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.
13 Perl has three typedefs that handle Perl's three main data types:
19 Each typedef has specific routines that manipulate the various data types.
21 =head2 What is an "IV"?
23 Perl uses a special typedef IV which is large enough to hold either an
26 Perl also uses two special typedefs, I32 and I16, which will always be at
27 least 32-bits and 16-bits long, respectively.
29 =head2 Working with SVs
31 An SV can be created and loaded with one command. There are four types of
32 values that can be loaded: an integer value (IV), a double (NV), a string,
33 (PV), and another scalar (SV).
35 The four routines are:
39 SV* newSVpv(char*, int);
42 To change the value of an *already-existing* SV, there are five routines:
44 void sv_setiv(SV*, IV);
45 void sv_setnv(SV*, double);
46 void sv_setpvn(SV*, char*, int)
47 void sv_setpv(SV*, char*);
48 void sv_setsv(SV*, SV*);
50 Notice that you can choose to specify the length of the string to be
51 assigned by using C<sv_setpvn> or C<newSVpv>, or you may allow Perl to
52 calculate the length by using C<sv_setpv> or by specifying 0 as the second
53 argument to C<newSVpv>. Be warned, though, that Perl will determine the
54 string's length by using C<strlen>, which depends on the string terminating
57 To access the actual value that an SV points to, you can use the macros:
63 which will automatically coerce the actual scalar type into an IV, double,
66 In the C<SvPV> macro, the length of the string returned is placed into the
67 variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
68 care what the length of the data is, use the global variable C<na>. Remember,
69 however, that Perl allows arbitrary strings of data that may both contain
70 NULs and not be terminated by a NUL.
72 If you want to know simply if the scalar value is TRUE, you can use:
76 Although Perl will automatically grow strings for you, if you need to force
77 Perl to allocate more memory for your SV, you can use the macro
79 SvGROW(SV*, STRLEN newlen)
81 which will determine if more memory needs to be allocated. If so, it will
82 call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
83 decrease, the allocated memory of an SV.
85 If you have an SV and want to know what kind of data Perl thinks is stored
86 in it, you can use the following macros to check the type of SV you have.
92 You can get and set the current length of the string stored in an SV with
96 SvCUR_set(SV*, I32 val)
98 You can also get a pointer to the end of the string stored in the SV
103 But note that these last three macros are valid only if C<SvPOK()> is true.
105 If you want to append something to the end of string stored in an C<SV*>,
106 you can use the following functions:
108 void sv_catpv(SV*, char*);
109 void sv_catpvn(SV*, char*, int);
110 void sv_catsv(SV*, SV*);
112 The first function calculates the length of the string to be appended by
113 using C<strlen>. In the second, you specify the length of the string
114 yourself. The third function extends the string stored in the first SV
115 with the string stored in the second SV. It also forces the second SV to
116 be interpreted as a string.
118 If you know the name of a scalar variable, you can get a pointer to its SV
119 by using the following:
121 SV* perl_get_sv("varname", FALSE);
123 This returns NULL if the variable does not exist.
125 If you want to know if this variable (or any other SV) is actually C<defined>,
130 The scalar C<undef> value is stored in an SV instance called C<sv_undef>. Its
131 address can be used whenever an C<SV*> is needed.
133 There are also the two values C<sv_yes> and C<sv_no>, which contain Boolean
134 TRUE and FALSE values, respectively. Like C<sv_undef>, their addresses can
135 be used whenever an C<SV*> is needed.
137 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&sv_undef>.
141 if (I-am-to-return-a-real-value) {
142 sv = sv_2mortal(newSViv(42));
146 This code tries to return a new SV (which contains the value 42) if it should
147 return a real value, or undef otherwise. Instead it has returned a null
148 pointer which, somewhere down the line, will cause a segmentation violation,
149 bus error, or just plain weird results. Change the zero to C<&sv_undef> in
150 the first line and all will be well.
152 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
153 call is not necessary. See the section on L<Mortality>.
155 =head2 What's Really Stored in an SV?
157 Recall that the usual method of determining the type of scalar you have is
158 to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
159 usually these macros will always return TRUE and calling the C<Sv*V>
160 macros will do the appropriate conversion of string to integer/double or
161 integer/double to string.
163 If you I<really> need to know if you have an integer, double, or string
164 pointer in an SV, you can use the following three macros instead:
170 These will tell you if you truly have an integer, double, or string pointer
171 stored in your SV. The "p" stands for private.
173 In general, though, it's best just to use the C<Sv*V> macros.
175 =head2 Working with AVs
177 There are two ways to create and load an AV. The first method creates just
182 The second method both creates the AV and initially populates it with SVs:
184 AV* av_make(I32 num, SV **ptr);
186 The second argument points to an array containing C<num> C<SV*>s. Once the
187 AV has been created, the SVs can be destroyed, if so desired.
189 Once the AV has been created, the following operations are possible on AVs:
191 void av_push(AV*, SV*);
194 void av_unshift(AV*, I32 num);
196 These should be familiar operations, with the exception of C<av_unshift>.
197 This routine adds C<num> elements at the front of the array with the C<undef>
198 value. You must then use C<av_store> (described below) to assign values
199 to these new elements.
201 Here are some other functions:
203 I32 av_len(AV*); /* Returns highest index value in array */
205 SV** av_fetch(AV*, I32 key, I32 lval);
206 /* Fetches value at key offset, but it stores an undef value
207 at the offset if lval is non-zero */
208 SV** av_store(AV*, I32 key, SV* val);
209 /* Stores val at offset key */
211 Take note that C<av_fetch> and C<av_store> return C<SV**>s, not C<SV*>s.
214 /* Clear out all elements, but leave the array */
216 /* Undefines the array, removing all elements */
217 void av_extend(AV*, I32 key);
218 /* Extend the array to a total of key elements */
220 If you know the name of an array variable, you can get a pointer to its AV
221 by using the following:
223 AV* perl_get_av("varname", FALSE);
225 This returns NULL if the variable does not exist.
227 =head2 Working with HVs
229 To create an HV, you use the following routine:
233 Once the HV has been created, the following operations are possible on HVs:
235 SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
236 SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
238 The C<klen> parameter is the length of the key being passed in. The C<val>
239 argument contains the SV pointer to the scalar being stored, and C<hash> is
240 the pre-computed hash value (zero if you want C<hv_store> to calculate it
241 for you). The C<lval> parameter indicates whether this fetch is actually a
242 part of a store operation.
244 Remember that C<hv_store> and C<hv_fetch> return C<SV**>s and not just
245 C<SV*>. To access the scalar value, you must first dereference
246 the return value. However, you should check to make sure that the return
247 value is not NULL before dereferencing it.
249 These two functions check if a hash table entry exists, and deletes it.
251 bool hv_exists(HV*, char* key, U32 klen);
252 SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
254 And more miscellaneous functions:
257 /* Clears all entries in hash table */
259 /* Undefines the hash table */
261 Perl keeps the actual data in linked list of structures with a typedef of HE.
262 These contain the actual key and value pointers (plus extra administrative
263 overhead). The key is a string pointer; the value is an C<SV*>. However,
264 once you have an C<HE*>, to get the actual key and value, use the routines
267 I32 hv_iterinit(HV*);
268 /* Prepares starting point to traverse hash table */
269 HE* hv_iternext(HV*);
270 /* Get the next entry, and return a pointer to a
271 structure that has both the key and value */
272 char* hv_iterkey(HE* entry, I32* retlen);
273 /* Get the key from an HE structure and also return
274 the length of the key string */
275 SV* hv_iterval(HV*, HE* entry);
276 /* Return a SV pointer to the value of the HE
278 SV* hv_iternextsv(HV*, char** key, I32* retlen);
279 /* This convenience routine combines hv_iternext,
280 hv_iterkey, and hv_iterval. The key and retlen
281 arguments are return values for the key and its
282 length. The value is returned in the SV* argument */
284 If you know the name of a hash variable, you can get a pointer to its HV
285 by using the following:
287 HV* perl_get_hv("varname", FALSE);
289 This returns NULL if the variable does not exist.
291 The hash algorithm, for those who are interested, is:
297 hash = hash * 33 + *s++;
301 References are a special type of scalar that point to other data types
302 (including references).
304 To create a reference, use the following command:
306 SV* newRV((SV*) thing);
308 The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. Once
309 you have a reference, you can use the following macro to dereference the
314 then call the appropriate routines, casting the returned C<SV*> to either an
315 C<AV*> or C<HV*>, if required.
317 To determine if an SV is a reference, you can use the following macro:
321 To discover what the reference actually refers to, you must use the following
322 macro and then check the value returned.
326 The most useful types that will be returned are:
334 SVt_PVMG Blessed Scalar
336 =head2 Blessed References and Class Objects
338 References are also used to support object-oriented programming. In the
339 OO lexicon, an object is simply a reference that has been blessed into a
340 package (or class). Once blessed, the programmer may now use the reference
341 to access the various methods in the class.
343 A reference can be blessed into a package with the following function:
345 SV* sv_bless(SV* sv, HV* stash);
347 The C<sv> argument must be a reference. The C<stash> argument specifies
348 which class the reference will belong to. See the section on L<Stashes>
349 for information on converting class names into stashes.
351 /* Still under construction */
353 Upgrades rv to reference if not already one. Creates new SV for rv to
355 If classname is non-null, the SV is blessed into the specified class.
358 SV* newSVrv(SV* rv, char* classname);
360 Copies integer or double into an SV whose reference is rv. SV is blessed
361 if classname is non-null.
363 SV* sv_setref_iv(SV* rv, char* classname, IV iv);
364 SV* sv_setref_nv(SV* rv, char* classname, NV iv);
366 Copies pointer (I<not a string!>) into an SV whose reference is rv.
367 SV is blessed if classname is non-null.
369 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
371 Copies string into an SV whose reference is rv.
372 Set length to 0 to let Perl calculate the string length.
373 SV is blessed if classname is non-null.
375 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
377 int sv_isa(SV* sv, char* name);
378 int sv_isobject(SV* sv);
380 =head1 Creating New Variables
382 To create a new Perl variable, which can be accessed from your Perl script,
383 use the following routines, depending on the variable type.
385 SV* perl_get_sv("varname", TRUE);
386 AV* perl_get_av("varname", TRUE);
387 HV* perl_get_hv("varname", TRUE);
389 Notice the use of TRUE as the second parameter. The new variable can now
390 be set, using the routines appropriate to the data type.
392 There are additional bits that may be OR'ed with the TRUE argument to enable
393 certain extra features. Those bits are:
395 0x02 Marks the variable as multiply defined, thus preventing the
396 "Identifier <varname> used only once: possible typo" warning.
397 0x04 Issues a "Had to create <varname> unexpectedly" warning if
398 the variable didn't actually exist. This is useful if
399 you expected the variable to exist already and want to propagate
400 this warning back to the user.
402 If the C<varname> argument does not contain a package specifier, it is
403 created in the current package.
405 =head1 XSUBs and the Argument Stack
407 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
408 An XSUB routine will have a stack that contains the arguments from the Perl
409 program, and a way to map from the Perl data structures to a C equivalent.
411 The stack arguments are accessible through the C<ST(n)> macro, which returns
412 the C<n>'th stack argument. Argument 0 is the first argument passed in the
413 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
416 Most of the time, output from the C routine can be handled through use of
417 the RETVAL and OUTPUT directives. However, there are some cases where the
418 argument stack is not already long enough to handle all the return values.
419 An example is the POSIX tzname() call, which takes no arguments, but returns
420 two, the local time zone's standard and summer time abbreviations.
422 To handle this situation, the PPCODE directive is used and the stack is
423 extended using the macro:
427 where C<sp> is the stack pointer, and C<num> is the number of elements the
428 stack should be extended by.
430 Now that there is room on the stack, values can be pushed on it using the
431 macros to push IVs, doubles, strings, and SV pointers respectively:
438 And now the Perl program calling C<tzname>, the two values will be assigned
441 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
443 An alternate (and possibly simpler) method to pushing values on the stack is
451 These macros automatically adjust the stack for you, if needed. Thus, you
452 do not need to call C<EXTEND> to extend the stack.
454 For more information, consult L<perlxs>.
456 =head1 Localizing Changes
458 Perl has a very handy construction
465 This construction is I<approximately> equivalent to
474 The biggest difference is that the first construction would would
475 reinstate the initial value of $var, irrespective of how control exits
476 the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
477 more efficient as well.
479 There is a way to achieve a similar task from C via Perl API: create a
480 I<pseudo-block>, and arrange for some changes to be automatically
481 undone at the end of it, either explicit, or via a non-local exit (via
482 die()). A I<block>-like construct is created by a pair of
483 C<ENTER>/C<LEAVE> macros (see L<perlcall/EXAMPLE/"Returning a
484 Scalar">). Such a construct may be created specially for some
485 important localized task, or an existing one (like boundaries of
486 enclosing Perl subroutine/block, or an existing pair for freeing TMPs)
487 may be used. (In the second case the overhead of additional
488 localization must be almost negligible.) Note that any XSUB is
489 automatically enclosed in an C<ENTER>/C<LEAVE> pair.
491 Inside such a I<pseudo-block> the following service is available:
495 =item C<SAVEINT(int i)>
497 =item C<SAVEIV(IV i)>
499 =item C<SAVEI16(I16 i)>
501 =item C<SAVEI32(I32 i)>
503 =item C<SAVELONG(long i)>
505 These macros arrange things to restore the value of integer variable
506 C<i> at the end of enclosing I<pseudo-block>.
512 These macros arrange things to restore the value of pointers C<s> and
513 C<p>. C<p> must be a pointer of a type which survives conversion to
514 C<SV*> and back, C<s> should be able to survive conversion to C<char*>
517 =item C<SAVEFREESV(SV *sv)>
519 The reference count of C<sv> would be decremented at the end of
520 I<pseudo-block>. This is similar to C<sv_2mortal>, which should (?) be
523 =item C<SAVEFREEOP(OP *op)>
525 The C<OP *> is op_free()ed at the end of I<pseudo-block>.
527 =item C<SAVEFREEPV(p)>
529 The chunk of memory which is pointed to by C<p> is Safefree()ed at the
530 end of I<pseudo-block>.
532 =item C<SAVECLEARSV(SV *sv)>
534 Clears a slot in the current scratchpad which corresponds to C<sv> at
535 the end of I<pseudo-block>.
537 =item C<SAVEDELETE(HV *hv, char *key, I32 length)>
539 The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
540 string pointed to by C<key> is Safefree()ed. If one has a I<key> in
541 short-lived storage, the corresponding string may be reallocated like
544 SAVEDELETE(defstash, savepv(tmpbuf), strlen(tmpbuf));
546 =item C<SAVEDESTRUCTOR(f,p)>
548 At the end of I<pseudo-block> the function C<f> is called with the
549 only argument (of type C<void*>) C<p>.
551 =item C<SAVESTACK_POS()>
553 The current offset on the Perl internal stack (cf. C<SP>) is restored
554 at the end of I<pseudo-block>.
558 The following API list contains functions, thus one needs to
559 provide pointers to the modifiable data explicitly (either C pointers,
560 or Perlish C<GV *>s):
564 =item C<SV* save_scalar(GV *gv)>
566 Equivalent to Perl code C<local $gv>.
568 =item C<AV* save_ary(GV *gv)>
570 =item C<HV* save_hash(GV *gv)>
572 Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
574 =item C<void save_item(SV *item)>
576 Duplicates the current value of C<SV>, on the exit from the current
577 C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
578 using the stored value.
580 =item C<void save_list(SV **sarg, I32 maxsarg)>
582 A variant of C<save_item> which takes multiple arguments via an array
583 C<sarg> of C<SV*> of length C<maxsarg>.
585 =item C<SV* save_svref(SV **sptr)>
587 Similar to C<save_scalar>, but will reinstate a C<SV *>.
589 =item C<void save_aptr(AV **aptr)>
591 =item C<void save_hptr(HV **hptr)>
593 Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
595 =item C<void save_nogv(GV *gv)>
597 Will postpone destruction of a I<stub> glob.
603 Perl uses an reference count-driven garbage collection mechanism. SV's,
604 AV's, or HV's (xV for short in the following) start their life with a
605 reference count of 1. If the reference count of an xV ever drops to 0,
606 then they will be destroyed and their memory made available for reuse.
608 This normally doesn't happen at the Perl level unless a variable is
609 undef'ed. At the internal level, however, reference counts can be
610 manipulated with the following macros:
612 int SvREFCNT(SV* sv);
613 void SvREFCNT_inc(SV* sv);
614 void SvREFCNT_dec(SV* sv);
616 However, there is one other function which manipulates the reference
617 count of its argument. The C<newRV> function, as you should recall,
618 creates a reference to the specified argument. As a side effect, it
619 increments the argument's reference count, which is ok in most
620 circumstances. But imagine you want to return a reference from an XS
621 function. You create a new SV which initially has a reference count
622 of 1. Then you call C<newRV>, passing the just-created SV. This returns
623 the reference as a new SV, but the reference count of the SV you passed
624 to C<newRV> has been incremented to 2. Now you return the reference and
625 forget about the SV. But Perl hasn't! Whenever the returned reference
626 is destroyed, the reference count of the original SV is decreased to 1
627 and nothing happens. The SV will hang around without any way to access
628 it until Perl itself terminates. This is a memory leak.
630 The correct procedure, then, is to call C<SvREFCNT_dec> on the SV after
631 C<newRV> has returned. Then, if and when the reference is destroyed,
632 the reference count of the SV will go to 0 and also be destroyed, stopping
635 There are some convenience functions available that can help with this
636 process. These functions introduce the concept of "mortality". An xV
637 that is mortal has had its reference count marked to be decremented,
638 but not actually decremented, until the "current context" is left.
639 Generally the "current context" means a single Perl statement, such as
640 a call to an XSUB function.
642 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
643 However, if you mortalize a variable twice, the reference count will
644 later be decremented twice.
646 You should be careful about creating mortal variables. Strange things
647 can happen if you make the same value mortal within multiple contexts,
648 or if you make a variable mortal multiple times. Doing the latter can
649 cause a variable to become invalid prematurely.
651 To create a mortal variable, use the functions:
655 SV* sv_mortalcopy(SV*)
657 The first call creates a mortal SV, the second converts an existing SV to
658 a mortal SV, the third creates a mortal copy of an existing SV (possibly
659 destroying it in the process).
661 The mortal routines are not for just SVs -- AVs and HVs can be made mortal
662 by passing their address (and casting them to C<SV*>) to the C<sv_2mortal> or
663 C<sv_mortalcopy> routines.
666 Beware that the sv_2mortal() call is eventually equivalent to
667 svREFCNT_dec(). A value can happily be mortal in two different contexts,
668 and it will be svREFCNT_dec()ed twice, once on exit from these
669 contexts. It can also be mortal twice in the same context. This means
670 that you should be very careful to make a value mortal exactly as many
671 times as it is needed. The value that go to the Perl stack I<should>
677 A stash is a hash table (associative array) that contains all of the
678 different objects that are contained within a package. Each key of the
679 stash is a symbol name (shared by all the different types of objects
680 that have the same name), and each value in the hash table is called a
681 GV (for Glob Value). This GV in turn contains references to the various
682 objects of that name, including (but not limited to) the following:
692 Perl stores various stashes in a separate GV structure (for global
693 variable) but represents them with an HV structure. The keys in this
694 larger GV are the various package names; the values are the C<GV*>s
695 which are stashes. It may help to think of a stash purely as an HV,
696 and that the term "GV" means the global variable hash.
698 To get the stash pointer for a particular package, use the function:
700 HV* gv_stashpv(char* name, I32 create)
701 HV* gv_stashsv(SV*, I32 create)
703 The first function takes a literal string, the second uses the string stored
704 in the SV. Remember that a stash is just a hash table, so you get back an
705 C<HV*>. The C<create> flag will create a new package if it is set.
707 The name that C<gv_stash*v> wants is the name of the package whose symbol table
708 you want. The default package is called C<main>. If you have multiply nested
709 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
712 Alternately, if you have an SV that is a blessed reference, you can find
713 out the stash pointer by using:
715 HV* SvSTASH(SvRV(SV*));
717 then use the following to get the package name itself:
719 char* HvNAME(HV* stash);
721 If you need to return a blessed value to your Perl script, you can use the
724 SV* sv_bless(SV*, HV* stash)
726 where the first argument, an C<SV*>, must be a reference, and the second
727 argument is a stash. The returned C<SV*> can now be used in the same way
730 For more information on references and blessings, consult L<perlref>.
734 [This section still under construction. Ignore everything here. Post no
735 bills. Everything not permitted is forbidden.]
737 Any SV may be magical, that is, it has special features that a normal
738 SV does not have. These features are stored in the SV structure in a
739 linked list of C<struct magic>s, typedef'ed to C<MAGIC>.
752 Note this is current as of patchlevel 0, and could change at any time.
754 =head2 Assigning Magic
756 Perl adds magic to an SV using the sv_magic function:
758 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
760 The C<sv> argument is a pointer to the SV that is to acquire a new magical
763 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
764 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
765 it to the beginning of the linked list of magical features. Any prior
766 entry of the same type of magic is deleted. Note that this can be
767 overridden, and multiple instances of the same type of magic can be
768 associated with an SV.
770 The C<name> and C<namlem> arguments are used to associate a string with
771 the magic, typically the name of a variable. C<namlem> is stored in the
772 C<mg_len> field and if C<name> is non-null and C<namlem> >= 0 a malloc'd
773 copy of the name is stored in C<mg_ptr> field.
775 The sv_magic function uses C<how> to determine which, if any, predefined
776 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
777 See the "Magic Virtual Table" section below. The C<how> argument is also
778 stored in the C<mg_type> field.
780 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
781 structure. If it is not the same as the C<sv> argument, the reference
782 count of the C<obj> object is incremented. If it is the same, or if
783 the C<how> argument is "#", or if it is a null pointer, then C<obj> is
784 merely stored, without the reference count being incremented.
786 There is also a function to add magic to an C<HV>:
788 void hv_magic(HV *hv, GV *gv, int how);
790 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
792 To remove the magic from an SV, call the function sv_unmagic:
794 void sv_unmagic(SV *sv, int type);
796 The C<type> argument should be equal to the C<how> value when the C<SV>
797 was initially made magical.
799 =head2 Magic Virtual Tables
801 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
802 C<MGVTBL>, which is a structure of function pointers and stands for
803 "Magic Virtual Table" to handle the various operations that might be
804 applied to that variable.
806 The C<MGVTBL> has five pointers to the following routine types:
808 int (*svt_get)(SV* sv, MAGIC* mg);
809 int (*svt_set)(SV* sv, MAGIC* mg);
810 U32 (*svt_len)(SV* sv, MAGIC* mg);
811 int (*svt_clear)(SV* sv, MAGIC* mg);
812 int (*svt_free)(SV* sv, MAGIC* mg);
814 This MGVTBL structure is set at compile-time in C<perl.h> and there are
815 currently 19 types (or 21 with overloading turned on). These different
816 structures contain pointers to various routines that perform additional
817 actions depending on which function is being called.
819 Function pointer Action taken
820 ---------------- ------------
821 svt_get Do something after the value of the SV is retrieved.
822 svt_set Do something after the SV is assigned a value.
823 svt_len Report on the SV's length.
824 svt_clear Clear something the SV represents.
825 svt_free Free any extra storage associated with the SV.
827 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
828 to an C<mg_type> of '\0') contains:
830 { magic_get, magic_set, magic_len, 0, 0 }
832 Thus, when an SV is determined to be magical and of type '\0', if a get
833 operation is being performed, the routine C<magic_get> is called. All
834 the various routines for the various magical types begin with C<magic_>.
836 The current kinds of Magic Virtual Tables are:
838 mg_type MGVTBL Type of magic
839 ------- ------ -------------------
841 A vtbl_amagic Operator Overloading
842 a vtbl_amagicelem Operator Overloading
843 c 0 Used in Operator Overloading
844 B vtbl_bm Boyer-Moore???
846 e vtbl_envelem %ENV hash element
847 g vtbl_mglob Regexp /g flag???
848 I vtbl_isa @ISA array
849 i vtbl_isaelem @ISA array element
850 L 0 (but sets RMAGICAL) Perl Module/Debugger???
851 l vtbl_dbline Debugger?
852 o vtbl_collxfrm Locale Collation
853 P vtbl_pack Tied Array or Hash
854 p vtbl_packelem Tied Array or Hash element
855 q vtbl_packelem Tied Scalar or Handle
856 S vtbl_sig Signal Hash
857 s vtbl_sigelem Signal Hash element
858 t vtbl_taint Taintedness
861 x vtbl_substr Substring???
863 # vtbl_arylen Array Length
864 . vtbl_pos $. scalar variable
865 ~ Reserved for extensions, but multiple extensions may clash
867 When an upper-case and lower-case letter both exist in the table, then the
868 upper-case letter is used to represent some kind of composite type (a list
869 or a hash), and the lower-case letter is used to represent an element of
874 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
876 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
877 If the SV does not have that magical feature, C<NULL> is returned. Also,
878 if the SV is not of type SVt_PVMG, Perl may core-dump.
880 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
882 This routine checks to see what types of magic C<sv> has. If the mg_type
883 field is an upper-case letter, then the mg_obj is copied to C<nsv>, but
884 the mg_type field is changed to be the lower-case letter.
886 =head1 Double-Typed SVs
888 Scalar variables normally contain only one type of value, an integer,
889 double, pointer, or reference. Perl will automatically convert the
890 actual scalar data from the stored type into the requested type.
892 Some scalar variables contain more than one type of scalar data. For
893 example, the variable C<$!> contains either the numeric value of C<errno>
894 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
896 To force multiple data values into an SV, you must do two things: use the
897 C<sv_set*v> routines to add the additional scalar type, then set a flag
898 so that Perl will believe it contains more than one type of data. The
899 four macros to set the flags are:
906 The particular macro you must use depends on which C<sv_set*v> routine
907 you called first. This is because every C<sv_set*v> routine turns on
908 only the bit for the particular type of data being set, and turns off
911 For example, to create a new Perl variable called "dberror" that contains
912 both the numeric and descriptive string error values, you could use the
916 extern char *dberror_list;
918 SV* sv = perl_get_sv("dberror", TRUE);
919 sv_setiv(sv, (IV) dberror);
920 sv_setpv(sv, dberror_list[dberror]);
923 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
924 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
926 =head1 Calling Perl Routines from within C Programs
928 There are four routines that can be used to call a Perl subroutine from
929 within a C program. These four are:
931 I32 perl_call_sv(SV*, I32);
932 I32 perl_call_pv(char*, I32);
933 I32 perl_call_method(char*, I32);
934 I32 perl_call_argv(char*, I32, register char**);
936 The routine most often used is C<perl_call_sv>. The C<SV*> argument
937 contains either the name of the Perl subroutine to be called, or a
938 reference to the subroutine. The second argument consists of flags
939 that control the context in which the subroutine is called, whether
940 or not the subroutine is being passed arguments, how errors should be
941 trapped, and how to treat return values.
943 All four routines return the number of arguments that the subroutine returned
946 When using any of these routines (except C<perl_call_argv>), the programmer
947 must manipulate the Perl stack. These include the following macros and
961 For more information, consult L<perlcall>.
963 =head1 Memory Allocation
965 It is strongly suggested that you use the version of malloc that is distributed
966 with Perl. It keeps pools of various sizes of unallocated memory to
967 satisfy allocation requests more quickly.
968 However, on some platforms, it may cause spurious malloc or free errors.
970 New(x, pointer, number, type);
971 Newc(x, pointer, number, type, cast);
972 Newz(x, pointer, number, type);
974 These three macros are used to allocate memory initially. The first argument
975 C<x> was a "magic cookie" that was used to keep track of who called the macro,
976 to help when debugging memory problems. However, the current code makes no
977 use of this feature (Larry has switched to using a run-time memory checker),
978 so this argument can be any number.
980 The second argument C<pointer> will point to the newly allocated memory.
981 The third and fourth arguments C<number> and C<type> specify how many of
982 the specified type of data structure should be allocated. The argument
983 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
984 should be used if the C<pointer> argument is different from the C<type>
987 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
988 to zero out all the newly allocated memory.
990 Renew(pointer, number, type);
991 Renewc(pointer, number, type, cast);
994 These three macros are used to change a memory buffer size or to free a
995 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
996 match those of C<New> and C<Newc> with the exception of not needing the
997 "magic cookie" argument.
999 Move(source, dest, number, type);
1000 Copy(source, dest, number, type);
1001 Zero(dest, number, type);
1003 These three macros are used to move, copy, or zero out previously allocated
1004 memory. The C<source> and C<dest> arguments point to the source and
1005 destination starting points. Perl will move, copy, or zero out C<number>
1006 instances of the size of the C<type> data structure (using the C<sizeof>
1011 =head2 Putting a C value on Perl stack
1013 A lot of opcodes (this is an elementary operation in the internal perl
1014 stack machine) put an SV* on the stack. However, as an optimization
1015 the corresponding SV is (usually) not recreated each time. The opcodes
1016 reuse specially assigned SVs (I<target>s) which are (as a corollary)
1017 not constantly freed/created.
1019 Each of the targets is created only once (but see
1020 L<Scratchpads and recursion> below), and when an opcode needs to put
1021 an integer, a double, or a string on stack, it just sets the
1022 corresponding parts of its I<target> and puts the I<target> on stack.
1024 The macro to put this target on stack is C<PUSHTARG>, and it is
1025 directly used in some opcodes, as well as indirectly in zillions of
1026 others, which use it via C<(X)PUSH[pni]>.
1030 The question remains on when the SVs which are I<target>s for opcodes
1031 are created. The answer is that they are created when the current unit
1032 - a subroutine or a file (for opcodes for statements outside of
1033 subroutines) - is compiled. During this time a special anonymous Perl
1034 array is created, which is called a scratchpad for the current
1037 Scratchpad keeps SVs which are lexicals for the current unit and are
1038 targets for opcodes. One can deduce that an SV lives on a scratchpad
1039 by looking on its flags: lexicals have C<SVs_PADMY> set, and
1040 I<target>s have C<SVs_PADTMP> set.
1042 The correspondence between OPs and I<target>s is not 1-to-1. Different
1043 OPs in the compile tree of the unit can use the same target, if this
1044 would not conflict with the expected life of the temporary.
1046 =head2 Scratchpads and recursions
1048 In fact it is not 100% true that a compiled unit contains a pointer to
1049 the scratchpad AV. In fact it contains a pointer to an AV of
1050 (initially) one element, and this element is the scratchpad AV. Why do
1051 we need an extra level of indirection?
1053 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1054 these can create several execution pointers going into the same
1055 subroutine. For the subroutine-child not write over the temporaries
1056 for the subroutine-parent (lifespan of which covers the call to the
1057 child), the parent and the child should have different
1058 scratchpads. (I<And> the lexicals should be separate anyway!)
1060 So each subroutine is born with an array of scratchpads (of length
1061 1). On each entry to the subroutine it is checked that the current
1062 depth of the recursion is not more than the length of this array, and
1063 if it is, new scratchpad is created and pushed into the array.
1065 The I<target>s on this scratchpad are C<undef>s, but they are already
1066 marked with correct flags.
1070 This is a listing of functions, macros, flags, and variables that may be
1071 useful to extension writers or that may be found while reading other
1082 Clears an array, making it empty.
1084 void av_clear _((AV* ar));
1088 Pre-extend an array. The C<key> is the index to which the array should be
1091 void av_extend _((AV* ar, I32 key));
1095 Returns the SV at the specified index in the array. The C<key> is the
1096 index. If C<lval> is set then the fetch will be part of a store. Check
1097 that the return value is non-null before dereferencing it to a C<SV*>.
1099 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1103 Returns the highest index in the array. Returns -1 if the array is empty.
1105 I32 av_len _((AV* ar));
1109 Creates a new AV and populates it with a list of SVs. The SVs are copied
1110 into the array, so they may be freed after the call to av_make. The new AV
1111 will have a reference count of 1.
1113 AV* av_make _((I32 size, SV** svp));
1117 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1120 SV* av_pop _((AV* ar));
1124 Pushes an SV onto the end of the array. The array will grow automatically
1125 to accommodate the addition.
1127 void av_push _((AV* ar, SV* val));
1131 Shifts an SV off the beginning of the array.
1133 SV* av_shift _((AV* ar));
1137 Stores an SV in an array. The array index is specified as C<key>. The
1138 return value will be null if the operation failed, otherwise it can be
1139 dereferenced to get the original C<SV*>.
1141 SV** av_store _((AV* ar, I32 key, SV* val));
1145 Undefines the array.
1147 void av_undef _((AV* ar));
1151 Unshift an SV onto the beginning of the array. The array will grow
1152 automatically to accommodate the addition.
1154 void av_unshift _((AV* ar, I32 num));
1158 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1159 constructor. This is always a C<char*>. See C<THIS> and
1160 L<perlxs/"Using XS With C++">.
1164 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1165 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1168 (void) Copy( s, d, n, t );
1172 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1173 function the same way you use the C C<printf> function. See C<warn>.
1177 Returns the stash of the CV.
1179 HV * CvSTASH( SV* sv )
1183 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1184 boolean which indicates whether subs are being single-stepped.
1185 Single-stepping is automatically turned on after every step. This is the C
1186 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1190 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1191 the SV which holds the name of the sub being debugged. This is the C
1192 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1193 The sub name can be found by
1195 SvPV( GvSV( DBsub ), na )
1199 Trace variable used when Perl is run in debugging mode, with the B<-d>
1200 switch. This is the C variable which corresponds to Perl's $DB::trace
1201 variable. See C<DBsingle>.
1205 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1210 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1214 The C variable which corresponds to Perl's $^W warning variable.
1218 Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
1222 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1223 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1224 to indicate the number of items on the stack.
1228 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1229 handled automatically by C<xsubpp>.
1233 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1234 handled automatically by C<xsubpp>.
1238 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1244 Used to extend the argument stack for an XSUB's return values.
1246 EXTEND( sp, int x );
1250 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1257 Used to indicate array context. See C<GIMME> and L<perlcall>.
1261 Indicates that arguments returned from a callback should be discarded. See
1266 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1270 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns C<G_SCALAR> or
1271 C<G_ARRAY> for scalar or array context.
1275 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1279 Used to indicate scalar context. See C<GIMME> and L<perlcall>.
1283 Returns a pointer to the stash for a specified package. If C<create> is set
1284 then the package will be created if it does not already exist. If C<create>
1285 is not set and the package does not exist then NULL is returned.
1287 HV* gv_stashpv _((char* name, I32 create));
1291 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1293 HV* gv_stashsv _((SV* sv, I32 create));
1297 Return the SV from the GV.
1301 Releases a hash entry from an iterator. See C<hv_iternext>.
1305 Clears a hash, making it empty.
1307 void hv_clear _((HV* tb));
1311 Deletes a key/value pair in the hash. The value SV is removed from the hash
1312 and returned to the caller. The C<klen> is the length of the key. The
1313 C<flags> value will normally be zero; if set to G_DISCARD then null will be
1316 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1320 Returns a boolean indicating whether the specified hash key exists. The
1321 C<klen> is the length of the key.
1323 bool hv_exists _((HV* tb, char* key, U32 klen));
1327 Returns the SV which corresponds to the specified key in the hash. The
1328 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1329 part of a store. Check that the return value is non-null before
1330 dereferencing it to a C<SV*>.
1332 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1336 Prepares a starting point to traverse a hash table.
1338 I32 hv_iterinit _((HV* tb));
1342 Returns the key from the current position of the hash iterator. See
1345 char* hv_iterkey _((HE* entry, I32* retlen));
1349 Returns entries from a hash iterator. See C<hv_iterinit>.
1351 HE* hv_iternext _((HV* tb));
1355 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1358 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1362 Returns the value from the current position of the hash iterator. See
1365 SV* hv_iterval _((HV* tb, HE* entry));
1369 Adds magic to a hash. See C<sv_magic>.
1371 void hv_magic _((HV* hv, GV* gv, int how));
1375 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1377 char *HvNAME (HV* stash)
1381 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1382 the length of the key. The C<hash> parameter is the pre-computed hash
1383 value; if it is zero then Perl will compute it. The return value will be
1384 null if the operation failed, otherwise it can be dereferenced to get the
1387 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1393 void hv_undef _((HV* tb));
1397 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
1400 int isALNUM (char c)
1404 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
1407 int isALPHA (char c)
1411 Returns a boolean indicating whether the C C<char> is an ascii digit.
1413 int isDIGIT (char c)
1417 Returns a boolean indicating whether the C C<char> is a lowercase character.
1419 int isLOWER (char c)
1423 Returns a boolean indicating whether the C C<char> is whitespace.
1425 int isSPACE (char c)
1429 Returns a boolean indicating whether the C C<char> is an uppercase character.
1431 int isUPPER (char c)
1435 Variable which is setup by C<xsubpp> to indicate the number of items on the
1436 stack. See L<perlxs/"Variable-length Parameter Lists">.
1440 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1441 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
1445 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1451 Stack marker variable for the XSUB. See C<dMARK>.
1455 Clear something magical that the SV represents. See C<sv_magic>.
1457 int mg_clear _((SV* sv));
1461 Copies the magic from one SV to another. See C<sv_magic>.
1463 int mg_copy _((SV *, SV *, char *, STRLEN));
1467 Finds the magic pointer for type matching the SV. See C<sv_magic>.
1469 MAGIC* mg_find _((SV* sv, int type));
1473 Free any magic storage used by the SV. See C<sv_magic>.
1475 int mg_free _((SV* sv));
1479 Do magic after a value is retrieved from the SV. See C<sv_magic>.
1481 int mg_get _((SV* sv));
1485 Report on the SV's length. See C<sv_magic>.
1487 U32 mg_len _((SV* sv));
1491 Turns on the magical status of an SV. See C<sv_magic>.
1493 void mg_magical _((SV* sv));
1497 Do magic after a value is assigned to the SV. See C<sv_magic>.
1499 int mg_set _((SV* sv));
1503 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
1504 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1507 (void) Move( s, d, n, t );
1511 A variable which may be used with C<SvPV> to tell Perl to calculate the
1516 The XSUB-writer's interface to the C C<malloc> function.
1518 void * New( x, void *ptr, int size, type )
1522 The XSUB-writer's interface to the C C<malloc> function, with cast.
1524 void * Newc( x, void *ptr, int size, type, cast )
1528 The XSUB-writer's interface to the C C<malloc> function. The allocated
1529 memory is zeroed with C<memzero>.
1531 void * Newz( x, void *ptr, int size, type )
1535 Creates a new AV. The reference count is set to 1.
1537 AV* newAV _((void));
1541 Creates a new HV. The reference count is set to 1.
1543 HV* newHV _((void));
1547 Creates an RV wrapper for an SV. The reference count for the original SV is
1550 SV* newRV _((SV* ref));
1554 Creates a new SV. The C<len> parameter indicates the number of bytes of
1555 pre-allocated string space the SV should have. The reference count for the new SV
1558 SV* newSV _((STRLEN len));
1562 Creates a new SV and copies an integer into it. The reference count for the SV is
1565 SV* newSViv _((IV i));
1569 Creates a new SV and copies a double into it. The reference count for the SV is
1572 SV* newSVnv _((NV i));
1576 Creates a new SV and copies a string into it. The reference count for the SV is
1577 set to 1. If C<len> is zero then Perl will compute the length.
1579 SV* newSVpv _((char* s, STRLEN len));
1583 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
1584 it will be upgraded to one. If C<classname> is non-null then the new SV will
1585 be blessed in the specified package. The new SV is returned and its
1586 reference count is 1.
1588 SV* newSVrv _((SV* rv, char* classname));
1592 Creates a new SV which is an exact duplicate of the original SV.
1594 SV* newSVsv _((SV* old));
1598 Used by C<xsubpp> to hook up XSUBs as Perl subs.
1602 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
1611 Null character pointer.
1627 The original stack mark for the XSUB. See C<dORIGMARK>.
1631 Allocates a new Perl interpreter. See L<perlembed>.
1633 =item perl_call_argv
1635 Performs a callback to the specified Perl sub. See L<perlcall>.
1637 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
1639 =item perl_call_method
1641 Performs a callback to the specified Perl method. The blessed object must
1642 be on the stack. See L<perlcall>.
1644 I32 perl_call_method _((char* methname, I32 flags));
1648 Performs a callback to the specified Perl sub. See L<perlcall>.
1650 I32 perl_call_pv _((char* subname, I32 flags));
1654 Performs a callback to the Perl sub whose name is in the SV. See
1657 I32 perl_call_sv _((SV* sv, I32 flags));
1659 =item perl_construct
1661 Initializes a new Perl interpreter. See L<perlembed>.
1665 Shuts down a Perl interpreter. See L<perlembed>.
1669 Tells Perl to C<eval> the string in the SV.
1671 I32 perl_eval_sv _((SV* sv, I32 flags));
1675 Releases a Perl interpreter. See L<perlembed>.
1679 Returns the AV of the specified Perl array. If C<create> is set and the
1680 Perl variable does not exist then it will be created. If C<create> is not
1681 set and the variable does not exist then null is returned.
1683 AV* perl_get_av _((char* name, I32 create));
1687 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
1688 variable does not exist then it will be created. If C<create> is not
1689 set and the variable does not exist then null is returned.
1691 CV* perl_get_cv _((char* name, I32 create));
1695 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
1696 variable does not exist then it will be created. If C<create> is not
1697 set and the variable does not exist then null is returned.
1699 HV* perl_get_hv _((char* name, I32 create));
1703 Returns the SV of the specified Perl scalar. If C<create> is set and the
1704 Perl variable does not exist then it will be created. If C<create> is not
1705 set and the variable does not exist then null is returned.
1707 SV* perl_get_sv _((char* name, I32 create));
1711 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
1713 =item perl_require_pv
1715 Tells Perl to C<require> a module.
1717 void perl_require_pv _((char* pv));
1721 Tells a Perl interpreter to run. See L<perlembed>.
1725 Pops an integer off the stack.
1731 Pops a long off the stack.
1737 Pops a string off the stack.
1743 Pops a double off the stack.
1749 Pops an SV off the stack.
1755 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
1761 Push an integer onto the stack. The stack must have room for this element.
1768 Push a double onto the stack. The stack must have room for this element.
1775 Push a string onto the stack. The stack must have room for this element.
1776 The C<len> indicates the length of the string. See C<XPUSHp>.
1778 PUSHp(char *c, int len )
1782 Push an SV onto the stack. The stack must have room for this element. See
1789 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
1790 See C<PUSHMARK> and L<perlcall> for other uses.
1796 The XSUB-writer's interface to the C C<realloc> function.
1798 void * Renew( void *ptr, int size, type )
1802 The XSUB-writer's interface to the C C<realloc> function, with cast.
1804 void * Renewc( void *ptr, int size, type, cast )
1808 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
1809 This is always the proper type for the XSUB.
1810 See L<perlxs/"The RETVAL Variable">.
1814 The XSUB-writer's interface to the C C<free> function.
1818 The XSUB-writer's interface to the C C<malloc> function.
1822 The XSUB-writer's interface to the C C<realloc> function.
1826 Copy a string to a safe spot. This does not use an SV.
1828 char* savepv _((char* sv));
1832 Copy a string to a safe spot. The C<len> indicates number of bytes to
1833 copy. This does not use an SV.
1835 char* savepvn _((char* sv, I32 len));
1839 Opening bracket for temporaries on a callback. See C<FREETMPS> and
1846 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
1851 Re-fetch the stack pointer. Used after a callback. See L<perlcall>.
1857 Used to access elements on the XSUB's stack.
1863 Test two strings to see if they are equal. Returns true or false.
1865 int strEQ( char *s1, char *s2 )
1869 Test two strings to see if the first, C<s1>, is greater than or equal to the
1870 second, C<s2>. Returns true or false.
1872 int strGE( char *s1, char *s2 )
1876 Test two strings to see if the first, C<s1>, is greater than the second,
1877 C<s2>. Returns true or false.
1879 int strGT( char *s1, char *s2 )
1883 Test two strings to see if the first, C<s1>, is less than or equal to the
1884 second, C<s2>. Returns true or false.
1886 int strLE( char *s1, char *s2 )
1890 Test two strings to see if the first, C<s1>, is less than the second,
1891 C<s2>. Returns true or false.
1893 int strLT( char *s1, char *s2 )
1897 Test two strings to see if they are different. Returns true or false.
1899 int strNE( char *s1, char *s2 )
1903 Test two strings to see if they are equal. The C<len> parameter indicates
1904 the number of bytes to compare. Returns true or false.
1906 int strnEQ( char *s1, char *s2 )
1910 Test two strings to see if they are different. The C<len> parameter
1911 indicates the number of bytes to compare. Returns true or false.
1913 int strnNE( char *s1, char *s2, int len )
1917 Marks an SV as mortal. The SV will be destroyed when the current context
1920 SV* sv_2mortal _((SV* sv));
1924 Blesses an SV into a specified package. The SV must be an RV. The package
1925 must be designated by its stash (see C<gv_stashpv()>). The reference count of the
1928 SV* sv_bless _((SV* sv, HV* stash));
1932 Concatenates the string onto the end of the string which is in the SV.
1934 void sv_catpv _((SV* sv, char* ptr));
1938 Concatenates the string onto the end of the string which is in the SV. The
1939 C<len> indicates number of bytes to copy.
1941 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
1945 Concatenates the string from SV C<ssv> onto the end of the string in SV
1948 void sv_catsv _((SV* dsv, SV* ssv));
1952 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1953 string in C<sv1> is less than, equal to, or greater than the string in
1956 I32 sv_cmp _((SV* sv1, SV* sv2));
1960 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1961 string in C<sv1> is less than, equal to, or greater than the string in
1964 I32 sv_cmp _((SV* sv1, SV* sv2));
1968 Returns the length of the string which is in the SV. See C<SvLEN>.
1974 Set the length of the string which is in the SV. See C<SvCUR>.
1976 SvCUR_set (SV* sv, int val )
1980 Auto-decrement of the value in the SV.
1982 void sv_dec _((SV* sv));
1986 Auto-decrement of the value in the SV.
1988 void sv_dec _((SV* sv));
1992 Returns a pointer to the last character in the string which is in the SV.
1993 See C<SvCUR>. Access the character as
1999 Returns a boolean indicating whether the strings in the two SVs are
2002 I32 sv_eq _((SV* sv1, SV* sv2));
2006 Expands the character buffer in the SV. Calls C<sv_grow> to perform the
2007 expansion if necessary. Returns a pointer to the character buffer.
2009 char * SvGROW( SV* sv, int len )
2013 Expands the character buffer in the SV. This will use C<sv_unref> and will
2014 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2019 Auto increment of the value in the SV.
2021 void sv_inc _((SV* sv));
2025 Returns a boolean indicating whether the SV contains an integer.
2031 Unsets the IV status of an SV.
2037 Tells an SV that it is an integer.
2043 Tells an SV that it is an integer and disables all other OK bits.
2049 Tells an SV that it is an integer and disables all other OK bits.
2055 Returns a boolean indicating whether the SV contains an integer. Checks the
2056 B<private> setting. Use C<SvIOK>.
2062 Returns a boolean indicating whether the SV is blessed into the specified
2063 class. This does not know how to check for subtype, so it doesn't work in
2064 an inheritance relationship.
2066 int sv_isa _((SV* sv, char* name));
2070 Returns the integer which is in the SV.
2076 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2077 object. If the SV is not an RV, or if the object is not blessed, then this
2080 int sv_isobject _((SV* sv));
2084 Returns the integer which is stored in the SV.
2090 Returns the size of the string buffer in the SV. See C<SvCUR>.
2096 Returns the length of the string in the SV. Use C<SvCUR>.
2098 STRLEN sv_len _((SV* sv));
2102 Returns the length of the string in the SV. Use C<SvCUR>.
2104 STRLEN sv_len _((SV* sv));
2108 Adds magic to an SV.
2110 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2114 Creates a new SV which is a copy of the original SV. The new SV is marked
2115 as mortal. The old SV may become invalid if it was marked as a temporary.
2117 SV* sv_mortalcopy _((SV* oldsv));
2121 Returns a boolean indicating whether the value is an SV.
2127 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2129 SV* sv_newmortal _((void));
2133 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2137 Returns a boolean indicating whether the SV contains a number, integer or
2144 Unsets the NV/IV status of an SV.
2150 Returns a boolean indicating whether the SV contains a number, integer or
2151 double. Checks the B<private> setting. Use C<SvNIOK>.
2153 int SvNIOKp (SV* SV)
2157 Returns a boolean indicating whether the SV contains a double.
2163 Unsets the NV status of an SV.
2169 Tells an SV that it is a double.
2175 Tells an SV that it is a double and disables all other OK bits.
2181 Tells an SV that it is a double and disables all other OK bits.
2187 Returns a boolean indicating whether the SV contains a double. Checks the
2188 B<private> setting. Use C<SvNOK>.
2194 Returns the double which is stored in the SV.
2196 double SvNV (SV* sv);
2200 Returns the double which is stored in the SV.
2202 double SvNVX (SV* sv);
2206 Returns a boolean indicating whether the SV contains a character string.
2212 Unsets the PV status of an SV.
2218 Tells an SV that it is a string.
2224 Tells an SV that it is a string and disables all other OK bits.
2230 Tells an SV that it is a string and disables all other OK bits.
2236 Returns a boolean indicating whether the SV contains a character string.
2237 Checks the B<private> setting. Use C<SvPOK>.
2243 Returns a pointer to the string in the SV, or a stringified form of the SV
2244 if the SV does not contain a string. If C<len> is C<na> then Perl will
2245 handle the length on its own.
2247 char * SvPV (SV* sv, int len )
2251 Returns a pointer to the string in the SV. The SV must contain a string.
2253 char * SvPVX (SV* sv)
2257 Returns the value of the object's reference count.
2259 int SvREFCNT (SV* sv);
2263 Decrements the reference count of the given SV.
2265 void SvREFCNT_dec (SV* sv)
2269 Increments the reference count of the given SV.
2271 void SvREFCNT_inc (SV* sv)
2275 Tests if the SV is an RV.
2281 Unsets the RV status of an SV.
2287 Tells an SV that it is an RV.
2293 Dereferences an RV to return the SV.
2299 Copies an integer into the given SV.
2301 void sv_setiv _((SV* sv, IV num));
2305 Copies a double into the given SV.
2307 void sv_setnv _((SV* sv, double num));
2311 Copies a string into an SV. The string must be null-terminated.
2313 void sv_setpv _((SV* sv, char* ptr));
2317 Copies a string into an SV. The C<len> parameter indicates the number of
2320 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2324 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
2325 argument will be upgraded to an RV. That RV will be modified to point to
2326 the new SV. The C<classname> argument indicates the package for the
2327 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2328 will be returned and will have a reference count of 1.
2330 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2334 Copies a double into a new SV, optionally blessing the SV. The C<rv>
2335 argument will be upgraded to an RV. That RV will be modified to point to
2336 the new SV. The C<classname> argument indicates the package for the
2337 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2338 will be returned and will have a reference count of 1.
2340 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2344 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
2345 argument will be upgraded to an RV. That RV will be modified to point to
2346 the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
2347 into the SV. The C<classname> argument indicates the package for the
2348 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2349 will be returned and will have a reference count of 1.
2351 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2353 Do not use with integral Perl types such as HV, AV, SV, CV, because those
2354 objects will become corrupted by the pointer copy process.
2356 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2360 Copies a string into a new SV, optionally blessing the SV. The length of the
2361 string must be specified with C<n>. The C<rv> argument will be upgraded to
2362 an RV. That RV will be modified to point to the new SV. The C<classname>
2363 argument indicates the package for the blessing. Set C<classname> to
2364 C<Nullch> to avoid the blessing. The new SV will be returned and will have
2365 a reference count of 1.
2367 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2369 Note that C<sv_setref_pv> copies the pointer while this copies the string.
2373 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
2374 The source SV may be destroyed if it is mortal or temporary.
2376 void sv_setsv _((SV* dsv, SV* ssv));
2380 A wrapper around C<sv_setsv>. Safe even if C<dst==ssv>.
2384 Returns the stash of the SV.
2386 HV * SvSTASH (SV* sv)
2390 Integer type flag for scalars. See C<svtype>.
2394 Pointer type flag for scalars. See C<svtype>.
2398 Type flag for arrays. See C<svtype>.
2402 Type flag for code refs. See C<svtype>.
2406 Type flag for hashes. See C<svtype>.
2410 Type flag for blessed scalars. See C<svtype>.
2414 Double type flag for scalars. See C<svtype>.
2418 Returns a boolean indicating whether Perl would evaluate the SV as true or
2419 false, defined or undefined.
2425 Returns the type of the SV. See C<svtype>.
2427 svtype SvTYPE (SV* sv)
2431 An enum of flags for Perl types. These are found in the file B<sv.h> in the
2432 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2436 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
2437 the upgrade if necessary. See C<svtype>.
2439 bool SvUPGRADE _((SV* sv, svtype mt));
2443 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
2447 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
2451 Unsets the RV status of the SV, and decrements the reference count of whatever was
2452 being referenced by the RV. This can almost be thought of as a reversal of
2453 C<newSVrv>. See C<SvROK_off>.
2455 void sv_unref _((SV* sv));
2459 Tells an SV to use C<ptr> to find its string value. Normally the string is
2460 stored inside the SV but sv_usepvn allows the SV to use an outside string.
2461 The C<ptr> should point to memory that was allocated by C<malloc>. The
2462 string length, C<len>, must be supplied. This function will realloc the
2463 memory pointed to by C<ptr>, so that pointer should not be freed or used by
2464 the programmer after giving it to sv_usepvn.
2466 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
2470 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
2474 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
2475 This is always the proper type for the C++ object. See C<CLASS> and
2476 L<perlxs/"Using XS With C++">.
2480 Converts the specified character to lowercase.
2482 int toLOWER (char c)
2486 Converts the specified character to uppercase.
2488 int toUPPER (char c)
2492 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
2493 function the same way you use the C C<printf> function. See C<croak()>.
2497 Push an integer onto the stack, extending the stack if necessary. See
2504 Push a double onto the stack, extending the stack if necessary. See
2511 Push a string onto the stack, extending the stack if necessary. The C<len>
2512 indicates the length of the string. See C<PUSHp>.
2514 XPUSHp(char *c, int len)
2518 Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
2524 Macro to declare an XSUB and its C parameter list. This is handled by
2529 Return from XSUB, indicating number of items on the stack. This is usually
2530 handled by C<xsubpp>.
2534 =item XSRETURN_EMPTY
2536 Return an empty list from an XSUB immediately.
2542 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
2548 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
2554 Return an double from an XSUB immediately. Uses C<XST_mNV>.
2560 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
2562 XSRETURN_PV(char *v);
2564 =item XSRETURN_UNDEF
2566 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
2572 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
2578 Place an integer into the specified position C<i> on the stack. The value is
2579 stored in a new mortal SV.
2581 XST_mIV( int i, IV v );
2585 Place a double into the specified position C<i> on the stack. The value is
2586 stored in a new mortal SV.
2588 XST_mNV( int i, NV v );
2592 Place C<&sv_no> into the specified position C<i> on the stack.
2598 Place a copy of a string into the specified position C<i> on the stack. The
2599 value is stored in a new mortal SV.
2601 XST_mPV( int i, char *v );
2605 Place C<&sv_undef> into the specified position C<i> on the stack.
2607 XST_mUNDEF( int i );
2611 Place C<&sv_yes> into the specified position C<i> on the stack.
2617 The version identifier for an XS module. This is usually handled
2618 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
2620 =item XS_VERSION_BOOTCHECK
2622 Macro to verify that a PM module's $VERSION variable matches the XS module's
2623 C<XS_VERSION> variable. This is usually handled automatically by
2624 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
2628 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
2629 destination, C<n> is the number of items, and C<t> is the type.
2631 (void) Zero( d, n, t );
2637 Jeff Okamoto <okamoto@corp.hp.com>
2639 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
2640 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
2641 Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
2643 API Listing by Dean Roehrich <roehrich@cray.com>.
2647 Version 23.1: 1996/10/19