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 simply 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
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 just 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 just
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 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 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
335 reference count of C<thing>, while C<newRV_noinc> does not. (For
336 historical reasons, "newRV" is a synonym for "newRV_inc".) Once you
337 have a reference, you can use the following macro to dereference the
342 then call the appropriate routines, casting the returned C<SV*> to either an
343 C<AV*> or C<HV*>, if required.
345 To determine if an SV is a reference, you can use the following macro:
349 To discover what type of value the reference refers to, you must use the
350 following macro and then check the value returned.
354 The most useful types that will be returned are:
363 SVt_PVGV Glob (possible a file handle)
364 SVt_PVMG Blessed or Magical Scalar
366 See the sv.h header file for more details.
368 =head2 Blessed References and Class Objects
370 References are also used to support object-oriented programming. In the
371 OO lexicon, an object is simply a reference that has been blessed into a
372 package (or class). Once blessed, the programmer may now use the reference
373 to access the various methods in the class.
375 A reference can be blessed into a package with the following function:
377 SV* sv_bless(SV* sv, HV* stash);
379 The C<sv> argument must be a reference. The C<stash> argument specifies
380 which class the reference will belong to. See the section on L<Stashes>
381 for information on converting class names into stashes.
383 /* Still under construction */
385 Upgrades rv to reference if not already one. Creates new SV for rv to
387 If classname is non-null, the SV is blessed into the specified class.
390 SV* newSVrv(SV* rv, char* classname);
392 Copies integer or double into an SV whose reference is rv. SV is blessed
393 if 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 classname is non-null.
401 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
403 Copies string into an SV whose reference is rv.
404 Set length to 0 to let Perl calculate the string length.
405 SV is blessed if classname is non-null.
407 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
409 int sv_isa(SV* sv, char* name);
410 int sv_isobject(SV* sv);
412 =head2 Creating New Variables
414 To create a new Perl variable with an undef value which can be accessed from
415 your Perl script, use the following routines, depending on the variable type.
417 SV* perl_get_sv("package::varname", TRUE);
418 AV* perl_get_av("package::varname", TRUE);
419 HV* perl_get_hv("package::varname", TRUE);
421 Notice the use of TRUE as the second parameter. The new variable can now
422 be set, using the routines appropriate to the data type.
424 There are additional macros whose values may be bitwise OR'ed with the
425 C<TRUE> argument to enable certain extra features. Those bits are:
427 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
428 "Indentifier <varname> used only once: possible typo" warning.
429 GV_ADDWARN Issues a "Had to create <varname> unexpectedly" warning if
430 the variable didn't actually exist. This is useful if
431 you expected the variable to exist already and want to
432 propagate this warning back to the user.
434 If the C<varname> argument does not contain a package specifier, it is
435 created in the current package.
437 =head2 Reference Counts and Mortality
439 Perl uses an reference count-driven garbage collection mechanism. SV's,
440 AV's, or HV's (xV for short in the following) start their life with a
441 reference count of 1. If the reference count of an xV ever drops to 0,
442 then they will be destroyed and their memory made available for reuse.
444 This normally doesn't happen at the Perl level unless a variable is
445 undef'ed or the last variable holding a reference to it is changed or
446 overwritten. At the internal level, however, reference counts can be
447 manipulated with the following macros:
449 int SvREFCNT(SV* sv);
450 SV* SvREFCNT_inc(SV* sv);
451 void SvREFCNT_dec(SV* sv);
453 However, there is one other function which manipulates the reference
454 count of its argument. The C<newRV_inc> function, as you should
455 recall, creates a reference to the specified argument. As a side
456 effect, it increments the argument's reference count. If this is not
457 what you want, use C<newRV_noinc> instead.
459 For example, imagine you want to return a reference from an XSUB
460 function. You create a new SV which initially has a reference count
461 of one. Then you call C<newRV_inc>, passing the just-created SV.
462 This returns the reference as a new SV, but the reference count of the
463 SV you passed to C<newRV_inc> has been incremented to two. Now you
464 return the reference and forget about the SV. But Perl hasn't!
465 Whenever the returned reference is destroyed, the reference count of
466 the original SV is decreased to one and nothing happens. The SV will
467 hang around without any way to access it until Perl itself terminates.
468 This is a memory leak.
470 The correct procedure, then, is to use C<newRV_noinc> instead of
471 C<newRV_inc>. Then, if and when the last reference is destroyed, the
472 reference count of the SV will go to 0 and also be destroyed, stopping
475 There are some convenience functions available that can help with the
476 destruction of old xV objects. These functions introduce the concept
477 of "mortality". An xV that is mortal has had its reference count
478 marked to be decremented, but not actually decremented, until "a short
479 time later". Generally the term "short time later" means a single
480 Perl statement, such as a call to an XSUB function. The actual
481 determinant for when mortal xV's have their reference count
482 decremented depends on two macros, SAVETMPS and FREETMPS. Take a look
483 at L<perlcall> and L<perlxs> for more details on these macros.
485 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
486 However, if you mortalize a variable twice, the reference count will
487 later be decremented twice.
489 You should be careful about creating mortal variables. Strange things
490 can happen if you make the same value mortal within multiple contexts,
491 or if you make a variable mortal multiple times.
493 To create a mortal variable, use the functions:
497 SV* sv_mortalcopy(SV*)
499 The first call creates a mortal SV, the second converts an existing
500 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
501 third creates a mortal copy of an existing SV.
503 The mortal routines are not for just SV's -- AV's and HV's can be made
504 mortal by passing their address (casted to C<SV*>) to the C<sv_2mortal> or
505 C<sv_mortalcopy> routines.
507 =head2 Stashes and Globs
509 A stash is a hash table (associative array) that contains all of the
510 different objects that are contained within a package. Each key of the
511 stash is a symbol name (shared by all the different types of objects
512 that have the same name), and each value in the hash table is called a
513 GV (for Glob Value). This GV in turn contains references to the various
514 objects of that name, including (but not limited to) the following:
524 There is a single stash called "defstash" that holds the items that exist
525 in the "main" package. To get at the items in other packages, append the
526 string "::" to the package name. The items in the "Foo" package are in
527 the stash "Foo::" in defstash. The items in the "Bar::Baz" package are
528 in the stash "Baz::" in "Bar::"'s stash.
530 To get the stash pointer for a particular package, use the function:
532 HV* gv_stashpv(char* name, I32 create)
533 HV* gv_stashsv(SV*, I32 create)
535 The first function takes a literal string, the second uses the string stored
536 in the SV. Remember that a stash is just a hash table, so you get back an
537 C<HV*>. The C<create> flag will create a new package if it is set.
539 The name that C<gv_stash*v> wants is the name of the package whose symbol table
540 you want. The default package is called C<main>. If you have multiply nested
541 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
544 Alternately, if you have an SV that is a blessed reference, you can find
545 out the stash pointer by using:
547 HV* SvSTASH(SvRV(SV*));
549 then use the following to get the package name itself:
551 char* HvNAME(HV* stash);
553 If you need to bless or re-bless an object you can use the following
556 SV* sv_bless(SV*, HV* stash)
558 where the first argument, an C<SV*>, must be a reference, and the second
559 argument is a stash. The returned C<SV*> can now be used in the same way
562 For more information on references and blessings, consult L<perlref>.
566 [This section still under construction. Ignore everything here. Post no
567 bills. Everything not permitted is forbidden.]
569 Any SV may be magical, that is, it has special features that a normal
570 SV does not have. These features are stored in the SV structure in a
571 linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
584 Note this is current as of patchlevel 0, and could change at any time.
586 =head2 Assigning Magic
588 Perl adds magic to an SV using the sv_magic function:
590 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
592 The C<sv> argument is a pointer to the SV that is to acquire a new magical
595 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
596 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
597 it to the beginning of the linked list of magical features. Any prior
598 entry of the same type of magic is deleted. Note that this can be
599 overridden, and multiple instances of the same type of magic can be
600 associated with an SV.
602 The C<name> and C<namlem> arguments are used to associate a string with
603 the magic, typically the name of a variable. C<namlem> is stored in the
604 C<mg_len> field and if C<name> is non-null and C<namlem> >= 0 a malloc'd
605 copy of the name is stored in C<mg_ptr> field.
607 The sv_magic function uses C<how> to determine which, if any, predefined
608 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
609 See the "Magic Virtual Table" section below. The C<how> argument is also
610 stored in the C<mg_type> field.
612 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
613 structure. If it is not the same as the C<sv> argument, the reference
614 count of the C<obj> object is incremented. If it is the same, or if
615 the C<how> argument is "#", or if it is a null pointer, then C<obj> is
616 merely stored, without the reference count being incremented.
618 There is also a function to add magic to an C<HV>:
620 void hv_magic(HV *hv, GV *gv, int how);
622 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
624 To remove the magic from an SV, call the function sv_unmagic:
626 void sv_unmagic(SV *sv, int type);
628 The C<type> argument should be equal to the C<how> value when the C<SV>
629 was initially made magical.
631 =head2 Magic Virtual Tables
633 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
634 C<MGVTBL>, which is a structure of function pointers and stands for
635 "Magic Virtual Table" to handle the various operations that might be
636 applied to that variable.
638 The C<MGVTBL> has five pointers to the following routine types:
640 int (*svt_get)(SV* sv, MAGIC* mg);
641 int (*svt_set)(SV* sv, MAGIC* mg);
642 U32 (*svt_len)(SV* sv, MAGIC* mg);
643 int (*svt_clear)(SV* sv, MAGIC* mg);
644 int (*svt_free)(SV* sv, MAGIC* mg);
646 This MGVTBL structure is set at compile-time in C<perl.h> and there are
647 currently 19 types (or 21 with overloading turned on). These different
648 structures contain pointers to various routines that perform additional
649 actions depending on which function is being called.
651 Function pointer Action taken
652 ---------------- ------------
653 svt_get Do something after the value of the SV is retrieved.
654 svt_set Do something after the SV is assigned a value.
655 svt_len Report on the SV's length.
656 svt_clear Clear something the SV represents.
657 svt_free Free any extra storage associated with the SV.
659 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
660 to an C<mg_type> of '\0') contains:
662 { magic_get, magic_set, magic_len, 0, 0 }
664 Thus, when an SV is determined to be magical and of type '\0', if a get
665 operation is being performed, the routine C<magic_get> is called. All
666 the various routines for the various magical types begin with C<magic_>.
668 The current kinds of Magic Virtual Tables are:
670 mg_type MGVTBL Type of magic
671 ------- ------ ----------------------------
673 A vtbl_amagic Operator Overloading
674 a vtbl_amagicelem Operator Overloading
675 c 0 Used in Operator Overloading
676 B vtbl_bm Boyer-Moore???
678 e vtbl_envelem %ENV hash element
679 g vtbl_mglob Regexp /g flag???
680 I vtbl_isa @ISA array
681 i vtbl_isaelem @ISA array element
682 L 0 (but sets RMAGICAL) Perl Module/Debugger???
683 l vtbl_dbline Debugger?
684 P vtbl_pack Tied Array or Hash
685 p vtbl_packelem Tied Array or Hash element
686 q vtbl_packelem Tied Scalar or Handle
687 S vtbl_sig Signal Hash
688 s vtbl_sigelem Signal Hash element
689 t vtbl_taint Taintedness
692 x vtbl_substr Substring???
694 # vtbl_arylen Array Length
695 . vtbl_pos $. scalar variable
696 ~ None Used by certain extensions
698 When an upper-case and lower-case letter both exist in the table, then the
699 upper-case letter is used to represent some kind of composite type (a list
700 or a hash), and the lower-case letter is used to represent an element of
703 The '~' magic type is defined specifically for use by extensions and
704 will not be used by perl itself. Extensions can use ~ magic to 'attach'
705 private information to variables (typically objects). This is especially
706 useful because there is no way for normal perl code to corrupt this
707 private information (unlike using extra elements of a hash object).
709 Note that because multiple extensions may be using ~ magic it is
710 important for extensions to take extra care with it. Typically only
711 using it on objects blessed into the same class as the extension
712 is sufficient. It may also be appropriate to add an I32 'signature'
713 at the top of the private data area and check that.
717 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
719 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
720 If the SV does not have that magical feature, C<NULL> is returned. Also,
721 if the SV is not of type SVt_PVMG, Perl may core-dump.
723 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
725 This routine checks to see what types of magic C<sv> has. If the mg_type
726 field is an upper-case letter, then the mg_obj is copied to C<nsv>, but
727 the mg_type field is changed to be the lower-case letter.
729 =head2 Double-Typed SV's
731 Scalar variables normally contain only one type of value, an integer,
732 double, pointer, or reference. Perl will automatically convert the
733 actual scalar data from the stored type into the requested type.
735 Some scalar variables contain more than one type of scalar data. For
736 example, the variable C<$!> contains either the numeric value of C<errno>
737 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
739 To force multiple data values into an SV, you must do two things: use the
740 C<sv_set*v> routines to add the additional scalar type, then set a flag
741 so that Perl will believe it contains more than one type of data. The
742 four macros to set the flags are:
749 The particular macro you must use depends on which C<sv_set*v> routine
750 you called first. This is because every C<sv_set*v> routine turns on
751 only the bit for the particular type of data being set, and turns off
754 For example, to create a new Perl variable called "dberror" that contains
755 both the numeric and descriptive string error values, you could use the
759 extern char *dberror_list;
761 SV* sv = perl_get_sv("dberror", TRUE);
762 sv_setiv(sv, (IV) dberror);
763 sv_setpv(sv, dberror_list[dberror]);
766 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
767 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
769 =head2 XSUB's and the Argument Stack
771 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
772 An XSUB routine will have a stack that contains the arguments from the Perl
773 program, and a way to map from the Perl data structures to a C equivalent.
775 The stack arguments are accessible through the C<ST(n)> macro, which returns
776 the C<n>'th stack argument. Argument 0 is the first argument passed in the
777 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
780 Most of the time, output from the C routine can be handled through use of
781 the RETVAL and OUTPUT directives. However, there are some cases where the
782 argument stack is not already long enough to handle all the return values.
783 An example is the POSIX tzname() call, which takes no arguments, but returns
784 two, the local time zone's standard and summer time abbreviations.
786 To handle this situation, the PPCODE directive is used and the stack is
787 extended using the macro:
791 where C<sp> is the stack pointer, and C<num> is the number of elements the
792 stack should be extended by.
794 Now that there is room on the stack, values can be pushed on it using the
795 macros to push IV's, doubles, strings, and SV pointers respectively:
802 And now the Perl program calling C<tzname>, the two values will be assigned
805 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
807 An alternate (and possibly simpler) method to pushing values on the stack is
815 These macros automatically adjust the stack for you, if needed. Thus, you
816 do not need to call C<EXTEND> to extend the stack.
818 For more information, consult L<perlxs> and L<perlxstut>.
820 =head2 Calling Perl Routines from within C Programs
822 There are four routines that can be used to call a Perl subroutine from
823 within a C program. These four are:
825 I32 perl_call_sv(SV*, I32);
826 I32 perl_call_pv(char*, I32);
827 I32 perl_call_method(char*, I32);
828 I32 perl_call_argv(char*, I32, register char**);
830 The routine most often used is C<perl_call_sv>. The C<SV*> argument
831 contains either the name of the Perl subroutine to be called, or a
832 reference to the subroutine. The second argument consists of flags
833 that control the context in which the subroutine is called, whether
834 or not the subroutine is being passed arguments, how errors should be
835 trapped, and how to treat return values.
837 All four routines return the number of arguments that the subroutine returned
840 When using any of these routines (except C<perl_call_argv>), the programmer
841 must manipulate the Perl stack. These include the following macros and
855 For a detailed description of calling conventions from C to Perl,
858 =head2 Memory Allocation
860 It is suggested that you use the version of malloc that is distributed
861 with Perl. It keeps pools of various sizes of unallocated memory in
862 satisfy allocation requests more quickly. However, on some platforms, it
863 may cause spurious malloc or free errors.
865 New(x, pointer, number, type);
866 Newc(x, pointer, number, type, cast);
867 Newz(x, pointer, number, type);
869 These three macros are used to allocate memory.
871 The first argument C<x> was a "magic cookie" that was used to keep track
872 of who called the macro, to help when debugging memory problems. However,
873 the current code makes no use of this feature (Larry has switched to using
874 a run-time memory checker), so this argument can be any number.
876 The second argument C<pointer> should be the name of a variable that will
877 point to the newly allocated memory.
879 The third and fourth arguments C<number> and C<type> specify how many of
880 the specified type of data structure should be allocated. The argument
881 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
882 should be used if the C<pointer> argument is different from the C<type>
885 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
886 to zero out all the newly allocated memory.
888 Renew(pointer, number, type);
889 Renewc(pointer, number, type, cast);
892 These three macros are used to change a memory buffer size or to free a
893 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
894 match those of C<New> and C<Newc> with the exception of not needing the
895 "magic cookie" argument.
897 Move(source, dest, number, type);
898 Copy(source, dest, number, type);
899 Zero(dest, number, type);
901 These three macros are used to move, copy, or zero out previously allocated
902 memory. The C<source> and C<dest> arguments point to the source and
903 destination starting points. Perl will move, copy, or zero out C<number>
904 instances of the size of the C<type> data structure (using the C<sizeof>
909 The most recent development releases of Perl has been experimenting with
910 removing Perl's dependency on the "normal" standard I/O suite and allowing
911 other stdio implementations to be used. This involves creating a new
912 abstraction layer that then calls whichever implementation of stdio Perl
913 was compiled with. All XSUB's should now use the functions in the PerlIO
914 abstraction layer and not make any assumptions about what kind of stdio
917 For a complete description of the PerlIO abstraction, consult L<perlapio>.
921 =head3 Putting a C value on Perl stack
923 A lot of opcodes (this is an elementary operation in the internal perl
924 stack machine) put an SV* on the stack. However, as an optimization
925 the corresponding SV is (usually) not recreated each time. The opcodes
926 reuse specially assigned SVs (I<target>s) which are (as a corollary)
927 not constantly freed/created.
929 Each of the targets is created only once (but see
930 L<Scratchpads and recursion> below), and when an opcode needs to put
931 an integer, a double, or a string on stack, it just sets the
932 corresponding parts of its I<target> and puts the I<target> on stack.
934 The macro to put this target on stack is C<PUSHTARG>, and it is
935 directly used in some opcodes, as well as indirectly in zillions of
936 others, which use it via C<(X)PUSH[pni]>.
940 The question remains on when the SV's which are I<target>s for opcodes
941 are created. The answer is that they are created when the current unit --
942 a subroutine or a file (for opcodes for statements outside of
943 subroutines) -- is compiled. During this time a special anonymous Perl
944 array is created, which is called a scratchpad for the current
947 A scratchpad keeps SV's which are lexicals for the current unit and are
948 targets for opcodes. One can deduce that an SV lives on a scratchpad
949 by looking on its flags: lexicals have C<SVs_PADMY> set, and
950 I<target>s have C<SVs_PADTMP> set.
952 The correspondence between OP's and I<target>s is not 1-to-1. Different
953 OP's in the compile tree of the unit can use the same target, if this
954 would not conflict with the expected life of the temporary.
956 =head3 Scratchpads and recursions
958 In fact it is not 100% true that a compiled unit contains a pointer to
959 the scratchpad AV. In fact it contains a pointer to an AV of
960 (initially) one element, and this element is the scratchpad AV. Why do
961 we need an extra level of indirection?
963 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
964 these can create several execution pointers going into the same
965 subroutine. For the subroutine-child not write over the temporaries
966 for the subroutine-parent (lifespan of which covers the call to the
967 child), the parent and the child should have different
968 scratchpads. (I<And> the lexicals should be separate anyway!)
970 So each subroutine is born with an array of scratchpads (of length 1).
971 On each entry to the subroutine it is checked that the current
972 depth of the recursion is not more than the length of this array, and
973 if it is, new scratchpad is created and pushed into the array.
975 The I<target>s on this scratchpad are C<undef>s, but they are already
976 marked with correct flags.
980 This is a listing of functions, macros, flags, and variables that may be
981 useful to extension writers or that may be found while reading other
992 Clears an array, making it empty.
994 void av_clear _((AV* ar));
998 Pre-extend an array. The C<key> is the index to which the array should be
1001 void av_extend _((AV* ar, I32 key));
1005 Returns the SV at the specified index in the array. The C<key> is the
1006 index. If C<lval> is set then the fetch will be part of a store. Check
1007 that the return value is non-null before dereferencing it to a C<SV*>.
1009 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1013 Returns the highest index in the array. Returns -1 if the array is empty.
1015 I32 av_len _((AV* ar));
1019 Creates a new AV and populates it with a list of SVs. The SVs are copied
1020 into the array, so they may be freed after the call to av_make. The new AV
1021 will have a reference count of 1.
1023 AV* av_make _((I32 size, SV** svp));
1027 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1030 SV* av_pop _((AV* ar));
1034 Pushes an SV onto the end of the array. The array will grow automatically
1035 to accommodate the addition.
1037 void av_push _((AV* ar, SV* val));
1041 Shifts an SV off the beginning of the array.
1043 SV* av_shift _((AV* ar));
1047 Stores an SV in an array. The array index is specified as C<key>. The
1048 return value will be null if the operation failed, otherwise it can be
1049 dereferenced to get the original C<SV*>.
1051 SV** av_store _((AV* ar, I32 key, SV* val));
1055 Undefines the array.
1057 void av_undef _((AV* ar));
1061 Unshift an SV onto the beginning of the array. The array will grow
1062 automatically to accommodate the addition.
1064 void av_unshift _((AV* ar, I32 num));
1068 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1069 constructor. This is always a C<char*>. See C<THIS> and
1070 L<perlxs/"Using XS With C++">.
1074 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1075 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1078 (void) Copy( s, d, n, t );
1082 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1083 function the same way you use the C C<printf> function. See C<warn>.
1087 Returns the stash of the CV.
1089 HV * CvSTASH( SV* sv )
1093 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1094 boolean which indicates whether subs are being single-stepped.
1095 Single-stepping is automatically turned on after every step. This is the C
1096 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1100 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1101 the SV which holds the name of the sub being debugged. This is the C
1102 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1103 The sub name can be found by
1105 SvPV( GvSV( DBsub ), na )
1109 Trace variable used when Perl is run in debugging mode, with the B<-d>
1110 switch. This is the C variable which corresponds to Perl's $DB::trace
1111 variable. See C<DBsingle>.
1115 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1120 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1124 The C variable which corresponds to Perl's $^W warning variable.
1128 Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
1132 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1133 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1134 to indicate the number of items on the stack.
1138 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1139 handled automatically by C<xsubpp>.
1143 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1144 handled automatically by C<xsubpp>.
1148 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1154 Used to extend the argument stack for an XSUB's return values.
1156 EXTEND( sp, int x );
1160 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1167 Used to indicate array context. See C<GIMME> and L<perlcall>.
1171 Indicates that arguments returned from a callback should be discarded. See
1176 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1180 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns C<G_SCALAR> or
1181 C<G_ARRAY> for scalar or array context.
1185 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1189 Used to indicate scalar context. See C<GIMME> and L<perlcall>.
1193 Returns a pointer to the stash for a specified package. If C<create> is set
1194 then the package will be created if it does not already exist. If C<create>
1195 is not set and the package does not exist then NULL is returned.
1197 HV* gv_stashpv _((char* name, I32 create));
1201 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1203 HV* gv_stashsv _((SV* sv, I32 create));
1207 Return the SV from the GV.
1211 Releases a hash entry from an iterator. See C<hv_iternext>.
1215 Clears a hash, making it empty.
1217 void hv_clear _((HV* tb));
1221 Deletes a key/value pair in the hash. The value SV is removed from the hash
1222 and returned to the caller. The C<klen> is the length of the key. The
1223 C<flags> value will normally be zero; if set to G_DISCARD then null will be
1226 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1230 Returns a boolean indicating whether the specified hash key exists. The
1231 C<klen> is the length of the key.
1233 bool hv_exists _((HV* tb, char* key, U32 klen));
1237 Returns the SV which corresponds to the specified key in the hash. The
1238 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1239 part of a store. Check that the return value is non-null before
1240 dereferencing it to a C<SV*>.
1242 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1246 Prepares a starting point to traverse a hash table.
1248 I32 hv_iterinit _((HV* tb));
1252 Returns the key from the current position of the hash iterator. See
1255 char* hv_iterkey _((HE* entry, I32* retlen));
1259 Returns entries from a hash iterator. See C<hv_iterinit>.
1261 HE* hv_iternext _((HV* tb));
1265 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1268 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1272 Returns the value from the current position of the hash iterator. See
1275 SV* hv_iterval _((HV* tb, HE* entry));
1279 Adds magic to a hash. See C<sv_magic>.
1281 void hv_magic _((HV* hv, GV* gv, int how));
1285 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1287 char *HvNAME (HV* stash)
1291 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1292 the length of the key. The C<hash> parameter is the pre-computed hash
1293 value; if it is zero then Perl will compute it. The return value will be
1294 null if the operation failed, otherwise it can be dereferenced to get the
1297 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1303 void hv_undef _((HV* tb));
1307 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
1310 int isALNUM (char c)
1314 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
1317 int isALPHA (char c)
1321 Returns a boolean indicating whether the C C<char> is an ascii digit.
1323 int isDIGIT (char c)
1327 Returns a boolean indicating whether the C C<char> is a lowercase character.
1329 int isLOWER (char c)
1333 Returns a boolean indicating whether the C C<char> is whitespace.
1335 int isSPACE (char c)
1339 Returns a boolean indicating whether the C C<char> is an uppercase character.
1341 int isUPPER (char c)
1345 Variable which is setup by C<xsubpp> to indicate the number of items on the
1346 stack. See L<perlxs/"Variable-length Parameter Lists">.
1350 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1351 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
1355 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1361 Stack marker variable for the XSUB. See C<dMARK>.
1365 Clear something magical that the SV represents. See C<sv_magic>.
1367 int mg_clear _((SV* sv));
1371 Copies the magic from one SV to another. See C<sv_magic>.
1373 int mg_copy _((SV *, SV *, char *, STRLEN));
1377 Finds the magic pointer for type matching the SV. See C<sv_magic>.
1379 MAGIC* mg_find _((SV* sv, int type));
1383 Free any magic storage used by the SV. See C<sv_magic>.
1385 int mg_free _((SV* sv));
1389 Do magic after a value is retrieved from the SV. See C<sv_magic>.
1391 int mg_get _((SV* sv));
1395 Report on the SV's length. See C<sv_magic>.
1397 U32 mg_len _((SV* sv));
1401 Turns on the magical status of an SV. See C<sv_magic>.
1403 void mg_magical _((SV* sv));
1407 Do magic after a value is assigned to the SV. See C<sv_magic>.
1409 int mg_set _((SV* sv));
1413 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
1414 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1417 (void) Move( s, d, n, t );
1421 A variable which may be used with C<SvPV> to tell Perl to calculate the
1426 The XSUB-writer's interface to the C C<malloc> function.
1428 void * New( x, void *ptr, int size, type )
1432 The XSUB-writer's interface to the C C<malloc> function, with cast.
1434 void * Newc( x, void *ptr, int size, type, cast )
1438 The XSUB-writer's interface to the C C<malloc> function. The allocated
1439 memory is zeroed with C<memzero>.
1441 void * Newz( x, void *ptr, int size, type )
1445 Creates a new AV. The reference count is set to 1.
1447 AV* newAV _((void));
1451 Creates a new HV. The reference count is set to 1.
1453 HV* newHV _((void));
1457 Creates an RV wrapper for an SV. The reference count for the original SV is
1460 SV* newRV_inc _((SV* ref));
1462 For historical reasons, "newRV" is a synonym for "newRV_inc".
1466 Creates an RV wrapper for an SV. The reference count for the original
1467 SV is B<not> incremented.
1469 SV* newRV_noinc _((SV* ref));
1473 Creates a new SV. The C<len> parameter indicates the number of bytes of
1474 pre-allocated string space the SV should have. The reference count for the new SV
1477 SV* newSV _((STRLEN len));
1481 Creates a new SV and copies an integer into it. The reference count for the SV is
1484 SV* newSViv _((IV i));
1488 Creates a new SV and copies a double into it. The reference count for the SV is
1491 SV* newSVnv _((NV i));
1495 Creates a new SV and copies a string into it. The reference count for the SV is
1496 set to 1. If C<len> is zero then Perl will compute the length.
1498 SV* newSVpv _((char* s, STRLEN len));
1502 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
1503 it will be upgraded to one. If C<classname> is non-null then the new SV will
1504 be blessed in the specified package. The new SV is returned and its
1505 reference count is 1.
1507 SV* newSVrv _((SV* rv, char* classname));
1511 Creates a new SV which is an exact duplicate of the original SV.
1513 SV* newSVsv _((SV* old));
1517 Used by C<xsubpp> to hook up XSUBs as Perl subs.
1521 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
1530 Null character pointer.
1546 The original stack mark for the XSUB. See C<dORIGMARK>.
1550 Allocates a new Perl interpreter. See L<perlembed>.
1552 =item perl_call_argv
1554 Performs a callback to the specified Perl sub. See L<perlcall>.
1556 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
1558 =item perl_call_method
1560 Performs a callback to the specified Perl method. The blessed object must
1561 be on the stack. See L<perlcall>.
1563 I32 perl_call_method _((char* methname, I32 flags));
1567 Performs a callback to the specified Perl sub. See L<perlcall>.
1569 I32 perl_call_pv _((char* subname, I32 flags));
1573 Performs a callback to the Perl sub whose name is in the SV. See
1576 I32 perl_call_sv _((SV* sv, I32 flags));
1578 =item perl_construct
1580 Initializes a new Perl interpreter. See L<perlembed>.
1584 Shuts down a Perl interpreter. See L<perlembed>.
1588 Tells Perl to C<eval> the string in the SV.
1590 I32 perl_eval_sv _((SV* sv, I32 flags));
1594 Releases a Perl interpreter. See L<perlembed>.
1598 Returns the AV of the specified Perl array. If C<create> is set and the
1599 Perl variable does not exist then it will be created. If C<create> is not
1600 set and the variable does not exist then null is returned.
1602 AV* perl_get_av _((char* name, I32 create));
1606 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
1607 variable does not exist then it will be created. If C<create> is not
1608 set and the variable does not exist then null is returned.
1610 CV* perl_get_cv _((char* name, I32 create));
1614 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
1615 variable does not exist then it will be created. If C<create> is not
1616 set and the variable does not exist then null is returned.
1618 HV* perl_get_hv _((char* name, I32 create));
1622 Returns the SV of the specified Perl scalar. If C<create> is set and the
1623 Perl variable does not exist then it will be created. If C<create> is not
1624 set and the variable does not exist then null is returned.
1626 SV* perl_get_sv _((char* name, I32 create));
1630 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
1632 =item perl_require_pv
1634 Tells Perl to C<require> a module.
1636 void perl_require_pv _((char* pv));
1640 Tells a Perl interpreter to run. See L<perlembed>.
1644 Pops an integer off the stack.
1650 Pops a long off the stack.
1656 Pops a string off the stack.
1662 Pops a double off the stack.
1668 Pops an SV off the stack.
1674 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
1680 Push an integer onto the stack. The stack must have room for this element.
1687 Push a double onto the stack. The stack must have room for this element.
1694 Push a string onto the stack. The stack must have room for this element.
1695 The C<len> indicates the length of the string. See C<XPUSHp>.
1697 PUSHp(char *c, int len )
1701 Push an SV onto the stack. The stack must have room for this element. See
1708 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
1709 See C<PUSHMARK> and L<perlcall> for other uses.
1715 The XSUB-writer's interface to the C C<realloc> function.
1717 void * Renew( void *ptr, int size, type )
1721 The XSUB-writer's interface to the C C<realloc> function, with cast.
1723 void * Renewc( void *ptr, int size, type, cast )
1727 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
1728 This is always the proper type for the XSUB.
1729 See L<perlxs/"The RETVAL Variable">.
1733 The XSUB-writer's interface to the C C<free> function.
1737 The XSUB-writer's interface to the C C<malloc> function.
1741 The XSUB-writer's interface to the C C<realloc> function.
1745 Copy a string to a safe spot. This does not use an SV.
1747 char* savepv _((char* sv));
1751 Copy a string to a safe spot. The C<len> indicates number of bytes to
1752 copy. This does not use an SV.
1754 char* savepvn _((char* sv, I32 len));
1758 Opening bracket for temporaries on a callback. See C<FREETMPS> and
1765 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
1770 Re-fetch the stack pointer. Used after a callback. See L<perlcall>.
1776 Used to access elements on the XSUB's stack.
1782 Test two strings to see if they are equal. Returns true or false.
1784 int strEQ( char *s1, char *s2 )
1788 Test two strings to see if the first, C<s1>, is greater than or equal to the
1789 second, C<s2>. Returns true or false.
1791 int strGE( char *s1, char *s2 )
1795 Test two strings to see if the first, C<s1>, is greater than the second,
1796 C<s2>. Returns true or false.
1798 int strGT( char *s1, char *s2 )
1802 Test two strings to see if the first, C<s1>, is less than or equal to the
1803 second, C<s2>. Returns true or false.
1805 int strLE( char *s1, char *s2 )
1809 Test two strings to see if the first, C<s1>, is less than the second,
1810 C<s2>. Returns true or false.
1812 int strLT( char *s1, char *s2 )
1816 Test two strings to see if they are different. Returns true or false.
1818 int strNE( char *s1, char *s2 )
1822 Test two strings to see if they are equal. The C<len> parameter indicates
1823 the number of bytes to compare. Returns true or false.
1825 int strnEQ( char *s1, char *s2 )
1829 Test two strings to see if they are different. The C<len> parameter
1830 indicates the number of bytes to compare. Returns true or false.
1832 int strnNE( char *s1, char *s2, int len )
1836 Marks an SV as mortal. The SV will be destroyed when the current context
1839 SV* sv_2mortal _((SV* sv));
1843 Blesses an SV into a specified package. The SV must be an RV. The package
1844 must be designated by its stash (see C<gv_stashpv()>). The reference count of the
1847 SV* sv_bless _((SV* sv, HV* stash));
1851 Concatenates the string onto the end of the string which is in the SV.
1853 void sv_catpv _((SV* sv, char* ptr));
1857 Concatenates the string onto the end of the string which is in the SV. The
1858 C<len> indicates number of bytes to copy.
1860 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
1864 Concatenates the string from SV C<ssv> onto the end of the string in SV
1867 void sv_catsv _((SV* dsv, SV* ssv));
1871 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1872 string in C<sv1> is less than, equal to, or greater than the string in
1875 I32 sv_cmp _((SV* sv1, SV* sv2));
1879 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1880 string in C<sv1> is less than, equal to, or greater than the string in
1883 I32 sv_cmp _((SV* sv1, SV* sv2));
1887 Returns the length of the string which is in the SV. See C<SvLEN>.
1893 Set the length of the string which is in the SV. See C<SvCUR>.
1895 SvCUR_set (SV* sv, int val )
1899 Auto-decrement of the value in the SV.
1901 void sv_dec _((SV* sv));
1905 Auto-decrement of the value in the SV.
1907 void sv_dec _((SV* sv));
1911 Returns a pointer to the last character in the string which is in the SV.
1912 See C<SvCUR>. Access the character as
1918 Returns a boolean indicating whether the strings in the two SVs are
1921 I32 sv_eq _((SV* sv1, SV* sv2));
1925 Expands the character buffer in the SV. Calls C<sv_grow> to perform the
1926 expansion if necessary. Returns a pointer to the character buffer.
1928 char * SvGROW( SV* sv, int len )
1932 Expands the character buffer in the SV. This will use C<sv_unref> and will
1933 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
1938 Auto increment of the value in the SV.
1940 void sv_inc _((SV* sv));
1944 Returns a boolean indicating whether the SV contains an integer.
1950 Unsets the IV status of an SV.
1956 Tells an SV that it is an integer.
1962 Tells an SV that it is an integer and disables all other OK bits.
1968 Tells an SV that it is an integer and disables all other OK bits.
1974 Returns a boolean indicating whether the SV contains an integer. Checks the
1975 B<private> setting. Use C<SvIOK>.
1981 Returns a boolean indicating whether the SV is blessed into the specified
1982 class. This does not know how to check for subtype, so it doesn't work in
1983 an inheritance relationship.
1985 int sv_isa _((SV* sv, char* name));
1989 Returns the integer which is in the SV.
1995 Returns a boolean indicating whether the SV is an RV pointing to a blessed
1996 object. If the SV is not an RV, or if the object is not blessed, then this
1999 int sv_isobject _((SV* sv));
2003 Returns the integer which is stored in the SV.
2009 Returns the size of the string buffer in the SV. See C<SvCUR>.
2015 Returns the length of the string in the SV. Use C<SvCUR>.
2017 STRLEN sv_len _((SV* sv));
2021 Returns the length of the string in the SV. Use C<SvCUR>.
2023 STRLEN sv_len _((SV* sv));
2027 Adds magic to an SV.
2029 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2033 Creates a new SV which is a copy of the original SV. The new SV is marked
2036 SV* sv_mortalcopy _((SV* oldsv));
2040 Returns a boolean indicating whether the value is an SV.
2046 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2048 SV* sv_newmortal _((void));
2052 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2056 Returns a boolean indicating whether the SV contains a number, integer or
2063 Unsets the NV/IV status of an SV.
2069 Returns a boolean indicating whether the SV contains a number, integer or
2070 double. Checks the B<private> setting. Use C<SvNIOK>.
2072 int SvNIOKp (SV* SV)
2076 Returns a boolean indicating whether the SV contains a double.
2082 Unsets the NV status of an SV.
2088 Tells an SV that it is a double.
2094 Tells an SV that it is a double and disables all other OK bits.
2100 Tells an SV that it is a double and disables all other OK bits.
2106 Returns a boolean indicating whether the SV contains a double. Checks the
2107 B<private> setting. Use C<SvNOK>.
2113 Returns the double which is stored in the SV.
2115 double SvNV (SV* sv);
2119 Returns the double which is stored in the SV.
2121 double SvNVX (SV* sv);
2125 Returns a boolean indicating whether the SV contains a character string.
2131 Unsets the PV status of an SV.
2137 Tells an SV that it is a string.
2143 Tells an SV that it is a string and disables all other OK bits.
2149 Tells an SV that it is a string and disables all other OK bits.
2155 Returns a boolean indicating whether the SV contains a character string.
2156 Checks the B<private> setting. Use C<SvPOK>.
2162 Returns a pointer to the string in the SV, or a stringified form of the SV
2163 if the SV does not contain a string. If C<len> is C<na> then Perl will
2164 handle the length on its own.
2166 char * SvPV (SV* sv, int len )
2170 Returns a pointer to the string in the SV. The SV must contain a string.
2172 char * SvPVX (SV* sv)
2176 Returns the value of the object's reference count.
2178 int SvREFCNT (SV* sv);
2182 Decrements the reference count of the given SV.
2184 void SvREFCNT_dec (SV* sv)
2188 Increments the reference count of the given SV.
2190 void SvREFCNT_inc (SV* sv)
2194 Tests if the SV is an RV.
2200 Unsets the RV status of an SV.
2206 Tells an SV that it is an RV.
2212 Dereferences an RV to return the SV.
2218 Copies an integer into the given SV.
2220 void sv_setiv _((SV* sv, IV num));
2224 Copies a double into the given SV.
2226 void sv_setnv _((SV* sv, double num));
2230 Copies a string into an SV. The string must be null-terminated.
2232 void sv_setpv _((SV* sv, char* ptr));
2236 Copies a string into an SV. The C<len> parameter indicates the number of
2239 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2243 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
2244 argument will be upgraded to an RV. That RV will be modified to point to
2245 the new SV. The C<classname> argument indicates the package for the
2246 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2247 will be returned and will have a reference count of 1.
2249 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2253 Copies a double into a new SV, optionally blessing the SV. The C<rv>
2254 argument will be upgraded to an RV. That RV will be modified to point to
2255 the new SV. The C<classname> argument indicates the package for the
2256 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2257 will be returned and will have a reference count of 1.
2259 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2263 Copies a pointer 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. If the C<pv> argument is NULL then C<sv_undef> will be placed
2266 into the SV. The C<classname> argument indicates the package for the
2267 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2268 will be returned and will have a reference count of 1.
2270 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2272 Do not use with integral Perl types such as HV, AV, SV, CV, because those
2273 objects will become corrupted by the pointer copy process.
2275 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2279 Copies a string into a new SV, optionally blessing the SV. The length of the
2280 string must be specified with C<n>. The C<rv> argument will be upgraded to
2281 an RV. That RV will be modified to point to the new SV. The C<classname>
2282 argument indicates the package for the blessing. Set C<classname> to
2283 C<Nullch> to avoid the blessing. The new SV will be returned and will have
2284 a reference count of 1.
2286 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2288 Note that C<sv_setref_pv> copies the pointer while this copies the string.
2292 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
2293 The source SV may be destroyed if it is mortal.
2295 void sv_setsv _((SV* dsv, SV* ssv));
2299 Returns the stash of the SV.
2301 HV * SvSTASH (SV* sv)
2305 Integer type flag for scalars. See C<svtype>.
2309 Pointer type flag for scalars. See C<svtype>.
2313 Type flag for arrays. See C<svtype>.
2317 Type flag for code refs. See C<svtype>.
2321 Type flag for hashes. See C<svtype>.
2325 Type flag for blessed scalars. See C<svtype>.
2329 Double type flag for scalars. See C<svtype>.
2333 Returns a boolean indicating whether Perl would evaluate the SV as true or
2334 false, defined or undefined.
2340 Returns the type of the SV. See C<svtype>.
2342 svtype SvTYPE (SV* sv)
2346 An enum of flags for Perl types. These are found in the file B<sv.h> in the
2347 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2351 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
2352 the upgrade if necessary. See C<svtype>.
2354 bool SvUPGRADE _((SV* sv, svtype mt));
2358 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
2362 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
2366 Unsets the RV status of the SV, and decrements the reference count of whatever was
2367 being referenced by the RV. This can almost be thought of as a reversal of
2368 C<newSVrv>. See C<SvROK_off>.
2370 void sv_unref _((SV* sv));
2374 Tells an SV to use C<ptr> to find its string value. Normally the string is
2375 stored inside the SV but sv_usepvn allows the SV to use an outside string.
2376 The C<ptr> should point to memory that was allocated by C<malloc>. The
2377 string length, C<len>, must be supplied. This function will realloc the
2378 memory pointed to by C<ptr>, so that pointer should not be freed or used by
2379 the programmer after giving it to sv_usepvn.
2381 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
2385 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
2389 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
2390 This is always the proper type for the C++ object. See C<CLASS> and
2391 L<perlxs/"Using XS With C++">.
2395 Converts the specified character to lowercase.
2397 int toLOWER (char c)
2401 Converts the specified character to uppercase.
2403 int toUPPER (char c)
2407 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
2408 function the same way you use the C C<printf> function. See C<croak()>.
2412 Push an integer onto the stack, extending the stack if necessary. See
2419 Push a double onto the stack, extending the stack if necessary. See
2426 Push a string onto the stack, extending the stack if necessary. The C<len>
2427 indicates the length of the string. See C<PUSHp>.
2429 XPUSHp(char *c, int len)
2433 Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
2439 Macro to declare an XSUB and its C parameter list. This is handled by
2444 Return from XSUB, indicating number of items on the stack. This is usually
2445 handled by C<xsubpp>.
2449 =item XSRETURN_EMPTY
2451 Return an empty list from an XSUB immediately.
2457 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
2463 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
2469 Return an double from an XSUB immediately. Uses C<XST_mNV>.
2475 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
2477 XSRETURN_PV(char *v);
2479 =item XSRETURN_UNDEF
2481 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
2487 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
2493 Place an integer into the specified position C<i> on the stack. The value is
2494 stored in a new mortal SV.
2496 XST_mIV( int i, IV v );
2500 Place a double into the specified position C<i> on the stack. The value is
2501 stored in a new mortal SV.
2503 XST_mNV( int i, NV v );
2507 Place C<&sv_no> into the specified position C<i> on the stack.
2513 Place a copy of a string into the specified position C<i> on the stack. The
2514 value is stored in a new mortal SV.
2516 XST_mPV( int i, char *v );
2520 Place C<&sv_undef> into the specified position C<i> on the stack.
2522 XST_mUNDEF( int i );
2526 Place C<&sv_yes> into the specified position C<i> on the stack.
2532 The version identifier for an XS module. This is usually handled
2533 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
2535 =item XS_VERSION_BOOTCHECK
2537 Macro to verify that a PM module's $VERSION variable matches the XS module's
2538 C<XS_VERSION> variable. This is usually handled automatically by
2539 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
2543 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
2544 destination, C<n> is the number of items, and C<t> is the type.
2546 (void) Zero( d, n, t );
2552 Jeff Okamoto <okamoto@corp.hp.com>
2554 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
2555 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
2556 Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
2558 API Listing by Dean Roehrich <roehrich@cray.com>.
2562 Version 25.2: 1996/12/16