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
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 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
388 If classname is non-null, the SV is blessed into the specified class.
391 SV* newSVrv(SV* rv, char* classname);
393 Copies integer or double into an SV whose reference is rv. SV is blessed
394 if classname is non-null.
396 SV* sv_setref_iv(SV* rv, char* classname, IV iv);
397 SV* sv_setref_nv(SV* rv, char* classname, NV iv);
399 Copies the pointer value (I<the address, not the string!>) into an SV whose
400 reference is rv. SV is blessed if classname is non-null.
402 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
404 Copies string into an SV whose reference is rv.
405 Set length to 0 to let Perl calculate the string length.
406 SV is blessed if classname is non-null.
408 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
410 int sv_isa(SV* sv, char* name);
411 int sv_isobject(SV* sv);
413 =head2 Creating New Variables
415 To create a new Perl variable with an undef value which can be accessed from
416 your Perl script, use the following routines, depending on the variable type.
418 SV* perl_get_sv("package::varname", TRUE);
419 AV* perl_get_av("package::varname", TRUE);
420 HV* perl_get_hv("package::varname", TRUE);
422 Notice the use of TRUE as the second parameter. The new variable can now
423 be set, using the routines appropriate to the data type.
425 There are additional macros whose values may be bitwise OR'ed with the
426 C<TRUE> argument to enable certain extra features. Those bits are:
428 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
429 "Indentifier <varname> used only once: possible typo" warning.
430 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
431 the variable did not exist before the function was called.
433 If you do not specify a package name, the variable is created in the current
436 =head2 Reference Counts and Mortality
438 Perl uses an reference count-driven garbage collection mechanism. SV's,
439 AV's, or HV's (xV for short in the following) start their life with a
440 reference count of 1. If the reference count of an xV ever drops to 0,
441 then it will be destroyed and its memory made available for reuse.
443 This normally doesn't happen at the Perl level unless a variable is
444 undef'ed or the last variable holding a reference to it is changed or
445 overwritten. At the internal level, however, reference counts can be
446 manipulated with the following macros:
448 int SvREFCNT(SV* sv);
449 SV* SvREFCNT_inc(SV* sv);
450 void SvREFCNT_dec(SV* sv);
452 However, there is one other function which manipulates the reference
453 count of its argument. The C<newRV_inc> function, you will recall,
454 creates a reference to the specified argument. As a side effect,
455 it increments the argument's reference count. If this is not what
456 you want, use C<newRV_noinc> instead.
458 For example, imagine you want to return a reference from an XSUB function.
459 Inside the XSUB routine, you create an SV which initially has a reference
460 count of one. Then you call C<newRV_inc>, passing it the just-created SV.
461 This returns the reference as a new SV, but the reference count of the
462 SV you passed to C<newRV_inc> has been incremented to two. Now you
463 return the reference from the XSUB routine and forget about the SV.
464 But Perl hasn't! Whenever the returned reference is destroyed, the
465 reference count of the original SV is decreased to one and nothing happens.
466 The SV will hang around without any way to access it until Perl itself
467 terminates. This is a memory leak.
469 The correct procedure, then, is to use C<newRV_noinc> instead of
470 C<newRV_inc>. Then, if and when the last reference is destroyed, the
471 reference count of the SV will go to zero and it will be destroyed,
472 stopping any memory leak.
474 There are some convenience functions available that can help with the
475 destruction of xV's. These functions introduce the concept of "mortality".
476 An xV that is mortal has had its reference count marked to be decremented,
477 but not actually decremented, until "a short time later". Generally the
478 term "short time later" means a single Perl statement, such as a call to
479 an XSUB function. The actual determinant for when mortal xV's have their
480 reference count decremented depends on two macros, SAVETMPS and FREETMPS.
481 See L<perlcall> and L<perlxs> for more details on these macros.
483 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
484 However, if you mortalize a variable twice, the reference count will
485 later be decremented twice.
487 You should be careful about creating mortal variables. Strange things
488 can happen if you make the same value mortal within multiple contexts,
489 or if you make a variable mortal multiple times.
491 To create a mortal variable, use the functions:
495 SV* sv_mortalcopy(SV*)
497 The first call creates a mortal SV, the second converts an existing
498 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
499 third creates a mortal copy of an existing SV.
501 The mortal routines are not just for SV's -- AV's and HV's can be made
502 mortal by passing their addresses (type-casted to C<SV*>) to the
503 C<sv_2mortal> or C<sv_mortalcopy> routines.
505 =head2 Stashes and Globs
507 A stash is a hash table (associative array) that contains all of the
508 different objects that are contained within a package. Each key of the
509 stash is a symbol name (shared by all the different types of objects
510 that have the same name), and each value in the hash table is called a
511 GV (for Glob Value). This GV in turn contains references to the various
512 objects of that name, including (but not limited to) the following:
522 There is a single stash called "defstash" that holds the items that exist
523 in the "main" package. To get at the items in other packages, append the
524 string "::" to the package name. The items in the "Foo" package are in
525 the stash "Foo::" in defstash. The items in the "Bar::Baz" package are
526 in the stash "Baz::" in "Bar::"'s stash.
528 To get the stash pointer for a particular package, use the function:
530 HV* gv_stashpv(char* name, I32 create)
531 HV* gv_stashsv(SV*, I32 create)
533 The first function takes a literal string, the second uses the string stored
534 in the SV. Remember that a stash is just a hash table, so you get back an
535 C<HV*>. The C<create> flag will create a new package if it is set.
537 The name that C<gv_stash*v> wants is the name of the package whose symbol table
538 you want. The default package is called C<main>. If you have multiply nested
539 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
542 Alternately, if you have an SV that is a blessed reference, you can find
543 out the stash pointer by using:
545 HV* SvSTASH(SvRV(SV*));
547 then use the following to get the package name itself:
549 char* HvNAME(HV* stash);
551 If you need to bless or re-bless an object you can use the following
554 SV* sv_bless(SV*, HV* stash)
556 where the first argument, an C<SV*>, must be a reference, and the second
557 argument is a stash. The returned C<SV*> can now be used in the same way
560 For more information on references and blessings, consult L<perlref>.
564 [This section still under construction. Ignore everything here. Post no
565 bills. Everything not permitted is forbidden.]
567 Any SV may be magical, that is, it has special features that a normal
568 SV does not have. These features are stored in the SV structure in a
569 linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
582 Note this is current as of patchlevel 0, and could change at any time.
584 =head2 Assigning Magic
586 Perl adds magic to an SV using the sv_magic function:
588 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
590 The C<sv> argument is a pointer to the SV that is to acquire a new magical
593 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
594 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
595 it to the beginning of the linked list of magical features. Any prior
596 entry of the same type of magic is deleted. Note that this can be
597 overridden, and multiple instances of the same type of magic can be
598 associated with an SV.
600 The C<name> and C<namlem> arguments are used to associate a string with
601 the magic, typically the name of a variable. C<namlem> is stored in the
602 C<mg_len> field and if C<name> is non-null and C<namlem> >= 0 a malloc'd
603 copy of the name is stored in C<mg_ptr> field.
605 The sv_magic function uses C<how> to determine which, if any, predefined
606 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
607 See the "Magic Virtual Table" section below. The C<how> argument is also
608 stored in the C<mg_type> field.
610 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
611 structure. If it is not the same as the C<sv> argument, the reference
612 count of the C<obj> object is incremented. If it is the same, or if
613 the C<how> argument is "#", or if it is a null pointer, then C<obj> is
614 merely stored, without the reference count being incremented.
616 There is also a function to add magic to an C<HV>:
618 void hv_magic(HV *hv, GV *gv, int how);
620 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
622 To remove the magic from an SV, call the function sv_unmagic:
624 void sv_unmagic(SV *sv, int type);
626 The C<type> argument should be equal to the C<how> value when the C<SV>
627 was initially made magical.
629 =head2 Magic Virtual Tables
631 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
632 C<MGVTBL>, which is a structure of function pointers and stands for
633 "Magic Virtual Table" to handle the various operations that might be
634 applied to that variable.
636 The C<MGVTBL> has five pointers to the following routine types:
638 int (*svt_get)(SV* sv, MAGIC* mg);
639 int (*svt_set)(SV* sv, MAGIC* mg);
640 U32 (*svt_len)(SV* sv, MAGIC* mg);
641 int (*svt_clear)(SV* sv, MAGIC* mg);
642 int (*svt_free)(SV* sv, MAGIC* mg);
644 This MGVTBL structure is set at compile-time in C<perl.h> and there are
645 currently 19 types (or 21 with overloading turned on). These different
646 structures contain pointers to various routines that perform additional
647 actions depending on which function is being called.
649 Function pointer Action taken
650 ---------------- ------------
651 svt_get Do something after the value of the SV is retrieved.
652 svt_set Do something after the SV is assigned a value.
653 svt_len Report on the SV's length.
654 svt_clear Clear something the SV represents.
655 svt_free Free any extra storage associated with the SV.
657 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
658 to an C<mg_type> of '\0') contains:
660 { magic_get, magic_set, magic_len, 0, 0 }
662 Thus, when an SV is determined to be magical and of type '\0', if a get
663 operation is being performed, the routine C<magic_get> is called. All
664 the various routines for the various magical types begin with C<magic_>.
666 The current kinds of Magic Virtual Tables are:
668 mg_type MGVTBL Type of magical
669 ------- ------ ----------------------------
671 A vtbl_amagic Operator Overloading
672 a vtbl_amagicelem Operator Overloading
673 c 0 Used in Operator Overloading
674 B vtbl_bm Boyer-Moore???
676 e vtbl_envelem %ENV hash element
677 g vtbl_mglob Regexp /g flag???
678 I vtbl_isa @ISA array
679 i vtbl_isaelem @ISA array element
680 L 0 (but sets RMAGICAL) Perl Module/Debugger???
681 l vtbl_dbline Debugger?
682 P vtbl_pack Tied Array or Hash
683 p vtbl_packelem Tied Array or Hash element
684 q vtbl_packelem Tied Scalar or Handle
685 S vtbl_sig Signal Hash
686 s vtbl_sigelem Signal Hash element
687 t vtbl_taint Taintedness
690 x vtbl_substr Substring???
691 y vtbl_vivary Shadow variable in foreach loop
693 # vtbl_arylen Array Length
694 . vtbl_pos $. scalar variable
695 ~ None Used by certain extensions
697 When an upper-case and lower-case letter both exist in the table, then the
698 upper-case letter is used to represent some kind of composite type (a list
699 or a hash), and the lower-case letter is used to represent an element of
702 The '~' magic type is defined specifically for use by extensions and
703 will not be used by perl itself. Extensions can use ~ magic to 'attach'
704 private information to variables (typically objects). This is especially
705 useful because there is no way for normal perl code to corrupt this
706 private information (unlike using extra elements of a hash object).
708 Note that because multiple extensions may be using ~ magic it is
709 important for extensions to take extra care with it. Typically only
710 using it on objects blessed into the same class as the extension
711 is sufficient. It may also be appropriate to add an I32 'signature'
712 at the top of the private data area and check that.
716 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
718 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
719 If the SV does not have that magical feature, C<NULL> is returned. Also,
720 if the SV is not of type SVt_PVMG, Perl may core-dump.
722 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
724 This routine checks to see what types of magic C<sv> has. If the mg_type
725 field is an upper-case letter, then the mg_obj is copied to C<nsv>, but
726 the mg_type field is changed to be the lower-case letter.
728 =head2 Double-Typed SV's
730 Scalar variables normally contain only one type of value, an integer,
731 double, pointer, or reference. Perl will automatically convert the
732 actual scalar data from the stored type into the requested type.
734 Some scalar variables contain more than one type of scalar data. For
735 example, the variable C<$!> contains either the numeric value of C<errno>
736 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
738 To force multiple data values into an SV, you must do two things: use the
739 C<sv_set*v> routines to add the additional scalar type, then set a flag
740 so that Perl will believe it contains more than one type of data. The
741 four macros to set the flags are:
748 The particular macro you must use depends on which C<sv_set*v> routine
749 you called first. This is because every C<sv_set*v> routine turns on
750 only the bit for the particular type of data being set, and turns off
753 For example, to create a new Perl variable called "dberror" that contains
754 both the numeric and descriptive string error values, you could use the
758 extern char *dberror_list;
760 SV* sv = perl_get_sv("dberror", TRUE);
761 sv_setiv(sv, (IV) dberror);
762 sv_setpv(sv, dberror_list[dberror]);
765 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
766 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
768 =head2 XSUB's and the Argument Stack
770 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
771 An XSUB routine will have a stack that contains the arguments from the Perl
772 program, and a way to map from the Perl data structures to a C equivalent.
774 The stack arguments are accessible through the C<ST(n)> macro, which returns
775 the C<n>'th stack argument. Argument 0 is the first argument passed in the
776 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
779 Most of the time, output from the C routine can be handled through use of
780 the RETVAL and OUTPUT directives. However, there are some cases where the
781 argument stack is not already long enough to handle all the return values.
782 An example is the POSIX tzname() call, which takes no arguments, but returns
783 two, the local time zone's standard and summer time abbreviations.
785 To handle this situation, the PPCODE directive is used and the stack is
786 extended using the macro:
790 where C<sp> is the stack pointer, and C<num> is the number of elements the
791 stack should be extended by.
793 Now that there is room on the stack, values can be pushed on it using the
794 macros to push IV's, doubles, strings, and SV pointers respectively:
801 And now the Perl program calling C<tzname>, the two values will be assigned
804 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
806 An alternate (and possibly simpler) method to pushing values on the stack is
814 These macros automatically adjust the stack for you, if needed. Thus, you
815 do not need to call C<EXTEND> to extend the stack.
817 For more information, consult L<perlxs> and L<perlxstut>.
819 =head2 Calling Perl Routines from within C Programs
821 There are four routines that can be used to call a Perl subroutine from
822 within a C program. These four are:
824 I32 perl_call_sv(SV*, I32);
825 I32 perl_call_pv(char*, I32);
826 I32 perl_call_method(char*, I32);
827 I32 perl_call_argv(char*, I32, register char**);
829 The routine most often used is C<perl_call_sv>. The C<SV*> argument
830 contains either the name of the Perl subroutine to be called, or a
831 reference to the subroutine. The second argument consists of flags
832 that control the context in which the subroutine is called, whether
833 or not the subroutine is being passed arguments, how errors should be
834 trapped, and how to treat return values.
836 All four routines return the number of arguments that the subroutine returned
839 When using any of these routines (except C<perl_call_argv>), the programmer
840 must manipulate the Perl stack. These include the following macros and
854 For a detailed description of calling conventions from C to Perl,
857 =head2 Memory Allocation
859 It is suggested that you use the version of malloc that is distributed
860 with Perl. It keeps pools of various sizes of unallocated memory in
861 order to satisfy allocation requests more quickly. However, on some
862 platforms, it may cause spurious malloc or free errors.
864 New(x, pointer, number, type);
865 Newc(x, pointer, number, type, cast);
866 Newz(x, pointer, number, type);
868 These three macros are used to initially allocate memory.
870 The first argument C<x> was a "magic cookie" that was used to keep track
871 of who called the macro, to help when debugging memory problems. However,
872 the current code makes no use of this feature (most Perl developers now
873 use run-time memory checkers), so this argument can be any number.
875 The second argument C<pointer> should be the name of a variable that will
876 point to the newly allocated memory.
878 The third and fourth arguments C<number> and C<type> specify how many of
879 the specified type of data structure should be allocated. The argument
880 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
881 should be used if the C<pointer> argument is different from the C<type>
884 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
885 to zero out all the newly allocated memory.
887 Renew(pointer, number, type);
888 Renewc(pointer, number, type, cast);
891 These three macros are used to change a memory buffer size or to free a
892 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
893 match those of C<New> and C<Newc> with the exception of not needing the
894 "magic cookie" argument.
896 Move(source, dest, number, type);
897 Copy(source, dest, number, type);
898 Zero(dest, number, type);
900 These three macros are used to move, copy, or zero out previously allocated
901 memory. The C<source> and C<dest> arguments point to the source and
902 destination starting points. Perl will move, copy, or zero out C<number>
903 instances of the size of the C<type> data structure (using the C<sizeof>
908 The most recent development releases of Perl has been experimenting with
909 removing Perl's dependency on the "normal" standard I/O suite and allowing
910 other stdio implementations to be used. This involves creating a new
911 abstraction layer that then calls whichever implementation of stdio Perl
912 was compiled with. All XSUB's should now use the functions in the PerlIO
913 abstraction layer and not make any assumptions about what kind of stdio
916 For a complete description of the PerlIO abstraction, consult L<perlapio>.
920 =head3 Putting a C value on Perl stack
922 A lot of opcodes (this is an elementary operation in the internal perl
923 stack machine) put an SV* on the stack. However, as an optimization
924 the corresponding SV is (usually) not recreated each time. The opcodes
925 reuse specially assigned SVs (I<target>s) which are (as a corollary)
926 not constantly freed/created.
928 Each of the targets is created only once (but see
929 L<Scratchpads and recursion> below), and when an opcode needs to put
930 an integer, a double, or a string on stack, it just sets the
931 corresponding parts of its I<target> and puts the I<target> on stack.
933 The macro to put this target on stack is C<PUSHTARG>, and it is
934 directly used in some opcodes, as well as indirectly in zillions of
935 others, which use it via C<(X)PUSH[pni]>.
939 The question remains on when the SV's which are I<target>s for opcodes
940 are created. The answer is that they are created when the current unit --
941 a subroutine or a file (for opcodes for statements outside of
942 subroutines) -- is compiled. During this time a special anonymous Perl
943 array is created, which is called a scratchpad for the current
946 A scratchpad keeps SV's which are lexicals for the current unit and are
947 targets for opcodes. One can deduce that an SV lives on a scratchpad
948 by looking on its flags: lexicals have C<SVs_PADMY> set, and
949 I<target>s have C<SVs_PADTMP> set.
951 The correspondence between OP's and I<target>s is not 1-to-1. Different
952 OP's in the compile tree of the unit can use the same target, if this
953 would not conflict with the expected life of the temporary.
955 =head3 Scratchpads and recursions
957 In fact it is not 100% true that a compiled unit contains a pointer to
958 the scratchpad AV. In fact it contains a pointer to an AV of
959 (initially) one element, and this element is the scratchpad AV. Why do
960 we need an extra level of indirection?
962 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
963 these can create several execution pointers going into the same
964 subroutine. For the subroutine-child not write over the temporaries
965 for the subroutine-parent (lifespan of which covers the call to the
966 child), the parent and the child should have different
967 scratchpads. (I<And> the lexicals should be separate anyway!)
969 So each subroutine is born with an array of scratchpads (of length 1).
970 On each entry to the subroutine it is checked that the current
971 depth of the recursion is not more than the length of this array, and
972 if it is, new scratchpad is created and pushed into the array.
974 The I<target>s on this scratchpad are C<undef>s, but they are already
975 marked with correct flags.
979 This is a listing of functions, macros, flags, and variables that may be
980 useful to extension writers or that may be found while reading other
991 Clears an array, making it empty.
993 void av_clear _((AV* ar));
997 Pre-extend an array. The C<key> is the index to which the array should be
1000 void av_extend _((AV* ar, I32 key));
1004 Returns the SV at the specified index in the array. The C<key> is the
1005 index. If C<lval> is set then the fetch will be part of a store. Check
1006 that the return value is non-null before dereferencing it to a C<SV*>.
1008 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1012 Returns the highest index in the array. Returns -1 if the array is empty.
1014 I32 av_len _((AV* ar));
1018 Creates a new AV and populates it with a list of SVs. The SVs are copied
1019 into the array, so they may be freed after the call to av_make. The new AV
1020 will have a reference count of 1.
1022 AV* av_make _((I32 size, SV** svp));
1026 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1029 SV* av_pop _((AV* ar));
1033 Pushes an SV onto the end of the array. The array will grow automatically
1034 to accommodate the addition.
1036 void av_push _((AV* ar, SV* val));
1040 Shifts an SV off the beginning of the array.
1042 SV* av_shift _((AV* ar));
1046 Stores an SV in an array. The array index is specified as C<key>. The
1047 return value will be null if the operation failed, otherwise it can be
1048 dereferenced to get the original C<SV*>.
1050 SV** av_store _((AV* ar, I32 key, SV* val));
1054 Undefines the array.
1056 void av_undef _((AV* ar));
1060 Unshift an SV onto the beginning of the array. The array will grow
1061 automatically to accommodate the addition.
1063 void av_unshift _((AV* ar, I32 num));
1067 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1068 constructor. This is always a C<char*>. See C<THIS> and
1069 L<perlxs/"Using XS With C++">.
1073 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1074 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1077 (void) Copy( s, d, n, t );
1081 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1082 function the same way you use the C C<printf> function. See C<warn>.
1086 Returns the stash of the CV.
1088 HV * CvSTASH( SV* sv )
1092 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1093 boolean which indicates whether subs are being single-stepped.
1094 Single-stepping is automatically turned on after every step. This is the C
1095 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1099 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1100 the SV which holds the name of the sub being debugged. This is the C
1101 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1102 The sub name can be found by
1104 SvPV( GvSV( DBsub ), na )
1108 Trace variable used when Perl is run in debugging mode, with the B<-d>
1109 switch. This is the C variable which corresponds to Perl's $DB::trace
1110 variable. See C<DBsingle>.
1114 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1119 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1123 The C variable which corresponds to Perl's $^W warning variable.
1127 Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
1131 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1132 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1133 to indicate the number of items on the stack.
1137 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1138 handled automatically by C<xsubpp>.
1142 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1143 handled automatically by C<xsubpp>.
1147 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1153 Used to extend the argument stack for an XSUB's return values.
1155 EXTEND( sp, int x );
1159 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1166 Used to indicate array context. See C<GIMME> and L<perlcall>.
1170 Indicates that arguments returned from a callback should be discarded. See
1175 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1179 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns C<G_SCALAR> or
1180 C<G_ARRAY> for scalar or array context.
1184 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1188 Used to indicate scalar context. See C<GIMME> and L<perlcall>.
1192 Returns a pointer to the stash for a specified package. If C<create> is set
1193 then the package will be created if it does not already exist. If C<create>
1194 is not set and the package does not exist then NULL is returned.
1196 HV* gv_stashpv _((char* name, I32 create));
1200 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1202 HV* gv_stashsv _((SV* sv, I32 create));
1206 Return the SV from the GV.
1210 Releases a hash entry from an iterator. See C<hv_iternext>.
1214 Clears a hash, making it empty.
1216 void hv_clear _((HV* tb));
1220 Deletes a key/value pair in the hash. The value SV is removed from the hash
1221 and returned to the caller. The C<klen> is the length of the key. The
1222 C<flags> value will normally be zero; if set to G_DISCARD then null will be
1225 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1229 Returns a boolean indicating whether the specified hash key exists. The
1230 C<klen> is the length of the key.
1232 bool hv_exists _((HV* tb, char* key, U32 klen));
1236 Returns the SV which corresponds to the specified key in the hash. The
1237 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1238 part of a store. Check that the return value is non-null before
1239 dereferencing it to a C<SV*>.
1241 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1245 Prepares a starting point to traverse a hash table.
1247 I32 hv_iterinit _((HV* tb));
1251 Returns the key from the current position of the hash iterator. See
1254 char* hv_iterkey _((HE* entry, I32* retlen));
1258 Returns entries from a hash iterator. See C<hv_iterinit>.
1260 HE* hv_iternext _((HV* tb));
1264 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1267 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1271 Returns the value from the current position of the hash iterator. See
1274 SV* hv_iterval _((HV* tb, HE* entry));
1278 Adds magic to a hash. See C<sv_magic>.
1280 void hv_magic _((HV* hv, GV* gv, int how));
1284 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1286 char *HvNAME (HV* stash)
1290 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1291 the length of the key. The C<hash> parameter is the pre-computed hash
1292 value; if it is zero then Perl will compute it. The return value will be
1293 null if the operation failed, otherwise it can be dereferenced to get the
1296 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1302 void hv_undef _((HV* tb));
1306 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
1309 int isALNUM (char c)
1313 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
1316 int isALPHA (char c)
1320 Returns a boolean indicating whether the C C<char> is an ascii digit.
1322 int isDIGIT (char c)
1326 Returns a boolean indicating whether the C C<char> is a lowercase character.
1328 int isLOWER (char c)
1332 Returns a boolean indicating whether the C C<char> is whitespace.
1334 int isSPACE (char c)
1338 Returns a boolean indicating whether the C C<char> is an uppercase character.
1340 int isUPPER (char c)
1344 Variable which is setup by C<xsubpp> to indicate the number of items on the
1345 stack. See L<perlxs/"Variable-length Parameter Lists">.
1349 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1350 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
1354 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1360 Stack marker variable for the XSUB. See C<dMARK>.
1364 Clear something magical that the SV represents. See C<sv_magic>.
1366 int mg_clear _((SV* sv));
1370 Copies the magic from one SV to another. See C<sv_magic>.
1372 int mg_copy _((SV *, SV *, char *, STRLEN));
1376 Finds the magic pointer for type matching the SV. See C<sv_magic>.
1378 MAGIC* mg_find _((SV* sv, int type));
1382 Free any magic storage used by the SV. See C<sv_magic>.
1384 int mg_free _((SV* sv));
1388 Do magic after a value is retrieved from the SV. See C<sv_magic>.
1390 int mg_get _((SV* sv));
1394 Report on the SV's length. See C<sv_magic>.
1396 U32 mg_len _((SV* sv));
1400 Turns on the magical status of an SV. See C<sv_magic>.
1402 void mg_magical _((SV* sv));
1406 Do magic after a value is assigned to the SV. See C<sv_magic>.
1408 int mg_set _((SV* sv));
1412 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
1413 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1416 (void) Move( s, d, n, t );
1420 A variable which may be used with C<SvPV> to tell Perl to calculate the
1425 The XSUB-writer's interface to the C C<malloc> function.
1427 void * New( x, void *ptr, int size, type )
1431 The XSUB-writer's interface to the C C<malloc> function, with cast.
1433 void * Newc( x, void *ptr, int size, type, cast )
1437 The XSUB-writer's interface to the C C<malloc> function. The allocated
1438 memory is zeroed with C<memzero>.
1440 void * Newz( x, void *ptr, int size, type )
1444 Creates a new AV. The reference count is set to 1.
1446 AV* newAV _((void));
1450 Creates a new HV. The reference count is set to 1.
1452 HV* newHV _((void));
1456 Creates an RV wrapper for an SV. The reference count for the original SV is
1459 SV* newRV_inc _((SV* ref));
1461 For historical reasons, "newRV" is a synonym for "newRV_inc".
1465 Creates an RV wrapper for an SV. The reference count for the original
1466 SV is B<not> incremented.
1468 SV* newRV_noinc _((SV* ref));
1472 Creates a new SV. The C<len> parameter indicates the number of bytes of
1473 pre-allocated string space the SV should have. The reference count for the
1476 SV* newSV _((STRLEN len));
1480 Creates a new SV and copies an integer into it. The reference count for the
1483 SV* newSViv _((IV i));
1487 Creates a new SV and copies a double into it. The reference count for the
1490 SV* newSVnv _((NV i));
1494 Creates a new SV and copies a string into it. The reference count for the
1495 SV is set to 1. If C<len> is zero then Perl will compute the length.
1497 SV* newSVpv _((char* s, STRLEN len));
1501 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
1502 it will be upgraded to one. If C<classname> is non-null then the new SV will
1503 be blessed in the specified package. The new SV is returned and its
1504 reference count is 1.
1505 SV* newSVrv _((SV* rv, char* classname));
1509 Creates a new SV which is an exact duplicate of the original SV.
1511 SV* newSVsv _((SV* old));
1515 Used by C<xsubpp> to hook up XSUBs as Perl subs.
1519 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
1528 Null character pointer.
1544 The original stack mark for the XSUB. See C<dORIGMARK>.
1548 Allocates a new Perl interpreter. See L<perlembed>.
1550 =item perl_call_argv
1552 Performs a callback to the specified Perl sub. See L<perlcall>.
1554 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
1556 =item perl_call_method
1558 Performs a callback to the specified Perl method. The blessed object must
1559 be on the stack. See L<perlcall>.
1561 I32 perl_call_method _((char* methname, I32 flags));
1565 Performs a callback to the specified Perl sub. See L<perlcall>.
1567 I32 perl_call_pv _((char* subname, I32 flags));
1571 Performs a callback to the Perl sub whose name is in the SV. See
1574 I32 perl_call_sv _((SV* sv, I32 flags));
1576 =item perl_construct
1578 Initializes a new Perl interpreter. See L<perlembed>.
1582 Shuts down a Perl interpreter. See L<perlembed>.
1586 Tells Perl to C<eval> the string in the SV.
1588 I32 perl_eval_sv _((SV* sv, I32 flags));
1592 Releases a Perl interpreter. See L<perlembed>.
1596 Returns the AV of the specified Perl array. If C<create> is set and the
1597 Perl variable does not exist then it will be created. If C<create> is not
1598 set and the variable does not exist then null is returned.
1600 AV* perl_get_av _((char* name, I32 create));
1604 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
1605 variable does not exist then it will be created. If C<create> is not
1606 set and the variable does not exist then null is returned.
1608 CV* perl_get_cv _((char* name, I32 create));
1612 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
1613 variable does not exist then it will be created. If C<create> is not
1614 set and the variable does not exist then null is returned.
1616 HV* perl_get_hv _((char* name, I32 create));
1620 Returns the SV of the specified Perl scalar. If C<create> is set and the
1621 Perl variable does not exist then it will be created. If C<create> is not
1622 set and the variable does not exist then null is returned.
1624 SV* perl_get_sv _((char* name, I32 create));
1628 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
1630 =item perl_require_pv
1632 Tells Perl to C<require> a module.
1634 void perl_require_pv _((char* pv));
1638 Tells a Perl interpreter to run. See L<perlembed>.
1642 Pops an integer off the stack.
1648 Pops a long off the stack.
1654 Pops a string off the stack.
1660 Pops a double off the stack.
1666 Pops an SV off the stack.
1672 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
1678 Push an integer onto the stack. The stack must have room for this element.
1685 Push a double onto the stack. The stack must have room for this element.
1692 Push a string onto the stack. The stack must have room for this element.
1693 The C<len> indicates the length of the string. See C<XPUSHp>.
1695 PUSHp(char *c, int len )
1699 Push an SV onto the stack. The stack must have room for this element. See
1706 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
1707 See C<PUSHMARK> and L<perlcall> for other uses.
1713 The XSUB-writer's interface to the C C<realloc> function.
1715 void * Renew( void *ptr, int size, type )
1719 The XSUB-writer's interface to the C C<realloc> function, with cast.
1721 void * Renewc( void *ptr, int size, type, cast )
1725 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
1726 This is always the proper type for the XSUB.
1727 See L<perlxs/"The RETVAL Variable">.
1731 The XSUB-writer's interface to the C C<free> function.
1735 The XSUB-writer's interface to the C C<malloc> function.
1739 The XSUB-writer's interface to the C C<realloc> function.
1743 Copy a string to a safe spot. This does not use an SV.
1745 char* savepv _((char* sv));
1749 Copy a string to a safe spot. The C<len> indicates number of bytes to
1750 copy. This does not use an SV.
1752 char* savepvn _((char* sv, I32 len));
1756 Opening bracket for temporaries on a callback. See C<FREETMPS> and
1763 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
1768 Re-fetch the stack pointer. Used after a callback. See L<perlcall>.
1774 Used to access elements on the XSUB's stack.
1780 Test two strings to see if they are equal. Returns true or false.
1782 int strEQ( char *s1, char *s2 )
1786 Test two strings to see if the first, C<s1>, is greater than or equal to the
1787 second, C<s2>. Returns true or false.
1789 int strGE( char *s1, char *s2 )
1793 Test two strings to see if the first, C<s1>, is greater than the second,
1794 C<s2>. Returns true or false.
1796 int strGT( char *s1, char *s2 )
1800 Test two strings to see if the first, C<s1>, is less than or equal to the
1801 second, C<s2>. Returns true or false.
1803 int strLE( char *s1, char *s2 )
1807 Test two strings to see if the first, C<s1>, is less than the second,
1808 C<s2>. Returns true or false.
1810 int strLT( char *s1, char *s2 )
1814 Test two strings to see if they are different. Returns true or false.
1816 int strNE( char *s1, char *s2 )
1820 Test two strings to see if they are equal. The C<len> parameter indicates
1821 the number of bytes to compare. Returns true or false.
1823 int strnEQ( char *s1, char *s2 )
1827 Test two strings to see if they are different. The C<len> parameter
1828 indicates the number of bytes to compare. Returns true or false.
1830 int strnNE( char *s1, char *s2, int len )
1834 Marks an SV as mortal. The SV will be destroyed when the current context
1837 SV* sv_2mortal _((SV* sv));
1841 Blesses an SV into a specified package. The SV must be an RV. The package
1842 must be designated by its stash (see C<gv_stashpv()>). The reference count
1843 of the SV is unaffected.
1845 SV* sv_bless _((SV* sv, HV* stash));
1849 Concatenates the string onto the end of the string which is in the SV.
1851 void sv_catpv _((SV* sv, char* ptr));
1855 Concatenates the string onto the end of the string which is in the SV. The
1856 C<len> indicates number of bytes to copy.
1858 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
1862 Concatenates the string from SV C<ssv> onto the end of the string in SV
1865 void sv_catsv _((SV* dsv, SV* ssv));
1869 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1870 string in C<sv1> is less than, equal to, or greater than the string in
1873 I32 sv_cmp _((SV* sv1, SV* sv2));
1877 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1878 string in C<sv1> is less than, equal to, or greater than the string in
1881 I32 sv_cmp _((SV* sv1, SV* sv2));
1885 Returns the length of the string which is in the SV. See C<SvLEN>.
1891 Set the length of the string which is in the SV. See C<SvCUR>.
1893 SvCUR_set (SV* sv, int val )
1897 Auto-decrement of the value in the SV.
1899 void sv_dec _((SV* sv));
1903 Auto-decrement of the value in the SV.
1905 void sv_dec _((SV* sv));
1909 Returns a pointer to the last character in the string which is in the SV.
1910 See C<SvCUR>. Access the character as
1916 Returns a boolean indicating whether the strings in the two SVs are
1919 I32 sv_eq _((SV* sv1, SV* sv2));
1923 Expands the character buffer in the SV. Calls C<sv_grow> to perform the
1924 expansion if necessary. Returns a pointer to the character buffer.
1926 char * SvGROW( SV* sv, int len )
1930 Expands the character buffer in the SV. This will use C<sv_unref> and will
1931 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
1936 Auto-increment of the value in the SV.
1938 void sv_inc _((SV* sv));
1942 Returns a boolean indicating whether the SV contains an integer.
1948 Unsets the IV status of an SV.
1954 Tells an SV that it is an integer.
1960 Tells an SV that it is an integer and disables all other OK bits.
1966 Tells an SV that it is an integer and disables all other OK bits.
1972 Returns a boolean indicating whether the SV contains an integer. Checks the
1973 B<private> setting. Use C<SvIOK>.
1979 Returns a boolean indicating whether the SV is blessed into the specified
1980 class. This does not know how to check for subtype, so it doesn't work in
1981 an inheritance relationship.
1983 int sv_isa _((SV* sv, char* name));
1987 Returns the integer which is in the SV.
1993 Returns a boolean indicating whether the SV is an RV pointing to a blessed
1994 object. If the SV is not an RV, or if the object is not blessed, then this
1997 int sv_isobject _((SV* sv));
2001 Returns the integer which is stored in the SV.
2007 Returns the size of the string buffer in the SV. See C<SvCUR>.
2013 Returns the length of the string in the SV. Use C<SvCUR>.
2015 STRLEN sv_len _((SV* sv));
2019 Returns the length of the string in the SV. Use C<SvCUR>.
2021 STRLEN sv_len _((SV* sv));
2025 Adds magic to an SV.
2027 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2031 Creates a new SV which is a copy of the original SV. The new SV is marked
2034 SV* sv_mortalcopy _((SV* oldsv));
2038 Returns a boolean indicating whether the value is an SV.
2044 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2046 SV* sv_newmortal _((void));
2050 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2054 Returns a boolean indicating whether the SV contains a number, integer or
2061 Unsets the NV/IV status of an SV.
2067 Returns a boolean indicating whether the SV contains a number, integer or
2068 double. Checks the B<private> setting. Use C<SvNIOK>.
2070 int SvNIOKp (SV* SV)
2074 Returns a boolean indicating whether the SV contains a double.
2080 Unsets the NV status of an SV.
2086 Tells an SV that it is a double.
2092 Tells an SV that it is a double and disables all other OK bits.
2098 Tells an SV that it is a double and disables all other OK bits.
2104 Returns a boolean indicating whether the SV contains a double. Checks the
2105 B<private> setting. Use C<SvNOK>.
2111 Returns the double which is stored in the SV.
2113 double SvNV (SV* sv);
2117 Returns the double which is stored in the SV.
2119 double SvNVX (SV* sv);
2123 Returns a boolean indicating whether the SV contains a character string.
2129 Unsets the PV status of an SV.
2135 Tells an SV that it is a string.
2141 Tells an SV that it is a string and disables all other OK bits.
2147 Tells an SV that it is a string and disables all other OK bits.
2153 Returns a boolean indicating whether the SV contains a character string.
2154 Checks the B<private> setting. Use C<SvPOK>.
2160 Returns a pointer to the string in the SV, or a stringified form of the SV
2161 if the SV does not contain a string. If C<len> is C<na> then Perl will
2162 handle the length on its own.
2164 char * SvPV (SV* sv, int len )
2168 Returns a pointer to the string in the SV. The SV must contain a string.
2170 char * SvPVX (SV* sv)
2174 Returns the value of the object's reference count.
2176 int SvREFCNT (SV* sv);
2180 Decrements the reference count of the given SV.
2182 void SvREFCNT_dec (SV* sv)
2186 Increments the reference count of the given SV.
2188 void SvREFCNT_inc (SV* sv)
2192 Tests if the SV is an RV.
2198 Unsets the RV status of an SV.
2204 Tells an SV that it is an RV.
2210 Dereferences an RV to return the SV.
2216 Copies an integer into the given SV.
2218 void sv_setiv _((SV* sv, IV num));
2222 Copies a double into the given SV.
2224 void sv_setnv _((SV* sv, double num));
2228 Copies a string into an SV. The string must be null-terminated.
2230 void sv_setpv _((SV* sv, char* ptr));
2234 Copies a string into an SV. The C<len> parameter indicates the number of
2237 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2241 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
2242 argument will be upgraded to an RV. That RV will be modified to point to
2243 the new SV. The C<classname> argument indicates the package for the
2244 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2245 will be returned and will have a reference count of 1.
2247 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2251 Copies a double into a new SV, optionally blessing the SV. The C<rv>
2252 argument will be upgraded to an RV. That RV will be modified to point to
2253 the new SV. The C<classname> argument indicates the package for the
2254 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2255 will be returned and will have a reference count of 1.
2257 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2261 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
2262 argument will be upgraded to an RV. That RV will be modified to point to
2263 the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
2264 into the SV. The C<classname> argument indicates the package for the
2265 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2266 will be returned and will have a reference count of 1.
2268 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2270 Do not use with integral Perl types such as HV, AV, SV, CV, because those
2271 objects will become corrupted by the pointer copy process.
2273 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2277 Copies a string into a new SV, optionally blessing the SV. The length of the
2278 string must be specified with C<n>. The C<rv> argument will be upgraded to
2279 an RV. That RV will be modified to point to the new SV. The C<classname>
2280 argument indicates the package for the blessing. Set C<classname> to
2281 C<Nullch> to avoid the blessing. The new SV will be returned and will have
2282 a reference count of 1.
2284 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2286 Note that C<sv_setref_pv> copies the pointer while this copies the string.
2290 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
2291 The source SV may be destroyed if it is mortal.
2293 void sv_setsv _((SV* dsv, SV* ssv));
2297 Returns the stash of the SV.
2299 HV * SvSTASH (SV* sv)
2303 Integer type flag for scalars. See C<svtype>.
2307 Pointer type flag for scalars. See C<svtype>.
2311 Type flag for arrays. See C<svtype>.
2315 Type flag for code refs. See C<svtype>.
2319 Type flag for hashes. See C<svtype>.
2323 Type flag for blessed scalars. See C<svtype>.
2327 Double type flag for scalars. See C<svtype>.
2331 Returns a boolean indicating whether Perl would evaluate the SV as true or
2332 false, defined or undefined.
2338 Returns the type of the SV. See C<svtype>.
2340 svtype SvTYPE (SV* sv)
2344 An enum of flags for Perl types. These are found in the file B<sv.h> in the
2345 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2349 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
2350 the upgrade if necessary. See C<svtype>.
2352 bool SvUPGRADE _((SV* sv, svtype mt));
2356 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
2360 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
2364 Unsets the RV status of the SV, and decrements the reference count of
2365 whatever was being referenced by the RV. This can almost be thought of
2366 as a reversal of C<newSVrv>. See C<SvROK_off>.
2368 void sv_unref _((SV* sv));
2372 Tells an SV to use C<ptr> to find its string value. Normally the string is
2373 stored inside the SV but sv_usepvn allows the SV to use an outside string.
2374 The C<ptr> should point to memory that was allocated by C<malloc>. The
2375 string length, C<len>, must be supplied. This function will realloc the
2376 memory pointed to by C<ptr>, so that pointer should not be freed or used by
2377 the programmer after giving it to sv_usepvn.
2379 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
2383 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
2387 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
2388 This is always the proper type for the C++ object. See C<CLASS> and
2389 L<perlxs/"Using XS With C++">.
2393 Converts the specified character to lowercase.
2395 int toLOWER (char c)
2399 Converts the specified character to uppercase.
2401 int toUPPER (char c)
2405 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
2406 function the same way you use the C C<printf> function. See C<croak()>.
2410 Push an integer onto the stack, extending the stack if necessary. See
2417 Push a double onto the stack, extending the stack if necessary. See
2424 Push a string onto the stack, extending the stack if necessary. The C<len>
2425 indicates the length of the string. See C<PUSHp>.
2427 XPUSHp(char *c, int len)
2431 Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
2437 Macro to declare an XSUB and its C parameter list. This is handled by
2442 Return from XSUB, indicating number of items on the stack. This is usually
2443 handled by C<xsubpp>.
2447 =item XSRETURN_EMPTY
2449 Return an empty list from an XSUB immediately.
2455 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
2461 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
2467 Return an double from an XSUB immediately. Uses C<XST_mNV>.
2473 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
2475 XSRETURN_PV(char *v);
2477 =item XSRETURN_UNDEF
2479 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
2485 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
2491 Place an integer into the specified position C<i> on the stack. The value is
2492 stored in a new mortal SV.
2494 XST_mIV( int i, IV v );
2498 Place a double into the specified position C<i> on the stack. The value is
2499 stored in a new mortal SV.
2501 XST_mNV( int i, NV v );
2505 Place C<&sv_no> into the specified position C<i> on the stack.
2511 Place a copy of a string into the specified position C<i> on the stack. The
2512 value is stored in a new mortal SV.
2514 XST_mPV( int i, char *v );
2518 Place C<&sv_undef> into the specified position C<i> on the stack.
2520 XST_mUNDEF( int i );
2524 Place C<&sv_yes> into the specified position C<i> on the stack.
2530 The version identifier for an XS module. This is usually handled
2531 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
2533 =item XS_VERSION_BOOTCHECK
2535 Macro to verify that a PM module's $VERSION variable matches the XS module's
2536 C<XS_VERSION> variable. This is usually handled automatically by
2537 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
2541 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
2542 destination, C<n> is the number of items, and C<t> is the type.
2544 (void) Zero( d, n, t );
2550 Jeff Okamoto <okamoto@corp.hp.com>
2552 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
2553 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
2554 Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
2556 API Listing by Dean Roehrich <roehrich@cray.com>.
2560 Version 26.1: 1996/12/20