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.
15 Perl has three typedefs that handle Perl's three main data types:
21 Each typedef has specific routines that manipulate the various data types.
23 =head2 What is an "IV"?
25 Perl uses a special typedef IV which is a simple integer type that is
26 guaranteed to be large enough to hold a pointer (as well as an integer).
28 Perl also uses two special typedefs, I32 and I16, which will always be at
29 least 32-bits and 16-bits long, respectively.
31 =head2 Working with SV's
33 An SV can be created and loaded with one command. There are four types of
34 values that can be loaded: an integer value (IV), a double (NV), a string,
35 (PV), and another scalar (SV).
37 The four routines are:
41 SV* newSVpv(char*, int);
44 To change the value of an *already-existing* SV, there are five routines:
46 void sv_setiv(SV*, IV);
47 void sv_setnv(SV*, double);
48 void sv_setpvn(SV*, char*, int)
49 void sv_setpv(SV*, char*);
50 void sv_setsv(SV*, SV*);
52 Notice that you can choose to specify the length of the string to be
53 assigned by using C<sv_setpvn> or C<newSVpv>, or you may allow Perl to
54 calculate the length by using C<sv_setpv> or by specifying 0 as the second
55 argument to C<newSVpv>. Be warned, though, that Perl will determine the
56 string's length by using C<strlen>, which depends on the string terminating
59 All SV's that will contain strings should, but need not, be terminated
60 with a NUL character. If it is not NUL-terminated there is a risk of
61 core dumps and corruptions from code which passes the string to C
62 functions or system calls which expect a NUL-terminated string.
63 Perl's own functions typically add a trailing NUL for this reason.
64 Nevertheless, you should be very careful when you pass a string stored
65 in an SV to a C function or system call.
67 To access the actual value that an SV points to, you can use the macros:
73 which will automatically coerce the actual scalar type into an IV, double,
76 In the C<SvPV> macro, the length of the string returned is placed into the
77 variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
78 care what the length of the data is, use the global variable C<na>. Remember,
79 however, that Perl allows arbitrary strings of data that may both contain
80 NUL's and might not be terminated by a NUL.
82 If you want to know if the scalar value is TRUE, you can use:
86 Although Perl will automatically grow strings for you, if you need to force
87 Perl to allocate more memory for your SV, you can use the macro
89 SvGROW(SV*, STRLEN newlen)
91 which will determine if more memory needs to be allocated. If so, it will
92 call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
93 decrease, the allocated memory of an SV and that it does not automatically
94 add a byte for the a trailing NUL (perl's own string functions typically do
95 C<SvGROW(sv, len + 1)>).
97 If you have an SV and want to know what kind of data Perl thinks is stored
98 in it, you can use the following macros to check the type of SV you have.
104 You can get and set the current length of the string stored in an SV with
105 the following macros:
108 SvCUR_set(SV*, I32 val)
110 You can also get a pointer to the end of the string stored in the SV
115 But note that these last three macros are valid only if C<SvPOK()> is true.
117 If you want to append something to the end of string stored in an C<SV*>,
118 you can use the following functions:
120 void sv_catpv(SV*, char*);
121 void sv_catpvn(SV*, char*, int);
122 void sv_catsv(SV*, SV*);
124 The first function calculates the length of the string to be appended by
125 using C<strlen>. In the second, you specify the length of the string
126 yourself. The third function extends the string stored in the first SV
127 with the string stored in the second SV. It also forces the second SV to
128 be interpreted as a string.
130 If you know the name of a scalar variable, you can get a pointer to its SV
131 by using the following:
133 SV* perl_get_sv("package::varname", FALSE);
135 This returns NULL if the variable does not exist.
137 If you want to know if this variable (or any other SV) is actually C<defined>,
142 The scalar C<undef> value is stored in an SV instance called C<sv_undef>. Its
143 address can be used whenever an C<SV*> is needed.
145 There are also the two values C<sv_yes> and C<sv_no>, which contain Boolean
146 TRUE and FALSE values, respectively. Like C<sv_undef>, their addresses can
147 be used whenever an C<SV*> is needed.
149 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&sv_undef>.
153 if (I-am-to-return-a-real-value) {
154 sv = sv_2mortal(newSViv(42));
158 This code tries to return a new SV (which contains the value 42) if it should
159 return a real value, or undef otherwise. Instead it has returned a null
160 pointer which, somewhere down the line, will cause a segmentation violation,
161 bus error, or just weird results. Change the zero to C<&sv_undef> in the first
162 line and all will be well.
164 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
165 call is not necessary (see the section on L<Mortality>).
167 =head2 What's Really Stored in an SV?
169 Recall that the usual method of determining the type of scalar you have is
170 to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
171 usually these macros will always return TRUE and calling the C<Sv*V>
172 macros will do the appropriate conversion of string to integer/double or
173 integer/double to string.
175 If you I<really> need to know if you have an integer, double, or string
176 pointer in an SV, you can use the following three macros instead:
182 These will tell you if you truly have an integer, double, or string pointer
183 stored in your SV. The "p" stands for private.
185 In general, though, it's best to use the C<Sv*V> macros.
187 =head2 Working with AV's
189 There are two ways to create and load an AV. The first method creates an
194 The second method both creates the AV and initially populates it with SV's:
196 AV* av_make(I32 num, SV **ptr);
198 The second argument points to an array containing C<num> C<SV*>'s. Once the
199 AV has been created, the SV's can be destroyed, if so desired.
201 Once the AV has been created, the following operations are possible on AV's:
203 void av_push(AV*, SV*);
206 void av_unshift(AV*, I32 num);
208 These should be familiar operations, with the exception of C<av_unshift>.
209 This routine adds C<num> elements at the front of the array with the C<undef>
210 value. You must then use C<av_store> (described below) to assign values
211 to these new elements.
213 Here are some other functions:
216 SV** av_fetch(AV*, I32 key, I32 lval);
217 SV** av_store(AV*, I32 key, SV* val);
219 The C<av_len> function returns the highest index value in array (just
220 like $#array in Perl). If the array is empty, -1 is returned. The
221 C<av_fetch> function returns the value at index C<key>, but if C<lval>
222 is non-zero, then C<av_fetch> will store an undef value at that index.
223 The C<av_store> function stores the value C<val> at index C<key>.
224 note that C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s
225 as their return value.
229 void av_extend(AV*, I32 key);
231 The C<av_clear> function deletes all the elements in the AV* array, but
232 does not actually delete the array itself. The C<av_undef> function will
233 delete all the elements in the array plus the array itself. The
234 C<av_extend> function extends the array so that it contains C<key>
235 elements. If C<key> is less than the current length of the array, then
238 If you know the name of an array variable, you can get a pointer to its AV
239 by using the following:
241 AV* perl_get_av("package::varname", FALSE);
243 This returns NULL if the variable does not exist.
245 =head2 Working with HV's
247 To create an HV, you use the following routine:
251 Once the HV has been created, the following operations are possible on HV's:
253 SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
254 SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
256 The C<klen> parameter is the length of the key being passed in (Note that
257 you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
258 length of the key). The C<val> argument contains the SV pointer to the
259 scalar being stored, and C<hash> is the pre-computed hash value (zero if
260 you want C<hv_store> to calculate it for you). The C<lval> parameter
261 indicates whether this fetch is actually a part of a store operation, in
262 which case a new undefined value will be added to the HV with the supplied
263 key and C<hv_fetch> will return as if the value had already existed.
265 Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
266 C<SV*>. To access the scalar value, you must first dereference the return
267 value. However, you should check to make sure that the return value is
268 not NULL before dereferencing it.
270 These two functions check if a hash table entry exists, and deletes it.
272 bool hv_exists(HV*, char* key, U32 klen);
273 SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
275 If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
276 create and return a mortal copy of the deleted value.
278 And more miscellaneous functions:
283 Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
284 table but does not actually delete the hash table. The C<hv_undef> deletes
285 both the entries and the hash table itself.
287 Perl keeps the actual data in linked list of structures with a typedef of HE.
288 These contain the actual key and value pointers (plus extra administrative
289 overhead). The key is a string pointer; the value is an C<SV*>. However,
290 once you have an C<HE*>, to get the actual key and value, use the routines
293 I32 hv_iterinit(HV*);
294 /* Prepares starting point to traverse hash table */
295 HE* hv_iternext(HV*);
296 /* Get the next entry, and return a pointer to a
297 structure that has both the key and value */
298 char* hv_iterkey(HE* entry, I32* retlen);
299 /* Get the key from an HE structure and also return
300 the length of the key string */
301 SV* hv_iterval(HV*, HE* entry);
302 /* Return a SV pointer to the value of the HE
304 SV* hv_iternextsv(HV*, char** key, I32* retlen);
305 /* This convenience routine combines hv_iternext,
306 hv_iterkey, and hv_iterval. The key and retlen
307 arguments are return values for the key and its
308 length. The value is returned in the SV* argument */
310 If you know the name of a hash variable, you can get a pointer to its HV
311 by using the following:
313 HV* perl_get_hv("package::varname", FALSE);
315 This returns NULL if the variable does not exist.
317 The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
323 hash = hash * 33 + *s++;
325 =head2 Hash API Extensions
327 Beginning with version 5.004, the following functions are also supported:
329 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
330 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
332 bool hv_exists_ent (HV* tb, SV* key, U32 hash);
333 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
335 SV* hv_iterkeysv (HE* entry);
337 Note that these functions take C<SV*> keys, which simplifies writing
338 of extension code that deals with hash structures. These functions
339 also allow passing of C<SV*> keys to C<tie> functions without forcing
340 you to stringify the keys (unlike the previous set of functions).
342 They also return and accept whole hash entries (C<HE*>), making their
343 use more efficient (since the hash number for a particular string
344 doesn't have to be recomputed every time). See L<API LISTING> later in
345 this document for detailed descriptions.
347 The following macros must always be used to access the contents of hash
348 entries. Note that the arguments to these macros must be simple
349 variables, since they may get evaluated more than once. See
350 L<API LISTING> later in this document for detailed descriptions of these
353 HePV(HE* he, STRLEN len)
357 HeSVKEY_force(HE* he)
358 HeSVKEY_set(HE* he, SV* sv)
360 These two lower level macros are defined, but must only be used when
361 dealing with keys that are not C<SV*>s:
369 References are a special type of scalar that point to other data types
370 (including references).
372 To create a reference, use either of the following functions:
374 SV* newRV_inc((SV*) thing);
375 SV* newRV_noinc((SV*) thing);
377 The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
378 functions are identical except that C<newRV_inc> increments the reference
379 count of the C<thing>, while C<newRV_noinc> does not. For historical
380 reasons, C<newRV> is a synonym for C<newRV_inc>.
382 Once you have a reference, you can use the following macro to dereference
387 then call the appropriate routines, casting the returned C<SV*> to either an
388 C<AV*> or C<HV*>, if required.
390 To determine if an SV is a reference, you can use the following macro:
394 To discover what type of value the reference refers to, use the following
395 macro and then check the return value.
399 The most useful types that will be returned are:
408 SVt_PVGV Glob (possible a file handle)
409 SVt_PVMG Blessed or Magical Scalar
411 See the sv.h header file for more details.
413 =head2 Blessed References and Class Objects
415 References are also used to support object-oriented programming. In the
416 OO lexicon, an object is simply a reference that has been blessed into a
417 package (or class). Once blessed, the programmer may now use the reference
418 to access the various methods in the class.
420 A reference can be blessed into a package with the following function:
422 SV* sv_bless(SV* sv, HV* stash);
424 The C<sv> argument must be a reference. The C<stash> argument specifies
425 which class the reference will belong to. See the section on L<Stashes>
426 for information on converting class names into stashes.
428 /* Still under construction */
430 Upgrades rv to reference if not already one. Creates new SV for rv to
431 point to. If C<classname> is non-null, the SV is blessed into the specified
432 class. SV is returned.
434 SV* newSVrv(SV* rv, char* classname);
436 Copies integer or double into an SV whose reference is C<rv>. SV is blessed
437 if C<classname> is non-null.
439 SV* sv_setref_iv(SV* rv, char* classname, IV iv);
440 SV* sv_setref_nv(SV* rv, char* classname, NV iv);
442 Copies the pointer value (I<the address, not the string!>) into an SV whose
443 reference is rv. SV is blessed if C<classname> is non-null.
445 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
447 Copies string into an SV whose reference is C<rv>. Set length to 0 to let
448 Perl calculate the string length. SV is blessed if C<classname> is non-null.
450 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
452 int sv_isa(SV* sv, char* name);
453 int sv_isobject(SV* sv);
455 =head2 Creating New Variables
457 To create a new Perl variable with an undef value which can be accessed from
458 your Perl script, use the following routines, depending on the variable type.
460 SV* perl_get_sv("package::varname", TRUE);
461 AV* perl_get_av("package::varname", TRUE);
462 HV* perl_get_hv("package::varname", TRUE);
464 Notice the use of TRUE as the second parameter. The new variable can now
465 be set, using the routines appropriate to the data type.
467 There are additional macros whose values may be bitwise OR'ed with the
468 C<TRUE> argument to enable certain extra features. Those bits are:
470 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
471 "Indentifier <varname> used only once: possible typo" warning.
472 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
473 the variable did not exist before the function was called.
475 If you do not specify a package name, the variable is created in the current
478 =head2 Reference Counts and Mortality
480 Perl uses an reference count-driven garbage collection mechanism. SV's,
481 AV's, or HV's (xV for short in the following) start their life with a
482 reference count of 1. If the reference count of an xV ever drops to 0,
483 then it will be destroyed and its memory made available for reuse.
485 This normally doesn't happen at the Perl level unless a variable is
486 undef'ed or the last variable holding a reference to it is changed or
487 overwritten. At the internal level, however, reference counts can be
488 manipulated with the following macros:
490 int SvREFCNT(SV* sv);
491 SV* SvREFCNT_inc(SV* sv);
492 void SvREFCNT_dec(SV* sv);
494 However, there is one other function which manipulates the reference
495 count of its argument. The C<newRV_inc> function, you will recall,
496 creates a reference to the specified argument. As a side effect,
497 it increments the argument's reference count. If this is not what
498 you want, use C<newRV_noinc> instead.
500 For example, imagine you want to return a reference from an XSUB function.
501 Inside the XSUB routine, you create an SV which initially has a reference
502 count of one. Then you call C<newRV_inc>, passing it the just-created SV.
503 This returns the reference as a new SV, but the reference count of the
504 SV you passed to C<newRV_inc> has been incremented to two. Now you
505 return the reference from the XSUB routine and forget about the SV.
506 But Perl hasn't! Whenever the returned reference is destroyed, the
507 reference count of the original SV is decreased to one and nothing happens.
508 The SV will hang around without any way to access it until Perl itself
509 terminates. This is a memory leak.
511 The correct procedure, then, is to use C<newRV_noinc> instead of
512 C<newRV_inc>. Then, if and when the last reference is destroyed,
513 the reference count of the SV will go to zero and it will be destroyed,
514 stopping any memory leak.
516 There are some convenience functions available that can help with the
517 destruction of xV's. These functions introduce the concept of "mortality".
518 An xV that is mortal has had its reference count marked to be decremented,
519 but not actually decremented, until "a short time later". Generally the
520 term "short time later" means a single Perl statement, such as a call to
521 an XSUB function. The actual determinant for when mortal xV's have their
522 reference count decremented depends on two macros, SAVETMPS and FREETMPS.
523 See L<perlcall> and L<perlxs> for more details on these macros.
525 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
526 However, if you mortalize a variable twice, the reference count will
527 later be decremented twice.
529 You should be careful about creating mortal variables. Strange things
530 can happen if you make the same value mortal within multiple contexts,
531 or if you make a variable mortal multiple times.
533 To create a mortal variable, use the functions:
537 SV* sv_mortalcopy(SV*)
539 The first call creates a mortal SV, the second converts an existing
540 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
541 third creates a mortal copy of an existing SV.
543 The mortal routines are not just for SV's -- AV's and HV's can be
544 made mortal by passing their address (type-casted to C<SV*>) to the
545 C<sv_2mortal> or C<sv_mortalcopy> routines.
547 =head2 Stashes and Globs
549 A "stash" is a hash that contains all of the different objects that
550 are contained within a package. Each key of the stash is a symbol
551 name (shared by all the different types of objects that have the same
552 name), and each value in the hash table is a GV (Glob Value). This GV
553 in turn contains references to the various objects of that name,
554 including (but not limited to) the following:
564 There is a single stash called "defstash" that holds the items that exist
565 in the "main" package. To get at the items in other packages, append the
566 string "::" to the package name. The items in the "Foo" package are in
567 the stash "Foo::" in defstash. The items in the "Bar::Baz" package are
568 in the stash "Baz::" in "Bar::"'s stash.
570 To get the stash pointer for a particular package, use the function:
572 HV* gv_stashpv(char* name, I32 create)
573 HV* gv_stashsv(SV*, I32 create)
575 The first function takes a literal string, the second uses the string stored
576 in the SV. Remember that a stash is just a hash table, so you get back an
577 C<HV*>. The C<create> flag will create a new package if it is set.
579 The name that C<gv_stash*v> wants is the name of the package whose symbol table
580 you want. The default package is called C<main>. If you have multiply nested
581 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
584 Alternately, if you have an SV that is a blessed reference, you can find
585 out the stash pointer by using:
587 HV* SvSTASH(SvRV(SV*));
589 then use the following to get the package name itself:
591 char* HvNAME(HV* stash);
593 If you need to bless or re-bless an object you can use the following
596 SV* sv_bless(SV*, HV* stash)
598 where the first argument, an C<SV*>, must be a reference, and the second
599 argument is a stash. The returned C<SV*> can now be used in the same way
602 For more information on references and blessings, consult L<perlref>.
604 =head2 Double-Typed SV's
606 Scalar variables normally contain only one type of value, an integer,
607 double, pointer, or reference. Perl will automatically convert the
608 actual scalar data from the stored type into the requested type.
610 Some scalar variables contain more than one type of scalar data. For
611 example, the variable C<$!> contains either the numeric value of C<errno>
612 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
614 To force multiple data values into an SV, you must do two things: use the
615 C<sv_set*v> routines to add the additional scalar type, then set a flag
616 so that Perl will believe it contains more than one type of data. The
617 four macros to set the flags are:
624 The particular macro you must use depends on which C<sv_set*v> routine
625 you called first. This is because every C<sv_set*v> routine turns on
626 only the bit for the particular type of data being set, and turns off
629 For example, to create a new Perl variable called "dberror" that contains
630 both the numeric and descriptive string error values, you could use the
634 extern char *dberror_list;
636 SV* sv = perl_get_sv("dberror", TRUE);
637 sv_setiv(sv, (IV) dberror);
638 sv_setpv(sv, dberror_list[dberror]);
641 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
642 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
644 =head2 Magic Variables
646 [This section still under construction. Ignore everything here. Post no
647 bills. Everything not permitted is forbidden.]
649 Any SV may be magical, that is, it has special features that a normal
650 SV does not have. These features are stored in the SV structure in a
651 linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
664 Note this is current as of patchlevel 0, and could change at any time.
666 =head2 Assigning Magic
668 Perl adds magic to an SV using the sv_magic function:
670 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
672 The C<sv> argument is a pointer to the SV that is to acquire a new magical
675 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
676 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
677 it to the beginning of the linked list of magical features. Any prior
678 entry of the same type of magic is deleted. Note that this can be
679 overridden, and multiple instances of the same type of magic can be
680 associated with an SV.
682 The C<name> and C<namlem> arguments are used to associate a string with
683 the magic, typically the name of a variable. C<namlem> is stored in the
684 C<mg_len> field and if C<name> is non-null and C<namlem> >= 0 a malloc'd
685 copy of the name is stored in C<mg_ptr> field.
687 The sv_magic function uses C<how> to determine which, if any, predefined
688 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
689 See the "Magic Virtual Table" section below. The C<how> argument is also
690 stored in the C<mg_type> field.
692 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
693 structure. If it is not the same as the C<sv> argument, the reference
694 count of the C<obj> object is incremented. If it is the same, or if
695 the C<how> argument is "#", or if it is a null pointer, then C<obj> is
696 merely stored, without the reference count being incremented.
698 There is also a function to add magic to an C<HV>:
700 void hv_magic(HV *hv, GV *gv, int how);
702 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
704 To remove the magic from an SV, call the function sv_unmagic:
706 void sv_unmagic(SV *sv, int type);
708 The C<type> argument should be equal to the C<how> value when the C<SV>
709 was initially made magical.
711 =head2 Magic Virtual Tables
713 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
714 C<MGVTBL>, which is a structure of function pointers and stands for
715 "Magic Virtual Table" to handle the various operations that might be
716 applied to that variable.
718 The C<MGVTBL> has five pointers to the following routine types:
720 int (*svt_get)(SV* sv, MAGIC* mg);
721 int (*svt_set)(SV* sv, MAGIC* mg);
722 U32 (*svt_len)(SV* sv, MAGIC* mg);
723 int (*svt_clear)(SV* sv, MAGIC* mg);
724 int (*svt_free)(SV* sv, MAGIC* mg);
726 This MGVTBL structure is set at compile-time in C<perl.h> and there are
727 currently 19 types (or 21 with overloading turned on). These different
728 structures contain pointers to various routines that perform additional
729 actions depending on which function is being called.
731 Function pointer Action taken
732 ---------------- ------------
733 svt_get Do something after the value of the SV is retrieved.
734 svt_set Do something after the SV is assigned a value.
735 svt_len Report on the SV's length.
736 svt_clear Clear something the SV represents.
737 svt_free Free any extra storage associated with the SV.
739 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
740 to an C<mg_type> of '\0') contains:
742 { magic_get, magic_set, magic_len, 0, 0 }
744 Thus, when an SV is determined to be magical and of type '\0', if a get
745 operation is being performed, the routine C<magic_get> is called. All
746 the various routines for the various magical types begin with C<magic_>.
748 The current kinds of Magic Virtual Tables are:
750 mg_type MGVTBL Type of magical
751 ------- ------ ----------------------------
753 A vtbl_amagic Operator Overloading
754 a vtbl_amagicelem Operator Overloading
755 c 0 Used in Operator Overloading
756 B vtbl_bm Boyer-Moore???
758 e vtbl_envelem %ENV hash element
759 g vtbl_mglob Regexp /g flag???
760 I vtbl_isa @ISA array
761 i vtbl_isaelem @ISA array element
762 L 0 (but sets RMAGICAL) Perl Module/Debugger???
763 l vtbl_dbline Debugger?
764 o vtbl_collxfrm Locale transformation
765 P vtbl_pack Tied Array or Hash
766 p vtbl_packelem Tied Array or Hash element
767 q vtbl_packelem Tied Scalar or Handle
768 S vtbl_sig Signal Hash
769 s vtbl_sigelem Signal Hash element
770 t vtbl_taint Taintedness
773 x vtbl_substr Substring???
774 y vtbl_itervar Shadow "foreach" iterator variable
776 # vtbl_arylen Array Length
777 . vtbl_pos $. scalar variable
778 ~ None Used by certain extensions
780 When an upper-case and lower-case letter both exist in the table, then the
781 upper-case letter is used to represent some kind of composite type (a list
782 or a hash), and the lower-case letter is used to represent an element of
785 The '~' magic type is defined specifically for use by extensions and
786 will not be used by perl itself. Extensions can use ~ magic to 'attach'
787 private information to variables (typically objects). This is especially
788 useful because there is no way for normal perl code to corrupt this
789 private information (unlike using extra elements of a hash object).
791 Note that because multiple extensions may be using ~ magic it is
792 important for extensions to take extra care with it. Typically only
793 using it on objects blessed into the same class as the extension
794 is sufficient. It may also be appropriate to add an I32 'signature'
795 at the top of the private data area and check that.
799 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
801 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
802 If the SV does not have that magical feature, C<NULL> is returned. Also,
803 if the SV is not of type SVt_PVMG, Perl may core-dump.
805 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
807 This routine checks to see what types of magic C<sv> has. If the mg_type
808 field is an upper-case letter, then the mg_obj is copied to C<nsv>, but
809 the mg_type field is changed to be the lower-case letter.
813 =head2 XSUB's and the Argument Stack
815 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
816 An XSUB routine will have a stack that contains the arguments from the Perl
817 program, and a way to map from the Perl data structures to a C equivalent.
819 The stack arguments are accessible through the C<ST(n)> macro, which returns
820 the C<n>'th stack argument. Argument 0 is the first argument passed in the
821 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
824 Most of the time, output from the C routine can be handled through use of
825 the RETVAL and OUTPUT directives. However, there are some cases where the
826 argument stack is not already long enough to handle all the return values.
827 An example is the POSIX tzname() call, which takes no arguments, but returns
828 two, the local time zone's standard and summer time abbreviations.
830 To handle this situation, the PPCODE directive is used and the stack is
831 extended using the macro:
835 where C<sp> is the stack pointer, and C<num> is the number of elements the
836 stack should be extended by.
838 Now that there is room on the stack, values can be pushed on it using the
839 macros to push IV's, doubles, strings, and SV pointers respectively:
846 And now the Perl program calling C<tzname>, the two values will be assigned
849 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
851 An alternate (and possibly simpler) method to pushing values on the stack is
859 These macros automatically adjust the stack for you, if needed. Thus, you
860 do not need to call C<EXTEND> to extend the stack.
862 For more information, consult L<perlxs> and L<perlxstut>.
864 =head2 Calling Perl Routines from within C Programs
866 There are four routines that can be used to call a Perl subroutine from
867 within a C program. These four are:
869 I32 perl_call_sv(SV*, I32);
870 I32 perl_call_pv(char*, I32);
871 I32 perl_call_method(char*, I32);
872 I32 perl_call_argv(char*, I32, register char**);
874 The routine most often used is C<perl_call_sv>. The C<SV*> argument
875 contains either the name of the Perl subroutine to be called, or a
876 reference to the subroutine. The second argument consists of flags
877 that control the context in which the subroutine is called, whether
878 or not the subroutine is being passed arguments, how errors should be
879 trapped, and how to treat return values.
881 All four routines return the number of arguments that the subroutine returned
884 When using any of these routines (except C<perl_call_argv>), the programmer
885 must manipulate the Perl stack. These include the following macros and
899 For a detailed description of calling conventions from C to Perl,
902 =head2 Memory Allocation
904 It is suggested that you use the version of malloc that is distributed
905 with Perl. It keeps pools of various sizes of unallocated memory in
906 order to satisfy allocation requests more quickly. However, on some
907 platforms, it may cause spurious malloc or free errors.
909 New(x, pointer, number, type);
910 Newc(x, pointer, number, type, cast);
911 Newz(x, pointer, number, type);
913 These three macros are used to initially allocate memory.
915 The first argument C<x> was a "magic cookie" that was used to keep track
916 of who called the macro, to help when debugging memory problems. However,
917 the current code makes no use of this feature (most Perl developers now
918 use run-time memory checkers), so this argument can be any number.
920 The second argument C<pointer> should be the name of a variable that will
921 point to the newly allocated memory.
923 The third and fourth arguments C<number> and C<type> specify how many of
924 the specified type of data structure should be allocated. The argument
925 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
926 should be used if the C<pointer> argument is different from the C<type>
929 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
930 to zero out all the newly allocated memory.
932 Renew(pointer, number, type);
933 Renewc(pointer, number, type, cast);
936 These three macros are used to change a memory buffer size or to free a
937 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
938 match those of C<New> and C<Newc> with the exception of not needing the
939 "magic cookie" argument.
941 Move(source, dest, number, type);
942 Copy(source, dest, number, type);
943 Zero(dest, number, type);
945 These three macros are used to move, copy, or zero out previously allocated
946 memory. The C<source> and C<dest> arguments point to the source and
947 destination starting points. Perl will move, copy, or zero out C<number>
948 instances of the size of the C<type> data structure (using the C<sizeof>
953 The most recent development releases of Perl has been experimenting with
954 removing Perl's dependency on the "normal" standard I/O suite and allowing
955 other stdio implementations to be used. This involves creating a new
956 abstraction layer that then calls whichever implementation of stdio Perl
957 was compiled with. All XSUB's should now use the functions in the PerlIO
958 abstraction layer and not make any assumptions about what kind of stdio
961 For a complete description of the PerlIO abstraction, consult L<perlapio>.
963 =head2 Putting a C value on Perl stack
965 A lot of opcodes (this is an elementary operation in the internal perl
966 stack machine) put an SV* on the stack. However, as an optimization
967 the corresponding SV is (usually) not recreated each time. The opcodes
968 reuse specially assigned SVs (I<target>s) which are (as a corollary)
969 not constantly freed/created.
971 Each of the targets is created only once (but see
972 L<Scratchpads and recursion> below), and when an opcode needs to put
973 an integer, a double, or a string on stack, it just sets the
974 corresponding parts of its I<target> and puts the I<target> on stack.
976 The macro to put this target on stack is C<PUSHTARG>, and it is
977 directly used in some opcodes, as well as indirectly in zillions of
978 others, which use it via C<(X)PUSH[pni]>.
982 The question remains on when the SV's which are I<target>s for opcodes
983 are created. The answer is that they are created when the current unit --
984 a subroutine or a file (for opcodes for statements outside of
985 subroutines) -- is compiled. During this time a special anonymous Perl
986 array is created, which is called a scratchpad for the current
989 A scratchpad keeps SV's which are lexicals for the current unit and are
990 targets for opcodes. One can deduce that an SV lives on a scratchpad
991 by looking on its flags: lexicals have C<SVs_PADMY> set, and
992 I<target>s have C<SVs_PADTMP> set.
994 The correspondence between OP's and I<target>s is not 1-to-1. Different
995 OP's in the compile tree of the unit can use the same target, if this
996 would not conflict with the expected life of the temporary.
998 =head2 Scratchpads and recursions
1000 In fact it is not 100% true that a compiled unit contains a pointer to
1001 the scratchpad AV. In fact it contains a pointer to an AV of
1002 (initially) one element, and this element is the scratchpad AV. Why do
1003 we need an extra level of indirection?
1005 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1006 these can create several execution pointers going into the same
1007 subroutine. For the subroutine-child not write over the temporaries
1008 for the subroutine-parent (lifespan of which covers the call to the
1009 child), the parent and the child should have different
1010 scratchpads. (I<And> the lexicals should be separate anyway!)
1012 So each subroutine is born with an array of scratchpads (of length 1).
1013 On each entry to the subroutine it is checked that the current
1014 depth of the recursion is not more than the length of this array, and
1015 if it is, new scratchpad is created and pushed into the array.
1017 The I<target>s on this scratchpad are C<undef>s, but they are already
1018 marked with correct flags.
1020 =head1 Compiled code
1024 Here we describe the internal form your code is converted to by
1025 Perl. Start with a simple example:
1029 This is converted to a tree similar to this one:
1037 (but slightly more complicated). This tree reflect the way Perl
1038 parsed your code, but has nothing to do with the execution order.
1039 There is an additional "thread" going through the nodes of the tree
1040 which shows the order of execution of the nodes. In our simplified
1041 example above it looks like:
1043 $b ---> $c ---> + ---> $a ---> assign-to
1045 But with the actual compile tree for C<$a = $b + $c> it is different:
1046 some nodes I<optimized away>. As a corollary, though the actual tree
1047 contains more nodes than our simplified example, the execution order
1048 is the same as in our example.
1050 =head2 Examining the tree
1052 If you have your perl compiled for debugging (usually done with C<-D
1053 optimize=-g> on C<Configure> command line), you may examine the
1054 compiled tree by specifying C<-Dx> on the Perl command line. The
1055 output takes several lines per node, and for C<$b+$c> it looks like
1060 FLAGS = (SCALAR,KIDS)
1062 TYPE = null ===> (4)
1064 FLAGS = (SCALAR,KIDS)
1066 3 TYPE = gvsv ===> 4
1072 TYPE = null ===> (5)
1074 FLAGS = (SCALAR,KIDS)
1076 4 TYPE = gvsv ===> 5
1082 This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1083 not optimized away (one per number in the left column). The immediate
1084 children of the given node correspond to C<{}> pairs on the same level
1085 of indentation, thus this listing corresponds to the tree:
1093 The execution order is indicated by C<===E<gt>> marks, thus it is C<3
1094 4 5 6> (node C<6> is not included into above listing), i.e.,
1095 C<gvsv gvsv add whatever>.
1097 =head2 Compile pass 1: check routines
1099 The tree is created by the I<pseudo-compiler> while yacc code feeds it
1100 the constructions it recognizes. Since yacc works bottom-up, so does
1101 the first pass of perl compilation.
1103 What makes this pass interesting for perl developers is that some
1104 optimization may be performed on this pass. This is optimization by
1105 so-called I<check routines>. The correspondence between node names
1106 and corresponding check routines is described in F<opcode.pl> (do not
1107 forget to run C<make regen_headers> if you modify this file).
1109 A check routine is called when the node is fully constructed except
1110 for the execution-order thread. Since at this time there is no
1111 back-links to the currently constructed node, one can do most any
1112 operation to the top-level node, including freeing it and/or creating
1113 new nodes above/below it.
1115 The check routine returns the node which should be inserted into the
1116 tree (if the top-level node was not modified, check routine returns
1119 By convention, check routines have names C<ck_*>. They are usually
1120 called from C<new*OP> subroutines (or C<convert>) (which in turn are
1121 called from F<perly.y>).
1123 =head2 Compile pass 1a: constant folding
1125 Immediately after the check routine is called the returned node is
1126 checked for being compile-time executable. If it is (the value is
1127 judged to be constant) it is immediately executed, and a I<constant>
1128 node with the "return value" of the corresponding subtree is
1129 substituted instead. The subtree is deleted.
1131 If constant folding was not performed, the execution-order thread is
1134 =head2 Compile pass 2: context propagation
1136 When a context for a part of compile tree is known, it is propagated
1137 down through the tree. Aat this time the context can have 5 values
1138 (instead of 2 for runtime context): void, boolean, scalar, list, and
1139 lvalue. In contrast with the pass 1 this pass is processed from top
1140 to bottom: a node's context determines the context for its children.
1142 Additional context-dependent optimizations are performed at this time.
1143 Since at this moment the compile tree contains back-references (via
1144 "thread" pointers), nodes cannot be free()d now. To allow
1145 optimized-away nodes at this stage, such nodes are null()ified instead
1146 of free()ing (i.e. their type is changed to OP_NULL).
1148 =head2 Compile pass 3: peephole optimization
1150 After the compile tree for a subroutine (or for an C<eval> or a file)
1151 is created, an additional pass over the code is performed. This pass
1152 is neither top-down or bottom-up, but in the execution order (with
1153 additional compilications for conditionals). These optimizations are
1154 done in the subroutine peep(). Optimizations performed at this stage
1155 are subject to the same restrictions as in the pass 2.
1159 This is a listing of functions, macros, flags, and variables that may be
1160 useful to extension writers or that may be found while reading other
1171 Clears an array, making it empty.
1173 void av_clear _((AV* ar));
1177 Pre-extend an array. The C<key> is the index to which the array should be
1180 void av_extend _((AV* ar, I32 key));
1184 Returns the SV at the specified index in the array. The C<key> is the
1185 index. If C<lval> is set then the fetch will be part of a store. Check
1186 that the return value is non-null before dereferencing it to a C<SV*>.
1188 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1192 Returns the highest index in the array. Returns -1 if the array is empty.
1194 I32 av_len _((AV* ar));
1198 Creates a new AV and populates it with a list of SVs. The SVs are copied
1199 into the array, so they may be freed after the call to av_make. The new AV
1200 will have a reference count of 1.
1202 AV* av_make _((I32 size, SV** svp));
1206 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1209 SV* av_pop _((AV* ar));
1213 Pushes an SV onto the end of the array. The array will grow automatically
1214 to accommodate the addition.
1216 void av_push _((AV* ar, SV* val));
1220 Shifts an SV off the beginning of the array.
1222 SV* av_shift _((AV* ar));
1226 Stores an SV in an array. The array index is specified as C<key>. The
1227 return value will be null if the operation failed, otherwise it can be
1228 dereferenced to get the original C<SV*>.
1230 SV** av_store _((AV* ar, I32 key, SV* val));
1234 Undefines the array.
1236 void av_undef _((AV* ar));
1240 Unshift an SV onto the beginning of the array. The array will grow
1241 automatically to accommodate the addition.
1243 void av_unshift _((AV* ar, I32 num));
1247 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1248 constructor. This is always a C<char*>. See C<THIS> and
1249 L<perlxs/"Using XS With C++">.
1253 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1254 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1257 (void) Copy( s, d, n, t );
1261 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1262 function the same way you use the C C<printf> function. See C<warn>.
1266 Returns the stash of the CV.
1268 HV * CvSTASH( SV* sv )
1272 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1273 boolean which indicates whether subs are being single-stepped.
1274 Single-stepping is automatically turned on after every step. This is the C
1275 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1279 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1280 the SV which holds the name of the sub being debugged. This is the C
1281 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1282 The sub name can be found by
1284 SvPV( GvSV( DBsub ), na )
1288 Trace variable used when Perl is run in debugging mode, with the B<-d>
1289 switch. This is the C variable which corresponds to Perl's $DB::trace
1290 variable. See C<DBsingle>.
1294 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1299 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1303 The C variable which corresponds to Perl's $^W warning variable.
1307 Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
1311 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1312 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1313 to indicate the number of items on the stack.
1317 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1318 handled automatically by C<xsubpp>.
1322 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1323 handled automatically by C<xsubpp>.
1327 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1333 Used to extend the argument stack for an XSUB's return values.
1335 EXTEND( sp, int x );
1339 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1346 Used to indicate array context. See C<GIMME> and L<perlcall>.
1350 Indicates that arguments returned from a callback should be discarded. See
1355 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1359 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns C<G_SCALAR> or
1360 C<G_ARRAY> for scalar or array context.
1364 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1368 Used to indicate scalar context. See C<GIMME> and L<perlcall>.
1372 Returns the glob with the given C<name> and a defined subroutine or
1373 C<NULL>. The glob lives in the given C<stash>, or in the stashes
1374 accessable via @ISA and @<UNIVERSAL>.
1376 The argument C<level> should be either 0 or -1. If C<level==0>, as a
1377 side-effect creates a glob with the given C<name> in the given
1378 C<stash> which in the case of success contains an alias for the
1379 subroutine, and sets up caching info for this glob. Similarly for all
1380 the searched stashes.
1382 This function grants C<"SUPER"> token as a postfix of the stash name.
1384 The GV returned from C<gv_fetchmeth> may be a method cache entry,
1385 which is not visible to Perl code. So when calling C<perl_call_sv>,
1386 you should not use the GV directly; instead, you should use the
1387 method's CV, which can be obtained from the GV with the C<GvCV> macro.
1389 GV* gv_fetchmeth _((HV* stash, char* name, STRLEN len, I32 level));
1391 =item gv_fetchmethod
1393 Returns the glob which contains the subroutine to call to invoke the
1394 method on the C<stash>. In fact in the presense of autoloading this may
1395 be the glob for "AUTOLOAD". In this case the corresponing variable
1396 $AUTOLOAD is already setup.
1398 Note that if you want to keep this glob for a long time, you need to
1399 check for it being "AUTOLOAD", since at the later time the the call
1400 may load a different subroutine due to $AUTOLOAD changing its value.
1401 Use the glob created via a side effect to do this.
1403 This function grants C<"SUPER"> token as a prefix of the method name.
1405 Has the same side-effects and as C<gv_fetchmeth> with C<level==0>.
1406 C<name> should be writable if contains C<':'> or C<'\''>.
1407 The warning against passing the GV returned by C<gv_fetchmeth> to
1408 C<perl_call_sv> apply equally to C<gv_fetchmethod>.
1410 GV* gv_fetchmethod _((HV* stash, char* name));
1414 Returns a pointer to the stash for a specified package. If C<create> is set
1415 then the package will be created if it does not already exist. If C<create>
1416 is not set and the package does not exist then NULL is returned.
1418 HV* gv_stashpv _((char* name, I32 create));
1422 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1424 HV* gv_stashsv _((SV* sv, I32 create));
1428 Return the SV from the GV.
1432 Releases a hash entry, such as while iterating though the hash, but
1433 delays actual freeing of key and value until the end of the current
1434 statement (or thereabouts) with C<sv_2mortal>. See C<hv_iternext>.
1436 void he_delayfree _((HV* hv, HE* hent));
1440 This flag, used in the length slot of hash entries and magic
1441 structures, specifies the structure contains a C<SV*> pointer where a
1442 C<char*> pointer is to be expected. (For information only--not to be used).
1446 Releases a hash entry, such as while iterating though the hash. See
1449 void he_free _((HV* hv, HE* hent));
1453 Returns the computed hash (type C<U32>) stored in the hash entry.
1459 Returns the actual pointer stored in the key slot of the hash entry.
1460 The pointer may be either C<char*> or C<SV*>, depending on the value of
1461 C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
1462 are usually preferable for finding the value of a key.
1468 If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
1469 holds an C<SV*> key. Otherwise, holds the actual length of the key.
1470 Can be assigned to. The C<HePV()> macro is usually preferable for finding
1477 Returns the key slot of the hash entry as a C<char*> value, doing any
1478 necessary dereferencing of possibly C<SV*> keys. The length of
1479 the string is placed in C<len> (this is a macro, so do I<not> use
1480 C<&len>). If you do not care about what the length of the key is,
1481 you may use the global variable C<na>. Remember though, that hash
1482 keys in perl are free to contain embedded nulls, so using C<strlen()>
1483 or similar is not a good way to find the length of hash keys.
1484 This is very similar to the C<SvPV()> macro described elsewhere in
1487 HePV(HE* he, STRLEN len)
1491 Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
1492 does not contain an C<SV*> key.
1498 Returns the key as an C<SV*>. Will create and return a temporary
1499 mortal C<SV*> if the hash entry contains only a C<char*> key.
1501 HeSVKEY_force(HE* he)
1505 Sets the key to a given C<SV*>, taking care to set the appropriate flags
1506 to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
1508 HeSVKEY_set(HE* he, SV* sv)
1512 Returns the value slot (type C<SV*>) stored in the hash entry.
1518 Clears a hash, making it empty.
1520 void hv_clear _((HV* tb));
1524 Deletes a key/value pair in the hash. The value SV is removed from the hash
1525 and returned to the caller. The C<klen> is the length of the key. The
1526 C<flags> value will normally be zero; if set to G_DISCARD then null will be
1529 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1533 Deletes a key/value pair in the hash. The value SV is removed from the hash
1534 and returned to the caller. The C<flags> value will normally be zero; if set
1535 to G_DISCARD then null will be returned. C<hash> can be a valid pre-computed
1536 hash value, or 0 to ask for it to be computed.
1538 SV* hv_delete_ent _((HV* tb, SV* key, I32 flags, U32 hash));
1542 Returns a boolean indicating whether the specified hash key exists. The
1543 C<klen> is the length of the key.
1545 bool hv_exists _((HV* tb, char* key, U32 klen));
1549 Returns a boolean indicating whether the specified hash key exists. C<hash>
1550 can be a valid pre-computed hash value, or 0 to ask for it to be computed.
1552 bool hv_exists_ent _((HV* tb, SV* key, U32 hash));
1556 Returns the SV which corresponds to the specified key in the hash. The
1557 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1558 part of a store. Check that the return value is non-null before
1559 dereferencing it to a C<SV*>.
1561 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1565 Returns the hash entry which corresponds to the specified key in the hash.
1566 C<hash> must be a valid pre-computed hash number for the given C<key>, or
1567 0 if you want the function to compute it. IF C<lval> is set then the
1568 fetch will be part of a store. Make sure the return value is non-null
1569 before accessing it. The return value when C<tb> is a tied hash
1570 is a pointer to a static location, so be sure to make a copy of the
1571 structure if you need to store it somewhere.
1573 HE* hv_fetch_ent _((HV* tb, SV* key, I32 lval, U32 hash));
1577 Prepares a starting point to traverse a hash table.
1579 I32 hv_iterinit _((HV* tb));
1583 Returns the key from the current position of the hash iterator. See
1586 char* hv_iterkey _((HE* entry, I32* retlen));
1590 Returns the key as an C<SV*> from the current position of the hash
1591 iterator. The return value will always be a mortal copy of the
1592 key. Also see C<hv_iterinit>.
1594 SV* hv_iterkeysv _((HE* entry));
1598 Returns entries from a hash iterator. See C<hv_iterinit>.
1600 HE* hv_iternext _((HV* tb));
1604 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1607 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1611 Returns the value from the current position of the hash iterator. See
1614 SV* hv_iterval _((HV* tb, HE* entry));
1618 Adds magic to a hash. See C<sv_magic>.
1620 void hv_magic _((HV* hv, GV* gv, int how));
1624 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1626 char *HvNAME (HV* stash)
1630 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1631 the length of the key. The C<hash> parameter is the pre-computed hash
1632 value; if it is zero then Perl will compute it. The return value will be
1633 null if the operation failed, otherwise it can be dereferenced to get the
1636 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1640 Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
1641 parameter is the pre-computed hash value; if it is zero then Perl will
1642 compute it. The return value is the new hash entry so created. It will be
1643 null if the operation failed or if the entry was stored in a tied hash.
1644 Otherwise the contents of the return value can be accessed using the
1645 C<He???> macros described here.
1647 HE* hv_store_ent _((HV* tb, SV* key, SV* val, U32 hash));
1653 void hv_undef _((HV* tb));
1657 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
1660 int isALNUM (char c)
1664 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
1667 int isALPHA (char c)
1671 Returns a boolean indicating whether the C C<char> is an ascii digit.
1673 int isDIGIT (char c)
1677 Returns a boolean indicating whether the C C<char> is a lowercase character.
1679 int isLOWER (char c)
1683 Returns a boolean indicating whether the C C<char> is whitespace.
1685 int isSPACE (char c)
1689 Returns a boolean indicating whether the C C<char> is an uppercase character.
1691 int isUPPER (char c)
1695 Variable which is setup by C<xsubpp> to indicate the number of items on the
1696 stack. See L<perlxs/"Variable-length Parameter Lists">.
1700 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1701 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
1705 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1711 Stack marker variable for the XSUB. See C<dMARK>.
1715 Clear something magical that the SV represents. See C<sv_magic>.
1717 int mg_clear _((SV* sv));
1721 Copies the magic from one SV to another. See C<sv_magic>.
1723 int mg_copy _((SV *, SV *, char *, STRLEN));
1727 Finds the magic pointer for type matching the SV. See C<sv_magic>.
1729 MAGIC* mg_find _((SV* sv, int type));
1733 Free any magic storage used by the SV. See C<sv_magic>.
1735 int mg_free _((SV* sv));
1739 Do magic after a value is retrieved from the SV. See C<sv_magic>.
1741 int mg_get _((SV* sv));
1745 Report on the SV's length. See C<sv_magic>.
1747 U32 mg_len _((SV* sv));
1751 Turns on the magical status of an SV. See C<sv_magic>.
1753 void mg_magical _((SV* sv));
1757 Do magic after a value is assigned to the SV. See C<sv_magic>.
1759 int mg_set _((SV* sv));
1763 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
1764 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1767 (void) Move( s, d, n, t );
1771 A variable which may be used with C<SvPV> to tell Perl to calculate the
1776 The XSUB-writer's interface to the C C<malloc> function.
1778 void * New( x, void *ptr, int size, type )
1782 The XSUB-writer's interface to the C C<malloc> function, with cast.
1784 void * Newc( x, void *ptr, int size, type, cast )
1788 The XSUB-writer's interface to the C C<malloc> function. The allocated
1789 memory is zeroed with C<memzero>.
1791 void * Newz( x, void *ptr, int size, type )
1795 Creates a new AV. The reference count is set to 1.
1797 AV* newAV _((void));
1801 Creates a new HV. The reference count is set to 1.
1803 HV* newHV _((void));
1807 Creates an RV wrapper for an SV. The reference count for the original SV is
1810 SV* newRV_inc _((SV* ref));
1812 For historical reasons, "newRV" is a synonym for "newRV_inc".
1816 Creates an RV wrapper for an SV. The reference count for the original
1817 SV is B<not> incremented.
1819 SV* newRV_noinc _((SV* ref));
1823 Creates a new SV. The C<len> parameter indicates the number of bytes of
1824 pre-allocated string space the SV should have. The reference count for the
1827 SV* newSV _((STRLEN len));
1831 Creates a new SV and copies an integer into it. The reference count for the
1834 SV* newSViv _((IV i));
1838 Creates a new SV and copies a double into it. The reference count for the
1841 SV* newSVnv _((NV i));
1845 Creates a new SV and copies a string into it. The reference count for the
1846 SV is set to 1. If C<len> is zero then Perl will compute the length.
1848 SV* newSVpv _((char* s, STRLEN len));
1852 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
1853 it will be upgraded to one. If C<classname> is non-null then the new SV will
1854 be blessed in the specified package. The new SV is returned and its
1855 reference count is 1.
1857 SV* newSVrv _((SV* rv, char* classname));
1861 Creates a new SV which is an exact duplicate of the original SV.
1863 SV* newSVsv _((SV* old));
1867 Used by C<xsubpp> to hook up XSUBs as Perl subs.
1871 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
1880 Null character pointer.
1896 The original stack mark for the XSUB. See C<dORIGMARK>.
1900 Allocates a new Perl interpreter. See L<perlembed>.
1902 =item perl_call_argv
1904 Performs a callback to the specified Perl sub. See L<perlcall>.
1906 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
1908 =item perl_call_method
1910 Performs a callback to the specified Perl method. The blessed object must
1911 be on the stack. See L<perlcall>.
1913 I32 perl_call_method _((char* methname, I32 flags));
1917 Performs a callback to the specified Perl sub. See L<perlcall>.
1919 I32 perl_call_pv _((char* subname, I32 flags));
1923 Performs a callback to the Perl sub whose name is in the SV. See
1926 I32 perl_call_sv _((SV* sv, I32 flags));
1928 =item perl_construct
1930 Initializes a new Perl interpreter. See L<perlembed>.
1934 Shuts down a Perl interpreter. See L<perlembed>.
1938 Tells Perl to C<eval> the string in the SV.
1940 I32 perl_eval_sv _((SV* sv, I32 flags));
1944 Releases a Perl interpreter. See L<perlembed>.
1948 Returns the AV of the specified Perl array. If C<create> is set and the
1949 Perl variable does not exist then it will be created. If C<create> is not
1950 set and the variable does not exist then null is returned.
1952 AV* perl_get_av _((char* name, I32 create));
1956 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
1957 variable does not exist then it will be created. If C<create> is not
1958 set and the variable does not exist then null is returned.
1960 CV* perl_get_cv _((char* name, I32 create));
1964 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
1965 variable does not exist then it will be created. If C<create> is not
1966 set and the variable does not exist then null is returned.
1968 HV* perl_get_hv _((char* name, I32 create));
1972 Returns the SV of the specified Perl scalar. If C<create> is set and the
1973 Perl variable does not exist then it will be created. If C<create> is not
1974 set and the variable does not exist then null is returned.
1976 SV* perl_get_sv _((char* name, I32 create));
1980 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
1982 =item perl_require_pv
1984 Tells Perl to C<require> a module.
1986 void perl_require_pv _((char* pv));
1990 Tells a Perl interpreter to run. See L<perlembed>.
1994 Pops an integer off the stack.
2000 Pops a long off the stack.
2006 Pops a string off the stack.
2012 Pops a double off the stack.
2018 Pops an SV off the stack.
2024 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2030 Push an integer onto the stack. The stack must have room for this element.
2037 Push a double onto the stack. The stack must have room for this element.
2044 Push a string onto the stack. The stack must have room for this element.
2045 The C<len> indicates the length of the string. See C<XPUSHp>.
2047 PUSHp(char *c, int len )
2051 Push an SV onto the stack. The stack must have room for this element. See
2058 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2059 See C<PUSHMARK> and L<perlcall> for other uses.
2065 The XSUB-writer's interface to the C C<realloc> function.
2067 void * Renew( void *ptr, int size, type )
2071 The XSUB-writer's interface to the C C<realloc> function, with cast.
2073 void * Renewc( void *ptr, int size, type, cast )
2077 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
2078 This is always the proper type for the XSUB.
2079 See L<perlxs/"The RETVAL Variable">.
2083 The XSUB-writer's interface to the C C<free> function.
2087 The XSUB-writer's interface to the C C<malloc> function.
2091 The XSUB-writer's interface to the C C<realloc> function.
2095 Copy a string to a safe spot. This does not use an SV.
2097 char* savepv _((char* sv));
2101 Copy a string to a safe spot. The C<len> indicates number of bytes to
2102 copy. This does not use an SV.
2104 char* savepvn _((char* sv, I32 len));
2108 Opening bracket for temporaries on a callback. See C<FREETMPS> and
2115 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2120 Re-fetch the stack pointer. Used after a callback. See L<perlcall>.
2126 Used to access elements on the XSUB's stack.
2132 Test two strings to see if they are equal. Returns true or false.
2134 int strEQ( char *s1, char *s2 )
2138 Test two strings to see if the first, C<s1>, is greater than or equal to the
2139 second, C<s2>. Returns true or false.
2141 int strGE( char *s1, char *s2 )
2145 Test two strings to see if the first, C<s1>, is greater than the second,
2146 C<s2>. Returns true or false.
2148 int strGT( char *s1, char *s2 )
2152 Test two strings to see if the first, C<s1>, is less than or equal to the
2153 second, C<s2>. Returns true or false.
2155 int strLE( char *s1, char *s2 )
2159 Test two strings to see if the first, C<s1>, is less than the second,
2160 C<s2>. Returns true or false.
2162 int strLT( char *s1, char *s2 )
2166 Test two strings to see if they are different. Returns true or false.
2168 int strNE( char *s1, char *s2 )
2172 Test two strings to see if they are equal. The C<len> parameter indicates
2173 the number of bytes to compare. Returns true or false.
2175 int strnEQ( char *s1, char *s2 )
2179 Test two strings to see if they are different. The C<len> parameter
2180 indicates the number of bytes to compare. Returns true or false.
2182 int strnNE( char *s1, char *s2, int len )
2186 Marks an SV as mortal. The SV will be destroyed when the current context
2189 SV* sv_2mortal _((SV* sv));
2193 Blesses an SV into a specified package. The SV must be an RV. The package
2194 must be designated by its stash (see C<gv_stashpv()>). The reference count
2195 of the SV is unaffected.
2197 SV* sv_bless _((SV* sv, HV* stash));
2201 Concatenates the string onto the end of the string which is in the SV.
2203 void sv_catpv _((SV* sv, char* ptr));
2207 Concatenates the string onto the end of the string which is in the SV. The
2208 C<len> indicates number of bytes to copy.
2210 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
2214 Concatenates the string from SV C<ssv> onto the end of the string in SV
2217 void sv_catsv _((SV* dsv, SV* ssv));
2221 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2222 string in C<sv1> is less than, equal to, or greater than the string in
2225 I32 sv_cmp _((SV* sv1, SV* sv2));
2229 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2230 string in C<sv1> is less than, equal to, or greater than the string in
2233 I32 sv_cmp _((SV* sv1, SV* sv2));
2237 Returns the length of the string which is in the SV. See C<SvLEN>.
2243 Set the length of the string which is in the SV. See C<SvCUR>.
2245 SvCUR_set (SV* sv, int val )
2249 Auto-decrement of the value in the SV.
2251 void sv_dec _((SV* sv));
2255 Auto-decrement of the value in the SV.
2257 void sv_dec _((SV* sv));
2261 Returns a pointer to the last character in the string which is in the SV.
2262 See C<SvCUR>. Access the character as
2268 Returns a boolean indicating whether the strings in the two SVs are
2271 I32 sv_eq _((SV* sv1, SV* sv2));
2275 Expands the character buffer in the SV. Calls C<sv_grow> to perform the
2276 expansion if necessary. Returns a pointer to the character buffer.
2278 char * SvGROW( SV* sv, int len )
2282 Expands the character buffer in the SV. This will use C<sv_unref> and will
2283 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2288 Auto-increment of the value in the SV.
2290 void sv_inc _((SV* sv));
2294 Returns a boolean indicating whether the SV contains an integer.
2300 Unsets the IV status of an SV.
2306 Tells an SV that it is an integer.
2312 Tells an SV that it is an integer and disables all other OK bits.
2318 Tells an SV that it is an integer and disables all other OK bits.
2324 Returns a boolean indicating whether the SV contains an integer. Checks the
2325 B<private> setting. Use C<SvIOK>.
2331 Returns a boolean indicating whether the SV is blessed into the specified
2332 class. This does not know how to check for subtype, so it doesn't work in
2333 an inheritance relationship.
2335 int sv_isa _((SV* sv, char* name));
2339 Returns the integer which is in the SV.
2345 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2346 object. If the SV is not an RV, or if the object is not blessed, then this
2349 int sv_isobject _((SV* sv));
2353 Returns the integer which is stored in the SV.
2359 Returns the size of the string buffer in the SV. See C<SvCUR>.
2365 Returns the length of the string in the SV. Use C<SvCUR>.
2367 STRLEN sv_len _((SV* sv));
2371 Returns the length of the string in the SV. Use C<SvCUR>.
2373 STRLEN sv_len _((SV* sv));
2377 Adds magic to an SV.
2379 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2383 Creates a new SV which is a copy of the original SV. The new SV is marked
2386 SV* sv_mortalcopy _((SV* oldsv));
2390 Returns a boolean indicating whether the value is an SV.
2396 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2398 SV* sv_newmortal _((void));
2402 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2406 Returns a boolean indicating whether the SV contains a number, integer or
2413 Unsets the NV/IV status of an SV.
2419 Returns a boolean indicating whether the SV contains a number, integer or
2420 double. Checks the B<private> setting. Use C<SvNIOK>.
2422 int SvNIOKp (SV* SV)
2426 Returns a boolean indicating whether the SV contains a double.
2432 Unsets the NV status of an SV.
2438 Tells an SV that it is a double.
2444 Tells an SV that it is a double and disables all other OK bits.
2450 Tells an SV that it is a double and disables all other OK bits.
2456 Returns a boolean indicating whether the SV contains a double. Checks the
2457 B<private> setting. Use C<SvNOK>.
2463 Returns the double which is stored in the SV.
2465 double SvNV (SV* sv);
2469 Returns the double which is stored in the SV.
2471 double SvNVX (SV* sv);
2475 Returns a boolean indicating whether the SV contains a character string.
2481 Unsets the PV status of an SV.
2487 Tells an SV that it is a string.
2493 Tells an SV that it is a string and disables all other OK bits.
2499 Tells an SV that it is a string and disables all other OK bits.
2505 Returns a boolean indicating whether the SV contains a character string.
2506 Checks the B<private> setting. Use C<SvPOK>.
2512 Returns a pointer to the string in the SV, or a stringified form of the SV
2513 if the SV does not contain a string. If C<len> is C<na> then Perl will
2514 handle the length on its own.
2516 char * SvPV (SV* sv, int len )
2520 Returns a pointer to the string in the SV. The SV must contain a string.
2522 char * SvPVX (SV* sv)
2526 Returns the value of the object's reference count.
2528 int SvREFCNT (SV* sv);
2532 Decrements the reference count of the given SV.
2534 void SvREFCNT_dec (SV* sv)
2538 Increments the reference count of the given SV.
2540 void SvREFCNT_inc (SV* sv)
2544 Tests if the SV is an RV.
2550 Unsets the RV status of an SV.
2556 Tells an SV that it is an RV.
2562 Dereferences an RV to return the SV.
2568 Copies an integer into the given SV.
2570 void sv_setiv _((SV* sv, IV num));
2574 Copies a double into the given SV.
2576 void sv_setnv _((SV* sv, double num));
2580 Copies a string into an SV. The string must be null-terminated.
2582 void sv_setpv _((SV* sv, char* ptr));
2586 Copies a string into an SV. The C<len> parameter indicates the number of
2589 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2593 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
2594 argument will be upgraded to an RV. That RV will be modified to point to
2595 the new SV. The C<classname> argument indicates the package for the
2596 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2597 will be returned and will have a reference count of 1.
2599 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2603 Copies a double into a new SV, optionally blessing the SV. The C<rv>
2604 argument will be upgraded to an RV. That RV will be modified to point to
2605 the new SV. The C<classname> argument indicates the package for the
2606 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2607 will be returned and will have a reference count of 1.
2609 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2613 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
2614 argument will be upgraded to an RV. That RV will be modified to point to
2615 the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
2616 into the SV. The C<classname> argument indicates the package for the
2617 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2618 will be returned and will have a reference count of 1.
2620 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2622 Do not use with integral Perl types such as HV, AV, SV, CV, because those
2623 objects will become corrupted by the pointer copy process.
2625 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2629 Copies a string into a new SV, optionally blessing the SV. The length of the
2630 string must be specified with C<n>. The C<rv> argument will be upgraded to
2631 an RV. That RV will be modified to point to the new SV. The C<classname>
2632 argument indicates the package for the blessing. Set C<classname> to
2633 C<Nullch> to avoid the blessing. The new SV will be returned and will have
2634 a reference count of 1.
2636 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2638 Note that C<sv_setref_pv> copies the pointer while this copies the string.
2642 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
2643 The source SV may be destroyed if it is mortal.
2645 void sv_setsv _((SV* dsv, SV* ssv));
2649 Returns the stash of the SV.
2651 HV * SvSTASH (SV* sv)
2655 Integer type flag for scalars. See C<svtype>.
2659 Pointer type flag for scalars. See C<svtype>.
2663 Type flag for arrays. See C<svtype>.
2667 Type flag for code refs. See C<svtype>.
2671 Type flag for hashes. See C<svtype>.
2675 Type flag for blessed scalars. See C<svtype>.
2679 Double type flag for scalars. See C<svtype>.
2683 Returns a boolean indicating whether Perl would evaluate the SV as true or
2684 false, defined or undefined.
2690 Returns the type of the SV. See C<svtype>.
2692 svtype SvTYPE (SV* sv)
2696 An enum of flags for Perl types. These are found in the file B<sv.h> in the
2697 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2701 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
2702 the upgrade if necessary. See C<svtype>.
2704 bool SvUPGRADE _((SV* sv, svtype mt));
2708 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
2712 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
2716 Unsets the RV status of the SV, and decrements the reference count of
2717 whatever was being referenced by the RV. This can almost be thought of
2718 as a reversal of C<newSVrv>. See C<SvROK_off>.
2720 void sv_unref _((SV* sv));
2724 Tells an SV to use C<ptr> to find its string value. Normally the string is
2725 stored inside the SV but sv_usepvn allows the SV to use an outside string.
2726 The C<ptr> should point to memory that was allocated by C<malloc>. The
2727 string length, C<len>, must be supplied. This function will realloc the
2728 memory pointed to by C<ptr>, so that pointer should not be freed or used by
2729 the programmer after giving it to sv_usepvn.
2731 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
2735 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
2739 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
2740 This is always the proper type for the C++ object. See C<CLASS> and
2741 L<perlxs/"Using XS With C++">.
2745 Converts the specified character to lowercase.
2747 int toLOWER (char c)
2751 Converts the specified character to uppercase.
2753 int toUPPER (char c)
2757 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
2758 function the same way you use the C C<printf> function. See C<croak()>.
2762 Push an integer onto the stack, extending the stack if necessary. See
2769 Push a double onto the stack, extending the stack if necessary. See
2776 Push a string onto the stack, extending the stack if necessary. The C<len>
2777 indicates the length of the string. See C<PUSHp>.
2779 XPUSHp(char *c, int len)
2783 Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
2789 Macro to declare an XSUB and its C parameter list. This is handled by
2794 Return from XSUB, indicating number of items on the stack. This is usually
2795 handled by C<xsubpp>.
2799 =item XSRETURN_EMPTY
2801 Return an empty list from an XSUB immediately.
2807 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
2813 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
2819 Return an double from an XSUB immediately. Uses C<XST_mNV>.
2825 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
2827 XSRETURN_PV(char *v);
2829 =item XSRETURN_UNDEF
2831 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
2837 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
2843 Place an integer into the specified position C<i> on the stack. The value is
2844 stored in a new mortal SV.
2846 XST_mIV( int i, IV v );
2850 Place a double into the specified position C<i> on the stack. The value is
2851 stored in a new mortal SV.
2853 XST_mNV( int i, NV v );
2857 Place C<&sv_no> into the specified position C<i> on the stack.
2863 Place a copy of a string into the specified position C<i> on the stack. The
2864 value is stored in a new mortal SV.
2866 XST_mPV( int i, char *v );
2870 Place C<&sv_undef> into the specified position C<i> on the stack.
2872 XST_mUNDEF( int i );
2876 Place C<&sv_yes> into the specified position C<i> on the stack.
2882 The version identifier for an XS module. This is usually handled
2883 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
2885 =item XS_VERSION_BOOTCHECK
2887 Macro to verify that a PM module's $VERSION variable matches the XS module's
2888 C<XS_VERSION> variable. This is usually handled automatically by
2889 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
2893 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
2894 destination, C<n> is the number of items, and C<t> is the type.
2896 (void) Zero( d, n, t );
2902 Jeff Okamoto <F<okamoto@corp.hp.com>>
2904 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
2905 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
2906 Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
2908 API Listing by Dean Roehrich <F<roehrich@cray.com>>.
2912 Version 31.2: 1997/3/5