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 a simple integer type that is
24 guaranteed to be large enough to hold a pointer (as well as an integer).
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 SV's
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 All SV's that will contain strings should, but need not, be terminated
58 with a NUL character. If it is not NUL-terminated there is a risk of
59 core dumps and corruptions from code which passes the string to C
60 functions or system calls which expect a NUL-terminated string.
61 Perl's own functions typically add a trailing NUL for this reason.
62 Nevertheless, you should be very careful when you pass a string stored
63 in an SV to a C function or system call.
65 To access the actual value that an SV points to, you can use the macros:
71 which will automatically coerce the actual scalar type into an IV, double,
74 In the C<SvPV> macro, the length of the string returned is placed into the
75 variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
76 care what the length of the data is, use the global variable C<na>. Remember,
77 however, that Perl allows arbitrary strings of data that may both contain
78 NUL's and might not be terminated by a NUL.
80 If you want to know if the scalar value is TRUE, you can use:
84 Although Perl will automatically grow strings for you, if you need to force
85 Perl to allocate more memory for your SV, you can use the macro
87 SvGROW(SV*, STRLEN newlen)
89 which will determine if more memory needs to be allocated. If so, it will
90 call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
91 decrease, the allocated memory of an SV and that it does not automatically
92 add a byte for the a trailing NUL (perl's own string functions typically do
93 C<SvGROW(sv, len + 1)>).
95 If you have an SV and want to know what kind of data Perl thinks is stored
96 in it, you can use the following macros to check the type of SV you have.
102 You can get and set the current length of the string stored in an SV with
103 the following macros:
106 SvCUR_set(SV*, I32 val)
108 You can also get a pointer to the end of the string stored in the SV
113 But note that these last three macros are valid only if C<SvPOK()> is true.
115 If you want to append something to the end of string stored in an C<SV*>,
116 you can use the following functions:
118 void sv_catpv(SV*, char*);
119 void sv_catpvn(SV*, char*, int);
120 void sv_catsv(SV*, SV*);
122 The first function calculates the length of the string to be appended by
123 using C<strlen>. In the second, you specify the length of the string
124 yourself. The third function extends the string stored in the first SV
125 with the string stored in the second SV. It also forces the second SV to
126 be interpreted as a string.
128 If you know the name of a scalar variable, you can get a pointer to its SV
129 by using the following:
131 SV* perl_get_sv("package::varname", FALSE);
133 This returns NULL if the variable does not exist.
135 If you want to know if this variable (or any other SV) is actually C<defined>,
140 The scalar C<undef> value is stored in an SV instance called C<sv_undef>. Its
141 address can be used whenever an C<SV*> is needed.
143 There are also the two values C<sv_yes> and C<sv_no>, which contain Boolean
144 TRUE and FALSE values, respectively. Like C<sv_undef>, their addresses can
145 be used whenever an C<SV*> is needed.
147 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&sv_undef>.
151 if (I-am-to-return-a-real-value) {
152 sv = sv_2mortal(newSViv(42));
156 This code tries to return a new SV (which contains the value 42) if it should
157 return a real value, or undef otherwise. Instead it has returned a null
158 pointer which, somewhere down the line, will cause a segmentation violation,
159 bus error, or just weird results. Change the zero to C<&sv_undef> in the first
160 line and all will be well.
162 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
163 call is not necessary (see the section on L<Mortality>).
165 =head2 What's Really Stored in an SV?
167 Recall that the usual method of determining the type of scalar you have is
168 to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
169 usually these macros will always return TRUE and calling the C<Sv*V>
170 macros will do the appropriate conversion of string to integer/double or
171 integer/double to string.
173 If you I<really> need to know if you have an integer, double, or string
174 pointer in an SV, you can use the following three macros instead:
180 These will tell you if you truly have an integer, double, or string pointer
181 stored in your SV. The "p" stands for private.
183 In general, though, it's best to use the C<Sv*V> macros.
185 =head2 Working with AV's
187 There are two ways to create and load an AV. The first method creates an
192 The second method both creates the AV and initially populates it with SV's:
194 AV* av_make(I32 num, SV **ptr);
196 The second argument points to an array containing C<num> C<SV*>'s. Once the
197 AV has been created, the SV's can be destroyed, if so desired.
199 Once the AV has been created, the following operations are possible on AV's:
201 void av_push(AV*, SV*);
204 void av_unshift(AV*, I32 num);
206 These should be familiar operations, with the exception of C<av_unshift>.
207 This routine adds C<num> elements at the front of the array with the C<undef>
208 value. You must then use C<av_store> (described below) to assign values
209 to these new elements.
211 Here are some other functions:
214 SV** av_fetch(AV*, I32 key, I32 lval);
215 SV** av_store(AV*, I32 key, SV* val);
217 The C<av_len> function returns the highest index value in array (just
218 like $#array in Perl). If the array is empty, -1 is returned. The
219 C<av_fetch> function returns the value at index C<key>, but if C<lval>
220 is non-zero, then C<av_fetch> will store an undef value at that index.
221 The C<av_store> function stores the value C<val> at index C<key>.
222 note that C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s
223 as their return value.
227 void av_extend(AV*, I32 key);
229 The C<av_clear> function deletes all the elements in the AV* array, but
230 does not actually delete the array itself. The C<av_undef> function will
231 delete all the elements in the array plus the array itself. The
232 C<av_extend> function extends the array so that it contains C<key>
233 elements. If C<key> is less than the current length of the array, then
236 If you know the name of an array variable, you can get a pointer to its AV
237 by using the following:
239 AV* perl_get_av("package::varname", FALSE);
241 This returns NULL if the variable does not exist.
243 =head2 Working with HV's
245 To create an HV, you use the following routine:
249 Once the HV has been created, the following operations are possible on HV's:
251 SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
252 SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
254 The C<klen> parameter is the length of the key being passed in (Note that
255 you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
256 length of the key). The C<val> argument contains the SV pointer to the
257 scalar being stored, and C<hash> is the pre-computed hash value (zero if
258 you want C<hv_store> to calculate it for you). The C<lval> parameter
259 indicates whether this fetch is actually a part of a store operation, in
260 which case a new undefined value will be added to the HV with the supplied
261 key and C<hv_fetch> will return as if the value had already existed.
263 Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
264 C<SV*>. To access the scalar value, you must first dereference the return
265 value. However, you should check to make sure that the return value is
266 not NULL before dereferencing it.
268 These two functions check if a hash table entry exists, and deletes it.
270 bool hv_exists(HV*, char* key, U32 klen);
271 SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
273 If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
274 create and return a mortal copy of the deleted value.
276 And more miscellaneous functions:
281 Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
282 table but does not actually delete the hash table. The C<hv_undef> deletes
283 both the entries and the hash table itself.
285 Perl keeps the actual data in linked list of structures with a typedef of HE.
286 These contain the actual key and value pointers (plus extra administrative
287 overhead). The key is a string pointer; the value is an C<SV*>. However,
288 once you have an C<HE*>, to get the actual key and value, use the routines
291 I32 hv_iterinit(HV*);
292 /* Prepares starting point to traverse hash table */
293 HE* hv_iternext(HV*);
294 /* Get the next entry, and return a pointer to a
295 structure that has both the key and value */
296 char* hv_iterkey(HE* entry, I32* retlen);
297 /* Get the key from an HE structure and also return
298 the length of the key string */
299 SV* hv_iterval(HV*, HE* entry);
300 /* Return a SV pointer to the value of the HE
302 SV* hv_iternextsv(HV*, char** key, I32* retlen);
303 /* This convenience routine combines hv_iternext,
304 hv_iterkey, and hv_iterval. The key and retlen
305 arguments are return values for the key and its
306 length. The value is returned in the SV* argument */
308 If you know the name of a hash variable, you can get a pointer to its HV
309 by using the following:
311 HV* perl_get_hv("package::varname", FALSE);
313 This returns NULL if the variable does not exist.
315 The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
321 hash = hash * 33 + *s++;
325 References are a special type of scalar that point to other data types
326 (including references).
328 To create a reference, use either of the following functions:
330 SV* newRV_inc((SV*) thing);
331 SV* newRV_noinc((SV*) thing);
333 The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
334 functions are identical except that C<newRV_inc> increments the reference
335 count of the C<thing>, while C<newRV_noinc> does not. For historical
336 reasons, C<newRV> is a synonym for C<newRV_inc>.
338 Once you have a reference, you can use the following macro to dereference
343 then call the appropriate routines, casting the returned C<SV*> to either an
344 C<AV*> or C<HV*>, if required.
346 To determine if an SV is a reference, you can use the following macro:
350 To discover what type of value the reference refers to, use the following
351 macro and then check the return value.
355 The most useful types that will be returned are:
364 SVt_PVGV Glob (possible a file handle)
365 SVt_PVMG Blessed or Magical Scalar
367 See the sv.h header file for more details.
369 =head2 Blessed References and Class Objects
371 References are also used to support object-oriented programming. In the
372 OO lexicon, an object is simply a reference that has been blessed into a
373 package (or class). Once blessed, the programmer may now use the reference
374 to access the various methods in the class.
376 A reference can be blessed into a package with the following function:
378 SV* sv_bless(SV* sv, HV* stash);
380 The C<sv> argument must be a reference. The C<stash> argument specifies
381 which class the reference will belong to. See the section on L<Stashes>
382 for information on converting class names into stashes.
384 /* Still under construction */
386 Upgrades rv to reference if not already one. Creates new SV for rv to
387 point to. If C<classname> is non-null, the SV is blessed into the specified
388 class. SV is returned.
390 SV* newSVrv(SV* rv, char* classname);
392 Copies integer or double into an SV whose reference is C<rv>. SV is blessed
393 if C<classname> is non-null.
395 SV* sv_setref_iv(SV* rv, char* classname, IV iv);
396 SV* sv_setref_nv(SV* rv, char* classname, NV iv);
398 Copies the pointer value (I<the address, not the string!>) into an SV whose
399 reference is rv. SV is blessed if C<classname> is non-null.
401 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
403 Copies string into an SV whose reference is C<rv>. Set length to 0 to let
404 Perl calculate the string length. SV is blessed if C<classname> is non-null.
406 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
408 int sv_isa(SV* sv, char* name);
409 int sv_isobject(SV* sv);
411 =head2 Creating New Variables
413 To create a new Perl variable with an undef value which can be accessed from
414 your Perl script, use the following routines, depending on the variable type.
416 SV* perl_get_sv("package::varname", TRUE);
417 AV* perl_get_av("package::varname", TRUE);
418 HV* perl_get_hv("package::varname", TRUE);
420 Notice the use of TRUE as the second parameter. The new variable can now
421 be set, using the routines appropriate to the data type.
423 There are additional macros whose values may be bitwise OR'ed with the
424 C<TRUE> argument to enable certain extra features. Those bits are:
426 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
427 "Indentifier <varname> used only once: possible typo" warning.
428 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
429 the variable did not exist before the function was called.
431 If you do not specify a package name, the variable is created in the current
434 =head2 Reference Counts and Mortality
436 Perl uses an reference count-driven garbage collection mechanism. SV's,
437 AV's, or HV's (xV for short in the following) start their life with a
438 reference count of 1. If the reference count of an xV ever drops to 0,
439 then it will be destroyed and its memory made available for reuse.
441 This normally doesn't happen at the Perl level unless a variable is
442 undef'ed or the last variable holding a reference to it is changed or
443 overwritten. At the internal level, however, reference counts can be
444 manipulated with the following macros:
446 int SvREFCNT(SV* sv);
447 SV* SvREFCNT_inc(SV* sv);
448 void SvREFCNT_dec(SV* sv);
450 However, there is one other function which manipulates the reference
451 count of its argument. The C<newRV_inc> function, you will recall,
452 creates a reference to the specified argument. As a side effect,
453 it increments the argument's reference count. If this is not what
454 you want, use C<newRV_noinc> instead.
456 For example, imagine you want to return a reference from an XSUB function.
457 Inside the XSUB routine, you create an SV which initially has a reference
458 count of one. Then you call C<newRV_inc>, passing it the just-created SV.
459 This returns the reference as a new SV, but the reference count of the
460 SV you passed to C<newRV_inc> has been incremented to two. Now you
461 return the reference from the XSUB routine and forget about the SV.
462 But Perl hasn't! Whenever the returned reference is destroyed, the
463 reference count of the original SV is decreased to one and nothing happens.
464 The SV will hang around without any way to access it until Perl itself
465 terminates. This is a memory leak.
467 The correct procedure, then, is to use C<newRV_noinc> instead of
468 C<newRV_inc>. Then, if and when the last reference is destroyed,
469 the reference count of the SV will go to zero and it will be destroyed,
470 stopping any memory leak.
472 There are some convenience functions available that can help with the
473 destruction of xV's. These functions introduce the concept of "mortality".
474 An xV that is mortal has had its reference count marked to be decremented,
475 but not actually decremented, until "a short time later". Generally the
476 term "short time later" means a single Perl statement, such as a call to
477 an XSUB function. The actual determinant for when mortal xV's have their
478 reference count decremented depends on two macros, SAVETMPS and FREETMPS.
479 See L<perlcall> and L<perlxs> for more details on these macros.
481 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
482 However, if you mortalize a variable twice, the reference count will
483 later be decremented twice.
485 You should be careful about creating mortal variables. Strange things
486 can happen if you make the same value mortal within multiple contexts,
487 or if you make a variable mortal multiple times.
489 To create a mortal variable, use the functions:
493 SV* sv_mortalcopy(SV*)
495 The first call creates a mortal SV, the second converts an existing
496 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
497 third creates a mortal copy of an existing SV.
499 The mortal routines are not just for SV's -- AV's and HV's can be
500 made mortal by passing their address (type-casted to C<SV*>) to the
501 C<sv_2mortal> or C<sv_mortalcopy> routines.
503 =head2 Stashes and Globs
505 A stash is a hash table (associative array) that contains all of the
506 different objects that are contained within a package. Each key of the
507 stash is a symbol name (shared by all the different types of objects
508 that have the same name), and each value in the hash table is called a
509 GV (for Glob Value). This GV in turn contains references to the various
510 objects of that name, including (but not limited to) the following:
520 There is a single stash called "defstash" that holds the items that exist
521 in the "main" package. To get at the items in other packages, append the
522 string "::" to the package name. The items in the "Foo" package are in
523 the stash "Foo::" in defstash. The items in the "Bar::Baz" package are
524 in the stash "Baz::" in "Bar::"'s stash.
526 To get the stash pointer for a particular package, use the function:
528 HV* gv_stashpv(char* name, I32 create)
529 HV* gv_stashsv(SV*, I32 create)
531 The first function takes a literal string, the second uses the string stored
532 in the SV. Remember that a stash is just a hash table, so you get back an
533 C<HV*>. The C<create> flag will create a new package if it is set.
535 The name that C<gv_stash*v> wants is the name of the package whose symbol table
536 you want. The default package is called C<main>. If you have multiply nested
537 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
540 Alternately, if you have an SV that is a blessed reference, you can find
541 out the stash pointer by using:
543 HV* SvSTASH(SvRV(SV*));
545 then use the following to get the package name itself:
547 char* HvNAME(HV* stash);
549 If you need to bless or re-bless an object you can use the following
552 SV* sv_bless(SV*, HV* stash)
554 where the first argument, an C<SV*>, must be a reference, and the second
555 argument is a stash. The returned C<SV*> can now be used in the same way
558 For more information on references and blessings, consult L<perlref>.
562 [This section still under construction. Ignore everything here. Post no
563 bills. Everything not permitted is forbidden.]
565 Any SV may be magical, that is, it has special features that a normal
566 SV does not have. These features are stored in the SV structure in a
567 linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
580 Note this is current as of patchlevel 0, and could change at any time.
582 =head2 Assigning Magic
584 Perl adds magic to an SV using the sv_magic function:
586 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
588 The C<sv> argument is a pointer to the SV that is to acquire a new magical
591 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
592 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
593 it to the beginning of the linked list of magical features. Any prior
594 entry of the same type of magic is deleted. Note that this can be
595 overridden, and multiple instances of the same type of magic can be
596 associated with an SV.
598 The C<name> and C<namlem> arguments are used to associate a string with
599 the magic, typically the name of a variable. C<namlem> is stored in the
600 C<mg_len> field and if C<name> is non-null and C<namlem> >= 0 a malloc'd
601 copy of the name is stored in C<mg_ptr> field.
603 The sv_magic function uses C<how> to determine which, if any, predefined
604 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
605 See the "Magic Virtual Table" section below. The C<how> argument is also
606 stored in the C<mg_type> field.
608 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
609 structure. If it is not the same as the C<sv> argument, the reference
610 count of the C<obj> object is incremented. If it is the same, or if
611 the C<how> argument is "#", or if it is a null pointer, then C<obj> is
612 merely stored, without the reference count being incremented.
614 There is also a function to add magic to an C<HV>:
616 void hv_magic(HV *hv, GV *gv, int how);
618 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
620 To remove the magic from an SV, call the function sv_unmagic:
622 void sv_unmagic(SV *sv, int type);
624 The C<type> argument should be equal to the C<how> value when the C<SV>
625 was initially made magical.
627 =head2 Magic Virtual Tables
629 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
630 C<MGVTBL>, which is a structure of function pointers and stands for
631 "Magic Virtual Table" to handle the various operations that might be
632 applied to that variable.
634 The C<MGVTBL> has five pointers to the following routine types:
636 int (*svt_get)(SV* sv, MAGIC* mg);
637 int (*svt_set)(SV* sv, MAGIC* mg);
638 U32 (*svt_len)(SV* sv, MAGIC* mg);
639 int (*svt_clear)(SV* sv, MAGIC* mg);
640 int (*svt_free)(SV* sv, MAGIC* mg);
642 This MGVTBL structure is set at compile-time in C<perl.h> and there are
643 currently 19 types (or 21 with overloading turned on). These different
644 structures contain pointers to various routines that perform additional
645 actions depending on which function is being called.
647 Function pointer Action taken
648 ---------------- ------------
649 svt_get Do something after the value of the SV is retrieved.
650 svt_set Do something after the SV is assigned a value.
651 svt_len Report on the SV's length.
652 svt_clear Clear something the SV represents.
653 svt_free Free any extra storage associated with the SV.
655 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
656 to an C<mg_type> of '\0') contains:
658 { magic_get, magic_set, magic_len, 0, 0 }
660 Thus, when an SV is determined to be magical and of type '\0', if a get
661 operation is being performed, the routine C<magic_get> is called. All
662 the various routines for the various magical types begin with C<magic_>.
664 The current kinds of Magic Virtual Tables are:
666 mg_type MGVTBL Type of magical
667 ------- ------ ----------------------------
669 A vtbl_amagic Operator Overloading
670 a vtbl_amagicelem Operator Overloading
671 c 0 Used in Operator Overloading
672 B vtbl_bm Boyer-Moore???
674 e vtbl_envelem %ENV hash element
675 g vtbl_mglob Regexp /g flag???
676 I vtbl_isa @ISA array
677 i vtbl_isaelem @ISA array element
678 L 0 (but sets RMAGICAL) Perl Module/Debugger???
679 l vtbl_dbline Debugger?
680 o vtbl_collxfrm Locale transformation
681 P vtbl_pack Tied Array or Hash
682 p vtbl_packelem Tied Array or Hash element
683 q vtbl_packelem Tied Scalar or Handle
684 S vtbl_sig Signal Hash
685 s vtbl_sigelem Signal Hash element
686 t vtbl_taint Taintedness
689 x vtbl_substr Substring???
690 y vtbl_itervar Shadow "foreach" iterator variable
692 # vtbl_arylen Array Length
693 . vtbl_pos $. scalar variable
694 ~ None Used by certain extensions
696 When an upper-case and lower-case letter both exist in the table, then the
697 upper-case letter is used to represent some kind of composite type (a list
698 or a hash), and the lower-case letter is used to represent an element of
701 The '~' magic type is defined specifically for use by extensions and
702 will not be used by perl itself. Extensions can use ~ magic to 'attach'
703 private information to variables (typically objects). This is especially
704 useful because there is no way for normal perl code to corrupt this
705 private information (unlike using extra elements of a hash object).
707 Note that because multiple extensions may be using ~ magic it is
708 important for extensions to take extra care with it. Typically only
709 using it on objects blessed into the same class as the extension
710 is sufficient. It may also be appropriate to add an I32 'signature'
711 at the top of the private data area and check that.
715 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
717 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
718 If the SV does not have that magical feature, C<NULL> is returned. Also,
719 if the SV is not of type SVt_PVMG, Perl may core-dump.
721 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
723 This routine checks to see what types of magic C<sv> has. If the mg_type
724 field is an upper-case letter, then the mg_obj is copied to C<nsv>, but
725 the mg_type field is changed to be the lower-case letter.
727 =head2 Double-Typed SV's
729 Scalar variables normally contain only one type of value, an integer,
730 double, pointer, or reference. Perl will automatically convert the
731 actual scalar data from the stored type into the requested type.
733 Some scalar variables contain more than one type of scalar data. For
734 example, the variable C<$!> contains either the numeric value of C<errno>
735 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
737 To force multiple data values into an SV, you must do two things: use the
738 C<sv_set*v> routines to add the additional scalar type, then set a flag
739 so that Perl will believe it contains more than one type of data. The
740 four macros to set the flags are:
747 The particular macro you must use depends on which C<sv_set*v> routine
748 you called first. This is because every C<sv_set*v> routine turns on
749 only the bit for the particular type of data being set, and turns off
752 For example, to create a new Perl variable called "dberror" that contains
753 both the numeric and descriptive string error values, you could use the
757 extern char *dberror_list;
759 SV* sv = perl_get_sv("dberror", TRUE);
760 sv_setiv(sv, (IV) dberror);
761 sv_setpv(sv, dberror_list[dberror]);
764 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
765 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
767 =head2 XSUB's and the Argument Stack
769 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
770 An XSUB routine will have a stack that contains the arguments from the Perl
771 program, and a way to map from the Perl data structures to a C equivalent.
773 The stack arguments are accessible through the C<ST(n)> macro, which returns
774 the C<n>'th stack argument. Argument 0 is the first argument passed in the
775 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
778 Most of the time, output from the C routine can be handled through use of
779 the RETVAL and OUTPUT directives. However, there are some cases where the
780 argument stack is not already long enough to handle all the return values.
781 An example is the POSIX tzname() call, which takes no arguments, but returns
782 two, the local time zone's standard and summer time abbreviations.
784 To handle this situation, the PPCODE directive is used and the stack is
785 extended using the macro:
789 where C<sp> is the stack pointer, and C<num> is the number of elements the
790 stack should be extended by.
792 Now that there is room on the stack, values can be pushed on it using the
793 macros to push IV's, doubles, strings, and SV pointers respectively:
800 And now the Perl program calling C<tzname>, the two values will be assigned
803 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
805 An alternate (and possibly simpler) method to pushing values on the stack is
813 These macros automatically adjust the stack for you, if needed. Thus, you
814 do not need to call C<EXTEND> to extend the stack.
816 For more information, consult L<perlxs> and L<perlxstut>.
818 =head2 Calling Perl Routines from within C Programs
820 There are four routines that can be used to call a Perl subroutine from
821 within a C program. These four are:
823 I32 perl_call_sv(SV*, I32);
824 I32 perl_call_pv(char*, I32);
825 I32 perl_call_method(char*, I32);
826 I32 perl_call_argv(char*, I32, register char**);
828 The routine most often used is C<perl_call_sv>. The C<SV*> argument
829 contains either the name of the Perl subroutine to be called, or a
830 reference to the subroutine. The second argument consists of flags
831 that control the context in which the subroutine is called, whether
832 or not the subroutine is being passed arguments, how errors should be
833 trapped, and how to treat return values.
835 All four routines return the number of arguments that the subroutine returned
838 When using any of these routines (except C<perl_call_argv>), the programmer
839 must manipulate the Perl stack. These include the following macros and
853 For a detailed description of calling conventions from C to Perl,
856 =head2 Memory Allocation
858 It is suggested that you use the version of malloc that is distributed
859 with Perl. It keeps pools of various sizes of unallocated memory in
860 order to satisfy allocation requests more quickly. However, on some
861 platforms, it may cause spurious malloc or free errors.
863 New(x, pointer, number, type);
864 Newc(x, pointer, number, type, cast);
865 Newz(x, pointer, number, type);
867 These three macros are used to initially allocate memory.
869 The first argument C<x> was a "magic cookie" that was used to keep track
870 of who called the macro, to help when debugging memory problems. However,
871 the current code makes no use of this feature (most Perl developers now
872 use run-time memory checkers), so this argument can be any number.
874 The second argument C<pointer> should be the name of a variable that will
875 point to the newly allocated memory.
877 The third and fourth arguments C<number> and C<type> specify how many of
878 the specified type of data structure should be allocated. The argument
879 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
880 should be used if the C<pointer> argument is different from the C<type>
883 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
884 to zero out all the newly allocated memory.
886 Renew(pointer, number, type);
887 Renewc(pointer, number, type, cast);
890 These three macros are used to change a memory buffer size or to free a
891 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
892 match those of C<New> and C<Newc> with the exception of not needing the
893 "magic cookie" argument.
895 Move(source, dest, number, type);
896 Copy(source, dest, number, type);
897 Zero(dest, number, type);
899 These three macros are used to move, copy, or zero out previously allocated
900 memory. The C<source> and C<dest> arguments point to the source and
901 destination starting points. Perl will move, copy, or zero out C<number>
902 instances of the size of the C<type> data structure (using the C<sizeof>
907 The most recent development releases of Perl has been experimenting with
908 removing Perl's dependency on the "normal" standard I/O suite and allowing
909 other stdio implementations to be used. This involves creating a new
910 abstraction layer that then calls whichever implementation of stdio Perl
911 was compiled with. All XSUB's should now use the functions in the PerlIO
912 abstraction layer and not make any assumptions about what kind of stdio
915 For a complete description of the PerlIO abstraction, consult L<perlapio>.
919 =head2 Putting a C value on Perl stack
921 A lot of opcodes (this is an elementary operation in the internal perl
922 stack machine) put an SV* on the stack. However, as an optimization
923 the corresponding SV is (usually) not recreated each time. The opcodes
924 reuse specially assigned SVs (I<target>s) which are (as a corollary)
925 not constantly freed/created.
927 Each of the targets is created only once (but see
928 L<Scratchpads and recursion> below), and when an opcode needs to put
929 an integer, a double, or a string on stack, it just sets the
930 corresponding parts of its I<target> and puts the I<target> on stack.
932 The macro to put this target on stack is C<PUSHTARG>, and it is
933 directly used in some opcodes, as well as indirectly in zillions of
934 others, which use it via C<(X)PUSH[pni]>.
938 The question remains on when the SV's which are I<target>s for opcodes
939 are created. The answer is that they are created when the current unit --
940 a subroutine or a file (for opcodes for statements outside of
941 subroutines) -- is compiled. During this time a special anonymous Perl
942 array is created, which is called a scratchpad for the current
945 A scratchpad keeps SV's which are lexicals for the current unit and are
946 targets for opcodes. One can deduce that an SV lives on a scratchpad
947 by looking on its flags: lexicals have C<SVs_PADMY> set, and
948 I<target>s have C<SVs_PADTMP> set.
950 The correspondence between OP's and I<target>s is not 1-to-1. Different
951 OP's in the compile tree of the unit can use the same target, if this
952 would not conflict with the expected life of the temporary.
954 =head2 Scratchpads and recursions
956 In fact it is not 100% true that a compiled unit contains a pointer to
957 the scratchpad AV. In fact it contains a pointer to an AV of
958 (initially) one element, and this element is the scratchpad AV. Why do
959 we need an extra level of indirection?
961 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
962 these can create several execution pointers going into the same
963 subroutine. For the subroutine-child not write over the temporaries
964 for the subroutine-parent (lifespan of which covers the call to the
965 child), the parent and the child should have different
966 scratchpads. (I<And> the lexicals should be separate anyway!)
968 So each subroutine is born with an array of scratchpads (of length 1).
969 On each entry to the subroutine it is checked that the current
970 depth of the recursion is not more than the length of this array, and
971 if it is, new scratchpad is created and pushed into the array.
973 The I<target>s on this scratchpad are C<undef>s, but they are already
974 marked with correct flags.
978 This is a listing of functions, macros, flags, and variables that may be
979 useful to extension writers or that may be found while reading other
990 Clears an array, making it empty.
992 void av_clear _((AV* ar));
996 Pre-extend an array. The C<key> is the index to which the array should be
999 void av_extend _((AV* ar, I32 key));
1003 Returns the SV at the specified index in the array. The C<key> is the
1004 index. If C<lval> is set then the fetch will be part of a store. Check
1005 that the return value is non-null before dereferencing it to a C<SV*>.
1007 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1011 Returns the highest index in the array. Returns -1 if the array is empty.
1013 I32 av_len _((AV* ar));
1017 Creates a new AV and populates it with a list of SVs. The SVs are copied
1018 into the array, so they may be freed after the call to av_make. The new AV
1019 will have a reference count of 1.
1021 AV* av_make _((I32 size, SV** svp));
1025 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1028 SV* av_pop _((AV* ar));
1032 Pushes an SV onto the end of the array. The array will grow automatically
1033 to accommodate the addition.
1035 void av_push _((AV* ar, SV* val));
1039 Shifts an SV off the beginning of the array.
1041 SV* av_shift _((AV* ar));
1045 Stores an SV in an array. The array index is specified as C<key>. The
1046 return value will be null if the operation failed, otherwise it can be
1047 dereferenced to get the original C<SV*>.
1049 SV** av_store _((AV* ar, I32 key, SV* val));
1053 Undefines the array.
1055 void av_undef _((AV* ar));
1059 Unshift an SV onto the beginning of the array. The array will grow
1060 automatically to accommodate the addition.
1062 void av_unshift _((AV* ar, I32 num));
1066 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1067 constructor. This is always a C<char*>. See C<THIS> and
1068 L<perlxs/"Using XS With C++">.
1072 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1073 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1076 (void) Copy( s, d, n, t );
1080 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1081 function the same way you use the C C<printf> function. See C<warn>.
1085 Returns the stash of the CV.
1087 HV * CvSTASH( SV* sv )
1091 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1092 boolean which indicates whether subs are being single-stepped.
1093 Single-stepping is automatically turned on after every step. This is the C
1094 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1098 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1099 the SV which holds the name of the sub being debugged. This is the C
1100 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1101 The sub name can be found by
1103 SvPV( GvSV( DBsub ), na )
1107 Trace variable used when Perl is run in debugging mode, with the B<-d>
1108 switch. This is the C variable which corresponds to Perl's $DB::trace
1109 variable. See C<DBsingle>.
1113 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1118 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1122 The C variable which corresponds to Perl's $^W warning variable.
1126 Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
1130 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1131 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1132 to indicate the number of items on the stack.
1136 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1137 handled automatically by C<xsubpp>.
1141 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1142 handled automatically by C<xsubpp>.
1146 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1152 Used to extend the argument stack for an XSUB's return values.
1154 EXTEND( sp, int x );
1158 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1165 Used to indicate array context. See C<GIMME> and L<perlcall>.
1169 Indicates that arguments returned from a callback should be discarded. See
1174 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1178 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns C<G_SCALAR> or
1179 C<G_ARRAY> for scalar or array context.
1183 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1187 Used to indicate scalar context. See C<GIMME> and L<perlcall>.
1191 Returns the glob with the given C<name> and a defined subroutine or
1192 C<NULL>. The glob lives in the given C<stash>, or in the stashes accessable
1193 via @ISA and @<UNIVERSAL>.
1195 As a side-effect creates a glob with the given C<name> in the given C<stash>
1196 which in the case of success contains an alias for the subroutine, and
1197 sets up caching info for this glob. Similarly for all the searched
1200 GV* gv_fetchmeth _((HV* stash, char* name, STRLEN len, I32 level));
1202 =item gv_fetchmethod
1204 Returns the glob which contains the subroutine to call to invoke the
1205 method on the C<stash>. In fact in the presense of autoloading this may
1206 be the glob for "AUTOLOAD". In this case the corresponing variable
1207 $AUTOLOAD is already setup.
1209 Note that if you want to keep this glob for a long time, you need to
1210 check for it being "AUTOLOAD", since at the later time the the call
1211 may load a different subroutine due to $AUTOLOAD changing its value.
1212 Use the glob created via a side effect to do this.
1214 This function grants C<"SUPER"> token as prefix of name or postfix of
1217 Has the same side-effects and as C<gv_fetchmeth()>. C<name> should be
1218 writable if contains C<':'> or C<'\''>.
1220 GV* gv_fetchmethod _((HV* stash, char* name));
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, such as while iterating though the hash, but
1243 delays actual freeing of key and value until the end of the current
1244 statement (or thereabouts) with C<sv_2mortal>. See C<hv_iternext>.
1246 void he_delayfree _((HV* hv, HE* hent));
1250 Releases a hash entry, such as while iterating though the hash. See
1253 void he_free _((HV* hv, HE* hent));
1257 Clears a hash, making it empty.
1259 void hv_clear _((HV* tb));
1263 Deletes a key/value pair in the hash. The value SV is removed from the hash
1264 and returned to the caller. The C<klen> is the length of the key. The
1265 C<flags> value will normally be zero; if set to G_DISCARD then null will be
1268 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1272 Returns a boolean indicating whether the specified hash key exists. The
1273 C<klen> is the length of the key.
1275 bool hv_exists _((HV* tb, char* key, U32 klen));
1279 Returns the SV which corresponds to the specified key in the hash. The
1280 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1281 part of a store. Check that the return value is non-null before
1282 dereferencing it to a C<SV*>.
1284 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1288 Prepares a starting point to traverse a hash table.
1290 I32 hv_iterinit _((HV* tb));
1294 Returns the key from the current position of the hash iterator. See
1297 char* hv_iterkey _((HE* entry, I32* retlen));
1301 Returns entries from a hash iterator. See C<hv_iterinit>.
1303 HE* hv_iternext _((HV* tb));
1307 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1310 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1314 Returns the value from the current position of the hash iterator. See
1317 SV* hv_iterval _((HV* tb, HE* entry));
1321 Adds magic to a hash. See C<sv_magic>.
1323 void hv_magic _((HV* hv, GV* gv, int how));
1327 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1329 char *HvNAME (HV* stash)
1333 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1334 the length of the key. The C<hash> parameter is the pre-computed hash
1335 value; if it is zero then Perl will compute it. The return value will be
1336 null if the operation failed, otherwise it can be dereferenced to get the
1339 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1345 void hv_undef _((HV* tb));
1349 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
1352 int isALNUM (char c)
1356 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
1359 int isALPHA (char c)
1363 Returns a boolean indicating whether the C C<char> is an ascii digit.
1365 int isDIGIT (char c)
1369 Returns a boolean indicating whether the C C<char> is a lowercase character.
1371 int isLOWER (char c)
1375 Returns a boolean indicating whether the C C<char> is whitespace.
1377 int isSPACE (char c)
1381 Returns a boolean indicating whether the C C<char> is an uppercase character.
1383 int isUPPER (char c)
1387 Variable which is setup by C<xsubpp> to indicate the number of items on the
1388 stack. See L<perlxs/"Variable-length Parameter Lists">.
1392 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1393 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
1397 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1403 Stack marker variable for the XSUB. See C<dMARK>.
1407 Clear something magical that the SV represents. See C<sv_magic>.
1409 int mg_clear _((SV* sv));
1413 Copies the magic from one SV to another. See C<sv_magic>.
1415 int mg_copy _((SV *, SV *, char *, STRLEN));
1419 Finds the magic pointer for type matching the SV. See C<sv_magic>.
1421 MAGIC* mg_find _((SV* sv, int type));
1425 Free any magic storage used by the SV. See C<sv_magic>.
1427 int mg_free _((SV* sv));
1431 Do magic after a value is retrieved from the SV. See C<sv_magic>.
1433 int mg_get _((SV* sv));
1437 Report on the SV's length. See C<sv_magic>.
1439 U32 mg_len _((SV* sv));
1443 Turns on the magical status of an SV. See C<sv_magic>.
1445 void mg_magical _((SV* sv));
1449 Do magic after a value is assigned to the SV. See C<sv_magic>.
1451 int mg_set _((SV* sv));
1455 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
1456 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1459 (void) Move( s, d, n, t );
1463 A variable which may be used with C<SvPV> to tell Perl to calculate the
1468 The XSUB-writer's interface to the C C<malloc> function.
1470 void * New( x, void *ptr, int size, type )
1474 The XSUB-writer's interface to the C C<malloc> function, with cast.
1476 void * Newc( x, void *ptr, int size, type, cast )
1480 The XSUB-writer's interface to the C C<malloc> function. The allocated
1481 memory is zeroed with C<memzero>.
1483 void * Newz( x, void *ptr, int size, type )
1487 Creates a new AV. The reference count is set to 1.
1489 AV* newAV _((void));
1493 Creates a new HV. The reference count is set to 1.
1495 HV* newHV _((void));
1499 Creates an RV wrapper for an SV. The reference count for the original SV is
1502 SV* newRV_inc _((SV* ref));
1504 For historical reasons, "newRV" is a synonym for "newRV_inc".
1508 Creates an RV wrapper for an SV. The reference count for the original
1509 SV is B<not> incremented.
1511 SV* newRV_noinc _((SV* ref));
1515 Creates a new SV. The C<len> parameter indicates the number of bytes of
1516 pre-allocated string space the SV should have. The reference count for the
1519 SV* newSV _((STRLEN len));
1523 Creates a new SV and copies an integer into it. The reference count for the
1526 SV* newSViv _((IV i));
1530 Creates a new SV and copies a double into it. The reference count for the
1533 SV* newSVnv _((NV i));
1537 Creates a new SV and copies a string into it. The reference count for the
1538 SV is set to 1. If C<len> is zero then Perl will compute the length.
1540 SV* newSVpv _((char* s, STRLEN len));
1544 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
1545 it will be upgraded to one. If C<classname> is non-null then the new SV will
1546 be blessed in the specified package. The new SV is returned and its
1547 reference count is 1.
1549 SV* newSVrv _((SV* rv, char* classname));
1553 Creates a new SV which is an exact duplicate of the original SV.
1555 SV* newSVsv _((SV* old));
1559 Used by C<xsubpp> to hook up XSUBs as Perl subs.
1563 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
1572 Null character pointer.
1588 The original stack mark for the XSUB. See C<dORIGMARK>.
1592 Allocates a new Perl interpreter. See L<perlembed>.
1594 =item perl_call_argv
1596 Performs a callback to the specified Perl sub. See L<perlcall>.
1598 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
1600 =item perl_call_method
1602 Performs a callback to the specified Perl method. The blessed object must
1603 be on the stack. See L<perlcall>.
1605 I32 perl_call_method _((char* methname, I32 flags));
1609 Performs a callback to the specified Perl sub. See L<perlcall>.
1611 I32 perl_call_pv _((char* subname, I32 flags));
1615 Performs a callback to the Perl sub whose name is in the SV. See
1618 I32 perl_call_sv _((SV* sv, I32 flags));
1620 =item perl_construct
1622 Initializes a new Perl interpreter. See L<perlembed>.
1626 Shuts down a Perl interpreter. See L<perlembed>.
1630 Tells Perl to C<eval> the string in the SV.
1632 I32 perl_eval_sv _((SV* sv, I32 flags));
1636 Releases a Perl interpreter. See L<perlembed>.
1640 Returns the AV of the specified Perl array. If C<create> is set and the
1641 Perl variable does not exist then it will be created. If C<create> is not
1642 set and the variable does not exist then null is returned.
1644 AV* perl_get_av _((char* name, I32 create));
1648 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
1649 variable does not exist then it will be created. If C<create> is not
1650 set and the variable does not exist then null is returned.
1652 CV* perl_get_cv _((char* name, I32 create));
1656 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
1657 variable does not exist then it will be created. If C<create> is not
1658 set and the variable does not exist then null is returned.
1660 HV* perl_get_hv _((char* name, I32 create));
1664 Returns the SV of the specified Perl scalar. If C<create> is set and the
1665 Perl variable does not exist then it will be created. If C<create> is not
1666 set and the variable does not exist then null is returned.
1668 SV* perl_get_sv _((char* name, I32 create));
1672 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
1674 =item perl_require_pv
1676 Tells Perl to C<require> a module.
1678 void perl_require_pv _((char* pv));
1682 Tells a Perl interpreter to run. See L<perlembed>.
1686 Pops an integer off the stack.
1692 Pops a long off the stack.
1698 Pops a string off the stack.
1704 Pops a double off the stack.
1710 Pops an SV off the stack.
1716 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
1722 Push an integer onto the stack. The stack must have room for this element.
1729 Push a double onto the stack. The stack must have room for this element.
1736 Push a string onto the stack. The stack must have room for this element.
1737 The C<len> indicates the length of the string. See C<XPUSHp>.
1739 PUSHp(char *c, int len )
1743 Push an SV onto the stack. The stack must have room for this element. See
1750 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
1751 See C<PUSHMARK> and L<perlcall> for other uses.
1757 The XSUB-writer's interface to the C C<realloc> function.
1759 void * Renew( void *ptr, int size, type )
1763 The XSUB-writer's interface to the C C<realloc> function, with cast.
1765 void * Renewc( void *ptr, int size, type, cast )
1769 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
1770 This is always the proper type for the XSUB.
1771 See L<perlxs/"The RETVAL Variable">.
1775 The XSUB-writer's interface to the C C<free> function.
1779 The XSUB-writer's interface to the C C<malloc> function.
1783 The XSUB-writer's interface to the C C<realloc> function.
1787 Copy a string to a safe spot. This does not use an SV.
1789 char* savepv _((char* sv));
1793 Copy a string to a safe spot. The C<len> indicates number of bytes to
1794 copy. This does not use an SV.
1796 char* savepvn _((char* sv, I32 len));
1800 Opening bracket for temporaries on a callback. See C<FREETMPS> and
1807 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
1812 Re-fetch the stack pointer. Used after a callback. See L<perlcall>.
1818 Used to access elements on the XSUB's stack.
1824 Test two strings to see if they are equal. Returns true or false.
1826 int strEQ( char *s1, char *s2 )
1830 Test two strings to see if the first, C<s1>, is greater than or equal to the
1831 second, C<s2>. Returns true or false.
1833 int strGE( char *s1, char *s2 )
1837 Test two strings to see if the first, C<s1>, is greater than the second,
1838 C<s2>. Returns true or false.
1840 int strGT( char *s1, char *s2 )
1844 Test two strings to see if the first, C<s1>, is less than or equal to the
1845 second, C<s2>. Returns true or false.
1847 int strLE( char *s1, char *s2 )
1851 Test two strings to see if the first, C<s1>, is less than the second,
1852 C<s2>. Returns true or false.
1854 int strLT( char *s1, char *s2 )
1858 Test two strings to see if they are different. Returns true or false.
1860 int strNE( char *s1, char *s2 )
1864 Test two strings to see if they are equal. The C<len> parameter indicates
1865 the number of bytes to compare. Returns true or false.
1867 int strnEQ( char *s1, char *s2 )
1871 Test two strings to see if they are different. The C<len> parameter
1872 indicates the number of bytes to compare. Returns true or false.
1874 int strnNE( char *s1, char *s2, int len )
1878 Marks an SV as mortal. The SV will be destroyed when the current context
1881 SV* sv_2mortal _((SV* sv));
1885 Blesses an SV into a specified package. The SV must be an RV. The package
1886 must be designated by its stash (see C<gv_stashpv()>). The reference count
1887 of the SV is unaffected.
1889 SV* sv_bless _((SV* sv, HV* stash));
1893 Concatenates the string onto the end of the string which is in the SV.
1895 void sv_catpv _((SV* sv, char* ptr));
1899 Concatenates the string onto the end of the string which is in the SV. The
1900 C<len> indicates number of bytes to copy.
1902 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
1906 Concatenates the string from SV C<ssv> onto the end of the string in SV
1909 void sv_catsv _((SV* dsv, SV* ssv));
1913 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1914 string in C<sv1> is less than, equal to, or greater than the string in
1917 I32 sv_cmp _((SV* sv1, SV* sv2));
1921 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1922 string in C<sv1> is less than, equal to, or greater than the string in
1925 I32 sv_cmp _((SV* sv1, SV* sv2));
1929 Returns the length of the string which is in the SV. See C<SvLEN>.
1935 Set the length of the string which is in the SV. See C<SvCUR>.
1937 SvCUR_set (SV* sv, int val )
1941 Auto-decrement of the value in the SV.
1943 void sv_dec _((SV* sv));
1947 Auto-decrement of the value in the SV.
1949 void sv_dec _((SV* sv));
1953 Returns a pointer to the last character in the string which is in the SV.
1954 See C<SvCUR>. Access the character as
1960 Returns a boolean indicating whether the strings in the two SVs are
1963 I32 sv_eq _((SV* sv1, SV* sv2));
1967 Expands the character buffer in the SV. Calls C<sv_grow> to perform the
1968 expansion if necessary. Returns a pointer to the character buffer.
1970 char * SvGROW( SV* sv, int len )
1974 Expands the character buffer in the SV. This will use C<sv_unref> and will
1975 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
1980 Auto-increment of the value in the SV.
1982 void sv_inc _((SV* sv));
1986 Returns a boolean indicating whether the SV contains an integer.
1992 Unsets the IV status of an SV.
1998 Tells an SV that it is an integer.
2004 Tells an SV that it is an integer and disables all other OK bits.
2010 Tells an SV that it is an integer and disables all other OK bits.
2016 Returns a boolean indicating whether the SV contains an integer. Checks the
2017 B<private> setting. Use C<SvIOK>.
2023 Returns a boolean indicating whether the SV is blessed into the specified
2024 class. This does not know how to check for subtype, so it doesn't work in
2025 an inheritance relationship.
2027 int sv_isa _((SV* sv, char* name));
2031 Returns the integer which is in the SV.
2037 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2038 object. If the SV is not an RV, or if the object is not blessed, then this
2041 int sv_isobject _((SV* sv));
2045 Returns the integer which is stored in the SV.
2051 Returns the size of the string buffer in the SV. See C<SvCUR>.
2057 Returns the length of the string in the SV. Use C<SvCUR>.
2059 STRLEN sv_len _((SV* sv));
2063 Returns the length of the string in the SV. Use C<SvCUR>.
2065 STRLEN sv_len _((SV* sv));
2069 Adds magic to an SV.
2071 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2075 Creates a new SV which is a copy of the original SV. The new SV is marked
2078 SV* sv_mortalcopy _((SV* oldsv));
2082 Returns a boolean indicating whether the value is an SV.
2088 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2090 SV* sv_newmortal _((void));
2094 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2098 Returns a boolean indicating whether the SV contains a number, integer or
2105 Unsets the NV/IV status of an SV.
2111 Returns a boolean indicating whether the SV contains a number, integer or
2112 double. Checks the B<private> setting. Use C<SvNIOK>.
2114 int SvNIOKp (SV* SV)
2118 Returns a boolean indicating whether the SV contains a double.
2124 Unsets the NV status of an SV.
2130 Tells an SV that it is a double.
2136 Tells an SV that it is a double and disables all other OK bits.
2142 Tells an SV that it is a double and disables all other OK bits.
2148 Returns a boolean indicating whether the SV contains a double. Checks the
2149 B<private> setting. Use C<SvNOK>.
2155 Returns the double which is stored in the SV.
2157 double SvNV (SV* sv);
2161 Returns the double which is stored in the SV.
2163 double SvNVX (SV* sv);
2167 Returns a boolean indicating whether the SV contains a character string.
2173 Unsets the PV status of an SV.
2179 Tells an SV that it is a string.
2185 Tells an SV that it is a string and disables all other OK bits.
2191 Tells an SV that it is a string and disables all other OK bits.
2197 Returns a boolean indicating whether the SV contains a character string.
2198 Checks the B<private> setting. Use C<SvPOK>.
2204 Returns a pointer to the string in the SV, or a stringified form of the SV
2205 if the SV does not contain a string. If C<len> is C<na> then Perl will
2206 handle the length on its own.
2208 char * SvPV (SV* sv, int len )
2212 Returns a pointer to the string in the SV. The SV must contain a string.
2214 char * SvPVX (SV* sv)
2218 Returns the value of the object's reference count.
2220 int SvREFCNT (SV* sv);
2224 Decrements the reference count of the given SV.
2226 void SvREFCNT_dec (SV* sv)
2230 Increments the reference count of the given SV.
2232 void SvREFCNT_inc (SV* sv)
2236 Tests if the SV is an RV.
2242 Unsets the RV status of an SV.
2248 Tells an SV that it is an RV.
2254 Dereferences an RV to return the SV.
2260 Copies an integer into the given SV.
2262 void sv_setiv _((SV* sv, IV num));
2266 Copies a double into the given SV.
2268 void sv_setnv _((SV* sv, double num));
2272 Copies a string into an SV. The string must be null-terminated.
2274 void sv_setpv _((SV* sv, char* ptr));
2278 Copies a string into an SV. The C<len> parameter indicates the number of
2281 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2285 Copies an integer 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. The C<classname> argument indicates the package for the
2288 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2289 will be returned and will have a reference count of 1.
2291 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2295 Copies a double into a new SV, optionally blessing the SV. The C<rv>
2296 argument will be upgraded to an RV. That RV will be modified to point to
2297 the new SV. The C<classname> argument indicates the package for the
2298 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2299 will be returned and will have a reference count of 1.
2301 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2305 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
2306 argument will be upgraded to an RV. That RV will be modified to point to
2307 the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
2308 into the SV. The C<classname> argument indicates the package for the
2309 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2310 will be returned and will have a reference count of 1.
2312 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2314 Do not use with integral Perl types such as HV, AV, SV, CV, because those
2315 objects will become corrupted by the pointer copy process.
2317 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2321 Copies a string into a new SV, optionally blessing the SV. The length of the
2322 string must be specified with C<n>. The C<rv> argument will be upgraded to
2323 an RV. That RV will be modified to point to the new SV. The C<classname>
2324 argument indicates the package for the blessing. Set C<classname> to
2325 C<Nullch> to avoid the blessing. The new SV will be returned and will have
2326 a reference count of 1.
2328 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2330 Note that C<sv_setref_pv> copies the pointer while this copies the string.
2334 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
2335 The source SV may be destroyed if it is mortal.
2337 void sv_setsv _((SV* dsv, SV* ssv));
2341 Returns the stash of the SV.
2343 HV * SvSTASH (SV* sv)
2347 Integer type flag for scalars. See C<svtype>.
2351 Pointer type flag for scalars. See C<svtype>.
2355 Type flag for arrays. See C<svtype>.
2359 Type flag for code refs. See C<svtype>.
2363 Type flag for hashes. See C<svtype>.
2367 Type flag for blessed scalars. See C<svtype>.
2371 Double type flag for scalars. See C<svtype>.
2375 Returns a boolean indicating whether Perl would evaluate the SV as true or
2376 false, defined or undefined.
2382 Returns the type of the SV. See C<svtype>.
2384 svtype SvTYPE (SV* sv)
2388 An enum of flags for Perl types. These are found in the file B<sv.h> in the
2389 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2393 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
2394 the upgrade if necessary. See C<svtype>.
2396 bool SvUPGRADE _((SV* sv, svtype mt));
2400 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
2404 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
2408 Unsets the RV status of the SV, and decrements the reference count of
2409 whatever was being referenced by the RV. This can almost be thought of
2410 as a reversal of C<newSVrv>. See C<SvROK_off>.
2412 void sv_unref _((SV* sv));
2416 Tells an SV to use C<ptr> to find its string value. Normally the string is
2417 stored inside the SV but sv_usepvn allows the SV to use an outside string.
2418 The C<ptr> should point to memory that was allocated by C<malloc>. The
2419 string length, C<len>, must be supplied. This function will realloc the
2420 memory pointed to by C<ptr>, so that pointer should not be freed or used by
2421 the programmer after giving it to sv_usepvn.
2423 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
2427 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
2431 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
2432 This is always the proper type for the C++ object. See C<CLASS> and
2433 L<perlxs/"Using XS With C++">.
2437 Converts the specified character to lowercase.
2439 int toLOWER (char c)
2443 Converts the specified character to uppercase.
2445 int toUPPER (char c)
2449 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
2450 function the same way you use the C C<printf> function. See C<croak()>.
2454 Push an integer onto the stack, extending the stack if necessary. See
2461 Push a double onto the stack, extending the stack if necessary. See
2468 Push a string onto the stack, extending the stack if necessary. The C<len>
2469 indicates the length of the string. See C<PUSHp>.
2471 XPUSHp(char *c, int len)
2475 Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
2481 Macro to declare an XSUB and its C parameter list. This is handled by
2486 Return from XSUB, indicating number of items on the stack. This is usually
2487 handled by C<xsubpp>.
2491 =item XSRETURN_EMPTY
2493 Return an empty list from an XSUB immediately.
2499 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
2505 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
2511 Return an double from an XSUB immediately. Uses C<XST_mNV>.
2517 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
2519 XSRETURN_PV(char *v);
2521 =item XSRETURN_UNDEF
2523 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
2529 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
2535 Place an integer into the specified position C<i> on the stack. The value is
2536 stored in a new mortal SV.
2538 XST_mIV( int i, IV v );
2542 Place a double into the specified position C<i> on the stack. The value is
2543 stored in a new mortal SV.
2545 XST_mNV( int i, NV v );
2549 Place C<&sv_no> into the specified position C<i> on the stack.
2555 Place a copy of a string into the specified position C<i> on the stack. The
2556 value is stored in a new mortal SV.
2558 XST_mPV( int i, char *v );
2562 Place C<&sv_undef> into the specified position C<i> on the stack.
2564 XST_mUNDEF( int i );
2568 Place C<&sv_yes> into the specified position C<i> on the stack.
2574 The version identifier for an XS module. This is usually handled
2575 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
2577 =item XS_VERSION_BOOTCHECK
2579 Macro to verify that a PM module's $VERSION variable matches the XS module's
2580 C<XS_VERSION> variable. This is usually handled automatically by
2581 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
2585 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
2586 destination, C<n> is the number of items, and C<t> is the type.
2588 (void) Zero( d, n, t );
2594 Jeff Okamoto <okamoto@corp.hp.com>
2596 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
2597 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
2598 Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
2600 API Listing by Dean Roehrich <roehrich@cray.com>.
2604 Version 30: 1997/1/17