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. The C<sv_set*()>
61 functions are not generic enough to operate on values that have "magic".
62 See L<Magic Virtual Tables> later in this document.
64 All SVs that will contain strings should, but need not, be terminated
65 with a NUL character. If it is not NUL-terminated there is a risk of
66 core dumps and corruptions from code which passes the string to C
67 functions or system calls which expect a NUL-terminated string.
68 Perl's own functions typically add a trailing NUL for this reason.
69 Nevertheless, you should be very careful when you pass a string stored
70 in an SV to a C function or system call.
72 To access the actual value that an SV points to, you can use the macros:
78 which will automatically coerce the actual scalar type into an IV, double,
81 In the C<SvPV> macro, the length of the string returned is placed into the
82 variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
83 care what the length of the data is, use the global variable C<na>. Remember,
84 however, that Perl allows arbitrary strings of data that may both contain
85 NULs and might not be terminated by a NUL.
87 If you want to know if the scalar value is TRUE, you can use:
91 Although Perl will automatically grow strings for you, if you need to force
92 Perl to allocate more memory for your SV, you can use the macro
94 SvGROW(SV*, STRLEN newlen)
96 which will determine if more memory needs to be allocated. If so, it will
97 call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
98 decrease, the allocated memory of an SV and that it does not automatically
99 add a byte for the a trailing NUL (perl's own string functions typically do
100 C<SvGROW(sv, len + 1)>).
102 If you have an SV and want to know what kind of data Perl thinks is stored
103 in it, you can use the following macros to check the type of SV you have.
109 You can get and set the current length of the string stored in an SV with
110 the following macros:
113 SvCUR_set(SV*, I32 val)
115 You can also get a pointer to the end of the string stored in the SV
120 But note that these last three macros are valid only if C<SvPOK()> is true.
122 If you want to append something to the end of string stored in an C<SV*>,
123 you can use the following functions:
125 void sv_catpv(SV*, char*);
126 void sv_catpvn(SV*, char*, int);
127 void sv_catpvf(SV*, const char*, ...);
128 void sv_catsv(SV*, SV*);
130 The first function calculates the length of the string to be appended by
131 using C<strlen>. In the second, you specify the length of the string
132 yourself. The third function processes its arguments like C<sprintf> and
133 appends the formatted output. The fourth function extends the string
134 stored in the first SV with the string stored in the second SV. It also
135 forces the second SV to be interpreted as a string. The C<sv_cat*()>
136 functions are not generic enough to operate on values that have "magic".
137 See L<Magic Virtual Tables> later in this document.
139 If you know the name of a scalar variable, you can get a pointer to its SV
140 by using the following:
142 SV* perl_get_sv("package::varname", FALSE);
144 This returns NULL if the variable does not exist.
146 If you want to know if this variable (or any other SV) is actually C<defined>,
151 The scalar C<undef> value is stored in an SV instance called C<sv_undef>. Its
152 address can be used whenever an C<SV*> is needed.
154 There are also the two values C<sv_yes> and C<sv_no>, which contain Boolean
155 TRUE and FALSE values, respectively. Like C<sv_undef>, their addresses can
156 be used whenever an C<SV*> is needed.
158 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&sv_undef>.
162 if (I-am-to-return-a-real-value) {
163 sv = sv_2mortal(newSViv(42));
167 This code tries to return a new SV (which contains the value 42) if it should
168 return a real value, or undef otherwise. Instead it has returned a NULL
169 pointer which, somewhere down the line, will cause a segmentation violation,
170 bus error, or just weird results. Change the zero to C<&sv_undef> in the first
171 line and all will be well.
173 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
174 call is not necessary (see L<Reference Counts and Mortality>).
176 =head2 What's Really Stored in an SV?
178 Recall that the usual method of determining the type of scalar you have is
179 to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
180 usually these macros will always return TRUE and calling the C<Sv*V>
181 macros will do the appropriate conversion of string to integer/double or
182 integer/double to string.
184 If you I<really> need to know if you have an integer, double, or string
185 pointer in an SV, you can use the following three macros instead:
191 These will tell you if you truly have an integer, double, or string pointer
192 stored in your SV. The "p" stands for private.
194 In general, though, it's best to use the C<Sv*V> macros.
196 =head2 Working with AVs
198 There are two ways to create and load an AV. The first method creates an
203 The second method both creates the AV and initially populates it with SVs:
205 AV* av_make(I32 num, SV **ptr);
207 The second argument points to an array containing C<num> C<SV*>'s. Once the
208 AV has been created, the SVs can be destroyed, if so desired.
210 Once the AV has been created, the following operations are possible on AVs:
212 void av_push(AV*, SV*);
215 void av_unshift(AV*, I32 num);
217 These should be familiar operations, with the exception of C<av_unshift>.
218 This routine adds C<num> elements at the front of the array with the C<undef>
219 value. You must then use C<av_store> (described below) to assign values
220 to these new elements.
222 Here are some other functions:
225 SV** av_fetch(AV*, I32 key, I32 lval);
226 SV** av_store(AV*, I32 key, SV* val);
228 The C<av_len> function returns the highest index value in array (just
229 like $#array in Perl). If the array is empty, -1 is returned. The
230 C<av_fetch> function returns the value at index C<key>, but if C<lval>
231 is non-zero, then C<av_fetch> will store an undef value at that index.
232 The C<av_store> function stores the value C<val> at index C<key>, and does
233 not increment the reference count of C<val>. Thus the caller is responsible
234 for taking care of that, and if C<av_store> returns NULL, the caller will
235 have to decrement the reference count to avoid a memory leak. Note that
236 C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s as their
241 void av_extend(AV*, I32 key);
243 The C<av_clear> function deletes all the elements in the AV* array, but
244 does not actually delete the array itself. The C<av_undef> function will
245 delete all the elements in the array plus the array itself. The
246 C<av_extend> function extends the array so that it contains C<key>
247 elements. If C<key> is less than the current length of the array, then
250 If you know the name of an array variable, you can get a pointer to its AV
251 by using the following:
253 AV* perl_get_av("package::varname", FALSE);
255 This returns NULL if the variable does not exist.
257 See L<Understanding the Magic of Tied Hashes and Arrays> for more
258 information on how to use the array access functions on tied arrays.
260 =head2 Working with HVs
262 To create an HV, you use the following routine:
266 Once the HV has been created, the following operations are possible on HVs:
268 SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
269 SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
271 The C<klen> parameter is the length of the key being passed in (Note that
272 you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
273 length of the key). The C<val> argument contains the SV pointer to the
274 scalar being stored, and C<hash> is the precomputed hash value (zero if
275 you want C<hv_store> to calculate it for you). The C<lval> parameter
276 indicates whether this fetch is actually a part of a store operation, in
277 which case a new undefined value will be added to the HV with the supplied
278 key and C<hv_fetch> will return as if the value had already existed.
280 Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
281 C<SV*>. To access the scalar value, you must first dereference the return
282 value. However, you should check to make sure that the return value is
283 not NULL before dereferencing it.
285 These two functions check if a hash table entry exists, and deletes it.
287 bool hv_exists(HV*, char* key, U32 klen);
288 SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
290 If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
291 create and return a mortal copy of the deleted value.
293 And more miscellaneous functions:
298 Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
299 table but does not actually delete the hash table. The C<hv_undef> deletes
300 both the entries and the hash table itself.
302 Perl keeps the actual data in linked list of structures with a typedef of HE.
303 These contain the actual key and value pointers (plus extra administrative
304 overhead). The key is a string pointer; the value is an C<SV*>. However,
305 once you have an C<HE*>, to get the actual key and value, use the routines
308 I32 hv_iterinit(HV*);
309 /* Prepares starting point to traverse hash table */
310 HE* hv_iternext(HV*);
311 /* Get the next entry, and return a pointer to a
312 structure that has both the key and value */
313 char* hv_iterkey(HE* entry, I32* retlen);
314 /* Get the key from an HE structure and also return
315 the length of the key string */
316 SV* hv_iterval(HV*, HE* entry);
317 /* Return a SV pointer to the value of the HE
319 SV* hv_iternextsv(HV*, char** key, I32* retlen);
320 /* This convenience routine combines hv_iternext,
321 hv_iterkey, and hv_iterval. The key and retlen
322 arguments are return values for the key and its
323 length. The value is returned in the SV* argument */
325 If you know the name of a hash variable, you can get a pointer to its HV
326 by using the following:
328 HV* perl_get_hv("package::varname", FALSE);
330 This returns NULL if the variable does not exist.
332 The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
338 hash = hash * 33 + *s++;
340 See L<Understanding the Magic of Tied Hashes and Arrays> for more
341 information on how to use the hash access functions on tied hashes.
343 =head2 Hash API Extensions
345 Beginning with version 5.004, the following functions are also supported:
347 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
348 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
350 bool hv_exists_ent (HV* tb, SV* key, U32 hash);
351 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
353 SV* hv_iterkeysv (HE* entry);
355 Note that these functions take C<SV*> keys, which simplifies writing
356 of extension code that deals with hash structures. These functions
357 also allow passing of C<SV*> keys to C<tie> functions without forcing
358 you to stringify the keys (unlike the previous set of functions).
360 They also return and accept whole hash entries (C<HE*>), making their
361 use more efficient (since the hash number for a particular string
362 doesn't have to be recomputed every time). See L<API LISTING> later in
363 this document for detailed descriptions.
365 The following macros must always be used to access the contents of hash
366 entries. Note that the arguments to these macros must be simple
367 variables, since they may get evaluated more than once. See
368 L<API LISTING> later in this document for detailed descriptions of these
371 HePV(HE* he, STRLEN len)
375 HeSVKEY_force(HE* he)
376 HeSVKEY_set(HE* he, SV* sv)
378 These two lower level macros are defined, but must only be used when
379 dealing with keys that are not C<SV*>s:
384 Note that both C<hv_store> and C<hv_store_ent> do not increment the
385 reference count of the stored C<val>, which is the caller's responsibility.
386 If these functions return a NULL value, the caller will usually have to
387 decrement the reference count of C<val> to avoid a memory leak.
391 References are a special type of scalar that point to other data types
392 (including references).
394 To create a reference, use either of the following functions:
396 SV* newRV_inc((SV*) thing);
397 SV* newRV_noinc((SV*) thing);
399 The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
400 functions are identical except that C<newRV_inc> increments the reference
401 count of the C<thing>, while C<newRV_noinc> does not. For historical
402 reasons, C<newRV> is a synonym for C<newRV_inc>.
404 Once you have a reference, you can use the following macro to dereference
409 then call the appropriate routines, casting the returned C<SV*> to either an
410 C<AV*> or C<HV*>, if required.
412 To determine if an SV is a reference, you can use the following macro:
416 To discover what type of value the reference refers to, use the following
417 macro and then check the return value.
421 The most useful types that will be returned are:
430 SVt_PVGV Glob (possible a file handle)
431 SVt_PVMG Blessed or Magical Scalar
433 See the sv.h header file for more details.
435 =head2 Blessed References and Class Objects
437 References are also used to support object-oriented programming. In the
438 OO lexicon, an object is simply a reference that has been blessed into a
439 package (or class). Once blessed, the programmer may now use the reference
440 to access the various methods in the class.
442 A reference can be blessed into a package with the following function:
444 SV* sv_bless(SV* sv, HV* stash);
446 The C<sv> argument must be a reference. The C<stash> argument specifies
447 which class the reference will belong to. See
448 L<Stashes and Globs> for information on converting class names into stashes.
450 /* Still under construction */
452 Upgrades rv to reference if not already one. Creates new SV for rv to
453 point to. If C<classname> is non-null, the SV is blessed into the specified
454 class. SV is returned.
456 SV* newSVrv(SV* rv, char* classname);
458 Copies integer or double into an SV whose reference is C<rv>. SV is blessed
459 if C<classname> is non-null.
461 SV* sv_setref_iv(SV* rv, char* classname, IV iv);
462 SV* sv_setref_nv(SV* rv, char* classname, NV iv);
464 Copies the pointer value (I<the address, not the string!>) into an SV whose
465 reference is rv. SV is blessed if C<classname> is non-null.
467 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
469 Copies string into an SV whose reference is C<rv>. Set length to 0 to let
470 Perl calculate the string length. SV is blessed if C<classname> is non-null.
472 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
474 int sv_isa(SV* sv, char* name);
475 int sv_isobject(SV* sv);
477 =head2 Creating New Variables
479 To create a new Perl variable with an undef value which can be accessed from
480 your Perl script, use the following routines, depending on the variable type.
482 SV* perl_get_sv("package::varname", TRUE);
483 AV* perl_get_av("package::varname", TRUE);
484 HV* perl_get_hv("package::varname", TRUE);
486 Notice the use of TRUE as the second parameter. The new variable can now
487 be set, using the routines appropriate to the data type.
489 There are additional macros whose values may be bitwise OR'ed with the
490 C<TRUE> argument to enable certain extra features. Those bits are:
492 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
493 "Name <varname> used only once: possible typo" warning.
494 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
495 the variable did not exist before the function was called.
497 If you do not specify a package name, the variable is created in the current
500 =head2 Reference Counts and Mortality
502 Perl uses an reference count-driven garbage collection mechanism. SVs,
503 AVs, or HVs (xV for short in the following) start their life with a
504 reference count of 1. If the reference count of an xV ever drops to 0,
505 then it will be destroyed and its memory made available for reuse.
507 This normally doesn't happen at the Perl level unless a variable is
508 undef'ed or the last variable holding a reference to it is changed or
509 overwritten. At the internal level, however, reference counts can be
510 manipulated with the following macros:
512 int SvREFCNT(SV* sv);
513 SV* SvREFCNT_inc(SV* sv);
514 void SvREFCNT_dec(SV* sv);
516 However, there is one other function which manipulates the reference
517 count of its argument. The C<newRV_inc> function, you will recall,
518 creates a reference to the specified argument. As a side effect,
519 it increments the argument's reference count. If this is not what
520 you want, use C<newRV_noinc> instead.
522 For example, imagine you want to return a reference from an XSUB function.
523 Inside the XSUB routine, you create an SV which initially has a reference
524 count of one. Then you call C<newRV_inc>, passing it the just-created SV.
525 This returns the reference as a new SV, but the reference count of the
526 SV you passed to C<newRV_inc> has been incremented to two. Now you
527 return the reference from the XSUB routine and forget about the SV.
528 But Perl hasn't! Whenever the returned reference is destroyed, the
529 reference count of the original SV is decreased to one and nothing happens.
530 The SV will hang around without any way to access it until Perl itself
531 terminates. This is a memory leak.
533 The correct procedure, then, is to use C<newRV_noinc> instead of
534 C<newRV_inc>. Then, if and when the last reference is destroyed,
535 the reference count of the SV will go to zero and it will be destroyed,
536 stopping any memory leak.
538 There are some convenience functions available that can help with the
539 destruction of xVs. These functions introduce the concept of "mortality".
540 An xV that is mortal has had its reference count marked to be decremented,
541 but not actually decremented, until "a short time later". Generally the
542 term "short time later" means a single Perl statement, such as a call to
543 an XSUB function. The actual determinant for when mortal xVs have their
544 reference count decremented depends on two macros, SAVETMPS and FREETMPS.
545 See L<perlcall> and L<perlxs> for more details on these macros.
547 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
548 However, if you mortalize a variable twice, the reference count will
549 later be decremented twice.
551 You should be careful about creating mortal variables. Strange things
552 can happen if you make the same value mortal within multiple contexts,
553 or if you make a variable mortal multiple times.
555 To create a mortal variable, use the functions:
559 SV* sv_mortalcopy(SV*)
561 The first call creates a mortal SV, the second converts an existing
562 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
563 third creates a mortal copy of an existing SV.
565 The mortal routines are not just for SVs -- AVs and HVs can be
566 made mortal by passing their address (type-casted to C<SV*>) to the
567 C<sv_2mortal> or C<sv_mortalcopy> routines.
569 =head2 Stashes and Globs
571 A "stash" is a hash that contains all of the different objects that
572 are contained within a package. Each key of the stash is a symbol
573 name (shared by all the different types of objects that have the same
574 name), and each value in the hash table is a GV (Glob Value). This GV
575 in turn contains references to the various objects of that name,
576 including (but not limited to) the following:
586 There is a single stash called "defstash" that holds the items that exist
587 in the "main" package. To get at the items in other packages, append the
588 string "::" to the package name. The items in the "Foo" package are in
589 the stash "Foo::" in defstash. The items in the "Bar::Baz" package are
590 in the stash "Baz::" in "Bar::"'s stash.
592 To get the stash pointer for a particular package, use the function:
594 HV* gv_stashpv(char* name, I32 create)
595 HV* gv_stashsv(SV*, I32 create)
597 The first function takes a literal string, the second uses the string stored
598 in the SV. Remember that a stash is just a hash table, so you get back an
599 C<HV*>. The C<create> flag will create a new package if it is set.
601 The name that C<gv_stash*v> wants is the name of the package whose symbol table
602 you want. The default package is called C<main>. If you have multiply nested
603 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
606 Alternately, if you have an SV that is a blessed reference, you can find
607 out the stash pointer by using:
609 HV* SvSTASH(SvRV(SV*));
611 then use the following to get the package name itself:
613 char* HvNAME(HV* stash);
615 If you need to bless or re-bless an object you can use the following
618 SV* sv_bless(SV*, HV* stash)
620 where the first argument, an C<SV*>, must be a reference, and the second
621 argument is a stash. The returned C<SV*> can now be used in the same way
624 For more information on references and blessings, consult L<perlref>.
626 =head2 Double-Typed SVs
628 Scalar variables normally contain only one type of value, an integer,
629 double, pointer, or reference. Perl will automatically convert the
630 actual scalar data from the stored type into the requested type.
632 Some scalar variables contain more than one type of scalar data. For
633 example, the variable C<$!> contains either the numeric value of C<errno>
634 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
636 To force multiple data values into an SV, you must do two things: use the
637 C<sv_set*v> routines to add the additional scalar type, then set a flag
638 so that Perl will believe it contains more than one type of data. The
639 four macros to set the flags are:
646 The particular macro you must use depends on which C<sv_set*v> routine
647 you called first. This is because every C<sv_set*v> routine turns on
648 only the bit for the particular type of data being set, and turns off
651 For example, to create a new Perl variable called "dberror" that contains
652 both the numeric and descriptive string error values, you could use the
656 extern char *dberror_list;
658 SV* sv = perl_get_sv("dberror", TRUE);
659 sv_setiv(sv, (IV) dberror);
660 sv_setpv(sv, dberror_list[dberror]);
663 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
664 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
666 =head2 Magic Variables
668 [This section still under construction. Ignore everything here. Post no
669 bills. Everything not permitted is forbidden.]
671 Any SV may be magical, that is, it has special features that a normal
672 SV does not have. These features are stored in the SV structure in a
673 linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
686 Note this is current as of patchlevel 0, and could change at any time.
688 =head2 Assigning Magic
690 Perl adds magic to an SV using the sv_magic function:
692 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
694 The C<sv> argument is a pointer to the SV that is to acquire a new magical
697 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
698 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
699 it to the beginning of the linked list of magical features. Any prior
700 entry of the same type of magic is deleted. Note that this can be
701 overridden, and multiple instances of the same type of magic can be
702 associated with an SV.
704 The C<name> and C<namlen> arguments are used to associate a string with
705 the magic, typically the name of a variable. C<namlen> is stored in the
706 C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
707 copy of the name is stored in C<mg_ptr> field.
709 The sv_magic function uses C<how> to determine which, if any, predefined
710 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
711 See the "Magic Virtual Table" section below. The C<how> argument is also
712 stored in the C<mg_type> field.
714 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
715 structure. If it is not the same as the C<sv> argument, the reference
716 count of the C<obj> object is incremented. If it is the same, or if
717 the C<how> argument is "#", or if it is a NULL pointer, then C<obj> is
718 merely stored, without the reference count being incremented.
720 There is also a function to add magic to an C<HV>:
722 void hv_magic(HV *hv, GV *gv, int how);
724 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
726 To remove the magic from an SV, call the function sv_unmagic:
728 void sv_unmagic(SV *sv, int type);
730 The C<type> argument should be equal to the C<how> value when the C<SV>
731 was initially made magical.
733 =head2 Magic Virtual Tables
735 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
736 C<MGVTBL>, which is a structure of function pointers and stands for
737 "Magic Virtual Table" to handle the various operations that might be
738 applied to that variable.
740 The C<MGVTBL> has five pointers to the following routine types:
742 int (*svt_get)(SV* sv, MAGIC* mg);
743 int (*svt_set)(SV* sv, MAGIC* mg);
744 U32 (*svt_len)(SV* sv, MAGIC* mg);
745 int (*svt_clear)(SV* sv, MAGIC* mg);
746 int (*svt_free)(SV* sv, MAGIC* mg);
748 This MGVTBL structure is set at compile-time in C<perl.h> and there are
749 currently 19 types (or 21 with overloading turned on). These different
750 structures contain pointers to various routines that perform additional
751 actions depending on which function is being called.
753 Function pointer Action taken
754 ---------------- ------------
755 svt_get Do something after the value of the SV is retrieved.
756 svt_set Do something after the SV is assigned a value.
757 svt_len Report on the SV's length.
758 svt_clear Clear something the SV represents.
759 svt_free Free any extra storage associated with the SV.
761 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
762 to an C<mg_type> of '\0') contains:
764 { magic_get, magic_set, magic_len, 0, 0 }
766 Thus, when an SV is determined to be magical and of type '\0', if a get
767 operation is being performed, the routine C<magic_get> is called. All
768 the various routines for the various magical types begin with C<magic_>.
770 The current kinds of Magic Virtual Tables are:
772 mg_type MGVTBL Type of magic
773 ------- ------ ----------------------------
774 \0 vtbl_sv Special scalar variable
775 A vtbl_amagic %OVERLOAD hash
776 a vtbl_amagicelem %OVERLOAD hash element
777 c (none) Holds overload table (AMT) on stash
778 B vtbl_bm Boyer-Moore (fast string search)
780 e vtbl_envelem %ENV hash element
781 f vtbl_fm Formline ('compiled' format)
782 g vtbl_mglob m//g target / study()ed string
783 I vtbl_isa @ISA array
784 i vtbl_isaelem @ISA array element
785 k vtbl_nkeys scalar(keys()) lvalue
786 L (none) Debugger %_<filename
787 l vtbl_dbline Debugger %_<filename element
788 o vtbl_collxfrm Locale transformation
789 P vtbl_pack Tied array or hash
790 p vtbl_packelem Tied array or hash element
791 q vtbl_packelem Tied scalar or handle
793 s vtbl_sigelem %SIG hash element
794 t vtbl_taint Taintedness
795 U vtbl_uvar Available for use by extensions
796 v vtbl_vec vec() lvalue
797 x vtbl_substr substr() lvalue
798 y vtbl_defelem Shadow "foreach" iterator variable /
799 smart parameter vivification
800 * vtbl_glob GV (typeglob)
801 # vtbl_arylen Array length ($#ary)
802 . vtbl_pos pos() lvalue
803 ~ (none) Available for use by extensions
805 When an uppercase and lowercase letter both exist in the table, then the
806 uppercase letter is used to represent some kind of composite type (a list
807 or a hash), and the lowercase letter is used to represent an element of
810 The '~' and 'U' magic types are defined specifically for use by
811 extensions and will not be used by perl itself. Extensions can use
812 '~' magic to 'attach' private information to variables (typically
813 objects). This is especially useful because there is no way for
814 normal perl code to corrupt this private information (unlike using
815 extra elements of a hash object).
817 Similarly, 'U' magic can be used much like tie() to call a C function
818 any time a scalar's value is used or changed. The C<MAGIC>'s
819 C<mg_ptr> field points to a C<ufuncs> structure:
822 I32 (*uf_val)(IV, SV*);
823 I32 (*uf_set)(IV, SV*);
827 When the SV is read from or written to, the C<uf_val> or C<uf_set>
828 function will be called with C<uf_index> as the first arg and a
829 pointer to the SV as the second.
831 Note that because multiple extensions may be using '~' or 'U' magic,
832 it is important for extensions to take extra care to avoid conflict.
833 Typically only using the magic on objects blessed into the same class
834 as the extension is sufficient. For '~' magic, it may also be
835 appropriate to add an I32 'signature' at the top of the private data
838 Also note that most of the C<sv_set*()> functions that modify scalars do
839 B<not> invoke 'set' magic on their targets. This must be done by the user
840 either by calling the C<SvSETMAGIC()> macro after calling these functions,
841 or by using one of the C<SvSetMagic*()> macros. Similarly, generic C code
842 must call the C<SvGETMAGIC()> macro to invoke any 'get' magic if they use
843 an SV obtained from external sources in functions that don't handle magic.
844 L<API LISTING> later in this document identifies such macros and functions.
845 For example, calls to the C<sv_cat*()> functions typically need to be
846 followed by C<SvSETMAGIC()>, but they don't need a prior C<SvGETMAGIC()>
847 since their implementation handles 'get' magic.
851 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
853 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
854 If the SV does not have that magical feature, C<NULL> is returned. Also,
855 if the SV is not of type SVt_PVMG, Perl may core dump.
857 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
859 This routine checks to see what types of magic C<sv> has. If the mg_type
860 field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
861 the mg_type field is changed to be the lowercase letter.
863 =head2 Understanding the Magic of Tied Hashes and Arrays
865 Tied hashes and arrays are magical beasts of the 'P' magic type.
867 WARNING: As of the 5.004 release, proper usage of the array and hash
868 access functions requires understanding a few caveats. Some
869 of these caveats are actually considered bugs in the API, to be fixed
870 in later releases, and are bracketed with [MAYCHANGE] below. If
871 you find yourself actually applying such information in this section, be
872 aware that the behavior may change in the future, umm, without warning.
874 The C<av_store> function, when given a tied array argument, merely
875 copies the magic of the array onto the value to be "stored", using
876 C<mg_copy>. It may also return NULL, indicating that the value did not
877 actually need to be stored in the array. [MAYCHANGE] After a call to
878 C<av_store> on a tied array, the caller will usually need to call
879 C<mg_set(val)> to actually invoke the perl level "STORE" method on the
880 TIEARRAY object. If C<av_store> did return NULL, a call to
881 C<SvREFCNT_dec(val)> will also be usually necessary to avoid a memory
884 The previous paragraph is applicable verbatim to tied hash access using the
885 C<hv_store> and C<hv_store_ent> functions as well.
887 C<av_fetch> and the corresponding hash functions C<hv_fetch> and
888 C<hv_fetch_ent> actually return an undefined mortal value whose magic
889 has been initialized using C<mg_copy>. Note the value so returned does not
890 need to be deallocated, as it is already mortal. [MAYCHANGE] But you will
891 need to call C<mg_get()> on the returned value in order to actually invoke
892 the perl level "FETCH" method on the underlying TIE object. Similarly,
893 you may also call C<mg_set()> on the return value after possibly assigning
894 a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
895 method on the TIE object. [/MAYCHANGE]
898 In other words, the array or hash fetch/store functions don't really
899 fetch and store actual values in the case of tied arrays and hashes. They
900 merely call C<mg_copy> to attach magic to the values that were meant to be
901 "stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
902 do the job of invoking the TIE methods on the underlying objects. Thus
903 the magic mechanism currently implements a kind of lazy access to arrays
906 Currently (as of perl version 5.004), use of the hash and array access
907 functions requires the user to be aware of whether they are operating on
908 "normal" hashes and arrays, or on their tied variants. The API may be
909 changed to provide more transparent access to both tied and normal data
910 types in future versions.
913 You would do well to understand that the TIEARRAY and TIEHASH interfaces
914 are mere sugar to invoke some perl method calls while using the uniform hash
915 and array syntax. The use of this sugar imposes some overhead (typically
916 about two to four extra opcodes per FETCH/STORE operation, in addition to
917 the creation of all the mortal variables required to invoke the methods).
918 This overhead will be comparatively small if the TIE methods are themselves
919 substantial, but if they are only a few statements long, the overhead
920 will not be insignificant.
922 =head2 Localizing changes
924 Perl has a very handy construction
931 This construction is I<approximately> equivalent to
940 The biggest difference is that the first construction would
941 reinstate the initial value of $var, irrespective of how control exits
942 the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
943 more efficient as well.
945 There is a way to achieve a similar task from C via Perl API: create a
946 I<pseudo-block>, and arrange for some changes to be automatically
947 undone at the end of it, either explicit, or via a non-local exit (via
948 die()). A I<block>-like construct is created by a pair of
949 C<ENTER>/C<LEAVE> macros (see L<perlcall/EXAMPLE/"Returning a
950 Scalar">). Such a construct may be created specially for some
951 important localized task, or an existing one (like boundaries of
952 enclosing Perl subroutine/block, or an existing pair for freeing TMPs)
953 may be used. (In the second case the overhead of additional
954 localization must be almost negligible.) Note that any XSUB is
955 automatically enclosed in an C<ENTER>/C<LEAVE> pair.
957 Inside such a I<pseudo-block> the following service is available:
961 =item C<SAVEINT(int i)>
963 =item C<SAVEIV(IV i)>
965 =item C<SAVEI32(I32 i)>
967 =item C<SAVELONG(long i)>
969 These macros arrange things to restore the value of integer variable
970 C<i> at the end of enclosing I<pseudo-block>.
976 These macros arrange things to restore the value of pointers C<s> and
977 C<p>. C<s> must be a pointer of a type which survives conversion to
978 C<SV*> and back, C<p> should be able to survive conversion to C<char*>
981 =item C<SAVEFREESV(SV *sv)>
983 The refcount of C<sv> would be decremented at the end of
984 I<pseudo-block>. This is similar to C<sv_2mortal>, which should (?) be
987 =item C<SAVEFREEOP(OP *op)>
989 The C<OP *> is op_free()ed at the end of I<pseudo-block>.
991 =item C<SAVEFREEPV(p)>
993 The chunk of memory which is pointed to by C<p> is Safefree()ed at the
994 end of I<pseudo-block>.
996 =item C<SAVECLEARSV(SV *sv)>
998 Clears a slot in the current scratchpad which corresponds to C<sv> at
999 the end of I<pseudo-block>.
1001 =item C<SAVEDELETE(HV *hv, char *key, I32 length)>
1003 The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
1004 string pointed to by C<key> is Safefree()ed. If one has a I<key> in
1005 short-lived storage, the corresponding string may be reallocated like
1008 SAVEDELETE(defstash, savepv(tmpbuf), strlen(tmpbuf));
1010 =item C<SAVEDESTRUCTOR(f,p)>
1012 At the end of I<pseudo-block> the function C<f> is called with the
1013 only argument (of type C<void*>) C<p>.
1015 =item C<SAVESTACK_POS()>
1017 The current offset on the Perl internal stack (cf. C<SP>) is restored
1018 at the end of I<pseudo-block>.
1022 The following API list contains functions, thus one needs to
1023 provide pointers to the modifiable data explicitly (either C pointers,
1024 or Perlish C<GV *>s). Where the above macros take C<int>, a similar
1025 function takes C<int *>.
1029 =item C<SV* save_scalar(GV *gv)>
1031 Equivalent to Perl code C<local $gv>.
1033 =item C<AV* save_ary(GV *gv)>
1035 =item C<HV* save_hash(GV *gv)>
1037 Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
1039 =item C<void save_item(SV *item)>
1041 Duplicates the current value of C<SV>, on the exit from the current
1042 C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
1043 using the stored value.
1045 =item C<void save_list(SV **sarg, I32 maxsarg)>
1047 A variant of C<save_item> which takes multiple arguments via an array
1048 C<sarg> of C<SV*> of length C<maxsarg>.
1050 =item C<SV* save_svref(SV **sptr)>
1052 Similar to C<save_scalar>, but will reinstate a C<SV *>.
1054 =item C<void save_aptr(AV **aptr)>
1056 =item C<void save_hptr(HV **hptr)>
1058 Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
1062 The C<Alias> module implements localization of the basic types within the
1063 I<caller's scope>. People who are interested in how to localize things in
1064 the containing scope should take a look there too.
1068 =head2 XSUBs and the Argument Stack
1070 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
1071 An XSUB routine will have a stack that contains the arguments from the Perl
1072 program, and a way to map from the Perl data structures to a C equivalent.
1074 The stack arguments are accessible through the C<ST(n)> macro, which returns
1075 the C<n>'th stack argument. Argument 0 is the first argument passed in the
1076 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
1079 Most of the time, output from the C routine can be handled through use of
1080 the RETVAL and OUTPUT directives. However, there are some cases where the
1081 argument stack is not already long enough to handle all the return values.
1082 An example is the POSIX tzname() call, which takes no arguments, but returns
1083 two, the local time zone's standard and summer time abbreviations.
1085 To handle this situation, the PPCODE directive is used and the stack is
1086 extended using the macro:
1090 where C<sp> is the stack pointer, and C<num> is the number of elements the
1091 stack should be extended by.
1093 Now that there is room on the stack, values can be pushed on it using the
1094 macros to push IVs, doubles, strings, and SV pointers respectively:
1101 And now the Perl program calling C<tzname>, the two values will be assigned
1104 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
1106 An alternate (and possibly simpler) method to pushing values on the stack is
1114 These macros automatically adjust the stack for you, if needed. Thus, you
1115 do not need to call C<EXTEND> to extend the stack.
1117 For more information, consult L<perlxs> and L<perlxstut>.
1119 =head2 Calling Perl Routines from within C Programs
1121 There are four routines that can be used to call a Perl subroutine from
1122 within a C program. These four are:
1124 I32 perl_call_sv(SV*, I32);
1125 I32 perl_call_pv(char*, I32);
1126 I32 perl_call_method(char*, I32);
1127 I32 perl_call_argv(char*, I32, register char**);
1129 The routine most often used is C<perl_call_sv>. The C<SV*> argument
1130 contains either the name of the Perl subroutine to be called, or a
1131 reference to the subroutine. The second argument consists of flags
1132 that control the context in which the subroutine is called, whether
1133 or not the subroutine is being passed arguments, how errors should be
1134 trapped, and how to treat return values.
1136 All four routines return the number of arguments that the subroutine returned
1139 When using any of these routines (except C<perl_call_argv>), the programmer
1140 must manipulate the Perl stack. These include the following macros and
1154 For a detailed description of calling conventions from C to Perl,
1155 consult L<perlcall>.
1157 =head2 Memory Allocation
1159 It is suggested that you use the version of malloc that is distributed
1160 with Perl. It keeps pools of various sizes of unallocated memory in
1161 order to satisfy allocation requests more quickly. However, on some
1162 platforms, it may cause spurious malloc or free errors.
1164 New(x, pointer, number, type);
1165 Newc(x, pointer, number, type, cast);
1166 Newz(x, pointer, number, type);
1168 These three macros are used to initially allocate memory.
1170 The first argument C<x> was a "magic cookie" that was used to keep track
1171 of who called the macro, to help when debugging memory problems. However,
1172 the current code makes no use of this feature (most Perl developers now
1173 use run-time memory checkers), so this argument can be any number.
1175 The second argument C<pointer> should be the name of a variable that will
1176 point to the newly allocated memory.
1178 The third and fourth arguments C<number> and C<type> specify how many of
1179 the specified type of data structure should be allocated. The argument
1180 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
1181 should be used if the C<pointer> argument is different from the C<type>
1184 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
1185 to zero out all the newly allocated memory.
1187 Renew(pointer, number, type);
1188 Renewc(pointer, number, type, cast);
1191 These three macros are used to change a memory buffer size or to free a
1192 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1193 match those of C<New> and C<Newc> with the exception of not needing the
1194 "magic cookie" argument.
1196 Move(source, dest, number, type);
1197 Copy(source, dest, number, type);
1198 Zero(dest, number, type);
1200 These three macros are used to move, copy, or zero out previously allocated
1201 memory. The C<source> and C<dest> arguments point to the source and
1202 destination starting points. Perl will move, copy, or zero out C<number>
1203 instances of the size of the C<type> data structure (using the C<sizeof>
1208 The most recent development releases of Perl has been experimenting with
1209 removing Perl's dependency on the "normal" standard I/O suite and allowing
1210 other stdio implementations to be used. This involves creating a new
1211 abstraction layer that then calls whichever implementation of stdio Perl
1212 was compiled with. All XSUBs should now use the functions in the PerlIO
1213 abstraction layer and not make any assumptions about what kind of stdio
1216 For a complete description of the PerlIO abstraction, consult L<perlapio>.
1218 =head2 Putting a C value on Perl stack
1220 A lot of opcodes (this is an elementary operation in the internal perl
1221 stack machine) put an SV* on the stack. However, as an optimization
1222 the corresponding SV is (usually) not recreated each time. The opcodes
1223 reuse specially assigned SVs (I<target>s) which are (as a corollary)
1224 not constantly freed/created.
1226 Each of the targets is created only once (but see
1227 L<Scratchpads and recursion> below), and when an opcode needs to put
1228 an integer, a double, or a string on stack, it just sets the
1229 corresponding parts of its I<target> and puts the I<target> on stack.
1231 The macro to put this target on stack is C<PUSHTARG>, and it is
1232 directly used in some opcodes, as well as indirectly in zillions of
1233 others, which use it via C<(X)PUSH[pni]>.
1237 The question remains on when the SVs which are I<target>s for opcodes
1238 are created. The answer is that they are created when the current unit --
1239 a subroutine or a file (for opcodes for statements outside of
1240 subroutines) -- is compiled. During this time a special anonymous Perl
1241 array is created, which is called a scratchpad for the current
1244 A scratchpad keeps SVs which are lexicals for the current unit and are
1245 targets for opcodes. One can deduce that an SV lives on a scratchpad
1246 by looking on its flags: lexicals have C<SVs_PADMY> set, and
1247 I<target>s have C<SVs_PADTMP> set.
1249 The correspondence between OPs and I<target>s is not 1-to-1. Different
1250 OPs in the compile tree of the unit can use the same target, if this
1251 would not conflict with the expected life of the temporary.
1253 =head2 Scratchpads and recursion
1255 In fact it is not 100% true that a compiled unit contains a pointer to
1256 the scratchpad AV. In fact it contains a pointer to an AV of
1257 (initially) one element, and this element is the scratchpad AV. Why do
1258 we need an extra level of indirection?
1260 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1261 these can create several execution pointers going into the same
1262 subroutine. For the subroutine-child not write over the temporaries
1263 for the subroutine-parent (lifespan of which covers the call to the
1264 child), the parent and the child should have different
1265 scratchpads. (I<And> the lexicals should be separate anyway!)
1267 So each subroutine is born with an array of scratchpads (of length 1).
1268 On each entry to the subroutine it is checked that the current
1269 depth of the recursion is not more than the length of this array, and
1270 if it is, new scratchpad is created and pushed into the array.
1272 The I<target>s on this scratchpad are C<undef>s, but they are already
1273 marked with correct flags.
1275 =head1 Compiled code
1279 Here we describe the internal form your code is converted to by
1280 Perl. Start with a simple example:
1284 This is converted to a tree similar to this one:
1292 (but slightly more complicated). This tree reflect the way Perl
1293 parsed your code, but has nothing to do with the execution order.
1294 There is an additional "thread" going through the nodes of the tree
1295 which shows the order of execution of the nodes. In our simplified
1296 example above it looks like:
1298 $b ---> $c ---> + ---> $a ---> assign-to
1300 But with the actual compile tree for C<$a = $b + $c> it is different:
1301 some nodes I<optimized away>. As a corollary, though the actual tree
1302 contains more nodes than our simplified example, the execution order
1303 is the same as in our example.
1305 =head2 Examining the tree
1307 If you have your perl compiled for debugging (usually done with C<-D
1308 optimize=-g> on C<Configure> command line), you may examine the
1309 compiled tree by specifying C<-Dx> on the Perl command line. The
1310 output takes several lines per node, and for C<$b+$c> it looks like
1315 FLAGS = (SCALAR,KIDS)
1317 TYPE = null ===> (4)
1319 FLAGS = (SCALAR,KIDS)
1321 3 TYPE = gvsv ===> 4
1327 TYPE = null ===> (5)
1329 FLAGS = (SCALAR,KIDS)
1331 4 TYPE = gvsv ===> 5
1337 This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1338 not optimized away (one per number in the left column). The immediate
1339 children of the given node correspond to C<{}> pairs on the same level
1340 of indentation, thus this listing corresponds to the tree:
1348 The execution order is indicated by C<===E<gt>> marks, thus it is C<3
1349 4 5 6> (node C<6> is not included into above listing), i.e.,
1350 C<gvsv gvsv add whatever>.
1352 =head2 Compile pass 1: check routines
1354 The tree is created by the I<pseudo-compiler> while yacc code feeds it
1355 the constructions it recognizes. Since yacc works bottom-up, so does
1356 the first pass of perl compilation.
1358 What makes this pass interesting for perl developers is that some
1359 optimization may be performed on this pass. This is optimization by
1360 so-called I<check routines>. The correspondence between node names
1361 and corresponding check routines is described in F<opcode.pl> (do not
1362 forget to run C<make regen_headers> if you modify this file).
1364 A check routine is called when the node is fully constructed except
1365 for the execution-order thread. Since at this time there is no
1366 back-links to the currently constructed node, one can do most any
1367 operation to the top-level node, including freeing it and/or creating
1368 new nodes above/below it.
1370 The check routine returns the node which should be inserted into the
1371 tree (if the top-level node was not modified, check routine returns
1374 By convention, check routines have names C<ck_*>. They are usually
1375 called from C<new*OP> subroutines (or C<convert>) (which in turn are
1376 called from F<perly.y>).
1378 =head2 Compile pass 1a: constant folding
1380 Immediately after the check routine is called the returned node is
1381 checked for being compile-time executable. If it is (the value is
1382 judged to be constant) it is immediately executed, and a I<constant>
1383 node with the "return value" of the corresponding subtree is
1384 substituted instead. The subtree is deleted.
1386 If constant folding was not performed, the execution-order thread is
1389 =head2 Compile pass 2: context propagation
1391 When a context for a part of compile tree is known, it is propagated
1392 down through the tree. Aat this time the context can have 5 values
1393 (instead of 2 for runtime context): void, boolean, scalar, list, and
1394 lvalue. In contrast with the pass 1 this pass is processed from top
1395 to bottom: a node's context determines the context for its children.
1397 Additional context-dependent optimizations are performed at this time.
1398 Since at this moment the compile tree contains back-references (via
1399 "thread" pointers), nodes cannot be free()d now. To allow
1400 optimized-away nodes at this stage, such nodes are null()ified instead
1401 of free()ing (i.e. their type is changed to OP_NULL).
1403 =head2 Compile pass 3: peephole optimization
1405 After the compile tree for a subroutine (or for an C<eval> or a file)
1406 is created, an additional pass over the code is performed. This pass
1407 is neither top-down or bottom-up, but in the execution order (with
1408 additional compilications for conditionals). These optimizations are
1409 done in the subroutine peep(). Optimizations performed at this stage
1410 are subject to the same restrictions as in the pass 2.
1414 This is a listing of functions, macros, flags, and variables that may be
1415 useful to extension writers or that may be found while reading other
1426 Clears an array, making it empty. Does not free the memory used by the
1429 void av_clear _((AV* ar));
1433 Pre-extend an array. The C<key> is the index to which the array should be
1436 void av_extend _((AV* ar, I32 key));
1440 Returns the SV at the specified index in the array. The C<key> is the
1441 index. If C<lval> is set then the fetch will be part of a store. Check
1442 that the return value is non-null before dereferencing it to a C<SV*>.
1444 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1445 information on how to use this function on tied arrays.
1447 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1451 Returns the highest index in the array. Returns -1 if the array is empty.
1453 I32 av_len _((AV* ar));
1457 Creates a new AV and populates it with a list of SVs. The SVs are copied
1458 into the array, so they may be freed after the call to av_make. The new AV
1459 will have a reference count of 1.
1461 AV* av_make _((I32 size, SV** svp));
1465 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1468 SV* av_pop _((AV* ar));
1472 Pushes an SV onto the end of the array. The array will grow automatically
1473 to accommodate the addition.
1475 void av_push _((AV* ar, SV* val));
1479 Shifts an SV off the beginning of the array.
1481 SV* av_shift _((AV* ar));
1485 Stores an SV in an array. The array index is specified as C<key>. The
1486 return value will be NULL if the operation failed or if the value did not
1487 need to be actually stored within the array (as in the case of tied arrays).
1488 Otherwise it can be dereferenced to get the original C<SV*>. Note that the
1489 caller is responsible for suitably incrementing the reference count of C<val>
1490 before the call, and decrementing it if the function returned NULL.
1492 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1493 information on how to use this function on tied arrays.
1495 SV** av_store _((AV* ar, I32 key, SV* val));
1499 Undefines the array. Frees the memory used by the array itself.
1501 void av_undef _((AV* ar));
1505 Unshift the given number of C<undef> values onto the beginning of the
1506 array. The array will grow automatically to accommodate the addition.
1507 You must then use C<av_store> to assign values to these new elements.
1509 void av_unshift _((AV* ar, I32 num));
1513 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1514 constructor. This is always a C<char*>. See C<THIS> and
1515 L<perlxs/"Using XS With C++">.
1519 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1520 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1521 the type. May fail on overlapping copies. See also C<Move>.
1523 (void) Copy( s, d, n, t );
1527 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1528 function the same way you use the C C<printf> function. See C<warn>.
1532 Returns the stash of the CV.
1534 HV * CvSTASH( SV* sv )
1538 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1539 boolean which indicates whether subs are being single-stepped.
1540 Single-stepping is automatically turned on after every step. This is the C
1541 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1545 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1546 the SV which holds the name of the sub being debugged. This is the C
1547 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1548 The sub name can be found by
1550 SvPV( GvSV( DBsub ), na )
1554 Trace variable used when Perl is run in debugging mode, with the B<-d>
1555 switch. This is the C variable which corresponds to Perl's $DB::trace
1556 variable. See C<DBsingle>.
1560 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1565 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1569 The C variable which corresponds to Perl's $^W warning variable.
1573 Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
1577 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1578 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1579 to indicate the number of items on the stack.
1583 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1584 handled automatically by C<xsubpp>.
1588 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1594 Used to extend the argument stack for an XSUB's return values.
1596 EXTEND( sp, int x );
1600 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1607 Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
1611 Indicates that arguments returned from a callback should be discarded. See
1616 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1620 A backward-compatible version of C<GIMME_V> which can only return
1621 C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
1625 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
1626 C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
1627 context, respectively.
1631 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1635 Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
1639 Used to indicate void context. See C<GIMME_V> and L<perlcall>.
1643 Returns the glob with the given C<name> and a defined subroutine or
1644 C<NULL>. The glob lives in the given C<stash>, or in the stashes
1645 accessable via @ISA and @<UNIVERSAL>.
1647 The argument C<level> should be either 0 or -1. If C<level==0>, as a
1648 side-effect creates a glob with the given C<name> in the given
1649 C<stash> which in the case of success contains an alias for the
1650 subroutine, and sets up caching info for this glob. Similarly for all
1651 the searched stashes.
1653 This function grants C<"SUPER"> token as a postfix of the stash name.
1655 The GV returned from C<gv_fetchmeth> may be a method cache entry,
1656 which is not visible to Perl code. So when calling C<perl_call_sv>,
1657 you should not use the GV directly; instead, you should use the
1658 method's CV, which can be obtained from the GV with the C<GvCV> macro.
1660 GV* gv_fetchmeth _((HV* stash, char* name, STRLEN len, I32 level));
1662 =item gv_fetchmethod
1664 =item gv_fetchmethod_autoload
1666 Returns the glob which contains the subroutine to call to invoke the
1667 method on the C<stash>. In fact in the presense of autoloading this may
1668 be the glob for "AUTOLOAD". In this case the corresponding variable
1669 $AUTOLOAD is already setup.
1671 The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
1672 lookup is performed if the given method is not present: non-zero means
1673 yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
1674 C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
1675 non-zero C<autoload> parameter.
1677 These functions grant C<"SUPER"> token as a prefix of the method name.
1679 Note that if you want to keep the returned glob for a long time, you
1680 need to check for it being "AUTOLOAD", since at the later time the call
1681 may load a different subroutine due to $AUTOLOAD changing its value.
1682 Use the glob created via a side effect to do this.
1684 These functions have the same side-effects and as C<gv_fetchmeth> with
1685 C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
1686 The warning against passing the GV returned by C<gv_fetchmeth> to
1687 C<perl_call_sv> apply equally to these functions.
1689 GV* gv_fetchmethod _((HV* stash, char* name));
1690 GV* gv_fetchmethod_autoload _((HV* stash, char* name,
1695 Returns a pointer to the stash for a specified package. If C<create> is set
1696 then the package will be created if it does not already exist. If C<create>
1697 is not set and the package does not exist then NULL is returned.
1699 HV* gv_stashpv _((char* name, I32 create));
1703 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1705 HV* gv_stashsv _((SV* sv, I32 create));
1709 Return the SV from the GV.
1713 This flag, used in the length slot of hash entries and magic
1714 structures, specifies the structure contains a C<SV*> pointer where a
1715 C<char*> pointer is to be expected. (For information only--not to be used).
1719 Returns the computed hash (type C<U32>) stored in the hash entry.
1725 Returns the actual pointer stored in the key slot of the hash entry.
1726 The pointer may be either C<char*> or C<SV*>, depending on the value of
1727 C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
1728 are usually preferable for finding the value of a key.
1734 If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
1735 holds an C<SV*> key. Otherwise, holds the actual length of the key.
1736 Can be assigned to. The C<HePV()> macro is usually preferable for finding
1743 Returns the key slot of the hash entry as a C<char*> value, doing any
1744 necessary dereferencing of possibly C<SV*> keys. The length of
1745 the string is placed in C<len> (this is a macro, so do I<not> use
1746 C<&len>). If you do not care about what the length of the key is,
1747 you may use the global variable C<na>. Remember though, that hash
1748 keys in perl are free to contain embedded nulls, so using C<strlen()>
1749 or similar is not a good way to find the length of hash keys.
1750 This is very similar to the C<SvPV()> macro described elsewhere in
1753 HePV(HE* he, STRLEN len)
1757 Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
1758 does not contain an C<SV*> key.
1764 Returns the key as an C<SV*>. Will create and return a temporary
1765 mortal C<SV*> if the hash entry contains only a C<char*> key.
1767 HeSVKEY_force(HE* he)
1771 Sets the key to a given C<SV*>, taking care to set the appropriate flags
1772 to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
1774 HeSVKEY_set(HE* he, SV* sv)
1778 Returns the value slot (type C<SV*>) stored in the hash entry.
1784 Clears a hash, making it empty.
1786 void hv_clear _((HV* tb));
1788 =item hv_delayfree_ent
1790 Releases a hash entry, such as while iterating though the hash, but
1791 delays actual freeing of key and value until the end of the current
1792 statement (or thereabouts) with C<sv_2mortal>. See C<hv_iternext>
1795 void hv_delayfree_ent _((HV* hv, HE* entry));
1799 Deletes a key/value pair in the hash. The value SV is removed from the hash
1800 and returned to the caller. The C<klen> is the length of the key. The
1801 C<flags> value will normally be zero; if set to G_DISCARD then NULL will be
1804 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1808 Deletes a key/value pair in the hash. The value SV is removed from the hash
1809 and returned to the caller. The C<flags> value will normally be zero; if set
1810 to G_DISCARD then NULL will be returned. C<hash> can be a valid precomputed
1811 hash value, or 0 to ask for it to be computed.
1813 SV* hv_delete_ent _((HV* tb, SV* key, I32 flags, U32 hash));
1817 Returns a boolean indicating whether the specified hash key exists. The
1818 C<klen> is the length of the key.
1820 bool hv_exists _((HV* tb, char* key, U32 klen));
1824 Returns a boolean indicating whether the specified hash key exists. C<hash>
1825 can be a valid precomputed hash value, or 0 to ask for it to be computed.
1827 bool hv_exists_ent _((HV* tb, SV* key, U32 hash));
1831 Returns the SV which corresponds to the specified key in the hash. The
1832 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1833 part of a store. Check that the return value is non-null before
1834 dereferencing it to a C<SV*>.
1836 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1837 information on how to use this function on tied hashes.
1839 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1843 Returns the hash entry which corresponds to the specified key in the hash.
1844 C<hash> must be a valid precomputed hash number for the given C<key>, or
1845 0 if you want the function to compute it. IF C<lval> is set then the
1846 fetch will be part of a store. Make sure the return value is non-null
1847 before accessing it. The return value when C<tb> is a tied hash
1848 is a pointer to a static location, so be sure to make a copy of the
1849 structure if you need to store it somewhere.
1851 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1852 information on how to use this function on tied hashes.
1854 HE* hv_fetch_ent _((HV* tb, SV* key, I32 lval, U32 hash));
1858 Releases a hash entry, such as while iterating though the hash. See
1859 C<hv_iternext> and C<hv_delayfree_ent>.
1861 void hv_free_ent _((HV* hv, HE* entry));
1865 Prepares a starting point to traverse a hash table.
1867 I32 hv_iterinit _((HV* tb));
1869 Note that hv_iterinit I<currently> returns the number of I<buckets> in
1870 the hash and I<not> the number of keys (as indicated in the Advanced
1871 Perl Programming book). This may change in future. Use the HvKEYS(hv)
1872 macro to find the number of keys in a hash.
1876 Returns the key from the current position of the hash iterator. See
1879 char* hv_iterkey _((HE* entry, I32* retlen));
1883 Returns the key as an C<SV*> from the current position of the hash
1884 iterator. The return value will always be a mortal copy of the
1885 key. Also see C<hv_iterinit>.
1887 SV* hv_iterkeysv _((HE* entry));
1891 Returns entries from a hash iterator. See C<hv_iterinit>.
1893 HE* hv_iternext _((HV* tb));
1897 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1900 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1904 Returns the value from the current position of the hash iterator. See
1907 SV* hv_iterval _((HV* tb, HE* entry));
1911 Adds magic to a hash. See C<sv_magic>.
1913 void hv_magic _((HV* hv, GV* gv, int how));
1917 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1919 char *HvNAME (HV* stash)
1923 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1924 the length of the key. The C<hash> parameter is the precomputed hash
1925 value; if it is zero then Perl will compute it. The return value will be
1926 NULL if the operation failed or if the value did not need to be actually
1927 stored within the hash (as in the case of tied hashes). Otherwise it can
1928 be dereferenced to get the original C<SV*>. Note that the caller is
1929 responsible for suitably incrementing the reference count of C<val>
1930 before the call, and decrementing it if the function returned NULL.
1932 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1933 information on how to use this function on tied hashes.
1935 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1939 Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
1940 parameter is the precomputed hash value; if it is zero then Perl will
1941 compute it. The return value is the new hash entry so created. It will be
1942 NULL if the operation failed or if the value did not need to be actually
1943 stored within the hash (as in the case of tied hashes). Otherwise the
1944 contents of the return value can be accessed using the C<He???> macros
1945 described here. Note that the caller is responsible for suitably
1946 incrementing the reference count of C<val> before the call, and decrementing
1947 it if the function returned NULL.
1949 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1950 information on how to use this function on tied hashes.
1952 HE* hv_store_ent _((HV* tb, SV* key, SV* val, U32 hash));
1958 void hv_undef _((HV* tb));
1962 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
1965 int isALNUM (char c)
1969 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
1972 int isALPHA (char c)
1976 Returns a boolean indicating whether the C C<char> is an ascii digit.
1978 int isDIGIT (char c)
1982 Returns a boolean indicating whether the C C<char> is a lowercase character.
1984 int isLOWER (char c)
1988 Returns a boolean indicating whether the C C<char> is whitespace.
1990 int isSPACE (char c)
1994 Returns a boolean indicating whether the C C<char> is an uppercase character.
1996 int isUPPER (char c)
2000 Variable which is setup by C<xsubpp> to indicate the number of items on the
2001 stack. See L<perlxs/"Variable-length Parameter Lists">.
2005 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
2006 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
2010 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
2016 Stack marker variable for the XSUB. See C<dMARK>.
2020 Clear something magical that the SV represents. See C<sv_magic>.
2022 int mg_clear _((SV* sv));
2026 Copies the magic from one SV to another. See C<sv_magic>.
2028 int mg_copy _((SV *, SV *, char *, STRLEN));
2032 Finds the magic pointer for type matching the SV. See C<sv_magic>.
2034 MAGIC* mg_find _((SV* sv, int type));
2038 Free any magic storage used by the SV. See C<sv_magic>.
2040 int mg_free _((SV* sv));
2044 Do magic after a value is retrieved from the SV. See C<sv_magic>.
2046 int mg_get _((SV* sv));
2050 Report on the SV's length. See C<sv_magic>.
2052 U32 mg_len _((SV* sv));
2056 Turns on the magical status of an SV. See C<sv_magic>.
2058 void mg_magical _((SV* sv));
2062 Do magic after a value is assigned to the SV. See C<sv_magic>.
2064 int mg_set _((SV* sv));
2068 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
2069 source, C<d> is the destination, C<n> is the number of items, and C<t> is
2070 the type. Can do overlapping moves. See also C<Copy>.
2072 (void) Move( s, d, n, t );
2076 A variable which may be used with C<SvPV> to tell Perl to calculate the
2081 The XSUB-writer's interface to the C C<malloc> function.
2083 void * New( x, void *ptr, int size, type )
2087 The XSUB-writer's interface to the C C<malloc> function, with cast.
2089 void * Newc( x, void *ptr, int size, type, cast )
2093 The XSUB-writer's interface to the C C<malloc> function. The allocated
2094 memory is zeroed with C<memzero>.
2096 void * Newz( x, void *ptr, int size, type )
2100 Creates a new AV. The reference count is set to 1.
2102 AV* newAV _((void));
2106 Creates a new HV. The reference count is set to 1.
2108 HV* newHV _((void));
2112 Creates an RV wrapper for an SV. The reference count for the original SV is
2115 SV* newRV_inc _((SV* ref));
2117 For historical reasons, "newRV" is a synonym for "newRV_inc".
2121 Creates an RV wrapper for an SV. The reference count for the original
2122 SV is B<not> incremented.
2124 SV* newRV_noinc _((SV* ref));
2128 Creates a new SV. The C<len> parameter indicates the number of bytes of
2129 preallocated string space the SV should have. The reference count for the
2132 SV* newSV _((STRLEN len));
2136 Creates a new SV and copies an integer into it. The reference count for the
2139 SV* newSViv _((IV i));
2143 Creates a new SV and copies a double into it. The reference count for the
2146 SV* newSVnv _((NV i));
2150 Creates a new SV and copies a string into it. The reference count for the
2151 SV is set to 1. If C<len> is zero then Perl will compute the length.
2153 SV* newSVpv _((char* s, STRLEN len));
2157 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
2158 it will be upgraded to one. If C<classname> is non-null then the new SV will
2159 be blessed in the specified package. The new SV is returned and its
2160 reference count is 1.
2162 SV* newSVrv _((SV* rv, char* classname));
2166 Creates a new SV which is an exact duplicate of the original SV.
2168 SV* newSVsv _((SV* old));
2172 Used by C<xsubpp> to hook up XSUBs as Perl subs.
2176 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
2185 Null character pointer.
2201 The original stack mark for the XSUB. See C<dORIGMARK>.
2205 Allocates a new Perl interpreter. See L<perlembed>.
2207 =item perl_call_argv
2209 Performs a callback to the specified Perl sub. See L<perlcall>.
2211 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
2213 =item perl_call_method
2215 Performs a callback to the specified Perl method. The blessed object must
2216 be on the stack. See L<perlcall>.
2218 I32 perl_call_method _((char* methname, I32 flags));
2222 Performs a callback to the specified Perl sub. See L<perlcall>.
2224 I32 perl_call_pv _((char* subname, I32 flags));
2228 Performs a callback to the Perl sub whose name is in the SV. See
2231 I32 perl_call_sv _((SV* sv, I32 flags));
2233 =item perl_construct
2235 Initializes a new Perl interpreter. See L<perlembed>.
2239 Shuts down a Perl interpreter. See L<perlembed>.
2243 Tells Perl to C<eval> the string in the SV.
2245 I32 perl_eval_sv _((SV* sv, I32 flags));
2249 Tells Perl to C<eval> the given string and return an SV* result.
2251 SV* perl_eval_pv _((char* p, I32 croak_on_error));
2255 Releases a Perl interpreter. See L<perlembed>.
2259 Returns the AV of the specified Perl array. If C<create> is set and the
2260 Perl variable does not exist then it will be created. If C<create> is not
2261 set and the variable does not exist then NULL is returned.
2263 AV* perl_get_av _((char* name, I32 create));
2267 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
2268 variable does not exist then it will be created. If C<create> is not
2269 set and the variable does not exist then NULL is returned.
2271 CV* perl_get_cv _((char* name, I32 create));
2275 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
2276 variable does not exist then it will be created. If C<create> is not
2277 set and the variable does not exist then NULL is returned.
2279 HV* perl_get_hv _((char* name, I32 create));
2283 Returns the SV of the specified Perl scalar. If C<create> is set and the
2284 Perl variable does not exist then it will be created. If C<create> is not
2285 set and the variable does not exist then NULL is returned.
2287 SV* perl_get_sv _((char* name, I32 create));
2291 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
2293 =item perl_require_pv
2295 Tells Perl to C<require> a module.
2297 void perl_require_pv _((char* pv));
2301 Tells a Perl interpreter to run. See L<perlembed>.
2305 Pops an integer off the stack.
2311 Pops a long off the stack.
2317 Pops a string off the stack.
2323 Pops a double off the stack.
2329 Pops an SV off the stack.
2335 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2341 Push an integer onto the stack. The stack must have room for this element.
2342 Handles 'set' magic. See C<XPUSHi>.
2348 Push a double onto the stack. The stack must have room for this element.
2349 Handles 'set' magic. See C<XPUSHn>.
2355 Push a string onto the stack. The stack must have room for this element.
2356 The C<len> indicates the length of the string. Handles 'set' magic. See
2359 PUSHp(char *c, int len )
2363 Push an SV onto the stack. The stack must have room for this element. Does
2364 not handle 'set' magic. See C<XPUSHs>.
2370 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2371 See C<PUSHMARK> and L<perlcall> for other uses.
2377 The XSUB-writer's interface to the C C<realloc> function.
2379 void * Renew( void *ptr, int size, type )
2383 The XSUB-writer's interface to the C C<realloc> function, with cast.
2385 void * Renewc( void *ptr, int size, type, cast )
2389 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
2390 This is always the proper type for the XSUB.
2391 See L<perlxs/"The RETVAL Variable">.
2395 The XSUB-writer's interface to the C C<free> function.
2399 The XSUB-writer's interface to the C C<malloc> function.
2403 The XSUB-writer's interface to the C C<realloc> function.
2407 Copy a string to a safe spot. This does not use an SV.
2409 char* savepv _((char* sv));
2413 Copy a string to a safe spot. The C<len> indicates number of bytes to
2414 copy. This does not use an SV.
2416 char* savepvn _((char* sv, I32 len));
2420 Opening bracket for temporaries on a callback. See C<FREETMPS> and
2427 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2432 Refetch the stack pointer. Used after a callback. See L<perlcall>.
2438 Used to access elements on the XSUB's stack.
2444 Test two strings to see if they are equal. Returns true or false.
2446 int strEQ( char *s1, char *s2 )
2450 Test two strings to see if the first, C<s1>, is greater than or equal to the
2451 second, C<s2>. Returns true or false.
2453 int strGE( char *s1, char *s2 )
2457 Test two strings to see if the first, C<s1>, is greater than the second,
2458 C<s2>. Returns true or false.
2460 int strGT( char *s1, char *s2 )
2464 Test two strings to see if the first, C<s1>, is less than or equal to the
2465 second, C<s2>. Returns true or false.
2467 int strLE( char *s1, char *s2 )
2471 Test two strings to see if the first, C<s1>, is less than the second,
2472 C<s2>. Returns true or false.
2474 int strLT( char *s1, char *s2 )
2478 Test two strings to see if they are different. Returns true or false.
2480 int strNE( char *s1, char *s2 )
2484 Test two strings to see if they are equal. The C<len> parameter indicates
2485 the number of bytes to compare. Returns true or false.
2487 int strnEQ( char *s1, char *s2 )
2491 Test two strings to see if they are different. The C<len> parameter
2492 indicates the number of bytes to compare. Returns true or false.
2494 int strnNE( char *s1, char *s2, int len )
2498 Marks an SV as mortal. The SV will be destroyed when the current context
2501 SV* sv_2mortal _((SV* sv));
2505 Blesses an SV into a specified package. The SV must be an RV. The package
2506 must be designated by its stash (see C<gv_stashpv()>). The reference count
2507 of the SV is unaffected.
2509 SV* sv_bless _((SV* sv, HV* stash));
2519 Concatenates the string onto the end of the string which is in the SV.
2520 Handles 'get' magic, but not 'set' magic. See C<SvCatMagicPV>.
2522 void sv_catpv _((SV* sv, char* ptr));
2526 Concatenates the string onto the end of the string which is in the SV. The
2527 C<len> indicates number of bytes to copy. Handles 'get' magic, but not
2528 'set' magic. See C<SvCatMagicPVN).
2530 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
2534 Processes its arguments like C<sprintf> and appends the formatted output
2535 to an SV. Handles 'get' magic, but not 'set' magic. C<SvSETMAGIC()> must
2536 typically be called after calling this function to handle 'set' magic.
2538 void sv_catpvf _((SV* sv, const char* pat, ...));
2542 Concatenates the string from SV C<ssv> onto the end of the string in SV
2543 C<dsv>. Handles 'get' magic, but not 'set' magic. See C<SvCatMagicSV).
2545 void sv_catsv _((SV* dsv, SV* ssv));
2549 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2550 string in C<sv1> is less than, equal to, or greater than the string in
2553 I32 sv_cmp _((SV* sv1, SV* sv2));
2557 Returns the length of the string which is in the SV. See C<SvLEN>.
2563 Set the length of the string which is in the SV. See C<SvCUR>.
2565 SvCUR_set (SV* sv, int val )
2569 Auto-decrement of the value in the SV.
2571 void sv_dec _((SV* sv));
2575 Returns a pointer to the last character in the string which is in the SV.
2576 See C<SvCUR>. Access the character as
2582 Returns a boolean indicating whether the strings in the two SVs are
2585 I32 sv_eq _((SV* sv1, SV* sv2));
2589 Invokes C<mg_get> on an SV if it has 'get' magic. This macro evaluates
2590 its argument more than once.
2592 void SvGETMAGIC( SV *sv )
2596 Expands the character buffer in the SV. Calls C<sv_grow> to perform the
2597 expansion if necessary. Returns a pointer to the character buffer.
2599 char * SvGROW( SV* sv, int len )
2603 Expands the character buffer in the SV. This will use C<sv_unref> and will
2604 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2609 Auto-increment of the value in the SV.
2611 void sv_inc _((SV* sv));
2615 Returns a boolean indicating whether the SV contains an integer.
2621 Unsets the IV status of an SV.
2627 Tells an SV that it is an integer.
2633 Tells an SV that it is an integer and disables all other OK bits.
2639 Returns a boolean indicating whether the SV contains an integer. Checks the
2640 B<private> setting. Use C<SvIOK>.
2646 Returns a boolean indicating whether the SV is blessed into the specified
2647 class. This does not know how to check for subtype, so it doesn't work in
2648 an inheritance relationship.
2650 int sv_isa _((SV* sv, char* name));
2654 Returns the integer which is in the SV.
2660 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2661 object. If the SV is not an RV, or if the object is not blessed, then this
2664 int sv_isobject _((SV* sv));
2668 Returns the integer which is stored in the SV.
2674 Returns the size of the string buffer in the SV. See C<SvCUR>.
2680 Returns the length of the string in the SV. Use C<SvCUR>.
2682 STRLEN sv_len _((SV* sv));
2686 Adds magic to an SV.
2688 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2692 Creates a new SV which is a copy of the original SV. The new SV is marked
2695 SV* sv_mortalcopy _((SV* oldsv));
2699 Returns a boolean indicating whether the value is an SV.
2705 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2707 SV* sv_newmortal _((void));
2711 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2715 Returns a boolean indicating whether the SV contains a number, integer or
2722 Unsets the NV/IV status of an SV.
2728 Returns a boolean indicating whether the SV contains a number, integer or
2729 double. Checks the B<private> setting. Use C<SvNIOK>.
2731 int SvNIOKp (SV* SV)
2735 Returns a boolean indicating whether the SV contains a double.
2741 Unsets the NV status of an SV.
2747 Tells an SV that it is a double.
2753 Tells an SV that it is a double and disables all other OK bits.
2759 Returns a boolean indicating whether the SV contains a double. Checks the
2760 B<private> setting. Use C<SvNOK>.
2766 Returns the double which is stored in the SV.
2768 double SvNV (SV* sv);
2772 Returns the double which is stored in the SV.
2774 double SvNVX (SV* sv);
2778 Returns a boolean indicating whether the SV contains a character string.
2784 Unsets the PV status of an SV.
2790 Tells an SV that it is a string.
2796 Tells an SV that it is a string and disables all other OK bits.
2802 Returns a boolean indicating whether the SV contains a character string.
2803 Checks the B<private> setting. Use C<SvPOK>.
2809 Returns a pointer to the string in the SV, or a stringified form of the SV
2810 if the SV does not contain a string. If C<len> is C<na> then Perl will
2811 handle the length on its own. Handles 'get' magic.
2813 char * SvPV (SV* sv, int len )
2817 Returns a pointer to the string in the SV. The SV must contain a string.
2819 char * SvPVX (SV* sv)
2823 Returns the value of the object's reference count.
2825 int SvREFCNT (SV* sv);
2829 Decrements the reference count of the given SV.
2831 void SvREFCNT_dec (SV* sv)
2835 Increments the reference count of the given SV.
2837 void SvREFCNT_inc (SV* sv)
2841 Tests if the SV is an RV.
2847 Unsets the RV status of an SV.
2853 Tells an SV that it is an RV.
2859 Dereferences an RV to return the SV.
2865 Invokes C<mg_set> on an SV if it has 'set' magic. This macro evaluates
2866 its argument more than once.
2868 void SvSETMAGIC( SV *sv )
2872 Taints an SV if tainting is enabled
2878 Checks to see if an SV is tainted. Returns TRUE if it is, FALSE if not.
2884 Untaints an SV. Be I<very> careful with this routine, as it short-circuits
2885 some of Perl's fundamental security features. XS module authors should
2886 not use this function unless they fully understand all the implications
2887 of unconditionally untainting the value. Untainting should be done in
2888 the standard perl fashion, via a carefully crafted regexp, rather than
2889 directly untainting variables.
2891 SvTAINTED_off (SV* sv);
2895 Marks an SV as tainted.
2897 SvTAINTED_on (SV* sv);
2901 A macro that calls C<sv_setiv>, and invokes 'set' magic on the SV.
2902 May evaluate arguments more than once.
2904 void SvSetMagicIV (SV* sv, IV num)
2908 A macro that calls C<sv_setnv>, and invokes 'set' magic on the SV.
2909 May evaluate arguments more than once.
2911 void SvSetMagicNV (SV* sv, double num)
2915 A macro that calls C<sv_setpv>, and invokes 'set' magic on the SV.
2916 May evaluate arguments more than once.
2918 void SvSetMagicPV (SV* sv, char *ptr)
2920 =item SvSetMagicPVIV
2922 A macro that calls C<sv_setpviv>, and invokes 'set' magic on the SV.
2923 May evaluate arguments more than once.
2925 void SvSetMagicPVIV (SV* sv, IV num)
2929 A macro that calls C<sv_setpvn>, and invokes 'set' magic on the SV.
2930 May evaluate arguments more than once.
2932 void SvSetMagicPVN (SV* sv, char* ptr, STRLEN len)
2936 Same as C<SvSetSV>, but also invokes 'set' magic on the SV.
2937 May evaluate arguments more than once.
2939 void SvSetMagicSV (SV* dsv, SV* ssv)
2941 =item SvSetMagicSV_nosteal
2943 Same as C<SvSetSV_nosteal>, but also invokes 'set' magic on the SV.
2944 May evaluate arguments more than once.
2946 void SvSetMagicSV_nosteal (SV* dsv, SV* ssv)
2950 A macro that calls C<sv_setuv>, and invokes 'set' magic on the SV.
2951 May evaluate arguments more than once.
2953 void SvSetMagicUV (SV* sv, UV num)
2957 Copies an integer into the given SV. Does not handle 'set' magic.
2958 See C<SvSetMagicIV>.
2960 void sv_setiv _((SV* sv, IV num));
2964 Copies a double into the given SV. Does not handle 'set' magic.
2965 See C<SvSetMagicNV>.
2967 void sv_setnv _((SV* sv, double num));
2971 Copies a string into an SV. The string must be null-terminated.
2972 Does not handle 'set' magic. See C<SvSetMagicPV>.
2974 void sv_setpv _((SV* sv, char* ptr));
2978 Copies an integer into the given SV, also updating its string value.
2979 Does not handle 'set' magic. See C<SvSetMagicPVIV>.
2981 void sv_setpviv _((SV* sv, IV num));
2985 Copies a string into an SV. The C<len> parameter indicates the number of
2986 bytes to be copied. Does not handle 'set' magic. See C<SvSetMagicPVN>.
2988 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2992 Processes its arguments like C<sprintf> and sets an SV to the formatted
2993 output. Does not handle 'set' magic. C<SvSETMAGIC()> must typically
2994 be called after calling this function to handle 'set' magic.
2996 void sv_setpvf _((SV* sv, const char* pat, ...));
3000 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
3001 argument will be upgraded to an RV. That RV will be modified to point to
3002 the new SV. The C<classname> argument indicates the package for the
3003 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3004 will be returned and will have a reference count of 1.
3006 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
3010 Copies a double into a new SV, optionally blessing the SV. The C<rv>
3011 argument will be upgraded to an RV. That RV will be modified to point to
3012 the new SV. The C<classname> argument indicates the package for the
3013 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3014 will be returned and will have a reference count of 1.
3016 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
3020 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
3021 argument will be upgraded to an RV. That RV will be modified to point to
3022 the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
3023 into the SV. The C<classname> argument indicates the package for the
3024 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3025 will be returned and will have a reference count of 1.
3027 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
3029 Do not use with integral Perl types such as HV, AV, SV, CV, because those
3030 objects will become corrupted by the pointer copy process.
3032 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
3036 Copies a string into a new SV, optionally blessing the SV. The length of the
3037 string must be specified with C<n>. The C<rv> argument will be upgraded to
3038 an RV. That RV will be modified to point to the new SV. The C<classname>
3039 argument indicates the package for the blessing. Set C<classname> to
3040 C<Nullch> to avoid the blessing. The new SV will be returned and will have
3041 a reference count of 1.
3043 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
3045 Note that C<sv_setref_pv> copies the pointer while this copies the string.
3049 Calls C<sv_setsv> if dsv is not the same as ssv. May evaluate arguments
3052 void SvSetSV (SV* dsv, SV* ssv)
3054 =item SvSetSV_nosteal
3056 Calls a non-destructive version of C<sv_setsv> if dsv is not the same as ssv.
3057 May evaluate arguments more than once.
3059 void SvSetSV_nosteal (SV* dsv, SV* ssv)
3063 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
3064 The source SV may be destroyed if it is mortal. Does not handle 'set' magic.
3065 See the macro forms C<SvSetSV>, C<SvSetSV_nosteal>, C<SvSetMagicSV> and
3066 C<SvSetMagicSV_nosteal>.
3068 void sv_setsv _((SV* dsv, SV* ssv));
3072 Copies an unsigned integer into the given SV. Does not handle 'set' magic.
3073 See C<SvSetMagicUV>.
3075 void sv_setuv _((SV* sv, UV num));
3079 Returns the stash of the SV.
3081 HV * SvSTASH (SV* sv)
3085 Integer type flag for scalars. See C<svtype>.
3089 Pointer type flag for scalars. See C<svtype>.
3093 Type flag for arrays. See C<svtype>.
3097 Type flag for code refs. See C<svtype>.
3101 Type flag for hashes. See C<svtype>.
3105 Type flag for blessed scalars. See C<svtype>.
3109 Double type flag for scalars. See C<svtype>.
3113 Returns a boolean indicating whether Perl would evaluate the SV as true or
3114 false, defined or undefined. Does not handle 'get' magic.
3120 Returns the type of the SV. See C<svtype>.
3122 svtype SvTYPE (SV* sv)
3126 An enum of flags for Perl types. These are found in the file B<sv.h> in the
3127 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
3131 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
3132 the upgrade if necessary. See C<svtype>.
3134 bool SvUPGRADE _((SV* sv, svtype mt));
3138 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
3142 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
3146 Unsets the RV status of the SV, and decrements the reference count of
3147 whatever was being referenced by the RV. This can almost be thought of
3148 as a reversal of C<newSVrv>. See C<SvROK_off>.
3150 void sv_unref _((SV* sv));
3156 Tells an SV to use C<ptr> to find its string value. Normally the string is
3157 stored inside the SV but sv_usepvn allows the SV to use an outside string.
3158 The C<ptr> should point to memory that was allocated by C<malloc>. The
3159 string length, C<len>, must be supplied. This function will realloc the
3160 memory pointed to by C<ptr>, so that pointer should not be freed or used by
3161 the programmer after giving it to sv_usepvn. Does not handle 'set' magic.
3162 See C<SvUseMagicPVN>.
3164 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
3168 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
3172 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
3173 This is always the proper type for the C++ object. See C<CLASS> and
3174 L<perlxs/"Using XS With C++">.
3178 Converts the specified character to lowercase.
3180 int toLOWER (char c)
3184 Converts the specified character to uppercase.
3186 int toUPPER (char c)
3190 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
3191 function the same way you use the C C<printf> function. See C<croak()>.
3195 Push an integer onto the stack, extending the stack if necessary. Handles
3196 'set' magic. See C<PUSHi>.
3202 Push a double onto the stack, extending the stack if necessary. Handles 'set'
3203 magic. See C<PUSHn>.
3209 Push a string onto the stack, extending the stack if necessary. The C<len>
3210 indicates the length of the string. Handles 'set' magic. See C<PUSHp>.
3212 XPUSHp(char *c, int len)
3216 Push an SV onto the stack, extending the stack if necessary. Does not
3217 handle 'set' magic. See C<PUSHs>.
3223 Macro to declare an XSUB and its C parameter list. This is handled by
3228 Return from XSUB, indicating number of items on the stack. This is usually
3229 handled by C<xsubpp>.
3233 =item XSRETURN_EMPTY
3235 Return an empty list from an XSUB immediately.
3241 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
3247 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
3253 Return an double from an XSUB immediately. Uses C<XST_mNV>.
3259 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
3261 XSRETURN_PV(char *v);
3263 =item XSRETURN_UNDEF
3265 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
3271 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
3277 Place an integer into the specified position C<i> on the stack. The value is
3278 stored in a new mortal SV.
3280 XST_mIV( int i, IV v );
3284 Place a double into the specified position C<i> on the stack. The value is
3285 stored in a new mortal SV.
3287 XST_mNV( int i, NV v );
3291 Place C<&sv_no> into the specified position C<i> on the stack.
3297 Place a copy of a string into the specified position C<i> on the stack. The
3298 value is stored in a new mortal SV.
3300 XST_mPV( int i, char *v );
3304 Place C<&sv_undef> into the specified position C<i> on the stack.
3306 XST_mUNDEF( int i );
3310 Place C<&sv_yes> into the specified position C<i> on the stack.
3316 The version identifier for an XS module. This is usually handled
3317 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
3319 =item XS_VERSION_BOOTCHECK
3321 Macro to verify that a PM module's $VERSION variable matches the XS module's
3322 C<XS_VERSION> variable. This is usually handled automatically by
3323 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
3327 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
3328 destination, C<n> is the number of items, and C<t> is the type.
3330 (void) Zero( d, n, t );
3336 Jeff Okamoto <F<okamoto@corp.hp.com>>
3338 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
3339 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
3340 Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
3341 Stephen McCamant, and Gurusamy Sarathy.
3343 API Listing by Dean Roehrich <F<roehrich@cray.com>>.
3347 Version 31.8: 1997/5/17