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>, though
99 this is rather less efficient than using a local variable. Remember,
100 however, that Perl allows arbitrary strings of data that may both contain
101 NULs and might not be terminated by a NUL.
103 If you want to know if the scalar value is TRUE, you can use:
107 Although Perl will automatically grow strings for you, if you need to force
108 Perl to allocate more memory for your SV, you can use the macro
110 SvGROW(SV*, STRLEN newlen)
112 which will determine if more memory needs to be allocated. If so, it will
113 call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
114 decrease, the allocated memory of an SV and that it does not automatically
115 add a byte for the a trailing NUL (perl's own string functions typically do
116 C<SvGROW(sv, len + 1)>).
118 If you have an SV and want to know what kind of data Perl thinks is stored
119 in it, you can use the following macros to check the type of SV you have.
125 You can get and set the current length of the string stored in an SV with
126 the following macros:
129 SvCUR_set(SV*, I32 val)
131 You can also get a pointer to the end of the string stored in the SV
136 But note that these last three macros are valid only if C<SvPOK()> is true.
138 If you want to append something to the end of string stored in an C<SV*>,
139 you can use the following functions:
141 void sv_catpv(SV*, char*);
142 void sv_catpvn(SV*, char*, int);
143 void sv_catpvf(SV*, const char*, ...);
144 void sv_catpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
145 void sv_catsv(SV*, SV*);
147 The first function calculates the length of the string to be appended by
148 using C<strlen>. In the second, you specify the length of the string
149 yourself. The third function processes its arguments like C<sprintf> and
150 appends the formatted output. The fourth function works like C<vsprintf>.
151 You can specify the address and length of an array of SVs instead of the
152 va_list argument. The fifth function extends the string stored in the first
153 SV with the string stored in the second SV. It also forces the second SV
154 to be interpreted as a string.
156 The C<sv_cat*()> functions are not generic enough to operate on values that
157 have "magic". See L<Magic Virtual Tables> later in this document.
159 If you know the name of a scalar variable, you can get a pointer to its SV
160 by using the following:
162 SV* perl_get_sv("package::varname", FALSE);
164 This returns NULL if the variable does not exist.
166 If you want to know if this variable (or any other SV) is actually C<defined>,
171 The scalar C<undef> value is stored in an SV instance called C<PL_sv_undef>. Its
172 address can be used whenever an C<SV*> is needed.
174 There are also the two values C<PL_sv_yes> and C<PL_sv_no>, which contain Boolean
175 TRUE and FALSE values, respectively. Like C<PL_sv_undef>, their addresses can
176 be used whenever an C<SV*> is needed.
178 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&PL_sv_undef>.
182 if (I-am-to-return-a-real-value) {
183 sv = sv_2mortal(newSViv(42));
187 This code tries to return a new SV (which contains the value 42) if it should
188 return a real value, or undef otherwise. Instead it has returned a NULL
189 pointer which, somewhere down the line, will cause a segmentation violation,
190 bus error, or just weird results. Change the zero to C<&PL_sv_undef> in the first
191 line and all will be well.
193 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
194 call is not necessary (see L<Reference Counts and Mortality>).
196 =head2 What's Really Stored in an SV?
198 Recall that the usual method of determining the type of scalar you have is
199 to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
200 usually these macros will always return TRUE and calling the C<Sv*V>
201 macros will do the appropriate conversion of string to integer/double or
202 integer/double to string.
204 If you I<really> need to know if you have an integer, double, or string
205 pointer in an SV, you can use the following three macros instead:
211 These will tell you if you truly have an integer, double, or string pointer
212 stored in your SV. The "p" stands for private.
214 In general, though, it's best to use the C<Sv*V> macros.
216 =head2 Working with AVs
218 There are two ways to create and load an AV. The first method creates an
223 The second method both creates the AV and initially populates it with SVs:
225 AV* av_make(I32 num, SV **ptr);
227 The second argument points to an array containing C<num> C<SV*>'s. Once the
228 AV has been created, the SVs can be destroyed, if so desired.
230 Once the AV has been created, the following operations are possible on AVs:
232 void av_push(AV*, SV*);
235 void av_unshift(AV*, I32 num);
237 These should be familiar operations, with the exception of C<av_unshift>.
238 This routine adds C<num> elements at the front of the array with the C<undef>
239 value. You must then use C<av_store> (described below) to assign values
240 to these new elements.
242 Here are some other functions:
245 SV** av_fetch(AV*, I32 key, I32 lval);
246 SV** av_store(AV*, I32 key, SV* val);
248 The C<av_len> function returns the highest index value in array (just
249 like $#array in Perl). If the array is empty, -1 is returned. The
250 C<av_fetch> function returns the value at index C<key>, but if C<lval>
251 is non-zero, then C<av_fetch> will store an undef value at that index.
252 The C<av_store> function stores the value C<val> at index C<key>, and does
253 not increment the reference count of C<val>. Thus the caller is responsible
254 for taking care of that, and if C<av_store> returns NULL, the caller will
255 have to decrement the reference count to avoid a memory leak. Note that
256 C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s as their
261 void av_extend(AV*, I32 key);
263 The C<av_clear> function deletes all the elements in the AV* array, but
264 does not actually delete the array itself. The C<av_undef> function will
265 delete all the elements in the array plus the array itself. The
266 C<av_extend> function extends the array so that it contains C<key>
267 elements. If C<key> is less than the current length of the array, then
270 If you know the name of an array variable, you can get a pointer to its AV
271 by using the following:
273 AV* perl_get_av("package::varname", FALSE);
275 This returns NULL if the variable does not exist.
277 See L<Understanding the Magic of Tied Hashes and Arrays> for more
278 information on how to use the array access functions on tied arrays.
280 =head2 Working with HVs
282 To create an HV, you use the following routine:
286 Once the HV has been created, the following operations are possible on HVs:
288 SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
289 SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
291 The C<klen> parameter is the length of the key being passed in (Note that
292 you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
293 length of the key). The C<val> argument contains the SV pointer to the
294 scalar being stored, and C<hash> is the precomputed hash value (zero if
295 you want C<hv_store> to calculate it for you). The C<lval> parameter
296 indicates whether this fetch is actually a part of a store operation, in
297 which case a new undefined value will be added to the HV with the supplied
298 key and C<hv_fetch> will return as if the value had already existed.
300 Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
301 C<SV*>. To access the scalar value, you must first dereference the return
302 value. However, you should check to make sure that the return value is
303 not NULL before dereferencing it.
305 These two functions check if a hash table entry exists, and deletes it.
307 bool hv_exists(HV*, char* key, U32 klen);
308 SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
310 If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
311 create and return a mortal copy of the deleted value.
313 And more miscellaneous functions:
318 Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
319 table but does not actually delete the hash table. The C<hv_undef> deletes
320 both the entries and the hash table itself.
322 Perl keeps the actual data in linked list of structures with a typedef of HE.
323 These contain the actual key and value pointers (plus extra administrative
324 overhead). The key is a string pointer; the value is an C<SV*>. However,
325 once you have an C<HE*>, to get the actual key and value, use the routines
328 I32 hv_iterinit(HV*);
329 /* Prepares starting point to traverse hash table */
330 HE* hv_iternext(HV*);
331 /* Get the next entry, and return a pointer to a
332 structure that has both the key and value */
333 char* hv_iterkey(HE* entry, I32* retlen);
334 /* Get the key from an HE structure and also return
335 the length of the key string */
336 SV* hv_iterval(HV*, HE* entry);
337 /* Return a SV pointer to the value of the HE
339 SV* hv_iternextsv(HV*, char** key, I32* retlen);
340 /* This convenience routine combines hv_iternext,
341 hv_iterkey, and hv_iterval. The key and retlen
342 arguments are return values for the key and its
343 length. The value is returned in the SV* argument */
345 If you know the name of a hash variable, you can get a pointer to its HV
346 by using the following:
348 HV* perl_get_hv("package::varname", FALSE);
350 This returns NULL if the variable does not exist.
352 The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
356 hash = (hash * 33) + *key++;
357 hash = hash + (hash >> 5); /* after 5.006 */
359 The last step was added in version 5.006 to improve distribution of
360 lower bits in the resulting hash value.
362 See L<Understanding the Magic of Tied Hashes and Arrays> for more
363 information on how to use the hash access functions on tied hashes.
365 =head2 Hash API Extensions
367 Beginning with version 5.004, the following functions are also supported:
369 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
370 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
372 bool hv_exists_ent (HV* tb, SV* key, U32 hash);
373 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
375 SV* hv_iterkeysv (HE* entry);
377 Note that these functions take C<SV*> keys, which simplifies writing
378 of extension code that deals with hash structures. These functions
379 also allow passing of C<SV*> keys to C<tie> functions without forcing
380 you to stringify the keys (unlike the previous set of functions).
382 They also return and accept whole hash entries (C<HE*>), making their
383 use more efficient (since the hash number for a particular string
384 doesn't have to be recomputed every time). See L<API LISTING> later in
385 this document for detailed descriptions.
387 The following macros must always be used to access the contents of hash
388 entries. Note that the arguments to these macros must be simple
389 variables, since they may get evaluated more than once. See
390 L<API LISTING> later in this document for detailed descriptions of these
393 HePV(HE* he, STRLEN len)
397 HeSVKEY_force(HE* he)
398 HeSVKEY_set(HE* he, SV* sv)
400 These two lower level macros are defined, but must only be used when
401 dealing with keys that are not C<SV*>s:
406 Note that both C<hv_store> and C<hv_store_ent> do not increment the
407 reference count of the stored C<val>, which is the caller's responsibility.
408 If these functions return a NULL value, the caller will usually have to
409 decrement the reference count of C<val> to avoid a memory leak.
413 References are a special type of scalar that point to other data types
414 (including references).
416 To create a reference, use either of the following functions:
418 SV* newRV_inc((SV*) thing);
419 SV* newRV_noinc((SV*) thing);
421 The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
422 functions are identical except that C<newRV_inc> increments the reference
423 count of the C<thing>, while C<newRV_noinc> does not. For historical
424 reasons, C<newRV> is a synonym for C<newRV_inc>.
426 Once you have a reference, you can use the following macro to dereference
431 then call the appropriate routines, casting the returned C<SV*> to either an
432 C<AV*> or C<HV*>, if required.
434 To determine if an SV is a reference, you can use the following macro:
438 To discover what type of value the reference refers to, use the following
439 macro and then check the return value.
443 The most useful types that will be returned are:
452 SVt_PVGV Glob (possible a file handle)
453 SVt_PVMG Blessed or Magical Scalar
455 See the sv.h header file for more details.
457 =head2 Blessed References and Class Objects
459 References are also used to support object-oriented programming. In the
460 OO lexicon, an object is simply a reference that has been blessed into a
461 package (or class). Once blessed, the programmer may now use the reference
462 to access the various methods in the class.
464 A reference can be blessed into a package with the following function:
466 SV* sv_bless(SV* sv, HV* stash);
468 The C<sv> argument must be a reference. The C<stash> argument specifies
469 which class the reference will belong to. See
470 L<Stashes and Globs> for information on converting class names into stashes.
472 /* Still under construction */
474 Upgrades rv to reference if not already one. Creates new SV for rv to
475 point to. If C<classname> is non-null, the SV is blessed into the specified
476 class. SV is returned.
478 SV* newSVrv(SV* rv, char* classname);
480 Copies integer or double into an SV whose reference is C<rv>. SV is blessed
481 if C<classname> is non-null.
483 SV* sv_setref_iv(SV* rv, char* classname, IV iv);
484 SV* sv_setref_nv(SV* rv, char* classname, NV iv);
486 Copies the pointer value (I<the address, not the string!>) into an SV whose
487 reference is rv. SV is blessed if C<classname> is non-null.
489 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
491 Copies string into an SV whose reference is C<rv>. Set length to 0 to let
492 Perl calculate the string length. SV is blessed if C<classname> is non-null.
494 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
496 Tests whether the SV is blessed into the specified class. It does not
497 check inheritance relationships.
499 int sv_isa(SV* sv, char* name);
501 Tests whether the SV is a reference to a blessed object.
503 int sv_isobject(SV* sv);
505 Tests whether the SV is derived from the specified class. SV can be either
506 a reference to a blessed object or a string containing a class name. This
507 is the function implementing the C<UNIVERSAL::isa> functionality.
509 bool sv_derived_from(SV* sv, char* name);
511 To check if you've got an object derived from a specific class you have
514 if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... }
516 =head2 Creating New Variables
518 To create a new Perl variable with an undef value which can be accessed from
519 your Perl script, use the following routines, depending on the variable type.
521 SV* perl_get_sv("package::varname", TRUE);
522 AV* perl_get_av("package::varname", TRUE);
523 HV* perl_get_hv("package::varname", TRUE);
525 Notice the use of TRUE as the second parameter. The new variable can now
526 be set, using the routines appropriate to the data type.
528 There are additional macros whose values may be bitwise OR'ed with the
529 C<TRUE> argument to enable certain extra features. Those bits are:
531 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
532 "Name <varname> used only once: possible typo" warning.
533 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
534 the variable did not exist before the function was called.
536 If you do not specify a package name, the variable is created in the current
539 =head2 Reference Counts and Mortality
541 Perl uses an reference count-driven garbage collection mechanism. SVs,
542 AVs, or HVs (xV for short in the following) start their life with a
543 reference count of 1. If the reference count of an xV ever drops to 0,
544 then it will be destroyed and its memory made available for reuse.
546 This normally doesn't happen at the Perl level unless a variable is
547 undef'ed or the last variable holding a reference to it is changed or
548 overwritten. At the internal level, however, reference counts can be
549 manipulated with the following macros:
551 int SvREFCNT(SV* sv);
552 SV* SvREFCNT_inc(SV* sv);
553 void SvREFCNT_dec(SV* sv);
555 However, there is one other function which manipulates the reference
556 count of its argument. The C<newRV_inc> function, you will recall,
557 creates a reference to the specified argument. As a side effect,
558 it increments the argument's reference count. If this is not what
559 you want, use C<newRV_noinc> instead.
561 For example, imagine you want to return a reference from an XSUB function.
562 Inside the XSUB routine, you create an SV which initially has a reference
563 count of one. Then you call C<newRV_inc>, passing it the just-created SV.
564 This returns the reference as a new SV, but the reference count of the
565 SV you passed to C<newRV_inc> has been incremented to two. Now you
566 return the reference from the XSUB routine and forget about the SV.
567 But Perl hasn't! Whenever the returned reference is destroyed, the
568 reference count of the original SV is decreased to one and nothing happens.
569 The SV will hang around without any way to access it until Perl itself
570 terminates. This is a memory leak.
572 The correct procedure, then, is to use C<newRV_noinc> instead of
573 C<newRV_inc>. Then, if and when the last reference is destroyed,
574 the reference count of the SV will go to zero and it will be destroyed,
575 stopping any memory leak.
577 There are some convenience functions available that can help with the
578 destruction of xVs. These functions introduce the concept of "mortality".
579 An xV that is mortal has had its reference count marked to be decremented,
580 but not actually decremented, until "a short time later". Generally the
581 term "short time later" means a single Perl statement, such as a call to
582 an XSUB function. The actual determinant for when mortal xVs have their
583 reference count decremented depends on two macros, SAVETMPS and FREETMPS.
584 See L<perlcall> and L<perlxs> for more details on these macros.
586 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
587 However, if you mortalize a variable twice, the reference count will
588 later be decremented twice.
590 You should be careful about creating mortal variables. Strange things
591 can happen if you make the same value mortal within multiple contexts,
592 or if you make a variable mortal multiple times.
594 To create a mortal variable, use the functions:
598 SV* sv_mortalcopy(SV*)
600 The first call creates a mortal SV, the second converts an existing
601 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
602 third creates a mortal copy of an existing SV.
604 The mortal routines are not just for SVs -- AVs and HVs can be
605 made mortal by passing their address (type-casted to C<SV*>) to the
606 C<sv_2mortal> or C<sv_mortalcopy> routines.
608 =head2 Stashes and Globs
610 A "stash" is a hash that contains all of the different objects that
611 are contained within a package. Each key of the stash is a symbol
612 name (shared by all the different types of objects that have the same
613 name), and each value in the hash table is a GV (Glob Value). This GV
614 in turn contains references to the various objects of that name,
615 including (but not limited to) the following:
624 There is a single stash called "PL_defstash" that holds the items that exist
625 in the "main" package. To get at the items in other packages, append the
626 string "::" to the package name. The items in the "Foo" package are in
627 the stash "Foo::" in PL_defstash. The items in the "Bar::Baz" package are
628 in the stash "Baz::" in "Bar::"'s stash.
630 To get the stash pointer for a particular package, use the function:
632 HV* gv_stashpv(char* name, I32 create)
633 HV* gv_stashsv(SV*, I32 create)
635 The first function takes a literal string, the second uses the string stored
636 in the SV. Remember that a stash is just a hash table, so you get back an
637 C<HV*>. The C<create> flag will create a new package if it is set.
639 The name that C<gv_stash*v> wants is the name of the package whose symbol table
640 you want. The default package is called C<main>. If you have multiply nested
641 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
644 Alternately, if you have an SV that is a blessed reference, you can find
645 out the stash pointer by using:
647 HV* SvSTASH(SvRV(SV*));
649 then use the following to get the package name itself:
651 char* HvNAME(HV* stash);
653 If you need to bless or re-bless an object you can use the following
656 SV* sv_bless(SV*, HV* stash)
658 where the first argument, an C<SV*>, must be a reference, and the second
659 argument is a stash. The returned C<SV*> can now be used in the same way
662 For more information on references and blessings, consult L<perlref>.
664 =head2 Double-Typed SVs
666 Scalar variables normally contain only one type of value, an integer,
667 double, pointer, or reference. Perl will automatically convert the
668 actual scalar data from the stored type into the requested type.
670 Some scalar variables contain more than one type of scalar data. For
671 example, the variable C<$!> contains either the numeric value of C<errno>
672 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
674 To force multiple data values into an SV, you must do two things: use the
675 C<sv_set*v> routines to add the additional scalar type, then set a flag
676 so that Perl will believe it contains more than one type of data. The
677 four macros to set the flags are:
684 The particular macro you must use depends on which C<sv_set*v> routine
685 you called first. This is because every C<sv_set*v> routine turns on
686 only the bit for the particular type of data being set, and turns off
689 For example, to create a new Perl variable called "dberror" that contains
690 both the numeric and descriptive string error values, you could use the
694 extern char *dberror_list;
696 SV* sv = perl_get_sv("dberror", TRUE);
697 sv_setiv(sv, (IV) dberror);
698 sv_setpv(sv, dberror_list[dberror]);
701 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
702 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
704 =head2 Magic Variables
706 [This section still under construction. Ignore everything here. Post no
707 bills. Everything not permitted is forbidden.]
709 Any SV may be magical, that is, it has special features that a normal
710 SV does not have. These features are stored in the SV structure in a
711 linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
724 Note this is current as of patchlevel 0, and could change at any time.
726 =head2 Assigning Magic
728 Perl adds magic to an SV using the sv_magic function:
730 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
732 The C<sv> argument is a pointer to the SV that is to acquire a new magical
735 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
736 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
737 it to the beginning of the linked list of magical features. Any prior
738 entry of the same type of magic is deleted. Note that this can be
739 overridden, and multiple instances of the same type of magic can be
740 associated with an SV.
742 The C<name> and C<namlen> arguments are used to associate a string with
743 the magic, typically the name of a variable. C<namlen> is stored in the
744 C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
745 copy of the name is stored in C<mg_ptr> field.
747 The sv_magic function uses C<how> to determine which, if any, predefined
748 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
749 See the "Magic Virtual Table" section below. The C<how> argument is also
750 stored in the C<mg_type> field.
752 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
753 structure. If it is not the same as the C<sv> argument, the reference
754 count of the C<obj> object is incremented. If it is the same, or if
755 the C<how> argument is "#", or if it is a NULL pointer, then C<obj> is
756 merely stored, without the reference count being incremented.
758 There is also a function to add magic to an C<HV>:
760 void hv_magic(HV *hv, GV *gv, int how);
762 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
764 To remove the magic from an SV, call the function sv_unmagic:
766 void sv_unmagic(SV *sv, int type);
768 The C<type> argument should be equal to the C<how> value when the C<SV>
769 was initially made magical.
771 =head2 Magic Virtual Tables
773 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
774 C<MGVTBL>, which is a structure of function pointers and stands for
775 "Magic Virtual Table" to handle the various operations that might be
776 applied to that variable.
778 The C<MGVTBL> has five pointers to the following routine types:
780 int (*svt_get)(SV* sv, MAGIC* mg);
781 int (*svt_set)(SV* sv, MAGIC* mg);
782 U32 (*svt_len)(SV* sv, MAGIC* mg);
783 int (*svt_clear)(SV* sv, MAGIC* mg);
784 int (*svt_free)(SV* sv, MAGIC* mg);
786 This MGVTBL structure is set at compile-time in C<perl.h> and there are
787 currently 19 types (or 21 with overloading turned on). These different
788 structures contain pointers to various routines that perform additional
789 actions depending on which function is being called.
791 Function pointer Action taken
792 ---------------- ------------
793 svt_get Do something after the value of the SV is retrieved.
794 svt_set Do something after the SV is assigned a value.
795 svt_len Report on the SV's length.
796 svt_clear Clear something the SV represents.
797 svt_free Free any extra storage associated with the SV.
799 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
800 to an C<mg_type> of '\0') contains:
802 { magic_get, magic_set, magic_len, 0, 0 }
804 Thus, when an SV is determined to be magical and of type '\0', if a get
805 operation is being performed, the routine C<magic_get> is called. All
806 the various routines for the various magical types begin with C<magic_>.
808 The current kinds of Magic Virtual Tables are:
810 mg_type MGVTBL Type of magic
811 ------- ------ ----------------------------
812 \0 vtbl_sv Special scalar variable
813 A vtbl_amagic %OVERLOAD hash
814 a vtbl_amagicelem %OVERLOAD hash element
815 c (none) Holds overload table (AMT) on stash
816 B vtbl_bm Boyer-Moore (fast string search)
818 e vtbl_envelem %ENV hash element
819 f vtbl_fm Formline ('compiled' format)
820 g vtbl_mglob m//g target / study()ed string
821 I vtbl_isa @ISA array
822 i vtbl_isaelem @ISA array element
823 k vtbl_nkeys scalar(keys()) lvalue
824 L (none) Debugger %_<filename
825 l vtbl_dbline Debugger %_<filename element
826 o vtbl_collxfrm Locale transformation
827 P vtbl_pack Tied array or hash
828 p vtbl_packelem Tied array or hash element
829 q vtbl_packelem Tied scalar or handle
831 s vtbl_sigelem %SIG hash element
832 t vtbl_taint Taintedness
833 U vtbl_uvar Available for use by extensions
834 v vtbl_vec vec() lvalue
835 x vtbl_substr substr() lvalue
836 y vtbl_defelem Shadow "foreach" iterator variable /
837 smart parameter vivification
838 * vtbl_glob GV (typeglob)
839 # vtbl_arylen Array length ($#ary)
840 . vtbl_pos pos() lvalue
841 ~ (none) Available for use by extensions
843 When an uppercase and lowercase letter both exist in the table, then the
844 uppercase letter is used to represent some kind of composite type (a list
845 or a hash), and the lowercase letter is used to represent an element of
848 The '~' and 'U' magic types are defined specifically for use by
849 extensions and will not be used by perl itself. Extensions can use
850 '~' magic to 'attach' private information to variables (typically
851 objects). This is especially useful because there is no way for
852 normal perl code to corrupt this private information (unlike using
853 extra elements of a hash object).
855 Similarly, 'U' magic can be used much like tie() to call a C function
856 any time a scalar's value is used or changed. The C<MAGIC>'s
857 C<mg_ptr> field points to a C<ufuncs> structure:
860 I32 (*uf_val)(IV, SV*);
861 I32 (*uf_set)(IV, SV*);
865 When the SV is read from or written to, the C<uf_val> or C<uf_set>
866 function will be called with C<uf_index> as the first arg and a
867 pointer to the SV as the second. A simple example of how to add 'U'
868 magic is shown below. Note that the ufuncs structure is copied by
869 sv_magic, so you can safely allocate it on the stack.
877 uf.uf_val = &my_get_fn;
878 uf.uf_set = &my_set_fn;
880 sv_magic(sv, 0, 'U', (char*)&uf, sizeof(uf));
882 Note that because multiple extensions may be using '~' or 'U' magic,
883 it is important for extensions to take extra care to avoid conflict.
884 Typically only using the magic on objects blessed into the same class
885 as the extension is sufficient. For '~' magic, it may also be
886 appropriate to add an I32 'signature' at the top of the private data
889 Also note that the C<sv_set*()> and C<sv_cat*()> functions described
890 earlier do B<not> invoke 'set' magic on their targets. This must
891 be done by the user either by calling the C<SvSETMAGIC()> macro after
892 calling these functions, or by using one of the C<sv_set*_mg()> or
893 C<sv_cat*_mg()> functions. Similarly, generic C code must call the
894 C<SvGETMAGIC()> macro to invoke any 'get' magic if they use an SV
895 obtained from external sources in functions that don't handle magic.
896 L<API LISTING> later in this document identifies such functions.
897 For example, calls to the C<sv_cat*()> functions typically need to be
898 followed by C<SvSETMAGIC()>, but they don't need a prior C<SvGETMAGIC()>
899 since their implementation handles 'get' magic.
903 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
905 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
906 If the SV does not have that magical feature, C<NULL> is returned. Also,
907 if the SV is not of type SVt_PVMG, Perl may core dump.
909 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
911 This routine checks to see what types of magic C<sv> has. If the mg_type
912 field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
913 the mg_type field is changed to be the lowercase letter.
915 =head2 Understanding the Magic of Tied Hashes and Arrays
917 Tied hashes and arrays are magical beasts of the 'P' magic type.
919 WARNING: As of the 5.004 release, proper usage of the array and hash
920 access functions requires understanding a few caveats. Some
921 of these caveats are actually considered bugs in the API, to be fixed
922 in later releases, and are bracketed with [MAYCHANGE] below. If
923 you find yourself actually applying such information in this section, be
924 aware that the behavior may change in the future, umm, without warning.
926 The perl tie function associates a variable with an object that implements
927 the various GET, SET etc methods. To perform the equivalent of the perl
928 tie function from an XSUB, you must mimic this behaviour. The code below
929 carries out the necessary steps - firstly it creates a new hash, and then
930 creates a second hash which it blesses into the class which will implement
931 the tie methods. Lastly it ties the two hashes together, and returns a
932 reference to the new tied hash. Note that the code below does NOT call the
933 TIEHASH method in the MyTie class -
934 see L<Calling Perl Routines from within C Programs> for details on how
945 tie = newRV_noinc((SV*)newHV());
946 stash = gv_stashpv("MyTie", TRUE);
947 sv_bless(tie, stash);
948 hv_magic(hash, tie, 'P');
949 RETVAL = newRV_noinc(hash);
953 The C<av_store> function, when given a tied array argument, merely
954 copies the magic of the array onto the value to be "stored", using
955 C<mg_copy>. It may also return NULL, indicating that the value did not
956 actually need to be stored in the array. [MAYCHANGE] After a call to
957 C<av_store> on a tied array, the caller will usually need to call
958 C<mg_set(val)> to actually invoke the perl level "STORE" method on the
959 TIEARRAY object. If C<av_store> did return NULL, a call to
960 C<SvREFCNT_dec(val)> will also be usually necessary to avoid a memory
963 The previous paragraph is applicable verbatim to tied hash access using the
964 C<hv_store> and C<hv_store_ent> functions as well.
966 C<av_fetch> and the corresponding hash functions C<hv_fetch> and
967 C<hv_fetch_ent> actually return an undefined mortal value whose magic
968 has been initialized using C<mg_copy>. Note the value so returned does not
969 need to be deallocated, as it is already mortal. [MAYCHANGE] But you will
970 need to call C<mg_get()> on the returned value in order to actually invoke
971 the perl level "FETCH" method on the underlying TIE object. Similarly,
972 you may also call C<mg_set()> on the return value after possibly assigning
973 a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
974 method on the TIE object. [/MAYCHANGE]
977 In other words, the array or hash fetch/store functions don't really
978 fetch and store actual values in the case of tied arrays and hashes. They
979 merely call C<mg_copy> to attach magic to the values that were meant to be
980 "stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
981 do the job of invoking the TIE methods on the underlying objects. Thus
982 the magic mechanism currently implements a kind of lazy access to arrays
985 Currently (as of perl version 5.004), use of the hash and array access
986 functions requires the user to be aware of whether they are operating on
987 "normal" hashes and arrays, or on their tied variants. The API may be
988 changed to provide more transparent access to both tied and normal data
989 types in future versions.
992 You would do well to understand that the TIEARRAY and TIEHASH interfaces
993 are mere sugar to invoke some perl method calls while using the uniform hash
994 and array syntax. The use of this sugar imposes some overhead (typically
995 about two to four extra opcodes per FETCH/STORE operation, in addition to
996 the creation of all the mortal variables required to invoke the methods).
997 This overhead will be comparatively small if the TIE methods are themselves
998 substantial, but if they are only a few statements long, the overhead
999 will not be insignificant.
1001 =head2 Localizing changes
1003 Perl has a very handy construction
1010 This construction is I<approximately> equivalent to
1019 The biggest difference is that the first construction would
1020 reinstate the initial value of $var, irrespective of how control exits
1021 the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
1022 more efficient as well.
1024 There is a way to achieve a similar task from C via Perl API: create a
1025 I<pseudo-block>, and arrange for some changes to be automatically
1026 undone at the end of it, either explicit, or via a non-local exit (via
1027 die()). A I<block>-like construct is created by a pair of
1028 C<ENTER>/C<LEAVE> macros (see L<perlcall/"Returning a Scalar">).
1029 Such a construct may be created specially for some important localized
1030 task, or an existing one (like boundaries of enclosing Perl
1031 subroutine/block, or an existing pair for freeing TMPs) may be
1032 used. (In the second case the overhead of additional localization must
1033 be almost negligible.) Note that any XSUB is automatically enclosed in
1034 an C<ENTER>/C<LEAVE> pair.
1036 Inside such a I<pseudo-block> the following service is available:
1040 =item C<SAVEINT(int i)>
1042 =item C<SAVEIV(IV i)>
1044 =item C<SAVEI32(I32 i)>
1046 =item C<SAVELONG(long i)>
1048 These macros arrange things to restore the value of integer variable
1049 C<i> at the end of enclosing I<pseudo-block>.
1051 =item C<SAVESPTR(s)>
1053 =item C<SAVEPPTR(p)>
1055 These macros arrange things to restore the value of pointers C<s> and
1056 C<p>. C<s> must be a pointer of a type which survives conversion to
1057 C<SV*> and back, C<p> should be able to survive conversion to C<char*>
1060 =item C<SAVEFREESV(SV *sv)>
1062 The refcount of C<sv> would be decremented at the end of
1063 I<pseudo-block>. This is similar to C<sv_2mortal>, which should (?) be
1066 =item C<SAVEFREEOP(OP *op)>
1068 The C<OP *> is op_free()ed at the end of I<pseudo-block>.
1070 =item C<SAVEFREEPV(p)>
1072 The chunk of memory which is pointed to by C<p> is Safefree()ed at the
1073 end of I<pseudo-block>.
1075 =item C<SAVECLEARSV(SV *sv)>
1077 Clears a slot in the current scratchpad which corresponds to C<sv> at
1078 the end of I<pseudo-block>.
1080 =item C<SAVEDELETE(HV *hv, char *key, I32 length)>
1082 The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
1083 string pointed to by C<key> is Safefree()ed. If one has a I<key> in
1084 short-lived storage, the corresponding string may be reallocated like
1087 SAVEDELETE(PL_defstash, savepv(tmpbuf), strlen(tmpbuf));
1089 =item C<SAVEDESTRUCTOR(f,p)>
1091 At the end of I<pseudo-block> the function C<f> is called with the
1092 only argument (of type C<void*>) C<p>.
1094 =item C<SAVESTACK_POS()>
1096 The current offset on the Perl internal stack (cf. C<SP>) is restored
1097 at the end of I<pseudo-block>.
1101 The following API list contains functions, thus one needs to
1102 provide pointers to the modifiable data explicitly (either C pointers,
1103 or Perlish C<GV *>s). Where the above macros take C<int>, a similar
1104 function takes C<int *>.
1108 =item C<SV* save_scalar(GV *gv)>
1110 Equivalent to Perl code C<local $gv>.
1112 =item C<AV* save_ary(GV *gv)>
1114 =item C<HV* save_hash(GV *gv)>
1116 Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
1118 =item C<void save_item(SV *item)>
1120 Duplicates the current value of C<SV>, on the exit from the current
1121 C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
1122 using the stored value.
1124 =item C<void save_list(SV **sarg, I32 maxsarg)>
1126 A variant of C<save_item> which takes multiple arguments via an array
1127 C<sarg> of C<SV*> of length C<maxsarg>.
1129 =item C<SV* save_svref(SV **sptr)>
1131 Similar to C<save_scalar>, but will reinstate a C<SV *>.
1133 =item C<void save_aptr(AV **aptr)>
1135 =item C<void save_hptr(HV **hptr)>
1137 Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
1141 The C<Alias> module implements localization of the basic types within the
1142 I<caller's scope>. People who are interested in how to localize things in
1143 the containing scope should take a look there too.
1147 =head2 XSUBs and the Argument Stack
1149 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
1150 An XSUB routine will have a stack that contains the arguments from the Perl
1151 program, and a way to map from the Perl data structures to a C equivalent.
1153 The stack arguments are accessible through the C<ST(n)> macro, which returns
1154 the C<n>'th stack argument. Argument 0 is the first argument passed in the
1155 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
1158 Most of the time, output from the C routine can be handled through use of
1159 the RETVAL and OUTPUT directives. However, there are some cases where the
1160 argument stack is not already long enough to handle all the return values.
1161 An example is the POSIX tzname() call, which takes no arguments, but returns
1162 two, the local time zone's standard and summer time abbreviations.
1164 To handle this situation, the PPCODE directive is used and the stack is
1165 extended using the macro:
1169 where C<SP> is the macro that represents the local copy of the stack pointer,
1170 and C<num> is the number of elements the stack should be extended by.
1172 Now that there is room on the stack, values can be pushed on it using the
1173 macros to push IVs, doubles, strings, and SV pointers respectively:
1180 And now the Perl program calling C<tzname>, the two values will be assigned
1183 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
1185 An alternate (and possibly simpler) method to pushing values on the stack is
1193 These macros automatically adjust the stack for you, if needed. Thus, you
1194 do not need to call C<EXTEND> to extend the stack.
1196 For more information, consult L<perlxs> and L<perlxstut>.
1198 =head2 Calling Perl Routines from within C Programs
1200 There are four routines that can be used to call a Perl subroutine from
1201 within a C program. These four are:
1203 I32 perl_call_sv(SV*, I32);
1204 I32 perl_call_pv(char*, I32);
1205 I32 perl_call_method(char*, I32);
1206 I32 perl_call_argv(char*, I32, register char**);
1208 The routine most often used is C<perl_call_sv>. The C<SV*> argument
1209 contains either the name of the Perl subroutine to be called, or a
1210 reference to the subroutine. The second argument consists of flags
1211 that control the context in which the subroutine is called, whether
1212 or not the subroutine is being passed arguments, how errors should be
1213 trapped, and how to treat return values.
1215 All four routines return the number of arguments that the subroutine returned
1218 When using any of these routines (except C<perl_call_argv>), the programmer
1219 must manipulate the Perl stack. These include the following macros and
1234 For a detailed description of calling conventions from C to Perl,
1235 consult L<perlcall>.
1237 =head2 Memory Allocation
1239 All memory meant to be used with the Perl API functions should be manipulated
1240 using the macros described in this section. The macros provide the necessary
1241 transparency between differences in the actual malloc implementation that is
1244 It is suggested that you enable the version of malloc that is distributed
1245 with Perl. It keeps pools of various sizes of unallocated memory in
1246 order to satisfy allocation requests more quickly. However, on some
1247 platforms, it may cause spurious malloc or free errors.
1249 New(x, pointer, number, type);
1250 Newc(x, pointer, number, type, cast);
1251 Newz(x, pointer, number, type);
1253 These three macros are used to initially allocate memory.
1255 The first argument C<x> was a "magic cookie" that was used to keep track
1256 of who called the macro, to help when debugging memory problems. However,
1257 the current code makes no use of this feature (most Perl developers now
1258 use run-time memory checkers), so this argument can be any number.
1260 The second argument C<pointer> should be the name of a variable that will
1261 point to the newly allocated memory.
1263 The third and fourth arguments C<number> and C<type> specify how many of
1264 the specified type of data structure should be allocated. The argument
1265 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
1266 should be used if the C<pointer> argument is different from the C<type>
1269 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
1270 to zero out all the newly allocated memory.
1272 Renew(pointer, number, type);
1273 Renewc(pointer, number, type, cast);
1276 These three macros are used to change a memory buffer size or to free a
1277 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1278 match those of C<New> and C<Newc> with the exception of not needing the
1279 "magic cookie" argument.
1281 Move(source, dest, number, type);
1282 Copy(source, dest, number, type);
1283 Zero(dest, number, type);
1285 These three macros are used to move, copy, or zero out previously allocated
1286 memory. The C<source> and C<dest> arguments point to the source and
1287 destination starting points. Perl will move, copy, or zero out C<number>
1288 instances of the size of the C<type> data structure (using the C<sizeof>
1293 The most recent development releases of Perl has been experimenting with
1294 removing Perl's dependency on the "normal" standard I/O suite and allowing
1295 other stdio implementations to be used. This involves creating a new
1296 abstraction layer that then calls whichever implementation of stdio Perl
1297 was compiled with. All XSUBs should now use the functions in the PerlIO
1298 abstraction layer and not make any assumptions about what kind of stdio
1301 For a complete description of the PerlIO abstraction, consult L<perlapio>.
1303 =head2 Putting a C value on Perl stack
1305 A lot of opcodes (this is an elementary operation in the internal perl
1306 stack machine) put an SV* on the stack. However, as an optimization
1307 the corresponding SV is (usually) not recreated each time. The opcodes
1308 reuse specially assigned SVs (I<target>s) which are (as a corollary)
1309 not constantly freed/created.
1311 Each of the targets is created only once (but see
1312 L<Scratchpads and recursion> below), and when an opcode needs to put
1313 an integer, a double, or a string on stack, it just sets the
1314 corresponding parts of its I<target> and puts the I<target> on stack.
1316 The macro to put this target on stack is C<PUSHTARG>, and it is
1317 directly used in some opcodes, as well as indirectly in zillions of
1318 others, which use it via C<(X)PUSH[pni]>.
1322 The question remains on when the SVs which are I<target>s for opcodes
1323 are created. The answer is that they are created when the current unit --
1324 a subroutine or a file (for opcodes for statements outside of
1325 subroutines) -- is compiled. During this time a special anonymous Perl
1326 array is created, which is called a scratchpad for the current
1329 A scratchpad keeps SVs which are lexicals for the current unit and are
1330 targets for opcodes. One can deduce that an SV lives on a scratchpad
1331 by looking on its flags: lexicals have C<SVs_PADMY> set, and
1332 I<target>s have C<SVs_PADTMP> set.
1334 The correspondence between OPs and I<target>s is not 1-to-1. Different
1335 OPs in the compile tree of the unit can use the same target, if this
1336 would not conflict with the expected life of the temporary.
1338 =head2 Scratchpads and recursion
1340 In fact it is not 100% true that a compiled unit contains a pointer to
1341 the scratchpad AV. In fact it contains a pointer to an AV of
1342 (initially) one element, and this element is the scratchpad AV. Why do
1343 we need an extra level of indirection?
1345 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1346 these can create several execution pointers going into the same
1347 subroutine. For the subroutine-child not write over the temporaries
1348 for the subroutine-parent (lifespan of which covers the call to the
1349 child), the parent and the child should have different
1350 scratchpads. (I<And> the lexicals should be separate anyway!)
1352 So each subroutine is born with an array of scratchpads (of length 1).
1353 On each entry to the subroutine it is checked that the current
1354 depth of the recursion is not more than the length of this array, and
1355 if it is, new scratchpad is created and pushed into the array.
1357 The I<target>s on this scratchpad are C<undef>s, but they are already
1358 marked with correct flags.
1360 =head1 Compiled code
1364 Here we describe the internal form your code is converted to by
1365 Perl. Start with a simple example:
1369 This is converted to a tree similar to this one:
1377 (but slightly more complicated). This tree reflects the way Perl
1378 parsed your code, but has nothing to do with the execution order.
1379 There is an additional "thread" going through the nodes of the tree
1380 which shows the order of execution of the nodes. In our simplified
1381 example above it looks like:
1383 $b ---> $c ---> + ---> $a ---> assign-to
1385 But with the actual compile tree for C<$a = $b + $c> it is different:
1386 some nodes I<optimized away>. As a corollary, though the actual tree
1387 contains more nodes than our simplified example, the execution order
1388 is the same as in our example.
1390 =head2 Examining the tree
1392 If you have your perl compiled for debugging (usually done with C<-D
1393 optimize=-g> on C<Configure> command line), you may examine the
1394 compiled tree by specifying C<-Dx> on the Perl command line. The
1395 output takes several lines per node, and for C<$b+$c> it looks like
1400 FLAGS = (SCALAR,KIDS)
1402 TYPE = null ===> (4)
1404 FLAGS = (SCALAR,KIDS)
1406 3 TYPE = gvsv ===> 4
1412 TYPE = null ===> (5)
1414 FLAGS = (SCALAR,KIDS)
1416 4 TYPE = gvsv ===> 5
1422 This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1423 not optimized away (one per number in the left column). The immediate
1424 children of the given node correspond to C<{}> pairs on the same level
1425 of indentation, thus this listing corresponds to the tree:
1433 The execution order is indicated by C<===E<gt>> marks, thus it is C<3
1434 4 5 6> (node C<6> is not included into above listing), i.e.,
1435 C<gvsv gvsv add whatever>.
1437 =head2 Compile pass 1: check routines
1439 The tree is created by the I<pseudo-compiler> while yacc code feeds it
1440 the constructions it recognizes. Since yacc works bottom-up, so does
1441 the first pass of perl compilation.
1443 What makes this pass interesting for perl developers is that some
1444 optimization may be performed on this pass. This is optimization by
1445 so-called I<check routines>. The correspondence between node names
1446 and corresponding check routines is described in F<opcode.pl> (do not
1447 forget to run C<make regen_headers> if you modify this file).
1449 A check routine is called when the node is fully constructed except
1450 for the execution-order thread. Since at this time there are no
1451 back-links to the currently constructed node, one can do most any
1452 operation to the top-level node, including freeing it and/or creating
1453 new nodes above/below it.
1455 The check routine returns the node which should be inserted into the
1456 tree (if the top-level node was not modified, check routine returns
1459 By convention, check routines have names C<ck_*>. They are usually
1460 called from C<new*OP> subroutines (or C<convert>) (which in turn are
1461 called from F<perly.y>).
1463 =head2 Compile pass 1a: constant folding
1465 Immediately after the check routine is called the returned node is
1466 checked for being compile-time executable. If it is (the value is
1467 judged to be constant) it is immediately executed, and a I<constant>
1468 node with the "return value" of the corresponding subtree is
1469 substituted instead. The subtree is deleted.
1471 If constant folding was not performed, the execution-order thread is
1474 =head2 Compile pass 2: context propagation
1476 When a context for a part of compile tree is known, it is propagated
1477 down through the tree. At this time the context can have 5 values
1478 (instead of 2 for runtime context): void, boolean, scalar, list, and
1479 lvalue. In contrast with the pass 1 this pass is processed from top
1480 to bottom: a node's context determines the context for its children.
1482 Additional context-dependent optimizations are performed at this time.
1483 Since at this moment the compile tree contains back-references (via
1484 "thread" pointers), nodes cannot be free()d now. To allow
1485 optimized-away nodes at this stage, such nodes are null()ified instead
1486 of free()ing (i.e. their type is changed to OP_NULL).
1488 =head2 Compile pass 3: peephole optimization
1490 After the compile tree for a subroutine (or for an C<eval> or a file)
1491 is created, an additional pass over the code is performed. This pass
1492 is neither top-down or bottom-up, but in the execution order (with
1493 additional complications for conditionals). These optimizations are
1494 done in the subroutine peep(). Optimizations performed at this stage
1495 are subject to the same restrictions as in the pass 2.
1499 This is a listing of functions, macros, flags, and variables that may be
1500 useful to extension writers or that may be found while reading other
1503 Note that all Perl API global variables must be referenced with the C<PL_>
1504 prefix. Some macros are provided for compatibility with the older,
1505 unadorned names, but this support will be removed in a future release.
1507 It is strongly recommended that all Perl API functions that don't begin
1508 with C<perl> be referenced with an explicit C<Perl_> prefix.
1510 The sort order of the listing is case insensitive, with any
1511 occurrences of '_' ignored for the purpose of sorting.
1517 Clears an array, making it empty. Does not free the memory used by the
1520 void av_clear (AV* ar)
1524 Pre-extend an array. The C<key> is the index to which the array should be
1527 void av_extend (AV* ar, I32 key)
1531 Returns the SV at the specified index in the array. The C<key> is the
1532 index. If C<lval> is set then the fetch will be part of a store. Check
1533 that the return value is non-null before dereferencing it to a C<SV*>.
1535 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1536 information on how to use this function on tied arrays.
1538 SV** av_fetch (AV* ar, I32 key, I32 lval)
1542 Same as C<av_len()>. Deprecated, use C<av_len()> instead.
1546 Returns the highest index in the array. Returns -1 if the array is empty.
1552 Creates a new AV and populates it with a list of SVs. The SVs are copied
1553 into the array, so they may be freed after the call to av_make. The new AV
1554 will have a reference count of 1.
1556 AV* av_make (I32 size, SV** svp)
1560 Pops an SV off the end of the array. Returns C<&PL_sv_undef> if the array is
1567 Pushes an SV onto the end of the array. The array will grow automatically
1568 to accommodate the addition.
1570 void av_push (AV* ar, SV* val)
1574 Shifts an SV off the beginning of the array.
1576 SV* av_shift (AV* ar)
1580 Stores an SV in an array. The array index is specified as C<key>. The
1581 return value will be NULL if the operation failed or if the value did not
1582 need to be actually stored within the array (as in the case of tied arrays).
1583 Otherwise it can be dereferenced to get the original C<SV*>. Note that the
1584 caller is responsible for suitably incrementing the reference count of C<val>
1585 before the call, and decrementing it if the function returned NULL.
1587 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1588 information on how to use this function on tied arrays.
1590 SV** av_store (AV* ar, I32 key, SV* val)
1594 Undefines the array. Frees the memory used by the array itself.
1596 void av_undef (AV* ar)
1600 Unshift the given number of C<undef> values onto the beginning of the
1601 array. The array will grow automatically to accommodate the addition.
1602 You must then use C<av_store> to assign values to these new elements.
1604 void av_unshift (AV* ar, I32 num)
1608 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1609 constructor. This is always a C<char*>. See C<THIS> and
1610 L<perlxs/"Using XS With C++">.
1614 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1615 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1616 the type. May fail on overlapping copies. See also C<Move>.
1618 void Copy( s, d, n, t )
1622 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1623 function the same way you use the C C<printf> function. See C<warn>.
1627 Returns the stash of the CV.
1629 HV* CvSTASH( SV* sv )
1633 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1634 boolean which indicates whether subs are being single-stepped.
1635 Single-stepping is automatically turned on after every step. This is the C
1636 variable which corresponds to Perl's $DB::single variable. See C<PL_DBsub>.
1640 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1641 the SV which holds the name of the sub being debugged. This is the C
1642 variable which corresponds to Perl's $DB::sub variable. See C<PL_DBsingle>.
1643 The sub name can be found by
1645 SvPV( GvSV( PL_DBsub ), len )
1649 Trace variable used when Perl is run in debugging mode, with the B<-d>
1650 switch. This is the C variable which corresponds to Perl's $DB::trace
1651 variable. See C<PL_DBsingle>.
1655 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1660 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1664 The C variable which corresponds to Perl's $^W warning variable.
1668 Declares a local copy of perl's stack pointer for the XSUB, available via
1669 the C<SP> macro. See C<SP>.
1673 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1674 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1675 to indicate the number of items on the stack.
1679 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1680 handled automatically by C<xsubpp>.
1684 Switches filehandle to binmode. C<iotype> is what C<IoTYPE(io)> would
1687 do_binmode(fp, iotype, TRUE);
1691 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1697 Used to extend the argument stack for an XSUB's return values.
1703 Analyses the string in order to make fast searches on it using fbm_instr() --
1704 the Boyer-Moore algorithm.
1706 void fbm_compile(SV* sv, U32 flags)
1710 Returns the location of the SV in the string delimited by C<str> and
1711 C<strend>. It returns C<Nullch> if the string can't be found. The
1712 C<sv> does not have to be fbm_compiled, but the search will not be as
1715 char* fbm_instr(char *str, char *strend, SV *sv, U32 flags)
1719 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1726 Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
1730 Indicates that arguments returned from a callback should be discarded. See
1735 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1739 A backward-compatible version of C<GIMME_V> which can only return
1740 C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
1744 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
1745 C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
1746 context, respectively.
1750 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1754 Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
1758 Returns the glob with the given C<name> and a defined subroutine or
1759 C<NULL>. The glob lives in the given C<stash>, or in the stashes
1760 accessible via @ISA and @UNIVERSAL.
1762 The argument C<level> should be either 0 or -1. If C<level==0>, as a
1763 side-effect creates a glob with the given C<name> in the given
1764 C<stash> which in the case of success contains an alias for the
1765 subroutine, and sets up caching info for this glob. Similarly for all
1766 the searched stashes.
1768 This function grants C<"SUPER"> token as a postfix of the stash name.
1770 The GV returned from C<gv_fetchmeth> may be a method cache entry,
1771 which is not visible to Perl code. So when calling C<perl_call_sv>,
1772 you should not use the GV directly; instead, you should use the
1773 method's CV, which can be obtained from the GV with the C<GvCV> macro.
1775 GV* gv_fetchmeth (HV* stash, char* name, STRLEN len, I32 level)
1777 =item gv_fetchmethod
1779 =item gv_fetchmethod_autoload
1781 Returns the glob which contains the subroutine to call to invoke the
1782 method on the C<stash>. In fact in the presense of autoloading this may
1783 be the glob for "AUTOLOAD". In this case the corresponding variable
1784 $AUTOLOAD is already setup.
1786 The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
1787 lookup is performed if the given method is not present: non-zero means
1788 yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
1789 C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
1790 non-zero C<autoload> parameter.
1792 These functions grant C<"SUPER"> token as a prefix of the method name.
1794 Note that if you want to keep the returned glob for a long time, you
1795 need to check for it being "AUTOLOAD", since at the later time the call
1796 may load a different subroutine due to $AUTOLOAD changing its value.
1797 Use the glob created via a side effect to do this.
1799 These functions have the same side-effects and as C<gv_fetchmeth> with
1800 C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
1801 The warning against passing the GV returned by C<gv_fetchmeth> to
1802 C<perl_call_sv> apply equally to these functions.
1804 GV* gv_fetchmethod (HV* stash, char* name)
1805 GV* gv_fetchmethod_autoload (HV* stash, char* name, I32 autoload)
1809 Used to indicate void context. See C<GIMME_V> and L<perlcall>.
1813 Returns a pointer to the stash for a specified package. If C<create> is set
1814 then the package will be created if it does not already exist. If C<create>
1815 is not set and the package does not exist then NULL is returned.
1817 HV* gv_stashpv (char* name, I32 create)
1821 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1823 HV* gv_stashsv (SV* sv, I32 create)
1827 Return the SV from the GV.
1831 This flag, used in the length slot of hash entries and magic
1832 structures, specifies the structure contains a C<SV*> pointer where a
1833 C<char*> pointer is to be expected. (For information only--not to be used).
1837 Returns the computed hash stored in the hash entry.
1843 Returns the actual pointer stored in the key slot of the hash entry.
1844 The pointer may be either C<char*> or C<SV*>, depending on the value of
1845 C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
1846 are usually preferable for finding the value of a key.
1852 If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
1853 holds an C<SV*> key. Otherwise, holds the actual length of the key.
1854 Can be assigned to. The C<HePV()> macro is usually preferable for finding
1861 Returns the key slot of the hash entry as a C<char*> value, doing any
1862 necessary dereferencing of possibly C<SV*> keys. The length of
1863 the string is placed in C<len> (this is a macro, so do I<not> use
1864 C<&len>). If you do not care about what the length of the key is,
1865 you may use the global variable C<PL_na>, though this is rather less
1866 efficient than using a local variable. Remember though, that hash
1867 keys in perl are free to contain embedded nulls, so using C<strlen()>
1868 or similar is not a good way to find the length of hash keys.
1869 This is very similar to the C<SvPV()> macro described elsewhere in
1872 char* HePV(HE* he, STRLEN len)
1876 Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
1877 does not contain an C<SV*> key.
1883 Returns the key as an C<SV*>. Will create and return a temporary
1884 mortal C<SV*> if the hash entry contains only a C<char*> key.
1886 HeSVKEY_force(HE* he)
1890 Sets the key to a given C<SV*>, taking care to set the appropriate flags
1891 to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
1893 HeSVKEY_set(HE* he, SV* sv)
1897 Returns the value slot (type C<SV*>) stored in the hash entry.
1903 Clears a hash, making it empty.
1905 void hv_clear (HV* tb)
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<klen> is the length of the key. The
1911 C<flags> value will normally be zero; if set to G_DISCARD then NULL will be
1914 SV* hv_delete (HV* tb, char* key, U32 klen, I32 flags)
1918 Deletes a key/value pair in the hash. The value SV is removed from the hash
1919 and returned to the caller. The C<flags> value will normally be zero; if set
1920 to G_DISCARD then NULL will be returned. C<hash> can be a valid precomputed
1921 hash value, or 0 to ask for it to be computed.
1923 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash)
1927 Returns a boolean indicating whether the specified hash key exists. The
1928 C<klen> is the length of the key.
1930 bool hv_exists (HV* tb, char* key, U32 klen)
1934 Returns a boolean indicating whether the specified hash key exists. C<hash>
1935 can be a valid precomputed hash value, or 0 to ask for it to be computed.
1937 bool hv_exists_ent (HV* tb, SV* key, U32 hash)
1941 Returns the SV which corresponds to the specified key in the hash. The
1942 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1943 part of a store. Check that the return value is non-null before
1944 dereferencing it to a C<SV*>.
1946 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1947 information on how to use this function on tied hashes.
1949 SV** hv_fetch (HV* tb, char* key, U32 klen, I32 lval)
1953 Returns the hash entry which corresponds to the specified key in the hash.
1954 C<hash> must be a valid precomputed hash number for the given C<key>, or
1955 0 if you want the function to compute it. IF C<lval> is set then the
1956 fetch will be part of a store. Make sure the return value is non-null
1957 before accessing it. The return value when C<tb> is a tied hash
1958 is a pointer to a static location, so be sure to make a copy of the
1959 structure if you need to store it somewhere.
1961 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1962 information on how to use this function on tied hashes.
1964 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash)
1968 Prepares a starting point to traverse a hash table.
1970 I32 hv_iterinit (HV* tb)
1972 Returns the number of keys in the hash (i.e. the same as C<HvKEYS(tb)>).
1973 The return value is currently only meaningful for hashes without tie
1976 NOTE: Before version 5.004_65, C<hv_iterinit> used to return the number
1977 of hash buckets that happen to be in use. If you still need that
1978 esoteric value, you can get it through the macro C<HvFILL(tb)>.
1982 Returns the key from the current position of the hash iterator. See
1985 char* hv_iterkey (HE* entry, I32* retlen)
1989 Returns the key as an C<SV*> from the current position of the hash
1990 iterator. The return value will always be a mortal copy of the
1991 key. Also see C<hv_iterinit>.
1993 SV* hv_iterkeysv (HE* entry)
1997 Returns entries from a hash iterator. See C<hv_iterinit>.
1999 HE* hv_iternext (HV* tb)
2003 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
2006 SV* hv_iternextsv (HV* hv, char** key, I32* retlen)
2010 Returns the value from the current position of the hash iterator. See
2013 SV* hv_iterval (HV* tb, HE* entry)
2017 Adds magic to a hash. See C<sv_magic>.
2019 void hv_magic (HV* hv, GV* gv, int how)
2023 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
2025 char* HvNAME (HV* stash)
2029 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
2030 the length of the key. The C<hash> parameter is the precomputed hash
2031 value; if it is zero then Perl will compute it. The return value will be
2032 NULL if the operation failed or if the value did not need to be actually
2033 stored within the hash (as in the case of tied hashes). Otherwise it can
2034 be dereferenced to get the original C<SV*>. Note that the caller is
2035 responsible for suitably incrementing the reference count of C<val>
2036 before the call, and decrementing it if the function returned NULL.
2038 See L<Understanding the Magic of Tied Hashes and Arrays> for more
2039 information on how to use this function on tied hashes.
2041 SV** hv_store (HV* tb, char* key, U32 klen, SV* val, U32 hash)
2045 Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
2046 parameter is the precomputed hash value; if it is zero then Perl will
2047 compute it. The return value is the new hash entry so created. It will be
2048 NULL if the operation failed or if the value did not need to be actually
2049 stored within the hash (as in the case of tied hashes). Otherwise the
2050 contents of the return value can be accessed using the C<He???> macros
2051 described here. Note that the caller is responsible for suitably
2052 incrementing the reference count of C<val> before the call, and decrementing
2053 it if the function returned NULL.
2055 See L<Understanding the Magic of Tied Hashes and Arrays> for more
2056 information on how to use this function on tied hashes.
2058 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash)
2064 void hv_undef (HV* tb)
2068 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
2071 int isALNUM (char c)
2075 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
2078 int isALPHA (char c)
2082 Returns a boolean indicating whether the C C<char> is an ascii digit.
2084 int isDIGIT (char c)
2088 Returns a boolean indicating whether the C C<char> is a lowercase character.
2090 int isLOWER (char c)
2094 Returns a boolean indicating whether the C C<char> is whitespace.
2096 int isSPACE (char c)
2100 Returns a boolean indicating whether the C C<char> is an uppercase character.
2102 int isUPPER (char c)
2106 Variable which is setup by C<xsubpp> to indicate the number of items on the
2107 stack. See L<perlxs/"Variable-length Parameter Lists">.
2111 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
2112 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
2116 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
2120 =item looks_like_number
2122 Test if an the content of an SV looks like a number (or is a number).
2124 int looks_like_number(SV*)
2129 Stack marker variable for the XSUB. See C<dMARK>.
2133 Clear something magical that the SV represents. See C<sv_magic>.
2135 int mg_clear (SV* sv)
2139 Copies the magic from one SV to another. See C<sv_magic>.
2141 int mg_copy (SV *, SV *, char *, STRLEN)
2145 Finds the magic pointer for type matching the SV. See C<sv_magic>.
2147 MAGIC* mg_find (SV* sv, int type)
2151 Free any magic storage used by the SV. See C<sv_magic>.
2153 int mg_free (SV* sv)
2157 Do magic after a value is retrieved from the SV. See C<sv_magic>.
2163 Report on the SV's length. See C<sv_magic>.
2169 Turns on the magical status of an SV. See C<sv_magic>.
2171 void mg_magical (SV* sv)
2175 Do magic after a value is assigned to the SV. See C<sv_magic>.
2181 C<modglobal> is a general purpose, interpreter global HV for use by
2182 extensions that need to keep information on a per-interpreter basis.
2183 In a pinch, it can also be used as a symbol table for extensions
2184 to share data among each other. It is a good idea to use keys
2185 prefixed by the package name of the extension that owns the data.
2189 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
2190 source, C<d> is the destination, C<n> is the number of items, and C<t> is
2191 the type. Can do overlapping moves. See also C<Copy>.
2193 void Move( s, d, n, t )
2197 A convenience variable which is typically used with C<SvPV> when one doesn't
2198 care about the length of the string. It is usually more efficient to
2199 declare a local variable and use that instead.
2203 The XSUB-writer's interface to the C C<malloc> function.
2205 void* New( x, void *ptr, int size, type )
2209 Creates a new AV. The reference count is set to 1.
2215 The XSUB-writer's interface to the C C<malloc> function, with cast.
2217 void* Newc( x, void *ptr, int size, type, cast )
2221 Creates a constant sub equivalent to Perl C<sub FOO () { 123 }>
2222 which is eligible for inlining at compile-time.
2224 void newCONSTSUB(HV* stash, char* name, SV* sv)
2228 Creates a new HV. The reference count is set to 1.
2234 Creates an RV wrapper for an SV. The reference count for the original SV is
2237 SV* newRV_inc (SV* ref)
2239 For historical reasons, "newRV" is a synonym for "newRV_inc".
2243 Creates an RV wrapper for an SV. The reference count for the original
2244 SV is B<not> incremented.
2246 SV* newRV_noinc (SV* ref)
2250 Creates a new SV. A non-zero C<len> parameter indicates the number of
2251 bytes of preallocated string space the SV should have. An extra byte
2252 for a tailing NUL is also reserved. (SvPOK is not set for the SV even
2253 if string space is allocated.) The reference count for the new SV is
2254 set to 1. C<id> is an integer id between 0 and 1299 (used to identify
2257 SV* NEWSV (int id, STRLEN len)
2261 Creates a new SV and copies an integer into it. The reference count for the
2268 Creates a new SV and copies a double into it. The reference count for the
2275 Creates a new SV and copies a string into it. The reference count for the
2276 SV is set to 1. If C<len> is zero then Perl will compute the length.
2278 SV* newSVpv (char* s, STRLEN len)
2282 Creates a new SV an initialize it with the string formatted like
2285 SV* newSVpvf(const char* pat, ...);
2289 Creates a new SV and copies a string into it. The reference count for the
2290 SV is set to 1. If C<len> is zero then Perl will create a zero length
2293 SV* newSVpvn (char* s, STRLEN len)
2297 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
2298 it will be upgraded to one. If C<classname> is non-null then the new SV will
2299 be blessed in the specified package. The new SV is returned and its
2300 reference count is 1.
2302 SV* newSVrv (SV* rv, char* classname)
2306 Creates a new SV which is an exact duplicate of the original SV.
2308 SV* newSVsv (SV* old)
2312 Used by C<xsubpp> to hook up XSUBs as Perl subs.
2316 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
2321 The XSUB-writer's interface to the C C<malloc> function. The allocated
2322 memory is zeroed with C<memzero>.
2324 void* Newz( x, void *ptr, int size, type )
2332 Null character pointer.
2348 The original stack mark for the XSUB. See C<dORIGMARK>.
2352 Allocates a new Perl interpreter. See L<perlembed>.
2354 =item perl_call_argv
2356 Performs a callback to the specified Perl sub. See L<perlcall>.
2358 I32 perl_call_argv (char* subname, I32 flags, char** argv)
2360 =item perl_call_method
2362 Performs a callback to the specified Perl method. The blessed object must
2363 be on the stack. See L<perlcall>.
2365 I32 perl_call_method (char* methname, I32 flags)
2369 Performs a callback to the specified Perl sub. See L<perlcall>.
2371 I32 perl_call_pv (char* subname, I32 flags)
2375 Performs a callback to the Perl sub whose name is in the SV. See
2378 I32 perl_call_sv (SV* sv, I32 flags)
2380 =item perl_construct
2382 Initializes a new Perl interpreter. See L<perlembed>.
2386 Shuts down a Perl interpreter. See L<perlembed>.
2390 Tells Perl to C<eval> the string in the SV.
2392 I32 perl_eval_sv (SV* sv, I32 flags)
2396 Tells Perl to C<eval> the given string and return an SV* result.
2398 SV* perl_eval_pv (char* p, I32 croak_on_error)
2402 Releases a Perl interpreter. See L<perlembed>.
2406 Returns the AV of the specified Perl array. If C<create> is set and the
2407 Perl variable does not exist then it will be created. If C<create> is not
2408 set and the variable does not exist then NULL is returned.
2410 AV* perl_get_av (char* name, I32 create)
2414 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
2415 variable does not exist then it will be created. If C<create> is not
2416 set and the variable does not exist then NULL is returned.
2418 CV* perl_get_cv (char* name, I32 create)
2422 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
2423 variable does not exist then it will be created. If C<create> is not
2424 set and the variable does not exist then NULL is returned.
2426 HV* perl_get_hv (char* name, I32 create)
2430 Returns the SV of the specified Perl scalar. If C<create> is set and the
2431 Perl variable does not exist then it will be created. If C<create> is not
2432 set and the variable does not exist then NULL is returned.
2434 SV* perl_get_sv (char* name, I32 create)
2438 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
2440 =item perl_require_pv
2442 Tells Perl to C<require> a module.
2444 void perl_require_pv (char* pv)
2448 Tells a Perl interpreter to run. See L<perlembed>.
2452 Pops an integer off the stack.
2458 Pops a long off the stack.
2464 Pops a string off the stack.
2470 Pops a double off the stack.
2476 Pops an SV off the stack.
2482 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2488 Push an integer onto the stack. The stack must have room for this element.
2489 Handles 'set' magic. See C<XPUSHi>.
2495 Push a double onto the stack. The stack must have room for this element.
2496 Handles 'set' magic. See C<XPUSHn>.
2498 void PUSHn(double d)
2502 Push a string onto the stack. The stack must have room for this element.
2503 The C<len> indicates the length of the string. Handles 'set' magic. See
2506 void PUSHp(char *c, int len )
2510 Push an SV onto the stack. The stack must have room for this element. Does
2511 not handle 'set' magic. See C<XPUSHs>.
2517 Push an unsigned integer onto the stack. The stack must have room for
2518 this element. See C<XPUSHu>.
2520 void PUSHu(unsigned int d)
2525 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2526 See C<PUSHMARK> and L<perlcall> for other uses.
2532 The XSUB-writer's interface to the C C<realloc> function.
2534 void* Renew( void *ptr, int size, type )
2538 The XSUB-writer's interface to the C C<realloc> function, with cast.
2540 void* Renewc( void *ptr, int size, type, cast )
2544 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
2545 This is always the proper type for the XSUB.
2546 See L<perlxs/"The RETVAL Variable">.
2550 The XSUB-writer's interface to the C C<free> function.
2554 The XSUB-writer's interface to the C C<malloc> function.
2558 The XSUB-writer's interface to the C C<realloc> function.
2562 Copy a string to a safe spot. This does not use an SV.
2564 char* savepv (char* sv)
2568 Copy a string to a safe spot. The C<len> indicates number of bytes to
2569 copy. This does not use an SV.
2571 char* savepvn (char* sv, I32 len)
2575 Opening bracket for temporaries on a callback. See C<FREETMPS> and
2582 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2587 Refetch the stack pointer. Used after a callback. See L<perlcall>.
2593 Used to access elements on the XSUB's stack.
2599 Test two strings to see if they are equal. Returns true or false.
2601 int strEQ( char *s1, char *s2 )
2605 Test two strings to see if the first, C<s1>, is greater than or equal to the
2606 second, C<s2>. Returns true or false.
2608 int strGE( char *s1, char *s2 )
2612 Test two strings to see if the first, C<s1>, is greater than the second,
2613 C<s2>. Returns true or false.
2615 int strGT( char *s1, char *s2 )
2619 Test two strings to see if the first, C<s1>, is less than or equal to the
2620 second, C<s2>. Returns true or false.
2622 int strLE( char *s1, char *s2 )
2626 Test two strings to see if the first, C<s1>, is less than the second,
2627 C<s2>. Returns true or false.
2629 int strLT( char *s1, char *s2 )
2633 Test two strings to see if they are different. Returns true or false.
2635 int strNE( char *s1, char *s2 )
2639 Test two strings to see if they are equal. The C<len> parameter indicates
2640 the number of bytes to compare. Returns true or false.
2642 int strnEQ( char *s1, char *s2 )
2646 Test two strings to see if they are different. The C<len> parameter
2647 indicates the number of bytes to compare. Returns true or false.
2649 int strnNE( char *s1, char *s2, int len )
2653 Marks an SV as mortal. The SV will be destroyed when the current context
2656 SV* sv_2mortal (SV* sv)
2660 Blesses an SV into a specified package. The SV must be an RV. The package
2661 must be designated by its stash (see C<gv_stashpv()>). The reference count
2662 of the SV is unaffected.
2664 SV* sv_bless (SV* sv, HV* stash)
2668 Concatenates the string onto the end of the string which is in the SV.
2669 Handles 'get' magic, but not 'set' magic. See C<sv_catpv_mg>.
2671 void sv_catpv (SV* sv, char* ptr)
2675 Like C<sv_catpv>, but also handles 'set' magic.
2677 void sv_catpvn (SV* sv, char* ptr)
2681 Concatenates the string onto the end of the string which is in the SV. The
2682 C<len> indicates number of bytes to copy. Handles 'get' magic, but not
2683 'set' magic. See C<sv_catpvn_mg>.
2685 void sv_catpvn (SV* sv, char* ptr, STRLEN len)
2689 Like C<sv_catpvn>, but also handles 'set' magic.
2691 void sv_catpvn_mg (SV* sv, char* ptr, STRLEN len)
2695 Processes its arguments like C<sprintf> and appends the formatted output
2696 to an SV. Handles 'get' magic, but not 'set' magic. C<SvSETMAGIC()> must
2697 typically be called after calling this function to handle 'set' magic.
2699 void sv_catpvf (SV* sv, const char* pat, ...)
2703 Like C<sv_catpvf>, but also handles 'set' magic.
2705 void sv_catpvf_mg (SV* sv, const char* pat, ...)
2709 Concatenates the string from SV C<ssv> onto the end of the string in SV
2710 C<dsv>. Handles 'get' magic, but not 'set' magic. See C<sv_catsv_mg>.
2712 void sv_catsv (SV* dsv, SV* ssv)
2716 Like C<sv_catsv>, but also handles 'set' magic.
2718 void sv_catsv_mg (SV* dsv, SV* ssv)
2722 Efficient removal of characters from the beginning of the string
2723 buffer. SvPOK(sv) must be true and the C<ptr> must be a pointer to
2724 somewhere inside the string buffer. The C<ptr> becomes the first
2725 character of the adjusted string.
2727 void sv_chop(SV* sv, char *ptr)
2732 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2733 string in C<sv1> is less than, equal to, or greater than the string in
2736 I32 sv_cmp (SV* sv1, SV* sv2)
2740 Returns the length of the string which is in the SV. See C<SvLEN>.
2746 Set the length of the string which is in the SV. See C<SvCUR>.
2748 void SvCUR_set (SV* sv, int val )
2752 Auto-decrement of the value in the SV.
2754 void sv_dec (SV* sv)
2756 =item sv_derived_from
2758 Returns a boolean indicating whether the SV is a subclass of the
2761 int sv_derived_from(SV* sv, char* class)
2763 =item sv_derived_from
2765 Returns a boolean indicating whether the SV is derived from the specified
2766 class. This is the function that implements C<UNIVERSAL::isa>. It works
2767 for class names as well as for objects.
2769 bool sv_derived_from _((SV* sv, char* name));
2773 Returns a pointer to the last character in the string which is in the SV.
2774 See C<SvCUR>. Access the character as
2780 Returns a boolean indicating whether the strings in the two SVs are
2783 I32 sv_eq (SV* sv1, SV* sv2)
2787 Invokes C<mg_get> on an SV if it has 'get' magic. This macro evaluates
2788 its argument more than once.
2790 void SvGETMAGIC( SV *sv )
2794 Expands the character buffer in the SV so that it has room for the
2795 indicated number of bytes (remember to reserve space for an extra
2796 trailing NUL character). Calls C<sv_grow> to perform the expansion if
2797 necessary. Returns a pointer to the character buffer.
2799 char* SvGROW( SV* sv, STRLEN len )
2803 Expands the character buffer in the SV. This will use C<sv_unref> and will
2804 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2809 Auto-increment of the value in the SV.
2811 void sv_inc (SV* sv)
2815 Inserts a string at the specified offset/length within the SV.
2816 Similar to the Perl substr() function.
2818 void sv_insert(SV *sv, STRLEN offset, STRLEN len,
2819 char *str, STRLEN strlen)
2823 Returns a boolean indicating whether the SV contains an integer.
2829 Unsets the IV status of an SV.
2831 void SvIOK_off (SV* sv)
2835 Tells an SV that it is an integer.
2837 void SvIOK_on (SV* sv)
2841 Tells an SV that it is an integer and disables all other OK bits.
2843 void SvIOK_only (SV* sv)
2847 Returns a boolean indicating whether the SV contains an integer. Checks the
2848 B<private> setting. Use C<SvIOK>.
2854 Returns a boolean indicating whether the SV is blessed into the specified
2855 class. This does not check for subtypes; use C<sv_derived_from> to verify
2856 an inheritance relationship.
2858 int sv_isa (SV* sv, char* name)
2862 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2863 object. If the SV is not an RV, or if the object is not blessed, then this
2866 int sv_isobject (SV* sv)
2870 Coerces the given SV to an integer and returns it.
2876 Returns the integer which is stored in the SV, assuming SvIOK is true.
2882 Returns the size of the string buffer in the SV. See C<SvCUR>.
2888 Returns the length of the string in the SV. Use C<SvCUR>.
2890 STRLEN sv_len (SV* sv)
2894 Adds magic to an SV.
2896 void sv_magic (SV* sv, SV* obj, int how, char* name, I32 namlen)
2900 Creates a new SV which is a copy of the original SV. The new SV is marked
2903 SV* sv_mortalcopy (SV* oldsv)
2907 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2909 SV* sv_newmortal (void)
2913 Returns a boolean indicating whether the SV contains a number, integer or
2920 Unsets the NV/IV status of an SV.
2922 void SvNIOK_off (SV* sv)
2926 Returns a boolean indicating whether the SV contains a number, integer or
2927 double. Checks the B<private> setting. Use C<SvNIOK>.
2929 int SvNIOKp (SV* SV)
2933 This is the C<false> SV. See C<PL_sv_yes>. Always refer to this as C<&PL_sv_no>.
2937 Returns a boolean indicating whether the SV contains a double.
2943 Unsets the NV status of an SV.
2945 void SvNOK_off (SV* sv)
2949 Tells an SV that it is a double.
2951 void SvNOK_on (SV* sv)
2955 Tells an SV that it is a double and disables all other OK bits.
2957 void SvNOK_only (SV* sv)
2961 Returns a boolean indicating whether the SV contains a double. Checks the
2962 B<private> setting. Use C<SvNOK>.
2968 Coerce the given SV to a double and return it.
2970 double SvNV (SV* sv)
2974 Returns the double which is stored in the SV, assuming SvNOK is true.
2976 double SvNVX (SV* sv)
2980 Returns a boolean indicating whether the value is an SV.
2986 Returns a boolean indicating whether the SvIVX is a valid offset value
2987 for the SvPVX. This hack is used internally to speed up removal of
2988 characters from the beginning of a SvPV. When SvOOK is true, then the
2989 start of the allocated string buffer is really (SvPVX - SvIVX).
2995 Returns a boolean indicating whether the SV contains a character string.
3001 Unsets the PV status of an SV.
3003 void SvPOK_off (SV* sv)
3007 Tells an SV that it is a string.
3009 void SvPOK_on (SV* sv)
3013 Tells an SV that it is a string and disables all other OK bits.
3015 void SvPOK_only (SV* sv)
3019 Returns a boolean indicating whether the SV contains a character string.
3020 Checks the B<private> setting. Use C<SvPOK>.
3026 Returns a pointer to the string in the SV, or a stringified form of the SV
3027 if the SV does not contain a string. Handles 'get' magic.
3029 char* SvPV (SV* sv, int len )
3033 Like <SvPV> but will force the SV into becoming a string (SvPOK). You
3034 want force if you are going to update the SvPVX directly.
3036 char* SvPV_force(SV* sv, int len)
3041 Returns a pointer to the string in the SV. The SV must contain a string.
3043 char* SvPVX (SV* sv)
3047 Returns the value of the object's reference count.
3049 int SvREFCNT (SV* sv)
3053 Decrements the reference count of the given SV.
3055 void SvREFCNT_dec (SV* sv)
3059 Increments the reference count of the given SV.
3061 void SvREFCNT_inc (SV* sv)
3065 Tests if the SV is an RV.
3071 Unsets the RV status of an SV.
3073 void SvROK_off (SV* sv)
3077 Tells an SV that it is an RV.
3079 void SvROK_on (SV* sv)
3083 Dereferences an RV to return the SV.
3089 Invokes C<mg_set> on an SV if it has 'set' magic. This macro evaluates
3090 its argument more than once.
3092 void SvSETMAGIC( SV *sv )
3096 Copies an integer into the given SV. Does not handle 'set' magic.
3099 void sv_setiv (SV* sv, IV num)
3103 Like C<sv_setiv>, but also handles 'set' magic.
3105 void sv_setiv_mg (SV* sv, IV num)
3109 Copies a double into the given SV. Does not handle 'set' magic.
3112 void sv_setnv (SV* sv, double num)
3116 Like C<sv_setnv>, but also handles 'set' magic.
3118 void sv_setnv_mg (SV* sv, double num)
3122 Copies a string into an SV. The string must be null-terminated.
3123 Does not handle 'set' magic. See C<sv_setpv_mg>.
3125 void sv_setpv (SV* sv, char* ptr)
3129 Like C<sv_setpv>, but also handles 'set' magic.
3131 void sv_setpv_mg (SV* sv, char* ptr)
3135 Copies an integer into the given SV, also updating its string value.
3136 Does not handle 'set' magic. See C<sv_setpviv_mg>.
3138 void sv_setpviv (SV* sv, IV num)
3142 Like C<sv_setpviv>, but also handles 'set' magic.
3144 void sv_setpviv_mg (SV* sv, IV num)
3148 Copies a string into an SV. The C<len> parameter indicates the number of
3149 bytes to be copied. Does not handle 'set' magic. See C<sv_setpvn_mg>.
3151 void sv_setpvn (SV* sv, char* ptr, STRLEN len)
3155 Like C<sv_setpvn>, but also handles 'set' magic.
3157 void sv_setpvn_mg (SV* sv, char* ptr, STRLEN len)
3161 Processes its arguments like C<sprintf> and sets an SV to the formatted
3162 output. Does not handle 'set' magic. See C<sv_setpvf_mg>.
3164 void sv_setpvf (SV* sv, const char* pat, ...)
3168 Like C<sv_setpvf>, but also handles 'set' magic.
3170 void sv_setpvf_mg (SV* sv, const char* pat, ...)
3174 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
3175 argument will be upgraded to an RV. That RV will be modified to point to
3176 the new SV. The C<classname> argument indicates the package for the
3177 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3178 will be returned and will have a reference count of 1.
3180 SV* sv_setref_iv (SV *rv, char *classname, IV iv)
3184 Copies a double into a new SV, optionally blessing the SV. The C<rv>
3185 argument will be upgraded to an RV. That RV will be modified to point to
3186 the new SV. The C<classname> argument indicates the package for the
3187 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3188 will be returned and will have a reference count of 1.
3190 SV* sv_setref_nv (SV *rv, char *classname, double nv)
3194 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
3195 argument will be upgraded to an RV. That RV will be modified to point to
3196 the new SV. If the C<pv> argument is NULL then C<PL_sv_undef> will be placed
3197 into the SV. The C<classname> argument indicates the package for the
3198 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3199 will be returned and will have a reference count of 1.
3201 SV* sv_setref_pv (SV *rv, char *classname, void* pv)
3203 Do not use with integral Perl types such as HV, AV, SV, CV, because those
3204 objects will become corrupted by the pointer copy process.
3206 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
3210 Copies a string into a new SV, optionally blessing the SV. The length of the
3211 string must be specified with C<n>. The C<rv> argument will be upgraded to
3212 an RV. That RV will be modified to point to the new SV. The C<classname>
3213 argument indicates the package for the blessing. Set C<classname> to
3214 C<Nullch> to avoid the blessing. The new SV will be returned and will have
3215 a reference count of 1.
3217 SV* sv_setref_pvn (SV *rv, char *classname, char* pv, I32 n)
3219 Note that C<sv_setref_pv> copies the pointer while this copies the string.
3223 Calls C<sv_setsv> if dsv is not the same as ssv. May evaluate arguments
3226 void SvSetSV (SV* dsv, SV* ssv)
3228 =item SvSetSV_nosteal
3230 Calls a non-destructive version of C<sv_setsv> if dsv is not the same as ssv.
3231 May evaluate arguments more than once.
3233 void SvSetSV_nosteal (SV* dsv, SV* ssv)
3237 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
3238 The source SV may be destroyed if it is mortal. Does not handle 'set' magic.
3239 See the macro forms C<SvSetSV>, C<SvSetSV_nosteal> and C<sv_setsv_mg>.
3241 void sv_setsv (SV* dsv, SV* ssv)
3245 Like C<sv_setsv>, but also handles 'set' magic.
3247 void sv_setsv_mg (SV* dsv, SV* ssv)
3251 Copies an unsigned integer into the given SV. Does not handle 'set' magic.
3254 void sv_setuv (SV* sv, UV num)
3258 Like C<sv_setuv>, but also handles 'set' magic.
3260 void sv_setuv_mg (SV* sv, UV num)
3264 Returns the stash of the SV.
3266 HV* SvSTASH (SV* sv)
3270 Taints an SV if tainting is enabled
3272 void SvTAINT (SV* sv)
3276 Checks to see if an SV is tainted. Returns TRUE if it is, FALSE if not.
3278 int SvTAINTED (SV* sv)
3282 Untaints an SV. Be I<very> careful with this routine, as it short-circuits
3283 some of Perl's fundamental security features. XS module authors should
3284 not use this function unless they fully understand all the implications
3285 of unconditionally untainting the value. Untainting should be done in
3286 the standard perl fashion, via a carefully crafted regexp, rather than
3287 directly untainting variables.
3289 void SvTAINTED_off (SV* sv)
3293 Marks an SV as tainted.
3295 void SvTAINTED_on (SV* sv)
3299 Integer type flag for scalars. See C<svtype>.
3303 Pointer type flag for scalars. See C<svtype>.
3307 Type flag for arrays. See C<svtype>.
3311 Type flag for code refs. See C<svtype>.
3315 Type flag for hashes. See C<svtype>.
3319 Type flag for blessed scalars. See C<svtype>.
3323 Double type flag for scalars. See C<svtype>.
3327 Returns a boolean indicating whether Perl would evaluate the SV as true or
3328 false, defined or undefined. Does not handle 'get' magic.
3334 Returns the type of the SV. See C<svtype>.
3336 svtype SvTYPE (SV* sv)
3340 An enum of flags for Perl types. These are found in the file B<sv.h> in the
3341 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
3345 This is the C<undef> SV. Always refer to this as C<&PL_sv_undef>.
3349 Unsets the RV status of the SV, and decrements the reference count of
3350 whatever was being referenced by the RV. This can almost be thought of
3351 as a reversal of C<newSVrv>. See C<SvROK_off>.
3353 void sv_unref (SV* sv)
3357 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
3358 the upgrade if necessary. See C<svtype>.
3360 bool SvUPGRADE (SV* sv, svtype mt)
3364 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
3368 Tells an SV to use C<ptr> to find its string value. Normally the string is
3369 stored inside the SV but sv_usepvn allows the SV to use an outside string.
3370 The C<ptr> should point to memory that was allocated by C<malloc>. The
3371 string length, C<len>, must be supplied. This function will realloc the
3372 memory pointed to by C<ptr>, so that pointer should not be freed or used by
3373 the programmer after giving it to sv_usepvn. Does not handle 'set' magic.
3374 See C<sv_usepvn_mg>.
3376 void sv_usepvn (SV* sv, char* ptr, STRLEN len)
3380 Like C<sv_usepvn>, but also handles 'set' magic.
3382 void sv_usepvn_mg (SV* sv, char* ptr, STRLEN len)
3384 =item sv_vcatpvfn(sv, pat, patlen, args, svargs, svmax, used_locale)
3386 Processes its arguments like C<vsprintf> and appends the formatted output
3387 to an SV. Uses an array of SVs if the C style variable argument list is
3388 missing (NULL). Indicates if locale information has been used for formatting.
3390 void sv_catpvfn _((SV* sv, const char* pat, STRLEN patlen,
3391 va_list *args, SV **svargs, I32 svmax,
3392 bool *used_locale));
3394 =item sv_vsetpvfn(sv, pat, patlen, args, svargs, svmax, used_locale)
3396 Works like C<vcatpvfn> but copies the text into the SV instead of
3399 void sv_setpvfn _((SV* sv, const char* pat, STRLEN patlen,
3400 va_list *args, SV **svargs, I32 svmax,
3401 bool *used_locale));
3405 Coerces the given SV to an unsigned integer and returns it.
3411 Returns the unsigned integer which is stored in the SV, assuming SvIOK is true.
3417 This is the C<true> SV. See C<PL_sv_no>. Always refer to this as C<&PL_sv_yes>.
3421 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
3422 This is always the proper type for the C++ object. See C<CLASS> and
3423 L<perlxs/"Using XS With C++">.
3427 Converts the specified character to lowercase.
3429 int toLOWER (char c)
3433 Converts the specified character to uppercase.
3435 int toUPPER (char c)
3439 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
3440 function the same way you use the C C<printf> function. See C<croak()>.
3444 Push an integer onto the stack, extending the stack if necessary. Handles
3445 'set' magic. See C<PUSHi>.
3451 Push a double onto the stack, extending the stack if necessary. Handles 'set'
3452 magic. See C<PUSHn>.
3458 Push a string onto the stack, extending the stack if necessary. The C<len>
3459 indicates the length of the string. Handles 'set' magic. See C<PUSHp>.
3461 XPUSHp(char *c, int len)
3465 Push an SV onto the stack, extending the stack if necessary. Does not
3466 handle 'set' magic. See C<PUSHs>.
3472 Push an unsigned integer onto the stack, extending the stack if
3473 necessary. See C<PUSHu>.
3477 Macro to declare an XSUB and its C parameter list. This is handled by
3482 Return from XSUB, indicating number of items on the stack. This is usually
3483 handled by C<xsubpp>.
3487 =item XSRETURN_EMPTY
3489 Return an empty list from an XSUB immediately.
3495 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
3501 Return C<&PL_sv_no> from an XSUB immediately. Uses C<XST_mNO>.
3507 Return an double from an XSUB immediately. Uses C<XST_mNV>.
3513 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
3515 XSRETURN_PV(char *v)
3517 =item XSRETURN_UNDEF
3519 Return C<&PL_sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
3525 Return C<&PL_sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
3531 Place an integer into the specified position C<i> on the stack. The value is
3532 stored in a new mortal SV.
3534 XST_mIV( int i, IV v )
3538 Place a double into the specified position C<i> on the stack. The value is
3539 stored in a new mortal SV.
3541 XST_mNV( int i, NV v )
3545 Place C<&PL_sv_no> into the specified position C<i> on the stack.
3551 Place a copy of a string into the specified position C<i> on the stack. The
3552 value is stored in a new mortal SV.
3554 XST_mPV( int i, char *v )
3558 Place C<&PL_sv_undef> into the specified position C<i> on the stack.
3564 Place C<&PL_sv_yes> into the specified position C<i> on the stack.
3570 The version identifier for an XS module. This is usually handled
3571 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
3573 =item XS_VERSION_BOOTCHECK
3575 Macro to verify that a PM module's $VERSION variable matches the XS module's
3576 C<XS_VERSION> variable. This is usually handled automatically by
3577 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
3581 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
3582 destination, C<n> is the number of items, and C<t> is the type.
3584 void Zero( d, n, t )
3590 Until May 1997, this document was maintained by Jeff Okamoto
3591 <okamoto@corp.hp.com>. It is now maintained as part of Perl itself.
3593 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
3594 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
3595 Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
3596 Stephen McCamant, and Gurusamy Sarathy.
3598 API Listing originally by Dean Roehrich <roehrich@cray.com>.