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.
13 Perl has three typedefs that handle Perl's three main data types:
19 Each typedef has specific routines that manipulate the various data types.
21 =head2 What is an "IV"?
23 Perl uses a special typedef IV which is a simple integer type that is
24 guaranteed to be large enough to hold a pointer (as well as an integer).
26 Perl also uses two special typedefs, I32 and I16, which will always be at
27 least 32-bits and 16-bits long, respectively.
29 =head2 Working with SV's
31 An SV can be created and loaded with one command. There are four types of
32 values that can be loaded: an integer value (IV), a double (NV), a string,
33 (PV), and another scalar (SV).
35 The four routines are:
39 SV* newSVpv(char*, int);
42 To change the value of an *already-existing* SV, there are five routines:
44 void sv_setiv(SV*, IV);
45 void sv_setnv(SV*, double);
46 void sv_setpvn(SV*, char*, int)
47 void sv_setpv(SV*, char*);
48 void sv_setsv(SV*, SV*);
50 Notice that you can choose to specify the length of the string to be
51 assigned by using C<sv_setpvn> or C<newSVpv>, or you may allow Perl to
52 calculate the length by using C<sv_setpv> or by specifying 0 as the second
53 argument to C<newSVpv>. Be warned, though, that Perl will determine the
54 string's length by using C<strlen>, which depends on the string terminating
57 All SV's that will contain strings should, but need not, be terminated
58 with a NUL character. If it is not NUL-terminated there is a risk of
59 core dumps and corruptions from code which passes the string to C
60 functions or system calls which expect a NUL-terminated string.
61 Perl's own functions typically add a trailing NUL for this reason.
62 Nevertheless, you should be very careful when you pass a string stored
63 in an SV to a C function or system call.
65 To access the actual value that an SV points to, you can use the macros:
71 which will automatically coerce the actual scalar type into an IV, double,
74 In the C<SvPV> macro, the length of the string returned is placed into the
75 variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
76 care what the length of the data is, use the global variable C<na>. Remember,
77 however, that Perl allows arbitrary strings of data that may both contain
78 NUL's and might not be terminated by a NUL.
80 If you want to know if the scalar value is TRUE, you can use:
84 Although Perl will automatically grow strings for you, if you need to force
85 Perl to allocate more memory for your SV, you can use the macro
87 SvGROW(SV*, STRLEN newlen)
89 which will determine if more memory needs to be allocated. If so, it will
90 call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
91 decrease, the allocated memory of an SV and that it does not automatically
92 add a byte for the a trailing NUL (perl's own string functions typically do
93 C<SvGROW(sv, len + 1)>).
95 If you have an SV and want to know what kind of data Perl thinks is stored
96 in it, you can use the following macros to check the type of SV you have.
102 You can get and set the current length of the string stored in an SV with
103 the following macros:
106 SvCUR_set(SV*, I32 val)
108 You can also get a pointer to the end of the string stored in the SV
113 But note that these last three macros are valid only if C<SvPOK()> is true.
115 If you want to append something to the end of string stored in an C<SV*>,
116 you can use the following functions:
118 void sv_catpv(SV*, char*);
119 void sv_catpvn(SV*, char*, int);
120 void sv_catsv(SV*, SV*);
122 The first function calculates the length of the string to be appended by
123 using C<strlen>. In the second, you specify the length of the string
124 yourself. The third function extends the string stored in the first SV
125 with the string stored in the second SV. It also forces the second SV to
126 be interpreted as a string.
128 If you know the name of a scalar variable, you can get a pointer to its SV
129 by using the following:
131 SV* perl_get_sv("package::varname", FALSE);
133 This returns NULL if the variable does not exist.
135 If you want to know if this variable (or any other SV) is actually C<defined>,
140 The scalar C<undef> value is stored in an SV instance called C<sv_undef>. Its
141 address can be used whenever an C<SV*> is needed.
143 There are also the two values C<sv_yes> and C<sv_no>, which contain Boolean
144 TRUE and FALSE values, respectively. Like C<sv_undef>, their addresses can
145 be used whenever an C<SV*> is needed.
147 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&sv_undef>.
151 if (I-am-to-return-a-real-value) {
152 sv = sv_2mortal(newSViv(42));
156 This code tries to return a new SV (which contains the value 42) if it should
157 return a real value, or undef otherwise. Instead it has returned a null
158 pointer which, somewhere down the line, will cause a segmentation violation,
159 bus error, or just weird results. Change the zero to C<&sv_undef> in the first
160 line and all will be well.
162 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
163 call is not necessary (see the section on L<Mortality>).
165 =head2 What's Really Stored in an SV?
167 Recall that the usual method of determining the type of scalar you have is
168 to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
169 usually these macros will always return TRUE and calling the C<Sv*V>
170 macros will do the appropriate conversion of string to integer/double or
171 integer/double to string.
173 If you I<really> need to know if you have an integer, double, or string
174 pointer in an SV, you can use the following three macros instead:
180 These will tell you if you truly have an integer, double, or string pointer
181 stored in your SV. The "p" stands for private.
183 In general, though, it's best to use the C<Sv*V> macros.
185 =head2 Working with AV's
187 There are two ways to create and load an AV. The first method creates an
192 The second method both creates the AV and initially populates it with SV's:
194 AV* av_make(I32 num, SV **ptr);
196 The second argument points to an array containing C<num> C<SV*>'s. Once the
197 AV has been created, the SV's can be destroyed, if so desired.
199 Once the AV has been created, the following operations are possible on AV's:
201 void av_push(AV*, SV*);
204 void av_unshift(AV*, I32 num);
206 These should be familiar operations, with the exception of C<av_unshift>.
207 This routine adds C<num> elements at the front of the array with the C<undef>
208 value. You must then use C<av_store> (described below) to assign values
209 to these new elements.
211 Here are some other functions:
214 SV** av_fetch(AV*, I32 key, I32 lval);
215 SV** av_store(AV*, I32 key, SV* val);
217 The C<av_len> function returns the highest index value in array (just
218 like $#array in Perl). If the array is empty, -1 is returned. The
219 C<av_fetch> function returns the value at index C<key>, but if C<lval>
220 is non-zero, then C<av_fetch> will store an undef value at that index.
221 The C<av_store> function stores the value C<val> at index C<key>.
222 note that C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s
223 as their return value.
227 void av_extend(AV*, I32 key);
229 The C<av_clear> function deletes all the elements in the AV* array, but
230 does not actually delete the array itself. The C<av_undef> function will
231 delete all the elements in the array plus the array itself. The
232 C<av_extend> function extends the array so that it contains C<key>
233 elements. If C<key> is less than the current length of the array, then
236 If you know the name of an array variable, you can get a pointer to its AV
237 by using the following:
239 AV* perl_get_av("package::varname", FALSE);
241 This returns NULL if the variable does not exist.
243 =head2 Working with HV's
245 To create an HV, you use the following routine:
249 Once the HV has been created, the following operations are possible on HV's:
251 SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
252 SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
254 The C<klen> parameter is the length of the key being passed in (Note that
255 you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
256 length of the key). The C<val> argument contains the SV pointer to the
257 scalar being stored, and C<hash> is the pre-computed hash value (zero if
258 you want C<hv_store> to calculate it for you). The C<lval> parameter
259 indicates whether this fetch is actually a part of a store operation, in
260 which case a new undefined value will be added to the HV with the supplied
261 key and C<hv_fetch> will return as if the value had already existed.
263 Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
264 C<SV*>. To access the scalar value, you must first dereference the return
265 value. However, you should check to make sure that the return value is
266 not NULL before dereferencing it.
268 These two functions check if a hash table entry exists, and deletes it.
270 bool hv_exists(HV*, char* key, U32 klen);
271 SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
273 If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
274 create and return a mortal copy of the deleted value.
276 And more miscellaneous functions:
281 Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
282 table but does not actually delete the hash table. The C<hv_undef> deletes
283 both the entries and the hash table itself.
285 Perl keeps the actual data in linked list of structures with a typedef of HE.
286 These contain the actual key and value pointers (plus extra administrative
287 overhead). The key is a string pointer; the value is an C<SV*>. However,
288 once you have an C<HE*>, to get the actual key and value, use the routines
291 I32 hv_iterinit(HV*);
292 /* Prepares starting point to traverse hash table */
293 HE* hv_iternext(HV*);
294 /* Get the next entry, and return a pointer to a
295 structure that has both the key and value */
296 char* hv_iterkey(HE* entry, I32* retlen);
297 /* Get the key from an HE structure and also return
298 the length of the key string */
299 SV* hv_iterval(HV*, HE* entry);
300 /* Return a SV pointer to the value of the HE
302 SV* hv_iternextsv(HV*, char** key, I32* retlen);
303 /* This convenience routine combines hv_iternext,
304 hv_iterkey, and hv_iterval. The key and retlen
305 arguments are return values for the key and its
306 length. The value is returned in the SV* argument */
308 If you know the name of a hash variable, you can get a pointer to its HV
309 by using the following:
311 HV* perl_get_hv("package::varname", FALSE);
313 This returns NULL if the variable does not exist.
315 The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
321 hash = hash * 33 + *s++;
325 References are a special type of scalar that point to other data types
326 (including references).
328 To create a reference, use either of the following functions:
330 SV* newRV_inc((SV*) thing);
331 SV* newRV_noinc((SV*) thing);
333 The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
334 functions are identical except that C<newRV_inc> increments the reference
335 count of the C<thing>, while C<newRV_noinc> does not. For historical
336 reasons, C<newRV> is a synonym for C<newRV_inc>.
338 Once you have a reference, you can use the following macro to dereference
343 then call the appropriate routines, casting the returned C<SV*> to either an
344 C<AV*> or C<HV*>, if required.
346 To determine if an SV is a reference, you can use the following macro:
350 To discover what type of value the reference refers to, use the following
351 macro and then check the return value.
355 The most useful types that will be returned are:
364 SVt_PVGV Glob (possible a file handle)
365 SVt_PVMG Blessed or Magical Scalar
367 See the sv.h header file for more details.
369 =head2 Blessed References and Class Objects
371 References are also used to support object-oriented programming. In the
372 OO lexicon, an object is simply a reference that has been blessed into a
373 package (or class). Once blessed, the programmer may now use the reference
374 to access the various methods in the class.
376 A reference can be blessed into a package with the following function:
378 SV* sv_bless(SV* sv, HV* stash);
380 The C<sv> argument must be a reference. The C<stash> argument specifies
381 which class the reference will belong to. See the section on L<Stashes>
382 for information on converting class names into stashes.
384 /* Still under construction */
386 Upgrades rv to reference if not already one. Creates new SV for rv to
387 point to. If C<classname> is non-null, the SV is blessed into the specified
388 class. SV is returned.
390 SV* newSVrv(SV* rv, char* classname);
392 Copies integer or double into an SV whose reference is C<rv>. SV is blessed
393 if C<classname> is non-null.
395 SV* sv_setref_iv(SV* rv, char* classname, IV iv);
396 SV* sv_setref_nv(SV* rv, char* classname, NV iv);
398 Copies the pointer value (I<the address, not the string!>) into an SV whose
399 reference is rv. SV is blessed if C<classname> is non-null.
401 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
403 Copies string into an SV whose reference is C<rv>. Set length to 0 to let
404 Perl calculate the string length. SV is blessed if C<classname> is non-null.
406 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
408 int sv_isa(SV* sv, char* name);
409 int sv_isobject(SV* sv);
411 =head2 Creating New Variables
413 To create a new Perl variable with an undef value which can be accessed from
414 your Perl script, use the following routines, depending on the variable type.
416 SV* perl_get_sv("package::varname", TRUE);
417 AV* perl_get_av("package::varname", TRUE);
418 HV* perl_get_hv("package::varname", TRUE);
420 Notice the use of TRUE as the second parameter. The new variable can now
421 be set, using the routines appropriate to the data type.
423 There are additional macros whose values may be bitwise OR'ed with the
424 C<TRUE> argument to enable certain extra features. Those bits are:
426 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
427 "Indentifier <varname> used only once: possible typo" warning.
428 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
429 the variable did not exist before the function was called.
431 If you do not specify a package name, the variable is created in the current
434 =head2 Reference Counts and Mortality
436 Perl uses an reference count-driven garbage collection mechanism. SV's,
437 AV's, or HV's (xV for short in the following) start their life with a
438 reference count of 1. If the reference count of an xV ever drops to 0,
439 then it will be destroyed and its memory made available for reuse.
441 This normally doesn't happen at the Perl level unless a variable is
442 undef'ed or the last variable holding a reference to it is changed or
443 overwritten. At the internal level, however, reference counts can be
444 manipulated with the following macros:
446 int SvREFCNT(SV* sv);
447 SV* SvREFCNT_inc(SV* sv);
448 void SvREFCNT_dec(SV* sv);
450 However, there is one other function which manipulates the reference
451 count of its argument. The C<newRV_inc> function, you will recall,
452 creates a reference to the specified argument. As a side effect,
453 it increments the argument's reference count. If this is not what
454 you want, use C<newRV_noinc> instead.
456 For example, imagine you want to return a reference from an XSUB function.
457 Inside the XSUB routine, you create an SV which initially has a reference
458 count of one. Then you call C<newRV_inc>, passing it the just-created SV.
459 This returns the reference as a new SV, but the reference count of the
460 SV you passed to C<newRV_inc> has been incremented to two. Now you
461 return the reference from the XSUB routine and forget about the SV.
462 But Perl hasn't! Whenever the returned reference is destroyed, the
463 reference count of the original SV is decreased to one and nothing happens.
464 The SV will hang around without any way to access it until Perl itself
465 terminates. This is a memory leak.
467 The correct procedure, then, is to use C<newRV_noinc> instead of
468 C<newRV_inc>. Then, if and when the last reference is destroyed,
469 the reference count of the SV will go to zero and it will be destroyed,
470 stopping any memory leak.
472 There are some convenience functions available that can help with the
473 destruction of xV's. These functions introduce the concept of "mortality".
474 An xV that is mortal has had its reference count marked to be decremented,
475 but not actually decremented, until "a short time later". Generally the
476 term "short time later" means a single Perl statement, such as a call to
477 an XSUB function. The actual determinant for when mortal xV's have their
478 reference count decremented depends on two macros, SAVETMPS and FREETMPS.
479 See L<perlcall> and L<perlxs> for more details on these macros.
481 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
482 However, if you mortalize a variable twice, the reference count will
483 later be decremented twice.
485 You should be careful about creating mortal variables. Strange things
486 can happen if you make the same value mortal within multiple contexts,
487 or if you make a variable mortal multiple times.
489 To create a mortal variable, use the functions:
493 SV* sv_mortalcopy(SV*)
495 The first call creates a mortal SV, the second converts an existing
496 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
497 third creates a mortal copy of an existing SV.
499 The mortal routines are not just for SV's -- AV's and HV's can be
500 made mortal by passing their address (type-casted to C<SV*>) to the
501 C<sv_2mortal> or C<sv_mortalcopy> routines.
503 =head2 Stashes and Globs
505 A stash is a hash table (associative array) that contains all of the
506 different objects that are contained within a package. Each key of the
507 stash is a symbol name (shared by all the different types of objects
508 that have the same name), and each value in the hash table is called a
509 GV (for Glob Value). This GV in turn contains references to the various
510 objects of that name, including (but not limited to) the following:
520 There is a single stash called "defstash" that holds the items that exist
521 in the "main" package. To get at the items in other packages, append the
522 string "::" to the package name. The items in the "Foo" package are in
523 the stash "Foo::" in defstash. The items in the "Bar::Baz" package are
524 in the stash "Baz::" in "Bar::"'s stash.
526 To get the stash pointer for a particular package, use the function:
528 HV* gv_stashpv(char* name, I32 create)
529 HV* gv_stashsv(SV*, I32 create)
531 The first function takes a literal string, the second uses the string stored
532 in the SV. Remember that a stash is just a hash table, so you get back an
533 C<HV*>. The C<create> flag will create a new package if it is set.
535 The name that C<gv_stash*v> wants is the name of the package whose symbol table
536 you want. The default package is called C<main>. If you have multiply nested
537 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
540 Alternately, if you have an SV that is a blessed reference, you can find
541 out the stash pointer by using:
543 HV* SvSTASH(SvRV(SV*));
545 then use the following to get the package name itself:
547 char* HvNAME(HV* stash);
549 If you need to bless or re-bless an object you can use the following
552 SV* sv_bless(SV*, HV* stash)
554 where the first argument, an C<SV*>, must be a reference, and the second
555 argument is a stash. The returned C<SV*> can now be used in the same way
558 For more information on references and blessings, consult L<perlref>.
562 [This section still under construction. Ignore everything here. Post no
563 bills. Everything not permitted is forbidden.]
565 Any SV may be magical, that is, it has special features that a normal
566 SV does not have. These features are stored in the SV structure in a
567 linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
580 Note this is current as of patchlevel 0, and could change at any time.
582 =head2 Assigning Magic
584 Perl adds magic to an SV using the sv_magic function:
586 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
588 The C<sv> argument is a pointer to the SV that is to acquire a new magical
591 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
592 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
593 it to the beginning of the linked list of magical features. Any prior
594 entry of the same type of magic is deleted. Note that this can be
595 overridden, and multiple instances of the same type of magic can be
596 associated with an SV.
598 The C<name> and C<namlem> arguments are used to associate a string with
599 the magic, typically the name of a variable. C<namlem> is stored in the
600 C<mg_len> field and if C<name> is non-null and C<namlem> >= 0 a malloc'd
601 copy of the name is stored in C<mg_ptr> field.
603 The sv_magic function uses C<how> to determine which, if any, predefined
604 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
605 See the "Magic Virtual Table" section below. The C<how> argument is also
606 stored in the C<mg_type> field.
608 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
609 structure. If it is not the same as the C<sv> argument, the reference
610 count of the C<obj> object is incremented. If it is the same, or if
611 the C<how> argument is "#", or if it is a null pointer, then C<obj> is
612 merely stored, without the reference count being incremented.
614 There is also a function to add magic to an C<HV>:
616 void hv_magic(HV *hv, GV *gv, int how);
618 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
620 To remove the magic from an SV, call the function sv_unmagic:
622 void sv_unmagic(SV *sv, int type);
624 The C<type> argument should be equal to the C<how> value when the C<SV>
625 was initially made magical.
627 =head2 Magic Virtual Tables
629 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
630 C<MGVTBL>, which is a structure of function pointers and stands for
631 "Magic Virtual Table" to handle the various operations that might be
632 applied to that variable.
634 The C<MGVTBL> has five pointers to the following routine types:
636 int (*svt_get)(SV* sv, MAGIC* mg);
637 int (*svt_set)(SV* sv, MAGIC* mg);
638 U32 (*svt_len)(SV* sv, MAGIC* mg);
639 int (*svt_clear)(SV* sv, MAGIC* mg);
640 int (*svt_free)(SV* sv, MAGIC* mg);
642 This MGVTBL structure is set at compile-time in C<perl.h> and there are
643 currently 19 types (or 21 with overloading turned on). These different
644 structures contain pointers to various routines that perform additional
645 actions depending on which function is being called.
647 Function pointer Action taken
648 ---------------- ------------
649 svt_get Do something after the value of the SV is retrieved.
650 svt_set Do something after the SV is assigned a value.
651 svt_len Report on the SV's length.
652 svt_clear Clear something the SV represents.
653 svt_free Free any extra storage associated with the SV.
655 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
656 to an C<mg_type> of '\0') contains:
658 { magic_get, magic_set, magic_len, 0, 0 }
660 Thus, when an SV is determined to be magical and of type '\0', if a get
661 operation is being performed, the routine C<magic_get> is called. All
662 the various routines for the various magical types begin with C<magic_>.
664 The current kinds of Magic Virtual Tables are:
666 mg_type MGVTBL Type of magical
667 ------- ------ ----------------------------
669 A vtbl_amagic Operator Overloading
670 a vtbl_amagicelem Operator Overloading
671 c 0 Used in Operator Overloading
672 B vtbl_bm Boyer-Moore???
674 e vtbl_envelem %ENV hash element
675 g vtbl_mglob Regexp /g flag???
676 I vtbl_isa @ISA array
677 i vtbl_isaelem @ISA array element
678 L 0 (but sets RMAGICAL) Perl Module/Debugger???
679 l vtbl_dbline Debugger?
680 P vtbl_pack Tied Array or Hash
681 p vtbl_packelem Tied Array or Hash element
682 q vtbl_packelem Tied Scalar or Handle
683 S vtbl_sig Signal Hash
684 s vtbl_sigelem Signal Hash element
685 t vtbl_taint Taintedness
688 x vtbl_substr Substring???
689 y vtbl_itervar Shadow "foreach" iterator variable
691 # vtbl_arylen Array Length
692 . vtbl_pos $. scalar variable
693 ~ None Used by certain extensions
695 When an upper-case and lower-case letter both exist in the table, then the
696 upper-case letter is used to represent some kind of composite type (a list
697 or a hash), and the lower-case letter is used to represent an element of
700 The '~' magic type is defined specifically for use by extensions and
701 will not be used by perl itself. Extensions can use ~ magic to 'attach'
702 private information to variables (typically objects). This is especially
703 useful because there is no way for normal perl code to corrupt this
704 private information (unlike using extra elements of a hash object).
706 Note that because multiple extensions may be using ~ magic it is
707 important for extensions to take extra care with it. Typically only
708 using it on objects blessed into the same class as the extension
709 is sufficient. It may also be appropriate to add an I32 'signature'
710 at the top of the private data area and check that.
714 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
716 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
717 If the SV does not have that magical feature, C<NULL> is returned. Also,
718 if the SV is not of type SVt_PVMG, Perl may core-dump.
720 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
722 This routine checks to see what types of magic C<sv> has. If the mg_type
723 field is an upper-case letter, then the mg_obj is copied to C<nsv>, but
724 the mg_type field is changed to be the lower-case letter.
726 =head2 Double-Typed SV's
728 Scalar variables normally contain only one type of value, an integer,
729 double, pointer, or reference. Perl will automatically convert the
730 actual scalar data from the stored type into the requested type.
732 Some scalar variables contain more than one type of scalar data. For
733 example, the variable C<$!> contains either the numeric value of C<errno>
734 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
736 To force multiple data values into an SV, you must do two things: use the
737 C<sv_set*v> routines to add the additional scalar type, then set a flag
738 so that Perl will believe it contains more than one type of data. The
739 four macros to set the flags are:
746 The particular macro you must use depends on which C<sv_set*v> routine
747 you called first. This is because every C<sv_set*v> routine turns on
748 only the bit for the particular type of data being set, and turns off
751 For example, to create a new Perl variable called "dberror" that contains
752 both the numeric and descriptive string error values, you could use the
756 extern char *dberror_list;
758 SV* sv = perl_get_sv("dberror", TRUE);
759 sv_setiv(sv, (IV) dberror);
760 sv_setpv(sv, dberror_list[dberror]);
763 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
764 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
766 =head2 XSUB's and the Argument Stack
768 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
769 An XSUB routine will have a stack that contains the arguments from the Perl
770 program, and a way to map from the Perl data structures to a C equivalent.
772 The stack arguments are accessible through the C<ST(n)> macro, which returns
773 the C<n>'th stack argument. Argument 0 is the first argument passed in the
774 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
777 Most of the time, output from the C routine can be handled through use of
778 the RETVAL and OUTPUT directives. However, there are some cases where the
779 argument stack is not already long enough to handle all the return values.
780 An example is the POSIX tzname() call, which takes no arguments, but returns
781 two, the local time zone's standard and summer time abbreviations.
783 To handle this situation, the PPCODE directive is used and the stack is
784 extended using the macro:
788 where C<sp> is the stack pointer, and C<num> is the number of elements the
789 stack should be extended by.
791 Now that there is room on the stack, values can be pushed on it using the
792 macros to push IV's, doubles, strings, and SV pointers respectively:
799 And now the Perl program calling C<tzname>, the two values will be assigned
802 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
804 An alternate (and possibly simpler) method to pushing values on the stack is
812 These macros automatically adjust the stack for you, if needed. Thus, you
813 do not need to call C<EXTEND> to extend the stack.
815 For more information, consult L<perlxs> and L<perlxstut>.
817 =head2 Calling Perl Routines from within C Programs
819 There are four routines that can be used to call a Perl subroutine from
820 within a C program. These four are:
822 I32 perl_call_sv(SV*, I32);
823 I32 perl_call_pv(char*, I32);
824 I32 perl_call_method(char*, I32);
825 I32 perl_call_argv(char*, I32, register char**);
827 The routine most often used is C<perl_call_sv>. The C<SV*> argument
828 contains either the name of the Perl subroutine to be called, or a
829 reference to the subroutine. The second argument consists of flags
830 that control the context in which the subroutine is called, whether
831 or not the subroutine is being passed arguments, how errors should be
832 trapped, and how to treat return values.
834 All four routines return the number of arguments that the subroutine returned
837 When using any of these routines (except C<perl_call_argv>), the programmer
838 must manipulate the Perl stack. These include the following macros and
852 For a detailed description of calling conventions from C to Perl,
855 =head2 Memory Allocation
857 It is suggested that you use the version of malloc that is distributed
858 with Perl. It keeps pools of various sizes of unallocated memory in
859 order to satisfy allocation requests more quickly. However, on some
860 platforms, it may cause spurious malloc or free errors.
862 New(x, pointer, number, type);
863 Newc(x, pointer, number, type, cast);
864 Newz(x, pointer, number, type);
866 These three macros are used to initially allocate memory.
868 The first argument C<x> was a "magic cookie" that was used to keep track
869 of who called the macro, to help when debugging memory problems. However,
870 the current code makes no use of this feature (most Perl developers now
871 use run-time memory checkers), so this argument can be any number.
873 The second argument C<pointer> should be the name of a variable that will
874 point to the newly allocated memory.
876 The third and fourth arguments C<number> and C<type> specify how many of
877 the specified type of data structure should be allocated. The argument
878 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
879 should be used if the C<pointer> argument is different from the C<type>
882 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
883 to zero out all the newly allocated memory.
885 Renew(pointer, number, type);
886 Renewc(pointer, number, type, cast);
889 These three macros are used to change a memory buffer size or to free a
890 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
891 match those of C<New> and C<Newc> with the exception of not needing the
892 "magic cookie" argument.
894 Move(source, dest, number, type);
895 Copy(source, dest, number, type);
896 Zero(dest, number, type);
898 These three macros are used to move, copy, or zero out previously allocated
899 memory. The C<source> and C<dest> arguments point to the source and
900 destination starting points. Perl will move, copy, or zero out C<number>
901 instances of the size of the C<type> data structure (using the C<sizeof>
906 The most recent development releases of Perl has been experimenting with
907 removing Perl's dependency on the "normal" standard I/O suite and allowing
908 other stdio implementations to be used. This involves creating a new
909 abstraction layer that then calls whichever implementation of stdio Perl
910 was compiled with. All XSUB's should now use the functions in the PerlIO
911 abstraction layer and not make any assumptions about what kind of stdio
914 For a complete description of the PerlIO abstraction, consult L<perlapio>.
918 =head2 Putting a C value on Perl stack
920 A lot of opcodes (this is an elementary operation in the internal perl
921 stack machine) put an SV* on the stack. However, as an optimization
922 the corresponding SV is (usually) not recreated each time. The opcodes
923 reuse specially assigned SVs (I<target>s) which are (as a corollary)
924 not constantly freed/created.
926 Each of the targets is created only once (but see
927 L<Scratchpads and recursion> below), and when an opcode needs to put
928 an integer, a double, or a string on stack, it just sets the
929 corresponding parts of its I<target> and puts the I<target> on stack.
931 The macro to put this target on stack is C<PUSHTARG>, and it is
932 directly used in some opcodes, as well as indirectly in zillions of
933 others, which use it via C<(X)PUSH[pni]>.
937 The question remains on when the SV's which are I<target>s for opcodes
938 are created. The answer is that they are created when the current unit --
939 a subroutine or a file (for opcodes for statements outside of
940 subroutines) -- is compiled. During this time a special anonymous Perl
941 array is created, which is called a scratchpad for the current
944 A scratchpad keeps SV's which are lexicals for the current unit and are
945 targets for opcodes. One can deduce that an SV lives on a scratchpad
946 by looking on its flags: lexicals have C<SVs_PADMY> set, and
947 I<target>s have C<SVs_PADTMP> set.
949 The correspondence between OP's and I<target>s is not 1-to-1. Different
950 OP's in the compile tree of the unit can use the same target, if this
951 would not conflict with the expected life of the temporary.
953 =head2 Scratchpads and recursions
955 In fact it is not 100% true that a compiled unit contains a pointer to
956 the scratchpad AV. In fact it contains a pointer to an AV of
957 (initially) one element, and this element is the scratchpad AV. Why do
958 we need an extra level of indirection?
960 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
961 these can create several execution pointers going into the same
962 subroutine. For the subroutine-child not write over the temporaries
963 for the subroutine-parent (lifespan of which covers the call to the
964 child), the parent and the child should have different
965 scratchpads. (I<And> the lexicals should be separate anyway!)
967 So each subroutine is born with an array of scratchpads (of length 1).
968 On each entry to the subroutine it is checked that the current
969 depth of the recursion is not more than the length of this array, and
970 if it is, new scratchpad is created and pushed into the array.
972 The I<target>s on this scratchpad are C<undef>s, but they are already
973 marked with correct flags.
977 This is a listing of functions, macros, flags, and variables that may be
978 useful to extension writers or that may be found while reading other
989 Clears an array, making it empty.
991 void av_clear _((AV* ar));
995 Pre-extend an array. The C<key> is the index to which the array should be
998 void av_extend _((AV* ar, I32 key));
1002 Returns the SV at the specified index in the array. The C<key> is the
1003 index. If C<lval> is set then the fetch will be part of a store. Check
1004 that the return value is non-null before dereferencing it to a C<SV*>.
1006 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1010 Returns the highest index in the array. Returns -1 if the array is empty.
1012 I32 av_len _((AV* ar));
1016 Creates a new AV and populates it with a list of SVs. The SVs are copied
1017 into the array, so they may be freed after the call to av_make. The new AV
1018 will have a reference count of 1.
1020 AV* av_make _((I32 size, SV** svp));
1024 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1027 SV* av_pop _((AV* ar));
1031 Pushes an SV onto the end of the array. The array will grow automatically
1032 to accommodate the addition.
1034 void av_push _((AV* ar, SV* val));
1038 Shifts an SV off the beginning of the array.
1040 SV* av_shift _((AV* ar));
1044 Stores an SV in an array. The array index is specified as C<key>. The
1045 return value will be null if the operation failed, otherwise it can be
1046 dereferenced to get the original C<SV*>.
1048 SV** av_store _((AV* ar, I32 key, SV* val));
1052 Undefines the array.
1054 void av_undef _((AV* ar));
1058 Unshift an SV onto the beginning of the array. The array will grow
1059 automatically to accommodate the addition.
1061 void av_unshift _((AV* ar, I32 num));
1065 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1066 constructor. This is always a C<char*>. See C<THIS> and
1067 L<perlxs/"Using XS With C++">.
1071 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1072 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1075 (void) Copy( s, d, n, t );
1079 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1080 function the same way you use the C C<printf> function. See C<warn>.
1084 Returns the stash of the CV.
1086 HV * CvSTASH( SV* sv )
1090 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1091 boolean which indicates whether subs are being single-stepped.
1092 Single-stepping is automatically turned on after every step. This is the C
1093 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1097 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1098 the SV which holds the name of the sub being debugged. This is the C
1099 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1100 The sub name can be found by
1102 SvPV( GvSV( DBsub ), na )
1106 Trace variable used when Perl is run in debugging mode, with the B<-d>
1107 switch. This is the C variable which corresponds to Perl's $DB::trace
1108 variable. See C<DBsingle>.
1112 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1117 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1121 The C variable which corresponds to Perl's $^W warning variable.
1125 Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
1129 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1130 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1131 to indicate the number of items on the stack.
1135 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1136 handled automatically by C<xsubpp>.
1140 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1141 handled automatically by C<xsubpp>.
1145 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1151 Used to extend the argument stack for an XSUB's return values.
1153 EXTEND( sp, int x );
1157 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1164 Used to indicate array context. See C<GIMME> and L<perlcall>.
1168 Indicates that arguments returned from a callback should be discarded. See
1173 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1177 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns C<G_SCALAR> or
1178 C<G_ARRAY> for scalar or array context.
1182 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1186 Used to indicate scalar context. See C<GIMME> and L<perlcall>.
1190 Returns the glob with the given C<name> and a defined subroutine or
1191 C<NULL>. The glob lives in the given C<stash>, or in the stashes accessable
1192 via @ISA and @<UNIVERSAL>.
1194 As a side-effect creates a glob with the given C<name> in the given C<stash>
1195 which in the case of success contains an alias for the subroutine, and
1196 sets up caching info for this glob. Similarly for all the searched
1199 GV* gv_fetchmeth _((HV* stash, char* name, STRLEN len, I32 level));
1201 =item gv_fetchmethod
1203 Returns the glob which contains the subroutine to call to invoke the
1204 method on the C<stash>. In fact in the presense of autoloading this may
1205 be the glob for "AUTOLOAD". In this case the corresponing variable
1206 $AUTOLOAD is already setup.
1208 Note that if you want to keep this glob for a long time, you need to
1209 check for it being "AUTOLOAD", since at the later time the the call
1210 may load a different subroutine due to $AUTOLOAD changing its value.
1211 Use the glob created via a side effect to do this.
1213 This function grants C<"SUPER"> token as prefix of name or postfix of
1216 Has the same side-effects and as C<gv_fetchmeth()>. C<name> should be
1217 writable if contains C<':'> or C<'\''>.
1219 GV* gv_fetchmethod _((HV* stash, char* name));
1223 Returns a pointer to the stash for a specified package. If C<create> is set
1224 then the package will be created if it does not already exist. If C<create>
1225 is not set and the package does not exist then NULL is returned.
1227 HV* gv_stashpv _((char* name, I32 create));
1231 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1233 HV* gv_stashsv _((SV* sv, I32 create));
1237 Return the SV from the GV.
1241 Releases a hash entry from an iterator. See C<hv_iternext>.
1245 Clears a hash, making it empty.
1247 void hv_clear _((HV* tb));
1251 Deletes a key/value pair in the hash. The value SV is removed from the hash
1252 and returned to the caller. The C<klen> is the length of the key. The
1253 C<flags> value will normally be zero; if set to G_DISCARD then null will be
1256 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1260 Returns a boolean indicating whether the specified hash key exists. The
1261 C<klen> is the length of the key.
1263 bool hv_exists _((HV* tb, char* key, U32 klen));
1267 Returns the SV which corresponds to the specified key in the hash. The
1268 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1269 part of a store. Check that the return value is non-null before
1270 dereferencing it to a C<SV*>.
1272 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1276 Prepares a starting point to traverse a hash table.
1278 I32 hv_iterinit _((HV* tb));
1282 Returns the key from the current position of the hash iterator. See
1285 char* hv_iterkey _((HE* entry, I32* retlen));
1289 Returns entries from a hash iterator. See C<hv_iterinit>.
1291 HE* hv_iternext _((HV* tb));
1295 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1298 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1302 Returns the value from the current position of the hash iterator. See
1305 SV* hv_iterval _((HV* tb, HE* entry));
1309 Adds magic to a hash. See C<sv_magic>.
1311 void hv_magic _((HV* hv, GV* gv, int how));
1315 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1317 char *HvNAME (HV* stash)
1321 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1322 the length of the key. The C<hash> parameter is the pre-computed hash
1323 value; if it is zero then Perl will compute it. The return value will be
1324 null if the operation failed, otherwise it can be dereferenced to get the
1327 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1333 void hv_undef _((HV* tb));
1337 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
1340 int isALNUM (char c)
1344 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
1347 int isALPHA (char c)
1351 Returns a boolean indicating whether the C C<char> is an ascii digit.
1353 int isDIGIT (char c)
1357 Returns a boolean indicating whether the C C<char> is a lowercase character.
1359 int isLOWER (char c)
1363 Returns a boolean indicating whether the C C<char> is whitespace.
1365 int isSPACE (char c)
1369 Returns a boolean indicating whether the C C<char> is an uppercase character.
1371 int isUPPER (char c)
1375 Variable which is setup by C<xsubpp> to indicate the number of items on the
1376 stack. See L<perlxs/"Variable-length Parameter Lists">.
1380 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1381 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
1385 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1391 Stack marker variable for the XSUB. See C<dMARK>.
1395 Clear something magical that the SV represents. See C<sv_magic>.
1397 int mg_clear _((SV* sv));
1401 Copies the magic from one SV to another. See C<sv_magic>.
1403 int mg_copy _((SV *, SV *, char *, STRLEN));
1407 Finds the magic pointer for type matching the SV. See C<sv_magic>.
1409 MAGIC* mg_find _((SV* sv, int type));
1413 Free any magic storage used by the SV. See C<sv_magic>.
1415 int mg_free _((SV* sv));
1419 Do magic after a value is retrieved from the SV. See C<sv_magic>.
1421 int mg_get _((SV* sv));
1425 Report on the SV's length. See C<sv_magic>.
1427 U32 mg_len _((SV* sv));
1431 Turns on the magical status of an SV. See C<sv_magic>.
1433 void mg_magical _((SV* sv));
1437 Do magic after a value is assigned to the SV. See C<sv_magic>.
1439 int mg_set _((SV* sv));
1443 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
1444 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1447 (void) Move( s, d, n, t );
1451 A variable which may be used with C<SvPV> to tell Perl to calculate the
1456 The XSUB-writer's interface to the C C<malloc> function.
1458 void * New( x, void *ptr, int size, type )
1462 The XSUB-writer's interface to the C C<malloc> function, with cast.
1464 void * Newc( x, void *ptr, int size, type, cast )
1468 The XSUB-writer's interface to the C C<malloc> function. The allocated
1469 memory is zeroed with C<memzero>.
1471 void * Newz( x, void *ptr, int size, type )
1475 Creates a new AV. The reference count is set to 1.
1477 AV* newAV _((void));
1481 Creates a new HV. The reference count is set to 1.
1483 HV* newHV _((void));
1487 Creates an RV wrapper for an SV. The reference count for the original SV is
1490 SV* newRV_inc _((SV* ref));
1492 For historical reasons, "newRV" is a synonym for "newRV_inc".
1496 Creates an RV wrapper for an SV. The reference count for the original
1497 SV is B<not> incremented.
1499 SV* newRV_noinc _((SV* ref));
1503 Creates a new SV. The C<len> parameter indicates the number of bytes of
1504 pre-allocated string space the SV should have. The reference count for the
1507 SV* newSV _((STRLEN len));
1511 Creates a new SV and copies an integer into it. The reference count for the
1514 SV* newSViv _((IV i));
1518 Creates a new SV and copies a double into it. The reference count for the
1521 SV* newSVnv _((NV i));
1525 Creates a new SV and copies a string into it. The reference count for the
1526 SV is set to 1. If C<len> is zero then Perl will compute the length.
1528 SV* newSVpv _((char* s, STRLEN len));
1532 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
1533 it will be upgraded to one. If C<classname> is non-null then the new SV will
1534 be blessed in the specified package. The new SV is returned and its
1535 reference count is 1.
1537 SV* newSVrv _((SV* rv, char* classname));
1541 Creates a new SV which is an exact duplicate of the original SV.
1543 SV* newSVsv _((SV* old));
1547 Used by C<xsubpp> to hook up XSUBs as Perl subs.
1551 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
1560 Null character pointer.
1576 The original stack mark for the XSUB. See C<dORIGMARK>.
1580 Allocates a new Perl interpreter. See L<perlembed>.
1582 =item perl_call_argv
1584 Performs a callback to the specified Perl sub. See L<perlcall>.
1586 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
1588 =item perl_call_method
1590 Performs a callback to the specified Perl method. The blessed object must
1591 be on the stack. See L<perlcall>.
1593 I32 perl_call_method _((char* methname, I32 flags));
1597 Performs a callback to the specified Perl sub. See L<perlcall>.
1599 I32 perl_call_pv _((char* subname, I32 flags));
1603 Performs a callback to the Perl sub whose name is in the SV. See
1606 I32 perl_call_sv _((SV* sv, I32 flags));
1608 =item perl_construct
1610 Initializes a new Perl interpreter. See L<perlembed>.
1614 Shuts down a Perl interpreter. See L<perlembed>.
1618 Tells Perl to C<eval> the string in the SV.
1620 I32 perl_eval_sv _((SV* sv, I32 flags));
1624 Releases a Perl interpreter. See L<perlembed>.
1628 Returns the AV of the specified Perl array. If C<create> is set and the
1629 Perl variable does not exist then it will be created. If C<create> is not
1630 set and the variable does not exist then null is returned.
1632 AV* perl_get_av _((char* name, I32 create));
1636 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
1637 variable does not exist then it will be created. If C<create> is not
1638 set and the variable does not exist then null is returned.
1640 CV* perl_get_cv _((char* name, I32 create));
1644 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
1645 variable does not exist then it will be created. If C<create> is not
1646 set and the variable does not exist then null is returned.
1648 HV* perl_get_hv _((char* name, I32 create));
1652 Returns the SV of the specified Perl scalar. If C<create> is set and the
1653 Perl variable does not exist then it will be created. If C<create> is not
1654 set and the variable does not exist then null is returned.
1656 SV* perl_get_sv _((char* name, I32 create));
1660 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
1662 =item perl_require_pv
1664 Tells Perl to C<require> a module.
1666 void perl_require_pv _((char* pv));
1670 Tells a Perl interpreter to run. See L<perlembed>.
1674 Pops an integer off the stack.
1680 Pops a long off the stack.
1686 Pops a string off the stack.
1692 Pops a double off the stack.
1698 Pops an SV off the stack.
1704 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
1710 Push an integer onto the stack. The stack must have room for this element.
1717 Push a double onto the stack. The stack must have room for this element.
1724 Push a string onto the stack. The stack must have room for this element.
1725 The C<len> indicates the length of the string. See C<XPUSHp>.
1727 PUSHp(char *c, int len )
1731 Push an SV onto the stack. The stack must have room for this element. See
1738 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
1739 See C<PUSHMARK> and L<perlcall> for other uses.
1745 The XSUB-writer's interface to the C C<realloc> function.
1747 void * Renew( void *ptr, int size, type )
1751 The XSUB-writer's interface to the C C<realloc> function, with cast.
1753 void * Renewc( void *ptr, int size, type, cast )
1757 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
1758 This is always the proper type for the XSUB.
1759 See L<perlxs/"The RETVAL Variable">.
1763 The XSUB-writer's interface to the C C<free> function.
1767 The XSUB-writer's interface to the C C<malloc> function.
1771 The XSUB-writer's interface to the C C<realloc> function.
1775 Copy a string to a safe spot. This does not use an SV.
1777 char* savepv _((char* sv));
1781 Copy a string to a safe spot. The C<len> indicates number of bytes to
1782 copy. This does not use an SV.
1784 char* savepvn _((char* sv, I32 len));
1788 Opening bracket for temporaries on a callback. See C<FREETMPS> and
1795 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
1800 Re-fetch the stack pointer. Used after a callback. See L<perlcall>.
1806 Used to access elements on the XSUB's stack.
1812 Test two strings to see if they are equal. Returns true or false.
1814 int strEQ( char *s1, char *s2 )
1818 Test two strings to see if the first, C<s1>, is greater than or equal to the
1819 second, C<s2>. Returns true or false.
1821 int strGE( char *s1, char *s2 )
1825 Test two strings to see if the first, C<s1>, is greater than the second,
1826 C<s2>. Returns true or false.
1828 int strGT( char *s1, char *s2 )
1832 Test two strings to see if the first, C<s1>, is less than or equal to the
1833 second, C<s2>. Returns true or false.
1835 int strLE( char *s1, char *s2 )
1839 Test two strings to see if the first, C<s1>, is less than the second,
1840 C<s2>. Returns true or false.
1842 int strLT( char *s1, char *s2 )
1846 Test two strings to see if they are different. Returns true or false.
1848 int strNE( char *s1, char *s2 )
1852 Test two strings to see if they are equal. The C<len> parameter indicates
1853 the number of bytes to compare. Returns true or false.
1855 int strnEQ( char *s1, char *s2 )
1859 Test two strings to see if they are different. The C<len> parameter
1860 indicates the number of bytes to compare. Returns true or false.
1862 int strnNE( char *s1, char *s2, int len )
1866 Marks an SV as mortal. The SV will be destroyed when the current context
1869 SV* sv_2mortal _((SV* sv));
1873 Blesses an SV into a specified package. The SV must be an RV. The package
1874 must be designated by its stash (see C<gv_stashpv()>). The reference count
1875 of the SV is unaffected.
1877 SV* sv_bless _((SV* sv, HV* stash));
1881 Concatenates the string onto the end of the string which is in the SV.
1883 void sv_catpv _((SV* sv, char* ptr));
1887 Concatenates the string onto the end of the string which is in the SV. The
1888 C<len> indicates number of bytes to copy.
1890 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
1894 Concatenates the string from SV C<ssv> onto the end of the string in SV
1897 void sv_catsv _((SV* dsv, SV* ssv));
1901 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1902 string in C<sv1> is less than, equal to, or greater than the string in
1905 I32 sv_cmp _((SV* sv1, SV* sv2));
1909 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
1910 string in C<sv1> is less than, equal to, or greater than the string in
1913 I32 sv_cmp _((SV* sv1, SV* sv2));
1917 Returns the length of the string which is in the SV. See C<SvLEN>.
1923 Set the length of the string which is in the SV. See C<SvCUR>.
1925 SvCUR_set (SV* sv, int val )
1929 Auto-decrement of the value in the SV.
1931 void sv_dec _((SV* sv));
1935 Auto-decrement of the value in the SV.
1937 void sv_dec _((SV* sv));
1941 Returns a pointer to the last character in the string which is in the SV.
1942 See C<SvCUR>. Access the character as
1948 Returns a boolean indicating whether the strings in the two SVs are
1951 I32 sv_eq _((SV* sv1, SV* sv2));
1955 Expands the character buffer in the SV. Calls C<sv_grow> to perform the
1956 expansion if necessary. Returns a pointer to the character buffer.
1958 char * SvGROW( SV* sv, int len )
1962 Expands the character buffer in the SV. This will use C<sv_unref> and will
1963 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
1968 Auto-increment of the value in the SV.
1970 void sv_inc _((SV* sv));
1974 Returns a boolean indicating whether the SV contains an integer.
1980 Unsets the IV status of an SV.
1986 Tells an SV that it is an integer.
1992 Tells an SV that it is an integer and disables all other OK bits.
1998 Tells an SV that it is an integer and disables all other OK bits.
2004 Returns a boolean indicating whether the SV contains an integer. Checks the
2005 B<private> setting. Use C<SvIOK>.
2011 Returns a boolean indicating whether the SV is blessed into the specified
2012 class. This does not know how to check for subtype, so it doesn't work in
2013 an inheritance relationship.
2015 int sv_isa _((SV* sv, char* name));
2019 Returns the integer which is in the SV.
2025 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2026 object. If the SV is not an RV, or if the object is not blessed, then this
2029 int sv_isobject _((SV* sv));
2033 Returns the integer which is stored in the SV.
2039 Returns the size of the string buffer in the SV. See C<SvCUR>.
2045 Returns the length of the string in the SV. Use C<SvCUR>.
2047 STRLEN sv_len _((SV* sv));
2051 Returns the length of the string in the SV. Use C<SvCUR>.
2053 STRLEN sv_len _((SV* sv));
2057 Adds magic to an SV.
2059 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2063 Creates a new SV which is a copy of the original SV. The new SV is marked
2066 SV* sv_mortalcopy _((SV* oldsv));
2070 Returns a boolean indicating whether the value is an SV.
2076 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2078 SV* sv_newmortal _((void));
2082 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2086 Returns a boolean indicating whether the SV contains a number, integer or
2093 Unsets the NV/IV status of an SV.
2099 Returns a boolean indicating whether the SV contains a number, integer or
2100 double. Checks the B<private> setting. Use C<SvNIOK>.
2102 int SvNIOKp (SV* SV)
2106 Returns a boolean indicating whether the SV contains a double.
2112 Unsets the NV status of an SV.
2118 Tells an SV that it is a double.
2124 Tells an SV that it is a double and disables all other OK bits.
2130 Tells an SV that it is a double and disables all other OK bits.
2136 Returns a boolean indicating whether the SV contains a double. Checks the
2137 B<private> setting. Use C<SvNOK>.
2143 Returns the double which is stored in the SV.
2145 double SvNV (SV* sv);
2149 Returns the double which is stored in the SV.
2151 double SvNVX (SV* sv);
2155 Returns a boolean indicating whether the SV contains a character string.
2161 Unsets the PV status of an SV.
2167 Tells an SV that it is a string.
2173 Tells an SV that it is a string and disables all other OK bits.
2179 Tells an SV that it is a string and disables all other OK bits.
2185 Returns a boolean indicating whether the SV contains a character string.
2186 Checks the B<private> setting. Use C<SvPOK>.
2192 Returns a pointer to the string in the SV, or a stringified form of the SV
2193 if the SV does not contain a string. If C<len> is C<na> then Perl will
2194 handle the length on its own.
2196 char * SvPV (SV* sv, int len )
2200 Returns a pointer to the string in the SV. The SV must contain a string.
2202 char * SvPVX (SV* sv)
2206 Returns the value of the object's reference count.
2208 int SvREFCNT (SV* sv);
2212 Decrements the reference count of the given SV.
2214 void SvREFCNT_dec (SV* sv)
2218 Increments the reference count of the given SV.
2220 void SvREFCNT_inc (SV* sv)
2224 Tests if the SV is an RV.
2230 Unsets the RV status of an SV.
2236 Tells an SV that it is an RV.
2242 Dereferences an RV to return the SV.
2248 Copies an integer into the given SV.
2250 void sv_setiv _((SV* sv, IV num));
2254 Copies a double into the given SV.
2256 void sv_setnv _((SV* sv, double num));
2260 Copies a string into an SV. The string must be null-terminated.
2262 void sv_setpv _((SV* sv, char* ptr));
2266 Copies a string into an SV. The C<len> parameter indicates the number of
2269 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2273 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
2274 argument will be upgraded to an RV. That RV will be modified to point to
2275 the new SV. The C<classname> argument indicates the package for the
2276 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2277 will be returned and will have a reference count of 1.
2279 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2283 Copies a double into a new SV, optionally blessing the SV. The C<rv>
2284 argument will be upgraded to an RV. That RV will be modified to point to
2285 the new SV. The C<classname> argument indicates the package for the
2286 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2287 will be returned and will have a reference count of 1.
2289 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2293 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
2294 argument will be upgraded to an RV. That RV will be modified to point to
2295 the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
2296 into the SV. The C<classname> argument indicates the package for the
2297 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
2298 will be returned and will have a reference count of 1.
2300 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2302 Do not use with integral Perl types such as HV, AV, SV, CV, because those
2303 objects will become corrupted by the pointer copy process.
2305 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2309 Copies a string into a new SV, optionally blessing the SV. The length of the
2310 string must be specified with C<n>. The C<rv> argument will be upgraded to
2311 an RV. That RV will be modified to point to the new SV. The C<classname>
2312 argument indicates the package for the blessing. Set C<classname> to
2313 C<Nullch> to avoid the blessing. The new SV will be returned and will have
2314 a reference count of 1.
2316 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2318 Note that C<sv_setref_pv> copies the pointer while this copies the string.
2322 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
2323 The source SV may be destroyed if it is mortal.
2325 void sv_setsv _((SV* dsv, SV* ssv));
2329 Returns the stash of the SV.
2331 HV * SvSTASH (SV* sv)
2335 Integer type flag for scalars. See C<svtype>.
2339 Pointer type flag for scalars. See C<svtype>.
2343 Type flag for arrays. See C<svtype>.
2347 Type flag for code refs. See C<svtype>.
2351 Type flag for hashes. See C<svtype>.
2355 Type flag for blessed scalars. See C<svtype>.
2359 Double type flag for scalars. See C<svtype>.
2363 Returns a boolean indicating whether Perl would evaluate the SV as true or
2364 false, defined or undefined.
2370 Returns the type of the SV. See C<svtype>.
2372 svtype SvTYPE (SV* sv)
2376 An enum of flags for Perl types. These are found in the file B<sv.h> in the
2377 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2381 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
2382 the upgrade if necessary. See C<svtype>.
2384 bool SvUPGRADE _((SV* sv, svtype mt));
2388 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
2392 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
2396 Unsets the RV status of the SV, and decrements the reference count of
2397 whatever was being referenced by the RV. This can almost be thought of
2398 as a reversal of C<newSVrv>. See C<SvROK_off>.
2400 void sv_unref _((SV* sv));
2404 Tells an SV to use C<ptr> to find its string value. Normally the string is
2405 stored inside the SV but sv_usepvn allows the SV to use an outside string.
2406 The C<ptr> should point to memory that was allocated by C<malloc>. The
2407 string length, C<len>, must be supplied. This function will realloc the
2408 memory pointed to by C<ptr>, so that pointer should not be freed or used by
2409 the programmer after giving it to sv_usepvn.
2411 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
2415 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
2419 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
2420 This is always the proper type for the C++ object. See C<CLASS> and
2421 L<perlxs/"Using XS With C++">.
2425 Converts the specified character to lowercase.
2427 int toLOWER (char c)
2431 Converts the specified character to uppercase.
2433 int toUPPER (char c)
2437 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
2438 function the same way you use the C C<printf> function. See C<croak()>.
2442 Push an integer onto the stack, extending the stack if necessary. See
2449 Push a double onto the stack, extending the stack if necessary. See
2456 Push a string onto the stack, extending the stack if necessary. The C<len>
2457 indicates the length of the string. See C<PUSHp>.
2459 XPUSHp(char *c, int len)
2463 Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
2469 Macro to declare an XSUB and its C parameter list. This is handled by
2474 Return from XSUB, indicating number of items on the stack. This is usually
2475 handled by C<xsubpp>.
2479 =item XSRETURN_EMPTY
2481 Return an empty list from an XSUB immediately.
2487 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
2493 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
2499 Return an double from an XSUB immediately. Uses C<XST_mNV>.
2505 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
2507 XSRETURN_PV(char *v);
2509 =item XSRETURN_UNDEF
2511 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
2517 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
2523 Place an integer into the specified position C<i> on the stack. The value is
2524 stored in a new mortal SV.
2526 XST_mIV( int i, IV v );
2530 Place a double into the specified position C<i> on the stack. The value is
2531 stored in a new mortal SV.
2533 XST_mNV( int i, NV v );
2537 Place C<&sv_no> into the specified position C<i> on the stack.
2543 Place a copy of a string into the specified position C<i> on the stack. The
2544 value is stored in a new mortal SV.
2546 XST_mPV( int i, char *v );
2550 Place C<&sv_undef> into the specified position C<i> on the stack.
2552 XST_mUNDEF( int i );
2556 Place C<&sv_yes> into the specified position C<i> on the stack.
2562 The version identifier for an XS module. This is usually handled
2563 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
2565 =item XS_VERSION_BOOTCHECK
2567 Macro to verify that a PM module's $VERSION variable matches the XS module's
2568 C<XS_VERSION> variable. This is usually handled automatically by
2569 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
2573 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
2574 destination, C<n> is the number of items, and C<t> is the type.
2576 (void) Zero( d, n, t );
2582 Jeff Okamoto <okamoto@corp.hp.com>
2584 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
2585 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
2586 Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
2588 API Listing by Dean Roehrich <roehrich@cray.com>.
2592 Version 28: 1996/12/27