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 SVs
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).
41 SV* newSVpv(char*, int);
42 SV* newSVpvn(char*, int);
43 SV* newSVpvf(const char*, ...);
46 To change the value of an *already-existing* SV, there are seven routines:
48 void sv_setiv(SV*, IV);
49 void sv_setuv(SV*, UV);
50 void sv_setnv(SV*, double);
51 void sv_setpv(SV*, char*);
52 void sv_setpvn(SV*, char*, int)
53 void sv_setpvf(SV*, const char*, ...);
54 void sv_setpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
55 void sv_setsv(SV*, SV*);
57 Notice that you can choose to specify the length of the string to be
58 assigned by using C<sv_setpvn>, C<newSVpvn>, or C<newSVpv>, or you may
59 allow Perl to calculate the length by using C<sv_setpv> or by specifying
60 0 as the second argument to C<newSVpv>. Be warned, though, that Perl will
61 determine the string's length by using C<strlen>, which depends on the
62 string terminating with a NUL character.
64 The arguments of C<sv_setpvf> are processed like C<sprintf>, and the
65 formatted output becomes the value.
67 C<sv_setpvfn> is an analogue of C<vsprintf>, but it allows you to specify
68 either a pointer to a variable argument list or the address and length of
69 an array of SVs. The last argument points to a boolean; on return, if that
70 boolean is true, then locale-specific information has been used to format
71 the string, and the string's contents are therefore untrustworty (see
72 L<perlsec>). This pointer may be NULL if that information is not
73 important. Note that this function requires you to specify the length of
76 The C<sv_set*()> functions are not generic enough to operate on values
77 that have "magic". See L<Magic Virtual Tables> later in this document.
79 All SVs that contain strings should be terminated with a NUL character.
80 If it is not NUL-terminated there is a risk of
81 core dumps and corruptions from code which passes the string to C
82 functions or system calls which expect a NUL-terminated string.
83 Perl's own functions typically add a trailing NUL for this reason.
84 Nevertheless, you should be very careful when you pass a string stored
85 in an SV to a C function or system call.
87 To access the actual value that an SV points to, you can use the macros:
93 which will automatically coerce the actual scalar type into an IV, double,
96 In the C<SvPV> macro, the length of the string returned is placed into the
97 variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
98 care what the length of the data is, use the global variable C<PL_na>. Remember,
99 however, that Perl allows arbitrary strings of data that may both contain
100 NULs and might not be terminated by a NUL.
102 If you want to know if the scalar value is TRUE, you can use:
106 Although Perl will automatically grow strings for you, if you need to force
107 Perl to allocate more memory for your SV, you can use the macro
109 SvGROW(SV*, STRLEN newlen)
111 which will determine if more memory needs to be allocated. If so, it will
112 call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
113 decrease, the allocated memory of an SV and that it does not automatically
114 add a byte for the a trailing NUL (perl's own string functions typically do
115 C<SvGROW(sv, len + 1)>).
117 If you have an SV and want to know what kind of data Perl thinks is stored
118 in it, you can use the following macros to check the type of SV you have.
124 You can get and set the current length of the string stored in an SV with
125 the following macros:
128 SvCUR_set(SV*, I32 val)
130 You can also get a pointer to the end of the string stored in the SV
135 But note that these last three macros are valid only if C<SvPOK()> is true.
137 If you want to append something to the end of string stored in an C<SV*>,
138 you can use the following functions:
140 void sv_catpv(SV*, char*);
141 void sv_catpvn(SV*, char*, int);
142 void sv_catpvf(SV*, const char*, ...);
143 void sv_catpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
144 void sv_catsv(SV*, SV*);
146 The first function calculates the length of the string to be appended by
147 using C<strlen>. In the second, you specify the length of the string
148 yourself. The third function processes its arguments like C<sprintf> and
149 appends the formatted output. The fourth function works like C<vsprintf>.
150 You can specify the address and length of an array of SVs instead of the
151 va_list argument. The fifth function extends the string stored in the first
152 SV with the string stored in the second SV. It also forces the second SV
153 to be interpreted as a string.
155 The C<sv_cat*()> functions are not generic enough to operate on values that
156 have "magic". See L<Magic Virtual Tables> later in this document.
158 If you know the name of a scalar variable, you can get a pointer to its SV
159 by using the following:
161 SV* perl_get_sv("package::varname", FALSE);
163 This returns NULL if the variable does not exist.
165 If you want to know if this variable (or any other SV) is actually C<defined>,
170 The scalar C<undef> value is stored in an SV instance called C<PL_sv_undef>. Its
171 address can be used whenever an C<SV*> is needed.
173 There are also the two values C<PL_sv_yes> and C<PL_sv_no>, which contain Boolean
174 TRUE and FALSE values, respectively. Like C<PL_sv_undef>, their addresses can
175 be used whenever an C<SV*> is needed.
177 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&PL_sv_undef>.
181 if (I-am-to-return-a-real-value) {
182 sv = sv_2mortal(newSViv(42));
186 This code tries to return a new SV (which contains the value 42) if it should
187 return a real value, or undef otherwise. Instead it has returned a NULL
188 pointer which, somewhere down the line, will cause a segmentation violation,
189 bus error, or just weird results. Change the zero to C<&PL_sv_undef> in the first
190 line and all will be well.
192 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
193 call is not necessary (see L<Reference Counts and Mortality>).
195 =head2 What's Really Stored in an SV?
197 Recall that the usual method of determining the type of scalar you have is
198 to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
199 usually these macros will always return TRUE and calling the C<Sv*V>
200 macros will do the appropriate conversion of string to integer/double or
201 integer/double to string.
203 If you I<really> need to know if you have an integer, double, or string
204 pointer in an SV, you can use the following three macros instead:
210 These will tell you if you truly have an integer, double, or string pointer
211 stored in your SV. The "p" stands for private.
213 In general, though, it's best to use the C<Sv*V> macros.
215 =head2 Working with AVs
217 There are two ways to create and load an AV. The first method creates an
222 The second method both creates the AV and initially populates it with SVs:
224 AV* av_make(I32 num, SV **ptr);
226 The second argument points to an array containing C<num> C<SV*>'s. Once the
227 AV has been created, the SVs can be destroyed, if so desired.
229 Once the AV has been created, the following operations are possible on AVs:
231 void av_push(AV*, SV*);
234 void av_unshift(AV*, I32 num);
236 These should be familiar operations, with the exception of C<av_unshift>.
237 This routine adds C<num> elements at the front of the array with the C<undef>
238 value. You must then use C<av_store> (described below) to assign values
239 to these new elements.
241 Here are some other functions:
244 SV** av_fetch(AV*, I32 key, I32 lval);
245 SV** av_store(AV*, I32 key, SV* val);
247 The C<av_len> function returns the highest index value in array (just
248 like $#array in Perl). If the array is empty, -1 is returned. The
249 C<av_fetch> function returns the value at index C<key>, but if C<lval>
250 is non-zero, then C<av_fetch> will store an undef value at that index.
251 The C<av_store> function stores the value C<val> at index C<key>, and does
252 not increment the reference count of C<val>. Thus the caller is responsible
253 for taking care of that, and if C<av_store> returns NULL, the caller will
254 have to decrement the reference count to avoid a memory leak. Note that
255 C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s as their
260 void av_extend(AV*, I32 key);
262 The C<av_clear> function deletes all the elements in the AV* array, but
263 does not actually delete the array itself. The C<av_undef> function will
264 delete all the elements in the array plus the array itself. The
265 C<av_extend> function extends the array so that it contains C<key>
266 elements. If C<key> is less than the current length of the array, then
269 If you know the name of an array variable, you can get a pointer to its AV
270 by using the following:
272 AV* perl_get_av("package::varname", FALSE);
274 This returns NULL if the variable does not exist.
276 See L<Understanding the Magic of Tied Hashes and Arrays> for more
277 information on how to use the array access functions on tied arrays.
279 =head2 Working with HVs
281 To create an HV, you use the following routine:
285 Once the HV has been created, the following operations are possible on HVs:
287 SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
288 SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
290 The C<klen> parameter is the length of the key being passed in (Note that
291 you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
292 length of the key). The C<val> argument contains the SV pointer to the
293 scalar being stored, and C<hash> is the precomputed hash value (zero if
294 you want C<hv_store> to calculate it for you). The C<lval> parameter
295 indicates whether this fetch is actually a part of a store operation, in
296 which case a new undefined value will be added to the HV with the supplied
297 key and C<hv_fetch> will return as if the value had already existed.
299 Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
300 C<SV*>. To access the scalar value, you must first dereference the return
301 value. However, you should check to make sure that the return value is
302 not NULL before dereferencing it.
304 These two functions check if a hash table entry exists, and deletes it.
306 bool hv_exists(HV*, char* key, U32 klen);
307 SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
309 If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
310 create and return a mortal copy of the deleted value.
312 And more miscellaneous functions:
317 Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
318 table but does not actually delete the hash table. The C<hv_undef> deletes
319 both the entries and the hash table itself.
321 Perl keeps the actual data in linked list of structures with a typedef of HE.
322 These contain the actual key and value pointers (plus extra administrative
323 overhead). The key is a string pointer; the value is an C<SV*>. However,
324 once you have an C<HE*>, to get the actual key and value, use the routines
327 I32 hv_iterinit(HV*);
328 /* Prepares starting point to traverse hash table */
329 HE* hv_iternext(HV*);
330 /* Get the next entry, and return a pointer to a
331 structure that has both the key and value */
332 char* hv_iterkey(HE* entry, I32* retlen);
333 /* Get the key from an HE structure and also return
334 the length of the key string */
335 SV* hv_iterval(HV*, HE* entry);
336 /* Return a SV pointer to the value of the HE
338 SV* hv_iternextsv(HV*, char** key, I32* retlen);
339 /* This convenience routine combines hv_iternext,
340 hv_iterkey, and hv_iterval. The key and retlen
341 arguments are return values for the key and its
342 length. The value is returned in the SV* argument */
344 If you know the name of a hash variable, you can get a pointer to its HV
345 by using the following:
347 HV* perl_get_hv("package::varname", FALSE);
349 This returns NULL if the variable does not exist.
351 The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
357 hash = hash * 33 + *s++;
359 See L<Understanding the Magic of Tied Hashes and Arrays> for more
360 information on how to use the hash access functions on tied hashes.
362 =head2 Hash API Extensions
364 Beginning with version 5.004, the following functions are also supported:
366 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
367 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
369 bool hv_exists_ent (HV* tb, SV* key, U32 hash);
370 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
372 SV* hv_iterkeysv (HE* entry);
374 Note that these functions take C<SV*> keys, which simplifies writing
375 of extension code that deals with hash structures. These functions
376 also allow passing of C<SV*> keys to C<tie> functions without forcing
377 you to stringify the keys (unlike the previous set of functions).
379 They also return and accept whole hash entries (C<HE*>), making their
380 use more efficient (since the hash number for a particular string
381 doesn't have to be recomputed every time). See L<API LISTING> later in
382 this document for detailed descriptions.
384 The following macros must always be used to access the contents of hash
385 entries. Note that the arguments to these macros must be simple
386 variables, since they may get evaluated more than once. See
387 L<API LISTING> later in this document for detailed descriptions of these
390 HePV(HE* he, STRLEN len)
394 HeSVKEY_force(HE* he)
395 HeSVKEY_set(HE* he, SV* sv)
397 These two lower level macros are defined, but must only be used when
398 dealing with keys that are not C<SV*>s:
403 Note that both C<hv_store> and C<hv_store_ent> do not increment the
404 reference count of the stored C<val>, which is the caller's responsibility.
405 If these functions return a NULL value, the caller will usually have to
406 decrement the reference count of C<val> to avoid a memory leak.
410 References are a special type of scalar that point to other data types
411 (including references).
413 To create a reference, use either of the following functions:
415 SV* newRV_inc((SV*) thing);
416 SV* newRV_noinc((SV*) thing);
418 The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
419 functions are identical except that C<newRV_inc> increments the reference
420 count of the C<thing>, while C<newRV_noinc> does not. For historical
421 reasons, C<newRV> is a synonym for C<newRV_inc>.
423 Once you have a reference, you can use the following macro to dereference
428 then call the appropriate routines, casting the returned C<SV*> to either an
429 C<AV*> or C<HV*>, if required.
431 To determine if an SV is a reference, you can use the following macro:
435 To discover what type of value the reference refers to, use the following
436 macro and then check the return value.
440 The most useful types that will be returned are:
449 SVt_PVGV Glob (possible a file handle)
450 SVt_PVMG Blessed or Magical Scalar
452 See the sv.h header file for more details.
454 =head2 Blessed References and Class Objects
456 References are also used to support object-oriented programming. In the
457 OO lexicon, an object is simply a reference that has been blessed into a
458 package (or class). Once blessed, the programmer may now use the reference
459 to access the various methods in the class.
461 A reference can be blessed into a package with the following function:
463 SV* sv_bless(SV* sv, HV* stash);
465 The C<sv> argument must be a reference. The C<stash> argument specifies
466 which class the reference will belong to. See
467 L<Stashes and Globs> for information on converting class names into stashes.
469 /* Still under construction */
471 Upgrades rv to reference if not already one. Creates new SV for rv to
472 point to. If C<classname> is non-null, the SV is blessed into the specified
473 class. SV is returned.
475 SV* newSVrv(SV* rv, char* classname);
477 Copies integer or double into an SV whose reference is C<rv>. SV is blessed
478 if C<classname> is non-null.
480 SV* sv_setref_iv(SV* rv, char* classname, IV iv);
481 SV* sv_setref_nv(SV* rv, char* classname, NV iv);
483 Copies the pointer value (I<the address, not the string!>) into an SV whose
484 reference is rv. SV is blessed if C<classname> is non-null.
486 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
488 Copies string into an SV whose reference is C<rv>. Set length to 0 to let
489 Perl calculate the string length. SV is blessed if C<classname> is non-null.
491 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
493 Tests whether the SV is blessed into the specified class. It does not
494 check inheritance relationships.
496 int sv_isa(SV* sv, char* name);
498 Tests whether the SV is a reference to a blessed object.
500 int sv_isobject(SV* sv);
502 Tests whether the SV is derived from the specified class. SV can be either
503 a reference to a blessed object or a string containing a class name. This
504 is the function implementing the C<UNIVERSAL::isa> functionality.
506 bool sv_derived_from(SV* sv, char* name);
508 To check if you've got an object derived from a specific class you have
511 if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... }
513 =head2 Creating New Variables
515 To create a new Perl variable with an undef value which can be accessed from
516 your Perl script, use the following routines, depending on the variable type.
518 SV* perl_get_sv("package::varname", TRUE);
519 AV* perl_get_av("package::varname", TRUE);
520 HV* perl_get_hv("package::varname", TRUE);
522 Notice the use of TRUE as the second parameter. The new variable can now
523 be set, using the routines appropriate to the data type.
525 There are additional macros whose values may be bitwise OR'ed with the
526 C<TRUE> argument to enable certain extra features. Those bits are:
528 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
529 "Name <varname> used only once: possible typo" warning.
530 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
531 the variable did not exist before the function was called.
533 If you do not specify a package name, the variable is created in the current
536 =head2 Reference Counts and Mortality
538 Perl uses an reference count-driven garbage collection mechanism. SVs,
539 AVs, or HVs (xV for short in the following) start their life with a
540 reference count of 1. If the reference count of an xV ever drops to 0,
541 then it will be destroyed and its memory made available for reuse.
543 This normally doesn't happen at the Perl level unless a variable is
544 undef'ed or the last variable holding a reference to it is changed or
545 overwritten. At the internal level, however, reference counts can be
546 manipulated with the following macros:
548 int SvREFCNT(SV* sv);
549 SV* SvREFCNT_inc(SV* sv);
550 void SvREFCNT_dec(SV* sv);
552 However, there is one other function which manipulates the reference
553 count of its argument. The C<newRV_inc> function, you will recall,
554 creates a reference to the specified argument. As a side effect,
555 it increments the argument's reference count. If this is not what
556 you want, use C<newRV_noinc> instead.
558 For example, imagine you want to return a reference from an XSUB function.
559 Inside the XSUB routine, you create an SV which initially has a reference
560 count of one. Then you call C<newRV_inc>, passing it the just-created SV.
561 This returns the reference as a new SV, but the reference count of the
562 SV you passed to C<newRV_inc> has been incremented to two. Now you
563 return the reference from the XSUB routine and forget about the SV.
564 But Perl hasn't! Whenever the returned reference is destroyed, the
565 reference count of the original SV is decreased to one and nothing happens.
566 The SV will hang around without any way to access it until Perl itself
567 terminates. This is a memory leak.
569 The correct procedure, then, is to use C<newRV_noinc> instead of
570 C<newRV_inc>. Then, if and when the last reference is destroyed,
571 the reference count of the SV will go to zero and it will be destroyed,
572 stopping any memory leak.
574 There are some convenience functions available that can help with the
575 destruction of xVs. These functions introduce the concept of "mortality".
576 An xV that is mortal has had its reference count marked to be decremented,
577 but not actually decremented, until "a short time later". Generally the
578 term "short time later" means a single Perl statement, such as a call to
579 an XSUB function. The actual determinant for when mortal xVs have their
580 reference count decremented depends on two macros, SAVETMPS and FREETMPS.
581 See L<perlcall> and L<perlxs> for more details on these macros.
583 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
584 However, if you mortalize a variable twice, the reference count will
585 later be decremented twice.
587 You should be careful about creating mortal variables. Strange things
588 can happen if you make the same value mortal within multiple contexts,
589 or if you make a variable mortal multiple times.
591 To create a mortal variable, use the functions:
595 SV* sv_mortalcopy(SV*)
597 The first call creates a mortal SV, the second converts an existing
598 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
599 third creates a mortal copy of an existing SV.
601 The mortal routines are not just for SVs -- AVs and HVs can be
602 made mortal by passing their address (type-casted to C<SV*>) to the
603 C<sv_2mortal> or C<sv_mortalcopy> routines.
605 =head2 Stashes and Globs
607 A "stash" is a hash that contains all of the different objects that
608 are contained within a package. Each key of the stash is a symbol
609 name (shared by all the different types of objects that have the same
610 name), and each value in the hash table is a GV (Glob Value). This GV
611 in turn contains references to the various objects of that name,
612 including (but not limited to) the following:
621 There is a single stash called "PL_defstash" that holds the items that exist
622 in the "main" package. To get at the items in other packages, append the
623 string "::" to the package name. The items in the "Foo" package are in
624 the stash "Foo::" in PL_defstash. The items in the "Bar::Baz" package are
625 in the stash "Baz::" in "Bar::"'s stash.
627 To get the stash pointer for a particular package, use the function:
629 HV* gv_stashpv(char* name, I32 create)
630 HV* gv_stashsv(SV*, I32 create)
632 The first function takes a literal string, the second uses the string stored
633 in the SV. Remember that a stash is just a hash table, so you get back an
634 C<HV*>. The C<create> flag will create a new package if it is set.
636 The name that C<gv_stash*v> wants is the name of the package whose symbol table
637 you want. The default package is called C<main>. If you have multiply nested
638 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
641 Alternately, if you have an SV that is a blessed reference, you can find
642 out the stash pointer by using:
644 HV* SvSTASH(SvRV(SV*));
646 then use the following to get the package name itself:
648 char* HvNAME(HV* stash);
650 If you need to bless or re-bless an object you can use the following
653 SV* sv_bless(SV*, HV* stash)
655 where the first argument, an C<SV*>, must be a reference, and the second
656 argument is a stash. The returned C<SV*> can now be used in the same way
659 For more information on references and blessings, consult L<perlref>.
661 =head2 Double-Typed SVs
663 Scalar variables normally contain only one type of value, an integer,
664 double, pointer, or reference. Perl will automatically convert the
665 actual scalar data from the stored type into the requested type.
667 Some scalar variables contain more than one type of scalar data. For
668 example, the variable C<$!> contains either the numeric value of C<errno>
669 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
671 To force multiple data values into an SV, you must do two things: use the
672 C<sv_set*v> routines to add the additional scalar type, then set a flag
673 so that Perl will believe it contains more than one type of data. The
674 four macros to set the flags are:
681 The particular macro you must use depends on which C<sv_set*v> routine
682 you called first. This is because every C<sv_set*v> routine turns on
683 only the bit for the particular type of data being set, and turns off
686 For example, to create a new Perl variable called "dberror" that contains
687 both the numeric and descriptive string error values, you could use the
691 extern char *dberror_list;
693 SV* sv = perl_get_sv("dberror", TRUE);
694 sv_setiv(sv, (IV) dberror);
695 sv_setpv(sv, dberror_list[dberror]);
698 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
699 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
701 =head2 Magic Variables
703 [This section still under construction. Ignore everything here. Post no
704 bills. Everything not permitted is forbidden.]
706 Any SV may be magical, that is, it has special features that a normal
707 SV does not have. These features are stored in the SV structure in a
708 linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
721 Note this is current as of patchlevel 0, and could change at any time.
723 =head2 Assigning Magic
725 Perl adds magic to an SV using the sv_magic function:
727 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
729 The C<sv> argument is a pointer to the SV that is to acquire a new magical
732 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
733 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
734 it to the beginning of the linked list of magical features. Any prior
735 entry of the same type of magic is deleted. Note that this can be
736 overridden, and multiple instances of the same type of magic can be
737 associated with an SV.
739 The C<name> and C<namlen> arguments are used to associate a string with
740 the magic, typically the name of a variable. C<namlen> is stored in the
741 C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
742 copy of the name is stored in C<mg_ptr> field.
744 The sv_magic function uses C<how> to determine which, if any, predefined
745 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
746 See the "Magic Virtual Table" section below. The C<how> argument is also
747 stored in the C<mg_type> field.
749 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
750 structure. If it is not the same as the C<sv> argument, the reference
751 count of the C<obj> object is incremented. If it is the same, or if
752 the C<how> argument is "#", or if it is a NULL pointer, then C<obj> is
753 merely stored, without the reference count being incremented.
755 There is also a function to add magic to an C<HV>:
757 void hv_magic(HV *hv, GV *gv, int how);
759 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
761 To remove the magic from an SV, call the function sv_unmagic:
763 void sv_unmagic(SV *sv, int type);
765 The C<type> argument should be equal to the C<how> value when the C<SV>
766 was initially made magical.
768 =head2 Magic Virtual Tables
770 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
771 C<MGVTBL>, which is a structure of function pointers and stands for
772 "Magic Virtual Table" to handle the various operations that might be
773 applied to that variable.
775 The C<MGVTBL> has five pointers to the following routine types:
777 int (*svt_get)(SV* sv, MAGIC* mg);
778 int (*svt_set)(SV* sv, MAGIC* mg);
779 U32 (*svt_len)(SV* sv, MAGIC* mg);
780 int (*svt_clear)(SV* sv, MAGIC* mg);
781 int (*svt_free)(SV* sv, MAGIC* mg);
783 This MGVTBL structure is set at compile-time in C<perl.h> and there are
784 currently 19 types (or 21 with overloading turned on). These different
785 structures contain pointers to various routines that perform additional
786 actions depending on which function is being called.
788 Function pointer Action taken
789 ---------------- ------------
790 svt_get Do something after the value of the SV is retrieved.
791 svt_set Do something after the SV is assigned a value.
792 svt_len Report on the SV's length.
793 svt_clear Clear something the SV represents.
794 svt_free Free any extra storage associated with the SV.
796 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
797 to an C<mg_type> of '\0') contains:
799 { magic_get, magic_set, magic_len, 0, 0 }
801 Thus, when an SV is determined to be magical and of type '\0', if a get
802 operation is being performed, the routine C<magic_get> is called. All
803 the various routines for the various magical types begin with C<magic_>.
805 The current kinds of Magic Virtual Tables are:
807 mg_type MGVTBL Type of magic
808 ------- ------ ----------------------------
809 \0 vtbl_sv Special scalar variable
810 A vtbl_amagic %OVERLOAD hash
811 a vtbl_amagicelem %OVERLOAD hash element
812 c (none) Holds overload table (AMT) on stash
813 B vtbl_bm Boyer-Moore (fast string search)
815 e vtbl_envelem %ENV hash element
816 f vtbl_fm Formline ('compiled' format)
817 g vtbl_mglob m//g target / study()ed string
818 I vtbl_isa @ISA array
819 i vtbl_isaelem @ISA array element
820 k vtbl_nkeys scalar(keys()) lvalue
821 L (none) Debugger %_<filename
822 l vtbl_dbline Debugger %_<filename element
823 o vtbl_collxfrm Locale transformation
824 P vtbl_pack Tied array or hash
825 p vtbl_packelem Tied array or hash element
826 q vtbl_packelem Tied scalar or handle
828 s vtbl_sigelem %SIG hash element
829 t vtbl_taint Taintedness
830 U vtbl_uvar Available for use by extensions
831 v vtbl_vec vec() lvalue
832 x vtbl_substr substr() lvalue
833 y vtbl_defelem Shadow "foreach" iterator variable /
834 smart parameter vivification
835 * vtbl_glob GV (typeglob)
836 # vtbl_arylen Array length ($#ary)
837 . vtbl_pos pos() lvalue
838 ~ (none) Available for use by extensions
840 When an uppercase and lowercase letter both exist in the table, then the
841 uppercase letter is used to represent some kind of composite type (a list
842 or a hash), and the lowercase letter is used to represent an element of
845 The '~' and 'U' magic types are defined specifically for use by
846 extensions and will not be used by perl itself. Extensions can use
847 '~' magic to 'attach' private information to variables (typically
848 objects). This is especially useful because there is no way for
849 normal perl code to corrupt this private information (unlike using
850 extra elements of a hash object).
852 Similarly, 'U' magic can be used much like tie() to call a C function
853 any time a scalar's value is used or changed. The C<MAGIC>'s
854 C<mg_ptr> field points to a C<ufuncs> structure:
857 I32 (*uf_val)(IV, SV*);
858 I32 (*uf_set)(IV, SV*);
862 When the SV is read from or written to, the C<uf_val> or C<uf_set>
863 function will be called with C<uf_index> as the first arg and a
864 pointer to the SV as the second. A simple example of how to add 'U'
865 magic is shown below. Note that the ufuncs structure is copied by
866 sv_magic, so you can safely allocate it on the stack.
874 uf.uf_val = &my_get_fn;
875 uf.uf_set = &my_set_fn;
877 sv_magic(sv, 0, 'U', (char*)&uf, sizeof(uf));
879 Note that because multiple extensions may be using '~' or 'U' magic,
880 it is important for extensions to take extra care to avoid conflict.
881 Typically only using the magic on objects blessed into the same class
882 as the extension is sufficient. For '~' magic, it may also be
883 appropriate to add an I32 'signature' at the top of the private data
886 Also note that the C<sv_set*()> and C<sv_cat*()> functions described
887 earlier do B<not> invoke 'set' magic on their targets. This must
888 be done by the user either by calling the C<SvSETMAGIC()> macro after
889 calling these functions, or by using one of the C<sv_set*_mg()> or
890 C<sv_cat*_mg()> functions. Similarly, generic C code must call the
891 C<SvGETMAGIC()> macro to invoke any 'get' magic if they use an SV
892 obtained from external sources in functions that don't handle magic.
893 L<API LISTING> later in this document identifies such functions.
894 For example, calls to the C<sv_cat*()> functions typically need to be
895 followed by C<SvSETMAGIC()>, but they don't need a prior C<SvGETMAGIC()>
896 since their implementation handles 'get' magic.
900 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
902 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
903 If the SV does not have that magical feature, C<NULL> is returned. Also,
904 if the SV is not of type SVt_PVMG, Perl may core dump.
906 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
908 This routine checks to see what types of magic C<sv> has. If the mg_type
909 field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
910 the mg_type field is changed to be the lowercase letter.
912 =head2 Understanding the Magic of Tied Hashes and Arrays
914 Tied hashes and arrays are magical beasts of the 'P' magic type.
916 WARNING: As of the 5.004 release, proper usage of the array and hash
917 access functions requires understanding a few caveats. Some
918 of these caveats are actually considered bugs in the API, to be fixed
919 in later releases, and are bracketed with [MAYCHANGE] below. If
920 you find yourself actually applying such information in this section, be
921 aware that the behavior may change in the future, umm, without warning.
923 The perl tie function associates a variable with an object that implements
924 the various GET, SET etc methods. To perform the equivalent of the perl
925 tie function from an XSUB, you must mimic this behaviour. The code below
926 carries out the necessary steps - firstly it creates a new hash, and then
927 creates a second hash which it blesses into the class which will implement
928 the tie methods. Lastly it ties the two hashes together, and returns a
929 reference to the new tied hash. Note that the code below does NOT call the
930 TIEHASH method in the MyTie class -
931 see L<Calling Perl Routines from within C Programs> for details on how
942 tie = newRV_noinc((SV*)newHV());
943 stash = gv_stashpv("MyTie", TRUE);
944 sv_bless(tie, stash);
945 hv_magic(hash, tie, 'P');
946 RETVAL = newRV_noinc(hash);
950 The C<av_store> function, when given a tied array argument, merely
951 copies the magic of the array onto the value to be "stored", using
952 C<mg_copy>. It may also return NULL, indicating that the value did not
953 actually need to be stored in the array. [MAYCHANGE] After a call to
954 C<av_store> on a tied array, the caller will usually need to call
955 C<mg_set(val)> to actually invoke the perl level "STORE" method on the
956 TIEARRAY object. If C<av_store> did return NULL, a call to
957 C<SvREFCNT_dec(val)> will also be usually necessary to avoid a memory
960 The previous paragraph is applicable verbatim to tied hash access using the
961 C<hv_store> and C<hv_store_ent> functions as well.
963 C<av_fetch> and the corresponding hash functions C<hv_fetch> and
964 C<hv_fetch_ent> actually return an undefined mortal value whose magic
965 has been initialized using C<mg_copy>. Note the value so returned does not
966 need to be deallocated, as it is already mortal. [MAYCHANGE] But you will
967 need to call C<mg_get()> on the returned value in order to actually invoke
968 the perl level "FETCH" method on the underlying TIE object. Similarly,
969 you may also call C<mg_set()> on the return value after possibly assigning
970 a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
971 method on the TIE object. [/MAYCHANGE]
974 In other words, the array or hash fetch/store functions don't really
975 fetch and store actual values in the case of tied arrays and hashes. They
976 merely call C<mg_copy> to attach magic to the values that were meant to be
977 "stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
978 do the job of invoking the TIE methods on the underlying objects. Thus
979 the magic mechanism currently implements a kind of lazy access to arrays
982 Currently (as of perl version 5.004), use of the hash and array access
983 functions requires the user to be aware of whether they are operating on
984 "normal" hashes and arrays, or on their tied variants. The API may be
985 changed to provide more transparent access to both tied and normal data
986 types in future versions.
989 You would do well to understand that the TIEARRAY and TIEHASH interfaces
990 are mere sugar to invoke some perl method calls while using the uniform hash
991 and array syntax. The use of this sugar imposes some overhead (typically
992 about two to four extra opcodes per FETCH/STORE operation, in addition to
993 the creation of all the mortal variables required to invoke the methods).
994 This overhead will be comparatively small if the TIE methods are themselves
995 substantial, but if they are only a few statements long, the overhead
996 will not be insignificant.
998 =head2 Localizing changes
1000 Perl has a very handy construction
1007 This construction is I<approximately> equivalent to
1016 The biggest difference is that the first construction would
1017 reinstate the initial value of $var, irrespective of how control exits
1018 the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
1019 more efficient as well.
1021 There is a way to achieve a similar task from C via Perl API: create a
1022 I<pseudo-block>, and arrange for some changes to be automatically
1023 undone at the end of it, either explicit, or via a non-local exit (via
1024 die()). A I<block>-like construct is created by a pair of
1025 C<ENTER>/C<LEAVE> macros (see L<perlcall/EXAMPLE/"Returning a
1026 Scalar">). Such a construct may be created specially for some
1027 important localized task, or an existing one (like boundaries of
1028 enclosing Perl subroutine/block, or an existing pair for freeing TMPs)
1029 may be used. (In the second case the overhead of additional
1030 localization must be almost negligible.) Note that any XSUB is
1031 automatically enclosed in an C<ENTER>/C<LEAVE> pair.
1033 Inside such a I<pseudo-block> the following service is available:
1037 =item C<SAVEINT(int i)>
1039 =item C<SAVEIV(IV i)>
1041 =item C<SAVEI32(I32 i)>
1043 =item C<SAVELONG(long i)>
1045 These macros arrange things to restore the value of integer variable
1046 C<i> at the end of enclosing I<pseudo-block>.
1048 =item C<SAVESPTR(s)>
1050 =item C<SAVEPPTR(p)>
1052 These macros arrange things to restore the value of pointers C<s> and
1053 C<p>. C<s> must be a pointer of a type which survives conversion to
1054 C<SV*> and back, C<p> should be able to survive conversion to C<char*>
1057 =item C<SAVEFREESV(SV *sv)>
1059 The refcount of C<sv> would be decremented at the end of
1060 I<pseudo-block>. This is similar to C<sv_2mortal>, which should (?) be
1063 =item C<SAVEFREEOP(OP *op)>
1065 The C<OP *> is op_free()ed at the end of I<pseudo-block>.
1067 =item C<SAVEFREEPV(p)>
1069 The chunk of memory which is pointed to by C<p> is Safefree()ed at the
1070 end of I<pseudo-block>.
1072 =item C<SAVECLEARSV(SV *sv)>
1074 Clears a slot in the current scratchpad which corresponds to C<sv> at
1075 the end of I<pseudo-block>.
1077 =item C<SAVEDELETE(HV *hv, char *key, I32 length)>
1079 The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
1080 string pointed to by C<key> is Safefree()ed. If one has a I<key> in
1081 short-lived storage, the corresponding string may be reallocated like
1084 SAVEDELETE(PL_defstash, savepv(tmpbuf), strlen(tmpbuf));
1086 =item C<SAVEDESTRUCTOR(f,p)>
1088 At the end of I<pseudo-block> the function C<f> is called with the
1089 only argument (of type C<void*>) C<p>.
1091 =item C<SAVESTACK_POS()>
1093 The current offset on the Perl internal stack (cf. C<SP>) is restored
1094 at the end of I<pseudo-block>.
1098 The following API list contains functions, thus one needs to
1099 provide pointers to the modifiable data explicitly (either C pointers,
1100 or Perlish C<GV *>s). Where the above macros take C<int>, a similar
1101 function takes C<int *>.
1105 =item C<SV* save_scalar(GV *gv)>
1107 Equivalent to Perl code C<local $gv>.
1109 =item C<AV* save_ary(GV *gv)>
1111 =item C<HV* save_hash(GV *gv)>
1113 Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
1115 =item C<void save_item(SV *item)>
1117 Duplicates the current value of C<SV>, on the exit from the current
1118 C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
1119 using the stored value.
1121 =item C<void save_list(SV **sarg, I32 maxsarg)>
1123 A variant of C<save_item> which takes multiple arguments via an array
1124 C<sarg> of C<SV*> of length C<maxsarg>.
1126 =item C<SV* save_svref(SV **sptr)>
1128 Similar to C<save_scalar>, but will reinstate a C<SV *>.
1130 =item C<void save_aptr(AV **aptr)>
1132 =item C<void save_hptr(HV **hptr)>
1134 Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
1138 The C<Alias> module implements localization of the basic types within the
1139 I<caller's scope>. People who are interested in how to localize things in
1140 the containing scope should take a look there too.
1144 =head2 XSUBs and the Argument Stack
1146 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
1147 An XSUB routine will have a stack that contains the arguments from the Perl
1148 program, and a way to map from the Perl data structures to a C equivalent.
1150 The stack arguments are accessible through the C<ST(n)> macro, which returns
1151 the C<n>'th stack argument. Argument 0 is the first argument passed in the
1152 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
1155 Most of the time, output from the C routine can be handled through use of
1156 the RETVAL and OUTPUT directives. However, there are some cases where the
1157 argument stack is not already long enough to handle all the return values.
1158 An example is the POSIX tzname() call, which takes no arguments, but returns
1159 two, the local time zone's standard and summer time abbreviations.
1161 To handle this situation, the PPCODE directive is used and the stack is
1162 extended using the macro:
1166 where C<SP> is the macro that represents the local copy of the stack pointer,
1167 and C<num> is the number of elements the stack should be extended by.
1169 Now that there is room on the stack, values can be pushed on it using the
1170 macros to push IVs, doubles, strings, and SV pointers respectively:
1177 And now the Perl program calling C<tzname>, the two values will be assigned
1180 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
1182 An alternate (and possibly simpler) method to pushing values on the stack is
1190 These macros automatically adjust the stack for you, if needed. Thus, you
1191 do not need to call C<EXTEND> to extend the stack.
1193 For more information, consult L<perlxs> and L<perlxstut>.
1195 =head2 Calling Perl Routines from within C Programs
1197 There are four routines that can be used to call a Perl subroutine from
1198 within a C program. These four are:
1200 I32 perl_call_sv(SV*, I32);
1201 I32 perl_call_pv(char*, I32);
1202 I32 perl_call_method(char*, I32);
1203 I32 perl_call_argv(char*, I32, register char**);
1205 The routine most often used is C<perl_call_sv>. The C<SV*> argument
1206 contains either the name of the Perl subroutine to be called, or a
1207 reference to the subroutine. The second argument consists of flags
1208 that control the context in which the subroutine is called, whether
1209 or not the subroutine is being passed arguments, how errors should be
1210 trapped, and how to treat return values.
1212 All four routines return the number of arguments that the subroutine returned
1215 When using any of these routines (except C<perl_call_argv>), the programmer
1216 must manipulate the Perl stack. These include the following macros and
1231 For a detailed description of calling conventions from C to Perl,
1232 consult L<perlcall>.
1234 =head2 Memory Allocation
1236 It is suggested that you use the version of malloc that is distributed
1237 with Perl. It keeps pools of various sizes of unallocated memory in
1238 order to satisfy allocation requests more quickly. However, on some
1239 platforms, it may cause spurious malloc or free errors.
1241 New(x, pointer, number, type);
1242 Newc(x, pointer, number, type, cast);
1243 Newz(x, pointer, number, type);
1245 These three macros are used to initially allocate memory.
1247 The first argument C<x> was a "magic cookie" that was used to keep track
1248 of who called the macro, to help when debugging memory problems. However,
1249 the current code makes no use of this feature (most Perl developers now
1250 use run-time memory checkers), so this argument can be any number.
1252 The second argument C<pointer> should be the name of a variable that will
1253 point to the newly allocated memory.
1255 The third and fourth arguments C<number> and C<type> specify how many of
1256 the specified type of data structure should be allocated. The argument
1257 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
1258 should be used if the C<pointer> argument is different from the C<type>
1261 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
1262 to zero out all the newly allocated memory.
1264 Renew(pointer, number, type);
1265 Renewc(pointer, number, type, cast);
1268 These three macros are used to change a memory buffer size or to free a
1269 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1270 match those of C<New> and C<Newc> with the exception of not needing the
1271 "magic cookie" argument.
1273 Move(source, dest, number, type);
1274 Copy(source, dest, number, type);
1275 Zero(dest, number, type);
1277 These three macros are used to move, copy, or zero out previously allocated
1278 memory. The C<source> and C<dest> arguments point to the source and
1279 destination starting points. Perl will move, copy, or zero out C<number>
1280 instances of the size of the C<type> data structure (using the C<sizeof>
1285 The most recent development releases of Perl has been experimenting with
1286 removing Perl's dependency on the "normal" standard I/O suite and allowing
1287 other stdio implementations to be used. This involves creating a new
1288 abstraction layer that then calls whichever implementation of stdio Perl
1289 was compiled with. All XSUBs should now use the functions in the PerlIO
1290 abstraction layer and not make any assumptions about what kind of stdio
1293 For a complete description of the PerlIO abstraction, consult L<perlapio>.
1295 =head2 Putting a C value on Perl stack
1297 A lot of opcodes (this is an elementary operation in the internal perl
1298 stack machine) put an SV* on the stack. However, as an optimization
1299 the corresponding SV is (usually) not recreated each time. The opcodes
1300 reuse specially assigned SVs (I<target>s) which are (as a corollary)
1301 not constantly freed/created.
1303 Each of the targets is created only once (but see
1304 L<Scratchpads and recursion> below), and when an opcode needs to put
1305 an integer, a double, or a string on stack, it just sets the
1306 corresponding parts of its I<target> and puts the I<target> on stack.
1308 The macro to put this target on stack is C<PUSHTARG>, and it is
1309 directly used in some opcodes, as well as indirectly in zillions of
1310 others, which use it via C<(X)PUSH[pni]>.
1314 The question remains on when the SVs which are I<target>s for opcodes
1315 are created. The answer is that they are created when the current unit --
1316 a subroutine or a file (for opcodes for statements outside of
1317 subroutines) -- is compiled. During this time a special anonymous Perl
1318 array is created, which is called a scratchpad for the current
1321 A scratchpad keeps SVs which are lexicals for the current unit and are
1322 targets for opcodes. One can deduce that an SV lives on a scratchpad
1323 by looking on its flags: lexicals have C<SVs_PADMY> set, and
1324 I<target>s have C<SVs_PADTMP> set.
1326 The correspondence between OPs and I<target>s is not 1-to-1. Different
1327 OPs in the compile tree of the unit can use the same target, if this
1328 would not conflict with the expected life of the temporary.
1330 =head2 Scratchpads and recursion
1332 In fact it is not 100% true that a compiled unit contains a pointer to
1333 the scratchpad AV. In fact it contains a pointer to an AV of
1334 (initially) one element, and this element is the scratchpad AV. Why do
1335 we need an extra level of indirection?
1337 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1338 these can create several execution pointers going into the same
1339 subroutine. For the subroutine-child not write over the temporaries
1340 for the subroutine-parent (lifespan of which covers the call to the
1341 child), the parent and the child should have different
1342 scratchpads. (I<And> the lexicals should be separate anyway!)
1344 So each subroutine is born with an array of scratchpads (of length 1).
1345 On each entry to the subroutine it is checked that the current
1346 depth of the recursion is not more than the length of this array, and
1347 if it is, new scratchpad is created and pushed into the array.
1349 The I<target>s on this scratchpad are C<undef>s, but they are already
1350 marked with correct flags.
1352 =head1 Compiled code
1356 Here we describe the internal form your code is converted to by
1357 Perl. Start with a simple example:
1361 This is converted to a tree similar to this one:
1369 (but slightly more complicated). This tree reflects the way Perl
1370 parsed your code, but has nothing to do with the execution order.
1371 There is an additional "thread" going through the nodes of the tree
1372 which shows the order of execution of the nodes. In our simplified
1373 example above it looks like:
1375 $b ---> $c ---> + ---> $a ---> assign-to
1377 But with the actual compile tree for C<$a = $b + $c> it is different:
1378 some nodes I<optimized away>. As a corollary, though the actual tree
1379 contains more nodes than our simplified example, the execution order
1380 is the same as in our example.
1382 =head2 Examining the tree
1384 If you have your perl compiled for debugging (usually done with C<-D
1385 optimize=-g> on C<Configure> command line), you may examine the
1386 compiled tree by specifying C<-Dx> on the Perl command line. The
1387 output takes several lines per node, and for C<$b+$c> it looks like
1392 FLAGS = (SCALAR,KIDS)
1394 TYPE = null ===> (4)
1396 FLAGS = (SCALAR,KIDS)
1398 3 TYPE = gvsv ===> 4
1404 TYPE = null ===> (5)
1406 FLAGS = (SCALAR,KIDS)
1408 4 TYPE = gvsv ===> 5
1414 This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1415 not optimized away (one per number in the left column). The immediate
1416 children of the given node correspond to C<{}> pairs on the same level
1417 of indentation, thus this listing corresponds to the tree:
1425 The execution order is indicated by C<===E<gt>> marks, thus it is C<3
1426 4 5 6> (node C<6> is not included into above listing), i.e.,
1427 C<gvsv gvsv add whatever>.
1429 =head2 Compile pass 1: check routines
1431 The tree is created by the I<pseudo-compiler> while yacc code feeds it
1432 the constructions it recognizes. Since yacc works bottom-up, so does
1433 the first pass of perl compilation.
1435 What makes this pass interesting for perl developers is that some
1436 optimization may be performed on this pass. This is optimization by
1437 so-called I<check routines>. The correspondence between node names
1438 and corresponding check routines is described in F<opcode.pl> (do not
1439 forget to run C<make regen_headers> if you modify this file).
1441 A check routine is called when the node is fully constructed except
1442 for the execution-order thread. Since at this time there are no
1443 back-links to the currently constructed node, one can do most any
1444 operation to the top-level node, including freeing it and/or creating
1445 new nodes above/below it.
1447 The check routine returns the node which should be inserted into the
1448 tree (if the top-level node was not modified, check routine returns
1451 By convention, check routines have names C<ck_*>. They are usually
1452 called from C<new*OP> subroutines (or C<convert>) (which in turn are
1453 called from F<perly.y>).
1455 =head2 Compile pass 1a: constant folding
1457 Immediately after the check routine is called the returned node is
1458 checked for being compile-time executable. If it is (the value is
1459 judged to be constant) it is immediately executed, and a I<constant>
1460 node with the "return value" of the corresponding subtree is
1461 substituted instead. The subtree is deleted.
1463 If constant folding was not performed, the execution-order thread is
1466 =head2 Compile pass 2: context propagation
1468 When a context for a part of compile tree is known, it is propagated
1469 down through the tree. At this time the context can have 5 values
1470 (instead of 2 for runtime context): void, boolean, scalar, list, and
1471 lvalue. In contrast with the pass 1 this pass is processed from top
1472 to bottom: a node's context determines the context for its children.
1474 Additional context-dependent optimizations are performed at this time.
1475 Since at this moment the compile tree contains back-references (via
1476 "thread" pointers), nodes cannot be free()d now. To allow
1477 optimized-away nodes at this stage, such nodes are null()ified instead
1478 of free()ing (i.e. their type is changed to OP_NULL).
1480 =head2 Compile pass 3: peephole optimization
1482 After the compile tree for a subroutine (or for an C<eval> or a file)
1483 is created, an additional pass over the code is performed. This pass
1484 is neither top-down or bottom-up, but in the execution order (with
1485 additional complications for conditionals). These optimizations are
1486 done in the subroutine peep(). Optimizations performed at this stage
1487 are subject to the same restrictions as in the pass 2.
1491 This is a listing of functions, macros, flags, and variables that may be
1492 useful to extension writers or that may be found while reading other
1495 Note that all Perl API global variables must be referenced with the C<PL_>
1496 prefix. Some macros are provided for compatibility with the older,
1497 unadorned names, but this support will be removed in a future release.
1499 It is strongly recommended that all Perl API functions that don't begin
1500 with C<perl> be referenced with an explicit C<Perl_> prefix.
1502 The sort order of the listing is case insensitive, with any
1503 occurrences of '_' ignored for the the purpose of sorting.
1509 Clears an array, making it empty. Does not free the memory used by the
1512 void av_clear (AV* ar)
1516 Pre-extend an array. The C<key> is the index to which the array should be
1519 void av_extend (AV* ar, I32 key)
1523 Returns the SV at the specified index in the array. The C<key> is the
1524 index. If C<lval> is set then the fetch will be part of a store. Check
1525 that the return value is non-null before dereferencing it to a C<SV*>.
1527 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1528 information on how to use this function on tied arrays.
1530 SV** av_fetch (AV* ar, I32 key, I32 lval)
1534 Same as C<av_len()>. Deprecated, use C<av_len()> instead.
1538 Returns the highest index in the array. Returns -1 if the array is empty.
1544 Creates a new AV and populates it with a list of SVs. The SVs are copied
1545 into the array, so they may be freed after the call to av_make. The new AV
1546 will have a reference count of 1.
1548 AV* av_make (I32 size, SV** svp)
1552 Pops an SV off the end of the array. Returns C<&PL_sv_undef> if the array is
1559 Pushes an SV onto the end of the array. The array will grow automatically
1560 to accommodate the addition.
1562 void av_push (AV* ar, SV* val)
1566 Shifts an SV off the beginning of the array.
1568 SV* av_shift (AV* ar)
1572 Stores an SV in an array. The array index is specified as C<key>. The
1573 return value will be NULL if the operation failed or if the value did not
1574 need to be actually stored within the array (as in the case of tied arrays).
1575 Otherwise it can be dereferenced to get the original C<SV*>. Note that the
1576 caller is responsible for suitably incrementing the reference count of C<val>
1577 before the call, and decrementing it if the function returned NULL.
1579 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1580 information on how to use this function on tied arrays.
1582 SV** av_store (AV* ar, I32 key, SV* val)
1586 Undefines the array. Frees the memory used by the array itself.
1588 void av_undef (AV* ar)
1592 Unshift the given number of C<undef> values onto the beginning of the
1593 array. The array will grow automatically to accommodate the addition.
1594 You must then use C<av_store> to assign values to these new elements.
1596 void av_unshift (AV* ar, I32 num)
1600 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1601 constructor. This is always a C<char*>. See C<THIS> and
1602 L<perlxs/"Using XS With C++">.
1606 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1607 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1608 the type. May fail on overlapping copies. See also C<Move>.
1610 void Copy( s, d, n, t )
1614 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1615 function the same way you use the C C<printf> function. See C<warn>.
1619 Returns the stash of the CV.
1621 HV* CvSTASH( SV* sv )
1625 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1626 boolean which indicates whether subs are being single-stepped.
1627 Single-stepping is automatically turned on after every step. This is the C
1628 variable which corresponds to Perl's $DB::single variable. See C<PL_DBsub>.
1632 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1633 the SV which holds the name of the sub being debugged. This is the C
1634 variable which corresponds to Perl's $DB::sub variable. See C<PL_DBsingle>.
1635 The sub name can be found by
1637 SvPV( GvSV( PL_DBsub ), PL_na )
1641 Trace variable used when Perl is run in debugging mode, with the B<-d>
1642 switch. This is the C variable which corresponds to Perl's $DB::trace
1643 variable. See C<PL_DBsingle>.
1647 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1652 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1656 The C variable which corresponds to Perl's $^W warning variable.
1660 Declares a local copy of perl's stack pointer for the XSUB, available via
1661 the C<SP> macro. See C<SP>.
1665 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1666 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1667 to indicate the number of items on the stack.
1671 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1672 handled automatically by C<xsubpp>.
1676 Switches filehandle to binmode. C<iotype> is what C<IoTYPE(io)> would
1679 do_binmode(fp, iotype, TRUE);
1683 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1689 Used to extend the argument stack for an XSUB's return values.
1695 Analyses the string in order to make fast searches on it using fbm_instr() --
1696 the Boyer-Moore algorithm.
1698 void fbm_compile(SV* sv, U32 flags)
1702 Returns the location of the SV in the string delimited by C<str> and
1703 C<strend>. It returns C<Nullch> if the string can't be found. The
1704 C<sv> does not have to be fbm_compiled, but the search will not be as
1707 char* fbm_instr(char *str, char *strend, SV *sv, U32 flags)
1711 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1718 Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
1722 Indicates that arguments returned from a callback should be discarded. See
1727 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1731 A backward-compatible version of C<GIMME_V> which can only return
1732 C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
1736 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
1737 C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
1738 context, respectively.
1742 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1746 Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
1750 Returns the glob with the given C<name> and a defined subroutine or
1751 C<NULL>. The glob lives in the given C<stash>, or in the stashes
1752 accessible via @ISA and @UNIVERSAL.
1754 The argument C<level> should be either 0 or -1. If C<level==0>, as a
1755 side-effect creates a glob with the given C<name> in the given
1756 C<stash> which in the case of success contains an alias for the
1757 subroutine, and sets up caching info for this glob. Similarly for all
1758 the searched stashes.
1760 This function grants C<"SUPER"> token as a postfix of the stash name.
1762 The GV returned from C<gv_fetchmeth> may be a method cache entry,
1763 which is not visible to Perl code. So when calling C<perl_call_sv>,
1764 you should not use the GV directly; instead, you should use the
1765 method's CV, which can be obtained from the GV with the C<GvCV> macro.
1767 GV* gv_fetchmeth (HV* stash, char* name, STRLEN len, I32 level)
1769 =item gv_fetchmethod
1771 =item gv_fetchmethod_autoload
1773 Returns the glob which contains the subroutine to call to invoke the
1774 method on the C<stash>. In fact in the presense of autoloading this may
1775 be the glob for "AUTOLOAD". In this case the corresponding variable
1776 $AUTOLOAD is already setup.
1778 The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
1779 lookup is performed if the given method is not present: non-zero means
1780 yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
1781 C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
1782 non-zero C<autoload> parameter.
1784 These functions grant C<"SUPER"> token as a prefix of the method name.
1786 Note that if you want to keep the returned glob for a long time, you
1787 need to check for it being "AUTOLOAD", since at the later time the call
1788 may load a different subroutine due to $AUTOLOAD changing its value.
1789 Use the glob created via a side effect to do this.
1791 These functions have the same side-effects and as C<gv_fetchmeth> with
1792 C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
1793 The warning against passing the GV returned by C<gv_fetchmeth> to
1794 C<perl_call_sv> apply equally to these functions.
1796 GV* gv_fetchmethod (HV* stash, char* name)
1797 GV* gv_fetchmethod_autoload (HV* stash, char* name, I32 autoload)
1801 Used to indicate void context. See C<GIMME_V> and L<perlcall>.
1805 Returns a pointer to the stash for a specified package. If C<create> is set
1806 then the package will be created if it does not already exist. If C<create>
1807 is not set and the package does not exist then NULL is returned.
1809 HV* gv_stashpv (char* name, I32 create)
1813 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1815 HV* gv_stashsv (SV* sv, I32 create)
1819 Return the SV from the GV.
1823 This flag, used in the length slot of hash entries and magic
1824 structures, specifies the structure contains a C<SV*> pointer where a
1825 C<char*> pointer is to be expected. (For information only--not to be used).
1829 Returns the computed hash stored in the hash entry.
1835 Returns the actual pointer stored in the key slot of the hash entry.
1836 The pointer may be either C<char*> or C<SV*>, depending on the value of
1837 C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
1838 are usually preferable for finding the value of a key.
1844 If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
1845 holds an C<SV*> key. Otherwise, holds the actual length of the key.
1846 Can be assigned to. The C<HePV()> macro is usually preferable for finding
1853 Returns the key slot of the hash entry as a C<char*> value, doing any
1854 necessary dereferencing of possibly C<SV*> keys. The length of
1855 the string is placed in C<len> (this is a macro, so do I<not> use
1856 C<&len>). If you do not care about what the length of the key is,
1857 you may use the global variable C<PL_na>. Remember though, that hash
1858 keys in perl are free to contain embedded nulls, so using C<strlen()>
1859 or similar is not a good way to find the length of hash keys.
1860 This is very similar to the C<SvPV()> macro described elsewhere in
1863 char* HePV(HE* he, STRLEN len)
1867 Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
1868 does not contain an C<SV*> key.
1874 Returns the key as an C<SV*>. Will create and return a temporary
1875 mortal C<SV*> if the hash entry contains only a C<char*> key.
1877 HeSVKEY_force(HE* he)
1881 Sets the key to a given C<SV*>, taking care to set the appropriate flags
1882 to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
1884 HeSVKEY_set(HE* he, SV* sv)
1888 Returns the value slot (type C<SV*>) stored in the hash entry.
1894 Clears a hash, making it empty.
1896 void hv_clear (HV* tb)
1900 Deletes a key/value pair in the hash. The value SV is removed from the hash
1901 and returned to the caller. The C<klen> is the length of the key. The
1902 C<flags> value will normally be zero; if set to G_DISCARD then NULL will be
1905 SV* hv_delete (HV* tb, char* key, U32 klen, I32 flags)
1909 Deletes a key/value pair in the hash. The value SV is removed from the hash
1910 and returned to the caller. The C<flags> value will normally be zero; if set
1911 to G_DISCARD then NULL will be returned. C<hash> can be a valid precomputed
1912 hash value, or 0 to ask for it to be computed.
1914 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash)
1918 Returns a boolean indicating whether the specified hash key exists. The
1919 C<klen> is the length of the key.
1921 bool hv_exists (HV* tb, char* key, U32 klen)
1925 Returns a boolean indicating whether the specified hash key exists. C<hash>
1926 can be a valid precomputed hash value, or 0 to ask for it to be computed.
1928 bool hv_exists_ent (HV* tb, SV* key, U32 hash)
1932 Returns the SV which corresponds to the specified key in the hash. The
1933 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1934 part of a store. Check that the return value is non-null before
1935 dereferencing it to a C<SV*>.
1937 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1938 information on how to use this function on tied hashes.
1940 SV** hv_fetch (HV* tb, char* key, U32 klen, I32 lval)
1944 Returns the hash entry which corresponds to the specified key in the hash.
1945 C<hash> must be a valid precomputed hash number for the given C<key>, or
1946 0 if you want the function to compute it. IF C<lval> is set then the
1947 fetch will be part of a store. Make sure the return value is non-null
1948 before accessing it. The return value when C<tb> is a tied hash
1949 is a pointer to a static location, so be sure to make a copy of the
1950 structure if you need to store it somewhere.
1952 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1953 information on how to use this function on tied hashes.
1955 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash)
1959 Prepares a starting point to traverse a hash table.
1961 I32 hv_iterinit (HV* tb)
1963 Returns the number of keys in the hash (i.e. the same as C<HvKEYS(tb)>).
1964 The return value is currently only meaningful for hashes without tie
1967 NOTE: Before version 5.004_65, C<hv_iterinit> used to return the number
1968 of hash buckets that happen to be in use. If you still need that
1969 esoteric value, you can get it through the macro C<HvFILL(tb)>.
1973 Returns the key from the current position of the hash iterator. See
1976 char* hv_iterkey (HE* entry, I32* retlen)
1980 Returns the key as an C<SV*> from the current position of the hash
1981 iterator. The return value will always be a mortal copy of the
1982 key. Also see C<hv_iterinit>.
1984 SV* hv_iterkeysv (HE* entry)
1988 Returns entries from a hash iterator. See C<hv_iterinit>.
1990 HE* hv_iternext (HV* tb)
1994 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1997 SV* hv_iternextsv (HV* hv, char** key, I32* retlen)
2001 Returns the value from the current position of the hash iterator. See
2004 SV* hv_iterval (HV* tb, HE* entry)
2008 Adds magic to a hash. See C<sv_magic>.
2010 void hv_magic (HV* hv, GV* gv, int how)
2014 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
2016 char* HvNAME (HV* stash)
2020 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
2021 the length of the key. The C<hash> parameter is the precomputed hash
2022 value; if it is zero then Perl will compute it. The return value will be
2023 NULL if the operation failed or if the value did not need to be actually
2024 stored within the hash (as in the case of tied hashes). Otherwise it can
2025 be dereferenced to get the original C<SV*>. Note that the caller is
2026 responsible for suitably incrementing the reference count of C<val>
2027 before the call, and decrementing it if the function returned NULL.
2029 See L<Understanding the Magic of Tied Hashes and Arrays> for more
2030 information on how to use this function on tied hashes.
2032 SV** hv_store (HV* tb, char* key, U32 klen, SV* val, U32 hash)
2036 Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
2037 parameter is the precomputed hash value; if it is zero then Perl will
2038 compute it. The return value is the new hash entry so created. It will be
2039 NULL if the operation failed or if the value did not need to be actually
2040 stored within the hash (as in the case of tied hashes). Otherwise the
2041 contents of the return value can be accessed using the C<He???> macros
2042 described here. Note that the caller is responsible for suitably
2043 incrementing the reference count of C<val> before the call, and decrementing
2044 it if the function returned NULL.
2046 See L<Understanding the Magic of Tied Hashes and Arrays> for more
2047 information on how to use this function on tied hashes.
2049 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash)
2055 void hv_undef (HV* tb)
2059 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
2062 int isALNUM (char c)
2066 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
2069 int isALPHA (char c)
2073 Returns a boolean indicating whether the C C<char> is an ascii digit.
2075 int isDIGIT (char c)
2079 Returns a boolean indicating whether the C C<char> is a lowercase character.
2081 int isLOWER (char c)
2085 Returns a boolean indicating whether the C C<char> is whitespace.
2087 int isSPACE (char c)
2091 Returns a boolean indicating whether the C C<char> is an uppercase character.
2093 int isUPPER (char c)
2097 Variable which is setup by C<xsubpp> to indicate the number of items on the
2098 stack. See L<perlxs/"Variable-length Parameter Lists">.
2102 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
2103 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
2107 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
2111 =item looks_like_number
2113 Test if an the content of an SV looks like a number (or is a number).
2115 int looks_like_number(SV*)
2120 Stack marker variable for the XSUB. See C<dMARK>.
2124 Clear something magical that the SV represents. See C<sv_magic>.
2126 int mg_clear (SV* sv)
2130 Copies the magic from one SV to another. See C<sv_magic>.
2132 int mg_copy (SV *, SV *, char *, STRLEN)
2136 Finds the magic pointer for type matching the SV. See C<sv_magic>.
2138 MAGIC* mg_find (SV* sv, int type)
2142 Free any magic storage used by the SV. See C<sv_magic>.
2144 int mg_free (SV* sv)
2148 Do magic after a value is retrieved from the SV. See C<sv_magic>.
2154 Report on the SV's length. See C<sv_magic>.
2160 Turns on the magical status of an SV. See C<sv_magic>.
2162 void mg_magical (SV* sv)
2166 Do magic after a value is assigned to the SV. See C<sv_magic>.
2172 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
2173 source, C<d> is the destination, C<n> is the number of items, and C<t> is
2174 the type. Can do overlapping moves. See also C<Copy>.
2176 void Move( s, d, n, t )
2180 A variable which may be used with C<SvPV> to tell Perl to calculate the
2185 The XSUB-writer's interface to the C C<malloc> function.
2187 void* New( x, void *ptr, int size, type )
2191 Creates a new AV. The reference count is set to 1.
2197 The XSUB-writer's interface to the C C<malloc> function, with cast.
2199 void* Newc( x, void *ptr, int size, type, cast )
2203 Creates a constant sub equivalent to Perl C<sub FOO () { 123 }>
2204 which is eligible for inlining at compile-time.
2206 void newCONSTSUB(HV* stash, char* name, SV* sv)
2210 Creates a new HV. The reference count is set to 1.
2216 Creates an RV wrapper for an SV. The reference count for the original SV is
2219 SV* newRV_inc (SV* ref)
2221 For historical reasons, "newRV" is a synonym for "newRV_inc".
2225 Creates an RV wrapper for an SV. The reference count for the original
2226 SV is B<not> incremented.
2228 SV* newRV_noinc (SV* ref)
2232 Creates a new SV. A non-zero C<len> parameter indicates the number of
2233 bytes of preallocated string space the SV should have. An extra byte
2234 for a tailing NUL is also reserved. (SvPOK is not set for the SV even
2235 if string space is allocated.) The reference count for the new SV is
2236 set to 1. C<id> is an integer id between 0 and 1299 (used to identify
2239 SV* NEWSV (int id, STRLEN len)
2243 Creates a new SV and copies an integer into it. The reference count for the
2250 Creates a new SV and copies a double into it. The reference count for the
2257 Creates a new SV and copies a string into it. The reference count for the
2258 SV is set to 1. If C<len> is zero then Perl will compute the length.
2260 SV* newSVpv (char* s, STRLEN len)
2264 Creates a new SV an initialize it with the string formatted like
2267 SV* newSVpvf(const char* pat, ...);
2271 Creates a new SV and copies a string into it. The reference count for the
2272 SV is set to 1. If C<len> is zero then Perl will create a zero length
2275 SV* newSVpvn (char* s, STRLEN len)
2279 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
2280 it will be upgraded to one. If C<classname> is non-null then the new SV will
2281 be blessed in the specified package. The new SV is returned and its
2282 reference count is 1.
2284 SV* newSVrv (SV* rv, char* classname)
2288 Creates a new SV which is an exact duplicate of the original SV.
2290 SV* newSVsv (SV* old)
2294 Used by C<xsubpp> to hook up XSUBs as Perl subs.
2298 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
2303 The XSUB-writer's interface to the C C<malloc> function. The allocated
2304 memory is zeroed with C<memzero>.
2306 void* Newz( x, void *ptr, int size, type )
2314 Null character pointer.
2330 The original stack mark for the XSUB. See C<dORIGMARK>.
2334 Allocates a new Perl interpreter. See L<perlembed>.
2336 =item perl_call_argv
2338 Performs a callback to the specified Perl sub. See L<perlcall>.
2340 I32 perl_call_argv (char* subname, I32 flags, char** argv)
2342 =item perl_call_method
2344 Performs a callback to the specified Perl method. The blessed object must
2345 be on the stack. See L<perlcall>.
2347 I32 perl_call_method (char* methname, I32 flags)
2351 Performs a callback to the specified Perl sub. See L<perlcall>.
2353 I32 perl_call_pv (char* subname, I32 flags)
2357 Performs a callback to the Perl sub whose name is in the SV. See
2360 I32 perl_call_sv (SV* sv, I32 flags)
2362 =item perl_construct
2364 Initializes a new Perl interpreter. See L<perlembed>.
2368 Shuts down a Perl interpreter. See L<perlembed>.
2372 Tells Perl to C<eval> the string in the SV.
2374 I32 perl_eval_sv (SV* sv, I32 flags)
2378 Tells Perl to C<eval> the given string and return an SV* result.
2380 SV* perl_eval_pv (char* p, I32 croak_on_error)
2384 Releases a Perl interpreter. See L<perlembed>.
2388 Returns the AV of the specified Perl array. If C<create> is set and the
2389 Perl variable does not exist then it will be created. If C<create> is not
2390 set and the variable does not exist then NULL is returned.
2392 AV* perl_get_av (char* name, I32 create)
2396 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
2397 variable does not exist then it will be created. If C<create> is not
2398 set and the variable does not exist then NULL is returned.
2400 CV* perl_get_cv (char* name, I32 create)
2404 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
2405 variable does not exist then it will be created. If C<create> is not
2406 set and the variable does not exist then NULL is returned.
2408 HV* perl_get_hv (char* name, I32 create)
2412 Returns the SV of the specified Perl scalar. If C<create> is set and the
2413 Perl variable does not exist then it will be created. If C<create> is not
2414 set and the variable does not exist then NULL is returned.
2416 SV* perl_get_sv (char* name, I32 create)
2420 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
2422 =item perl_require_pv
2424 Tells Perl to C<require> a module.
2426 void perl_require_pv (char* pv)
2430 Tells a Perl interpreter to run. See L<perlembed>.
2434 Pops an integer off the stack.
2440 Pops a long off the stack.
2446 Pops a string off the stack.
2452 Pops a double off the stack.
2458 Pops an SV off the stack.
2464 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2470 Push an integer onto the stack. The stack must have room for this element.
2471 Handles 'set' magic. See C<XPUSHi>.
2477 Push a double onto the stack. The stack must have room for this element.
2478 Handles 'set' magic. See C<XPUSHn>.
2480 void PUSHn(double d)
2484 Push a string onto the stack. The stack must have room for this element.
2485 The C<len> indicates the length of the string. Handles 'set' magic. See
2488 void PUSHp(char *c, int len )
2492 Push an SV onto the stack. The stack must have room for this element. Does
2493 not handle 'set' magic. See C<XPUSHs>.
2499 Push an unsigned integer onto the stack. The stack must have room for
2500 this element. See C<XPUSHu>.
2502 void PUSHu(unsigned int d)
2507 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2508 See C<PUSHMARK> and L<perlcall> for other uses.
2514 The XSUB-writer's interface to the C C<realloc> function.
2516 void* Renew( void *ptr, int size, type )
2520 The XSUB-writer's interface to the C C<realloc> function, with cast.
2522 void* Renewc( void *ptr, int size, type, cast )
2526 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
2527 This is always the proper type for the XSUB.
2528 See L<perlxs/"The RETVAL Variable">.
2532 The XSUB-writer's interface to the C C<free> function.
2536 The XSUB-writer's interface to the C C<malloc> function.
2540 The XSUB-writer's interface to the C C<realloc> function.
2544 Copy a string to a safe spot. This does not use an SV.
2546 char* savepv (char* sv)
2550 Copy a string to a safe spot. The C<len> indicates number of bytes to
2551 copy. This does not use an SV.
2553 char* savepvn (char* sv, I32 len)
2557 Opening bracket for temporaries on a callback. See C<FREETMPS> and
2564 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2569 Refetch the stack pointer. Used after a callback. See L<perlcall>.
2575 Used to access elements on the XSUB's stack.
2581 Test two strings to see if they are equal. Returns true or false.
2583 int strEQ( char *s1, char *s2 )
2587 Test two strings to see if the first, C<s1>, is greater than or equal to the
2588 second, C<s2>. Returns true or false.
2590 int strGE( char *s1, char *s2 )
2594 Test two strings to see if the first, C<s1>, is greater than the second,
2595 C<s2>. Returns true or false.
2597 int strGT( char *s1, char *s2 )
2601 Test two strings to see if the first, C<s1>, is less than or equal to the
2602 second, C<s2>. Returns true or false.
2604 int strLE( char *s1, char *s2 )
2608 Test two strings to see if the first, C<s1>, is less than the second,
2609 C<s2>. Returns true or false.
2611 int strLT( char *s1, char *s2 )
2615 Test two strings to see if they are different. Returns true or false.
2617 int strNE( char *s1, char *s2 )
2621 Test two strings to see if they are equal. The C<len> parameter indicates
2622 the number of bytes to compare. Returns true or false.
2624 int strnEQ( char *s1, char *s2 )
2628 Test two strings to see if they are different. The C<len> parameter
2629 indicates the number of bytes to compare. Returns true or false.
2631 int strnNE( char *s1, char *s2, int len )
2635 Marks an SV as mortal. The SV will be destroyed when the current context
2638 SV* sv_2mortal (SV* sv)
2642 Blesses an SV into a specified package. The SV must be an RV. The package
2643 must be designated by its stash (see C<gv_stashpv()>). The reference count
2644 of the SV is unaffected.
2646 SV* sv_bless (SV* sv, HV* stash)
2650 Concatenates the string onto the end of the string which is in the SV.
2651 Handles 'get' magic, but not 'set' magic. See C<sv_catpv_mg>.
2653 void sv_catpv (SV* sv, char* ptr)
2657 Like C<sv_catpv>, but also handles 'set' magic.
2659 void sv_catpvn (SV* sv, char* ptr)
2663 Concatenates the string onto the end of the string which is in the SV. The
2664 C<len> indicates number of bytes to copy. Handles 'get' magic, but not
2665 'set' magic. See C<sv_catpvn_mg>.
2667 void sv_catpvn (SV* sv, char* ptr, STRLEN len)
2671 Like C<sv_catpvn>, but also handles 'set' magic.
2673 void sv_catpvn_mg (SV* sv, char* ptr, STRLEN len)
2677 Processes its arguments like C<sprintf> and appends the formatted output
2678 to an SV. Handles 'get' magic, but not 'set' magic. C<SvSETMAGIC()> must
2679 typically be called after calling this function to handle 'set' magic.
2681 void sv_catpvf (SV* sv, const char* pat, ...)
2685 Like C<sv_catpvf>, but also handles 'set' magic.
2687 void sv_catpvf_mg (SV* sv, const char* pat, ...)
2691 Concatenates the string from SV C<ssv> onto the end of the string in SV
2692 C<dsv>. Handles 'get' magic, but not 'set' magic. See C<sv_catsv_mg>.
2694 void sv_catsv (SV* dsv, SV* ssv)
2698 Like C<sv_catsv>, but also handles 'set' magic.
2700 void sv_catsv_mg (SV* dsv, SV* ssv)
2704 Efficient removal of characters from the beginning of the string
2705 buffer. SvPOK(sv) must be true and the C<ptr> must be a pointer to
2706 somewhere inside the string buffer. The C<ptr> becomes the first
2707 character of the adjusted string.
2709 void sv_chop(SV* sv, char *ptr)
2714 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2715 string in C<sv1> is less than, equal to, or greater than the string in
2718 I32 sv_cmp (SV* sv1, SV* sv2)
2722 Returns the length of the string which is in the SV. See C<SvLEN>.
2728 Set the length of the string which is in the SV. See C<SvCUR>.
2730 void SvCUR_set (SV* sv, int val )
2734 Auto-decrement of the value in the SV.
2736 void sv_dec (SV* sv)
2738 =item sv_derived_from
2740 Returns a boolean indicating whether the SV is a subclass of the
2743 int sv_derived_from(SV* sv, char* class)
2745 =item sv_derived_from
2747 Returns a boolean indicating whether the SV is derived from the specified
2748 class. This is the function that implements C<UNIVERSAL::isa>. It works
2749 for class names as well as for objects.
2751 bool sv_derived_from _((SV* sv, char* name));
2755 Returns a pointer to the last character in the string which is in the SV.
2756 See C<SvCUR>. Access the character as
2762 Returns a boolean indicating whether the strings in the two SVs are
2765 I32 sv_eq (SV* sv1, SV* sv2)
2769 Invokes C<mg_get> on an SV if it has 'get' magic. This macro evaluates
2770 its argument more than once.
2772 void SvGETMAGIC( SV *sv )
2776 Expands the character buffer in the SV so that it has room for the
2777 indicated number of bytes (remember to reserve space for an extra
2778 trailing NUL character). Calls C<sv_grow> to perform the expansion if
2779 necessary. Returns a pointer to the character buffer.
2781 char* SvGROW( SV* sv, STRLEN len )
2785 Expands the character buffer in the SV. This will use C<sv_unref> and will
2786 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2791 Auto-increment of the value in the SV.
2793 void sv_inc (SV* sv)
2797 Inserts a string at the specified offset/length within the SV.
2798 Similar to the Perl substr() function.
2800 void sv_insert(SV *sv, STRLEN offset, STRLEN len,
2801 char *str, STRLEN strlen)
2805 Returns a boolean indicating whether the SV contains an integer.
2811 Unsets the IV status of an SV.
2813 void SvIOK_off (SV* sv)
2817 Tells an SV that it is an integer.
2819 void SvIOK_on (SV* sv)
2823 Tells an SV that it is an integer and disables all other OK bits.
2825 void SvIOK_only (SV* sv)
2829 Returns a boolean indicating whether the SV contains an integer. Checks the
2830 B<private> setting. Use C<SvIOK>.
2836 Returns a boolean indicating whether the SV is blessed into the specified
2837 class. This does not check for subtypes; use C<sv_derived_from> to verify
2838 an inheritance relationship.
2840 int sv_isa (SV* sv, char* name)
2844 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2845 object. If the SV is not an RV, or if the object is not blessed, then this
2848 int sv_isobject (SV* sv)
2852 Returns the integer which is in the SV.
2858 Returns the integer which is stored in the SV.
2864 Returns the size of the string buffer in the SV. See C<SvCUR>.
2870 Returns the length of the string in the SV. Use C<SvCUR>.
2872 STRLEN sv_len (SV* sv)
2876 Adds magic to an SV.
2878 void sv_magic (SV* sv, SV* obj, int how, char* name, I32 namlen)
2882 Creates a new SV which is a copy of the original SV. The new SV is marked
2885 SV* sv_mortalcopy (SV* oldsv)
2889 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2891 SV* sv_newmortal (void)
2895 Returns a boolean indicating whether the SV contains a number, integer or
2902 Unsets the NV/IV status of an SV.
2904 void SvNIOK_off (SV* sv)
2908 Returns a boolean indicating whether the SV contains a number, integer or
2909 double. Checks the B<private> setting. Use C<SvNIOK>.
2911 int SvNIOKp (SV* SV)
2915 This is the C<false> SV. See C<PL_sv_yes>. Always refer to this as C<&PL_sv_no>.
2919 Returns a boolean indicating whether the SV contains a double.
2925 Unsets the NV status of an SV.
2927 void SvNOK_off (SV* sv)
2931 Tells an SV that it is a double.
2933 void SvNOK_on (SV* sv)
2937 Tells an SV that it is a double and disables all other OK bits.
2939 void SvNOK_only (SV* sv)
2943 Returns a boolean indicating whether the SV contains a double. Checks the
2944 B<private> setting. Use C<SvNOK>.
2950 Returns the double which is stored in the SV.
2952 double SvNV (SV* sv)
2956 Returns the double which is stored in the SV.
2958 double SvNVX (SV* sv)
2962 Returns a boolean indicating whether the value is an SV.
2968 Returns a boolean indicating whether the SvIVX is a valid offset value
2969 for the SvPVX. This hack is used internally to speed up removal of
2970 characters from the beginning of a SvPV. When SvOOK is true, then the
2971 start of the allocated string buffer is really (SvPVX - SvIVX).
2977 Returns a boolean indicating whether the SV contains a character string.
2983 Unsets the PV status of an SV.
2985 void SvPOK_off (SV* sv)
2989 Tells an SV that it is a string.
2991 void SvPOK_on (SV* sv)
2995 Tells an SV that it is a string and disables all other OK bits.
2997 void SvPOK_only (SV* sv)
3001 Returns a boolean indicating whether the SV contains a character string.
3002 Checks the B<private> setting. Use C<SvPOK>.
3008 Returns a pointer to the string in the SV, or a stringified form of the SV
3009 if the SV does not contain a string. If C<len> is C<PL_na> then Perl will
3010 handle the length on its own. Handles 'get' magic.
3012 char* SvPV (SV* sv, int len )
3016 Like <SvPV> but will force the SV into becoming a string (SvPOK). You
3017 want force if you are going to update the SvPVX directly.
3019 char* SvPV_force(SV* sv, int len)
3024 Returns a pointer to the string in the SV. The SV must contain a string.
3026 char* SvPVX (SV* sv)
3030 Returns the value of the object's reference count.
3032 int SvREFCNT (SV* sv)
3036 Decrements the reference count of the given SV.
3038 void SvREFCNT_dec (SV* sv)
3042 Increments the reference count of the given SV.
3044 void SvREFCNT_inc (SV* sv)
3048 Tests if the SV is an RV.
3054 Unsets the RV status of an SV.
3056 void SvROK_off (SV* sv)
3060 Tells an SV that it is an RV.
3062 void SvROK_on (SV* sv)
3066 Dereferences an RV to return the SV.
3072 Invokes C<mg_set> on an SV if it has 'set' magic. This macro evaluates
3073 its argument more than once.
3075 void SvSETMAGIC( SV *sv )
3079 Copies an integer into the given SV. Does not handle 'set' magic.
3082 void sv_setiv (SV* sv, IV num)
3086 Like C<sv_setiv>, but also handles 'set' magic.
3088 void sv_setiv_mg (SV* sv, IV num)
3092 Copies a double into the given SV. Does not handle 'set' magic.
3095 void sv_setnv (SV* sv, double num)
3099 Like C<sv_setnv>, but also handles 'set' magic.
3101 void sv_setnv_mg (SV* sv, double num)
3105 Copies a string into an SV. The string must be null-terminated.
3106 Does not handle 'set' magic. See C<sv_setpv_mg>.
3108 void sv_setpv (SV* sv, char* ptr)
3112 Like C<sv_setpv>, but also handles 'set' magic.
3114 void sv_setpv_mg (SV* sv, char* ptr)
3118 Copies an integer into the given SV, also updating its string value.
3119 Does not handle 'set' magic. See C<sv_setpviv_mg>.
3121 void sv_setpviv (SV* sv, IV num)
3125 Like C<sv_setpviv>, but also handles 'set' magic.
3127 void sv_setpviv_mg (SV* sv, IV num)
3131 Copies a string into an SV. The C<len> parameter indicates the number of
3132 bytes to be copied. Does not handle 'set' magic. See C<sv_setpvn_mg>.
3134 void sv_setpvn (SV* sv, char* ptr, STRLEN len)
3138 Like C<sv_setpvn>, but also handles 'set' magic.
3140 void sv_setpvn_mg (SV* sv, char* ptr, STRLEN len)
3144 Processes its arguments like C<sprintf> and sets an SV to the formatted
3145 output. Does not handle 'set' magic. See C<sv_setpvf_mg>.
3147 void sv_setpvf (SV* sv, const char* pat, ...)
3151 Like C<sv_setpvf>, but also handles 'set' magic.
3153 void sv_setpvf_mg (SV* sv, const char* pat, ...)
3157 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
3158 argument will be upgraded to an RV. That RV will be modified to point to
3159 the new SV. The C<classname> argument indicates the package for the
3160 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3161 will be returned and will have a reference count of 1.
3163 SV* sv_setref_iv (SV *rv, char *classname, IV iv)
3167 Copies a double into a new SV, optionally blessing the SV. The C<rv>
3168 argument will be upgraded to an RV. That RV will be modified to point to
3169 the new SV. The C<classname> argument indicates the package for the
3170 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3171 will be returned and will have a reference count of 1.
3173 SV* sv_setref_nv (SV *rv, char *classname, double nv)
3177 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
3178 argument will be upgraded to an RV. That RV will be modified to point to
3179 the new SV. If the C<pv> argument is NULL then C<PL_sv_undef> will be placed
3180 into the SV. The C<classname> argument indicates the package for the
3181 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3182 will be returned and will have a reference count of 1.
3184 SV* sv_setref_pv (SV *rv, char *classname, void* pv)
3186 Do not use with integral Perl types such as HV, AV, SV, CV, because those
3187 objects will become corrupted by the pointer copy process.
3189 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
3193 Copies a string into a new SV, optionally blessing the SV. The length of the
3194 string must be specified with C<n>. The C<rv> argument will be upgraded to
3195 an RV. That RV will be modified to point to the new SV. The C<classname>
3196 argument indicates the package for the blessing. Set C<classname> to
3197 C<Nullch> to avoid the blessing. The new SV will be returned and will have
3198 a reference count of 1.
3200 SV* sv_setref_pvn (SV *rv, char *classname, char* pv, I32 n)
3202 Note that C<sv_setref_pv> copies the pointer while this copies the string.
3206 Calls C<sv_setsv> if dsv is not the same as ssv. May evaluate arguments
3209 void SvSetSV (SV* dsv, SV* ssv)
3211 =item SvSetSV_nosteal
3213 Calls a non-destructive version of C<sv_setsv> if dsv is not the same as ssv.
3214 May evaluate arguments more than once.
3216 void SvSetSV_nosteal (SV* dsv, SV* ssv)
3220 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
3221 The source SV may be destroyed if it is mortal. Does not handle 'set' magic.
3222 See the macro forms C<SvSetSV>, C<SvSetSV_nosteal> and C<sv_setsv_mg>.
3224 void sv_setsv (SV* dsv, SV* ssv)
3228 Like C<sv_setsv>, but also handles 'set' magic.
3230 void sv_setsv_mg (SV* dsv, SV* ssv)
3234 Copies an unsigned integer into the given SV. Does not handle 'set' magic.
3237 void sv_setuv (SV* sv, UV num)
3241 Like C<sv_setuv>, but also handles 'set' magic.
3243 void sv_setuv_mg (SV* sv, UV num)
3247 Returns the stash of the SV.
3249 HV* SvSTASH (SV* sv)
3253 Taints an SV if tainting is enabled
3255 void SvTAINT (SV* sv)
3259 Checks to see if an SV is tainted. Returns TRUE if it is, FALSE if not.
3261 int SvTAINTED (SV* sv)
3265 Untaints an SV. Be I<very> careful with this routine, as it short-circuits
3266 some of Perl's fundamental security features. XS module authors should
3267 not use this function unless they fully understand all the implications
3268 of unconditionally untainting the value. Untainting should be done in
3269 the standard perl fashion, via a carefully crafted regexp, rather than
3270 directly untainting variables.
3272 void SvTAINTED_off (SV* sv)
3276 Marks an SV as tainted.
3278 void SvTAINTED_on (SV* sv)
3282 Integer type flag for scalars. See C<svtype>.
3286 Pointer type flag for scalars. See C<svtype>.
3290 Type flag for arrays. See C<svtype>.
3294 Type flag for code refs. See C<svtype>.
3298 Type flag for hashes. See C<svtype>.
3302 Type flag for blessed scalars. See C<svtype>.
3306 Double type flag for scalars. See C<svtype>.
3310 Returns a boolean indicating whether Perl would evaluate the SV as true or
3311 false, defined or undefined. Does not handle 'get' magic.
3317 Returns the type of the SV. See C<svtype>.
3319 svtype SvTYPE (SV* sv)
3323 An enum of flags for Perl types. These are found in the file B<sv.h> in the
3324 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
3328 This is the C<undef> SV. Always refer to this as C<&PL_sv_undef>.
3332 Unsets the RV status of the SV, and decrements the reference count of
3333 whatever was being referenced by the RV. This can almost be thought of
3334 as a reversal of C<newSVrv>. See C<SvROK_off>.
3336 void sv_unref (SV* sv)
3340 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
3341 the upgrade if necessary. See C<svtype>.
3343 bool SvUPGRADE (SV* sv, svtype mt)
3347 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
3351 Tells an SV to use C<ptr> to find its string value. Normally the string is
3352 stored inside the SV but sv_usepvn allows the SV to use an outside string.
3353 The C<ptr> should point to memory that was allocated by C<malloc>. The
3354 string length, C<len>, must be supplied. This function will realloc the
3355 memory pointed to by C<ptr>, so that pointer should not be freed or used by
3356 the programmer after giving it to sv_usepvn. Does not handle 'set' magic.
3357 See C<sv_usepvn_mg>.
3359 void sv_usepvn (SV* sv, char* ptr, STRLEN len)
3363 Like C<sv_usepvn>, but also handles 'set' magic.
3365 void sv_usepvn_mg (SV* sv, char* ptr, STRLEN len)
3367 =item sv_vcatpvfn(sv, pat, patlen, args, svargs, svmax, used_locale)
3369 Processes its arguments like C<vsprintf> and appends the formatted output
3370 to an SV. Uses an array of SVs if the C style variable argument list is
3371 missing (NULL). Indicates if locale information has been used for formatting.
3373 void sv_catpvfn _((SV* sv, const char* pat, STRLEN patlen,
3374 va_list *args, SV **svargs, I32 svmax,
3375 bool *used_locale));
3377 =item sv_vsetpvfn(sv, pat, patlen, args, svargs, svmax, used_locale)
3379 Works like C<vcatpvfn> but copies the text into the SV instead of
3382 void sv_setpvfn _((SV* sv, const char* pat, STRLEN patlen,
3383 va_list *args, SV **svargs, I32 svmax,
3384 bool *used_locale));
3388 Returns the unsigned integer which is in the SV.
3394 Returns the unsigned integer which is stored in the SV.
3400 This is the C<true> SV. See C<PL_sv_no>. Always refer to this as C<&PL_sv_yes>.
3404 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
3405 This is always the proper type for the C++ object. See C<CLASS> and
3406 L<perlxs/"Using XS With C++">.
3410 Converts the specified character to lowercase.
3412 int toLOWER (char c)
3416 Converts the specified character to uppercase.
3418 int toUPPER (char c)
3422 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
3423 function the same way you use the C C<printf> function. See C<croak()>.
3427 Push an integer onto the stack, extending the stack if necessary. Handles
3428 'set' magic. See C<PUSHi>.
3434 Push a double onto the stack, extending the stack if necessary. Handles 'set'
3435 magic. See C<PUSHn>.
3441 Push a string onto the stack, extending the stack if necessary. The C<len>
3442 indicates the length of the string. Handles 'set' magic. See C<PUSHp>.
3444 XPUSHp(char *c, int len)
3448 Push an SV onto the stack, extending the stack if necessary. Does not
3449 handle 'set' magic. See C<PUSHs>.
3455 Push an unsigned integer onto the stack, extending the stack if
3456 necessary. See C<PUSHu>.
3460 Macro to declare an XSUB and its C parameter list. This is handled by
3465 Return from XSUB, indicating number of items on the stack. This is usually
3466 handled by C<xsubpp>.
3470 =item XSRETURN_EMPTY
3472 Return an empty list from an XSUB immediately.
3478 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
3484 Return C<&PL_sv_no> from an XSUB immediately. Uses C<XST_mNO>.
3490 Return an double from an XSUB immediately. Uses C<XST_mNV>.
3496 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
3498 XSRETURN_PV(char *v)
3500 =item XSRETURN_UNDEF
3502 Return C<&PL_sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
3508 Return C<&PL_sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
3514 Place an integer into the specified position C<i> on the stack. The value is
3515 stored in a new mortal SV.
3517 XST_mIV( int i, IV v )
3521 Place a double into the specified position C<i> on the stack. The value is
3522 stored in a new mortal SV.
3524 XST_mNV( int i, NV v )
3528 Place C<&PL_sv_no> into the specified position C<i> on the stack.
3534 Place a copy of a string into the specified position C<i> on the stack. The
3535 value is stored in a new mortal SV.
3537 XST_mPV( int i, char *v )
3541 Place C<&PL_sv_undef> into the specified position C<i> on the stack.
3547 Place C<&PL_sv_yes> into the specified position C<i> on the stack.
3553 The version identifier for an XS module. This is usually handled
3554 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
3556 =item XS_VERSION_BOOTCHECK
3558 Macro to verify that a PM module's $VERSION variable matches the XS module's
3559 C<XS_VERSION> variable. This is usually handled automatically by
3560 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
3564 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
3565 destination, C<n> is the number of items, and C<t> is the type.
3567 void Zero( d, n, t )
3573 Until May 1997, this document was maintained by Jeff Okamoto
3574 <okamoto@corp.hp.com>. It is now maintained as part of Perl itself.
3576 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
3577 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
3578 Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
3579 Stephen McCamant, and Gurusamy Sarathy.
3581 API Listing originally by Dean Roehrich <roehrich@cray.com>.