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 magic
769 ------- ------ ----------------------------
770 \0 vtbl_sv Special scalar variable
771 A vtbl_amagic %OVERLOAD hash
772 a vtbl_amagicelem %OVERLOAD hash element
773 c (none) Holds overload table (AMT) on stash
774 B vtbl_bm Boyer-Moore (fast string search)
776 e vtbl_envelem %ENV hash element
777 f vtbl_fm Formline ('compiled' format)
778 g vtbl_mglob m//g target / study()ed string
779 I vtbl_isa @ISA array
780 i vtbl_isaelem @ISA array element
781 k vtbl_nkeys scalar(keys()) lvalue
782 L (none) Debugger %_<filename
783 l vtbl_dbline Debugger %_<filename element
784 o vtbl_collxfrm Locale transformation
785 P vtbl_pack Tied array or hash
786 p vtbl_packelem Tied array or hash element
787 q vtbl_packelem Tied scalar or handle
789 s vtbl_sigelem %SIG hash element
790 t vtbl_taint Taintedness
791 U vtbl_uvar Available for use by extensions
792 v vtbl_vec vec() lvalue
793 x vtbl_substr substr() lvalue
794 y vtbl_defelem Shadow "foreach" iterator variable /
795 smart parameter vivification
796 * vtbl_glob GV (typeglob)
797 # vtbl_arylen Array length ($#ary)
798 . vtbl_pos pos() lvalue
799 ~ (none) Available for use by extensions
801 When an uppercase and lowercase letter both exist in the table, then the
802 uppercase letter is used to represent some kind of composite type (a list
803 or a hash), and the lowercase letter is used to represent an element of
806 The '~' and 'U' magic types are defined specifically for use by
807 extensions and will not be used by perl itself. Extensions can use
808 '~' magic to 'attach' private information to variables (typically
809 objects). This is especially useful because there is no way for
810 normal perl code to corrupt this private information (unlike using
811 extra elements of a hash object).
813 Similarly, 'U' magic can be used much like tie() to call a C function
814 any time a scalar's value is used or changed. The C<MAGIC>'s
815 C<mg_ptr> field points to a C<ufuncs> structure:
818 I32 (*uf_val)(IV, SV*);
819 I32 (*uf_set)(IV, SV*);
823 When the SV is read from or written to, the C<uf_val> or C<uf_set>
824 function will be called with C<uf_index> as the first arg and a
825 pointer to the SV as the second.
827 Note that because multiple extensions may be using '~' or 'U' magic,
828 it is important for extensions to take extra care to avoid conflict.
829 Typically only using the magic on objects blessed into the same class
830 as the extension is sufficient. For '~' magic, it may also be
831 appropriate to add an I32 'signature' at the top of the private data
836 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
838 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
839 If the SV does not have that magical feature, C<NULL> is returned. Also,
840 if the SV is not of type SVt_PVMG, Perl may core dump.
842 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
844 This routine checks to see what types of magic C<sv> has. If the mg_type
845 field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
846 the mg_type field is changed to be the lowercase letter.
848 =head2 Understanding the Magic of Tied Hashes and Arrays
850 Tied hashes and arrays are magical beasts of the 'P' magic type.
852 WARNING: As of the 5.004 release, proper usage of the array and hash
853 access functions requires understanding a few caveats. Some
854 of these caveats are actually considered bugs in the API, to be fixed
855 in later releases, and are bracketed with [MAYCHANGE] below. If
856 you find yourself actually applying such information in this section, be
857 aware that the behavior may change in the future, umm, without warning.
859 The C<av_store> function, when given a tied array argument, merely
860 copies the magic of the array onto the value to be "stored", using
861 C<mg_copy>. It may also return NULL, indicating that the value did not
862 actually need to be stored in the array. [MAYCHANGE] After a call to
863 C<av_store> on a tied array, the caller will usually need to call
864 C<mg_set(val)> to actually invoke the perl level "STORE" method on the
865 TIEARRAY object. If C<av_store> did return NULL, a call to
866 C<SvREFCNT_dec(val)> will also be usually necessary to avoid a memory
869 The previous paragraph is applicable verbatim to tied hash access using the
870 C<hv_store> and C<hv_store_ent> functions as well.
872 C<av_fetch> and the corresponding hash functions C<hv_fetch> and
873 C<hv_fetch_ent> actually return an undefined mortal value whose magic
874 has been initialized using C<mg_copy>. Note the value so returned does not
875 need to be deallocated, as it is already mortal. [MAYCHANGE] But you will
876 need to call C<mg_get()> on the returned value in order to actually invoke
877 the perl level "FETCH" method on the underlying TIE object. Similarly,
878 you may also call C<mg_set()> on the return value after possibly assigning
879 a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
880 method on the TIE object. [/MAYCHANGE]
883 In other words, the array or hash fetch/store functions don't really
884 fetch and store actual values in the case of tied arrays and hashes. They
885 merely call C<mg_copy> to attach magic to the values that were meant to be
886 "stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
887 do the job of invoking the TIE methods on the underlying objects. Thus
888 the magic mechanism currently implements a kind of lazy access to arrays
891 Currently (as of perl version 5.004), use of the hash and array access
892 functions requires the user to be aware of whether they are operating on
893 "normal" hashes and arrays, or on their tied variants. The API may be
894 changed to provide more transparent access to both tied and normal data
895 types in future versions.
898 You would do well to understand that the TIEARRAY and TIEHASH interfaces
899 are mere sugar to invoke some perl method calls while using the uniform hash
900 and array syntax. The use of this sugar imposes some overhead (typically
901 about two to four extra opcodes per FETCH/STORE operation, in addition to
902 the creation of all the mortal variables required to invoke the methods).
903 This overhead will be comparatively small if the TIE methods are themselves
904 substantial, but if they are only a few statements long, the overhead
905 will not be insignificant.
909 =head2 XSUBs and the Argument Stack
911 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
912 An XSUB routine will have a stack that contains the arguments from the Perl
913 program, and a way to map from the Perl data structures to a C equivalent.
915 The stack arguments are accessible through the C<ST(n)> macro, which returns
916 the C<n>'th stack argument. Argument 0 is the first argument passed in the
917 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
920 Most of the time, output from the C routine can be handled through use of
921 the RETVAL and OUTPUT directives. However, there are some cases where the
922 argument stack is not already long enough to handle all the return values.
923 An example is the POSIX tzname() call, which takes no arguments, but returns
924 two, the local time zone's standard and summer time abbreviations.
926 To handle this situation, the PPCODE directive is used and the stack is
927 extended using the macro:
931 where C<sp> is the stack pointer, and C<num> is the number of elements the
932 stack should be extended by.
934 Now that there is room on the stack, values can be pushed on it using the
935 macros to push IVs, doubles, strings, and SV pointers respectively:
942 And now the Perl program calling C<tzname>, the two values will be assigned
945 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
947 An alternate (and possibly simpler) method to pushing values on the stack is
955 These macros automatically adjust the stack for you, if needed. Thus, you
956 do not need to call C<EXTEND> to extend the stack.
958 For more information, consult L<perlxs> and L<perlxstut>.
960 =head2 Calling Perl Routines from within C Programs
962 There are four routines that can be used to call a Perl subroutine from
963 within a C program. These four are:
965 I32 perl_call_sv(SV*, I32);
966 I32 perl_call_pv(char*, I32);
967 I32 perl_call_method(char*, I32);
968 I32 perl_call_argv(char*, I32, register char**);
970 The routine most often used is C<perl_call_sv>. The C<SV*> argument
971 contains either the name of the Perl subroutine to be called, or a
972 reference to the subroutine. The second argument consists of flags
973 that control the context in which the subroutine is called, whether
974 or not the subroutine is being passed arguments, how errors should be
975 trapped, and how to treat return values.
977 All four routines return the number of arguments that the subroutine returned
980 When using any of these routines (except C<perl_call_argv>), the programmer
981 must manipulate the Perl stack. These include the following macros and
995 For a detailed description of calling conventions from C to Perl,
998 =head2 Memory Allocation
1000 It is suggested that you use the version of malloc that is distributed
1001 with Perl. It keeps pools of various sizes of unallocated memory in
1002 order to satisfy allocation requests more quickly. However, on some
1003 platforms, it may cause spurious malloc or free errors.
1005 New(x, pointer, number, type);
1006 Newc(x, pointer, number, type, cast);
1007 Newz(x, pointer, number, type);
1009 These three macros are used to initially allocate memory.
1011 The first argument C<x> was a "magic cookie" that was used to keep track
1012 of who called the macro, to help when debugging memory problems. However,
1013 the current code makes no use of this feature (most Perl developers now
1014 use run-time memory checkers), so this argument can be any number.
1016 The second argument C<pointer> should be the name of a variable that will
1017 point to the newly allocated memory.
1019 The third and fourth arguments C<number> and C<type> specify how many of
1020 the specified type of data structure should be allocated. The argument
1021 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
1022 should be used if the C<pointer> argument is different from the C<type>
1025 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
1026 to zero out all the newly allocated memory.
1028 Renew(pointer, number, type);
1029 Renewc(pointer, number, type, cast);
1032 These three macros are used to change a memory buffer size or to free a
1033 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1034 match those of C<New> and C<Newc> with the exception of not needing the
1035 "magic cookie" argument.
1037 Move(source, dest, number, type);
1038 Copy(source, dest, number, type);
1039 Zero(dest, number, type);
1041 These three macros are used to move, copy, or zero out previously allocated
1042 memory. The C<source> and C<dest> arguments point to the source and
1043 destination starting points. Perl will move, copy, or zero out C<number>
1044 instances of the size of the C<type> data structure (using the C<sizeof>
1049 The most recent development releases of Perl has been experimenting with
1050 removing Perl's dependency on the "normal" standard I/O suite and allowing
1051 other stdio implementations to be used. This involves creating a new
1052 abstraction layer that then calls whichever implementation of stdio Perl
1053 was compiled with. All XSUBs should now use the functions in the PerlIO
1054 abstraction layer and not make any assumptions about what kind of stdio
1057 For a complete description of the PerlIO abstraction, consult L<perlapio>.
1059 =head2 Putting a C value on Perl stack
1061 A lot of opcodes (this is an elementary operation in the internal perl
1062 stack machine) put an SV* on the stack. However, as an optimization
1063 the corresponding SV is (usually) not recreated each time. The opcodes
1064 reuse specially assigned SVs (I<target>s) which are (as a corollary)
1065 not constantly freed/created.
1067 Each of the targets is created only once (but see
1068 L<Scratchpads and recursion> below), and when an opcode needs to put
1069 an integer, a double, or a string on stack, it just sets the
1070 corresponding parts of its I<target> and puts the I<target> on stack.
1072 The macro to put this target on stack is C<PUSHTARG>, and it is
1073 directly used in some opcodes, as well as indirectly in zillions of
1074 others, which use it via C<(X)PUSH[pni]>.
1078 The question remains on when the SVs which are I<target>s for opcodes
1079 are created. The answer is that they are created when the current unit --
1080 a subroutine or a file (for opcodes for statements outside of
1081 subroutines) -- is compiled. During this time a special anonymous Perl
1082 array is created, which is called a scratchpad for the current
1085 A scratchpad keeps SVs which are lexicals for the current unit and are
1086 targets for opcodes. One can deduce that an SV lives on a scratchpad
1087 by looking on its flags: lexicals have C<SVs_PADMY> set, and
1088 I<target>s have C<SVs_PADTMP> set.
1090 The correspondence between OPs and I<target>s is not 1-to-1. Different
1091 OPs in the compile tree of the unit can use the same target, if this
1092 would not conflict with the expected life of the temporary.
1094 =head2 Scratchpads and recursion
1096 In fact it is not 100% true that a compiled unit contains a pointer to
1097 the scratchpad AV. In fact it contains a pointer to an AV of
1098 (initially) one element, and this element is the scratchpad AV. Why do
1099 we need an extra level of indirection?
1101 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1102 these can create several execution pointers going into the same
1103 subroutine. For the subroutine-child not write over the temporaries
1104 for the subroutine-parent (lifespan of which covers the call to the
1105 child), the parent and the child should have different
1106 scratchpads. (I<And> the lexicals should be separate anyway!)
1108 So each subroutine is born with an array of scratchpads (of length 1).
1109 On each entry to the subroutine it is checked that the current
1110 depth of the recursion is not more than the length of this array, and
1111 if it is, new scratchpad is created and pushed into the array.
1113 The I<target>s on this scratchpad are C<undef>s, but they are already
1114 marked with correct flags.
1116 =head1 Compiled code
1120 Here we describe the internal form your code is converted to by
1121 Perl. Start with a simple example:
1125 This is converted to a tree similar to this one:
1133 (but slightly more complicated). This tree reflect the way Perl
1134 parsed your code, but has nothing to do with the execution order.
1135 There is an additional "thread" going through the nodes of the tree
1136 which shows the order of execution of the nodes. In our simplified
1137 example above it looks like:
1139 $b ---> $c ---> + ---> $a ---> assign-to
1141 But with the actual compile tree for C<$a = $b + $c> it is different:
1142 some nodes I<optimized away>. As a corollary, though the actual tree
1143 contains more nodes than our simplified example, the execution order
1144 is the same as in our example.
1146 =head2 Examining the tree
1148 If you have your perl compiled for debugging (usually done with C<-D
1149 optimize=-g> on C<Configure> command line), you may examine the
1150 compiled tree by specifying C<-Dx> on the Perl command line. The
1151 output takes several lines per node, and for C<$b+$c> it looks like
1156 FLAGS = (SCALAR,KIDS)
1158 TYPE = null ===> (4)
1160 FLAGS = (SCALAR,KIDS)
1162 3 TYPE = gvsv ===> 4
1168 TYPE = null ===> (5)
1170 FLAGS = (SCALAR,KIDS)
1172 4 TYPE = gvsv ===> 5
1178 This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1179 not optimized away (one per number in the left column). The immediate
1180 children of the given node correspond to C<{}> pairs on the same level
1181 of indentation, thus this listing corresponds to the tree:
1189 The execution order is indicated by C<===E<gt>> marks, thus it is C<3
1190 4 5 6> (node C<6> is not included into above listing), i.e.,
1191 C<gvsv gvsv add whatever>.
1193 =head2 Compile pass 1: check routines
1195 The tree is created by the I<pseudo-compiler> while yacc code feeds it
1196 the constructions it recognizes. Since yacc works bottom-up, so does
1197 the first pass of perl compilation.
1199 What makes this pass interesting for perl developers is that some
1200 optimization may be performed on this pass. This is optimization by
1201 so-called I<check routines>. The correspondence between node names
1202 and corresponding check routines is described in F<opcode.pl> (do not
1203 forget to run C<make regen_headers> if you modify this file).
1205 A check routine is called when the node is fully constructed except
1206 for the execution-order thread. Since at this time there is no
1207 back-links to the currently constructed node, one can do most any
1208 operation to the top-level node, including freeing it and/or creating
1209 new nodes above/below it.
1211 The check routine returns the node which should be inserted into the
1212 tree (if the top-level node was not modified, check routine returns
1215 By convention, check routines have names C<ck_*>. They are usually
1216 called from C<new*OP> subroutines (or C<convert>) (which in turn are
1217 called from F<perly.y>).
1219 =head2 Compile pass 1a: constant folding
1221 Immediately after the check routine is called the returned node is
1222 checked for being compile-time executable. If it is (the value is
1223 judged to be constant) it is immediately executed, and a I<constant>
1224 node with the "return value" of the corresponding subtree is
1225 substituted instead. The subtree is deleted.
1227 If constant folding was not performed, the execution-order thread is
1230 =head2 Compile pass 2: context propagation
1232 When a context for a part of compile tree is known, it is propagated
1233 down through the tree. Aat this time the context can have 5 values
1234 (instead of 2 for runtime context): void, boolean, scalar, list, and
1235 lvalue. In contrast with the pass 1 this pass is processed from top
1236 to bottom: a node's context determines the context for its children.
1238 Additional context-dependent optimizations are performed at this time.
1239 Since at this moment the compile tree contains back-references (via
1240 "thread" pointers), nodes cannot be free()d now. To allow
1241 optimized-away nodes at this stage, such nodes are null()ified instead
1242 of free()ing (i.e. their type is changed to OP_NULL).
1244 =head2 Compile pass 3: peephole optimization
1246 After the compile tree for a subroutine (or for an C<eval> or a file)
1247 is created, an additional pass over the code is performed. This pass
1248 is neither top-down or bottom-up, but in the execution order (with
1249 additional compilications for conditionals). These optimizations are
1250 done in the subroutine peep(). Optimizations performed at this stage
1251 are subject to the same restrictions as in the pass 2.
1255 This is a listing of functions, macros, flags, and variables that may be
1256 useful to extension writers or that may be found while reading other
1267 Clears an array, making it empty. Does not free the memory used by the
1270 void av_clear _((AV* ar));
1274 Pre-extend an array. The C<key> is the index to which the array should be
1277 void av_extend _((AV* ar, I32 key));
1281 Returns the SV at the specified index in the array. The C<key> is the
1282 index. If C<lval> is set then the fetch will be part of a store. Check
1283 that the return value is non-null before dereferencing it to a C<SV*>.
1285 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1286 information on how to use this function on tied arrays.
1288 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1292 Returns the highest index in the array. Returns -1 if the array is empty.
1294 I32 av_len _((AV* ar));
1298 Creates a new AV and populates it with a list of SVs. The SVs are copied
1299 into the array, so they may be freed after the call to av_make. The new AV
1300 will have a reference count of 1.
1302 AV* av_make _((I32 size, SV** svp));
1306 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1309 SV* av_pop _((AV* ar));
1313 Pushes an SV onto the end of the array. The array will grow automatically
1314 to accommodate the addition.
1316 void av_push _((AV* ar, SV* val));
1320 Shifts an SV off the beginning of the array.
1322 SV* av_shift _((AV* ar));
1326 Stores an SV in an array. The array index is specified as C<key>. The
1327 return value will be NULL if the operation failed or if the value did not
1328 need to be actually stored within the array (as in the case of tied arrays).
1329 Otherwise it can be dereferenced to get the original C<SV*>. Note that the
1330 caller is responsible for suitably incrementing the reference count of C<val>
1331 before the call, and decrementing it if the function returned NULL.
1333 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1334 information on how to use this function on tied arrays.
1336 SV** av_store _((AV* ar, I32 key, SV* val));
1340 Undefines the array. Frees the memory used by the array itself.
1342 void av_undef _((AV* ar));
1346 Unshift the given number of C<undef> values onto the beginning of the
1347 array. The array will grow automatically to accommodate the addition.
1348 You must then use C<av_store> to assign values to these new elements.
1350 void av_unshift _((AV* ar, I32 num));
1354 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1355 constructor. This is always a C<char*>. See C<THIS> and
1356 L<perlxs/"Using XS With C++">.
1360 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1361 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1362 the type. May fail on overlapping copies. See also C<Move>.
1364 (void) Copy( s, d, n, t );
1368 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1369 function the same way you use the C C<printf> function. See C<warn>.
1373 Returns the stash of the CV.
1375 HV * CvSTASH( SV* sv )
1379 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1380 boolean which indicates whether subs are being single-stepped.
1381 Single-stepping is automatically turned on after every step. This is the C
1382 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1386 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1387 the SV which holds the name of the sub being debugged. This is the C
1388 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1389 The sub name can be found by
1391 SvPV( GvSV( DBsub ), na )
1395 Trace variable used when Perl is run in debugging mode, with the B<-d>
1396 switch. This is the C variable which corresponds to Perl's $DB::trace
1397 variable. See C<DBsingle>.
1401 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1406 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1410 The C variable which corresponds to Perl's $^W warning variable.
1414 Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
1418 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1419 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1420 to indicate the number of items on the stack.
1424 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1425 handled automatically by C<xsubpp>.
1429 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1435 Used to extend the argument stack for an XSUB's return values.
1437 EXTEND( sp, int x );
1441 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1448 Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
1452 Indicates that arguments returned from a callback should be discarded. See
1457 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1461 A backward-compatible version of C<GIMME_V> which can only return
1462 C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
1466 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
1467 C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
1468 context, respectively.
1472 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1476 Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
1480 Used to indicate void context. See C<GIMME_V> and L<perlcall>.
1484 Returns the glob with the given C<name> and a defined subroutine or
1485 C<NULL>. The glob lives in the given C<stash>, or in the stashes
1486 accessable via @ISA and @<UNIVERSAL>.
1488 The argument C<level> should be either 0 or -1. If C<level==0>, as a
1489 side-effect creates a glob with the given C<name> in the given
1490 C<stash> which in the case of success contains an alias for the
1491 subroutine, and sets up caching info for this glob. Similarly for all
1492 the searched stashes.
1494 This function grants C<"SUPER"> token as a postfix of the stash name.
1496 The GV returned from C<gv_fetchmeth> may be a method cache entry,
1497 which is not visible to Perl code. So when calling C<perl_call_sv>,
1498 you should not use the GV directly; instead, you should use the
1499 method's CV, which can be obtained from the GV with the C<GvCV> macro.
1501 GV* gv_fetchmeth _((HV* stash, char* name, STRLEN len, I32 level));
1503 =item gv_fetchmethod
1505 =item gv_fetchmethod_autoload
1507 Returns the glob which contains the subroutine to call to invoke the
1508 method on the C<stash>. In fact in the presense of autoloading this may
1509 be the glob for "AUTOLOAD". In this case the corresponding variable
1510 $AUTOLOAD is already setup.
1512 The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
1513 lookup is performed if the given method is not present: non-zero means
1514 yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
1515 C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
1516 non-zero C<autoload> parameter.
1518 These functions grant C<"SUPER"> token as a prefix of the method name.
1520 Note that if you want to keep the returned glob for a long time, you
1521 need to check for it being "AUTOLOAD", since at the later time the call
1522 may load a different subroutine due to $AUTOLOAD changing its value.
1523 Use the glob created via a side effect to do this.
1525 These functions have the same side-effects and as C<gv_fetchmeth> with
1526 C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
1527 The warning against passing the GV returned by C<gv_fetchmeth> to
1528 C<perl_call_sv> apply equally to these functions.
1530 GV* gv_fetchmethod _((HV* stash, char* name));
1531 GV* gv_fetchmethod_autoload _((HV* stash, char* name,
1536 Returns a pointer to the stash for a specified package. If C<create> is set
1537 then the package will be created if it does not already exist. If C<create>
1538 is not set and the package does not exist then NULL is returned.
1540 HV* gv_stashpv _((char* name, I32 create));
1544 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1546 HV* gv_stashsv _((SV* sv, I32 create));
1550 Return the SV from the GV.
1554 This flag, used in the length slot of hash entries and magic
1555 structures, specifies the structure contains a C<SV*> pointer where a
1556 C<char*> pointer is to be expected. (For information only--not to be used).
1560 Returns the computed hash (type C<U32>) stored in the hash entry.
1566 Returns the actual pointer stored in the key slot of the hash entry.
1567 The pointer may be either C<char*> or C<SV*>, depending on the value of
1568 C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
1569 are usually preferable for finding the value of a key.
1575 If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
1576 holds an C<SV*> key. Otherwise, holds the actual length of the key.
1577 Can be assigned to. The C<HePV()> macro is usually preferable for finding
1584 Returns the key slot of the hash entry as a C<char*> value, doing any
1585 necessary dereferencing of possibly C<SV*> keys. The length of
1586 the string is placed in C<len> (this is a macro, so do I<not> use
1587 C<&len>). If you do not care about what the length of the key is,
1588 you may use the global variable C<na>. Remember though, that hash
1589 keys in perl are free to contain embedded nulls, so using C<strlen()>
1590 or similar is not a good way to find the length of hash keys.
1591 This is very similar to the C<SvPV()> macro described elsewhere in
1594 HePV(HE* he, STRLEN len)
1598 Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
1599 does not contain an C<SV*> key.
1605 Returns the key as an C<SV*>. Will create and return a temporary
1606 mortal C<SV*> if the hash entry contains only a C<char*> key.
1608 HeSVKEY_force(HE* he)
1612 Sets the key to a given C<SV*>, taking care to set the appropriate flags
1613 to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
1615 HeSVKEY_set(HE* he, SV* sv)
1619 Returns the value slot (type C<SV*>) stored in the hash entry.
1625 Clears a hash, making it empty.
1627 void hv_clear _((HV* tb));
1629 =item hv_delayfree_ent
1631 Releases a hash entry, such as while iterating though the hash, but
1632 delays actual freeing of key and value until the end of the current
1633 statement (or thereabouts) with C<sv_2mortal>. See C<hv_iternext>
1636 void hv_delayfree_ent _((HV* hv, HE* entry));
1640 Deletes a key/value pair in the hash. The value SV is removed from the hash
1641 and returned to the caller. The C<klen> is the length of the key. The
1642 C<flags> value will normally be zero; if set to G_DISCARD then NULL will be
1645 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1649 Deletes a key/value pair in the hash. The value SV is removed from the hash
1650 and returned to the caller. The C<flags> value will normally be zero; if set
1651 to G_DISCARD then NULL will be returned. C<hash> can be a valid precomputed
1652 hash value, or 0 to ask for it to be computed.
1654 SV* hv_delete_ent _((HV* tb, SV* key, I32 flags, U32 hash));
1658 Returns a boolean indicating whether the specified hash key exists. The
1659 C<klen> is the length of the key.
1661 bool hv_exists _((HV* tb, char* key, U32 klen));
1665 Returns a boolean indicating whether the specified hash key exists. C<hash>
1666 can be a valid precomputed hash value, or 0 to ask for it to be computed.
1668 bool hv_exists_ent _((HV* tb, SV* key, U32 hash));
1672 Returns the SV which corresponds to the specified key in the hash. The
1673 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1674 part of a store. Check that the return value is non-null before
1675 dereferencing it to a C<SV*>.
1677 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1678 information on how to use this function on tied hashes.
1680 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1684 Returns the hash entry which corresponds to the specified key in the hash.
1685 C<hash> must be a valid precomputed hash number for the given C<key>, or
1686 0 if you want the function to compute it. IF C<lval> is set then the
1687 fetch will be part of a store. Make sure the return value is non-null
1688 before accessing it. The return value when C<tb> is a tied hash
1689 is a pointer to a static location, so be sure to make a copy of the
1690 structure if you need to store it somewhere.
1692 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1693 information on how to use this function on tied hashes.
1695 HE* hv_fetch_ent _((HV* tb, SV* key, I32 lval, U32 hash));
1699 Releases a hash entry, such as while iterating though the hash. See
1700 C<hv_iternext> and C<hv_delayfree_ent>.
1702 void hv_free_ent _((HV* hv, HE* entry));
1706 Prepares a starting point to traverse a hash table.
1708 I32 hv_iterinit _((HV* tb));
1712 Returns the key from the current position of the hash iterator. See
1715 char* hv_iterkey _((HE* entry, I32* retlen));
1719 Returns the key as an C<SV*> from the current position of the hash
1720 iterator. The return value will always be a mortal copy of the
1721 key. Also see C<hv_iterinit>.
1723 SV* hv_iterkeysv _((HE* entry));
1727 Returns entries from a hash iterator. See C<hv_iterinit>.
1729 HE* hv_iternext _((HV* tb));
1733 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1736 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1740 Returns the value from the current position of the hash iterator. See
1743 SV* hv_iterval _((HV* tb, HE* entry));
1747 Adds magic to a hash. See C<sv_magic>.
1749 void hv_magic _((HV* hv, GV* gv, int how));
1753 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1755 char *HvNAME (HV* stash)
1759 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1760 the length of the key. The C<hash> parameter is the precomputed hash
1761 value; if it is zero then Perl will compute it. The return value will be
1762 NULL if the operation failed or if the value did not need to be actually
1763 stored within the hash (as in the case of tied hashes). Otherwise it can
1764 be dereferenced to get the original C<SV*>. Note that the caller is
1765 responsible for suitably incrementing the reference count of C<val>
1766 before the call, and decrementing it if the function returned NULL.
1768 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1769 information on how to use this function on tied hashes.
1771 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1775 Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
1776 parameter is the precomputed hash value; if it is zero then Perl will
1777 compute it. The return value is the new hash entry so created. It will be
1778 NULL if the operation failed or if the value did not need to be actually
1779 stored within the hash (as in the case of tied hashes). Otherwise the
1780 contents of the return value can be accessed using the C<He???> macros
1781 described here. Note that the caller is responsible for suitably
1782 incrementing the reference count of C<val> before the call, and decrementing
1783 it if the function returned NULL.
1785 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1786 information on how to use this function on tied hashes.
1788 HE* hv_store_ent _((HV* tb, SV* key, SV* val, U32 hash));
1794 void hv_undef _((HV* tb));
1798 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
1801 int isALNUM (char c)
1805 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
1808 int isALPHA (char c)
1812 Returns a boolean indicating whether the C C<char> is an ascii digit.
1814 int isDIGIT (char c)
1818 Returns a boolean indicating whether the C C<char> is a lowercase character.
1820 int isLOWER (char c)
1824 Returns a boolean indicating whether the C C<char> is whitespace.
1826 int isSPACE (char c)
1830 Returns a boolean indicating whether the C C<char> is an uppercase character.
1832 int isUPPER (char c)
1836 Variable which is setup by C<xsubpp> to indicate the number of items on the
1837 stack. See L<perlxs/"Variable-length Parameter Lists">.
1841 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1842 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
1846 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1852 Stack marker variable for the XSUB. See C<dMARK>.
1856 Clear something magical that the SV represents. See C<sv_magic>.
1858 int mg_clear _((SV* sv));
1862 Copies the magic from one SV to another. See C<sv_magic>.
1864 int mg_copy _((SV *, SV *, char *, STRLEN));
1868 Finds the magic pointer for type matching the SV. See C<sv_magic>.
1870 MAGIC* mg_find _((SV* sv, int type));
1874 Free any magic storage used by the SV. See C<sv_magic>.
1876 int mg_free _((SV* sv));
1880 Do magic after a value is retrieved from the SV. See C<sv_magic>.
1882 int mg_get _((SV* sv));
1886 Report on the SV's length. See C<sv_magic>.
1888 U32 mg_len _((SV* sv));
1892 Turns on the magical status of an SV. See C<sv_magic>.
1894 void mg_magical _((SV* sv));
1898 Do magic after a value is assigned to the SV. See C<sv_magic>.
1900 int mg_set _((SV* sv));
1904 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
1905 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1906 the type. Can do overlapping moves. See also C<Copy>.
1908 (void) Move( s, d, n, t );
1912 A variable which may be used with C<SvPV> to tell Perl to calculate the
1917 The XSUB-writer's interface to the C C<malloc> function.
1919 void * New( x, void *ptr, int size, type )
1923 The XSUB-writer's interface to the C C<malloc> function, with cast.
1925 void * Newc( x, void *ptr, int size, type, cast )
1929 The XSUB-writer's interface to the C C<malloc> function. The allocated
1930 memory is zeroed with C<memzero>.
1932 void * Newz( x, void *ptr, int size, type )
1936 Creates a new AV. The reference count is set to 1.
1938 AV* newAV _((void));
1942 Creates a new HV. The reference count is set to 1.
1944 HV* newHV _((void));
1948 Creates an RV wrapper for an SV. The reference count for the original SV is
1951 SV* newRV_inc _((SV* ref));
1953 For historical reasons, "newRV" is a synonym for "newRV_inc".
1957 Creates an RV wrapper for an SV. The reference count for the original
1958 SV is B<not> incremented.
1960 SV* newRV_noinc _((SV* ref));
1964 Creates a new SV. The C<len> parameter indicates the number of bytes of
1965 preallocated string space the SV should have. The reference count for the
1968 SV* newSV _((STRLEN len));
1972 Creates a new SV and copies an integer into it. The reference count for the
1975 SV* newSViv _((IV i));
1979 Creates a new SV and copies a double into it. The reference count for the
1982 SV* newSVnv _((NV i));
1986 Creates a new SV and copies a string into it. The reference count for the
1987 SV is set to 1. If C<len> is zero then Perl will compute the length.
1989 SV* newSVpv _((char* s, STRLEN len));
1993 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
1994 it will be upgraded to one. If C<classname> is non-null then the new SV will
1995 be blessed in the specified package. The new SV is returned and its
1996 reference count is 1.
1998 SV* newSVrv _((SV* rv, char* classname));
2002 Creates a new SV which is an exact duplicate of the original SV.
2004 SV* newSVsv _((SV* old));
2008 Used by C<xsubpp> to hook up XSUBs as Perl subs.
2012 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
2021 Null character pointer.
2037 The original stack mark for the XSUB. See C<dORIGMARK>.
2041 Allocates a new Perl interpreter. See L<perlembed>.
2043 =item perl_call_argv
2045 Performs a callback to the specified Perl sub. See L<perlcall>.
2047 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
2049 =item perl_call_method
2051 Performs a callback to the specified Perl method. The blessed object must
2052 be on the stack. See L<perlcall>.
2054 I32 perl_call_method _((char* methname, I32 flags));
2058 Performs a callback to the specified Perl sub. See L<perlcall>.
2060 I32 perl_call_pv _((char* subname, I32 flags));
2064 Performs a callback to the Perl sub whose name is in the SV. See
2067 I32 perl_call_sv _((SV* sv, I32 flags));
2069 =item perl_construct
2071 Initializes a new Perl interpreter. See L<perlembed>.
2075 Shuts down a Perl interpreter. See L<perlembed>.
2079 Tells Perl to C<eval> the string in the SV.
2081 I32 perl_eval_sv _((SV* sv, I32 flags));
2085 Tells Perl to C<eval> the given string and return an SV* result.
2087 SV* perl_eval_pv _((char* p, I32 croak_on_error));
2091 Releases a Perl interpreter. See L<perlembed>.
2095 Returns the AV of the specified Perl array. If C<create> is set and the
2096 Perl variable does not exist then it will be created. If C<create> is not
2097 set and the variable does not exist then NULL is returned.
2099 AV* perl_get_av _((char* name, I32 create));
2103 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
2104 variable does not exist then it will be created. If C<create> is not
2105 set and the variable does not exist then NULL is returned.
2107 CV* perl_get_cv _((char* name, I32 create));
2111 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
2112 variable does not exist then it will be created. If C<create> is not
2113 set and the variable does not exist then NULL is returned.
2115 HV* perl_get_hv _((char* name, I32 create));
2119 Returns the SV of the specified Perl scalar. If C<create> is set and the
2120 Perl variable does not exist then it will be created. If C<create> is not
2121 set and the variable does not exist then NULL is returned.
2123 SV* perl_get_sv _((char* name, I32 create));
2127 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
2129 =item perl_require_pv
2131 Tells Perl to C<require> a module.
2133 void perl_require_pv _((char* pv));
2137 Tells a Perl interpreter to run. See L<perlembed>.
2141 Pops an integer off the stack.
2147 Pops a long off the stack.
2153 Pops a string off the stack.
2159 Pops a double off the stack.
2165 Pops an SV off the stack.
2171 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2177 Push an integer onto the stack. The stack must have room for this element.
2184 Push a double onto the stack. The stack must have room for this element.
2191 Push a string onto the stack. The stack must have room for this element.
2192 The C<len> indicates the length of the string. See C<XPUSHp>.
2194 PUSHp(char *c, int len )
2198 Push an SV onto the stack. The stack must have room for this element. See
2205 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2206 See C<PUSHMARK> and L<perlcall> for other uses.
2212 The XSUB-writer's interface to the C C<realloc> function.
2214 void * Renew( void *ptr, int size, type )
2218 The XSUB-writer's interface to the C C<realloc> function, with cast.
2220 void * Renewc( void *ptr, int size, type, cast )
2224 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
2225 This is always the proper type for the XSUB.
2226 See L<perlxs/"The RETVAL Variable">.
2230 The XSUB-writer's interface to the C C<free> function.
2234 The XSUB-writer's interface to the C C<malloc> function.
2238 The XSUB-writer's interface to the C C<realloc> function.
2242 Copy a string to a safe spot. This does not use an SV.
2244 char* savepv _((char* sv));
2248 Copy a string to a safe spot. The C<len> indicates number of bytes to
2249 copy. This does not use an SV.
2251 char* savepvn _((char* sv, I32 len));
2255 Opening bracket for temporaries on a callback. See C<FREETMPS> and
2262 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2267 Refetch the stack pointer. Used after a callback. See L<perlcall>.
2273 Used to access elements on the XSUB's stack.
2279 Test two strings to see if they are equal. Returns true or false.
2281 int strEQ( char *s1, char *s2 )
2285 Test two strings to see if the first, C<s1>, is greater than or equal to the
2286 second, C<s2>. Returns true or false.
2288 int strGE( char *s1, char *s2 )
2292 Test two strings to see if the first, C<s1>, is greater than the second,
2293 C<s2>. Returns true or false.
2295 int strGT( char *s1, char *s2 )
2299 Test two strings to see if the first, C<s1>, is less than or equal to the
2300 second, C<s2>. Returns true or false.
2302 int strLE( char *s1, char *s2 )
2306 Test two strings to see if the first, C<s1>, is less than the second,
2307 C<s2>. Returns true or false.
2309 int strLT( char *s1, char *s2 )
2313 Test two strings to see if they are different. Returns true or false.
2315 int strNE( char *s1, char *s2 )
2319 Test two strings to see if they are equal. The C<len> parameter indicates
2320 the number of bytes to compare. Returns true or false.
2322 int strnEQ( char *s1, char *s2 )
2326 Test two strings to see if they are different. The C<len> parameter
2327 indicates the number of bytes to compare. Returns true or false.
2329 int strnNE( char *s1, char *s2, int len )
2333 Marks an SV as mortal. The SV will be destroyed when the current context
2336 SV* sv_2mortal _((SV* sv));
2340 Blesses an SV into a specified package. The SV must be an RV. The package
2341 must be designated by its stash (see C<gv_stashpv()>). The reference count
2342 of the SV is unaffected.
2344 SV* sv_bless _((SV* sv, HV* stash));
2348 Concatenates the string onto the end of the string which is in the SV.
2350 void sv_catpv _((SV* sv, char* ptr));
2354 Concatenates the string onto the end of the string which is in the SV. The
2355 C<len> indicates number of bytes to copy.
2357 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
2361 Processes its arguments like C<sprintf> and appends the formatted output
2364 void sv_catpvf _((SV* sv, const char* pat, ...));
2368 Concatenates the string from SV C<ssv> onto the end of the string in SV
2371 void sv_catsv _((SV* dsv, SV* ssv));
2375 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2376 string in C<sv1> is less than, equal to, or greater than the string in
2379 I32 sv_cmp _((SV* sv1, SV* sv2));
2383 Returns the length of the string which is in the SV. See C<SvLEN>.
2389 Set the length of the string which is in the SV. See C<SvCUR>.
2391 SvCUR_set (SV* sv, int val )
2395 Auto-decrement of the value in the SV.
2397 void sv_dec _((SV* sv));
2401 Returns a pointer to the last character in the string which is in the SV.
2402 See C<SvCUR>. Access the character as
2408 Returns a boolean indicating whether the strings in the two SVs are
2411 I32 sv_eq _((SV* sv1, SV* sv2));
2415 Expands the character buffer in the SV. Calls C<sv_grow> to perform the
2416 expansion if necessary. Returns a pointer to the character buffer.
2418 char * SvGROW( SV* sv, int len )
2422 Expands the character buffer in the SV. This will use C<sv_unref> and will
2423 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2428 Auto-increment of the value in the SV.
2430 void sv_inc _((SV* sv));
2434 Returns a boolean indicating whether the SV contains an integer.
2440 Unsets the IV status of an SV.
2446 Tells an SV that it is an integer.
2452 Tells an SV that it is an integer and disables all other OK bits.
2458 Returns a boolean indicating whether the SV contains an integer. Checks the
2459 B<private> setting. Use C<SvIOK>.
2465 Returns a boolean indicating whether the SV is blessed into the specified
2466 class. This does not know how to check for subtype, so it doesn't work in
2467 an inheritance relationship.
2469 int sv_isa _((SV* sv, char* name));
2473 Returns the integer which is in the SV.
2479 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2480 object. If the SV is not an RV, or if the object is not blessed, then this
2483 int sv_isobject _((SV* sv));
2487 Returns the integer which is stored in the SV.
2493 Returns the size of the string buffer in the SV. See C<SvCUR>.
2499 Returns the length of the string in the SV. Use C<SvCUR>.
2501 STRLEN sv_len _((SV* sv));
2505 Adds magic to an SV.
2507 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2511 Creates a new SV which is a copy of the original SV. The new SV is marked
2514 SV* sv_mortalcopy _((SV* oldsv));
2518 Returns a boolean indicating whether the value is an SV.
2524 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2526 SV* sv_newmortal _((void));
2530 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2534 Returns a boolean indicating whether the SV contains a number, integer or
2541 Unsets the NV/IV status of an SV.
2547 Returns a boolean indicating whether the SV contains a number, integer or
2548 double. Checks the B<private> setting. Use C<SvNIOK>.
2550 int SvNIOKp (SV* SV)
2554 Returns a boolean indicating whether the SV contains a double.
2560 Unsets the NV status of an SV.
2566 Tells an SV that it is a double.
2572 Tells an SV that it is a double and disables all other OK bits.
2578 Returns a boolean indicating whether the SV contains a double. Checks the
2579 B<private> setting. Use C<SvNOK>.
2585 Returns the double which is stored in the SV.
2587 double SvNV (SV* sv);
2591 Returns the double which is stored in the SV.
2593 double SvNVX (SV* sv);
2597 Returns a boolean indicating whether the SV contains a character string.
2603 Unsets the PV status of an SV.
2609 Tells an SV that it is a string.
2615 Tells an SV that it is a string and disables all other OK bits.
2621 Returns a boolean indicating whether the SV contains a character string.
2622 Checks the B<private> setting. Use C<SvPOK>.
2628 Returns a pointer to the string in the SV, or a stringified form of the SV
2629 if the SV does not contain a string. If C<len> is C<na> then Perl will
2630 handle the length on its own.
2632 char * SvPV (SV* sv, int len )
2636 Returns a pointer to the string in the SV. The SV must contain a string.
2638 char * SvPVX (SV* sv)
2642 Returns the value of the object's reference count.
2644 int SvREFCNT (SV* sv);
2648 Decrements the reference count of the given SV.
2650 void SvREFCNT_dec (SV* sv)
2654 Increments the reference count of the given SV.
2656 void SvREFCNT_inc (SV* sv)
2660 Tests if the SV is an RV.
2666 Unsets the RV status of an SV.
2672 Tells an SV that it is an RV.
2678 Dereferences an RV to return the SV.
2684 Copies an integer into the given SV.
2686 void sv_setiv _((SV* sv, IV num));
2690 Copies a double into the given SV.
2692 void sv_setnv _((SV* sv, double num));
2696 Copies a string into an SV. The string must be null-terminated.
2698 void sv_setpv _((SV* sv, char* ptr));
2702 Copies a string into an SV. The C<len> parameter indicates the number of
2705 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2709 Processes its arguments like C<sprintf> and sets an SV to the formatted
2712 void sv_setpvf _((SV* sv, const char* pat, ...));
2716 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
2717 argument will be upgraded to an RV. That RV will be modified to point to
2718 the new SV. The C<classname> argument indicates the package for the
2719 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2720 will be returned and will have a reference count of 1.
2722 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2726 Copies a double into a new SV, optionally blessing the SV. The C<rv>
2727 argument will be upgraded to an RV. That RV will be modified to point to
2728 the new SV. The C<classname> argument indicates the package for the
2729 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2730 will be returned and will have a reference count of 1.
2732 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2736 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
2737 argument will be upgraded to an RV. That RV will be modified to point to
2738 the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
2739 into the SV. The C<classname> argument indicates the package for the
2740 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2741 will be returned and will have a reference count of 1.
2743 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2745 Do not use with integral Perl types such as HV, AV, SV, CV, because those
2746 objects will become corrupted by the pointer copy process.
2748 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2752 Copies a string into a new SV, optionally blessing the SV. The length of the
2753 string must be specified with C<n>. The C<rv> argument will be upgraded to
2754 an RV. That RV will be modified to point to the new SV. The C<classname>
2755 argument indicates the package for the blessing. Set C<classname> to
2756 C<Nullch> to avoid the blessing. The new SV will be returned and will have
2757 a reference count of 1.
2759 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2761 Note that C<sv_setref_pv> copies the pointer while this copies the string.
2765 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
2766 The source SV may be destroyed if it is mortal.
2768 void sv_setsv _((SV* dsv, SV* ssv));
2772 Returns the stash of the SV.
2774 HV * SvSTASH (SV* sv)
2778 Integer type flag for scalars. See C<svtype>.
2782 Pointer type flag for scalars. See C<svtype>.
2786 Type flag for arrays. See C<svtype>.
2790 Type flag for code refs. See C<svtype>.
2794 Type flag for hashes. See C<svtype>.
2798 Type flag for blessed scalars. See C<svtype>.
2802 Double type flag for scalars. See C<svtype>.
2806 Returns a boolean indicating whether Perl would evaluate the SV as true or
2807 false, defined or undefined.
2813 Returns the type of the SV. See C<svtype>.
2815 svtype SvTYPE (SV* sv)
2819 An enum of flags for Perl types. These are found in the file B<sv.h> in the
2820 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2824 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
2825 the upgrade if necessary. See C<svtype>.
2827 bool SvUPGRADE _((SV* sv, svtype mt));
2831 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
2835 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
2839 Unsets the RV status of the SV, and decrements the reference count of
2840 whatever was being referenced by the RV. This can almost be thought of
2841 as a reversal of C<newSVrv>. See C<SvROK_off>.
2843 void sv_unref _((SV* sv));
2847 Tells an SV to use C<ptr> to find its string value. Normally the string is
2848 stored inside the SV but sv_usepvn allows the SV to use an outside string.
2849 The C<ptr> should point to memory that was allocated by C<malloc>. The
2850 string length, C<len>, must be supplied. This function will realloc the
2851 memory pointed to by C<ptr>, so that pointer should not be freed or used by
2852 the programmer after giving it to sv_usepvn.
2854 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
2858 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
2862 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
2863 This is always the proper type for the C++ object. See C<CLASS> and
2864 L<perlxs/"Using XS With C++">.
2868 Converts the specified character to lowercase.
2870 int toLOWER (char c)
2874 Converts the specified character to uppercase.
2876 int toUPPER (char c)
2880 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
2881 function the same way you use the C C<printf> function. See C<croak()>.
2885 Push an integer onto the stack, extending the stack if necessary. See
2892 Push a double onto the stack, extending the stack if necessary. See
2899 Push a string onto the stack, extending the stack if necessary. The C<len>
2900 indicates the length of the string. See C<PUSHp>.
2902 XPUSHp(char *c, int len)
2906 Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
2912 Macro to declare an XSUB and its C parameter list. This is handled by
2917 Return from XSUB, indicating number of items on the stack. This is usually
2918 handled by C<xsubpp>.
2922 =item XSRETURN_EMPTY
2924 Return an empty list from an XSUB immediately.
2930 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
2936 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
2942 Return an double from an XSUB immediately. Uses C<XST_mNV>.
2948 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
2950 XSRETURN_PV(char *v);
2952 =item XSRETURN_UNDEF
2954 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
2960 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
2966 Place an integer into the specified position C<i> on the stack. The value is
2967 stored in a new mortal SV.
2969 XST_mIV( int i, IV v );
2973 Place a double into the specified position C<i> on the stack. The value is
2974 stored in a new mortal SV.
2976 XST_mNV( int i, NV v );
2980 Place C<&sv_no> into the specified position C<i> on the stack.
2986 Place a copy of a string into the specified position C<i> on the stack. The
2987 value is stored in a new mortal SV.
2989 XST_mPV( int i, char *v );
2993 Place C<&sv_undef> into the specified position C<i> on the stack.
2995 XST_mUNDEF( int i );
2999 Place C<&sv_yes> into the specified position C<i> on the stack.
3005 The version identifier for an XS module. This is usually handled
3006 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
3008 =item XS_VERSION_BOOTCHECK
3010 Macro to verify that a PM module's $VERSION variable matches the XS module's
3011 C<XS_VERSION> variable. This is usually handled automatically by
3012 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
3016 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
3017 destination, C<n> is the number of items, and C<t> is the type.
3019 (void) Zero( d, n, t );
3025 Jeff Okamoto <F<okamoto@corp.hp.com>>
3027 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
3028 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
3029 Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer, and
3032 API Listing by Dean Roehrich <F<roehrich@cray.com>>.
3036 Version 31.8: 1997/5/17