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 simply want to know 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. Since 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 to just 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 just creates
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*>. In order 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 actually discover what the reference 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 already exist 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 timezone'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 refcount 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 just for 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 magicalness
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 in order to
967 more quickly satisfy allocation requests.
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 initially allocate memory. 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 This is a listing of functions, macros, flags, and variables that may be
1012 useful to extension writers or that may be found while reading other
1023 Clears an array, making it empty.
1025 void av_clear _((AV* ar));
1029 Pre-extend an array. The C<key> is the index to which the array should be
1032 void av_extend _((AV* ar, I32 key));
1036 Returns the SV at the specified index in the array. The C<key> is the
1037 index. If C<lval> is set then the fetch will be part of a store. Check
1038 that the return value is non-null before dereferencing it to a C<SV*>.
1040 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1044 Returns the highest index in the array. Returns -1 if the array is empty.
1046 I32 av_len _((AV* ar));
1050 Creates a new AV and populates it with a list of SVs. The SVs are copied
1051 into the array, so they may be freed after the call to av_make. The new AV
1052 will have a refcount of 1.
1054 AV* av_make _((I32 size, SV** svp));
1058 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1061 SV* av_pop _((AV* ar));
1065 Pushes an SV onto the end of the array. The array will grow automatically
1066 to accommodate the addition.
1068 void av_push _((AV* ar, SV* val));
1072 Shifts an SV off the beginning of the array.
1074 SV* av_shift _((AV* ar));
1078 Stores an SV in an array. The array index is specified as C<key>. The
1079 return value will be null if the operation failed, otherwise it can be
1080 dereferenced to get the original C<SV*>.
1082 SV** av_store _((AV* ar, I32 key, SV* val));
1086 Undefines the array.
1088 void av_undef _((AV* ar));
1092 Unshift an SV onto the beginning of the array. The array will grow
1093 automatically to accommodate the addition.
1095 void av_unshift _((AV* ar, I32 num));
1099 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1100 constructor. This is always a C<char*>. See C<THIS> and
1101 L<perlxs/"Using XS With C++">.
1105 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1106 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1109 (void) Copy( s, d, n, t );
1113 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1114 function the same way you use the C C<printf> function. See C<warn>.
1118 Returns the stash of the CV.
1120 HV * CvSTASH( SV* sv )
1124 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1125 boolean which indicates whether subs are being single-stepped.
1126 Single-stepping is automatically turned on after every step. This is the C
1127 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1131 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1132 the SV which holds the name of the sub being debugged. This is the C
1133 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1134 The sub name can be found by
1136 SvPV( GvSV( DBsub ), na )
1140 Trace variable used when Perl is run in debugging mode, with the B<-d>
1141 switch. This is the C variable which corresponds to Perl's $DB::trace
1142 variable. See C<DBsingle>.
1146 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1151 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1155 The C variable which corresponds to Perl's $^W warning variable.
1159 Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
1163 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1164 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1165 to indicate the number of items on the stack.
1169 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1170 handled automatically by C<xsubpp>.
1174 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1175 handled automatically by C<xsubpp>.
1179 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1185 Used to extend the argument stack for an XSUB's return values.
1187 EXTEND( sp, int x );
1191 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1198 Used to indicate array context. See C<GIMME> and L<perlcall>.
1202 Indicates that arguments returned from a callback should be discarded. See
1207 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1211 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns C<G_SCALAR> or
1212 C<G_ARRAY> for scalar or array context.
1216 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1220 Used to indicate scalar context. See C<GIMME> and L<perlcall>.
1224 Returns a pointer to the stash for a specified package. If C<create> is set
1225 then the package will be created if it does not already exist. If C<create>
1226 is not set and the package does not exist then NULL is returned.
1228 HV* gv_stashpv _((char* name, I32 create));
1232 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1234 HV* gv_stashsv _((SV* sv, I32 create));
1238 Return the SV from the GV.
1242 Releases a hash entry from an iterator. See C<hv_iternext>.
1246 Clears a hash, making it empty.
1248 void hv_clear _((HV* tb));
1252 Deletes a key/value pair in the hash. The value SV is removed from the hash
1253 and returned to the caller. The C<klen> is the length of the key. The
1254 C<flags> value will normally be zero; if set to G_DISCARD then null will be
1257 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1261 Returns a boolean indicating whether the specified hash key exists. The
1262 C<klen> is the length of the key.
1264 bool hv_exists _((HV* tb, char* key, U32 klen));
1268 Returns the SV which corresponds to the specified key in the hash. The
1269 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1270 part of a store. Check that the return value is non-null before
1271 dereferencing it to a C<SV*>.
1273 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1277 Prepares a starting point to traverse a hash table.
1279 I32 hv_iterinit _((HV* tb));
1283 Returns the key from the current position of the hash iterator. See
1286 char* hv_iterkey _((HE* entry, I32* retlen));
1290 Returns entries from a hash iterator. See C<hv_iterinit>.
1292 HE* hv_iternext _((HV* tb));
1296 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1299 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1303 Returns the value from the current position of the hash iterator. See
1306 SV* hv_iterval _((HV* tb, HE* entry));
1310 Adds magic to a hash. See C<sv_magic>.
1312 void hv_magic _((HV* hv, GV* gv, int how));
1316 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1318 char *HvNAME (HV* stash)
1322 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1323 the length of the key. The C<hash> parameter is the pre-computed hash
1324 value; if it is zero then Perl will compute it. The return value will be
1325 null if the operation failed, otherwise it can be dereferenced to get the
1328 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1334 void hv_undef _((HV* tb));
1338 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
1341 int isALNUM (char c)
1345 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
1348 int isALPHA (char c)
1352 Returns a boolean indicating whether the C C<char> is an ascii digit.
1354 int isDIGIT (char c)
1358 Returns a boolean indicating whether the C C<char> is a lowercase character.
1360 int isLOWER (char c)
1364 Returns a boolean indicating whether the C C<char> is whitespace.
1366 int isSPACE (char c)
1370 Returns a boolean indicating whether the C C<char> is an uppercase character.
1372 int isUPPER (char c)
1376 Variable which is setup by C<xsubpp> to indicate the number of items on the
1377 stack. See L<perlxs/"Variable-length Parameter Lists">.
1381 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1382 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
1386 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1392 Stack marker variable for the XSUB. See C<dMARK>.
1396 Clear something magical that the SV represents. See C<sv_magic>.
1398 int mg_clear _((SV* sv));
1402 Copies the magic from one SV to another. See C<sv_magic>.
1404 int mg_copy _((SV *, SV *, char *, STRLEN));
1408 Finds the magic pointer for type matching the SV. See C<sv_magic>.
1410 MAGIC* mg_find _((SV* sv, int type));
1414 Free any magic storage used by the SV. See C<sv_magic>.
1416 int mg_free _((SV* sv));
1420 Do magic after a value is retrieved from the SV. See C<sv_magic>.
1422 int mg_get _((SV* sv));
1426 Report on the SV's length. See C<sv_magic>.
1428 U32 mg_len _((SV* sv));
1432 Turns on the magical status of an SV. See C<sv_magic>.
1434 void mg_magical _((SV* sv));
1438 Do magic after a value is assigned to the SV. See C<sv_magic>.
1440 int mg_set _((SV* sv));
1444 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
1445 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1448 (void) Move( s, d, n, t );
1452 A variable which may be used with C<SvPV> to tell Perl to calculate the
1457 The XSUB-writer's interface to the C C<malloc> function.
1459 void * New( x, void *ptr, int size, type )
1463 The XSUB-writer's interface to the C C<malloc> function, with cast.
1465 void * Newc( x, void *ptr, int size, type, cast )
1469 The XSUB-writer's interface to the C C<malloc> function. The allocated
1470 memory is zeroed with C<memzero>.
1472 void * Newz( x, void *ptr, int size, type )
1476 Creates a new AV. The refcount is set to 1.
1478 AV* newAV _((void));
1482 Creates a new HV. The refcount is set to 1.
1484 HV* newHV _((void));
1488 Creates an RV wrapper for an SV. The refcount for the original SV is
1491 SV* newRV _((SV* ref));
1495 Creates a new SV. The C<len> parameter indicates the number of bytes of
1496 pre-allocated string space the SV should have. The refcount for the new SV
1499 SV* newSV _((STRLEN len));
1503 Creates a new SV and copies an integer into it. The refcount for the SV is
1506 SV* newSViv _((IV i));
1510 Creates a new SV and copies a double into it. The refcount for the SV is
1513 SV* newSVnv _((NV i));
1517 Creates a new SV and copies a string into it. The refcount for the SV is
1518 set to 1. If C<len> is zero then Perl will compute the length.
1520 SV* newSVpv _((char* s, STRLEN len));
1524 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
1525 it will be upgraded to one. If C<classname> is non-null then the new SV will
1526 be blessed in the specified package. The new SV is returned and its
1529 SV* newSVrv _((SV* rv, char* classname));
1533 Creates a new SV which is an exact duplicate of the original SV.
1535 SV* newSVsv _((SV* old));
1539 Used by C<xsubpp> to hook up XSUBs as Perl subs.
1543 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
1552 Null character pointer.
1568 The original stack mark for the XSUB. See C<dORIGMARK>.
1572 Allocates a new Perl interpreter. See L<perlembed>.
1574 =item perl_call_argv
1576 Performs a callback to the specified Perl sub. See L<perlcall>.
1578 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
1580 =item perl_call_method
1582 Performs a callback to the specified Perl method. The blessed object must
1583 be on the stack. See L<perlcall>.
1585 I32 perl_call_method _((char* methname, I32 flags));
1589 Performs a callback to the specified Perl sub. See L<perlcall>.
1591 I32 perl_call_pv _((char* subname, I32 flags));
1595 Performs a callback to the Perl sub whose name is in the SV. See
1598 I32 perl_call_sv _((SV* sv, I32 flags));
1600 =item perl_construct
1602 Initializes a new Perl interpreter. See L<perlembed>.
1606 Shuts down a Perl interpreter. See L<perlembed>.
1610 Tells Perl to C<eval> the string in the SV.
1612 I32 perl_eval_sv _((SV* sv, I32 flags));
1616 Releases a Perl interpreter. See L<perlembed>.
1620 Returns the AV of the specified Perl array. If C<create> is set and the
1621 Perl variable does not exist then it will be created. If C<create> is not
1622 set and the variable does not exist then null is returned.
1624 AV* perl_get_av _((char* name, I32 create));
1628 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
1629 variable does not exist then it will be created. If C<create> is not
1630 set and the variable does not exist then null is returned.
1632 CV* perl_get_cv _((char* name, I32 create));
1636 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
1637 variable does not exist then it will be created. If C<create> is not
1638 set and the variable does not exist then null is returned.
1640 HV* perl_get_hv _((char* name, I32 create));
1644 Returns the SV of the specified Perl scalar. If C<create> is set and the
1645 Perl variable does not exist then it will be created. If C<create> is not
1646 set and the variable does not exist then null is returned.
1648 SV* perl_get_sv _((char* name, I32 create));
1652 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
1654 =item perl_require_pv
1656 Tells Perl to C<require> a module.
1658 void perl_require_pv _((char* pv));
1662 Tells a Perl interpreter to run. See L<perlembed>.
1666 Pops an integer off the stack.
1672 Pops a long off the stack.
1678 Pops a string off the stack.
1684 Pops a double off the stack.
1690 Pops an SV off the stack.
1696 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
1702 Push an integer onto the stack. The stack must have room for this element.
1709 Push a double onto the stack. The stack must have room for this element.
1716 Push a string onto the stack. The stack must have room for this element.
1717 The C<len> indicates the length of the string. See C<XPUSHp>.
1719 PUSHp(char *c, int len )
1723 Push an SV onto the stack. The stack must have room for this element. See
1730 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
1731 See C<PUSHMARK> and L<perlcall> for other uses.
1737 The XSUB-writer's interface to the C C<realloc> function.
1739 void * Renew( void *ptr, int size, type )
1743 The XSUB-writer's interface to the C C<realloc> function, with cast.
1745 void * Renewc( void *ptr, int size, type, cast )
1749 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
1750 This is always the proper type for the XSUB.
1751 See L<perlxs/"The RETVAL Variable">.
1755 The XSUB-writer's interface to the C C<free> function.
1759 The XSUB-writer's interface to the C C<malloc> function.
1763 The XSUB-writer's interface to the C C<realloc> function.
1767 Copy a string to a safe spot. This does not use an SV.
1769 char* savepv _((char* sv));
1773 Copy a string to a safe spot. The C<len> indicates number of bytes to
1774 copy. This does not use an SV.
1776 char* savepvn _((char* sv, I32 len));
1780 Opening bracket for temporaries on a callback. See C<FREETMPS> and
1787 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
1792 Refetch the stack pointer. Used after a callback. See L<perlcall>.
1798 Used to access elements on the XSUB's stack.
1804 Test two strings to see if they are equal. Returns true or false.
1806 int strEQ( char *s1, char *s2 )
1810 Test two strings to see if the first, C<s1>, is greater than or equal to the
1811 second, C<s2>. Returns true or false.
1813 int strGE( char *s1, char *s2 )
1817 Test two strings to see if the first, C<s1>, is greater than the second,
1818 C<s2>. Returns true or false.
1820 int strGT( char *s1, char *s2 )
1824 Test two strings to see if the first, C<s1>, is less than or equal to the
1825 second, C<s2>. Returns true or false.
1827 int strLE( char *s1, char *s2 )
1831 Test two strings to see if the first, C<s1>, is less than the second,
1832 C<s2>. Returns true or false.
1834 int strLT( char *s1, char *s2 )
1838 Test two strings to see if they are different. Returns true or false.
1840 int strNE( char *s1, char *s2 )
1844 Test two strings to see if they are equal. The C<len> parameter indicates
1845 the number of bytes to compare. Returns true or false.
1847 int strnEQ( char *s1, char *s2 )
1851 Test two strings to see if they are different. The C<len> parameter
1852 indicates the number of bytes to compare. Returns true or false.
1854 int strnNE( char *s1, char *s2, int len )
1858 Marks an SV as mortal. The SV will be destroyed when the current context
1861 SV* sv_2mortal _((SV* sv));
1865 Blesses an SV into a specified package. The SV must be an RV. The package
1866 must be designated by its stash (see C<gv_stashpv()>). The refcount of the
1869 SV* sv_bless _((SV* sv, HV* stash));
1873 Concatenates the string onto the end of the string which is in the SV.
1875 void sv_catpv _((SV* sv, char* ptr));
1879 Concatenates the string onto the end of the string which is in the SV. The
1880 C<len> indicates number of bytes to copy.
1882 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
1886 Concatenates the string from SV C<ssv> onto the end of the string in SV
1889 void sv_catsv _((SV* dsv, SV* ssv));
1893 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1894 string in C<sv1> is less than, equal to, or greater than the string in
1897 I32 sv_cmp _((SV* sv1, SV* sv2));
1901 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1902 string in C<sv1> is less than, equal to, or greater than the string in
1905 I32 sv_cmp _((SV* sv1, SV* sv2));
1909 Returns the length of the string which is in the SV. See C<SvLEN>.
1915 Set the length of the string which is in the SV. See C<SvCUR>.
1917 SvCUR_set (SV* sv, int val )
1921 Autodecrement of the value in the SV.
1923 void sv_dec _((SV* sv));
1927 Autodecrement of the value in the SV.
1929 void sv_dec _((SV* sv));
1933 Returns a pointer to the last character in the string which is in the SV.
1934 See C<SvCUR>. Access the character as
1940 Returns a boolean indicating whether the strings in the two SVs are
1943 I32 sv_eq _((SV* sv1, SV* sv2));
1947 Expands the character buffer in the SV. Calls C<sv_grow> to perform the
1948 expansion if necessary. Returns a pointer to the character buffer.
1950 char * SvGROW( SV* sv, int len )
1954 Expands the character buffer in the SV. This will use C<sv_unref> and will
1955 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
1960 Autoincrement of the value in the SV.
1962 void sv_inc _((SV* sv));
1966 Returns a boolean indicating whether the SV contains an integer.
1972 Unsets the IV status of an SV.
1978 Tells an SV that it is an integer.
1984 Tells an SV that it is an integer and disables all other OK bits.
1990 Tells an SV that it is an integer and disables all other OK bits.
1996 Returns a boolean indicating whether the SV contains an integer. Checks the
1997 B<private> setting. Use C<SvIOK>.
2003 Returns a boolean indicating whether the SV is blessed into the specified
2004 class. This does not know how to check for subtype, so it doesn't work in
2005 an inheritance relationship.
2007 int sv_isa _((SV* sv, char* name));
2011 Returns the integer which is in the SV.
2017 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2018 object. If the SV is not an RV, or if the object is not blessed, then this
2021 int sv_isobject _((SV* sv));
2025 Returns the integer which is stored in the SV.
2031 Returns the size of the string buffer in the SV. See C<SvCUR>.
2037 Returns the length of the string in the SV. Use C<SvCUR>.
2039 STRLEN sv_len _((SV* sv));
2043 Returns the length of the string in the SV. Use C<SvCUR>.
2045 STRLEN sv_len _((SV* sv));
2049 Adds magic to an SV.
2051 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2055 Creates a new SV which is a copy of the original SV. The new SV is marked
2056 as mortal. The old SV may become invalid if it was marked as a temporary.
2058 SV* sv_mortalcopy _((SV* oldsv));
2062 Returns a boolean indicating whether the value is an SV.
2068 Creates a new SV which is mortal. The refcount of the SV is set to 1.
2070 SV* sv_newmortal _((void));
2074 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2078 Returns a boolean indicating whether the SV contains a number, integer or
2085 Unsets the NV/IV status of an SV.
2091 Returns a boolean indicating whether the SV contains a number, integer or
2092 double. Checks the B<private> setting. Use C<SvNIOK>.
2094 int SvNIOKp (SV* SV)
2098 Returns a boolean indicating whether the SV contains a double.
2104 Unsets the NV status of an SV.
2110 Tells an SV that it is a double.
2116 Tells an SV that it is a double and disables all other OK bits.
2122 Tells an SV that it is a double and disables all other OK bits.
2128 Returns a boolean indicating whether the SV contains a double. Checks the
2129 B<private> setting. Use C<SvNOK>.
2135 Returns the double which is stored in the SV.
2137 double SvNV (SV* sv);
2141 Returns the double which is stored in the SV.
2143 double SvNVX (SV* sv);
2147 Returns a boolean indicating whether the SV contains a character string.
2153 Unsets the PV status of an SV.
2159 Tells an SV that it is a string.
2165 Tells an SV that it is a string and disables all other OK bits.
2171 Tells an SV that it is a string and disables all other OK bits.
2177 Returns a boolean indicating whether the SV contains a character string.
2178 Checks the B<private> setting. Use C<SvPOK>.
2184 Returns a pointer to the string in the SV, or a stringified form of the SV
2185 if the SV does not contain a string. If C<len> is C<na> then Perl will
2186 handle the length on its own.
2188 char * SvPV (SV* sv, int len )
2192 Returns a pointer to the string in the SV. The SV must contain a string.
2194 char * SvPVX (SV* sv)
2198 Returns the value of the object's refcount.
2200 int SvREFCNT (SV* sv);
2204 Decrements the refcount of the given SV.
2206 void SvREFCNT_dec (SV* sv)
2210 Increments the refcount of the given SV.
2212 void SvREFCNT_inc (SV* sv)
2216 Tests if the SV is an RV.
2222 Unsets the RV status of an SV.
2228 Tells an SV that it is an RV.
2234 Dereferences an RV to return the SV.
2240 Copies an integer into the given SV.
2242 void sv_setiv _((SV* sv, IV num));
2246 Copies a double into the given SV.
2248 void sv_setnv _((SV* sv, double num));
2252 Copies a string into an SV. The string must be null-terminated.
2254 void sv_setpv _((SV* sv, char* ptr));
2258 Copies a string into an SV. The C<len> parameter indicates the number of
2261 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2265 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
2266 argument will be upgraded to an RV. That RV will be modified to point to
2267 the new SV. The C<classname> argument indicates the package for the
2268 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2269 will be returned and will have a refcount of 1.
2271 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2275 Copies a double into a new SV, optionally blessing the SV. The C<rv>
2276 argument will be upgraded to an RV. That RV will be modified to point to
2277 the new SV. The C<classname> argument indicates the package for the
2278 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2279 will be returned and will have a refcount of 1.
2281 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2285 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
2286 argument will be upgraded to an RV. That RV will be modified to point to
2287 the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
2288 into the SV. The C<classname> argument indicates the package for the
2289 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2290 will be returned and will have a refcount of 1.
2292 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2294 Do not use with integral Perl types such as HV, AV, SV, CV, because those
2295 objects will become corrupted by the pointer copy process.
2297 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2301 Copies a string into a new SV, optionally blessing the SV. The length of the
2302 string must be specified with C<n>. The C<rv> argument will be upgraded to
2303 an RV. That RV will be modified to point to the new SV. The C<classname>
2304 argument indicates the package for the blessing. Set C<classname> to
2305 C<Nullch> to avoid the blessing. The new SV will be returned and will have
2308 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2310 Note that C<sv_setref_pv> copies the pointer while this copies the string.
2314 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
2315 The source SV may be destroyed if it is mortal or temporary.
2317 void sv_setsv _((SV* dsv, SV* ssv));
2321 A wrapper around C<sv_setsv>. Safe even if C<dst==ssv>.
2325 Returns the stash of the SV.
2327 HV * SvSTASH (SV* sv)
2331 Integer type flag for scalars. See C<svtype>.
2335 Pointer type flag for scalars. See C<svtype>.
2339 Type flag for arrays. See C<svtype>.
2343 Type flag for code refs. See C<svtype>.
2347 Type flag for hashes. See C<svtype>.
2351 Type flag for blessed scalars. See C<svtype>.
2355 Double type flag for scalars. See C<svtype>.
2359 Returns a boolean indicating whether Perl would evaluate the SV as true or
2360 false, defined or undefined.
2366 Returns the type of the SV. See C<svtype>.
2368 svtype SvTYPE (SV* sv)
2372 An enum of flags for Perl types. These are found in the file B<sv.h> in the
2373 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2377 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
2378 the upgrade if necessary. See C<svtype>.
2380 bool SvUPGRADE _((SV* sv, svtype mt));
2384 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
2388 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
2392 Unsets the RV status of the SV, and decrements the refcount of whatever was
2393 being referenced by the RV. This can almost be thought of as a reversal of
2394 C<newSVrv>. See C<SvROK_off>.
2396 void sv_unref _((SV* sv));
2400 Tells an SV to use C<ptr> to find its string value. Normally the string is
2401 stored inside the SV but sv_usepvn allows the SV to use an outside string.
2402 The C<ptr> should point to memory that was allocated by C<malloc>. The
2403 string length, C<len>, must be supplied. This function will realloc the
2404 memory pointed to by C<ptr>, so that pointer should not be freed or used by
2405 the programmer after giving it to sv_usepvn.
2407 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
2411 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
2415 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
2416 This is always the proper type for the C++ object. See C<CLASS> and
2417 L<perlxs/"Using XS With C++">.
2421 Converts the specified character to lowercase.
2423 int toLOWER (char c)
2427 Converts the specified character to uppercase.
2429 int toUPPER (char c)
2433 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
2434 function the same way you use the C C<printf> function. See C<croak()>.
2438 Push an integer onto the stack, extending the stack if necessary. See
2445 Push a double onto the stack, extending the stack if necessary. See
2452 Push a string onto the stack, extending the stack if necessary. The C<len>
2453 indicates the length of the string. See C<PUSHp>.
2455 XPUSHp(char *c, int len)
2459 Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
2465 Macro to declare an XSUB and its C parameter list. This is handled by
2470 Return from XSUB, indicating number of items on the stack. This is usually
2471 handled by C<xsubpp>.
2475 =item XSRETURN_EMPTY
2477 Return an empty list from an XSUB immediately.
2483 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
2489 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
2495 Return an double from an XSUB immediately. Uses C<XST_mNV>.
2501 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
2503 XSRETURN_PV(char *v);
2505 =item XSRETURN_UNDEF
2507 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
2513 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
2519 Place an integer into the specified position C<i> on the stack. The value is
2520 stored in a new mortal SV.
2522 XST_mIV( int i, IV v );
2526 Place a double into the specified position C<i> on the stack. The value is
2527 stored in a new mortal SV.
2529 XST_mNV( int i, NV v );
2533 Place C<&sv_no> into the specified position C<i> on the stack.
2539 Place a copy of a string into the specified position C<i> on the stack. The
2540 value is stored in a new mortal SV.
2542 XST_mPV( int i, char *v );
2546 Place C<&sv_undef> into the specified position C<i> on the stack.
2548 XST_mUNDEF( int i );
2552 Place C<&sv_yes> into the specified position C<i> on the stack.
2558 The version identifier for an XS module. This is usually handled
2559 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
2561 =item XS_VERSION_BOOTCHECK
2563 Macro to verify that a PM module's $VERSION variable matches the XS module's
2564 C<XS_VERSION> variable. This is usually handled automatically by
2565 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
2569 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
2570 destination, C<n> is the number of items, and C<t> is the type.
2572 (void) Zero( d, n, t );
2578 Jeff Okamoto <okamoto@corp.hp.com>
2580 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
2581 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
2582 Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
2584 API Listing by Dean Roehrich <roehrich@cray.com>.
2588 Version 23.1: 1996/10/19