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.
660 The mortal routines are not just for SVs -- AVs and HVs can be made mortal
661 by passing their address (and casting them to C<SV*>) to the C<sv_2mortal> or
662 C<sv_mortalcopy> routines.
665 Beware that the sv_2mortal() call is eventually equivalent to
666 svREFCNT_dec(). A value can happily be mortal in two different contexts,
667 and it will be svREFCNT_dec()ed twice, once on exit from these
668 contexts. It can also be mortal twice in the same context. This means
669 that you should be very careful to make a value mortal exactly as many
670 times as it is needed. The value that go to the Perl stack I<should>
676 A stash is a hash table (associative array) that contains all of the
677 different objects that are contained within a package. Each key of the
678 stash is a symbol name (shared by all the different types of objects
679 that have the same name), and each value in the hash table is called a
680 GV (for Glob Value). This GV in turn contains references to the various
681 objects of that name, including (but not limited to) the following:
691 Perl stores various stashes in a separate GV structure (for global
692 variable) but represents them with an HV structure. The keys in this
693 larger GV are the various package names; the values are the C<GV*>s
694 which are stashes. It may help to think of a stash purely as an HV,
695 and that the term "GV" means the global variable hash.
697 To get the stash pointer for a particular package, use the function:
699 HV* gv_stashpv(char* name, I32 create)
700 HV* gv_stashsv(SV*, I32 create)
702 The first function takes a literal string, the second uses the string stored
703 in the SV. Remember that a stash is just a hash table, so you get back an
704 C<HV*>. The C<create> flag will create a new package if it is set.
706 The name that C<gv_stash*v> wants is the name of the package whose symbol table
707 you want. The default package is called C<main>. If you have multiply nested
708 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
711 Alternately, if you have an SV that is a blessed reference, you can find
712 out the stash pointer by using:
714 HV* SvSTASH(SvRV(SV*));
716 then use the following to get the package name itself:
718 char* HvNAME(HV* stash);
720 If you need to return a blessed value to your Perl script, you can use the
723 SV* sv_bless(SV*, HV* stash)
725 where the first argument, an C<SV*>, must be a reference, and the second
726 argument is a stash. The returned C<SV*> can now be used in the same way
729 For more information on references and blessings, consult L<perlref>.
733 [This section still under construction. Ignore everything here. Post no
734 bills. Everything not permitted is forbidden.]
736 Any SV may be magical, that is, it has special features that a normal
737 SV does not have. These features are stored in the SV structure in a
738 linked list of C<struct magic>s, typedef'ed to C<MAGIC>.
751 Note this is current as of patchlevel 0, and could change at any time.
753 =head2 Assigning Magic
755 Perl adds magic to an SV using the sv_magic function:
757 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
759 The C<sv> argument is a pointer to the SV that is to acquire a new magical
762 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
763 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
764 it to the beginning of the linked list of magical features. Any prior
765 entry of the same type of magic is deleted. Note that this can be
766 overridden, and multiple instances of the same type of magic can be
767 associated with an SV.
769 The C<name> and C<namlem> arguments are used to associate a string with
770 the magic, typically the name of a variable. C<namlem> is stored in the
771 C<mg_len> field and if C<name> is non-null and C<namlem> >= 0 a malloc'd
772 copy of the name is stored in C<mg_ptr> field.
774 The sv_magic function uses C<how> to determine which, if any, predefined
775 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
776 See the "Magic Virtual Table" section below. The C<how> argument is also
777 stored in the C<mg_type> field.
779 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
780 structure. If it is not the same as the C<sv> argument, the reference
781 count of the C<obj> object is incremented. If it is the same, or if
782 the C<how> argument is "#", or if it is a null pointer, then C<obj> is
783 merely stored, without the reference count being incremented.
785 There is also a function to add magic to an C<HV>:
787 void hv_magic(HV *hv, GV *gv, int how);
789 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
791 To remove the magic from an SV, call the function sv_unmagic:
793 void sv_unmagic(SV *sv, int type);
795 The C<type> argument should be equal to the C<how> value when the C<SV>
796 was initially made magical.
798 =head2 Magic Virtual Tables
800 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
801 C<MGVTBL>, which is a structure of function pointers and stands for
802 "Magic Virtual Table" to handle the various operations that might be
803 applied to that variable.
805 The C<MGVTBL> has five pointers to the following routine types:
807 int (*svt_get)(SV* sv, MAGIC* mg);
808 int (*svt_set)(SV* sv, MAGIC* mg);
809 U32 (*svt_len)(SV* sv, MAGIC* mg);
810 int (*svt_clear)(SV* sv, MAGIC* mg);
811 int (*svt_free)(SV* sv, MAGIC* mg);
813 This MGVTBL structure is set at compile-time in C<perl.h> and there are
814 currently 19 types (or 21 with overloading turned on). These different
815 structures contain pointers to various routines that perform additional
816 actions depending on which function is being called.
818 Function pointer Action taken
819 ---------------- ------------
820 svt_get Do something after the value of the SV is retrieved.
821 svt_set Do something after the SV is assigned a value.
822 svt_len Report on the SV's length.
823 svt_clear Clear something the SV represents.
824 svt_free Free any extra storage associated with the SV.
826 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
827 to an C<mg_type> of '\0') contains:
829 { magic_get, magic_set, magic_len, 0, 0 }
831 Thus, when an SV is determined to be magical and of type '\0', if a get
832 operation is being performed, the routine C<magic_get> is called. All
833 the various routines for the various magical types begin with C<magic_>.
835 The current kinds of Magic Virtual Tables are:
837 mg_type MGVTBL Type of magicalness
838 ------- ------ -------------------
840 A vtbl_amagic Operator Overloading
841 a vtbl_amagicelem Operator Overloading
842 c 0 Used in Operator Overloading
843 B vtbl_bm Boyer-Moore???
845 e vtbl_envelem %ENV hash element
846 g vtbl_mglob Regexp /g flag???
847 I vtbl_isa @ISA array
848 i vtbl_isaelem @ISA array element
849 L 0 (but sets RMAGICAL) Perl Module/Debugger???
850 l vtbl_dbline Debugger?
851 P vtbl_pack Tied Array or Hash
852 p vtbl_packelem Tied Array or Hash element
853 q vtbl_packelem Tied Scalar or Handle
854 S vtbl_sig Signal Hash
855 s vtbl_sigelem Signal Hash element
856 t vtbl_taint Taintedness
859 x vtbl_substr Substring???
861 # vtbl_arylen Array Length
862 . vtbl_pos $. scalar variable
863 ~ Reserved for extensions, but multiple extensions may clash
865 When an upper-case and lower-case letter both exist in the table, then the
866 upper-case letter is used to represent some kind of composite type (a list
867 or a hash), and the lower-case letter is used to represent an element of
872 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
874 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
875 If the SV does not have that magical feature, C<NULL> is returned. Also,
876 if the SV is not of type SVt_PVMG, Perl may core-dump.
878 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
880 This routine checks to see what types of magic C<sv> has. If the mg_type
881 field is an upper-case letter, then the mg_obj is copied to C<nsv>, but
882 the mg_type field is changed to be the lower-case letter.
884 =head1 Double-Typed SVs
886 Scalar variables normally contain only one type of value, an integer,
887 double, pointer, or reference. Perl will automatically convert the
888 actual scalar data from the stored type into the requested type.
890 Some scalar variables contain more than one type of scalar data. For
891 example, the variable C<$!> contains either the numeric value of C<errno>
892 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
894 To force multiple data values into an SV, you must do two things: use the
895 C<sv_set*v> routines to add the additional scalar type, then set a flag
896 so that Perl will believe it contains more than one type of data. The
897 four macros to set the flags are:
904 The particular macro you must use depends on which C<sv_set*v> routine
905 you called first. This is because every C<sv_set*v> routine turns on
906 only the bit for the particular type of data being set, and turns off
909 For example, to create a new Perl variable called "dberror" that contains
910 both the numeric and descriptive string error values, you could use the
914 extern char *dberror_list;
916 SV* sv = perl_get_sv("dberror", TRUE);
917 sv_setiv(sv, (IV) dberror);
918 sv_setpv(sv, dberror_list[dberror]);
921 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
922 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
924 =head1 Calling Perl Routines from within C Programs
926 There are four routines that can be used to call a Perl subroutine from
927 within a C program. These four are:
929 I32 perl_call_sv(SV*, I32);
930 I32 perl_call_pv(char*, I32);
931 I32 perl_call_method(char*, I32);
932 I32 perl_call_argv(char*, I32, register char**);
934 The routine most often used is C<perl_call_sv>. The C<SV*> argument
935 contains either the name of the Perl subroutine to be called, or a
936 reference to the subroutine. The second argument consists of flags
937 that control the context in which the subroutine is called, whether
938 or not the subroutine is being passed arguments, how errors should be
939 trapped, and how to treat return values.
941 All four routines return the number of arguments that the subroutine returned
944 When using any of these routines (except C<perl_call_argv>), the programmer
945 must manipulate the Perl stack. These include the following macros and
959 For more information, consult L<perlcall>.
961 =head1 Memory Allocation
963 It is strongly suggested that you use the version of malloc that is distributed
964 with Perl. It keeps pools of various sizes of unallocated memory in order to
965 more quickly satisfy allocation requests.
966 However, on some platforms, it may cause spurious malloc or free errors.
968 New(x, pointer, number, type);
969 Newc(x, pointer, number, type, cast);
970 Newz(x, pointer, number, type);
972 These three macros are used to initially allocate memory. The first argument
973 C<x> was a "magic cookie" that was used to keep track of who called the macro,
974 to help when debugging memory problems. However, the current code makes no
975 use of this feature (Larry has switched to using a run-time memory checker),
976 so this argument can be any number.
978 The second argument C<pointer> will point to the newly allocated memory.
979 The third and fourth arguments C<number> and C<type> specify how many of
980 the specified type of data structure should be allocated. The argument
981 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
982 should be used if the C<pointer> argument is different from the C<type>
985 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
986 to zero out all the newly allocated memory.
988 Renew(pointer, number, type);
989 Renewc(pointer, number, type, cast);
992 These three macros are used to change a memory buffer size or to free a
993 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
994 match those of C<New> and C<Newc> with the exception of not needing the
995 "magic cookie" argument.
997 Move(source, dest, number, type);
998 Copy(source, dest, number, type);
999 Zero(dest, number, type);
1001 These three macros are used to move, copy, or zero out previously allocated
1002 memory. The C<source> and C<dest> arguments point to the source and
1003 destination starting points. Perl will move, copy, or zero out C<number>
1004 instances of the size of the C<type> data structure (using the C<sizeof>
1009 This is a listing of functions, macros, flags, and variables that may be
1010 useful to extension writers or that may be found while reading other
1021 Clears an array, making it empty.
1023 void av_clear _((AV* ar));
1027 Pre-extend an array. The C<key> is the index to which the array should be
1030 void av_extend _((AV* ar, I32 key));
1034 Returns the SV at the specified index in the array. The C<key> is the
1035 index. If C<lval> is set then the fetch will be part of a store. Check
1036 that the return value is non-null before dereferencing it to a C<SV*>.
1038 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1042 Returns the highest index in the array. Returns -1 if the array is empty.
1044 I32 av_len _((AV* ar));
1048 Creates a new AV and populates it with a list of SVs. The SVs are copied
1049 into the array, so they may be freed after the call to av_make. The new AV
1050 will have a refcount of 1.
1052 AV* av_make _((I32 size, SV** svp));
1056 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1059 SV* av_pop _((AV* ar));
1063 Pushes an SV onto the end of the array. The array will grow automatically
1064 to accommodate the addition.
1066 void av_push _((AV* ar, SV* val));
1070 Shifts an SV off the beginning of the array.
1072 SV* av_shift _((AV* ar));
1076 Stores an SV in an array. The array index is specified as C<key>. The
1077 return value will be null if the operation failed, otherwise it can be
1078 dereferenced to get the original C<SV*>.
1080 SV** av_store _((AV* ar, I32 key, SV* val));
1084 Undefines the array.
1086 void av_undef _((AV* ar));
1090 Unshift an SV onto the beginning of the array. The array will grow
1091 automatically to accommodate the addition.
1093 void av_unshift _((AV* ar, I32 num));
1097 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1098 constructor. This is always a C<char*>. See C<THIS> and
1099 L<perlxs/"Using XS With C++">.
1103 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1104 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1107 (void) Copy( s, d, n, t );
1111 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1112 function the same way you use the C C<printf> function. See C<warn>.
1116 Returns the stash of the CV.
1118 HV * CvSTASH( SV* sv )
1122 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1123 boolean which indicates whether subs are being single-stepped.
1124 Single-stepping is automatically turned on after every step. This is the C
1125 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1129 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1130 the SV which holds the name of the sub being debugged. This is the C
1131 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1132 The sub name can be found by
1134 SvPV( GvSV( DBsub ), na )
1138 Trace variable used when Perl is run in debugging mode, with the B<-d>
1139 switch. This is the C variable which corresponds to Perl's $DB::trace
1140 variable. See C<DBsingle>.
1144 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1149 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1153 The C variable which corresponds to Perl's $^W warning variable.
1157 Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
1161 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1162 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1163 to indicate the number of items on the stack.
1167 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1168 handled automatically by C<xsubpp>.
1172 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1173 handled automatically by C<xsubpp>.
1177 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1183 Used to extend the argument stack for an XSUB's return values.
1185 EXTEND( sp, int x );
1189 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1196 Used to indicate array context. See C<GIMME> and L<perlcall>.
1200 Indicates that arguments returned from a callback should be discarded. See
1205 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1209 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns C<G_SCALAR> or
1210 C<G_ARRAY> for scalar or array context.
1214 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1218 Used to indicate scalar context. See C<GIMME> and L<perlcall>.
1222 Returns a pointer to the stash for a specified package. If C<create> is set
1223 then the package will be created if it does not already exist. If C<create>
1224 is not set and the package does not exist then NULL is returned.
1226 HV* gv_stashpv _((char* name, I32 create));
1230 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1232 HV* gv_stashsv _((SV* sv, I32 create));
1236 Return the SV from the GV.
1240 Releases a hash entry from an iterator. See C<hv_iternext>.
1244 Clears a hash, making it empty.
1246 void hv_clear _((HV* tb));
1250 Deletes a key/value pair in the hash. The value SV is removed from the hash
1251 and returned to the caller. The C<klen> is the length of the key. The
1252 C<flags> value will normally be zero; if set to G_DISCARD then null will be
1255 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1259 Returns a boolean indicating whether the specified hash key exists. The
1260 C<klen> is the length of the key.
1262 bool hv_exists _((HV* tb, char* key, U32 klen));
1266 Returns the SV which corresponds to the specified key in the hash. The
1267 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1268 part of a store. Check that the return value is non-null before
1269 dereferencing it to a C<SV*>.
1271 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1275 Prepares a starting point to traverse a hash table.
1277 I32 hv_iterinit _((HV* tb));
1281 Returns the key from the current position of the hash iterator. See
1284 char* hv_iterkey _((HE* entry, I32* retlen));
1288 Returns entries from a hash iterator. See C<hv_iterinit>.
1290 HE* hv_iternext _((HV* tb));
1294 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1297 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1301 Returns the value from the current position of the hash iterator. See
1304 SV* hv_iterval _((HV* tb, HE* entry));
1308 Adds magic to a hash. See C<sv_magic>.
1310 void hv_magic _((HV* hv, GV* gv, int how));
1314 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1316 char *HvNAME (HV* stash)
1320 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1321 the length of the key. The C<hash> parameter is the pre-computed hash
1322 value; if it is zero then Perl will compute it. The return value will be
1323 null if the operation failed, otherwise it can be dereferenced to get the
1326 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1332 void hv_undef _((HV* tb));
1336 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
1339 int isALNUM (char c)
1343 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
1346 int isALPHA (char c)
1350 Returns a boolean indicating whether the C C<char> is an ascii digit.
1352 int isDIGIT (char c)
1356 Returns a boolean indicating whether the C C<char> is a lowercase character.
1358 int isLOWER (char c)
1362 Returns a boolean indicating whether the C C<char> is whitespace.
1364 int isSPACE (char c)
1368 Returns a boolean indicating whether the C C<char> is an uppercase character.
1370 int isUPPER (char c)
1374 Variable which is setup by C<xsubpp> to indicate the number of items on the
1375 stack. See L<perlxs/"Variable-length Parameter Lists">.
1379 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1380 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
1384 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1390 Stack marker variable for the XSUB. See C<dMARK>.
1394 Clear something magical that the SV represents. See C<sv_magic>.
1396 int mg_clear _((SV* sv));
1400 Copies the magic from one SV to another. See C<sv_magic>.
1402 int mg_copy _((SV *, SV *, char *, STRLEN));
1406 Finds the magic pointer for type matching the SV. See C<sv_magic>.
1408 MAGIC* mg_find _((SV* sv, int type));
1412 Free any magic storage used by the SV. See C<sv_magic>.
1414 int mg_free _((SV* sv));
1418 Do magic after a value is retrieved from the SV. See C<sv_magic>.
1420 int mg_get _((SV* sv));
1424 Report on the SV's length. See C<sv_magic>.
1426 U32 mg_len _((SV* sv));
1430 Turns on the magical status of an SV. See C<sv_magic>.
1432 void mg_magical _((SV* sv));
1436 Do magic after a value is assigned to the SV. See C<sv_magic>.
1438 int mg_set _((SV* sv));
1442 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
1443 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1446 (void) Move( s, d, n, t );
1450 A variable which may be used with C<SvPV> to tell Perl to calculate the
1455 The XSUB-writer's interface to the C C<malloc> function.
1457 void * New( x, void *ptr, int size, type )
1461 The XSUB-writer's interface to the C C<malloc> function, with cast.
1463 void * Newc( x, void *ptr, int size, type, cast )
1467 The XSUB-writer's interface to the C C<malloc> function. The allocated
1468 memory is zeroed with C<memzero>.
1470 void * Newz( x, void *ptr, int size, type )
1474 Creates a new AV. The refcount is set to 1.
1476 AV* newAV _((void));
1480 Creates a new HV. The refcount is set to 1.
1482 HV* newHV _((void));
1486 Creates an RV wrapper for an SV. The refcount for the original SV is
1489 SV* newRV _((SV* ref));
1493 Creates a new SV. The C<len> parameter indicates the number of bytes of
1494 pre-allocated string space the SV should have. The refcount for the new SV
1497 SV* newSV _((STRLEN len));
1501 Creates a new SV and copies an integer into it. The refcount for the SV is
1504 SV* newSViv _((IV i));
1508 Creates a new SV and copies a double into it. The refcount for the SV is
1511 SV* newSVnv _((NV i));
1515 Creates a new SV and copies a string into it. The refcount for the SV is
1516 set to 1. If C<len> is zero then Perl will compute the length.
1518 SV* newSVpv _((char* s, STRLEN len));
1522 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
1523 it will be upgraded to one. If C<classname> is non-null then the new SV will
1524 be blessed in the specified package. The new SV is returned and its
1527 SV* newSVrv _((SV* rv, char* classname));
1531 Creates a new SV which is an exact duplicate of the original SV.
1533 SV* newSVsv _((SV* old));
1537 Used by C<xsubpp> to hook up XSUBs as Perl subs.
1541 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
1550 Null character pointer.
1566 The original stack mark for the XSUB. See C<dORIGMARK>.
1570 Allocates a new Perl interpreter. See L<perlembed>.
1572 =item perl_call_argv
1574 Performs a callback to the specified Perl sub. See L<perlcall>.
1576 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
1578 =item perl_call_method
1580 Performs a callback to the specified Perl method. The blessed object must
1581 be on the stack. See L<perlcall>.
1583 I32 perl_call_method _((char* methname, I32 flags));
1587 Performs a callback to the specified Perl sub. See L<perlcall>.
1589 I32 perl_call_pv _((char* subname, I32 flags));
1593 Performs a callback to the Perl sub whose name is in the SV. See
1596 I32 perl_call_sv _((SV* sv, I32 flags));
1598 =item perl_construct
1600 Initializes a new Perl interpreter. See L<perlembed>.
1604 Shuts down a Perl interpreter. See L<perlembed>.
1608 Tells Perl to C<eval> the string in the SV.
1610 I32 perl_eval_sv _((SV* sv, I32 flags));
1614 Releases a Perl interpreter. See L<perlembed>.
1618 Returns the AV of the specified Perl array. If C<create> is set and the
1619 Perl variable does not exist then it will be created. If C<create> is not
1620 set and the variable does not exist then null is returned.
1622 AV* perl_get_av _((char* name, I32 create));
1626 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
1627 variable does not exist then it will be created. If C<create> is not
1628 set and the variable does not exist then null is returned.
1630 CV* perl_get_cv _((char* name, I32 create));
1634 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
1635 variable does not exist then it will be created. If C<create> is not
1636 set and the variable does not exist then null is returned.
1638 HV* perl_get_hv _((char* name, I32 create));
1642 Returns the SV of the specified Perl scalar. If C<create> is set and the
1643 Perl variable does not exist then it will be created. If C<create> is not
1644 set and the variable does not exist then null is returned.
1646 SV* perl_get_sv _((char* name, I32 create));
1650 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
1652 =item perl_require_pv
1654 Tells Perl to C<require> a module.
1656 void perl_require_pv _((char* pv));
1660 Tells a Perl interpreter to run. See L<perlembed>.
1664 Pops an integer off the stack.
1670 Pops a long off the stack.
1676 Pops a string off the stack.
1682 Pops a double off the stack.
1688 Pops an SV off the stack.
1694 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
1700 Push an integer onto the stack. The stack must have room for this element.
1707 Push a double onto the stack. The stack must have room for this element.
1714 Push a string onto the stack. The stack must have room for this element.
1715 The C<len> indicates the length of the string. See C<XPUSHp>.
1717 PUSHp(char *c, int len )
1721 Push an SV onto the stack. The stack must have room for this element. See
1728 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
1729 See C<PUSHMARK> and L<perlcall> for other uses.
1735 The XSUB-writer's interface to the C C<realloc> function.
1737 void * Renew( void *ptr, int size, type )
1741 The XSUB-writer's interface to the C C<realloc> function, with cast.
1743 void * Renewc( void *ptr, int size, type, cast )
1747 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
1748 This is always the proper type for the XSUB.
1749 See L<perlxs/"The RETVAL Variable">.
1753 The XSUB-writer's interface to the C C<free> function.
1757 The XSUB-writer's interface to the C C<malloc> function.
1761 The XSUB-writer's interface to the C C<realloc> function.
1765 Copy a string to a safe spot. This does not use an SV.
1767 char* savepv _((char* sv));
1771 Copy a string to a safe spot. The C<len> indicates number of bytes to
1772 copy. This does not use an SV.
1774 char* savepvn _((char* sv, I32 len));
1778 Opening bracket for temporaries on a callback. See C<FREETMPS> and
1785 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
1790 Refetch the stack pointer. Used after a callback. See L<perlcall>.
1796 Used to access elements on the XSUB's stack.
1802 Test two strings to see if they are equal. Returns true or false.
1804 int strEQ( char *s1, char *s2 )
1808 Test two strings to see if the first, C<s1>, is greater than or equal to the
1809 second, C<s2>. Returns true or false.
1811 int strGE( char *s1, char *s2 )
1815 Test two strings to see if the first, C<s1>, is greater than the second,
1816 C<s2>. Returns true or false.
1818 int strGT( char *s1, char *s2 )
1822 Test two strings to see if the first, C<s1>, is less than or equal to the
1823 second, C<s2>. Returns true or false.
1825 int strLE( char *s1, char *s2 )
1829 Test two strings to see if the first, C<s1>, is less than the second,
1830 C<s2>. Returns true or false.
1832 int strLT( char *s1, char *s2 )
1836 Test two strings to see if they are different. Returns true or false.
1838 int strNE( char *s1, char *s2 )
1842 Test two strings to see if they are equal. The C<len> parameter indicates
1843 the number of bytes to compare. Returns true or false.
1845 int strnEQ( char *s1, char *s2 )
1849 Test two strings to see if they are different. The C<len> parameter
1850 indicates the number of bytes to compare. Returns true or false.
1852 int strnNE( char *s1, char *s2, int len )
1856 Marks an SV as mortal. The SV will be destroyed when the current context
1859 SV* sv_2mortal _((SV* sv));
1863 Blesses an SV into a specified package. The SV must be an RV. The package
1864 must be designated by its stash (see C<gv_stashpv()>). The refcount of the
1867 SV* sv_bless _((SV* sv, HV* stash));
1871 Concatenates the string onto the end of the string which is in the SV.
1873 void sv_catpv _((SV* sv, char* ptr));
1877 Concatenates the string onto the end of the string which is in the SV. The
1878 C<len> indicates number of bytes to copy.
1880 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
1884 Concatenates the string from SV C<ssv> onto the end of the string in SV
1887 void sv_catsv _((SV* dsv, SV* ssv));
1891 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1892 string in C<sv1> is less than, equal to, or greater than the string in
1895 I32 sv_cmp _((SV* sv1, SV* sv2));
1899 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1900 string in C<sv1> is less than, equal to, or greater than the string in
1903 I32 sv_cmp _((SV* sv1, SV* sv2));
1907 Returns the length of the string which is in the SV. See C<SvLEN>.
1913 Set the length of the string which is in the SV. See C<SvCUR>.
1915 SvCUR_set (SV* sv, int val )
1919 Autodecrement of the value in the SV.
1921 void sv_dec _((SV* sv));
1925 Autodecrement of the value in the SV.
1927 void sv_dec _((SV* sv));
1931 Returns a pointer to the last character in the string which is in the SV.
1932 See C<SvCUR>. Access the character as
1938 Returns a boolean indicating whether the strings in the two SVs are
1941 I32 sv_eq _((SV* sv1, SV* sv2));
1945 Expands the character buffer in the SV. Calls C<sv_grow> to perform the
1946 expansion if necessary. Returns a pointer to the character buffer.
1948 char * SvGROW( SV* sv, int len )
1952 Expands the character buffer in the SV. This will use C<sv_unref> and will
1953 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
1958 Autoincrement of the value in the SV.
1960 void sv_inc _((SV* sv));
1964 Returns a boolean indicating whether the SV contains an integer.
1970 Unsets the IV status of an SV.
1976 Tells an SV that it is an integer.
1982 Tells an SV that it is an integer and disables all other OK bits.
1988 Tells an SV that it is an integer and disables all other OK bits.
1994 Returns a boolean indicating whether the SV contains an integer. Checks the
1995 B<private> setting. Use C<SvIOK>.
2001 Returns a boolean indicating whether the SV is blessed into the specified
2002 class. This does not know how to check for subtype, so it doesn't work in
2003 an inheritance relationship.
2005 int sv_isa _((SV* sv, char* name));
2009 Returns the integer which is in the SV.
2015 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2016 object. If the SV is not an RV, or if the object is not blessed, then this
2019 int sv_isobject _((SV* sv));
2023 Returns the integer which is stored in the SV.
2029 Returns the size of the string buffer in the SV. See C<SvCUR>.
2035 Returns the length of the string in the SV. Use C<SvCUR>.
2037 STRLEN sv_len _((SV* sv));
2041 Returns the length of the string in the SV. Use C<SvCUR>.
2043 STRLEN sv_len _((SV* sv));
2047 Adds magic to an SV.
2049 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2053 Creates a new SV which is a copy of the original SV. The new SV is marked
2056 SV* sv_mortalcopy _((SV* oldsv));
2060 Returns a boolean indicating whether the value is an SV.
2066 Creates a new SV which is mortal. The refcount of the SV is set to 1.
2068 SV* sv_newmortal _((void));
2072 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2076 Returns a boolean indicating whether the SV contains a number, integer or
2083 Unsets the NV/IV status of an SV.
2089 Returns a boolean indicating whether the SV contains a number, integer or
2090 double. Checks the B<private> setting. Use C<SvNIOK>.
2092 int SvNIOKp (SV* SV)
2096 Returns a boolean indicating whether the SV contains a double.
2102 Unsets the NV status of an SV.
2108 Tells an SV that it is a double.
2114 Tells an SV that it is a double and disables all other OK bits.
2120 Tells an SV that it is a double and disables all other OK bits.
2126 Returns a boolean indicating whether the SV contains a double. Checks the
2127 B<private> setting. Use C<SvNOK>.
2133 Returns the double which is stored in the SV.
2135 double SvNV (SV* sv);
2139 Returns the double which is stored in the SV.
2141 double SvNVX (SV* sv);
2145 Returns a boolean indicating whether the SV contains a character string.
2151 Unsets the PV status of an SV.
2157 Tells an SV that it is a string.
2163 Tells an SV that it is a string and disables all other OK bits.
2169 Tells an SV that it is a string and disables all other OK bits.
2175 Returns a boolean indicating whether the SV contains a character string.
2176 Checks the B<private> setting. Use C<SvPOK>.
2182 Returns a pointer to the string in the SV, or a stringified form of the SV
2183 if the SV does not contain a string. If C<len> is C<na> then Perl will
2184 handle the length on its own.
2186 char * SvPV (SV* sv, int len )
2190 Returns a pointer to the string in the SV. The SV must contain a string.
2192 char * SvPVX (SV* sv)
2196 Returns the value of the object's refcount.
2198 int SvREFCNT (SV* sv);
2202 Decrements the refcount of the given SV.
2204 void SvREFCNT_dec (SV* sv)
2208 Increments the refcount of the given SV.
2210 void SvREFCNT_inc (SV* sv)
2214 Tests if the SV is an RV.
2220 Unsets the RV status of an SV.
2226 Tells an SV that it is an RV.
2232 Dereferences an RV to return the SV.
2238 Copies an integer into the given SV.
2240 void sv_setiv _((SV* sv, IV num));
2244 Copies a double into the given SV.
2246 void sv_setnv _((SV* sv, double num));
2250 Copies a string into an SV. The string must be null-terminated.
2252 void sv_setpv _((SV* sv, char* ptr));
2256 Copies a string into an SV. The C<len> parameter indicates the number of
2259 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2263 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
2264 argument will be upgraded to an RV. That RV will be modified to point to
2265 the new SV. The C<classname> argument indicates the package for the
2266 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2267 will be returned and will have a refcount of 1.
2269 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2273 Copies a double into a new SV, optionally blessing the SV. The C<rv>
2274 argument will be upgraded to an RV. That RV will be modified to point to
2275 the new SV. The C<classname> argument indicates the package for the
2276 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2277 will be returned and will have a refcount of 1.
2279 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2283 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
2284 argument will be upgraded to an RV. That RV will be modified to point to
2285 the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
2286 into the SV. The C<classname> argument indicates the package for the
2287 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2288 will be returned and will have a refcount of 1.
2290 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2292 Do not use with integral Perl types such as HV, AV, SV, CV, because those
2293 objects will become corrupted by the pointer copy process.
2295 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2299 Copies a string into a new SV, optionally blessing the SV. The length of the
2300 string must be specified with C<n>. The C<rv> argument will be upgraded to
2301 an RV. That RV will be modified to point to the new SV. The C<classname>
2302 argument indicates the package for the blessing. Set C<classname> to
2303 C<Nullch> to avoid the blessing. The new SV will be returned and will have
2306 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2308 Note that C<sv_setref_pv> copies the pointer while this copies the string.
2312 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
2313 The source SV may be destroyed if it is mortal.
2315 void sv_setsv _((SV* dsv, SV* ssv));
2319 Returns the stash of the SV.
2321 HV * SvSTASH (SV* sv)
2325 Integer type flag for scalars. See C<svtype>.
2329 Pointer type flag for scalars. See C<svtype>.
2333 Type flag for arrays. See C<svtype>.
2337 Type flag for code refs. See C<svtype>.
2341 Type flag for hashes. See C<svtype>.
2345 Type flag for blessed scalars. See C<svtype>.
2349 Double type flag for scalars. See C<svtype>.
2353 Returns a boolean indicating whether Perl would evaluate the SV as true or
2354 false, defined or undefined.
2360 Returns the type of the SV. See C<svtype>.
2362 svtype SvTYPE (SV* sv)
2366 An enum of flags for Perl types. These are found in the file B<sv.h> in the
2367 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2371 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
2372 the upgrade if necessary. See C<svtype>.
2374 bool SvUPGRADE _((SV* sv, svtype mt));
2378 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
2382 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
2386 Unsets the RV status of the SV, and decrements the refcount of whatever was
2387 being referenced by the RV. This can almost be thought of as a reversal of
2388 C<newSVrv>. See C<SvROK_off>.
2390 void sv_unref _((SV* sv));
2394 Tells an SV to use C<ptr> to find its string value. Normally the string is
2395 stored inside the SV but sv_usepvn allows the SV to use an outside string.
2396 The C<ptr> should point to memory that was allocated by C<malloc>. The
2397 string length, C<len>, must be supplied. This function will realloc the
2398 memory pointed to by C<ptr>, so that pointer should not be freed or used by
2399 the programmer after giving it to sv_usepvn.
2401 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
2405 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
2409 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
2410 This is always the proper type for the C++ object. See C<CLASS> and
2411 L<perlxs/"Using XS With C++">.
2415 Converts the specified character to lowercase.
2417 int toLOWER (char c)
2421 Converts the specified character to uppercase.
2423 int toUPPER (char c)
2427 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
2428 function the same way you use the C C<printf> function. See C<croak()>.
2432 Push an integer onto the stack, extending the stack if necessary. See
2439 Push a double onto the stack, extending the stack if necessary. See
2446 Push a string onto the stack, extending the stack if necessary. The C<len>
2447 indicates the length of the string. See C<PUSHp>.
2449 XPUSHp(char *c, int len)
2453 Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
2459 Macro to declare an XSUB and its C parameter list. This is handled by
2464 Return from XSUB, indicating number of items on the stack. This is usually
2465 handled by C<xsubpp>.
2469 =item XSRETURN_EMPTY
2471 Return an empty list from an XSUB immediately.
2477 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
2483 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
2489 Return an double from an XSUB immediately. Uses C<XST_mNV>.
2495 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
2497 XSRETURN_PV(char *v);
2499 =item XSRETURN_UNDEF
2501 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
2507 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
2513 Place an integer into the specified position C<i> on the stack. The value is
2514 stored in a new mortal SV.
2516 XST_mIV( int i, IV v );
2520 Place a double into the specified position C<i> on the stack. The value is
2521 stored in a new mortal SV.
2523 XST_mNV( int i, NV v );
2527 Place C<&sv_no> into the specified position C<i> on the stack.
2533 Place a copy of a string into the specified position C<i> on the stack. The
2534 value is stored in a new mortal SV.
2536 XST_mPV( int i, char *v );
2540 Place C<&sv_undef> into the specified position C<i> on the stack.
2542 XST_mUNDEF( int i );
2546 Place C<&sv_yes> into the specified position C<i> on the stack.
2552 The version identifier for an XS module. This is usually handled
2553 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
2555 =item XS_VERSION_BOOTCHECK
2557 Macro to verify that a PM module's $VERSION variable matches the XS module's
2558 C<XS_VERSION> variable. This is usually handled automatically by
2559 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
2563 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
2564 destination, C<n> is the number of items, and C<t> is the type.
2566 (void) Zero( d, n, t );
2572 Jeff Okamoto <okamoto@corp.hp.com>
2574 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
2575 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
2576 Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
2578 API Listing by Dean Roehrich <roehrich@cray.com>.
2582 Version 23.1: 1996/10/19