C<ptr>, so that pointer should not be freed or used by
3276 the programmer after giving it to sv_usepvn. Does not handle 'set' magic.
3277 See C<sv_usepvn_mg>.
3279 void sv_usepvn (SV* sv, char* ptr, STRLEN len)
3283 Like C<sv_usepvn>, but also handles 'set' magic.
3285 void sv_usepvn_mg (SV* sv, char* ptr, STRLEN len)
3289 Returns the unsigned integer which is in the SV.
3295 Returns the unsigned integer which is stored in the SV.
3301 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
3305 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
3306 This is always the proper type for the C++ object. See C<CLASS> and
3307 L<perlxs/"Using XS With C++">.
3311 Converts the specified character to lowercase.
3313 int toLOWER (char c)
3317 Converts the specified character to uppercase.
3319 int toUPPER (char c)
3323 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
3324 function the same way you use the C C<printf> function. See C<croak()>.
3328 Push an integer onto the stack, extending the stack if necessary. Handles
3329 'set' magic. See C<PUSHi>.
3335 Push a double onto the stack, extending the stack if necessary. Handles 'set'
3336 magic. See C<PUSHn>.
3342 Push a string onto the stack, extending the stack if necessary. The C<len>
3343 indicates the length of the string. Handles 'set' magic. See C<PUSHp>.
3345 XPUSHp(char *c, int len)
3349 Push an SV onto the stack, extending the stack if necessary. Does not
3350 handle 'set' magic. See C<PUSHs>.
3356 Push an unsigned integer onto the stack, extending the stack if
3357 necessary. See C<PUSHu>.
3361 Macro to declare an XSUB and its C parameter list. This is handled by
3366 Return from XSUB, indicating number of items on the stack. This is usually
3367 handled by C<xsubpp>.
3371 =item XSRETURN_EMPTY
3373 Return an empty list from an XSUB immediately.
3379 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
3385 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
3391 Return an double from an XSUB immediately. Uses C<XST_mNV>.
3397 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
3399 XSRETURN_PV(char *v)
3401 =item XSRETURN_UNDEF
3403 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
3409 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
3415 Place an integer into the specified position C<i> on the stack. The value is
3416 stored in a new mortal SV.
3418 XST_mIV( int i, IV v )
3422 Place a double into the specified position C<i> on the stack. The value is
3423 stored in a new mortal SV.
3425 XST_mNV( int i, NV v )
3429 Place C<&sv_no> into the specified position C<i> on the stack.
3435 Place a copy of a string into the specified position C<i> on the stack. The
3436 value is stored in a new mortal SV.
3438 XST_mPV( int i, char *v )
3442 Place C<&sv_undef> into the specified position C<i> on the stack.
3448 Place C<&sv_yes> into the specified position C<i> on the stack.
3454 The version identifier for an XS module. This is usually handled
3455 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
3457 =item XS_VERSION_BOOTCHECK
3459 Macro to verify that a PM module's $VERSION variable matches the XS module's
3460 C<XS_VERSION> variable. This is usually handled automatically by
3461 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
3465 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
3466 destination, C<n> is the number of items, and C<t> is the type.
3468 void Zero( d, n, t )
3474 Until May 1997, this document was maintained by Jeff Okamoto
3475 <okamoto@corp.hp.com>. It is now maintained as part of Perl itself.
3477 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
3478 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
3479 Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
3480 Stephen McCamant, and Gurusamy Sarathy.
3482 API Listing originally by Dean Roehrich <roehrich@cray.com>.