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 It is suggested that you use the version of malloc that is distributed
1240 with Perl. It keeps pools of various sizes of unallocated memory in
1241 order to satisfy allocation requests more quickly. However, on some
1242 platforms, it may cause spurious malloc or free errors.
1244 New(x, pointer, number, type);
1245 Newc(x, pointer, number, type, cast);
1246 Newz(x, pointer, number, type);
1248 These three macros are used to initially allocate memory.
1250 The first argument C<x> was a "magic cookie" that was used to keep track
1251 of who called the macro, to help when debugging memory problems. However,
1252 the current code makes no use of this feature (most Perl developers now
1253 use run-time memory checkers), so this argument can be any number.
1255 The second argument C<pointer> should be the name of a variable that will
1256 point to the newly allocated memory.
1258 The third and fourth arguments C<number> and C<type> specify how many of
1259 the specified type of data structure should be allocated. The argument
1260 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
1261 should be used if the C<pointer> argument is different from the C<type>
1264 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
1265 to zero out all the newly allocated memory.
1267 Renew(pointer, number, type);
1268 Renewc(pointer, number, type, cast);
1271 These three macros are used to change a memory buffer size or to free a
1272 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1273 match those of C<New> and C<Newc> with the exception of not needing the
1274 "magic cookie" argument.
1276 Move(source, dest, number, type);
1277 Copy(source, dest, number, type);
1278 Zero(dest, number, type);
1280 These three macros are used to move, copy, or zero out previously allocated
1281 memory. The C<source> and C<dest> arguments point to the source and
1282 destination starting points. Perl will move, copy, or zero out C<number>
1283 instances of the size of the C<type> data structure (using the C<sizeof>
1288 The most recent development releases of Perl has been experimenting with
1289 removing Perl's dependency on the "normal" standard I/O suite and allowing
1290 other stdio implementations to be used. This involves creating a new
1291 abstraction layer that then calls whichever implementation of stdio Perl
1292 was compiled with. All XSUBs should now use the functions in the PerlIO
1293 abstraction layer and not make any assumptions about what kind of stdio
1296 For a complete description of the PerlIO abstraction, consult L<perlapio>.
1298 =head2 Putting a C value on Perl stack
1300 A lot of opcodes (this is an elementary operation in the internal perl
1301 stack machine) put an SV* on the stack. However, as an optimization
1302 the corresponding SV is (usually) not recreated each time. The opcodes
1303 reuse specially assigned SVs (I<target>s) which are (as a corollary)
1304 not constantly freed/created.
1306 Each of the targets is created only once (but see
1307 L<Scratchpads and recursion> below), and when an opcode needs to put
1308 an integer, a double, or a string on stack, it just sets the
1309 corresponding parts of its I<target> and puts the I<target> on stack.
1311 The macro to put this target on stack is C<PUSHTARG>, and it is
1312 directly used in some opcodes, as well as indirectly in zillions of
1313 others, which use it via C<(X)PUSH[pni]>.
1317 The question remains on when the SVs which are I<target>s for opcodes
1318 are created. The answer is that they are created when the current unit --
1319 a subroutine or a file (for opcodes for statements outside of
1320 subroutines) -- is compiled. During this time a special anonymous Perl
1321 array is created, which is called a scratchpad for the current
1324 A scratchpad keeps SVs which are lexicals for the current unit and are
1325 targets for opcodes. One can deduce that an SV lives on a scratchpad
1326 by looking on its flags: lexicals have C<SVs_PADMY> set, and
1327 I<target>s have C<SVs_PADTMP> set.
1329 The correspondence between OPs and I<target>s is not 1-to-1. Different
1330 OPs in the compile tree of the unit can use the same target, if this
1331 would not conflict with the expected life of the temporary.
1333 =head2 Scratchpads and recursion
1335 In fact it is not 100% true that a compiled unit contains a pointer to
1336 the scratchpad AV. In fact it contains a pointer to an AV of
1337 (initially) one element, and this element is the scratchpad AV. Why do
1338 we need an extra level of indirection?
1340 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1341 these can create several execution pointers going into the same
1342 subroutine. For the subroutine-child not write over the temporaries
1343 for the subroutine-parent (lifespan of which covers the call to the
1344 child), the parent and the child should have different
1345 scratchpads. (I<And> the lexicals should be separate anyway!)
1347 So each subroutine is born with an array of scratchpads (of length 1).
1348 On each entry to the subroutine it is checked that the current
1349 depth of the recursion is not more than the length of this array, and
1350 if it is, new scratchpad is created and pushed into the array.
1352 The I<target>s on this scratchpad are C<undef>s, but they are already
1353 marked with correct flags.
1355 =head1 Compiled code
1359 Here we describe the internal form your code is converted to by
1360 Perl. Start with a simple example:
1364 This is converted to a tree similar to this one:
1372 (but slightly more complicated). This tree reflects the way Perl
1373 parsed your code, but has nothing to do with the execution order.
1374 There is an additional "thread" going through the nodes of the tree
1375 which shows the order of execution of the nodes. In our simplified
1376 example above it looks like:
1378 $b ---> $c ---> + ---> $a ---> assign-to
1380 But with the actual compile tree for C<$a = $b + $c> it is different:
1381 some nodes I<optimized away>. As a corollary, though the actual tree
1382 contains more nodes than our simplified example, the execution order
1383 is the same as in our example.
1385 =head2 Examining the tree
1387 If you have your perl compiled for debugging (usually done with C<-D
1388 optimize=-g> on C<Configure> command line), you may examine the
1389 compiled tree by specifying C<-Dx> on the Perl command line. The
1390 output takes several lines per node, and for C<$b+$c> it looks like
1395 FLAGS = (SCALAR,KIDS)
1397 TYPE = null ===> (4)
1399 FLAGS = (SCALAR,KIDS)
1401 3 TYPE = gvsv ===> 4
1407 TYPE = null ===> (5)
1409 FLAGS = (SCALAR,KIDS)
1411 4 TYPE = gvsv ===> 5
1417 This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1418 not optimized away (one per number in the left column). The immediate
1419 children of the given node correspond to C<{}> pairs on the same level
1420 of indentation, thus this listing corresponds to the tree:
1428 The execution order is indicated by C<===E<gt>> marks, thus it is C<3
1429 4 5 6> (node C<6> is not included into above listing), i.e.,
1430 C<gvsv gvsv add whatever>.
1432 =head2 Compile pass 1: check routines
1434 The tree is created by the I<pseudo-compiler> while yacc code feeds it
1435 the constructions it recognizes. Since yacc works bottom-up, so does
1436 the first pass of perl compilation.
1438 What makes this pass interesting for perl developers is that some
1439 optimization may be performed on this pass. This is optimization by
1440 so-called I<check routines>. The correspondence between node names
1441 and corresponding check routines is described in F<opcode.pl> (do not
1442 forget to run C<make regen_headers> if you modify this file).
1444 A check routine is called when the node is fully constructed except
1445 for the execution-order thread. Since at this time there are no
1446 back-links to the currently constructed node, one can do most any
1447 operation to the top-level node, including freeing it and/or creating
1448 new nodes above/below it.
1450 The check routine returns the node which should be inserted into the
1451 tree (if the top-level node was not modified, check routine returns
1454 By convention, check routines have names C<ck_*>. They are usually
1455 called from C<new*OP> subroutines (or C<convert>) (which in turn are
1456 called from F<perly.y>).
1458 =head2 Compile pass 1a: constant folding
1460 Immediately after the check routine is called the returned node is
1461 checked for being compile-time executable. If it is (the value is
1462 judged to be constant) it is immediately executed, and a I<constant>
1463 node with the "return value" of the corresponding subtree is
1464 substituted instead. The subtree is deleted.
1466 If constant folding was not performed, the execution-order thread is
1469 =head2 Compile pass 2: context propagation
1471 When a context for a part of compile tree is known, it is propagated
1472 down through the tree. At this time the context can have 5 values
1473 (instead of 2 for runtime context): void, boolean, scalar, list, and
1474 lvalue. In contrast with the pass 1 this pass is processed from top
1475 to bottom: a node's context determines the context for its children.
1477 Additional context-dependent optimizations are performed at this time.
1478 Since at this moment the compile tree contains back-references (via
1479 "thread" pointers), nodes cannot be free()d now. To allow
1480 optimized-away nodes at this stage, such nodes are null()ified instead
1481 of free()ing (i.e. their type is changed to OP_NULL).
1483 =head2 Compile pass 3: peephole optimization
1485 After the compile tree for a subroutine (or for an C<eval> or a file)
1486 is created, an additional pass over the code is performed. This pass
1487 is neither top-down or bottom-up, but in the execution order (with
1488 additional complications for conditionals). These optimizations are
1489 done in the subroutine peep(). Optimizations performed at this stage
1490 are subject to the same restrictions as in the pass 2.
1494 This is a listing of functions, macros, flags, and variables that may be
1495 useful to extension writers or that may be found while reading other
1498 Note that all Perl API global variables must be referenced with the C<PL_>
1499 prefix. Some macros are provided for compatibility with the older,
1500 unadorned names, but this support will be removed in a future release.
1502 It is strongly recommended that all Perl API functions that don't begin
1503 with C<perl> be referenced with an explicit C<Perl_> prefix.
1505 The sort order of the listing is case insensitive, with any
1506 occurrences of '_' ignored for the purpose of sorting.
1512 Clears an array, making it empty. Does not free the memory used by the
1515 void av_clear (AV* ar)
1519 Pre-extend an array. The C<key> is the index to which the array should be
1522 void av_extend (AV* ar, I32 key)
1526 Returns the SV at the specified index in the array. The C<key> is the
1527 index. If C<lval> is set then the fetch will be part of a store. Check
1528 that the return value is non-null before dereferencing it to a C<SV*>.
1530 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1531 information on how to use this function on tied arrays.
1533 SV** av_fetch (AV* ar, I32 key, I32 lval)
1537 Same as C<av_len()>. Deprecated, use C<av_len()> instead.
1541 Returns the highest index in the array. Returns -1 if the array is empty.
1547 Creates a new AV and populates it with a list of SVs. The SVs are copied
1548 into the array, so they may be freed after the call to av_make. The new AV
1549 will have a reference count of 1.
1551 AV* av_make (I32 size, SV** svp)
1555 Pops an SV off the end of the array. Returns C<&PL_sv_undef> if the array is
1562 Pushes an SV onto the end of the array. The array will grow automatically
1563 to accommodate the addition.
1565 void av_push (AV* ar, SV* val)
1569 Shifts an SV off the beginning of the array.
1571 SV* av_shift (AV* ar)
1575 Stores an SV in an array. The array index is specified as C<key>. The
1576 return value will be NULL if the operation failed or if the value did not
1577 need to be actually stored within the array (as in the case of tied arrays).
1578 Otherwise it can be dereferenced to get the original C<SV*>. Note that the
1579 caller is responsible for suitably incrementing the reference count of C<val>
1580 before the call, and decrementing it if the function returned NULL.
1582 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1583 information on how to use this function on tied arrays.
1585 SV** av_store (AV* ar, I32 key, SV* val)
1589 Undefines the array. Frees the memory used by the array itself.
1591 void av_undef (AV* ar)
1595 Unshift the given number of C<undef> values onto the beginning of the
1596 array. The array will grow automatically to accommodate the addition.
1597 You must then use C<av_store> to assign values to these new elements.
1599 void av_unshift (AV* ar, I32 num)
1603 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1604 constructor. This is always a C<char*>. See C<THIS> and
1605 L<perlxs/"Using XS With C++">.
1609 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1610 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1611 the type. May fail on overlapping copies. See also C<Move>.
1613 void Copy( s, d, n, t )
1617 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1618 function the same way you use the C C<printf> function. See C<warn>.
1622 Returns the stash of the CV.
1624 HV* CvSTASH( SV* sv )
1628 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1629 boolean which indicates whether subs are being single-stepped.
1630 Single-stepping is automatically turned on after every step. This is the C
1631 variable which corresponds to Perl's $DB::single variable. See C<PL_DBsub>.
1635 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1636 the SV which holds the name of the sub being debugged. This is the C
1637 variable which corresponds to Perl's $DB::sub variable. See C<PL_DBsingle>.
1638 The sub name can be found by
1640 SvPV( GvSV( PL_DBsub ), len )
1644 Trace variable used when Perl is run in debugging mode, with the B<-d>
1645 switch. This is the C variable which corresponds to Perl's $DB::trace
1646 variable. See C<PL_DBsingle>.
1650 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1655 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1659 The C variable which corresponds to Perl's $^W warning variable.
1663 Declares a local copy of perl's stack pointer for the XSUB, available via
1664 the C<SP> macro. See C<SP>.
1668 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1669 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1670 to indicate the number of items on the stack.
1674 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1675 handled automatically by C<xsubpp>.
1679 Switches filehandle to binmode. C<iotype> is what C<IoTYPE(io)> would
1682 do_binmode(fp, iotype, TRUE);
1686 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1692 Used to extend the argument stack for an XSUB's return values.
1698 Analyses the string in order to make fast searches on it using fbm_instr() --
1699 the Boyer-Moore algorithm.
1701 void fbm_compile(SV* sv, U32 flags)
1705 Returns the location of the SV in the string delimited by C<str> and
1706 C<strend>. It returns C<Nullch> if the string can't be found. The
1707 C<sv> does not have to be fbm_compiled, but the search will not be as
1710 char* fbm_instr(char *str, char *strend, SV *sv, U32 flags)
1714 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1721 Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
1725 Indicates that arguments returned from a callback should be discarded. See
1730 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1734 A backward-compatible version of C<GIMME_V> which can only return
1735 C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
1739 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
1740 C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
1741 context, respectively.
1745 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1749 Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
1753 Returns the glob with the given C<name> and a defined subroutine or
1754 C<NULL>. The glob lives in the given C<stash>, or in the stashes
1755 accessible via @ISA and @UNIVERSAL.
1757 The argument C<level> should be either 0 or -1. If C<level==0>, as a
1758 side-effect creates a glob with the given C<name> in the given
1759 C<stash> which in the case of success contains an alias for the
1760 subroutine, and sets up caching info for this glob. Similarly for all
1761 the searched stashes.
1763 This function grants C<"SUPER"> token as a postfix of the stash name.
1765 The GV returned from C<gv_fetchmeth> may be a method cache entry,
1766 which is not visible to Perl code. So when calling C<perl_call_sv>,
1767 you should not use the GV directly; instead, you should use the
1768 method's CV, which can be obtained from the GV with the C<GvCV> macro.
1770 GV* gv_fetchmeth (HV* stash, char* name, STRLEN len, I32 level)
1772 =item gv_fetchmethod
1774 =item gv_fetchmethod_autoload
1776 Returns the glob which contains the subroutine to call to invoke the
1777 method on the C<stash>. In fact in the presense of autoloading this may
1778 be the glob for "AUTOLOAD". In this case the corresponding variable
1779 $AUTOLOAD is already setup.
1781 The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
1782 lookup is performed if the given method is not present: non-zero means
1783 yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
1784 C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
1785 non-zero C<autoload> parameter.
1787 These functions grant C<"SUPER"> token as a prefix of the method name.
1789 Note that if you want to keep the returned glob for a long time, you
1790 need to check for it being "AUTOLOAD", since at the later time the call
1791 may load a different subroutine due to $AUTOLOAD changing its value.
1792 Use the glob created via a side effect to do this.
1794 These functions have the same side-effects and as C<gv_fetchmeth> with
1795 C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
1796 The warning against passing the GV returned by C<gv_fetchmeth> to
1797 C<perl_call_sv> apply equally to these functions.
1799 GV* gv_fetchmethod (HV* stash, char* name)
1800 GV* gv_fetchmethod_autoload (HV* stash, char* name, I32 autoload)
1804 Used to indicate void context. See C<GIMME_V> and L<perlcall>.
1808 Returns a pointer to the stash for a specified package. If C<create> is set
1809 then the package will be created if it does not already exist. If C<create>
1810 is not set and the package does not exist then NULL is returned.
1812 HV* gv_stashpv (char* name, I32 create)
1816 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1818 HV* gv_stashsv (SV* sv, I32 create)
1822 Return the SV from the GV.
1826 This flag, used in the length slot of hash entries and magic
1827 structures, specifies the structure contains a C<SV*> pointer where a
1828 C<char*> pointer is to be expected. (For information only--not to be used).
1832 Returns the computed hash stored in the hash entry.
1838 Returns the actual pointer stored in the key slot of the hash entry.
1839 The pointer may be either C<char*> or C<SV*>, depending on the value of
1840 C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
1841 are usually preferable for finding the value of a key.
1847 If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
1848 holds an C<SV*> key. Otherwise, holds the actual length of the key.
1849 Can be assigned to. The C<HePV()> macro is usually preferable for finding
1856 Returns the key slot of the hash entry as a C<char*> value, doing any
1857 necessary dereferencing of possibly C<SV*> keys. The length of
1858 the string is placed in C<len> (this is a macro, so do I<not> use
1859 C<&len>). If you do not care about what the length of the key is,
1860 you may use the global variable C<PL_na>, though this is rather less
1861 efficient than using a local variable. Remember though, that hash
1862 keys in perl are free to contain embedded nulls, so using C<strlen()>
1863 or similar is not a good way to find the length of hash keys.
1864 This is very similar to the C<SvPV()> macro described elsewhere in
1867 char* HePV(HE* he, STRLEN len)
1871 Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
1872 does not contain an C<SV*> key.
1878 Returns the key as an C<SV*>. Will create and return a temporary
1879 mortal C<SV*> if the hash entry contains only a C<char*> key.
1881 HeSVKEY_force(HE* he)
1885 Sets the key to a given C<SV*>, taking care to set the appropriate flags
1886 to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
1888 HeSVKEY_set(HE* he, SV* sv)
1892 Returns the value slot (type C<SV*>) stored in the hash entry.
1898 Clears a hash, making it empty.
1900 void hv_clear (HV* tb)
1904 Deletes a key/value pair in the hash. The value SV is removed from the hash
1905 and returned to the caller. The C<klen> is the length of the key. The
1906 C<flags> value will normally be zero; if set to G_DISCARD then NULL will be
1909 SV* hv_delete (HV* tb, char* key, U32 klen, I32 flags)
1913 Deletes a key/value pair in the hash. The value SV is removed from the hash
1914 and returned to the caller. The C<flags> value will normally be zero; if set
1915 to G_DISCARD then NULL will be returned. C<hash> can be a valid precomputed
1916 hash value, or 0 to ask for it to be computed.
1918 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash)
1922 Returns a boolean indicating whether the specified hash key exists. The
1923 C<klen> is the length of the key.
1925 bool hv_exists (HV* tb, char* key, U32 klen)
1929 Returns a boolean indicating whether the specified hash key exists. C<hash>
1930 can be a valid precomputed hash value, or 0 to ask for it to be computed.
1932 bool hv_exists_ent (HV* tb, SV* key, U32 hash)
1936 Returns the SV which corresponds to the specified key in the hash. The
1937 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1938 part of a store. Check that the return value is non-null before
1939 dereferencing it to a C<SV*>.
1941 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1942 information on how to use this function on tied hashes.
1944 SV** hv_fetch (HV* tb, char* key, U32 klen, I32 lval)
1948 Returns the hash entry which corresponds to the specified key in the hash.
1949 C<hash> must be a valid precomputed hash number for the given C<key>, or
1950 0 if you want the function to compute it. IF C<lval> is set then the
1951 fetch will be part of a store. Make sure the return value is non-null
1952 before accessing it. The return value when C<tb> is a tied hash
1953 is a pointer to a static location, so be sure to make a copy of the
1954 structure if you need to store it somewhere.
1956 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1957 information on how to use this function on tied hashes.
1959 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash)
1963 Prepares a starting point to traverse a hash table.
1965 I32 hv_iterinit (HV* tb)
1967 Returns the number of keys in the hash (i.e. the same as C<HvKEYS(tb)>).
1968 The return value is currently only meaningful for hashes without tie
1971 NOTE: Before version 5.004_65, C<hv_iterinit> used to return the number
1972 of hash buckets that happen to be in use. If you still need that
1973 esoteric value, you can get it through the macro C<HvFILL(tb)>.
1977 Returns the key from the current position of the hash iterator. See
1980 char* hv_iterkey (HE* entry, I32* retlen)
1984 Returns the key as an C<SV*> from the current position of the hash
1985 iterator. The return value will always be a mortal copy of the
1986 key. Also see C<hv_iterinit>.
1988 SV* hv_iterkeysv (HE* entry)
1992 Returns entries from a hash iterator. See C<hv_iterinit>.
1994 HE* hv_iternext (HV* tb)
1998 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
2001 SV* hv_iternextsv (HV* hv, char** key, I32* retlen)
2005 Returns the value from the current position of the hash iterator. See
2008 SV* hv_iterval (HV* tb, HE* entry)
2012 Adds magic to a hash. See C<sv_magic>.
2014 void hv_magic (HV* hv, GV* gv, int how)
2018 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
2020 char* HvNAME (HV* stash)
2024 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
2025 the length of the key. The C<hash> parameter is the precomputed hash
2026 value; if it is zero then Perl will compute it. The return value will be
2027 NULL if the operation failed or if the value did not need to be actually
2028 stored within the hash (as in the case of tied hashes). Otherwise it can
2029 be dereferenced to get the original C<SV*>. Note that the caller is
2030 responsible for suitably incrementing the reference count of C<val>
2031 before the call, and decrementing it if the function returned NULL.
2033 See L<Understanding the Magic of Tied Hashes and Arrays> for more
2034 information on how to use this function on tied hashes.
2036 SV** hv_store (HV* tb, char* key, U32 klen, SV* val, U32 hash)
2040 Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
2041 parameter is the precomputed hash value; if it is zero then Perl will
2042 compute it. The return value is the new hash entry so created. It will be
2043 NULL if the operation failed or if the value did not need to be actually
2044 stored within the hash (as in the case of tied hashes). Otherwise the
2045 contents of the return value can be accessed using the C<He???> macros
2046 described here. Note that the caller is responsible for suitably
2047 incrementing the reference count of C<val> before the call, and decrementing
2048 it if the function returned NULL.
2050 See L<Understanding the Magic of Tied Hashes and Arrays> for more
2051 information on how to use this function on tied hashes.
2053 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash)
2059 void hv_undef (HV* tb)
2063 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
2066 int isALNUM (char c)
2070 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
2073 int isALPHA (char c)
2077 Returns a boolean indicating whether the C C<char> is an ascii digit.
2079 int isDIGIT (char c)
2083 Returns a boolean indicating whether the C C<char> is a lowercase character.
2085 int isLOWER (char c)
2089 Returns a boolean indicating whether the C C<char> is whitespace.
2091 int isSPACE (char c)
2095 Returns a boolean indicating whether the C C<char> is an uppercase character.
2097 int isUPPER (char c)
2101 Variable which is setup by C<xsubpp> to indicate the number of items on the
2102 stack. See L<perlxs/"Variable-length Parameter Lists">.
2106 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
2107 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
2111 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
2115 =item looks_like_number
2117 Test if an the content of an SV looks like a number (or is a number).
2119 int looks_like_number(SV*)
2124 Stack marker variable for the XSUB. See C<dMARK>.
2128 Clear something magical that the SV represents. See C<sv_magic>.
2130 int mg_clear (SV* sv)
2134 Copies the magic from one SV to another. See C<sv_magic>.
2136 int mg_copy (SV *, SV *, char *, STRLEN)
2140 Finds the magic pointer for type matching the SV. See C<sv_magic>.
2142 MAGIC* mg_find (SV* sv, int type)
2146 Free any magic storage used by the SV. See C<sv_magic>.
2148 int mg_free (SV* sv)
2152 Do magic after a value is retrieved from the SV. See C<sv_magic>.
2158 Report on the SV's length. See C<sv_magic>.
2164 Turns on the magical status of an SV. See C<sv_magic>.
2166 void mg_magical (SV* sv)
2170 Do magic after a value is assigned to the SV. See C<sv_magic>.
2176 C<modglobal> is a general purpose, interpreter global HV for use by
2177 extensions. While it could hold extension specific information, it is
2178 meant primarily for information that needs to be shared between
2179 extensions. Moreover, while it could be used for any kind of
2180 information, it is meant for information that should be not accessible
2181 in the usual way from the perl symbol table.
2185 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
2186 source, C<d> is the destination, C<n> is the number of items, and C<t> is
2187 the type. Can do overlapping moves. See also C<Copy>.
2189 void Move( s, d, n, t )
2193 A convenience variable which is typically used with C<SvPV> when one doesn't
2194 care about the length of the string. It is usually more efficient to
2195 declare a local variable and use that instead.
2199 The XSUB-writer's interface to the C C<malloc> function.
2201 void* New( x, void *ptr, int size, type )
2205 Creates a new AV. The reference count is set to 1.
2211 The XSUB-writer's interface to the C C<malloc> function, with cast.
2213 void* Newc( x, void *ptr, int size, type, cast )
2217 Creates a constant sub equivalent to Perl C<sub FOO () { 123 }>
2218 which is eligible for inlining at compile-time.
2220 void newCONSTSUB(HV* stash, char* name, SV* sv)
2224 Creates a new HV. The reference count is set to 1.
2230 Creates an RV wrapper for an SV. The reference count for the original SV is
2233 SV* newRV_inc (SV* ref)
2235 For historical reasons, "newRV" is a synonym for "newRV_inc".
2239 Creates an RV wrapper for an SV. The reference count for the original
2240 SV is B<not> incremented.
2242 SV* newRV_noinc (SV* ref)
2246 Creates a new SV. A non-zero C<len> parameter indicates the number of
2247 bytes of preallocated string space the SV should have. An extra byte
2248 for a tailing NUL is also reserved. (SvPOK is not set for the SV even
2249 if string space is allocated.) The reference count for the new SV is
2250 set to 1. C<id> is an integer id between 0 and 1299 (used to identify
2253 SV* NEWSV (int id, STRLEN len)
2257 Creates a new SV and copies an integer into it. The reference count for the
2264 Creates a new SV and copies a double into it. The reference count for the
2271 Creates a new SV and copies a string into it. The reference count for the
2272 SV is set to 1. If C<len> is zero then Perl will compute the length.
2274 SV* newSVpv (char* s, STRLEN len)
2278 Creates a new SV an initialize it with the string formatted like
2281 SV* newSVpvf(const char* pat, ...);
2285 Creates a new SV and copies a string into it. The reference count for the
2286 SV is set to 1. If C<len> is zero then Perl will create a zero length
2289 SV* newSVpvn (char* s, STRLEN len)
2293 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
2294 it will be upgraded to one. If C<classname> is non-null then the new SV will
2295 be blessed in the specified package. The new SV is returned and its
2296 reference count is 1.
2298 SV* newSVrv (SV* rv, char* classname)
2302 Creates a new SV which is an exact duplicate of the original SV.
2304 SV* newSVsv (SV* old)
2308 Used by C<xsubpp> to hook up XSUBs as Perl subs.
2312 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
2317 The XSUB-writer's interface to the C C<malloc> function. The allocated
2318 memory is zeroed with C<memzero>.
2320 void* Newz( x, void *ptr, int size, type )
2328 Null character pointer.
2344 The original stack mark for the XSUB. See C<dORIGMARK>.
2348 Allocates a new Perl interpreter. See L<perlembed>.
2350 =item perl_call_argv
2352 Performs a callback to the specified Perl sub. See L<perlcall>.
2354 I32 perl_call_argv (char* subname, I32 flags, char** argv)
2356 =item perl_call_method
2358 Performs a callback to the specified Perl method. The blessed object must
2359 be on the stack. See L<perlcall>.
2361 I32 perl_call_method (char* methname, I32 flags)
2365 Performs a callback to the specified Perl sub. See L<perlcall>.
2367 I32 perl_call_pv (char* subname, I32 flags)
2371 Performs a callback to the Perl sub whose name is in the SV. See
2374 I32 perl_call_sv (SV* sv, I32 flags)
2376 =item perl_construct
2378 Initializes a new Perl interpreter. See L<perlembed>.
2382 Shuts down a Perl interpreter. See L<perlembed>.
2386 Tells Perl to C<eval> the string in the SV.
2388 I32 perl_eval_sv (SV* sv, I32 flags)
2392 Tells Perl to C<eval> the given string and return an SV* result.
2394 SV* perl_eval_pv (char* p, I32 croak_on_error)
2398 Releases a Perl interpreter. See L<perlembed>.
2402 Returns the AV of the specified Perl array. If C<create> is set and the
2403 Perl variable does not exist then it will be created. If C<create> is not
2404 set and the variable does not exist then NULL is returned.
2406 AV* perl_get_av (char* name, I32 create)
2410 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
2411 variable does not exist then it will be created. If C<create> is not
2412 set and the variable does not exist then NULL is returned.
2414 CV* perl_get_cv (char* name, I32 create)
2418 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
2419 variable does not exist then it will be created. If C<create> is not
2420 set and the variable does not exist then NULL is returned.
2422 HV* perl_get_hv (char* name, I32 create)
2426 Returns the SV of the specified Perl scalar. If C<create> is set and the
2427 Perl variable does not exist then it will be created. If C<create> is not
2428 set and the variable does not exist then NULL is returned.
2430 SV* perl_get_sv (char* name, I32 create)
2434 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
2436 =item perl_require_pv
2438 Tells Perl to C<require> a module.
2440 void perl_require_pv (char* pv)
2444 Tells a Perl interpreter to run. See L<perlembed>.
2448 Pops an integer off the stack.
2454 Pops a long off the stack.
2460 Pops a string off the stack.
2466 Pops a double off the stack.
2472 Pops an SV off the stack.
2478 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2484 Push an integer onto the stack. The stack must have room for this element.
2485 Handles 'set' magic. See C<XPUSHi>.
2491 Push a double onto the stack. The stack must have room for this element.
2492 Handles 'set' magic. See C<XPUSHn>.
2494 void PUSHn(double d)
2498 Push a string onto the stack. The stack must have room for this element.
2499 The C<len> indicates the length of the string. Handles 'set' magic. See
2502 void PUSHp(char *c, int len )
2506 Push an SV onto the stack. The stack must have room for this element. Does
2507 not handle 'set' magic. See C<XPUSHs>.
2513 Push an unsigned integer onto the stack. The stack must have room for
2514 this element. See C<XPUSHu>.
2516 void PUSHu(unsigned int d)
2521 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2522 See C<PUSHMARK> and L<perlcall> for other uses.
2528 The XSUB-writer's interface to the C C<realloc> function.
2530 void* Renew( void *ptr, int size, type )
2534 The XSUB-writer's interface to the C C<realloc> function, with cast.
2536 void* Renewc( void *ptr, int size, type, cast )
2540 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
2541 This is always the proper type for the XSUB.
2542 See L<perlxs/"The RETVAL Variable">.
2546 The XSUB-writer's interface to the C C<free> function.
2550 The XSUB-writer's interface to the C C<malloc> function.
2554 The XSUB-writer's interface to the C C<realloc> function.
2558 Copy a string to a safe spot. This does not use an SV.
2560 char* savepv (char* sv)
2564 Copy a string to a safe spot. The C<len> indicates number of bytes to
2565 copy. This does not use an SV.
2567 char* savepvn (char* sv, I32 len)
2571 Opening bracket for temporaries on a callback. See C<FREETMPS> and
2578 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2583 Refetch the stack pointer. Used after a callback. See L<perlcall>.
2589 Used to access elements on the XSUB's stack.
2595 Test two strings to see if they are equal. Returns true or false.
2597 int strEQ( char *s1, char *s2 )
2601 Test two strings to see if the first, C<s1>, is greater than or equal to the
2602 second, C<s2>. Returns true or false.
2604 int strGE( char *s1, char *s2 )
2608 Test two strings to see if the first, C<s1>, is greater than the second,
2609 C<s2>. Returns true or false.
2611 int strGT( char *s1, char *s2 )
2615 Test two strings to see if the first, C<s1>, is less than or equal to the
2616 second, C<s2>. Returns true or false.
2618 int strLE( char *s1, char *s2 )
2622 Test two strings to see if the first, C<s1>, is less than the second,
2623 C<s2>. Returns true or false.
2625 int strLT( char *s1, char *s2 )
2629 Test two strings to see if they are different. Returns true or false.
2631 int strNE( char *s1, char *s2 )
2635 Test two strings to see if they are equal. The C<len> parameter indicates
2636 the number of bytes to compare. Returns true or false.
2638 int strnEQ( char *s1, char *s2 )
2642 Test two strings to see if they are different. The C<len> parameter
2643 indicates the number of bytes to compare. Returns true or false.
2645 int strnNE( char *s1, char *s2, int len )
2649 Marks an SV as mortal. The SV will be destroyed when the current context
2652 SV* sv_2mortal (SV* sv)
2656 Blesses an SV into a specified package. The SV must be an RV. The package
2657 must be designated by its stash (see C<gv_stashpv()>). The reference count
2658 of the SV is unaffected.
2660 SV* sv_bless (SV* sv, HV* stash)
2664 Concatenates the string onto the end of the string which is in the SV.
2665 Handles 'get' magic, but not 'set' magic. See C<sv_catpv_mg>.
2667 void sv_catpv (SV* sv, char* ptr)
2671 Like C<sv_catpv>, but also handles 'set' magic.
2673 void sv_catpvn (SV* sv, char* ptr)
2677 Concatenates the string onto the end of the string which is in the SV. The
2678 C<len> indicates number of bytes to copy. Handles 'get' magic, but not
2679 'set' magic. See C<sv_catpvn_mg>.
2681 void sv_catpvn (SV* sv, char* ptr, STRLEN len)
2685 Like C<sv_catpvn>, but also handles 'set' magic.
2687 void sv_catpvn_mg (SV* sv, char* ptr, STRLEN len)
2691 Processes its arguments like C<sprintf> and appends the formatted output
2692 to an SV. Handles 'get' magic, but not 'set' magic. C<SvSETMAGIC()> must
2693 typically be called after calling this function to handle 'set' magic.
2695 void sv_catpvf (SV* sv, const char* pat, ...)
2699 Like C<sv_catpvf>, but also handles 'set' magic.
2701 void sv_catpvf_mg (SV* sv, const char* pat, ...)
2705 Concatenates the string from SV C<ssv> onto the end of the string in SV
2706 C<dsv>. Handles 'get' magic, but not 'set' magic. See C<sv_catsv_mg>.
2708 void sv_catsv (SV* dsv, SV* ssv)
2712 Like C<sv_catsv>, but also handles 'set' magic.
2714 void sv_catsv_mg (SV* dsv, SV* ssv)
2718 Efficient removal of characters from the beginning of the string
2719 buffer. SvPOK(sv) must be true and the C<ptr> must be a pointer to
2720 somewhere inside the string buffer. The C<ptr> becomes the first
2721 character of the adjusted string.
2723 void sv_chop(SV* sv, char *ptr)
2728 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2729 string in C<sv1> is less than, equal to, or greater than the string in
2732 I32 sv_cmp (SV* sv1, SV* sv2)
2736 Returns the length of the string which is in the SV. See C<SvLEN>.
2742 Set the length of the string which is in the SV. See C<SvCUR>.
2744 void SvCUR_set (SV* sv, int val )
2748 Auto-decrement of the value in the SV.
2750 void sv_dec (SV* sv)
2752 =item sv_derived_from
2754 Returns a boolean indicating whether the SV is a subclass of the
2757 int sv_derived_from(SV* sv, char* class)
2759 =item sv_derived_from
2761 Returns a boolean indicating whether the SV is derived from the specified
2762 class. This is the function that implements C<UNIVERSAL::isa>. It works
2763 for class names as well as for objects.
2765 bool sv_derived_from _((SV* sv, char* name));
2769 Returns a pointer to the last character in the string which is in the SV.
2770 See C<SvCUR>. Access the character as
2776 Returns a boolean indicating whether the strings in the two SVs are
2779 I32 sv_eq (SV* sv1, SV* sv2)
2783 Invokes C<mg_get> on an SV if it has 'get' magic. This macro evaluates
2784 its argument more than once.
2786 void SvGETMAGIC( SV *sv )
2790 Expands the character buffer in the SV so that it has room for the
2791 indicated number of bytes (remember to reserve space for an extra
2792 trailing NUL character). Calls C<sv_grow> to perform the expansion if
2793 necessary. Returns a pointer to the character buffer.
2795 char* SvGROW( SV* sv, STRLEN len )
2799 Expands the character buffer in the SV. This will use C<sv_unref> and will
2800 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2805 Auto-increment of the value in the SV.
2807 void sv_inc (SV* sv)
2811 Inserts a string at the specified offset/length within the SV.
2812 Similar to the Perl substr() function.
2814 void sv_insert(SV *sv, STRLEN offset, STRLEN len,
2815 char *str, STRLEN strlen)
2819 Returns a boolean indicating whether the SV contains an integer.
2825 Unsets the IV status of an SV.
2827 void SvIOK_off (SV* sv)
2831 Tells an SV that it is an integer.
2833 void SvIOK_on (SV* sv)
2837 Tells an SV that it is an integer and disables all other OK bits.
2839 void SvIOK_only (SV* sv)
2843 Returns a boolean indicating whether the SV contains an integer. Checks the
2844 B<private> setting. Use C<SvIOK>.
2850 Returns a boolean indicating whether the SV is blessed into the specified
2851 class. This does not check for subtypes; use C<sv_derived_from> to verify
2852 an inheritance relationship.
2854 int sv_isa (SV* sv, char* name)
2858 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2859 object. If the SV is not an RV, or if the object is not blessed, then this
2862 int sv_isobject (SV* sv)
2866 Returns the integer which is in the SV.
2872 Returns the integer which is stored in the SV.
2878 Returns the size of the string buffer in the SV. See C<SvCUR>.
2884 Returns the length of the string in the SV. Use C<SvCUR>.
2886 STRLEN sv_len (SV* sv)
2890 Adds magic to an SV.
2892 void sv_magic (SV* sv, SV* obj, int how, char* name, I32 namlen)
2896 Creates a new SV which is a copy of the original SV. The new SV is marked
2899 SV* sv_mortalcopy (SV* oldsv)
2903 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2905 SV* sv_newmortal (void)
2909 Returns a boolean indicating whether the SV contains a number, integer or
2916 Unsets the NV/IV status of an SV.
2918 void SvNIOK_off (SV* sv)
2922 Returns a boolean indicating whether the SV contains a number, integer or
2923 double. Checks the B<private> setting. Use C<SvNIOK>.
2925 int SvNIOKp (SV* SV)
2929 This is the C<false> SV. See C<PL_sv_yes>. Always refer to this as C<&PL_sv_no>.
2933 Returns a boolean indicating whether the SV contains a double.
2939 Unsets the NV status of an SV.
2941 void SvNOK_off (SV* sv)
2945 Tells an SV that it is a double.
2947 void SvNOK_on (SV* sv)
2951 Tells an SV that it is a double and disables all other OK bits.
2953 void SvNOK_only (SV* sv)
2957 Returns a boolean indicating whether the SV contains a double. Checks the
2958 B<private> setting. Use C<SvNOK>.
2964 Returns the double which is stored in the SV.
2966 double SvNV (SV* sv)
2970 Returns the double which is stored in the SV.
2972 double SvNVX (SV* sv)
2976 Returns a boolean indicating whether the value is an SV.
2982 Returns a boolean indicating whether the SvIVX is a valid offset value
2983 for the SvPVX. This hack is used internally to speed up removal of
2984 characters from the beginning of a SvPV. When SvOOK is true, then the
2985 start of the allocated string buffer is really (SvPVX - SvIVX).
2991 Returns a boolean indicating whether the SV contains a character string.
2997 Unsets the PV status of an SV.
2999 void SvPOK_off (SV* sv)
3003 Tells an SV that it is a string.
3005 void SvPOK_on (SV* sv)
3009 Tells an SV that it is a string and disables all other OK bits.
3011 void SvPOK_only (SV* sv)
3015 Returns a boolean indicating whether the SV contains a character string.
3016 Checks the B<private> setting. Use C<SvPOK>.
3022 Returns a pointer to the string in the SV, or a stringified form of the SV
3023 if the SV does not contain a string. Handles 'get' magic.
3025 char* SvPV (SV* sv, int len )
3029 Like <SvPV> but will force the SV into becoming a string (SvPOK). You
3030 want force if you are going to update the SvPVX directly.
3032 char* SvPV_force(SV* sv, int len)
3037 Returns a pointer to the string in the SV. The SV must contain a string.
3039 char* SvPVX (SV* sv)
3043 Returns the value of the object's reference count.
3045 int SvREFCNT (SV* sv)
3049 Decrements the reference count of the given SV.
3051 void SvREFCNT_dec (SV* sv)
3055 Increments the reference count of the given SV.
3057 void SvREFCNT_inc (SV* sv)
3061 Tests if the SV is an RV.
3067 Unsets the RV status of an SV.
3069 void SvROK_off (SV* sv)
3073 Tells an SV that it is an RV.
3075 void SvROK_on (SV* sv)
3079 Dereferences an RV to return the SV.
3085 Invokes C<mg_set> on an SV if it has 'set' magic. This macro evaluates
3086 its argument more than once.
3088 void SvSETMAGIC( SV *sv )
3092 Copies an integer into the given SV. Does not handle 'set' magic.
3095 void sv_setiv (SV* sv, IV num)
3099 Like C<sv_setiv>, but also handles 'set' magic.
3101 void sv_setiv_mg (SV* sv, IV num)
3105 Copies a double into the given SV. Does not handle 'set' magic.
3108 void sv_setnv (SV* sv, double num)
3112 Like C<sv_setnv>, but also handles 'set' magic.
3114 void sv_setnv_mg (SV* sv, double num)
3118 Copies a string into an SV. The string must be null-terminated.
3119 Does not handle 'set' magic. See C<sv_setpv_mg>.
3121 void sv_setpv (SV* sv, char* ptr)
3125 Like C<sv_setpv>, but also handles 'set' magic.
3127 void sv_setpv_mg (SV* sv, char* ptr)
3131 Copies an integer into the given SV, also updating its string value.
3132 Does not handle 'set' magic. See C<sv_setpviv_mg>.
3134 void sv_setpviv (SV* sv, IV num)
3138 Like C<sv_setpviv>, but also handles 'set' magic.
3140 void sv_setpviv_mg (SV* sv, IV num)
3144 Copies a string into an SV. The C<len> parameter indicates the number of
3145 bytes to be copied. Does not handle 'set' magic. See C<sv_setpvn_mg>.
3147 void sv_setpvn (SV* sv, char* ptr, STRLEN len)
3151 Like C<sv_setpvn>, but also handles 'set' magic.
3153 void sv_setpvn_mg (SV* sv, char* ptr, STRLEN len)
3157 Processes its arguments like C<sprintf> and sets an SV to the formatted
3158 output. Does not handle 'set' magic. See C<sv_setpvf_mg>.
3160 void sv_setpvf (SV* sv, const char* pat, ...)
3164 Like C<sv_setpvf>, but also handles 'set' magic.
3166 void sv_setpvf_mg (SV* sv, const char* pat, ...)
3170 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
3171 argument will be upgraded to an RV. That RV will be modified to point to
3172 the new SV. The C<classname> argument indicates the package for the
3173 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3174 will be returned and will have a reference count of 1.
3176 SV* sv_setref_iv (SV *rv, char *classname, IV iv)
3180 Copies a double into a new SV, optionally blessing the SV. The C<rv>
3181 argument will be upgraded to an RV. That RV will be modified to point to
3182 the new SV. The C<classname> argument indicates the package for the
3183 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3184 will be returned and will have a reference count of 1.
3186 SV* sv_setref_nv (SV *rv, char *classname, double nv)
3190 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
3191 argument will be upgraded to an RV. That RV will be modified to point to
3192 the new SV. If the C<pv> argument is NULL then C<PL_sv_undef> will be placed
3193 into the SV. The C<classname> argument indicates the package for the
3194 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3195 will be returned and will have a reference count of 1.
3197 SV* sv_setref_pv (SV *rv, char *classname, void* pv)
3199 Do not use with integral Perl types such as HV, AV, SV, CV, because those
3200 objects will become corrupted by the pointer copy process.
3202 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
3206 Copies a string into a new SV, optionally blessing the SV. The length of the
3207 string must be specified with C<n>. The C<rv> argument will be upgraded to
3208 an RV. That RV will be modified to point to the new SV. The C<classname>
3209 argument indicates the package for the blessing. Set C<classname> to
3210 C<Nullch> to avoid the blessing. The new SV will be returned and will have
3211 a reference count of 1.
3213 SV* sv_setref_pvn (SV *rv, char *classname, char* pv, I32 n)
3215 Note that C<sv_setref_pv> copies the pointer while this copies the string.
3219 Calls C<sv_setsv> if dsv is not the same as ssv. May evaluate arguments
3222 void SvSetSV (SV* dsv, SV* ssv)
3224 =item SvSetSV_nosteal
3226 Calls a non-destructive version of C<sv_setsv> if dsv is not the same as ssv.
3227 May evaluate arguments more than once.
3229 void SvSetSV_nosteal (SV* dsv, SV* ssv)
3233 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
3234 The source SV may be destroyed if it is mortal. Does not handle 'set' magic.
3235 See the macro forms C<SvSetSV>, C<SvSetSV_nosteal> and C<sv_setsv_mg>.
3237 void sv_setsv (SV* dsv, SV* ssv)
3241 Like C<sv_setsv>, but also handles 'set' magic.
3243 void sv_setsv_mg (SV* dsv, SV* ssv)
3247 Copies an unsigned integer into the given SV. Does not handle 'set' magic.
3250 void sv_setuv (SV* sv, UV num)
3254 Like C<sv_setuv>, but also handles 'set' magic.
3256 void sv_setuv_mg (SV* sv, UV num)
3260 Returns the stash of the SV.
3262 HV* SvSTASH (SV* sv)
3266 Taints an SV if tainting is enabled
3268 void SvTAINT (SV* sv)
3272 Checks to see if an SV is tainted. Returns TRUE if it is, FALSE if not.
3274 int SvTAINTED (SV* sv)
3278 Untaints an SV. Be I<very> careful with this routine, as it short-circuits
3279 some of Perl's fundamental security features. XS module authors should
3280 not use this function unless they fully understand all the implications
3281 of unconditionally untainting the value. Untainting should be done in
3282 the standard perl fashion, via a carefully crafted regexp, rather than
3283 directly untainting variables.
3285 void SvTAINTED_off (SV* sv)
3289 Marks an SV as tainted.
3291 void SvTAINTED_on (SV* sv)
3295 Integer type flag for scalars. See C<svtype>.
3299 Pointer type flag for scalars. See C<svtype>.
3303 Type flag for arrays. See C<svtype>.
3307 Type flag for code refs. See C<svtype>.
3311 Type flag for hashes. See C<svtype>.
3315 Type flag for blessed scalars. See C<svtype>.
3319 Double type flag for scalars. See C<svtype>.
3323 Returns a boolean indicating whether Perl would evaluate the SV as true or
3324 false, defined or undefined. Does not handle 'get' magic.
3330 Returns the type of the SV. See C<svtype>.
3332 svtype SvTYPE (SV* sv)
3336 An enum of flags for Perl types. These are found in the file B<sv.h> in the
3337 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
3341 This is the C<undef> SV. Always refer to this as C<&PL_sv_undef>.
3345 Unsets the RV status of the SV, and decrements the reference count of
3346 whatever was being referenced by the RV. This can almost be thought of
3347 as a reversal of C<newSVrv>. See C<SvROK_off>.
3349 void sv_unref (SV* sv)
3353 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
3354 the upgrade if necessary. See C<svtype>.
3356 bool SvUPGRADE (SV* sv, svtype mt)
3360 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
3364 Tells an SV to use C<ptr> to find its string value. Normally the string is
3365 stored inside the SV but sv_usepvn allows the SV to use an outside string.
3366 The C<ptr> should point to memory that was allocated by C<malloc>. The
3367 string length, C<len>, must be supplied. This function will realloc the
3368 memory pointed to by C<ptr>, so that pointer should not be freed or used by
3369 the programmer after giving it to sv_usepvn. Does not handle 'set' magic.
3370 See C<sv_usepvn_mg>.
3372 void sv_usepvn (SV* sv, char* ptr, STRLEN len)
3376 Like C<sv_usepvn>, but also handles 'set' magic.
3378 void sv_usepvn_mg (SV* sv, char* ptr, STRLEN len)
3380 =item sv_vcatpvfn(sv, pat, patlen, args, svargs, svmax, used_locale)
3382 Processes its arguments like C<vsprintf> and appends the formatted output
3383 to an SV. Uses an array of SVs if the C style variable argument list is
3384 missing (NULL). Indicates if locale information has been used for formatting.
3386 void sv_catpvfn _((SV* sv, const char* pat, STRLEN patlen,
3387 va_list *args, SV **svargs, I32 svmax,
3388 bool *used_locale));
3390 =item sv_vsetpvfn(sv, pat, patlen, args, svargs, svmax, used_locale)
3392 Works like C<vcatpvfn> but copies the text into the SV instead of
3395 void sv_setpvfn _((SV* sv, const char* pat, STRLEN patlen,
3396 va_list *args, SV **svargs, I32 svmax,
3397 bool *used_locale));
3401 Returns the unsigned integer which is in the SV.
3407 Returns the unsigned integer which is stored in the SV.
3413 This is the C<true> SV. See C<PL_sv_no>. Always refer to this as C<&PL_sv_yes>.
3417 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
3418 This is always the proper type for the C++ object. See C<CLASS> and
3419 L<perlxs/"Using XS With C++">.
3423 Converts the specified character to lowercase.
3425 int toLOWER (char c)
3429 Converts the specified character to uppercase.
3431 int toUPPER (char c)
3435 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
3436 function the same way you use the C C<printf> function. See C<croak()>.
3440 Push an integer onto the stack, extending the stack if necessary. Handles
3441 'set' magic. See C<PUSHi>.
3447 Push a double onto the stack, extending the stack if necessary. Handles 'set'
3448 magic. See C<PUSHn>.
3454 Push a string onto the stack, extending the stack if necessary. The C<len>
3455 indicates the length of the string. Handles 'set' magic. See C<PUSHp>.
3457 XPUSHp(char *c, int len)
3461 Push an SV onto the stack, extending the stack if necessary. Does not
3462 handle 'set' magic. See C<PUSHs>.
3468 Push an unsigned integer onto the stack, extending the stack if
3469 necessary. See C<PUSHu>.
3473 Macro to declare an XSUB and its C parameter list. This is handled by
3478 Return from XSUB, indicating number of items on the stack. This is usually
3479 handled by C<xsubpp>.
3483 =item XSRETURN_EMPTY
3485 Return an empty list from an XSUB immediately.
3491 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
3497 Return C<&PL_sv_no> from an XSUB immediately. Uses C<XST_mNO>.
3503 Return an double from an XSUB immediately. Uses C<XST_mNV>.
3509 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
3511 XSRETURN_PV(char *v)
3513 =item XSRETURN_UNDEF
3515 Return C<&PL_sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
3521 Return C<&PL_sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
3527 Place an integer into the specified position C<i> on the stack. The value is
3528 stored in a new mortal SV.
3530 XST_mIV( int i, IV v )
3534 Place a double into the specified position C<i> on the stack. The value is
3535 stored in a new mortal SV.
3537 XST_mNV( int i, NV v )
3541 Place C<&PL_sv_no> into the specified position C<i> on the stack.
3547 Place a copy of a string into the specified position C<i> on the stack. The
3548 value is stored in a new mortal SV.
3550 XST_mPV( int i, char *v )
3554 Place C<&PL_sv_undef> into the specified position C<i> on the stack.
3560 Place C<&PL_sv_yes> into the specified position C<i> on the stack.
3566 The version identifier for an XS module. This is usually handled
3567 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
3569 =item XS_VERSION_BOOTCHECK
3571 Macro to verify that a PM module's $VERSION variable matches the XS module's
3572 C<XS_VERSION> variable. This is usually handled automatically by
3573 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
3577 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
3578 destination, C<n> is the number of items, and C<t> is the type.
3580 void Zero( d, n, t )
3586 Until May 1997, this document was maintained by Jeff Okamoto
3587 <okamoto@corp.hp.com>. It is now maintained as part of Perl itself.
3589 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
3590 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
3591 Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
3592 Stephen McCamant, and Gurusamy Sarathy.
3594 API Listing originally by Dean Roehrich <roehrich@cray.com>.