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).
37 The five routines are:
41 SV* newSVpv(char*, int);
42 SV* newSVpvf(const char*, ...);
45 To change the value of an *already-existing* SV, there are six routines:
47 void sv_setiv(SV*, IV);
48 void sv_setnv(SV*, double);
49 void sv_setpv(SV*, char*);
50 void sv_setpvn(SV*, char*, int)
51 void sv_setpvf(SV*, const char*, ...);
52 void sv_setsv(SV*, SV*);
54 Notice that you can choose to specify the length of the string to be
55 assigned by using C<sv_setpvn> or C<newSVpv>, or you may allow Perl to
56 calculate the length by using C<sv_setpv> or by specifying 0 as the second
57 argument to C<newSVpv>. Be warned, though, that Perl will determine the
58 string's length by using C<strlen>, which depends on the string terminating
59 with a NUL character. The arguments of C<sv_setpvf> are processed like
60 C<sprintf>, and the formatted output becomes the value.
62 All SVs that will contain strings should, but need not, be terminated
63 with a NUL character. If it is not NUL-terminated there is a risk of
64 core dumps and corruptions from code which passes the string to C
65 functions or system calls which expect a NUL-terminated string.
66 Perl's own functions typically add a trailing NUL for this reason.
67 Nevertheless, you should be very careful when you pass a string stored
68 in an SV to a C function or system call.
70 To access the actual value that an SV points to, you can use the macros:
76 which will automatically coerce the actual scalar type into an IV, double,
79 In the C<SvPV> macro, the length of the string returned is placed into the
80 variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
81 care what the length of the data is, use the global variable C<na>. Remember,
82 however, that Perl allows arbitrary strings of data that may both contain
83 NULs and might not be terminated by a NUL.
85 If you want to know if the scalar value is TRUE, you can use:
89 Although Perl will automatically grow strings for you, if you need to force
90 Perl to allocate more memory for your SV, you can use the macro
92 SvGROW(SV*, STRLEN newlen)
94 which will determine if more memory needs to be allocated. If so, it will
95 call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
96 decrease, the allocated memory of an SV and that it does not automatically
97 add a byte for the a trailing NUL (perl's own string functions typically do
98 C<SvGROW(sv, len + 1)>).
100 If you have an SV and want to know what kind of data Perl thinks is stored
101 in it, you can use the following macros to check the type of SV you have.
107 You can get and set the current length of the string stored in an SV with
108 the following macros:
111 SvCUR_set(SV*, I32 val)
113 You can also get a pointer to the end of the string stored in the SV
118 But note that these last three macros are valid only if C<SvPOK()> is true.
120 If you want to append something to the end of string stored in an C<SV*>,
121 you can use the following functions:
123 void sv_catpv(SV*, char*);
124 void sv_catpvn(SV*, char*, int);
125 void sv_catpvf(SV*, const char*, ...);
126 void sv_catsv(SV*, SV*);
128 The first function calculates the length of the string to be appended by
129 using C<strlen>. In the second, you specify the length of the string
130 yourself. The third function processes its arguments like C<sprintf> and
131 appends the formatted output. The fourth function extends the string
132 stored in the first SV with the string stored in the second SV. It also
133 forces the second SV to be interpreted as a string.
135 If you know the name of a scalar variable, you can get a pointer to its SV
136 by using the following:
138 SV* perl_get_sv("package::varname", FALSE);
140 This returns NULL if the variable does not exist.
142 If you want to know if this variable (or any other SV) is actually C<defined>,
147 The scalar C<undef> value is stored in an SV instance called C<sv_undef>. Its
148 address can be used whenever an C<SV*> is needed.
150 There are also the two values C<sv_yes> and C<sv_no>, which contain Boolean
151 TRUE and FALSE values, respectively. Like C<sv_undef>, their addresses can
152 be used whenever an C<SV*> is needed.
154 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&sv_undef>.
158 if (I-am-to-return-a-real-value) {
159 sv = sv_2mortal(newSViv(42));
163 This code tries to return a new SV (which contains the value 42) if it should
164 return a real value, or undef otherwise. Instead it has returned a NULL
165 pointer which, somewhere down the line, will cause a segmentation violation,
166 bus error, or just weird results. Change the zero to C<&sv_undef> in the first
167 line and all will be well.
169 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
170 call is not necessary (see L<Reference Counts and Mortality>).
172 =head2 What's Really Stored in an SV?
174 Recall that the usual method of determining the type of scalar you have is
175 to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
176 usually these macros will always return TRUE and calling the C<Sv*V>
177 macros will do the appropriate conversion of string to integer/double or
178 integer/double to string.
180 If you I<really> need to know if you have an integer, double, or string
181 pointer in an SV, you can use the following three macros instead:
187 These will tell you if you truly have an integer, double, or string pointer
188 stored in your SV. The "p" stands for private.
190 In general, though, it's best to use the C<Sv*V> macros.
192 =head2 Working with AVs
194 There are two ways to create and load an AV. The first method creates an
199 The second method both creates the AV and initially populates it with SVs:
201 AV* av_make(I32 num, SV **ptr);
203 The second argument points to an array containing C<num> C<SV*>'s. Once the
204 AV has been created, the SVs can be destroyed, if so desired.
206 Once the AV has been created, the following operations are possible on AVs:
208 void av_push(AV*, SV*);
211 void av_unshift(AV*, I32 num);
213 These should be familiar operations, with the exception of C<av_unshift>.
214 This routine adds C<num> elements at the front of the array with the C<undef>
215 value. You must then use C<av_store> (described below) to assign values
216 to these new elements.
218 Here are some other functions:
221 SV** av_fetch(AV*, I32 key, I32 lval);
222 SV** av_store(AV*, I32 key, SV* val);
224 The C<av_len> function returns the highest index value in array (just
225 like $#array in Perl). If the array is empty, -1 is returned. The
226 C<av_fetch> function returns the value at index C<key>, but if C<lval>
227 is non-zero, then C<av_fetch> will store an undef value at that index.
228 The C<av_store> function stores the value C<val> at index C<key>, and does
229 not increment the reference count of C<val>. Thus the caller is responsible
230 for taking care of that, and if C<av_store> returns NULL, the caller will
231 have to decrement the reference count to avoid a memory leak. Note that
232 C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s as their
237 void av_extend(AV*, I32 key);
239 The C<av_clear> function deletes all the elements in the AV* array, but
240 does not actually delete the array itself. The C<av_undef> function will
241 delete all the elements in the array plus the array itself. The
242 C<av_extend> function extends the array so that it contains C<key>
243 elements. If C<key> is less than the current length of the array, then
246 If you know the name of an array variable, you can get a pointer to its AV
247 by using the following:
249 AV* perl_get_av("package::varname", FALSE);
251 This returns NULL if the variable does not exist.
253 See L<Understanding the Magic of Tied Hashes and Arrays> for more
254 information on how to use the array access functions on tied arrays.
256 =head2 Working with HVs
258 To create an HV, you use the following routine:
262 Once the HV has been created, the following operations are possible on HVs:
264 SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
265 SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
267 The C<klen> parameter is the length of the key being passed in (Note that
268 you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
269 length of the key). The C<val> argument contains the SV pointer to the
270 scalar being stored, and C<hash> is the precomputed hash value (zero if
271 you want C<hv_store> to calculate it for you). The C<lval> parameter
272 indicates whether this fetch is actually a part of a store operation, in
273 which case a new undefined value will be added to the HV with the supplied
274 key and C<hv_fetch> will return as if the value had already existed.
276 Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
277 C<SV*>. To access the scalar value, you must first dereference the return
278 value. However, you should check to make sure that the return value is
279 not NULL before dereferencing it.
281 These two functions check if a hash table entry exists, and deletes it.
283 bool hv_exists(HV*, char* key, U32 klen);
284 SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
286 If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
287 create and return a mortal copy of the deleted value.
289 And more miscellaneous functions:
294 Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
295 table but does not actually delete the hash table. The C<hv_undef> deletes
296 both the entries and the hash table itself.
298 Perl keeps the actual data in linked list of structures with a typedef of HE.
299 These contain the actual key and value pointers (plus extra administrative
300 overhead). The key is a string pointer; the value is an C<SV*>. However,
301 once you have an C<HE*>, to get the actual key and value, use the routines
304 I32 hv_iterinit(HV*);
305 /* Prepares starting point to traverse hash table */
306 HE* hv_iternext(HV*);
307 /* Get the next entry, and return a pointer to a
308 structure that has both the key and value */
309 char* hv_iterkey(HE* entry, I32* retlen);
310 /* Get the key from an HE structure and also return
311 the length of the key string */
312 SV* hv_iterval(HV*, HE* entry);
313 /* Return a SV pointer to the value of the HE
315 SV* hv_iternextsv(HV*, char** key, I32* retlen);
316 /* This convenience routine combines hv_iternext,
317 hv_iterkey, and hv_iterval. The key and retlen
318 arguments are return values for the key and its
319 length. The value is returned in the SV* argument */
321 If you know the name of a hash variable, you can get a pointer to its HV
322 by using the following:
324 HV* perl_get_hv("package::varname", FALSE);
326 This returns NULL if the variable does not exist.
328 The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
334 hash = hash * 33 + *s++;
336 See L<Understanding the Magic of Tied Hashes and Arrays> for more
337 information on how to use the hash access functions on tied hashes.
339 =head2 Hash API Extensions
341 Beginning with version 5.004, the following functions are also supported:
343 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
344 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
346 bool hv_exists_ent (HV* tb, SV* key, U32 hash);
347 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
349 SV* hv_iterkeysv (HE* entry);
351 Note that these functions take C<SV*> keys, which simplifies writing
352 of extension code that deals with hash structures. These functions
353 also allow passing of C<SV*> keys to C<tie> functions without forcing
354 you to stringify the keys (unlike the previous set of functions).
356 They also return and accept whole hash entries (C<HE*>), making their
357 use more efficient (since the hash number for a particular string
358 doesn't have to be recomputed every time). See L<API LISTING> later in
359 this document for detailed descriptions.
361 The following macros must always be used to access the contents of hash
362 entries. Note that the arguments to these macros must be simple
363 variables, since they may get evaluated more than once. See
364 L<API LISTING> later in this document for detailed descriptions of these
367 HePV(HE* he, STRLEN len)
371 HeSVKEY_force(HE* he)
372 HeSVKEY_set(HE* he, SV* sv)
374 These two lower level macros are defined, but must only be used when
375 dealing with keys that are not C<SV*>s:
380 Note that both C<hv_store> and C<hv_store_ent> do not increment the
381 reference count of the stored C<val>, which is the caller's responsibility.
382 If these functions return a NULL value, the caller will usually have to
383 decrement the reference count of C<val> to avoid a memory leak.
387 References are a special type of scalar that point to other data types
388 (including references).
390 To create a reference, use either of the following functions:
392 SV* newRV_inc((SV*) thing);
393 SV* newRV_noinc((SV*) thing);
395 The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
396 functions are identical except that C<newRV_inc> increments the reference
397 count of the C<thing>, while C<newRV_noinc> does not. For historical
398 reasons, C<newRV> is a synonym for C<newRV_inc>.
400 Once you have a reference, you can use the following macro to dereference
405 then call the appropriate routines, casting the returned C<SV*> to either an
406 C<AV*> or C<HV*>, if required.
408 To determine if an SV is a reference, you can use the following macro:
412 To discover what type of value the reference refers to, use the following
413 macro and then check the return value.
417 The most useful types that will be returned are:
426 SVt_PVGV Glob (possible a file handle)
427 SVt_PVMG Blessed or Magical Scalar
429 See the sv.h header file for more details.
431 =head2 Blessed References and Class Objects
433 References are also used to support object-oriented programming. In the
434 OO lexicon, an object is simply a reference that has been blessed into a
435 package (or class). Once blessed, the programmer may now use the reference
436 to access the various methods in the class.
438 A reference can be blessed into a package with the following function:
440 SV* sv_bless(SV* sv, HV* stash);
442 The C<sv> argument must be a reference. The C<stash> argument specifies
443 which class the reference will belong to. See
444 L<Stashes and Globs> for information on converting class names into stashes.
446 /* Still under construction */
448 Upgrades rv to reference if not already one. Creates new SV for rv to
449 point to. If C<classname> is non-null, the SV is blessed into the specified
450 class. SV is returned.
452 SV* newSVrv(SV* rv, char* classname);
454 Copies integer or double into an SV whose reference is C<rv>. SV is blessed
455 if C<classname> is non-null.
457 SV* sv_setref_iv(SV* rv, char* classname, IV iv);
458 SV* sv_setref_nv(SV* rv, char* classname, NV iv);
460 Copies the pointer value (I<the address, not the string!>) into an SV whose
461 reference is rv. SV is blessed if C<classname> is non-null.
463 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
465 Copies string into an SV whose reference is C<rv>. Set length to 0 to let
466 Perl calculate the string length. SV is blessed if C<classname> is non-null.
468 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
470 int sv_isa(SV* sv, char* name);
471 int sv_isobject(SV* sv);
473 =head2 Creating New Variables
475 To create a new Perl variable with an undef value which can be accessed from
476 your Perl script, use the following routines, depending on the variable type.
478 SV* perl_get_sv("package::varname", TRUE);
479 AV* perl_get_av("package::varname", TRUE);
480 HV* perl_get_hv("package::varname", TRUE);
482 Notice the use of TRUE as the second parameter. The new variable can now
483 be set, using the routines appropriate to the data type.
485 There are additional macros whose values may be bitwise OR'ed with the
486 C<TRUE> argument to enable certain extra features. Those bits are:
488 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
489 "Name <varname> used only once: possible typo" warning.
490 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
491 the variable did not exist before the function was called.
493 If you do not specify a package name, the variable is created in the current
496 =head2 Reference Counts and Mortality
498 Perl uses an reference count-driven garbage collection mechanism. SVs,
499 AVs, or HVs (xV for short in the following) start their life with a
500 reference count of 1. If the reference count of an xV ever drops to 0,
501 then it will be destroyed and its memory made available for reuse.
503 This normally doesn't happen at the Perl level unless a variable is
504 undef'ed or the last variable holding a reference to it is changed or
505 overwritten. At the internal level, however, reference counts can be
506 manipulated with the following macros:
508 int SvREFCNT(SV* sv);
509 SV* SvREFCNT_inc(SV* sv);
510 void SvREFCNT_dec(SV* sv);
512 However, there is one other function which manipulates the reference
513 count of its argument. The C<newRV_inc> function, you will recall,
514 creates a reference to the specified argument. As a side effect,
515 it increments the argument's reference count. If this is not what
516 you want, use C<newRV_noinc> instead.
518 For example, imagine you want to return a reference from an XSUB function.
519 Inside the XSUB routine, you create an SV which initially has a reference
520 count of one. Then you call C<newRV_inc>, passing it the just-created SV.
521 This returns the reference as a new SV, but the reference count of the
522 SV you passed to C<newRV_inc> has been incremented to two. Now you
523 return the reference from the XSUB routine and forget about the SV.
524 But Perl hasn't! Whenever the returned reference is destroyed, the
525 reference count of the original SV is decreased to one and nothing happens.
526 The SV will hang around without any way to access it until Perl itself
527 terminates. This is a memory leak.
529 The correct procedure, then, is to use C<newRV_noinc> instead of
530 C<newRV_inc>. Then, if and when the last reference is destroyed,
531 the reference count of the SV will go to zero and it will be destroyed,
532 stopping any memory leak.
534 There are some convenience functions available that can help with the
535 destruction of xVs. These functions introduce the concept of "mortality".
536 An xV that is mortal has had its reference count marked to be decremented,
537 but not actually decremented, until "a short time later". Generally the
538 term "short time later" means a single Perl statement, such as a call to
539 an XSUB function. The actual determinant for when mortal xVs have their
540 reference count decremented depends on two macros, SAVETMPS and FREETMPS.
541 See L<perlcall> and L<perlxs> for more details on these macros.
543 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
544 However, if you mortalize a variable twice, the reference count will
545 later be decremented twice.
547 You should be careful about creating mortal variables. Strange things
548 can happen if you make the same value mortal within multiple contexts,
549 or if you make a variable mortal multiple times.
551 To create a mortal variable, use the functions:
555 SV* sv_mortalcopy(SV*)
557 The first call creates a mortal SV, the second converts an existing
558 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
559 third creates a mortal copy of an existing SV.
561 The mortal routines are not just for SVs -- AVs and HVs can be
562 made mortal by passing their address (type-casted to C<SV*>) to the
563 C<sv_2mortal> or C<sv_mortalcopy> routines.
565 =head2 Stashes and Globs
567 A "stash" is a hash that contains all of the different objects that
568 are contained within a package. Each key of the stash is a symbol
569 name (shared by all the different types of objects that have the same
570 name), and each value in the hash table is a GV (Glob Value). This GV
571 in turn contains references to the various objects of that name,
572 including (but not limited to) the following:
582 There is a single stash called "defstash" that holds the items that exist
583 in the "main" package. To get at the items in other packages, append the
584 string "::" to the package name. The items in the "Foo" package are in
585 the stash "Foo::" in defstash. The items in the "Bar::Baz" package are
586 in the stash "Baz::" in "Bar::"'s stash.
588 To get the stash pointer for a particular package, use the function:
590 HV* gv_stashpv(char* name, I32 create)
591 HV* gv_stashsv(SV*, I32 create)
593 The first function takes a literal string, the second uses the string stored
594 in the SV. Remember that a stash is just a hash table, so you get back an
595 C<HV*>. The C<create> flag will create a new package if it is set.
597 The name that C<gv_stash*v> wants is the name of the package whose symbol table
598 you want. The default package is called C<main>. If you have multiply nested
599 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
602 Alternately, if you have an SV that is a blessed reference, you can find
603 out the stash pointer by using:
605 HV* SvSTASH(SvRV(SV*));
607 then use the following to get the package name itself:
609 char* HvNAME(HV* stash);
611 If you need to bless or re-bless an object you can use the following
614 SV* sv_bless(SV*, HV* stash)
616 where the first argument, an C<SV*>, must be a reference, and the second
617 argument is a stash. The returned C<SV*> can now be used in the same way
620 For more information on references and blessings, consult L<perlref>.
622 =head2 Double-Typed SVs
624 Scalar variables normally contain only one type of value, an integer,
625 double, pointer, or reference. Perl will automatically convert the
626 actual scalar data from the stored type into the requested type.
628 Some scalar variables contain more than one type of scalar data. For
629 example, the variable C<$!> contains either the numeric value of C<errno>
630 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
632 To force multiple data values into an SV, you must do two things: use the
633 C<sv_set*v> routines to add the additional scalar type, then set a flag
634 so that Perl will believe it contains more than one type of data. The
635 four macros to set the flags are:
642 The particular macro you must use depends on which C<sv_set*v> routine
643 you called first. This is because every C<sv_set*v> routine turns on
644 only the bit for the particular type of data being set, and turns off
647 For example, to create a new Perl variable called "dberror" that contains
648 both the numeric and descriptive string error values, you could use the
652 extern char *dberror_list;
654 SV* sv = perl_get_sv("dberror", TRUE);
655 sv_setiv(sv, (IV) dberror);
656 sv_setpv(sv, dberror_list[dberror]);
659 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
660 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
662 =head2 Magic Variables
664 [This section still under construction. Ignore everything here. Post no
665 bills. Everything not permitted is forbidden.]
667 Any SV may be magical, that is, it has special features that a normal
668 SV does not have. These features are stored in the SV structure in a
669 linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
682 Note this is current as of patchlevel 0, and could change at any time.
684 =head2 Assigning Magic
686 Perl adds magic to an SV using the sv_magic function:
688 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
690 The C<sv> argument is a pointer to the SV that is to acquire a new magical
693 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
694 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
695 it to the beginning of the linked list of magical features. Any prior
696 entry of the same type of magic is deleted. Note that this can be
697 overridden, and multiple instances of the same type of magic can be
698 associated with an SV.
700 The C<name> and C<namlen> arguments are used to associate a string with
701 the magic, typically the name of a variable. C<namlen> is stored in the
702 C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
703 copy of the name is stored in C<mg_ptr> field.
705 The sv_magic function uses C<how> to determine which, if any, predefined
706 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
707 See the "Magic Virtual Table" section below. The C<how> argument is also
708 stored in the C<mg_type> field.
710 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
711 structure. If it is not the same as the C<sv> argument, the reference
712 count of the C<obj> object is incremented. If it is the same, or if
713 the C<how> argument is "#", or if it is a NULL pointer, then C<obj> is
714 merely stored, without the reference count being incremented.
716 There is also a function to add magic to an C<HV>:
718 void hv_magic(HV *hv, GV *gv, int how);
720 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
722 To remove the magic from an SV, call the function sv_unmagic:
724 void sv_unmagic(SV *sv, int type);
726 The C<type> argument should be equal to the C<how> value when the C<SV>
727 was initially made magical.
729 =head2 Magic Virtual Tables
731 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
732 C<MGVTBL>, which is a structure of function pointers and stands for
733 "Magic Virtual Table" to handle the various operations that might be
734 applied to that variable.
736 The C<MGVTBL> has five pointers to the following routine types:
738 int (*svt_get)(SV* sv, MAGIC* mg);
739 int (*svt_set)(SV* sv, MAGIC* mg);
740 U32 (*svt_len)(SV* sv, MAGIC* mg);
741 int (*svt_clear)(SV* sv, MAGIC* mg);
742 int (*svt_free)(SV* sv, MAGIC* mg);
744 This MGVTBL structure is set at compile-time in C<perl.h> and there are
745 currently 19 types (or 21 with overloading turned on). These different
746 structures contain pointers to various routines that perform additional
747 actions depending on which function is being called.
749 Function pointer Action taken
750 ---------------- ------------
751 svt_get Do something after the value of the SV is retrieved.
752 svt_set Do something after the SV is assigned a value.
753 svt_len Report on the SV's length.
754 svt_clear Clear something the SV represents.
755 svt_free Free any extra storage associated with the SV.
757 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
758 to an C<mg_type> of '\0') contains:
760 { magic_get, magic_set, magic_len, 0, 0 }
762 Thus, when an SV is determined to be magical and of type '\0', if a get
763 operation is being performed, the routine C<magic_get> is called. All
764 the various routines for the various magical types begin with C<magic_>.
766 The current kinds of Magic Virtual Tables are:
768 mg_type MGVTBL Type of magical
769 ------- ------ ----------------------------
771 A vtbl_amagic Operator Overloading
772 a vtbl_amagicelem Operator Overloading
773 c 0 Used in Operator Overloading
774 B vtbl_bm Boyer-Moore???
776 e vtbl_envelem %ENV hash element
777 g vtbl_mglob Regexp /g flag???
778 I vtbl_isa @ISA array
779 i vtbl_isaelem @ISA array element
780 L 0 (but sets RMAGICAL) Perl Module/Debugger???
781 l vtbl_dbline Debugger?
782 o vtbl_collxfrm Locale transformation
783 P vtbl_pack Tied Array or Hash
784 p vtbl_packelem Tied Array or Hash element
785 q vtbl_packelem Tied Scalar or Handle
786 S vtbl_sig Signal Hash
787 s vtbl_sigelem Signal Hash element
788 t vtbl_taint Taintedness
791 x vtbl_substr Substring???
792 y vtbl_itervar Shadow "foreach" iterator variable
794 # vtbl_arylen Array Length
795 . vtbl_pos $. scalar variable
796 ~ None Used by certain extensions
798 When an uppercase and lowercase letter both exist in the table, then the
799 uppercase letter is used to represent some kind of composite type (a list
800 or a hash), and the lowercase letter is used to represent an element of
803 The '~' magic type is defined specifically for use by extensions and
804 will not be used by perl itself. Extensions can use ~ magic to 'attach'
805 private information to variables (typically objects). This is especially
806 useful because there is no way for normal perl code to corrupt this
807 private information (unlike using extra elements of a hash object).
809 Note that because multiple extensions may be using ~ magic it is
810 important for extensions to take extra care with it. Typically only
811 using it on objects blessed into the same class as the extension
812 is sufficient. It may also be appropriate to add an I32 'signature'
813 at the top of the private data area and check that.
817 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
819 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
820 If the SV does not have that magical feature, C<NULL> is returned. Also,
821 if the SV is not of type SVt_PVMG, Perl may core dump.
823 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
825 This routine checks to see what types of magic C<sv> has. If the mg_type
826 field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
827 the mg_type field is changed to be the lowercase letter.
829 =head2 Understanding the Magic of Tied Hashes and Arrays
831 Tied hashes and arrays are magical beasts of the 'P' magic type.
832 Proper usage of the array and hash access functions on them requires
833 understanding a few caveats.
835 The C<av_store> function, when given a tied array argument, merely
836 copies the magic of the array onto the value to be "stored", using
837 C<mg_copy>. It may also return NULL, indicating that the value did not
838 actually need to be stored in the array. After a call to C<av_store> on
839 a tied array, the caller will usually need to call C<mg_get(val)> to
840 actually invoke the perl level "STORE" method on the TIEARRAY object. If
841 C<av_store> did return NULL, a call to C<SvREFCNT_dec(val)> will also be
842 usually necessary to avoid a memory leak.
844 The previous paragraph is applicable verbatim to tied hash access using the
845 C<hv_store> and C<hv_store_ent> functions as well.
847 C<av_fetch> and the corresponding hash functions C<hv_fetch> and
848 C<hv_fetch_ent> actually return an undefined mortal value whose magic
849 has been initialized using C<mg_copy>. Note the value so returned does not
850 need to be deallocated, as it is already mortal. But you will need to
851 call C<mg_get()> on the returned value in order to actually invoke the
852 perl level "FETCH" method on the underlying TIE object. Similarly,
853 you may also call C<mg_set()> on the return value after possibly assigning
854 a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
855 method on the TIE object.
857 In other words, the array or hash fetch/store functions don't really
858 fetch and store actual values in the case of tied arrays and hashes. They
859 merely call C<mg_copy> to attach magic to the values that were meant to be
860 "stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
861 do the job of invoking the TIE methods on the underlying objects. Thus
862 the magic mechanism actually implements a kind of lazy access to arrays
865 Currently (as of perl version 5.004), use of the hash and array access
866 functions requires the user to be aware of whether they are operating on
867 "normal" hashes and arrays, or on their tied variants. A simpler API
868 interface that provides transparent access to both tied and normal data
869 types may be available in future versions.
871 You would do well to understand that the TIEARRAY and TIEHASH interfaces
872 are mere sugar to invoke some perl method calls while using the uniform hash
873 and array syntax. The use of this sugar imposes some overhead (typically
874 about two to four extra opcodes per FETCH/STORE operation, in addition to
875 the creation of all the mortal variables required to invoke the methods).
876 This overhead will be comparatively small if the TIE methods are themselves
877 substantial, but if they are only a few statements long, the overhead
878 will not be insignificant.
882 =head2 XSUBs and the Argument Stack
884 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
885 An XSUB routine will have a stack that contains the arguments from the Perl
886 program, and a way to map from the Perl data structures to a C equivalent.
888 The stack arguments are accessible through the C<ST(n)> macro, which returns
889 the C<n>'th stack argument. Argument 0 is the first argument passed in the
890 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
893 Most of the time, output from the C routine can be handled through use of
894 the RETVAL and OUTPUT directives. However, there are some cases where the
895 argument stack is not already long enough to handle all the return values.
896 An example is the POSIX tzname() call, which takes no arguments, but returns
897 two, the local time zone's standard and summer time abbreviations.
899 To handle this situation, the PPCODE directive is used and the stack is
900 extended using the macro:
904 where C<sp> is the stack pointer, and C<num> is the number of elements the
905 stack should be extended by.
907 Now that there is room on the stack, values can be pushed on it using the
908 macros to push IVs, doubles, strings, and SV pointers respectively:
915 And now the Perl program calling C<tzname>, the two values will be assigned
918 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
920 An alternate (and possibly simpler) method to pushing values on the stack is
928 These macros automatically adjust the stack for you, if needed. Thus, you
929 do not need to call C<EXTEND> to extend the stack.
931 For more information, consult L<perlxs> and L<perlxstut>.
933 =head2 Calling Perl Routines from within C Programs
935 There are four routines that can be used to call a Perl subroutine from
936 within a C program. These four are:
938 I32 perl_call_sv(SV*, I32);
939 I32 perl_call_pv(char*, I32);
940 I32 perl_call_method(char*, I32);
941 I32 perl_call_argv(char*, I32, register char**);
943 The routine most often used is C<perl_call_sv>. The C<SV*> argument
944 contains either the name of the Perl subroutine to be called, or a
945 reference to the subroutine. The second argument consists of flags
946 that control the context in which the subroutine is called, whether
947 or not the subroutine is being passed arguments, how errors should be
948 trapped, and how to treat return values.
950 All four routines return the number of arguments that the subroutine returned
953 When using any of these routines (except C<perl_call_argv>), the programmer
954 must manipulate the Perl stack. These include the following macros and
968 For a detailed description of calling conventions from C to Perl,
971 =head2 Memory Allocation
973 It is suggested that you use the version of malloc that is distributed
974 with Perl. It keeps pools of various sizes of unallocated memory in
975 order to satisfy allocation requests more quickly. However, on some
976 platforms, it may cause spurious malloc or free errors.
978 New(x, pointer, number, type);
979 Newc(x, pointer, number, type, cast);
980 Newz(x, pointer, number, type);
982 These three macros are used to initially allocate memory.
984 The first argument C<x> was a "magic cookie" that was used to keep track
985 of who called the macro, to help when debugging memory problems. However,
986 the current code makes no use of this feature (most Perl developers now
987 use run-time memory checkers), so this argument can be any number.
989 The second argument C<pointer> should be the name of a variable that will
990 point to the newly allocated memory.
992 The third and fourth arguments C<number> and C<type> specify how many of
993 the specified type of data structure should be allocated. The argument
994 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
995 should be used if the C<pointer> argument is different from the C<type>
998 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
999 to zero out all the newly allocated memory.
1001 Renew(pointer, number, type);
1002 Renewc(pointer, number, type, cast);
1005 These three macros are used to change a memory buffer size or to free a
1006 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1007 match those of C<New> and C<Newc> with the exception of not needing the
1008 "magic cookie" argument.
1010 Move(source, dest, number, type);
1011 Copy(source, dest, number, type);
1012 Zero(dest, number, type);
1014 These three macros are used to move, copy, or zero out previously allocated
1015 memory. The C<source> and C<dest> arguments point to the source and
1016 destination starting points. Perl will move, copy, or zero out C<number>
1017 instances of the size of the C<type> data structure (using the C<sizeof>
1022 The most recent development releases of Perl has been experimenting with
1023 removing Perl's dependency on the "normal" standard I/O suite and allowing
1024 other stdio implementations to be used. This involves creating a new
1025 abstraction layer that then calls whichever implementation of stdio Perl
1026 was compiled with. All XSUBs should now use the functions in the PerlIO
1027 abstraction layer and not make any assumptions about what kind of stdio
1030 For a complete description of the PerlIO abstraction, consult L<perlapio>.
1032 =head2 Putting a C value on Perl stack
1034 A lot of opcodes (this is an elementary operation in the internal perl
1035 stack machine) put an SV* on the stack. However, as an optimization
1036 the corresponding SV is (usually) not recreated each time. The opcodes
1037 reuse specially assigned SVs (I<target>s) which are (as a corollary)
1038 not constantly freed/created.
1040 Each of the targets is created only once (but see
1041 L<Scratchpads and recursion> below), and when an opcode needs to put
1042 an integer, a double, or a string on stack, it just sets the
1043 corresponding parts of its I<target> and puts the I<target> on stack.
1045 The macro to put this target on stack is C<PUSHTARG>, and it is
1046 directly used in some opcodes, as well as indirectly in zillions of
1047 others, which use it via C<(X)PUSH[pni]>.
1051 The question remains on when the SVs which are I<target>s for opcodes
1052 are created. The answer is that they are created when the current unit --
1053 a subroutine or a file (for opcodes for statements outside of
1054 subroutines) -- is compiled. During this time a special anonymous Perl
1055 array is created, which is called a scratchpad for the current
1058 A scratchpad keeps SVs which are lexicals for the current unit and are
1059 targets for opcodes. One can deduce that an SV lives on a scratchpad
1060 by looking on its flags: lexicals have C<SVs_PADMY> set, and
1061 I<target>s have C<SVs_PADTMP> set.
1063 The correspondence between OPs and I<target>s is not 1-to-1. Different
1064 OPs in the compile tree of the unit can use the same target, if this
1065 would not conflict with the expected life of the temporary.
1067 =head2 Scratchpads and recursion
1069 In fact it is not 100% true that a compiled unit contains a pointer to
1070 the scratchpad AV. In fact it contains a pointer to an AV of
1071 (initially) one element, and this element is the scratchpad AV. Why do
1072 we need an extra level of indirection?
1074 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1075 these can create several execution pointers going into the same
1076 subroutine. For the subroutine-child not write over the temporaries
1077 for the subroutine-parent (lifespan of which covers the call to the
1078 child), the parent and the child should have different
1079 scratchpads. (I<And> the lexicals should be separate anyway!)
1081 So each subroutine is born with an array of scratchpads (of length 1).
1082 On each entry to the subroutine it is checked that the current
1083 depth of the recursion is not more than the length of this array, and
1084 if it is, new scratchpad is created and pushed into the array.
1086 The I<target>s on this scratchpad are C<undef>s, but they are already
1087 marked with correct flags.
1089 =head1 Compiled code
1093 Here we describe the internal form your code is converted to by
1094 Perl. Start with a simple example:
1098 This is converted to a tree similar to this one:
1106 (but slightly more complicated). This tree reflect the way Perl
1107 parsed your code, but has nothing to do with the execution order.
1108 There is an additional "thread" going through the nodes of the tree
1109 which shows the order of execution of the nodes. In our simplified
1110 example above it looks like:
1112 $b ---> $c ---> + ---> $a ---> assign-to
1114 But with the actual compile tree for C<$a = $b + $c> it is different:
1115 some nodes I<optimized away>. As a corollary, though the actual tree
1116 contains more nodes than our simplified example, the execution order
1117 is the same as in our example.
1119 =head2 Examining the tree
1121 If you have your perl compiled for debugging (usually done with C<-D
1122 optimize=-g> on C<Configure> command line), you may examine the
1123 compiled tree by specifying C<-Dx> on the Perl command line. The
1124 output takes several lines per node, and for C<$b+$c> it looks like
1129 FLAGS = (SCALAR,KIDS)
1131 TYPE = null ===> (4)
1133 FLAGS = (SCALAR,KIDS)
1135 3 TYPE = gvsv ===> 4
1141 TYPE = null ===> (5)
1143 FLAGS = (SCALAR,KIDS)
1145 4 TYPE = gvsv ===> 5
1151 This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1152 not optimized away (one per number in the left column). The immediate
1153 children of the given node correspond to C<{}> pairs on the same level
1154 of indentation, thus this listing corresponds to the tree:
1162 The execution order is indicated by C<===E<gt>> marks, thus it is C<3
1163 4 5 6> (node C<6> is not included into above listing), i.e.,
1164 C<gvsv gvsv add whatever>.
1166 =head2 Compile pass 1: check routines
1168 The tree is created by the I<pseudo-compiler> while yacc code feeds it
1169 the constructions it recognizes. Since yacc works bottom-up, so does
1170 the first pass of perl compilation.
1172 What makes this pass interesting for perl developers is that some
1173 optimization may be performed on this pass. This is optimization by
1174 so-called I<check routines>. The correspondence between node names
1175 and corresponding check routines is described in F<opcode.pl> (do not
1176 forget to run C<make regen_headers> if you modify this file).
1178 A check routine is called when the node is fully constructed except
1179 for the execution-order thread. Since at this time there is no
1180 back-links to the currently constructed node, one can do most any
1181 operation to the top-level node, including freeing it and/or creating
1182 new nodes above/below it.
1184 The check routine returns the node which should be inserted into the
1185 tree (if the top-level node was not modified, check routine returns
1188 By convention, check routines have names C<ck_*>. They are usually
1189 called from C<new*OP> subroutines (or C<convert>) (which in turn are
1190 called from F<perly.y>).
1192 =head2 Compile pass 1a: constant folding
1194 Immediately after the check routine is called the returned node is
1195 checked for being compile-time executable. If it is (the value is
1196 judged to be constant) it is immediately executed, and a I<constant>
1197 node with the "return value" of the corresponding subtree is
1198 substituted instead. The subtree is deleted.
1200 If constant folding was not performed, the execution-order thread is
1203 =head2 Compile pass 2: context propagation
1205 When a context for a part of compile tree is known, it is propagated
1206 down through the tree. Aat this time the context can have 5 values
1207 (instead of 2 for runtime context): void, boolean, scalar, list, and
1208 lvalue. In contrast with the pass 1 this pass is processed from top
1209 to bottom: a node's context determines the context for its children.
1211 Additional context-dependent optimizations are performed at this time.
1212 Since at this moment the compile tree contains back-references (via
1213 "thread" pointers), nodes cannot be free()d now. To allow
1214 optimized-away nodes at this stage, such nodes are null()ified instead
1215 of free()ing (i.e. their type is changed to OP_NULL).
1217 =head2 Compile pass 3: peephole optimization
1219 After the compile tree for a subroutine (or for an C<eval> or a file)
1220 is created, an additional pass over the code is performed. This pass
1221 is neither top-down or bottom-up, but in the execution order (with
1222 additional compilications for conditionals). These optimizations are
1223 done in the subroutine peep(). Optimizations performed at this stage
1224 are subject to the same restrictions as in the pass 2.
1228 This is a listing of functions, macros, flags, and variables that may be
1229 useful to extension writers or that may be found while reading other
1240 Clears an array, making it empty. Does not free the memory used by the
1243 void av_clear _((AV* ar));
1247 Pre-extend an array. The C<key> is the index to which the array should be
1250 void av_extend _((AV* ar, I32 key));
1254 Returns the SV at the specified index in the array. The C<key> is the
1255 index. If C<lval> is set then the fetch will be part of a store. Check
1256 that the return value is non-null before dereferencing it to a C<SV*>.
1258 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1259 information on how to use this function on tied arrays.
1261 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1265 Returns the highest index in the array. Returns -1 if the array is empty.
1267 I32 av_len _((AV* ar));
1271 Creates a new AV and populates it with a list of SVs. The SVs are copied
1272 into the array, so they may be freed after the call to av_make. The new AV
1273 will have a reference count of 1.
1275 AV* av_make _((I32 size, SV** svp));
1279 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1282 SV* av_pop _((AV* ar));
1286 Pushes an SV onto the end of the array. The array will grow automatically
1287 to accommodate the addition.
1289 void av_push _((AV* ar, SV* val));
1293 Shifts an SV off the beginning of the array.
1295 SV* av_shift _((AV* ar));
1299 Stores an SV in an array. The array index is specified as C<key>. The
1300 return value will be NULL if the operation failed or if the value did not
1301 need to be actually stored within the array (as in the case of tied arrays).
1302 Otherwise it can be dereferenced to get the original C<SV*>. Note that the
1303 caller is responsible for suitably incrementing the reference count of C<val>
1304 before the call, and decrementing it if the function returned NULL.
1306 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1307 information on how to use this function on tied arrays.
1309 SV** av_store _((AV* ar, I32 key, SV* val));
1313 Undefines the array. Frees the memory used by the array itself.
1315 void av_undef _((AV* ar));
1319 Unshift the given number of C<undef> values onto the beginning of the
1320 array. The array will grow automatically to accommodate the addition.
1321 You must then use C<av_store> to assign values to these new elements.
1323 void av_unshift _((AV* ar, I32 num));
1327 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1328 constructor. This is always a C<char*>. See C<THIS> and
1329 L<perlxs/"Using XS With C++">.
1333 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1334 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1335 the type. May fail on overlapping copies. See also C<Move>.
1337 (void) Copy( s, d, n, t );
1341 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1342 function the same way you use the C C<printf> function. See C<warn>.
1346 Returns the stash of the CV.
1348 HV * CvSTASH( SV* sv )
1352 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1353 boolean which indicates whether subs are being single-stepped.
1354 Single-stepping is automatically turned on after every step. This is the C
1355 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1359 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1360 the SV which holds the name of the sub being debugged. This is the C
1361 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1362 The sub name can be found by
1364 SvPV( GvSV( DBsub ), na )
1368 Trace variable used when Perl is run in debugging mode, with the B<-d>
1369 switch. This is the C variable which corresponds to Perl's $DB::trace
1370 variable. See C<DBsingle>.
1374 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1379 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1383 The C variable which corresponds to Perl's $^W warning variable.
1387 Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
1391 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1392 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1393 to indicate the number of items on the stack.
1397 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1398 handled automatically by C<xsubpp>.
1402 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1403 handled automatically by C<xsubpp>.
1407 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1413 Used to extend the argument stack for an XSUB's return values.
1415 EXTEND( sp, int x );
1419 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1426 Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
1430 Indicates that arguments returned from a callback should be discarded. See
1435 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1439 A backward-compatible version of C<GIMME_V> which can only return
1440 C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
1444 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
1445 C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
1446 context, respectively.
1450 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1454 Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
1458 Used to indicate void context. See C<GIMME_V> and L<perlcall>.
1462 Returns the glob with the given C<name> and a defined subroutine or
1463 C<NULL>. The glob lives in the given C<stash>, or in the stashes
1464 accessable via @ISA and @<UNIVERSAL>.
1466 The argument C<level> should be either 0 or -1. If C<level==0>, as a
1467 side-effect creates a glob with the given C<name> in the given
1468 C<stash> which in the case of success contains an alias for the
1469 subroutine, and sets up caching info for this glob. Similarly for all
1470 the searched stashes.
1472 This function grants C<"SUPER"> token as a postfix of the stash name.
1474 The GV returned from C<gv_fetchmeth> may be a method cache entry,
1475 which is not visible to Perl code. So when calling C<perl_call_sv>,
1476 you should not use the GV directly; instead, you should use the
1477 method's CV, which can be obtained from the GV with the C<GvCV> macro.
1479 GV* gv_fetchmeth _((HV* stash, char* name, STRLEN len, I32 level));
1481 =item gv_fetchmethod
1483 =item gv_fetchmethod_autoload
1485 Returns the glob which contains the subroutine to call to invoke the
1486 method on the C<stash>. In fact in the presense of autoloading this may
1487 be the glob for "AUTOLOAD". In this case the corresponding variable
1488 $AUTOLOAD is already setup.
1490 The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
1491 lookup is performed if the given method is not present: non-zero means
1492 yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
1493 C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
1494 non-zero C<autoload> parameter.
1496 These functions grant C<"SUPER"> token as a prefix of the method name.
1498 Note that if you want to keep the returned glob for a long time, you
1499 need to check for it being "AUTOLOAD", since at the later time the call
1500 may load a different subroutine due to $AUTOLOAD changing its value.
1501 Use the glob created via a side effect to do this.
1503 These functions have the same side-effects and as C<gv_fetchmeth> with
1504 C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
1505 The warning against passing the GV returned by C<gv_fetchmeth> to
1506 C<perl_call_sv> apply equally to these functions.
1508 GV* gv_fetchmethod _((HV* stash, char* name));
1509 GV* gv_fetchmethod_autoload _((HV* stash, char* name,
1514 Returns a pointer to the stash for a specified package. If C<create> is set
1515 then the package will be created if it does not already exist. If C<create>
1516 is not set and the package does not exist then NULL is returned.
1518 HV* gv_stashpv _((char* name, I32 create));
1522 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1524 HV* gv_stashsv _((SV* sv, I32 create));
1528 Return the SV from the GV.
1532 This flag, used in the length slot of hash entries and magic
1533 structures, specifies the structure contains a C<SV*> pointer where a
1534 C<char*> pointer is to be expected. (For information only--not to be used).
1538 Returns the computed hash (type C<U32>) stored in the hash entry.
1544 Returns the actual pointer stored in the key slot of the hash entry.
1545 The pointer may be either C<char*> or C<SV*>, depending on the value of
1546 C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
1547 are usually preferable for finding the value of a key.
1553 If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
1554 holds an C<SV*> key. Otherwise, holds the actual length of the key.
1555 Can be assigned to. The C<HePV()> macro is usually preferable for finding
1562 Returns the key slot of the hash entry as a C<char*> value, doing any
1563 necessary dereferencing of possibly C<SV*> keys. The length of
1564 the string is placed in C<len> (this is a macro, so do I<not> use
1565 C<&len>). If you do not care about what the length of the key is,
1566 you may use the global variable C<na>. Remember though, that hash
1567 keys in perl are free to contain embedded nulls, so using C<strlen()>
1568 or similar is not a good way to find the length of hash keys.
1569 This is very similar to the C<SvPV()> macro described elsewhere in
1572 HePV(HE* he, STRLEN len)
1576 Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
1577 does not contain an C<SV*> key.
1583 Returns the key as an C<SV*>. Will create and return a temporary
1584 mortal C<SV*> if the hash entry contains only a C<char*> key.
1586 HeSVKEY_force(HE* he)
1590 Sets the key to a given C<SV*>, taking care to set the appropriate flags
1591 to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
1593 HeSVKEY_set(HE* he, SV* sv)
1597 Returns the value slot (type C<SV*>) stored in the hash entry.
1603 Clears a hash, making it empty.
1605 void hv_clear _((HV* tb));
1607 =item hv_delayfree_ent
1609 Releases a hash entry, such as while iterating though the hash, but
1610 delays actual freeing of key and value until the end of the current
1611 statement (or thereabouts) with C<sv_2mortal>. See C<hv_iternext>
1614 void hv_delayfree_ent _((HV* hv, HE* entry));
1618 Deletes a key/value pair in the hash. The value SV is removed from the hash
1619 and returned to the caller. The C<klen> is the length of the key. The
1620 C<flags> value will normally be zero; if set to G_DISCARD then NULL will be
1623 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1627 Deletes a key/value pair in the hash. The value SV is removed from the hash
1628 and returned to the caller. The C<flags> value will normally be zero; if set
1629 to G_DISCARD then NULL will be returned. C<hash> can be a valid precomputed
1630 hash value, or 0 to ask for it to be computed.
1632 SV* hv_delete_ent _((HV* tb, SV* key, I32 flags, U32 hash));
1636 Returns a boolean indicating whether the specified hash key exists. The
1637 C<klen> is the length of the key.
1639 bool hv_exists _((HV* tb, char* key, U32 klen));
1643 Returns a boolean indicating whether the specified hash key exists. C<hash>
1644 can be a valid precomputed hash value, or 0 to ask for it to be computed.
1646 bool hv_exists_ent _((HV* tb, SV* key, U32 hash));
1650 Returns the SV which corresponds to the specified key in the hash. The
1651 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1652 part of a store. Check that the return value is non-null before
1653 dereferencing it to a C<SV*>.
1655 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1656 information on how to use this function on tied hashes.
1658 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1662 Returns the hash entry which corresponds to the specified key in the hash.
1663 C<hash> must be a valid precomputed hash number for the given C<key>, or
1664 0 if you want the function to compute it. IF C<lval> is set then the
1665 fetch will be part of a store. Make sure the return value is non-null
1666 before accessing it. The return value when C<tb> is a tied hash
1667 is a pointer to a static location, so be sure to make a copy of the
1668 structure if you need to store it somewhere.
1670 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1671 information on how to use this function on tied hashes.
1673 HE* hv_fetch_ent _((HV* tb, SV* key, I32 lval, U32 hash));
1677 Releases a hash entry, such as while iterating though the hash. See
1678 C<hv_iternext> and C<hv_delayfree_ent>.
1680 void hv_free_ent _((HV* hv, HE* entry));
1684 Prepares a starting point to traverse a hash table.
1686 I32 hv_iterinit _((HV* tb));
1690 Returns the key from the current position of the hash iterator. See
1693 char* hv_iterkey _((HE* entry, I32* retlen));
1697 Returns the key as an C<SV*> from the current position of the hash
1698 iterator. The return value will always be a mortal copy of the
1699 key. Also see C<hv_iterinit>.
1701 SV* hv_iterkeysv _((HE* entry));
1705 Returns entries from a hash iterator. See C<hv_iterinit>.
1707 HE* hv_iternext _((HV* tb));
1711 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1714 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1718 Returns the value from the current position of the hash iterator. See
1721 SV* hv_iterval _((HV* tb, HE* entry));
1725 Adds magic to a hash. See C<sv_magic>.
1727 void hv_magic _((HV* hv, GV* gv, int how));
1731 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1733 char *HvNAME (HV* stash)
1737 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1738 the length of the key. The C<hash> parameter is the precomputed hash
1739 value; if it is zero then Perl will compute it. The return value will be
1740 NULL if the operation failed or if the value did not need to be actually
1741 stored within the hash (as in the case of tied hashes). Otherwise it can
1742 be dereferenced to get the original C<SV*>. Note that the caller is
1743 responsible for suitably incrementing the reference count of C<val>
1744 before the call, and decrementing it if the function returned NULL.
1746 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1747 information on how to use this function on tied hashes.
1749 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1753 Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
1754 parameter is the precomputed hash value; if it is zero then Perl will
1755 compute it. The return value is the new hash entry so created. It will be
1756 NULL if the operation failed or if the value did not need to be actually
1757 stored within the hash (as in the case of tied hashes). Otherwise the
1758 contents of the return value can be accessed using the C<He???> macros
1759 described here. Note that the caller is responsible for suitably
1760 incrementing the reference count of C<val> before the call, and decrementing
1761 it if the function returned NULL.
1763 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1764 information on how to use this function on tied hashes.
1766 HE* hv_store_ent _((HV* tb, SV* key, SV* val, U32 hash));
1772 void hv_undef _((HV* tb));
1776 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
1779 int isALNUM (char c)
1783 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
1786 int isALPHA (char c)
1790 Returns a boolean indicating whether the C C<char> is an ascii digit.
1792 int isDIGIT (char c)
1796 Returns a boolean indicating whether the C C<char> is a lowercase character.
1798 int isLOWER (char c)
1802 Returns a boolean indicating whether the C C<char> is whitespace.
1804 int isSPACE (char c)
1808 Returns a boolean indicating whether the C C<char> is an uppercase character.
1810 int isUPPER (char c)
1814 Variable which is setup by C<xsubpp> to indicate the number of items on the
1815 stack. See L<perlxs/"Variable-length Parameter Lists">.
1819 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1820 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
1824 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1830 Stack marker variable for the XSUB. See C<dMARK>.
1834 Clear something magical that the SV represents. See C<sv_magic>.
1836 int mg_clear _((SV* sv));
1840 Copies the magic from one SV to another. See C<sv_magic>.
1842 int mg_copy _((SV *, SV *, char *, STRLEN));
1846 Finds the magic pointer for type matching the SV. See C<sv_magic>.
1848 MAGIC* mg_find _((SV* sv, int type));
1852 Free any magic storage used by the SV. See C<sv_magic>.
1854 int mg_free _((SV* sv));
1858 Do magic after a value is retrieved from the SV. See C<sv_magic>.
1860 int mg_get _((SV* sv));
1864 Report on the SV's length. See C<sv_magic>.
1866 U32 mg_len _((SV* sv));
1870 Turns on the magical status of an SV. See C<sv_magic>.
1872 void mg_magical _((SV* sv));
1876 Do magic after a value is assigned to the SV. See C<sv_magic>.
1878 int mg_set _((SV* sv));
1882 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
1883 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1884 the type. Can do overlapping moves. See also C<Copy>.
1886 (void) Move( s, d, n, t );
1890 A variable which may be used with C<SvPV> to tell Perl to calculate the
1895 The XSUB-writer's interface to the C C<malloc> function.
1897 void * New( x, void *ptr, int size, type )
1901 The XSUB-writer's interface to the C C<malloc> function, with cast.
1903 void * Newc( x, void *ptr, int size, type, cast )
1907 The XSUB-writer's interface to the C C<malloc> function. The allocated
1908 memory is zeroed with C<memzero>.
1910 void * Newz( x, void *ptr, int size, type )
1914 Creates a new AV. The reference count is set to 1.
1916 AV* newAV _((void));
1920 Creates a new HV. The reference count is set to 1.
1922 HV* newHV _((void));
1926 Creates an RV wrapper for an SV. The reference count for the original SV is
1929 SV* newRV_inc _((SV* ref));
1931 For historical reasons, "newRV" is a synonym for "newRV_inc".
1935 Creates an RV wrapper for an SV. The reference count for the original
1936 SV is B<not> incremented.
1938 SV* newRV_noinc _((SV* ref));
1942 Creates a new SV. The C<len> parameter indicates the number of bytes of
1943 preallocated string space the SV should have. The reference count for the
1946 SV* newSV _((STRLEN len));
1950 Creates a new SV and copies an integer into it. The reference count for the
1953 SV* newSViv _((IV i));
1957 Creates a new SV and copies a double into it. The reference count for the
1960 SV* newSVnv _((NV i));
1964 Creates a new SV and copies a string into it. The reference count for the
1965 SV is set to 1. If C<len> is zero then Perl will compute the length.
1967 SV* newSVpv _((char* s, STRLEN len));
1971 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
1972 it will be upgraded to one. If C<classname> is non-null then the new SV will
1973 be blessed in the specified package. The new SV is returned and its
1974 reference count is 1.
1976 SV* newSVrv _((SV* rv, char* classname));
1980 Creates a new SV which is an exact duplicate of the original SV.
1982 SV* newSVsv _((SV* old));
1986 Used by C<xsubpp> to hook up XSUBs as Perl subs.
1990 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
1999 Null character pointer.
2015 The original stack mark for the XSUB. See C<dORIGMARK>.
2019 Allocates a new Perl interpreter. See L<perlembed>.
2021 =item perl_call_argv
2023 Performs a callback to the specified Perl sub. See L<perlcall>.
2025 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
2027 =item perl_call_method
2029 Performs a callback to the specified Perl method. The blessed object must
2030 be on the stack. See L<perlcall>.
2032 I32 perl_call_method _((char* methname, I32 flags));
2036 Performs a callback to the specified Perl sub. See L<perlcall>.
2038 I32 perl_call_pv _((char* subname, I32 flags));
2042 Performs a callback to the Perl sub whose name is in the SV. See
2045 I32 perl_call_sv _((SV* sv, I32 flags));
2047 =item perl_construct
2049 Initializes a new Perl interpreter. See L<perlembed>.
2053 Shuts down a Perl interpreter. See L<perlembed>.
2057 Tells Perl to C<eval> the string in the SV.
2059 I32 perl_eval_sv _((SV* sv, I32 flags));
2063 Tells Perl to C<eval> the given string and return an SV* result.
2065 SV* perl_eval_pv _((char* p, I32 croak_on_error));
2069 Releases a Perl interpreter. See L<perlembed>.
2073 Returns the AV of the specified Perl array. If C<create> is set and the
2074 Perl variable does not exist then it will be created. If C<create> is not
2075 set and the variable does not exist then NULL is returned.
2077 AV* perl_get_av _((char* name, I32 create));
2081 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
2082 variable does not exist then it will be created. If C<create> is not
2083 set and the variable does not exist then NULL is returned.
2085 CV* perl_get_cv _((char* name, I32 create));
2089 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
2090 variable does not exist then it will be created. If C<create> is not
2091 set and the variable does not exist then NULL is returned.
2093 HV* perl_get_hv _((char* name, I32 create));
2097 Returns the SV of the specified Perl scalar. If C<create> is set and the
2098 Perl variable does not exist then it will be created. If C<create> is not
2099 set and the variable does not exist then NULL is returned.
2101 SV* perl_get_sv _((char* name, I32 create));
2105 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
2107 =item perl_require_pv
2109 Tells Perl to C<require> a module.
2111 void perl_require_pv _((char* pv));
2115 Tells a Perl interpreter to run. See L<perlembed>.
2119 Pops an integer off the stack.
2125 Pops a long off the stack.
2131 Pops a string off the stack.
2137 Pops a double off the stack.
2143 Pops an SV off the stack.
2149 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2155 Push an integer onto the stack. The stack must have room for this element.
2162 Push a double onto the stack. The stack must have room for this element.
2169 Push a string onto the stack. The stack must have room for this element.
2170 The C<len> indicates the length of the string. See C<XPUSHp>.
2172 PUSHp(char *c, int len )
2176 Push an SV onto the stack. The stack must have room for this element. See
2183 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2184 See C<PUSHMARK> and L<perlcall> for other uses.
2190 The XSUB-writer's interface to the C C<realloc> function.
2192 void * Renew( void *ptr, int size, type )
2196 The XSUB-writer's interface to the C C<realloc> function, with cast.
2198 void * Renewc( void *ptr, int size, type, cast )
2202 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
2203 This is always the proper type for the XSUB.
2204 See L<perlxs/"The RETVAL Variable">.
2208 The XSUB-writer's interface to the C C<free> function.
2212 The XSUB-writer's interface to the C C<malloc> function.
2216 The XSUB-writer's interface to the C C<realloc> function.
2220 Copy a string to a safe spot. This does not use an SV.
2222 char* savepv _((char* sv));
2226 Copy a string to a safe spot. The C<len> indicates number of bytes to
2227 copy. This does not use an SV.
2229 char* savepvn _((char* sv, I32 len));
2233 Opening bracket for temporaries on a callback. See C<FREETMPS> and
2240 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2245 Refetch the stack pointer. Used after a callback. See L<perlcall>.
2251 Used to access elements on the XSUB's stack.
2257 Test two strings to see if they are equal. Returns true or false.
2259 int strEQ( char *s1, char *s2 )
2263 Test two strings to see if the first, C<s1>, is greater than or equal to the
2264 second, C<s2>. Returns true or false.
2266 int strGE( char *s1, char *s2 )
2270 Test two strings to see if the first, C<s1>, is greater than the second,
2271 C<s2>. Returns true or false.
2273 int strGT( char *s1, char *s2 )
2277 Test two strings to see if the first, C<s1>, is less than or equal to the
2278 second, C<s2>. Returns true or false.
2280 int strLE( char *s1, char *s2 )
2284 Test two strings to see if the first, C<s1>, is less than the second,
2285 C<s2>. Returns true or false.
2287 int strLT( char *s1, char *s2 )
2291 Test two strings to see if they are different. Returns true or false.
2293 int strNE( char *s1, char *s2 )
2297 Test two strings to see if they are equal. The C<len> parameter indicates
2298 the number of bytes to compare. Returns true or false.
2300 int strnEQ( char *s1, char *s2 )
2304 Test two strings to see if they are different. The C<len> parameter
2305 indicates the number of bytes to compare. Returns true or false.
2307 int strnNE( char *s1, char *s2, int len )
2311 Marks an SV as mortal. The SV will be destroyed when the current context
2314 SV* sv_2mortal _((SV* sv));
2318 Blesses an SV into a specified package. The SV must be an RV. The package
2319 must be designated by its stash (see C<gv_stashpv()>). The reference count
2320 of the SV is unaffected.
2322 SV* sv_bless _((SV* sv, HV* stash));
2326 Concatenates the string onto the end of the string which is in the SV.
2328 void sv_catpv _((SV* sv, char* ptr));
2332 Concatenates the string onto the end of the string which is in the SV. The
2333 C<len> indicates number of bytes to copy.
2335 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
2339 Processes its arguments like C<sprintf> and appends the formatted output
2342 void sv_catpvf _((SV* sv, const char* pat, ...));
2346 Concatenates the string from SV C<ssv> onto the end of the string in SV
2349 void sv_catsv _((SV* dsv, SV* ssv));
2353 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2354 string in C<sv1> is less than, equal to, or greater than the string in
2357 I32 sv_cmp _((SV* sv1, SV* sv2));
2361 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2362 string in C<sv1> is less than, equal to, or greater than the string in
2365 I32 sv_cmp _((SV* sv1, SV* sv2));
2369 Returns the length of the string which is in the SV. See C<SvLEN>.
2375 Set the length of the string which is in the SV. See C<SvCUR>.
2377 SvCUR_set (SV* sv, int val )
2381 Auto-decrement of the value in the SV.
2383 void sv_dec _((SV* sv));
2387 Auto-decrement of the value in the SV.
2389 void sv_dec _((SV* sv));
2393 Returns a pointer to the last character in the string which is in the SV.
2394 See C<SvCUR>. Access the character as
2400 Returns a boolean indicating whether the strings in the two SVs are
2403 I32 sv_eq _((SV* sv1, SV* sv2));
2407 Expands the character buffer in the SV. Calls C<sv_grow> to perform the
2408 expansion if necessary. Returns a pointer to the character buffer.
2410 char * SvGROW( SV* sv, int len )
2414 Expands the character buffer in the SV. This will use C<sv_unref> and will
2415 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2420 Auto-increment of the value in the SV.
2422 void sv_inc _((SV* sv));
2426 Returns a boolean indicating whether the SV contains an integer.
2432 Unsets the IV status of an SV.
2438 Tells an SV that it is an integer.
2444 Tells an SV that it is an integer and disables all other OK bits.
2450 Tells an SV that it is an integer and disables all other OK bits.
2456 Returns a boolean indicating whether the SV contains an integer. Checks the
2457 B<private> setting. Use C<SvIOK>.
2463 Returns a boolean indicating whether the SV is blessed into the specified
2464 class. This does not know how to check for subtype, so it doesn't work in
2465 an inheritance relationship.
2467 int sv_isa _((SV* sv, char* name));
2471 Returns the integer which is in the SV.
2477 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2478 object. If the SV is not an RV, or if the object is not blessed, then this
2481 int sv_isobject _((SV* sv));
2485 Returns the integer which is stored in the SV.
2491 Returns the size of the string buffer in the SV. See C<SvCUR>.
2497 Returns the length of the string in the SV. Use C<SvCUR>.
2499 STRLEN sv_len _((SV* sv));
2503 Returns the length of the string in the SV. Use C<SvCUR>.
2505 STRLEN sv_len _((SV* sv));
2509 Adds magic to an SV.
2511 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2515 Creates a new SV which is a copy of the original SV. The new SV is marked
2518 SV* sv_mortalcopy _((SV* oldsv));
2522 Returns a boolean indicating whether the value is an SV.
2528 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2530 SV* sv_newmortal _((void));
2534 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2538 Returns a boolean indicating whether the SV contains a number, integer or
2545 Unsets the NV/IV status of an SV.
2551 Returns a boolean indicating whether the SV contains a number, integer or
2552 double. Checks the B<private> setting. Use C<SvNIOK>.
2554 int SvNIOKp (SV* SV)
2558 Returns a boolean indicating whether the SV contains a double.
2564 Unsets the NV status of an SV.
2570 Tells an SV that it is a double.
2576 Tells an SV that it is a double and disables all other OK bits.
2582 Tells an SV that it is a double and disables all other OK bits.
2588 Returns a boolean indicating whether the SV contains a double. Checks the
2589 B<private> setting. Use C<SvNOK>.
2595 Returns the double which is stored in the SV.
2597 double SvNV (SV* sv);
2601 Returns the double which is stored in the SV.
2603 double SvNVX (SV* sv);
2607 Returns a boolean indicating whether the SV contains a character string.
2613 Unsets the PV status of an SV.
2619 Tells an SV that it is a string.
2625 Tells an SV that it is a string and disables all other OK bits.
2631 Tells an SV that it is a string and disables all other OK bits.
2637 Returns a boolean indicating whether the SV contains a character string.
2638 Checks the B<private> setting. Use C<SvPOK>.
2644 Returns a pointer to the string in the SV, or a stringified form of the SV
2645 if the SV does not contain a string. If C<len> is C<na> then Perl will
2646 handle the length on its own.
2648 char * SvPV (SV* sv, int len )
2652 Returns a pointer to the string in the SV. The SV must contain a string.
2654 char * SvPVX (SV* sv)
2658 Returns the value of the object's reference count.
2660 int SvREFCNT (SV* sv);
2664 Decrements the reference count of the given SV.
2666 void SvREFCNT_dec (SV* sv)
2670 Increments the reference count of the given SV.
2672 void SvREFCNT_inc (SV* sv)
2676 Tests if the SV is an RV.
2682 Unsets the RV status of an SV.
2688 Tells an SV that it is an RV.
2694 Dereferences an RV to return the SV.
2700 Copies an integer into the given SV.
2702 void sv_setiv _((SV* sv, IV num));
2706 Copies a double into the given SV.
2708 void sv_setnv _((SV* sv, double num));
2712 Copies a string into an SV. The string must be null-terminated.
2714 void sv_setpv _((SV* sv, char* ptr));
2718 Copies a string into an SV. The C<len> parameter indicates the number of
2721 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2725 Processes its arguments like C<sprintf> and sets an SV to the formatted
2728 void sv_setpvf _((SV* sv, const char* pat, ...));
2732 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
2733 argument will be upgraded to an RV. That RV will be modified to point to
2734 the new SV. The C<classname> argument indicates the package for the
2735 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2736 will be returned and will have a reference count of 1.
2738 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2742 Copies a double into a new SV, optionally blessing the SV. The C<rv>
2743 argument will be upgraded to an RV. That RV will be modified to point to
2744 the new SV. The C<classname> argument indicates the package for the
2745 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2746 will be returned and will have a reference count of 1.
2748 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2752 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
2753 argument will be upgraded to an RV. That RV will be modified to point to
2754 the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
2755 into the SV. The C<classname> argument indicates the package for the
2756 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2757 will be returned and will have a reference count of 1.
2759 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2761 Do not use with integral Perl types such as HV, AV, SV, CV, because those
2762 objects will become corrupted by the pointer copy process.
2764 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2768 Copies a string into a new SV, optionally blessing the SV. The length of the
2769 string must be specified with C<n>. The C<rv> argument will be upgraded to
2770 an RV. That RV will be modified to point to the new SV. The C<classname>
2771 argument indicates the package for the blessing. Set C<classname> to
2772 C<Nullch> to avoid the blessing. The new SV will be returned and will have
2773 a reference count of 1.
2775 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2777 Note that C<sv_setref_pv> copies the pointer while this copies the string.
2781 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
2782 The source SV may be destroyed if it is mortal.
2784 void sv_setsv _((SV* dsv, SV* ssv));
2788 Returns the stash of the SV.
2790 HV * SvSTASH (SV* sv)
2794 Integer type flag for scalars. See C<svtype>.
2798 Pointer type flag for scalars. See C<svtype>.
2802 Type flag for arrays. See C<svtype>.
2806 Type flag for code refs. See C<svtype>.
2810 Type flag for hashes. See C<svtype>.
2814 Type flag for blessed scalars. See C<svtype>.
2818 Double type flag for scalars. See C<svtype>.
2822 Returns a boolean indicating whether Perl would evaluate the SV as true or
2823 false, defined or undefined.
2829 Returns the type of the SV. See C<svtype>.
2831 svtype SvTYPE (SV* sv)
2835 An enum of flags for Perl types. These are found in the file B<sv.h> in the
2836 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2840 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
2841 the upgrade if necessary. See C<svtype>.
2843 bool SvUPGRADE _((SV* sv, svtype mt));
2847 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
2851 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
2855 Unsets the RV status of the SV, and decrements the reference count of
2856 whatever was being referenced by the RV. This can almost be thought of
2857 as a reversal of C<newSVrv>. See C<SvROK_off>.
2859 void sv_unref _((SV* sv));
2863 Tells an SV to use C<ptr> to find its string value. Normally the string is
2864 stored inside the SV but sv_usepvn allows the SV to use an outside string.
2865 The C<ptr> should point to memory that was allocated by C<malloc>. The
2866 string length, C<len>, must be supplied. This function will realloc the
2867 memory pointed to by C<ptr>, so that pointer should not be freed or used by
2868 the programmer after giving it to sv_usepvn.
2870 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
2874 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
2878 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
2879 This is always the proper type for the C++ object. See C<CLASS> and
2880 L<perlxs/"Using XS With C++">.
2884 Converts the specified character to lowercase.
2886 int toLOWER (char c)
2890 Converts the specified character to uppercase.
2892 int toUPPER (char c)
2896 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
2897 function the same way you use the C C<printf> function. See C<croak()>.
2901 Push an integer onto the stack, extending the stack if necessary. See
2908 Push a double onto the stack, extending the stack if necessary. See
2915 Push a string onto the stack, extending the stack if necessary. The C<len>
2916 indicates the length of the string. See C<PUSHp>.
2918 XPUSHp(char *c, int len)
2922 Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
2928 Macro to declare an XSUB and its C parameter list. This is handled by
2933 Return from XSUB, indicating number of items on the stack. This is usually
2934 handled by C<xsubpp>.
2938 =item XSRETURN_EMPTY
2940 Return an empty list from an XSUB immediately.
2946 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
2952 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
2958 Return an double from an XSUB immediately. Uses C<XST_mNV>.
2964 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
2966 XSRETURN_PV(char *v);
2968 =item XSRETURN_UNDEF
2970 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
2976 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
2982 Place an integer into the specified position C<i> on the stack. The value is
2983 stored in a new mortal SV.
2985 XST_mIV( int i, IV v );
2989 Place a double into the specified position C<i> on the stack. The value is
2990 stored in a new mortal SV.
2992 XST_mNV( int i, NV v );
2996 Place C<&sv_no> into the specified position C<i> on the stack.
3002 Place a copy of a string into the specified position C<i> on the stack. The
3003 value is stored in a new mortal SV.
3005 XST_mPV( int i, char *v );
3009 Place C<&sv_undef> into the specified position C<i> on the stack.
3011 XST_mUNDEF( int i );
3015 Place C<&sv_yes> into the specified position C<i> on the stack.
3021 The version identifier for an XS module. This is usually handled
3022 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
3024 =item XS_VERSION_BOOTCHECK
3026 Macro to verify that a PM module's $VERSION variable matches the XS module's
3027 C<XS_VERSION> variable. This is usually handled automatically by
3028 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
3032 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
3033 destination, C<n> is the number of items, and C<t> is the type.
3035 (void) Zero( d, n, t );
3041 Jeff Okamoto <F<okamoto@corp.hp.com>>
3043 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
3044 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
3045 Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
3047 API Listing by Dean Roehrich <F<roehrich@cray.com>>.
3051 Version 31.8: 1997/5/17