3 perlguts - Perl's Internal Functions
7 This document attempts to describe some of the internal functions of the
8 Perl executable. It is far from complete and probably contains many errors.
9 Please refer any questions or comments to the author below.
15 Perl has three typedefs that handle Perl's three main data types:
21 Each typedef has specific routines that manipulate the various data types.
23 =head2 What is an "IV"?
25 Perl uses a special typedef IV which is a simple integer type that is
26 guaranteed to be large enough to hold a pointer (as well as an integer).
28 Perl also uses two special typedefs, I32 and I16, which will always be at
29 least 32-bits and 16-bits long, respectively.
31 =head2 Working with SVs
33 An SV can be created and loaded with one command. There are four types of
34 values that can be loaded: an integer value (IV), a double (NV), a string,
35 (PV), and another scalar (SV).
41 SV* newSVpv(const char*, int);
42 SV* newSVpvn(const char*, int);
43 SV* newSVpvf(const char*, ...);
46 To change the value of an *already-existing* SV, there are seven routines:
48 void sv_setiv(SV*, IV);
49 void sv_setuv(SV*, UV);
50 void sv_setnv(SV*, double);
51 void sv_setpv(SV*, const char*);
52 void sv_setpvn(SV*, const char*, int)
53 void sv_setpvf(SV*, const char*, ...);
54 void sv_setpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
55 void sv_setsv(SV*, SV*);
57 Notice that you can choose to specify the length of the string to be
58 assigned by using C<sv_setpvn>, C<newSVpvn>, or C<newSVpv>, or you may
59 allow Perl to calculate the length by using C<sv_setpv> or by specifying
60 0 as the second argument to C<newSVpv>. Be warned, though, that Perl will
61 determine the string's length by using C<strlen>, which depends on the
62 string terminating with a NUL character.
64 The arguments of C<sv_setpvf> are processed like C<sprintf>, and the
65 formatted output becomes the value.
67 C<sv_setpvfn> is an analogue of C<vsprintf>, but it allows you to specify
68 either a pointer to a variable argument list or the address and length of
69 an array of SVs. The last argument points to a boolean; on return, if that
70 boolean is true, then locale-specific information has been used to format
71 the string, and the string's contents are therefore untrustworthy (see
72 L<perlsec>). This pointer may be NULL if that information is not
73 important. Note that this function requires you to specify the length of
76 The C<sv_set*()> functions are not generic enough to operate on values
77 that have "magic". See L<Magic Virtual Tables> later in this document.
79 All SVs that contain strings should be terminated with a NUL character.
80 If it is not NUL-terminated there is a risk of
81 core dumps and corruptions from code which passes the string to C
82 functions or system calls which expect a NUL-terminated string.
83 Perl's own functions typically add a trailing NUL for this reason.
84 Nevertheless, you should be very careful when you pass a string stored
85 in an SV to a C function or system call.
87 To access the actual value that an SV points to, you can use the macros:
94 which will automatically coerce the actual scalar type into an IV, double,
97 In the C<SvPV> macro, the length of the string returned is placed into the
98 variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do
99 not care what the length of the data is, use the C<SvPV_nolen> macro.
100 Historically the C<SvPV> macro with the global variable C<PL_na> has been
101 used in this case. But that can be quite inefficient because C<PL_na> must
102 be accessed in thread-local storage in threaded Perl. In any case, remember
103 that Perl allows arbitrary strings of data that may both contain NULs and
104 might not be terminated by a NUL.
106 Also remember that C doesn't allow you to safely say C<foo(SvPV(s, len),
107 len);>. It might work with your compiler, but it won't work for everyone.
108 Break this sort of statement up into separate assignments:
116 If you want to know if the scalar value is TRUE, you can use:
120 Although Perl will automatically grow strings for you, if you need to force
121 Perl to allocate more memory for your SV, you can use the macro
123 SvGROW(SV*, STRLEN newlen)
125 which will determine if more memory needs to be allocated. If so, it will
126 call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
127 decrease, the allocated memory of an SV and that it does not automatically
128 add a byte for the a trailing NUL (perl's own string functions typically do
129 C<SvGROW(sv, len + 1)>).
131 If you have an SV and want to know what kind of data Perl thinks is stored
132 in it, you can use the following macros to check the type of SV you have.
138 You can get and set the current length of the string stored in an SV with
139 the following macros:
142 SvCUR_set(SV*, I32 val)
144 You can also get a pointer to the end of the string stored in the SV
149 But note that these last three macros are valid only if C<SvPOK()> is true.
151 If you want to append something to the end of string stored in an C<SV*>,
152 you can use the following functions:
154 void sv_catpv(SV*, const char*);
155 void sv_catpvn(SV*, const char*, STRLEN);
156 void sv_catpvf(SV*, const char*, ...);
157 void sv_catpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
158 void sv_catsv(SV*, SV*);
160 The first function calculates the length of the string to be appended by
161 using C<strlen>. In the second, you specify the length of the string
162 yourself. The third function processes its arguments like C<sprintf> and
163 appends the formatted output. The fourth function works like C<vsprintf>.
164 You can specify the address and length of an array of SVs instead of the
165 va_list argument. The fifth function extends the string stored in the first
166 SV with the string stored in the second SV. It also forces the second SV
167 to be interpreted as a string.
169 The C<sv_cat*()> functions are not generic enough to operate on values that
170 have "magic". See L<Magic Virtual Tables> later in this document.
172 If you know the name of a scalar variable, you can get a pointer to its SV
173 by using the following:
175 SV* perl_get_sv("package::varname", FALSE);
177 This returns NULL if the variable does not exist.
179 If you want to know if this variable (or any other SV) is actually C<defined>,
184 The scalar C<undef> value is stored in an SV instance called C<PL_sv_undef>. Its
185 address can be used whenever an C<SV*> is needed.
187 There are also the two values C<PL_sv_yes> and C<PL_sv_no>, which contain Boolean
188 TRUE and FALSE values, respectively. Like C<PL_sv_undef>, their addresses can
189 be used whenever an C<SV*> is needed.
191 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&PL_sv_undef>.
195 if (I-am-to-return-a-real-value) {
196 sv = sv_2mortal(newSViv(42));
200 This code tries to return a new SV (which contains the value 42) if it should
201 return a real value, or undef otherwise. Instead it has returned a NULL
202 pointer which, somewhere down the line, will cause a segmentation violation,
203 bus error, or just weird results. Change the zero to C<&PL_sv_undef> in the first
204 line and all will be well.
206 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
207 call is not necessary (see L<Reference Counts and Mortality>).
209 =head2 What's Really Stored in an SV?
211 Recall that the usual method of determining the type of scalar you have is
212 to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
213 usually these macros will always return TRUE and calling the C<Sv*V>
214 macros will do the appropriate conversion of string to integer/double or
215 integer/double to string.
217 If you I<really> need to know if you have an integer, double, or string
218 pointer in an SV, you can use the following three macros instead:
224 These will tell you if you truly have an integer, double, or string pointer
225 stored in your SV. The "p" stands for private.
227 In general, though, it's best to use the C<Sv*V> macros.
229 =head2 Working with AVs
231 There are two ways to create and load an AV. The first method creates an
236 The second method both creates the AV and initially populates it with SVs:
238 AV* av_make(I32 num, SV **ptr);
240 The second argument points to an array containing C<num> C<SV*>'s. Once the
241 AV has been created, the SVs can be destroyed, if so desired.
243 Once the AV has been created, the following operations are possible on AVs:
245 void av_push(AV*, SV*);
248 void av_unshift(AV*, I32 num);
250 These should be familiar operations, with the exception of C<av_unshift>.
251 This routine adds C<num> elements at the front of the array with the C<undef>
252 value. You must then use C<av_store> (described below) to assign values
253 to these new elements.
255 Here are some other functions:
258 SV** av_fetch(AV*, I32 key, I32 lval);
259 SV** av_store(AV*, I32 key, SV* val);
261 The C<av_len> function returns the highest index value in array (just
262 like $#array in Perl). If the array is empty, -1 is returned. The
263 C<av_fetch> function returns the value at index C<key>, but if C<lval>
264 is non-zero, then C<av_fetch> will store an undef value at that index.
265 The C<av_store> function stores the value C<val> at index C<key>, and does
266 not increment the reference count of C<val>. Thus the caller is responsible
267 for taking care of that, and if C<av_store> returns NULL, the caller will
268 have to decrement the reference count to avoid a memory leak. Note that
269 C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s as their
274 void av_extend(AV*, I32 key);
276 The C<av_clear> function deletes all the elements in the AV* array, but
277 does not actually delete the array itself. The C<av_undef> function will
278 delete all the elements in the array plus the array itself. The
279 C<av_extend> function extends the array so that it contains at least C<key+1>
280 elements. If C<key+1> is less than the currently allocated length of the array,
281 then nothing is done.
283 If you know the name of an array variable, you can get a pointer to its AV
284 by using the following:
286 AV* perl_get_av("package::varname", FALSE);
288 This returns NULL if the variable does not exist.
290 See L<Understanding the Magic of Tied Hashes and Arrays> for more
291 information on how to use the array access functions on tied arrays.
293 =head2 Working with HVs
295 To create an HV, you use the following routine:
299 Once the HV has been created, the following operations are possible on HVs:
301 SV** hv_store(HV*, const char* key, U32 klen, SV* val, U32 hash);
302 SV** hv_fetch(HV*, const char* key, U32 klen, I32 lval);
304 The C<klen> parameter is the length of the key being passed in (Note that
305 you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
306 length of the key). The C<val> argument contains the SV pointer to the
307 scalar being stored, and C<hash> is the precomputed hash value (zero if
308 you want C<hv_store> to calculate it for you). The C<lval> parameter
309 indicates whether this fetch is actually a part of a store operation, in
310 which case a new undefined value will be added to the HV with the supplied
311 key and C<hv_fetch> will return as if the value had already existed.
313 Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
314 C<SV*>. To access the scalar value, you must first dereference the return
315 value. However, you should check to make sure that the return value is
316 not NULL before dereferencing it.
318 These two functions check if a hash table entry exists, and deletes it.
320 bool hv_exists(HV*, const char* key, U32 klen);
321 SV* hv_delete(HV*, const char* key, U32 klen, I32 flags);
323 If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
324 create and return a mortal copy of the deleted value.
326 And more miscellaneous functions:
331 Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
332 table but does not actually delete the hash table. The C<hv_undef> deletes
333 both the entries and the hash table itself.
335 Perl keeps the actual data in linked list of structures with a typedef of HE.
336 These contain the actual key and value pointers (plus extra administrative
337 overhead). The key is a string pointer; the value is an C<SV*>. However,
338 once you have an C<HE*>, to get the actual key and value, use the routines
341 I32 hv_iterinit(HV*);
342 /* Prepares starting point to traverse hash table */
343 HE* hv_iternext(HV*);
344 /* Get the next entry, and return a pointer to a
345 structure that has both the key and value */
346 char* hv_iterkey(HE* entry, I32* retlen);
347 /* Get the key from an HE structure and also return
348 the length of the key string */
349 SV* hv_iterval(HV*, HE* entry);
350 /* Return a SV pointer to the value of the HE
352 SV* hv_iternextsv(HV*, char** key, I32* retlen);
353 /* This convenience routine combines hv_iternext,
354 hv_iterkey, and hv_iterval. The key and retlen
355 arguments are return values for the key and its
356 length. The value is returned in the SV* argument */
358 If you know the name of a hash variable, you can get a pointer to its HV
359 by using the following:
361 HV* perl_get_hv("package::varname", FALSE);
363 This returns NULL if the variable does not exist.
365 The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
369 hash = (hash * 33) + *key++;
370 hash = hash + (hash >> 5); /* after 5.6 */
372 The last step was added in version 5.6 to improve distribution of
373 lower bits in the resulting hash value.
375 See L<Understanding the Magic of Tied Hashes and Arrays> for more
376 information on how to use the hash access functions on tied hashes.
378 =head2 Hash API Extensions
380 Beginning with version 5.004, the following functions are also supported:
382 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
383 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
385 bool hv_exists_ent (HV* tb, SV* key, U32 hash);
386 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
388 SV* hv_iterkeysv (HE* entry);
390 Note that these functions take C<SV*> keys, which simplifies writing
391 of extension code that deals with hash structures. These functions
392 also allow passing of C<SV*> keys to C<tie> functions without forcing
393 you to stringify the keys (unlike the previous set of functions).
395 They also return and accept whole hash entries (C<HE*>), making their
396 use more efficient (since the hash number for a particular string
397 doesn't have to be recomputed every time). See L<API LISTING> later in
398 this document for detailed descriptions.
400 The following macros must always be used to access the contents of hash
401 entries. Note that the arguments to these macros must be simple
402 variables, since they may get evaluated more than once. See
403 L<API LISTING> later in this document for detailed descriptions of these
406 HePV(HE* he, STRLEN len)
410 HeSVKEY_force(HE* he)
411 HeSVKEY_set(HE* he, SV* sv)
413 These two lower level macros are defined, but must only be used when
414 dealing with keys that are not C<SV*>s:
419 Note that both C<hv_store> and C<hv_store_ent> do not increment the
420 reference count of the stored C<val>, which is the caller's responsibility.
421 If these functions return a NULL value, the caller will usually have to
422 decrement the reference count of C<val> to avoid a memory leak.
426 References are a special type of scalar that point to other data types
427 (including references).
429 To create a reference, use either of the following functions:
431 SV* newRV_inc((SV*) thing);
432 SV* newRV_noinc((SV*) thing);
434 The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
435 functions are identical except that C<newRV_inc> increments the reference
436 count of the C<thing>, while C<newRV_noinc> does not. For historical
437 reasons, C<newRV> is a synonym for C<newRV_inc>.
439 Once you have a reference, you can use the following macro to dereference
444 then call the appropriate routines, casting the returned C<SV*> to either an
445 C<AV*> or C<HV*>, if required.
447 To determine if an SV is a reference, you can use the following macro:
451 To discover what type of value the reference refers to, use the following
452 macro and then check the return value.
456 The most useful types that will be returned are:
465 SVt_PVGV Glob (possible a file handle)
466 SVt_PVMG Blessed or Magical Scalar
468 See the sv.h header file for more details.
470 =head2 Blessed References and Class Objects
472 References are also used to support object-oriented programming. In the
473 OO lexicon, an object is simply a reference that has been blessed into a
474 package (or class). Once blessed, the programmer may now use the reference
475 to access the various methods in the class.
477 A reference can be blessed into a package with the following function:
479 SV* sv_bless(SV* sv, HV* stash);
481 The C<sv> argument must be a reference. The C<stash> argument specifies
482 which class the reference will belong to. See
483 L<Stashes and Globs> for information on converting class names into stashes.
485 /* Still under construction */
487 Upgrades rv to reference if not already one. Creates new SV for rv to
488 point to. If C<classname> is non-null, the SV is blessed into the specified
489 class. SV is returned.
491 SV* newSVrv(SV* rv, const char* classname);
493 Copies integer or double into an SV whose reference is C<rv>. SV is blessed
494 if C<classname> is non-null.
496 SV* sv_setref_iv(SV* rv, const char* classname, IV iv);
497 SV* sv_setref_nv(SV* rv, const char* classname, NV iv);
499 Copies the pointer value (I<the address, not the string!>) into an SV whose
500 reference is rv. SV is blessed if C<classname> is non-null.
502 SV* sv_setref_pv(SV* rv, const char* classname, PV iv);
504 Copies string into an SV whose reference is C<rv>. Set length to 0 to let
505 Perl calculate the string length. SV is blessed if C<classname> is non-null.
507 SV* sv_setref_pvn(SV* rv, const char* classname, PV iv, STRLEN length);
509 Tests whether the SV is blessed into the specified class. It does not
510 check inheritance relationships.
512 int sv_isa(SV* sv, const char* name);
514 Tests whether the SV is a reference to a blessed object.
516 int sv_isobject(SV* sv);
518 Tests whether the SV is derived from the specified class. SV can be either
519 a reference to a blessed object or a string containing a class name. This
520 is the function implementing the C<UNIVERSAL::isa> functionality.
522 bool sv_derived_from(SV* sv, const char* name);
524 To check if you've got an object derived from a specific class you have
527 if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... }
529 =head2 Creating New Variables
531 To create a new Perl variable with an undef value which can be accessed from
532 your Perl script, use the following routines, depending on the variable type.
534 SV* perl_get_sv("package::varname", TRUE);
535 AV* perl_get_av("package::varname", TRUE);
536 HV* perl_get_hv("package::varname", TRUE);
538 Notice the use of TRUE as the second parameter. The new variable can now
539 be set, using the routines appropriate to the data type.
541 There are additional macros whose values may be bitwise OR'ed with the
542 C<TRUE> argument to enable certain extra features. Those bits are:
544 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
545 "Name <varname> used only once: possible typo" warning.
546 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
547 the variable did not exist before the function was called.
549 If you do not specify a package name, the variable is created in the current
552 =head2 Reference Counts and Mortality
554 Perl uses an reference count-driven garbage collection mechanism. SVs,
555 AVs, or HVs (xV for short in the following) start their life with a
556 reference count of 1. If the reference count of an xV ever drops to 0,
557 then it will be destroyed and its memory made available for reuse.
559 This normally doesn't happen at the Perl level unless a variable is
560 undef'ed or the last variable holding a reference to it is changed or
561 overwritten. At the internal level, however, reference counts can be
562 manipulated with the following macros:
564 int SvREFCNT(SV* sv);
565 SV* SvREFCNT_inc(SV* sv);
566 void SvREFCNT_dec(SV* sv);
568 However, there is one other function which manipulates the reference
569 count of its argument. The C<newRV_inc> function, you will recall,
570 creates a reference to the specified argument. As a side effect,
571 it increments the argument's reference count. If this is not what
572 you want, use C<newRV_noinc> instead.
574 For example, imagine you want to return a reference from an XSUB function.
575 Inside the XSUB routine, you create an SV which initially has a reference
576 count of one. Then you call C<newRV_inc>, passing it the just-created SV.
577 This returns the reference as a new SV, but the reference count of the
578 SV you passed to C<newRV_inc> has been incremented to two. Now you
579 return the reference from the XSUB routine and forget about the SV.
580 But Perl hasn't! Whenever the returned reference is destroyed, the
581 reference count of the original SV is decreased to one and nothing happens.
582 The SV will hang around without any way to access it until Perl itself
583 terminates. This is a memory leak.
585 The correct procedure, then, is to use C<newRV_noinc> instead of
586 C<newRV_inc>. Then, if and when the last reference is destroyed,
587 the reference count of the SV will go to zero and it will be destroyed,
588 stopping any memory leak.
590 There are some convenience functions available that can help with the
591 destruction of xVs. These functions introduce the concept of "mortality".
592 An xV that is mortal has had its reference count marked to be decremented,
593 but not actually decremented, until "a short time later". Generally the
594 term "short time later" means a single Perl statement, such as a call to
595 an XSUB function. The actual determinant for when mortal xVs have their
596 reference count decremented depends on two macros, SAVETMPS and FREETMPS.
597 See L<perlcall> and L<perlxs> for more details on these macros.
599 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
600 However, if you mortalize a variable twice, the reference count will
601 later be decremented twice.
603 You should be careful about creating mortal variables. Strange things
604 can happen if you make the same value mortal within multiple contexts,
605 or if you make a variable mortal multiple times.
607 To create a mortal variable, use the functions:
611 SV* sv_mortalcopy(SV*)
613 The first call creates a mortal SV, the second converts an existing
614 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
615 third creates a mortal copy of an existing SV.
617 The mortal routines are not just for SVs -- AVs and HVs can be
618 made mortal by passing their address (type-casted to C<SV*>) to the
619 C<sv_2mortal> or C<sv_mortalcopy> routines.
621 =head2 Stashes and Globs
623 A "stash" is a hash that contains all of the different objects that
624 are contained within a package. Each key of the stash is a symbol
625 name (shared by all the different types of objects that have the same
626 name), and each value in the hash table is a GV (Glob Value). This GV
627 in turn contains references to the various objects of that name,
628 including (but not limited to) the following:
637 There is a single stash called "PL_defstash" that holds the items that exist
638 in the "main" package. To get at the items in other packages, append the
639 string "::" to the package name. The items in the "Foo" package are in
640 the stash "Foo::" in PL_defstash. The items in the "Bar::Baz" package are
641 in the stash "Baz::" in "Bar::"'s stash.
643 To get the stash pointer for a particular package, use the function:
645 HV* gv_stashpv(const char* name, I32 create)
646 HV* gv_stashsv(SV*, I32 create)
648 The first function takes a literal string, the second uses the string stored
649 in the SV. Remember that a stash is just a hash table, so you get back an
650 C<HV*>. The C<create> flag will create a new package if it is set.
652 The name that C<gv_stash*v> wants is the name of the package whose symbol table
653 you want. The default package is called C<main>. If you have multiply nested
654 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
657 Alternately, if you have an SV that is a blessed reference, you can find
658 out the stash pointer by using:
660 HV* SvSTASH(SvRV(SV*));
662 then use the following to get the package name itself:
664 char* HvNAME(HV* stash);
666 If you need to bless or re-bless an object you can use the following
669 SV* sv_bless(SV*, HV* stash)
671 where the first argument, an C<SV*>, must be a reference, and the second
672 argument is a stash. The returned C<SV*> can now be used in the same way
675 For more information on references and blessings, consult L<perlref>.
677 =head2 Double-Typed SVs
679 Scalar variables normally contain only one type of value, an integer,
680 double, pointer, or reference. Perl will automatically convert the
681 actual scalar data from the stored type into the requested type.
683 Some scalar variables contain more than one type of scalar data. For
684 example, the variable C<$!> contains either the numeric value of C<errno>
685 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
687 To force multiple data values into an SV, you must do two things: use the
688 C<sv_set*v> routines to add the additional scalar type, then set a flag
689 so that Perl will believe it contains more than one type of data. The
690 four macros to set the flags are:
697 The particular macro you must use depends on which C<sv_set*v> routine
698 you called first. This is because every C<sv_set*v> routine turns on
699 only the bit for the particular type of data being set, and turns off
702 For example, to create a new Perl variable called "dberror" that contains
703 both the numeric and descriptive string error values, you could use the
707 extern char *dberror_list;
709 SV* sv = perl_get_sv("dberror", TRUE);
710 sv_setiv(sv, (IV) dberror);
711 sv_setpv(sv, dberror_list[dberror]);
714 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
715 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
717 =head2 Magic Variables
719 [This section still under construction. Ignore everything here. Post no
720 bills. Everything not permitted is forbidden.]
722 Any SV may be magical, that is, it has special features that a normal
723 SV does not have. These features are stored in the SV structure in a
724 linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
737 Note this is current as of patchlevel 0, and could change at any time.
739 =head2 Assigning Magic
741 Perl adds magic to an SV using the sv_magic function:
743 void sv_magic(SV* sv, SV* obj, int how, const char* name, I32 namlen);
745 The C<sv> argument is a pointer to the SV that is to acquire a new magical
748 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
749 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
750 it to the beginning of the linked list of magical features. Any prior
751 entry of the same type of magic is deleted. Note that this can be
752 overridden, and multiple instances of the same type of magic can be
753 associated with an SV.
755 The C<name> and C<namlen> arguments are used to associate a string with
756 the magic, typically the name of a variable. C<namlen> is stored in the
757 C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
758 copy of the name is stored in C<mg_ptr> field.
760 The sv_magic function uses C<how> to determine which, if any, predefined
761 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
762 See the "Magic Virtual Table" section below. The C<how> argument is also
763 stored in the C<mg_type> field.
765 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
766 structure. If it is not the same as the C<sv> argument, the reference
767 count of the C<obj> object is incremented. If it is the same, or if
768 the C<how> argument is "#", or if it is a NULL pointer, then C<obj> is
769 merely stored, without the reference count being incremented.
771 There is also a function to add magic to an C<HV>:
773 void hv_magic(HV *hv, GV *gv, int how);
775 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
777 To remove the magic from an SV, call the function sv_unmagic:
779 void sv_unmagic(SV *sv, int type);
781 The C<type> argument should be equal to the C<how> value when the C<SV>
782 was initially made magical.
784 =head2 Magic Virtual Tables
786 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
787 C<MGVTBL>, which is a structure of function pointers and stands for
788 "Magic Virtual Table" to handle the various operations that might be
789 applied to that variable.
791 The C<MGVTBL> has five pointers to the following routine types:
793 int (*svt_get)(SV* sv, MAGIC* mg);
794 int (*svt_set)(SV* sv, MAGIC* mg);
795 U32 (*svt_len)(SV* sv, MAGIC* mg);
796 int (*svt_clear)(SV* sv, MAGIC* mg);
797 int (*svt_free)(SV* sv, MAGIC* mg);
799 This MGVTBL structure is set at compile-time in C<perl.h> and there are
800 currently 19 types (or 21 with overloading turned on). These different
801 structures contain pointers to various routines that perform additional
802 actions depending on which function is being called.
804 Function pointer Action taken
805 ---------------- ------------
806 svt_get Do something after the value of the SV is retrieved.
807 svt_set Do something after the SV is assigned a value.
808 svt_len Report on the SV's length.
809 svt_clear Clear something the SV represents.
810 svt_free Free any extra storage associated with the SV.
812 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
813 to an C<mg_type> of '\0') contains:
815 { magic_get, magic_set, magic_len, 0, 0 }
817 Thus, when an SV is determined to be magical and of type '\0', if a get
818 operation is being performed, the routine C<magic_get> is called. All
819 the various routines for the various magical types begin with C<magic_>.
821 The current kinds of Magic Virtual Tables are:
823 mg_type MGVTBL Type of magic
824 ------- ------ ----------------------------
825 \0 vtbl_sv Special scalar variable
826 A vtbl_amagic %OVERLOAD hash
827 a vtbl_amagicelem %OVERLOAD hash element
828 c (none) Holds overload table (AMT) on stash
829 B vtbl_bm Boyer-Moore (fast string search)
831 e vtbl_envelem %ENV hash element
832 f vtbl_fm Formline ('compiled' format)
833 g vtbl_mglob m//g target / study()ed string
834 I vtbl_isa @ISA array
835 i vtbl_isaelem @ISA array element
836 k vtbl_nkeys scalar(keys()) lvalue
837 L (none) Debugger %_<filename
838 l vtbl_dbline Debugger %_<filename element
839 o vtbl_collxfrm Locale transformation
840 P vtbl_pack Tied array or hash
841 p vtbl_packelem Tied array or hash element
842 q vtbl_packelem Tied scalar or handle
844 s vtbl_sigelem %SIG hash element
845 t vtbl_taint Taintedness
846 U vtbl_uvar Available for use by extensions
847 v vtbl_vec vec() lvalue
848 x vtbl_substr substr() lvalue
849 y vtbl_defelem Shadow "foreach" iterator variable /
850 smart parameter vivification
851 * vtbl_glob GV (typeglob)
852 # vtbl_arylen Array length ($#ary)
853 . vtbl_pos pos() lvalue
854 ~ (none) Available for use by extensions
856 When an uppercase and lowercase letter both exist in the table, then the
857 uppercase letter is used to represent some kind of composite type (a list
858 or a hash), and the lowercase letter is used to represent an element of
861 The '~' and 'U' magic types are defined specifically for use by
862 extensions and will not be used by perl itself. Extensions can use
863 '~' magic to 'attach' private information to variables (typically
864 objects). This is especially useful because there is no way for
865 normal perl code to corrupt this private information (unlike using
866 extra elements of a hash object).
868 Similarly, 'U' magic can be used much like tie() to call a C function
869 any time a scalar's value is used or changed. The C<MAGIC>'s
870 C<mg_ptr> field points to a C<ufuncs> structure:
873 I32 (*uf_val)(IV, SV*);
874 I32 (*uf_set)(IV, SV*);
878 When the SV is read from or written to, the C<uf_val> or C<uf_set>
879 function will be called with C<uf_index> as the first arg and a
880 pointer to the SV as the second. A simple example of how to add 'U'
881 magic is shown below. Note that the ufuncs structure is copied by
882 sv_magic, so you can safely allocate it on the stack.
890 uf.uf_val = &my_get_fn;
891 uf.uf_set = &my_set_fn;
893 sv_magic(sv, 0, 'U', (char*)&uf, sizeof(uf));
895 Note that because multiple extensions may be using '~' or 'U' magic,
896 it is important for extensions to take extra care to avoid conflict.
897 Typically only using the magic on objects blessed into the same class
898 as the extension is sufficient. For '~' magic, it may also be
899 appropriate to add an I32 'signature' at the top of the private data
902 Also note that the C<sv_set*()> and C<sv_cat*()> functions described
903 earlier do B<not> invoke 'set' magic on their targets. This must
904 be done by the user either by calling the C<SvSETMAGIC()> macro after
905 calling these functions, or by using one of the C<sv_set*_mg()> or
906 C<sv_cat*_mg()> functions. Similarly, generic C code must call the
907 C<SvGETMAGIC()> macro to invoke any 'get' magic if they use an SV
908 obtained from external sources in functions that don't handle magic.
909 L<API LISTING> later in this document identifies such functions.
910 For example, calls to the C<sv_cat*()> functions typically need to be
911 followed by C<SvSETMAGIC()>, but they don't need a prior C<SvGETMAGIC()>
912 since their implementation handles 'get' magic.
916 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
918 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
919 If the SV does not have that magical feature, C<NULL> is returned. Also,
920 if the SV is not of type SVt_PVMG, Perl may core dump.
922 int mg_copy(SV* sv, SV* nsv, const char* key, STRLEN klen);
924 This routine checks to see what types of magic C<sv> has. If the mg_type
925 field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
926 the mg_type field is changed to be the lowercase letter.
928 =head2 Understanding the Magic of Tied Hashes and Arrays
930 Tied hashes and arrays are magical beasts of the 'P' magic type.
932 WARNING: As of the 5.004 release, proper usage of the array and hash
933 access functions requires understanding a few caveats. Some
934 of these caveats are actually considered bugs in the API, to be fixed
935 in later releases, and are bracketed with [MAYCHANGE] below. If
936 you find yourself actually applying such information in this section, be
937 aware that the behavior may change in the future, umm, without warning.
939 The perl tie function associates a variable with an object that implements
940 the various GET, SET etc methods. To perform the equivalent of the perl
941 tie function from an XSUB, you must mimic this behaviour. The code below
942 carries out the necessary steps - firstly it creates a new hash, and then
943 creates a second hash which it blesses into the class which will implement
944 the tie methods. Lastly it ties the two hashes together, and returns a
945 reference to the new tied hash. Note that the code below does NOT call the
946 TIEHASH method in the MyTie class -
947 see L<Calling Perl Routines from within C Programs> for details on how
958 tie = newRV_noinc((SV*)newHV());
959 stash = gv_stashpv("MyTie", TRUE);
960 sv_bless(tie, stash);
961 hv_magic(hash, tie, 'P');
962 RETVAL = newRV_noinc(hash);
966 The C<av_store> function, when given a tied array argument, merely
967 copies the magic of the array onto the value to be "stored", using
968 C<mg_copy>. It may also return NULL, indicating that the value did not
969 actually need to be stored in the array. [MAYCHANGE] After a call to
970 C<av_store> on a tied array, the caller will usually need to call
971 C<mg_set(val)> to actually invoke the perl level "STORE" method on the
972 TIEARRAY object. If C<av_store> did return NULL, a call to
973 C<SvREFCNT_dec(val)> will also be usually necessary to avoid a memory
976 The previous paragraph is applicable verbatim to tied hash access using the
977 C<hv_store> and C<hv_store_ent> functions as well.
979 C<av_fetch> and the corresponding hash functions C<hv_fetch> and
980 C<hv_fetch_ent> actually return an undefined mortal value whose magic
981 has been initialized using C<mg_copy>. Note the value so returned does not
982 need to be deallocated, as it is already mortal. [MAYCHANGE] But you will
983 need to call C<mg_get()> on the returned value in order to actually invoke
984 the perl level "FETCH" method on the underlying TIE object. Similarly,
985 you may also call C<mg_set()> on the return value after possibly assigning
986 a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
987 method on the TIE object. [/MAYCHANGE]
990 In other words, the array or hash fetch/store functions don't really
991 fetch and store actual values in the case of tied arrays and hashes. They
992 merely call C<mg_copy> to attach magic to the values that were meant to be
993 "stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
994 do the job of invoking the TIE methods on the underlying objects. Thus
995 the magic mechanism currently implements a kind of lazy access to arrays
998 Currently (as of perl version 5.004), use of the hash and array access
999 functions requires the user to be aware of whether they are operating on
1000 "normal" hashes and arrays, or on their tied variants. The API may be
1001 changed to provide more transparent access to both tied and normal data
1002 types in future versions.
1005 You would do well to understand that the TIEARRAY and TIEHASH interfaces
1006 are mere sugar to invoke some perl method calls while using the uniform hash
1007 and array syntax. The use of this sugar imposes some overhead (typically
1008 about two to four extra opcodes per FETCH/STORE operation, in addition to
1009 the creation of all the mortal variables required to invoke the methods).
1010 This overhead will be comparatively small if the TIE methods are themselves
1011 substantial, but if they are only a few statements long, the overhead
1012 will not be insignificant.
1014 =head2 Localizing changes
1016 Perl has a very handy construction
1023 This construction is I<approximately> equivalent to
1032 The biggest difference is that the first construction would
1033 reinstate the initial value of $var, irrespective of how control exits
1034 the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
1035 more efficient as well.
1037 There is a way to achieve a similar task from C via Perl API: create a
1038 I<pseudo-block>, and arrange for some changes to be automatically
1039 undone at the end of it, either explicit, or via a non-local exit (via
1040 die()). A I<block>-like construct is created by a pair of
1041 C<ENTER>/C<LEAVE> macros (see L<perlcall/"Returning a Scalar">).
1042 Such a construct may be created specially for some important localized
1043 task, or an existing one (like boundaries of enclosing Perl
1044 subroutine/block, or an existing pair for freeing TMPs) may be
1045 used. (In the second case the overhead of additional localization must
1046 be almost negligible.) Note that any XSUB is automatically enclosed in
1047 an C<ENTER>/C<LEAVE> pair.
1049 Inside such a I<pseudo-block> the following service is available:
1053 =item C<SAVEINT(int i)>
1055 =item C<SAVEIV(IV i)>
1057 =item C<SAVEI32(I32 i)>
1059 =item C<SAVELONG(long i)>
1061 These macros arrange things to restore the value of integer variable
1062 C<i> at the end of enclosing I<pseudo-block>.
1064 =item C<SAVESPTR(s)>
1066 =item C<SAVEPPTR(p)>
1068 These macros arrange things to restore the value of pointers C<s> and
1069 C<p>. C<s> must be a pointer of a type which survives conversion to
1070 C<SV*> and back, C<p> should be able to survive conversion to C<char*>
1073 =item C<SAVEFREESV(SV *sv)>
1075 The refcount of C<sv> would be decremented at the end of
1076 I<pseudo-block>. This is similar to C<sv_2mortal>, which should (?) be
1079 =item C<SAVEFREEOP(OP *op)>
1081 The C<OP *> is op_free()ed at the end of I<pseudo-block>.
1083 =item C<SAVEFREEPV(p)>
1085 The chunk of memory which is pointed to by C<p> is Safefree()ed at the
1086 end of I<pseudo-block>.
1088 =item C<SAVECLEARSV(SV *sv)>
1090 Clears a slot in the current scratchpad which corresponds to C<sv> at
1091 the end of I<pseudo-block>.
1093 =item C<SAVEDELETE(HV *hv, char *key, I32 length)>
1095 The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
1096 string pointed to by C<key> is Safefree()ed. If one has a I<key> in
1097 short-lived storage, the corresponding string may be reallocated like
1100 SAVEDELETE(PL_defstash, savepv(tmpbuf), strlen(tmpbuf));
1102 =item C<SAVEDESTRUCTOR(f,p)>
1104 At the end of I<pseudo-block> the function C<f> is called with the
1105 only argument (of type C<void*>) C<p>.
1107 =item C<SAVESTACK_POS()>
1109 The current offset on the Perl internal stack (cf. C<SP>) is restored
1110 at the end of I<pseudo-block>.
1114 The following API list contains functions, thus one needs to
1115 provide pointers to the modifiable data explicitly (either C pointers,
1116 or Perlish C<GV *>s). Where the above macros take C<int>, a similar
1117 function takes C<int *>.
1121 =item C<SV* save_scalar(GV *gv)>
1123 Equivalent to Perl code C<local $gv>.
1125 =item C<AV* save_ary(GV *gv)>
1127 =item C<HV* save_hash(GV *gv)>
1129 Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
1131 =item C<void save_item(SV *item)>
1133 Duplicates the current value of C<SV>, on the exit from the current
1134 C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
1135 using the stored value.
1137 =item C<void save_list(SV **sarg, I32 maxsarg)>
1139 A variant of C<save_item> which takes multiple arguments via an array
1140 C<sarg> of C<SV*> of length C<maxsarg>.
1142 =item C<SV* save_svref(SV **sptr)>
1144 Similar to C<save_scalar>, but will reinstate a C<SV *>.
1146 =item C<void save_aptr(AV **aptr)>
1148 =item C<void save_hptr(HV **hptr)>
1150 Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
1154 The C<Alias> module implements localization of the basic types within the
1155 I<caller's scope>. People who are interested in how to localize things in
1156 the containing scope should take a look there too.
1160 =head2 XSUBs and the Argument Stack
1162 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
1163 An XSUB routine will have a stack that contains the arguments from the Perl
1164 program, and a way to map from the Perl data structures to a C equivalent.
1166 The stack arguments are accessible through the C<ST(n)> macro, which returns
1167 the C<n>'th stack argument. Argument 0 is the first argument passed in the
1168 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
1171 Most of the time, output from the C routine can be handled through use of
1172 the RETVAL and OUTPUT directives. However, there are some cases where the
1173 argument stack is not already long enough to handle all the return values.
1174 An example is the POSIX tzname() call, which takes no arguments, but returns
1175 two, the local time zone's standard and summer time abbreviations.
1177 To handle this situation, the PPCODE directive is used and the stack is
1178 extended using the macro:
1182 where C<SP> is the macro that represents the local copy of the stack pointer,
1183 and C<num> is the number of elements the stack should be extended by.
1185 Now that there is room on the stack, values can be pushed on it using the
1186 macros to push IVs, doubles, strings, and SV pointers respectively:
1193 And now the Perl program calling C<tzname>, the two values will be assigned
1196 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
1198 An alternate (and possibly simpler) method to pushing values on the stack is
1206 These macros automatically adjust the stack for you, if needed. Thus, you
1207 do not need to call C<EXTEND> to extend the stack.
1209 For more information, consult L<perlxs> and L<perlxstut>.
1211 =head2 Calling Perl Routines from within C Programs
1213 There are four routines that can be used to call a Perl subroutine from
1214 within a C program. These four are:
1216 I32 perl_call_sv(SV*, I32);
1217 I32 perl_call_pv(const char*, I32);
1218 I32 perl_call_method(const char*, I32);
1219 I32 perl_call_argv(const char*, I32, register char**);
1221 The routine most often used is C<perl_call_sv>. The C<SV*> argument
1222 contains either the name of the Perl subroutine to be called, or a
1223 reference to the subroutine. The second argument consists of flags
1224 that control the context in which the subroutine is called, whether
1225 or not the subroutine is being passed arguments, how errors should be
1226 trapped, and how to treat return values.
1228 All four routines return the number of arguments that the subroutine returned
1231 When using any of these routines (except C<perl_call_argv>), the programmer
1232 must manipulate the Perl stack. These include the following macros and
1247 For a detailed description of calling conventions from C to Perl,
1248 consult L<perlcall>.
1250 =head2 Memory Allocation
1252 All memory meant to be used with the Perl API functions should be manipulated
1253 using the macros described in this section. The macros provide the necessary
1254 transparency between differences in the actual malloc implementation that is
1257 It is suggested that you enable the version of malloc that is distributed
1258 with Perl. It keeps pools of various sizes of unallocated memory in
1259 order to satisfy allocation requests more quickly. However, on some
1260 platforms, it may cause spurious malloc or free errors.
1262 New(x, pointer, number, type);
1263 Newc(x, pointer, number, type, cast);
1264 Newz(x, pointer, number, type);
1266 These three macros are used to initially allocate memory.
1268 The first argument C<x> was a "magic cookie" that was used to keep track
1269 of who called the macro, to help when debugging memory problems. However,
1270 the current code makes no use of this feature (most Perl developers now
1271 use run-time memory checkers), so this argument can be any number.
1273 The second argument C<pointer> should be the name of a variable that will
1274 point to the newly allocated memory.
1276 The third and fourth arguments C<number> and C<type> specify how many of
1277 the specified type of data structure should be allocated. The argument
1278 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
1279 should be used if the C<pointer> argument is different from the C<type>
1282 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
1283 to zero out all the newly allocated memory.
1285 Renew(pointer, number, type);
1286 Renewc(pointer, number, type, cast);
1289 These three macros are used to change a memory buffer size or to free a
1290 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1291 match those of C<New> and C<Newc> with the exception of not needing the
1292 "magic cookie" argument.
1294 Move(source, dest, number, type);
1295 Copy(source, dest, number, type);
1296 Zero(dest, number, type);
1298 These three macros are used to move, copy, or zero out previously allocated
1299 memory. The C<source> and C<dest> arguments point to the source and
1300 destination starting points. Perl will move, copy, or zero out C<number>
1301 instances of the size of the C<type> data structure (using the C<sizeof>
1306 The most recent development releases of Perl has been experimenting with
1307 removing Perl's dependency on the "normal" standard I/O suite and allowing
1308 other stdio implementations to be used. This involves creating a new
1309 abstraction layer that then calls whichever implementation of stdio Perl
1310 was compiled with. All XSUBs should now use the functions in the PerlIO
1311 abstraction layer and not make any assumptions about what kind of stdio
1314 For a complete description of the PerlIO abstraction, consult L<perlapio>.
1316 =head2 Putting a C value on Perl stack
1318 A lot of opcodes (this is an elementary operation in the internal perl
1319 stack machine) put an SV* on the stack. However, as an optimization
1320 the corresponding SV is (usually) not recreated each time. The opcodes
1321 reuse specially assigned SVs (I<target>s) which are (as a corollary)
1322 not constantly freed/created.
1324 Each of the targets is created only once (but see
1325 L<Scratchpads and recursion> below), and when an opcode needs to put
1326 an integer, a double, or a string on stack, it just sets the
1327 corresponding parts of its I<target> and puts the I<target> on stack.
1329 The macro to put this target on stack is C<PUSHTARG>, and it is
1330 directly used in some opcodes, as well as indirectly in zillions of
1331 others, which use it via C<(X)PUSH[pni]>.
1335 The question remains on when the SVs which are I<target>s for opcodes
1336 are created. The answer is that they are created when the current unit --
1337 a subroutine or a file (for opcodes for statements outside of
1338 subroutines) -- is compiled. During this time a special anonymous Perl
1339 array is created, which is called a scratchpad for the current
1342 A scratchpad keeps SVs which are lexicals for the current unit and are
1343 targets for opcodes. One can deduce that an SV lives on a scratchpad
1344 by looking on its flags: lexicals have C<SVs_PADMY> set, and
1345 I<target>s have C<SVs_PADTMP> set.
1347 The correspondence between OPs and I<target>s is not 1-to-1. Different
1348 OPs in the compile tree of the unit can use the same target, if this
1349 would not conflict with the expected life of the temporary.
1351 =head2 Scratchpads and recursion
1353 In fact it is not 100% true that a compiled unit contains a pointer to
1354 the scratchpad AV. In fact it contains a pointer to an AV of
1355 (initially) one element, and this element is the scratchpad AV. Why do
1356 we need an extra level of indirection?
1358 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1359 these can create several execution pointers going into the same
1360 subroutine. For the subroutine-child not write over the temporaries
1361 for the subroutine-parent (lifespan of which covers the call to the
1362 child), the parent and the child should have different
1363 scratchpads. (I<And> the lexicals should be separate anyway!)
1365 So each subroutine is born with an array of scratchpads (of length 1).
1366 On each entry to the subroutine it is checked that the current
1367 depth of the recursion is not more than the length of this array, and
1368 if it is, new scratchpad is created and pushed into the array.
1370 The I<target>s on this scratchpad are C<undef>s, but they are already
1371 marked with correct flags.
1373 =head1 Compiled code
1377 Here we describe the internal form your code is converted to by
1378 Perl. Start with a simple example:
1382 This is converted to a tree similar to this one:
1390 (but slightly more complicated). This tree reflects the way Perl
1391 parsed your code, but has nothing to do with the execution order.
1392 There is an additional "thread" going through the nodes of the tree
1393 which shows the order of execution of the nodes. In our simplified
1394 example above it looks like:
1396 $b ---> $c ---> + ---> $a ---> assign-to
1398 But with the actual compile tree for C<$a = $b + $c> it is different:
1399 some nodes I<optimized away>. As a corollary, though the actual tree
1400 contains more nodes than our simplified example, the execution order
1401 is the same as in our example.
1403 =head2 Examining the tree
1405 If you have your perl compiled for debugging (usually done with C<-D
1406 optimize=-g> on C<Configure> command line), you may examine the
1407 compiled tree by specifying C<-Dx> on the Perl command line. The
1408 output takes several lines per node, and for C<$b+$c> it looks like
1413 FLAGS = (SCALAR,KIDS)
1415 TYPE = null ===> (4)
1417 FLAGS = (SCALAR,KIDS)
1419 3 TYPE = gvsv ===> 4
1425 TYPE = null ===> (5)
1427 FLAGS = (SCALAR,KIDS)
1429 4 TYPE = gvsv ===> 5
1435 This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1436 not optimized away (one per number in the left column). The immediate
1437 children of the given node correspond to C<{}> pairs on the same level
1438 of indentation, thus this listing corresponds to the tree:
1446 The execution order is indicated by C<===E<gt>> marks, thus it is C<3
1447 4 5 6> (node C<6> is not included into above listing), i.e.,
1448 C<gvsv gvsv add whatever>.
1450 =head2 Compile pass 1: check routines
1452 The tree is created by the I<pseudo-compiler> while yacc code feeds it
1453 the constructions it recognizes. Since yacc works bottom-up, so does
1454 the first pass of perl compilation.
1456 What makes this pass interesting for perl developers is that some
1457 optimization may be performed on this pass. This is optimization by
1458 so-called I<check routines>. The correspondence between node names
1459 and corresponding check routines is described in F<opcode.pl> (do not
1460 forget to run C<make regen_headers> if you modify this file).
1462 A check routine is called when the node is fully constructed except
1463 for the execution-order thread. Since at this time there are no
1464 back-links to the currently constructed node, one can do most any
1465 operation to the top-level node, including freeing it and/or creating
1466 new nodes above/below it.
1468 The check routine returns the node which should be inserted into the
1469 tree (if the top-level node was not modified, check routine returns
1472 By convention, check routines have names C<ck_*>. They are usually
1473 called from C<new*OP> subroutines (or C<convert>) (which in turn are
1474 called from F<perly.y>).
1476 =head2 Compile pass 1a: constant folding
1478 Immediately after the check routine is called the returned node is
1479 checked for being compile-time executable. If it is (the value is
1480 judged to be constant) it is immediately executed, and a I<constant>
1481 node with the "return value" of the corresponding subtree is
1482 substituted instead. The subtree is deleted.
1484 If constant folding was not performed, the execution-order thread is
1487 =head2 Compile pass 2: context propagation
1489 When a context for a part of compile tree is known, it is propagated
1490 down through the tree. At this time the context can have 5 values
1491 (instead of 2 for runtime context): void, boolean, scalar, list, and
1492 lvalue. In contrast with the pass 1 this pass is processed from top
1493 to bottom: a node's context determines the context for its children.
1495 Additional context-dependent optimizations are performed at this time.
1496 Since at this moment the compile tree contains back-references (via
1497 "thread" pointers), nodes cannot be free()d now. To allow
1498 optimized-away nodes at this stage, such nodes are null()ified instead
1499 of free()ing (i.e. their type is changed to OP_NULL).
1501 =head2 Compile pass 3: peephole optimization
1503 After the compile tree for a subroutine (or for an C<eval> or a file)
1504 is created, an additional pass over the code is performed. This pass
1505 is neither top-down or bottom-up, but in the execution order (with
1506 additional complications for conditionals). These optimizations are
1507 done in the subroutine peep(). Optimizations performed at this stage
1508 are subject to the same restrictions as in the pass 2.
1510 =head1 The Perl Internal API
1512 WARNING: This information is subject to radical changes prior to
1513 the Perl 5.6 release. Use with caution.
1515 =head2 Background and PERL_IMPLICIT_CONTEXT
1517 The Perl interpreter can be regarded as a closed box: it has an API
1518 for feeding it code or otherwise making it do things, but it also has
1519 functions for its own use. This smells a lot like an object, and
1520 there are ways for you to build Perl so that you can have multiple
1521 interpreters, with one interpreter represented either as a C++ object,
1522 a C structure, or inside a thread. The thread, the C structure, or
1523 the C++ object will contain all the context, the state of that
1526 Three macros control the major Perl build flavors: MULTIPLICITY,
1527 USE_THREADS and PERL_OBJECT. The MULTIPLICITY build has a C structure
1528 that packages all the interpreter state, there is a similar thread-specific
1529 data structure under USE_THREADS, and the PERL_OBJECT build has a C++
1530 class to maintain interpreter state. In all three cases,
1531 PERL_IMPLICIT_CONTEXT is also normally defined, and enables the
1532 support for passing in a "hidden" first argument that represents all three
1535 All this obviously requires a way for the Perl internal functions to be
1536 C++ methods, subroutines taking some kind of structure as the first
1537 argument, or subroutines taking nothing as the first argument. To
1538 enable these three very different ways of building the interpreter,
1539 the Perl source (as it does in so many other situations) makes heavy
1540 use of macros and subroutine naming conventions.
1542 First problem: deciding which functions will be public API functions and
1543 which will be private. Those functions whose names begin C<Perl_> are
1544 public, and those whose names begin C<S_> are private (think "S" for
1545 "secret" or "static").
1547 Some functions have no prefix (e.g., restore_rsfp in toke.c). These
1548 are not parts of the object or pseudo-structure because you need to
1549 pass pointers to them to other subroutines.
1551 Second problem: there must be a syntax so that the same subroutine
1552 declarations and calls can pass a structure as their first argument,
1553 or pass nothing. To solve this, the subroutines are named and
1554 declared in a particular way. Here's a typical start of a static
1555 function used within the Perl guts:
1558 S_incline(pTHX_ char *s)
1560 STATIC becomes "static" in C, and is #define'd to nothing in C++.
1562 A public function (i.e. part of the internal API, but not necessarily
1563 sanctioned for use in extensions) begins like this:
1566 Perl_sv_setsv(pTHX_ SV* dsv, SV* ssv)
1568 C<pTHX_> is one of a number of macros (in perl.h) that hide the
1569 details of the interpreter's context. THX stands for "thread", "this",
1570 or "thingy", as the case may be. (And no, George Lucas is not involved. :-)
1571 The first character could be 'p' for a B<p>rototype, 'a' for B<a>rgument,
1572 or 'd' for B<d>eclaration.
1574 When Perl is built without PERL_IMPLICIT_CONTEXT, there is no first
1575 argument containing the interpreter's context. The trailing underscore
1576 in the pTHX_ macro indicates that the macro expansion needs a comma
1577 after the context argument because other arguments follow it. If
1578 PERL_IMPLICIT_CONTEXT is not defined, pTHX_ will be ignored, and the
1579 subroutine is not prototyped to take the extra argument. The form of the
1580 macro without the trailing underscore is used when there are no additional
1583 When a core function calls another, it must pass the context. This
1584 is normally hidden via macros. Consider C<sv_setsv>. It expands
1585 something like this:
1587 ifdef PERL_IMPLICIT_CONTEXT
1588 define sv_setsv(a,b) Perl_sv_setsv(aTHX_ a, b)
1589 /* can't do this for vararg functions, see below */
1591 define sv_setsv Perl_sv_setsv
1594 This works well, and means that XS authors can gleefully write:
1598 and still have it work under all the modes Perl could have been
1601 Under PERL_OBJECT in the core, that will translate to either:
1603 CPerlObj::Perl_sv_setsv(foo,bar); # in CPerlObj functions,
1604 # C++ takes care of 'this'
1607 pPerl->Perl_sv_setsv(foo,bar); # in truly static functions,
1610 Under PERL_OBJECT in extensions (aka PERL_CAPI), or under
1611 MULTIPLICITY/USE_THREADS w/ PERL_IMPLICIT_CONTEXT in both core
1612 and extensions, it will be:
1614 Perl_sv_setsv(aTHX_ foo, bar); # the canonical Perl "API"
1615 # for all build flavors
1617 This doesn't work so cleanly for varargs functions, though, as macros
1618 imply that the number of arguments is known in advance. Instead we
1619 either need to spell them out fully, passing C<aTHX_> as the first
1620 argument (the Perl core tends to do this with functions like
1621 Perl_warner), or use a context-free version.
1623 The context-free version of Perl_warner is called
1624 Perl_warner_nocontext, and does not take the extra argument. Instead
1625 it does dTHX; to get the context from thread-local storage. We
1626 C<#define warner Perl_warner_nocontext> so that extensions get source
1627 compatibility at the expense of performance. (Passing an arg is
1628 cheaper than grabbing it from thread-local storage.)
1630 You can ignore [pad]THX[xo] when browsing the Perl headers/sources.
1631 Those are strictly for use within the core. Extensions and embedders
1632 need only be aware of [pad]THX.
1634 =head2 How do I use all this in extensions?
1636 When Perl is built with PERL_IMPLICIT_CONTEXT, extensions that call
1637 any functions in the Perl API will need to pass the initial context
1638 argument somehow. The kicker is that you will need to write it in
1639 such a way that the extension still compiles when Perl hasn't been
1640 built with PERL_IMPLICIT_CONTEXT enabled.
1642 There are three ways to do this. First, the easy but inefficient way,
1643 which is also the default, in order to maintain source compatibility
1644 with extensions: whenever XSUB.h is #included, it redefines the aTHX
1645 and aTHX_ macros to call a function that will return the context.
1646 Thus, something like:
1650 in your extesion will translate to this when PERL_IMPLICIT_CONTEXT is
1653 Perl_sv_setsv(GetPerlInterpreter(), asv, bsv);
1655 or to this otherwise:
1657 Perl_sv_setsv(asv, bsv);
1659 You have to do nothing new in your extension to get this; since
1660 the Perl library provides GetPerlInterpreter(), it will all just
1663 The second, more efficient way is to use the following template for
1666 #define PERL_NO_GET_CONTEXT /* we want efficiency */
1671 static my_private_function(int arg1, int arg2);
1674 my_private_function(int arg1, int arg2)
1676 dTHX; /* fetch context */
1677 ... call many Perl API functions ...
1682 MODULE = Foo PACKAGE = Foo
1690 my_private_function(arg, 10);
1692 Note that the only two changes from the normal way of writing an
1693 extension is the addition of a C<#define PERL_NO_GET_CONTEXT> before
1694 including the Perl headers, followed by a C<dTHX;> declaration at
1695 the start of every function that will call the Perl API. (You'll
1696 know which functions need this, because the C compiler will complain
1697 that there's an undeclared identifier in those functions.) No changes
1698 are needed for the XSUBs themselves, because the XS() macro is
1699 correctly defined to pass in the implicit context if needed.
1701 The third, even more efficient way is to ape how it is done within
1705 #define PERL_NO_GET_CONTEXT /* we want efficiency */
1710 /* pTHX_ only needed for functions that call Perl API */
1711 static my_private_function(pTHX_ int arg1, int arg2);
1714 my_private_function(pTHX_ int arg1, int arg2)
1716 /* dTHX; not needed here, because THX is an argument */
1717 ... call Perl API functions ...
1722 MODULE = Foo PACKAGE = Foo
1730 my_private_function(aTHX_ arg, 10);
1732 This implementation never has to fetch the context using a function
1733 call, since it is always passed as an extra argument. Depending on
1734 your needs for simplicity or efficiency, you may mix the previous
1735 two approaches freely.
1737 Never add a comma after C<pTHX> yourself--always use the form of the
1738 macro with the underscore for functions that take explicit arguments,
1739 or the form without the argument for functions with no explicit arguments.
1741 =head2 Future Plans and PERL_IMPLICIT_SYS
1743 Just as PERL_IMPLICIT_CONTEXT provides a way to bundle up everything
1744 that the interpreter knows about itself and pass it around, so too are
1745 there plans to allow the interpreter to bundle up everything it knows
1746 about the environment it's running on. This is enabled with the
1747 PERL_IMPLICIT_SYS macro. Currently it only works with PERL_OBJECT,
1748 but is mostly there for MULTIPLICITY and USE_THREADS (see inside
1751 This allows the ability to provide an extra pointer (called the "host"
1752 environment) for all the system calls. This makes it possible for
1753 all the system stuff to maintain their own state, broken down into
1754 seven C structures. These are thin wrappers around the usual system
1755 calls (see win32/perllib.c) for the default perl executable, but for a
1756 more ambitious host (like the one that would do fork() emulation) all
1757 the extra work needed to pretend that different interpreters are
1758 actually different "processes", would be done here.
1760 The Perl engine/interpreter and the host are orthogonal entities.
1761 There could be one or more interpreters in a process, and one or
1762 more "hosts", with free association between them.
1766 This is a listing of functions, macros, flags, and variables that may be
1767 used by extension writers. The interfaces of any functions that are not
1768 listed here are subject to change without notice. For this reason,
1769 blindly using functions listed in proto.h is to be avoided when writing
1772 Note that all Perl API global variables must be referenced with the C<PL_>
1773 prefix. Some macros are provided for compatibility with the older,
1774 unadorned names, but this support may be disabled in a future release.
1776 The sort order of the listing is case insensitive, with any
1777 occurrences of '_' ignored for the purpose of sorting.
1783 Clears an array, making it empty. Does not free the memory used by the
1786 void av_clear (AV* ar)
1790 Pre-extend an array. The C<key> is the index to which the array should be
1793 void av_extend (AV* ar, I32 key)
1797 Returns the SV at the specified index in the array. The C<key> is the
1798 index. If C<lval> is set then the fetch will be part of a store. Check
1799 that the return value is non-null before dereferencing it to a C<SV*>.
1801 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1802 information on how to use this function on tied arrays.
1804 SV** av_fetch (AV* ar, I32 key, I32 lval)
1808 Same as C<av_len()>. Deprecated, use C<av_len()> instead.
1812 Returns the highest index in the array. Returns -1 if the array is empty.
1818 Creates a new AV and populates it with a list of SVs. The SVs are copied
1819 into the array, so they may be freed after the call to av_make. The new AV
1820 will have a reference count of 1.
1822 AV* av_make (I32 size, SV** svp)
1826 Pops an SV off the end of the array. Returns C<&PL_sv_undef> if the array is
1833 Pushes an SV onto the end of the array. The array will grow automatically
1834 to accommodate the addition.
1836 void av_push (AV* ar, SV* val)
1840 Shifts an SV off the beginning of the array.
1842 SV* av_shift (AV* ar)
1846 Stores an SV in an array. The array index is specified as C<key>. The
1847 return value will be NULL if the operation failed or if the value did not
1848 need to be actually stored within the array (as in the case of tied arrays).
1849 Otherwise it can be dereferenced to get the original C<SV*>. Note that the
1850 caller is responsible for suitably incrementing the reference count of C<val>
1851 before the call, and decrementing it if the function returned NULL.
1853 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1854 information on how to use this function on tied arrays.
1856 SV** av_store (AV* ar, I32 key, SV* val)
1860 Undefines the array. Frees the memory used by the array itself.
1862 void av_undef (AV* ar)
1866 Unshift the given number of C<undef> values onto the beginning of the
1867 array. The array will grow automatically to accommodate the addition.
1868 You must then use C<av_store> to assign values to these new elements.
1870 void av_unshift (AV* ar, I32 num)
1874 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1875 constructor. This is always a C<char*>. See C<THIS> and
1876 L<perlxs/"Using XS With C++">.
1880 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1881 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1882 the type. May fail on overlapping copies. See also C<Move>.
1884 void Copy( s, d, n, t )
1888 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1889 function the same way you use the C C<printf> function. See C<warn>.
1893 Returns the stash of the CV.
1895 HV* CvSTASH( SV* sv )
1899 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1900 boolean which indicates whether subs are being single-stepped.
1901 Single-stepping is automatically turned on after every step. This is the C
1902 variable which corresponds to Perl's $DB::single variable. See C<PL_DBsub>.
1906 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1907 the SV which holds the name of the sub being debugged. This is the C
1908 variable which corresponds to Perl's $DB::sub variable. See C<PL_DBsingle>.
1909 The sub name can be found by
1911 SvPV( GvSV( PL_DBsub ), len )
1915 Trace variable used when Perl is run in debugging mode, with the B<-d>
1916 switch. This is the C variable which corresponds to Perl's $DB::trace
1917 variable. See C<PL_DBsingle>.
1921 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1926 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1930 The C variable which corresponds to Perl's $^W warning variable.
1934 Declares a local copy of perl's stack pointer for the XSUB, available via
1935 the C<SP> macro. See C<SP>.
1939 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1940 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1941 to indicate the number of items on the stack.
1945 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1946 handled automatically by C<xsubpp>.
1950 Switches filehandle to binmode. C<iotype> is what C<IoTYPE(io)> would
1953 do_binmode(fp, iotype, TRUE);
1957 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1963 Used to extend the argument stack for an XSUB's return values.
1969 Analyses the string in order to make fast searches on it using fbm_instr() --
1970 the Boyer-Moore algorithm.
1972 void fbm_compile(SV* sv, U32 flags)
1976 Returns the location of the SV in the string delimited by C<str> and
1977 C<strend>. It returns C<Nullch> if the string can't be found. The
1978 C<sv> does not have to be fbm_compiled, but the search will not be as
1981 char* fbm_instr(char *str, char *strend, SV *sv, U32 flags)
1985 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1992 Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
1996 Indicates that arguments returned from a callback should be discarded. See
2001 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
2005 A backward-compatible version of C<GIMME_V> which can only return
2006 C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
2010 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
2011 C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
2012 context, respectively.
2016 Indicates that no arguments are being sent to a callback. See L<perlcall>.
2020 Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
2024 Returns the glob with the given C<name> and a defined subroutine or
2025 C<NULL>. The glob lives in the given C<stash>, or in the stashes
2026 accessible via @ISA and @UNIVERSAL.
2028 The argument C<level> should be either 0 or -1. If C<level==0>, as a
2029 side-effect creates a glob with the given C<name> in the given
2030 C<stash> which in the case of success contains an alias for the
2031 subroutine, and sets up caching info for this glob. Similarly for all
2032 the searched stashes.
2034 This function grants C<"SUPER"> token as a postfix of the stash name.
2036 The GV returned from C<gv_fetchmeth> may be a method cache entry,
2037 which is not visible to Perl code. So when calling C<perl_call_sv>,
2038 you should not use the GV directly; instead, you should use the
2039 method's CV, which can be obtained from the GV with the C<GvCV> macro.
2041 GV* gv_fetchmeth (HV* stash, const char* name, STRLEN len, I32 level)
2043 =item gv_fetchmethod
2045 =item gv_fetchmethod_autoload
2047 Returns the glob which contains the subroutine to call to invoke the
2048 method on the C<stash>. In fact in the presence of autoloading this may
2049 be the glob for "AUTOLOAD". In this case the corresponding variable
2050 $AUTOLOAD is already setup.
2052 The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
2053 lookup is performed if the given method is not present: non-zero means
2054 yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
2055 C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
2056 non-zero C<autoload> parameter.
2058 These functions grant C<"SUPER"> token as a prefix of the method name.
2060 Note that if you want to keep the returned glob for a long time, you
2061 need to check for it being "AUTOLOAD", since at the later time the call
2062 may load a different subroutine due to $AUTOLOAD changing its value.
2063 Use the glob created via a side effect to do this.
2065 These functions have the same side-effects and as C<gv_fetchmeth> with
2066 C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
2067 The warning against passing the GV returned by C<gv_fetchmeth> to
2068 C<perl_call_sv> apply equally to these functions.
2070 GV* gv_fetchmethod (HV* stash, const char* name)
2071 GV* gv_fetchmethod_autoload (HV* stash, const char* name, I32 autoload)
2075 Used to indicate void context. See C<GIMME_V> and L<perlcall>.
2079 Returns a pointer to the stash for a specified package. If C<create> is set
2080 then the package will be created if it does not already exist. If C<create>
2081 is not set and the package does not exist then NULL is returned.
2083 HV* gv_stashpv (const char* name, I32 create)
2087 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
2089 HV* gv_stashsv (SV* sv, I32 create)
2093 Return the SV from the GV.
2097 This flag, used in the length slot of hash entries and magic
2098 structures, specifies the structure contains a C<SV*> pointer where a
2099 C<char*> pointer is to be expected. (For information only--not to be used).
2103 Returns the computed hash stored in the hash entry.
2109 Returns the actual pointer stored in the key slot of the hash entry.
2110 The pointer may be either C<char*> or C<SV*>, depending on the value of
2111 C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
2112 are usually preferable for finding the value of a key.
2118 If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
2119 holds an C<SV*> key. Otherwise, holds the actual length of the key.
2120 Can be assigned to. The C<HePV()> macro is usually preferable for finding
2127 Returns the key slot of the hash entry as a C<char*> value, doing any
2128 necessary dereferencing of possibly C<SV*> keys. The length of
2129 the string is placed in C<len> (this is a macro, so do I<not> use
2130 C<&len>). If you do not care about what the length of the key is,
2131 you may use the global variable C<PL_na>, though this is rather less
2132 efficient than using a local variable. Remember though, that hash
2133 keys in perl are free to contain embedded nulls, so using C<strlen()>
2134 or similar is not a good way to find the length of hash keys.
2135 This is very similar to the C<SvPV()> macro described elsewhere in
2138 char* HePV(HE* he, STRLEN len)
2142 Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
2143 does not contain an C<SV*> key.
2149 Returns the key as an C<SV*>. Will create and return a temporary
2150 mortal C<SV*> if the hash entry contains only a C<char*> key.
2152 HeSVKEY_force(HE* he)
2156 Sets the key to a given C<SV*>, taking care to set the appropriate flags
2157 to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
2159 HeSVKEY_set(HE* he, SV* sv)
2163 Returns the value slot (type C<SV*>) stored in the hash entry.
2169 Clears a hash, making it empty.
2171 void hv_clear (HV* tb)
2175 Deletes a key/value pair in the hash. The value SV is removed from the hash
2176 and returned to the caller. The C<klen> is the length of the key. The
2177 C<flags> value will normally be zero; if set to G_DISCARD then NULL will be
2180 SV* hv_delete (HV* tb, const char* key, U32 klen, I32 flags)
2184 Deletes a key/value pair in the hash. The value SV is removed from the hash
2185 and returned to the caller. The C<flags> value will normally be zero; if set
2186 to G_DISCARD then NULL will be returned. C<hash> can be a valid precomputed
2187 hash value, or 0 to ask for it to be computed.
2189 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash)
2193 Returns a boolean indicating whether the specified hash key exists. The
2194 C<klen> is the length of the key.
2196 bool hv_exists (HV* tb, const char* key, U32 klen)
2200 Returns a boolean indicating whether the specified hash key exists. C<hash>
2201 can be a valid precomputed hash value, or 0 to ask for it to be computed.
2203 bool hv_exists_ent (HV* tb, SV* key, U32 hash)
2207 Returns the SV which corresponds to the specified key in the hash. The
2208 C<klen> is the length of the key. If C<lval> is set then the fetch will be
2209 part of a store. Check that the return value is non-null before
2210 dereferencing it to a C<SV*>.
2212 See L<Understanding the Magic of Tied Hashes and Arrays> for more
2213 information on how to use this function on tied hashes.
2215 SV** hv_fetch (HV* tb, const char* key, U32 klen, I32 lval)
2219 Returns the hash entry which corresponds to the specified key in the hash.
2220 C<hash> must be a valid precomputed hash number for the given C<key>, or
2221 0 if you want the function to compute it. IF C<lval> is set then the
2222 fetch will be part of a store. Make sure the return value is non-null
2223 before accessing it. The return value when C<tb> is a tied hash
2224 is a pointer to a static location, so be sure to make a copy of the
2225 structure if you need to store it somewhere.
2227 See L<Understanding the Magic of Tied Hashes and Arrays> for more
2228 information on how to use this function on tied hashes.
2230 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash)
2234 Prepares a starting point to traverse a hash table.
2236 I32 hv_iterinit (HV* tb)
2238 Returns the number of keys in the hash (i.e. the same as C<HvKEYS(tb)>).
2239 The return value is currently only meaningful for hashes without tie
2242 NOTE: Before version 5.004_65, C<hv_iterinit> used to return the number
2243 of hash buckets that happen to be in use. If you still need that
2244 esoteric value, you can get it through the macro C<HvFILL(tb)>.
2248 Returns the key from the current position of the hash iterator. See
2251 char* hv_iterkey (HE* entry, I32* retlen)
2255 Returns the key as an C<SV*> from the current position of the hash
2256 iterator. The return value will always be a mortal copy of the
2257 key. Also see C<hv_iterinit>.
2259 SV* hv_iterkeysv (HE* entry)
2263 Returns entries from a hash iterator. See C<hv_iterinit>.
2265 HE* hv_iternext (HV* tb)
2269 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
2272 SV* hv_iternextsv (HV* hv, char** key, I32* retlen)
2276 Returns the value from the current position of the hash iterator. See
2279 SV* hv_iterval (HV* tb, HE* entry)
2283 Adds magic to a hash. See C<sv_magic>.
2285 void hv_magic (HV* hv, GV* gv, int how)
2289 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
2291 char* HvNAME (HV* stash)
2295 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
2296 the length of the key. The C<hash> parameter is the precomputed hash
2297 value; if it is zero then Perl will compute it. The return value will be
2298 NULL if the operation failed or if the value did not need to be actually
2299 stored within the hash (as in the case of tied hashes). Otherwise it can
2300 be dereferenced to get the original C<SV*>. Note that the caller is
2301 responsible for suitably incrementing the reference count of C<val>
2302 before the call, and decrementing it if the function returned NULL.
2304 See L<Understanding the Magic of Tied Hashes and Arrays> for more
2305 information on how to use this function on tied hashes.
2307 SV** hv_store (HV* tb, const char* key, U32 klen, SV* val, U32 hash)
2311 Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
2312 parameter is the precomputed hash value; if it is zero then Perl will
2313 compute it. The return value is the new hash entry so created. It will be
2314 NULL if the operation failed or if the value did not need to be actually
2315 stored within the hash (as in the case of tied hashes). Otherwise the
2316 contents of the return value can be accessed using the C<He???> macros
2317 described here. Note that the caller is responsible for suitably
2318 incrementing the reference count of C<val> before the call, and decrementing
2319 it if the function returned NULL.
2321 See L<Understanding the Magic of Tied Hashes and Arrays> for more
2322 information on how to use this function on tied hashes.
2324 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash)
2330 void hv_undef (HV* tb)
2334 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
2337 int isALNUM (char c)
2341 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
2344 int isALPHA (char c)
2348 Returns a boolean indicating whether the C C<char> is an ascii digit.
2350 int isDIGIT (char c)
2354 Returns a boolean indicating whether the C C<char> is a lowercase character.
2356 int isLOWER (char c)
2360 Returns a boolean indicating whether the C C<char> is whitespace.
2362 int isSPACE (char c)
2366 Returns a boolean indicating whether the C C<char> is an uppercase character.
2368 int isUPPER (char c)
2372 Variable which is setup by C<xsubpp> to indicate the number of items on the
2373 stack. See L<perlxs/"Variable-length Parameter Lists">.
2377 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
2378 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
2382 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
2386 =item looks_like_number
2388 Test if an the content of an SV looks like a number (or is a number).
2390 int looks_like_number(SV*)
2395 Stack marker variable for the XSUB. See C<dMARK>.
2399 Clear something magical that the SV represents. See C<sv_magic>.
2401 int mg_clear (SV* sv)
2405 Copies the magic from one SV to another. See C<sv_magic>.
2407 int mg_copy (SV *, SV *, const char *, STRLEN)
2411 Finds the magic pointer for type matching the SV. See C<sv_magic>.
2413 MAGIC* mg_find (SV* sv, int type)
2417 Free any magic storage used by the SV. See C<sv_magic>.
2419 int mg_free (SV* sv)
2423 Do magic after a value is retrieved from the SV. See C<sv_magic>.
2429 Report on the SV's length. See C<sv_magic>.
2435 Turns on the magical status of an SV. See C<sv_magic>.
2437 void mg_magical (SV* sv)
2441 Do magic after a value is assigned to the SV. See C<sv_magic>.
2447 C<modglobal> is a general purpose, interpreter global HV for use by
2448 extensions that need to keep information on a per-interpreter basis.
2449 In a pinch, it can also be used as a symbol table for extensions
2450 to share data among each other. It is a good idea to use keys
2451 prefixed by the package name of the extension that owns the data.
2455 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
2456 source, C<d> is the destination, C<n> is the number of items, and C<t> is
2457 the type. Can do overlapping moves. See also C<Copy>.
2459 void Move( s, d, n, t )
2463 A convenience variable which is typically used with C<SvPV> when one doesn't
2464 care about the length of the string. It is usually more efficient to
2465 either declare a local variable and use that instead or to use the C<SvPV_nolen>
2470 The XSUB-writer's interface to the C C<malloc> function.
2472 void* New( x, void *ptr, int size, type )
2476 Creates a new AV. The reference count is set to 1.
2482 The XSUB-writer's interface to the C C<malloc> function, with cast.
2484 void* Newc( x, void *ptr, int size, type, cast )
2488 Creates a constant sub equivalent to Perl C<sub FOO () { 123 }>
2489 which is eligible for inlining at compile-time.
2491 void newCONSTSUB(HV* stash, char* name, SV* sv)
2495 Creates a new HV. The reference count is set to 1.
2501 Creates an RV wrapper for an SV. The reference count for the original SV is
2504 SV* newRV_inc (SV* ref)
2506 For historical reasons, "newRV" is a synonym for "newRV_inc".
2510 Creates an RV wrapper for an SV. The reference count for the original
2511 SV is B<not> incremented.
2513 SV* newRV_noinc (SV* ref)
2517 Creates a new SV. A non-zero C<len> parameter indicates the number of
2518 bytes of preallocated string space the SV should have. An extra byte
2519 for a tailing NUL is also reserved. (SvPOK is not set for the SV even
2520 if string space is allocated.) The reference count for the new SV is
2521 set to 1. C<id> is an integer id between 0 and 1299 (used to identify
2524 SV* NEWSV (int id, STRLEN len)
2528 Creates a new SV and copies an integer into it. The reference count for the
2535 Creates a new SV and copies a double into it. The reference count for the
2542 Creates a new SV and copies a string into it. The reference count for the
2543 SV is set to 1. If C<len> is zero, Perl will compute the length using
2544 strlen(). For efficiency, consider using C<newSVpvn> instead.
2546 SV* newSVpv (const char* s, STRLEN len)
2550 Creates a new SV an initialize it with the string formatted like
2553 SV* newSVpvf(const char* pat, ...)
2557 Creates a new SV and copies a string into it. The reference count for the
2558 SV is set to 1. Note that if C<len> is zero, Perl will create a zero length
2559 string. You are responsible for ensuring that the source string is at least
2562 SV* newSVpvn (const char* s, STRLEN len)
2566 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
2567 it will be upgraded to one. If C<classname> is non-null then the new SV will
2568 be blessed in the specified package. The new SV is returned and its
2569 reference count is 1.
2571 SV* newSVrv (SV* rv, const char* classname)
2575 Creates a new SV which is an exact duplicate of the original SV.
2577 SV* newSVsv (SV* old)
2581 Used by C<xsubpp> to hook up XSUBs as Perl subs.
2585 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
2590 The XSUB-writer's interface to the C C<malloc> function. The allocated
2591 memory is zeroed with C<memzero>.
2593 void* Newz( x, void *ptr, int size, type )
2601 Null character pointer.
2617 The original stack mark for the XSUB. See C<dORIGMARK>.
2621 Allocates a new Perl interpreter. See L<perlembed>.
2623 =item perl_call_argv
2625 Performs a callback to the specified Perl sub. See L<perlcall>.
2627 I32 perl_call_argv (const char* subname, I32 flags, char** argv)
2629 =item perl_call_method
2631 Performs a callback to the specified Perl method. The blessed object must
2632 be on the stack. See L<perlcall>.
2634 I32 perl_call_method (const char* methname, I32 flags)
2638 Performs a callback to the specified Perl sub. See L<perlcall>.
2640 I32 perl_call_pv (const char* subname, I32 flags)
2644 Performs a callback to the Perl sub whose name is in the SV. See
2647 I32 perl_call_sv (SV* sv, I32 flags)
2649 =item perl_construct
2651 Initializes a new Perl interpreter. See L<perlembed>.
2655 Shuts down a Perl interpreter. See L<perlembed>.
2659 Tells Perl to C<eval> the string in the SV.
2661 I32 perl_eval_sv (SV* sv, I32 flags)
2665 Tells Perl to C<eval> the given string and return an SV* result.
2667 SV* perl_eval_pv (const char* p, I32 croak_on_error)
2671 Releases a Perl interpreter. See L<perlembed>.
2675 Returns the AV of the specified Perl array. If C<create> is set and the
2676 Perl variable does not exist then it will be created. If C<create> is not
2677 set and the variable does not exist then NULL is returned.
2679 AV* perl_get_av (const char* name, I32 create)
2683 Returns the CV of the specified Perl subroutine. If C<create> is set and
2684 the Perl subroutine does not exist then it will be declared (which has
2685 the same effect as saying C<sub name;>). If C<create> is not
2686 set and the subroutine does not exist then NULL is returned.
2688 CV* perl_get_cv (const char* name, I32 create)
2692 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
2693 variable does not exist then it will be created. If C<create> is not
2694 set and the variable does not exist then NULL is returned.
2696 HV* perl_get_hv (const char* name, I32 create)
2700 Returns the SV of the specified Perl scalar. If C<create> is set and the
2701 Perl variable does not exist then it will be created. If C<create> is not
2702 set and the variable does not exist then NULL is returned.
2704 SV* perl_get_sv (const char* name, I32 create)
2708 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
2710 =item perl_require_pv
2712 Tells Perl to C<require> a module.
2714 void perl_require_pv (const char* pv)
2718 Tells a Perl interpreter to run. See L<perlembed>.
2722 Pops an integer off the stack.
2728 Pops a long off the stack.
2734 Pops a string off the stack.
2740 Pops a double off the stack.
2746 Pops an SV off the stack.
2752 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2758 Push an integer onto the stack. The stack must have room for this element.
2759 Handles 'set' magic. See C<XPUSHi>.
2765 Push a double onto the stack. The stack must have room for this element.
2766 Handles 'set' magic. See C<XPUSHn>.
2768 void PUSHn(double d)
2772 Push a string onto the stack. The stack must have room for this element.
2773 The C<len> indicates the length of the string. Handles 'set' magic. See
2776 void PUSHp(char *c, int len )
2780 Push an SV onto the stack. The stack must have room for this element. Does
2781 not handle 'set' magic. See C<XPUSHs>.
2787 Push an unsigned integer onto the stack. The stack must have room for
2788 this element. See C<XPUSHu>.
2790 void PUSHu(unsigned int d)
2795 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2796 See C<PUSHMARK> and L<perlcall> for other uses.
2802 The XSUB-writer's interface to the C C<realloc> function.
2804 void* Renew( void *ptr, int size, type )
2808 The XSUB-writer's interface to the C C<realloc> function, with cast.
2810 void* Renewc( void *ptr, int size, type, cast )
2814 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
2815 This is always the proper type for the XSUB.
2816 See L<perlxs/"The RETVAL Variable">.
2820 The XSUB-writer's interface to the C C<free> function.
2824 The XSUB-writer's interface to the C C<malloc> function.
2828 The XSUB-writer's interface to the C C<realloc> function.
2832 Copy a string to a safe spot. This does not use an SV.
2834 char* savepv (const char* sv)
2838 Copy a string to a safe spot. The C<len> indicates number of bytes to
2839 copy. This does not use an SV.
2841 char* savepvn (const char* sv, I32 len)
2845 Opening bracket for temporaries on a callback. See C<FREETMPS> and
2852 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2857 Refetch the stack pointer. Used after a callback. See L<perlcall>.
2863 Used to access elements on the XSUB's stack.
2869 Test two strings to see if they are equal. Returns true or false.
2871 int strEQ( char *s1, char *s2 )
2875 Test two strings to see if the first, C<s1>, is greater than or equal to the
2876 second, C<s2>. Returns true or false.
2878 int strGE( char *s1, char *s2 )
2882 Test two strings to see if the first, C<s1>, is greater than the second,
2883 C<s2>. Returns true or false.
2885 int strGT( char *s1, char *s2 )
2889 Test two strings to see if the first, C<s1>, is less than or equal to the
2890 second, C<s2>. Returns true or false.
2892 int strLE( char *s1, char *s2 )
2896 Test two strings to see if the first, C<s1>, is less than the second,
2897 C<s2>. Returns true or false.
2899 int strLT( char *s1, char *s2 )
2903 Test two strings to see if they are different. Returns true or false.
2905 int strNE( char *s1, char *s2 )
2909 Test two strings to see if they are equal. The C<len> parameter indicates
2910 the number of bytes to compare. Returns true or false.
2911 (A wrapper for C<strncmp>).
2913 int strnEQ( const char *s1, const char *s2, size_t len )
2917 Test two strings to see if they are different. The C<len> parameter
2918 indicates the number of bytes to compare. Returns true or false.
2919 (A wrapper for C<strncmp>).
2921 int strnNE( const char *s1, const char *s2, size_t len )
2925 Marks an SV as mortal. The SV will be destroyed when the current context
2928 SV* sv_2mortal (SV* sv)
2932 Blesses an SV into a specified package. The SV must be an RV. The package
2933 must be designated by its stash (see C<gv_stashpv()>). The reference count
2934 of the SV is unaffected.
2936 SV* sv_bless (SV* sv, HV* stash)
2940 Concatenates the string onto the end of the string which is in the SV.
2941 Handles 'get' magic, but not 'set' magic. See C<sv_catpv_mg>.
2943 void sv_catpv (SV* sv, const char* ptr)
2947 Like C<sv_catpv>, but also handles 'set' magic.
2949 void sv_catpvn (SV* sv, const char* ptr)
2953 Concatenates the string onto the end of the string which is in the SV. The
2954 C<len> indicates number of bytes to copy. Handles 'get' magic, but not
2955 'set' magic. See C<sv_catpvn_mg>.
2957 void sv_catpvn (SV* sv, const char* ptr, STRLEN len)
2961 Like C<sv_catpvn>, but also handles 'set' magic.
2963 void sv_catpvn_mg (SV* sv, const char* ptr, STRLEN len)
2967 Processes its arguments like C<sprintf> and appends the formatted output
2968 to an SV. Handles 'get' magic, but not 'set' magic. C<SvSETMAGIC()> must
2969 typically be called after calling this function to handle 'set' magic.
2971 void sv_catpvf (SV* sv, const char* pat, ...)
2975 Like C<sv_catpvf>, but also handles 'set' magic.
2977 void sv_catpvf_mg (SV* sv, const char* pat, ...)
2981 Concatenates the string from SV C<ssv> onto the end of the string in SV
2982 C<dsv>. Handles 'get' magic, but not 'set' magic. See C<sv_catsv_mg>.
2984 void sv_catsv (SV* dsv, SV* ssv)
2988 Like C<sv_catsv>, but also handles 'set' magic.
2990 void sv_catsv_mg (SV* dsv, SV* ssv)
2994 Efficient removal of characters from the beginning of the string
2995 buffer. SvPOK(sv) must be true and the C<ptr> must be a pointer to
2996 somewhere inside the string buffer. The C<ptr> becomes the first
2997 character of the adjusted string.
2999 void sv_chop(SV* sv, const char *ptr)
3004 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
3005 string in C<sv1> is less than, equal to, or greater than the string in
3008 I32 sv_cmp (SV* sv1, SV* sv2)
3012 Returns the length of the string which is in the SV. See C<SvLEN>.
3018 Set the length of the string which is in the SV. See C<SvCUR>.
3020 void SvCUR_set (SV* sv, int val)
3024 Auto-decrement of the value in the SV.
3026 void sv_dec (SV* sv)
3028 =item sv_derived_from
3030 Returns a boolean indicating whether the SV is derived from the specified
3031 class. This is the function that implements C<UNIVERSAL::isa>. It works
3032 for class names as well as for objects.
3034 bool sv_derived_from (SV* sv, const char* name);
3038 Returns a pointer to the last character in the string which is in the SV.
3039 See C<SvCUR>. Access the character as
3045 Returns a boolean indicating whether the strings in the two SVs are
3048 I32 sv_eq (SV* sv1, SV* sv2)
3052 Invokes C<mg_get> on an SV if it has 'get' magic. This macro evaluates
3053 its argument more than once.
3055 void SvGETMAGIC(SV *sv)
3059 Expands the character buffer in the SV so that it has room for the
3060 indicated number of bytes (remember to reserve space for an extra
3061 trailing NUL character). Calls C<sv_grow> to perform the expansion if
3062 necessary. Returns a pointer to the character buffer.
3064 char* SvGROW(SV* sv, STRLEN len)
3068 Expands the character buffer in the SV. This will use C<sv_unref> and will
3069 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
3074 Auto-increment of the value in the SV.
3076 void sv_inc (SV* sv)
3080 Inserts a string at the specified offset/length within the SV.
3081 Similar to the Perl substr() function.
3083 void sv_insert(SV *sv, STRLEN offset, STRLEN len,
3084 char *str, STRLEN strlen)
3088 Returns a boolean indicating whether the SV contains an integer.
3094 Unsets the IV status of an SV.
3096 void SvIOK_off (SV* sv)
3100 Tells an SV that it is an integer.
3102 void SvIOK_on (SV* sv)
3106 Tells an SV that it is an integer and disables all other OK bits.
3108 void SvIOK_only (SV* sv)
3112 Returns a boolean indicating whether the SV contains an integer. Checks the
3113 B<private> setting. Use C<SvIOK>.
3119 Returns a boolean indicating whether the SV is blessed into the specified
3120 class. This does not check for subtypes; use C<sv_derived_from> to verify
3121 an inheritance relationship.
3123 int sv_isa (SV* sv, char* name)
3127 Returns a boolean indicating whether the SV is an RV pointing to a blessed
3128 object. If the SV is not an RV, or if the object is not blessed, then this
3131 int sv_isobject (SV* sv)
3135 Coerces the given SV to an integer and returns it.
3141 Returns the integer which is stored in the SV, assuming SvIOK is true.
3147 Returns the size of the string buffer in the SV. See C<SvCUR>.
3153 Returns the length of the string in the SV. Use C<SvCUR>.
3155 STRLEN sv_len (SV* sv)
3159 Adds magic to an SV.
3161 void sv_magic (SV* sv, SV* obj, int how, const char* name, I32 namlen)
3165 Creates a new SV which is a copy of the original SV. The new SV is marked
3168 SV* sv_mortalcopy (SV* oldsv)
3172 Creates a new SV which is mortal. The reference count of the SV is set to 1.
3174 SV* sv_newmortal (void)
3178 Returns a boolean indicating whether the SV contains a number, integer or
3185 Unsets the NV/IV status of an SV.
3187 void SvNIOK_off (SV* sv)
3191 Returns a boolean indicating whether the SV contains a number, integer or
3192 double. Checks the B<private> setting. Use C<SvNIOK>.
3194 int SvNIOKp (SV* SV)
3198 This is the C<false> SV. See C<PL_sv_yes>. Always refer to this as C<&PL_sv_no>.
3202 Returns a boolean indicating whether the SV contains a double.
3208 Unsets the NV status of an SV.
3210 void SvNOK_off (SV* sv)
3214 Tells an SV that it is a double.
3216 void SvNOK_on (SV* sv)
3220 Tells an SV that it is a double and disables all other OK bits.
3222 void SvNOK_only (SV* sv)
3226 Returns a boolean indicating whether the SV contains a double. Checks the
3227 B<private> setting. Use C<SvNOK>.
3233 Coerce the given SV to a double and return it.
3235 double SvNV (SV* sv)
3239 Returns the double which is stored in the SV, assuming SvNOK is true.
3241 double SvNVX (SV* sv)
3245 Returns a boolean indicating whether the value is an SV.
3251 Returns a boolean indicating whether the SvIVX is a valid offset value
3252 for the SvPVX. This hack is used internally to speed up removal of
3253 characters from the beginning of a SvPV. When SvOOK is true, then the
3254 start of the allocated string buffer is really (SvPVX - SvIVX).
3260 Returns a boolean indicating whether the SV contains a character string.
3266 Unsets the PV status of an SV.
3268 void SvPOK_off (SV* sv)
3272 Tells an SV that it is a string.
3274 void SvPOK_on (SV* sv)
3278 Tells an SV that it is a string and disables all other OK bits.
3280 void SvPOK_only (SV* sv)
3284 Returns a boolean indicating whether the SV contains a character string.
3285 Checks the B<private> setting. Use C<SvPOK>.
3291 Returns a pointer to the string in the SV, or a stringified form of the SV
3292 if the SV does not contain a string. Handles 'get' magic.
3294 char* SvPV (SV* sv, STRLEN len)
3298 Like <SvPV> but will force the SV into becoming a string (SvPOK). You
3299 want force if you are going to update the SvPVX directly.
3301 char* SvPV_force(SV* sv, STRLEN len)
3305 Returns a pointer to the string in the SV, or a stringified form of the SV
3306 if the SV does not contain a string. Handles 'get' magic.
3308 char* SvPV_nolen (SV* sv)
3312 Returns a pointer to the string in the SV. The SV must contain a string.
3314 char* SvPVX (SV* sv)
3318 Returns the value of the object's reference count.
3320 int SvREFCNT (SV* sv)
3324 Decrements the reference count of the given SV.
3326 void SvREFCNT_dec (SV* sv)
3330 Increments the reference count of the given SV.
3332 void SvREFCNT_inc (SV* sv)
3336 Tests if the SV is an RV.
3342 Unsets the RV status of an SV.
3344 void SvROK_off (SV* sv)
3348 Tells an SV that it is an RV.
3350 void SvROK_on (SV* sv)
3354 Dereferences an RV to return the SV.
3360 Invokes C<mg_set> on an SV if it has 'set' magic. This macro evaluates
3361 its argument more than once.
3363 void SvSETMAGIC( SV *sv )
3367 Copies an integer into the given SV. Does not handle 'set' magic.
3370 void sv_setiv (SV* sv, IV num)
3374 Like C<sv_setiv>, but also handles 'set' magic.
3376 void sv_setiv_mg (SV* sv, IV num)
3380 Copies a double into the given SV. Does not handle 'set' magic.
3383 void sv_setnv (SV* sv, double num)
3387 Like C<sv_setnv>, but also handles 'set' magic.
3389 void sv_setnv_mg (SV* sv, double num)
3393 Copies a string into an SV. The string must be null-terminated.
3394 Does not handle 'set' magic. See C<sv_setpv_mg>.
3396 void sv_setpv (SV* sv, const char* ptr)
3400 Like C<sv_setpv>, but also handles 'set' magic.
3402 void sv_setpv_mg (SV* sv, const char* ptr)
3406 Copies an integer into the given SV, also updating its string value.
3407 Does not handle 'set' magic. See C<sv_setpviv_mg>.
3409 void sv_setpviv (SV* sv, IV num)
3413 Like C<sv_setpviv>, but also handles 'set' magic.
3415 void sv_setpviv_mg (SV* sv, IV num)
3419 Copies a string into an SV. The C<len> parameter indicates the number of
3420 bytes to be copied. Does not handle 'set' magic. See C<sv_setpvn_mg>.
3422 void sv_setpvn (SV* sv, const char* ptr, STRLEN len)
3426 Like C<sv_setpvn>, but also handles 'set' magic.
3428 void sv_setpvn_mg (SV* sv, const char* ptr, STRLEN len)
3432 Processes its arguments like C<sprintf> and sets an SV to the formatted
3433 output. Does not handle 'set' magic. See C<sv_setpvf_mg>.
3435 void sv_setpvf (SV* sv, const char* pat, ...)
3439 Like C<sv_setpvf>, but also handles 'set' magic.
3441 void sv_setpvf_mg (SV* sv, const char* pat, ...)
3445 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
3446 argument will be upgraded to an RV. That RV will be modified to point to
3447 the new SV. The C<classname> argument indicates the package for the
3448 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3449 will be returned and will have a reference count of 1.
3451 SV* sv_setref_iv (SV *rv, char *classname, IV iv)
3455 Copies a double into a new SV, optionally blessing the SV. The C<rv>
3456 argument will be upgraded to an RV. That RV will be modified to point to
3457 the new SV. The C<classname> argument indicates the package for the
3458 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3459 will be returned and will have a reference count of 1.
3461 SV* sv_setref_nv (SV *rv, char *classname, double nv)
3465 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
3466 argument will be upgraded to an RV. That RV will be modified to point to
3467 the new SV. If the C<pv> argument is NULL then C<PL_sv_undef> will be placed
3468 into the SV. The C<classname> argument indicates the package for the
3469 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3470 will be returned and will have a reference count of 1.
3472 SV* sv_setref_pv (SV *rv, char *classname, void* pv)
3474 Do not use with integral Perl types such as HV, AV, SV, CV, because those
3475 objects will become corrupted by the pointer copy process.
3477 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
3481 Copies a string into a new SV, optionally blessing the SV. The length of the
3482 string must be specified with C<n>. The C<rv> argument will be upgraded to
3483 an RV. That RV will be modified to point to the new SV. The C<classname>
3484 argument indicates the package for the blessing. Set C<classname> to
3485 C<Nullch> to avoid the blessing. The new SV will be returned and will have
3486 a reference count of 1.
3488 SV* sv_setref_pvn (SV *rv, char *classname, char* pv, I32 n)
3490 Note that C<sv_setref_pv> copies the pointer while this copies the string.
3494 Calls C<sv_setsv> if dsv is not the same as ssv. May evaluate arguments
3497 void SvSetSV (SV* dsv, SV* ssv)
3499 =item SvSetSV_nosteal
3501 Calls a non-destructive version of C<sv_setsv> if dsv is not the same as ssv.
3502 May evaluate arguments more than once.
3504 void SvSetSV_nosteal (SV* dsv, SV* ssv)
3508 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
3509 The source SV may be destroyed if it is mortal. Does not handle 'set' magic.
3510 See the macro forms C<SvSetSV>, C<SvSetSV_nosteal> and C<sv_setsv_mg>.
3512 void sv_setsv (SV* dsv, SV* ssv)
3516 Like C<sv_setsv>, but also handles 'set' magic.
3518 void sv_setsv_mg (SV* dsv, SV* ssv)
3522 Copies an unsigned integer into the given SV. Does not handle 'set' magic.
3525 void sv_setuv (SV* sv, UV num)
3529 Like C<sv_setuv>, but also handles 'set' magic.
3531 void sv_setuv_mg (SV* sv, UV num)
3535 Returns the stash of the SV.
3537 HV* SvSTASH (SV* sv)
3541 Taints an SV if tainting is enabled
3543 void SvTAINT (SV* sv)
3547 Checks to see if an SV is tainted. Returns TRUE if it is, FALSE if not.
3549 int SvTAINTED (SV* sv)
3553 Untaints an SV. Be I<very> careful with this routine, as it short-circuits
3554 some of Perl's fundamental security features. XS module authors should
3555 not use this function unless they fully understand all the implications
3556 of unconditionally untainting the value. Untainting should be done in
3557 the standard perl fashion, via a carefully crafted regexp, rather than
3558 directly untainting variables.
3560 void SvTAINTED_off (SV* sv)
3564 Marks an SV as tainted.
3566 void SvTAINTED_on (SV* sv)
3570 Integer type flag for scalars. See C<svtype>.
3574 Pointer type flag for scalars. See C<svtype>.
3578 Type flag for arrays. See C<svtype>.
3582 Type flag for code refs. See C<svtype>.
3586 Type flag for hashes. See C<svtype>.
3590 Type flag for blessed scalars. See C<svtype>.
3594 Double type flag for scalars. See C<svtype>.
3598 Returns a boolean indicating whether Perl would evaluate the SV as true or
3599 false, defined or undefined. Does not handle 'get' magic.
3605 Returns the type of the SV. See C<svtype>.
3607 svtype SvTYPE (SV* sv)
3611 An enum of flags for Perl types. These are found in the file B<sv.h> in the
3612 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
3616 This is the C<undef> SV. Always refer to this as C<&PL_sv_undef>.
3620 Unsets the RV status of the SV, and decrements the reference count of
3621 whatever was being referenced by the RV. This can almost be thought of
3622 as a reversal of C<newSVrv>. See C<SvROK_off>.
3624 void sv_unref (SV* sv)
3628 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
3629 the upgrade if necessary. See C<svtype>.
3631 bool SvUPGRADE (SV* sv, svtype mt)
3635 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
3639 Tells an SV to use C<ptr> to find its string value. Normally the string is
3640 stored inside the SV but sv_usepvn allows the SV to use an outside string.
3641 The C<ptr> should point to memory that was allocated by C<malloc>. The
3642 string length, C<len>, must be supplied. This function will realloc the
3643 memory pointed to by C<ptr>, so that pointer should not be freed or used by
3644 the programmer after giving it to sv_usepvn. Does not handle 'set' magic.
3645 See C<sv_usepvn_mg>.
3647 void sv_usepvn (SV* sv, char* ptr, STRLEN len)
3651 Like C<sv_usepvn>, but also handles 'set' magic.
3653 void sv_usepvn_mg (SV* sv, char* ptr, STRLEN len)
3657 Processes its arguments like C<vsprintf> and appends the formatted output
3658 to an SV. Uses an array of SVs if the C style variable argument list is
3659 missing (NULL). When running with taint checks enabled, indicates via
3660 C<maybe_tainted> if results are untrustworthy (often due to the use of
3663 void sv_catpvfn (SV* sv, const char* pat, STRLEN patlen,
3664 va_list *args, SV **svargs, I32 svmax,
3665 bool *maybe_tainted);
3669 Works like C<vcatpvfn> but copies the text into the SV instead of
3672 void sv_setpvfn (SV* sv, const char* pat, STRLEN patlen,
3673 va_list *args, SV **svargs, I32 svmax,
3674 bool *maybe_tainted);
3678 Coerces the given SV to an unsigned integer and returns it.
3684 Returns the unsigned integer which is stored in the SV, assuming SvIOK is true.
3690 This is the C<true> SV. See C<PL_sv_no>. Always refer to this as C<&PL_sv_yes>.
3694 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
3695 This is always the proper type for the C++ object. See C<CLASS> and
3696 L<perlxs/"Using XS With C++">.
3700 Converts the specified character to lowercase.
3702 int toLOWER (char c)
3706 Converts the specified character to uppercase.
3708 int toUPPER (char c)
3712 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
3713 function the same way you use the C C<printf> function. See C<croak()>.
3717 Push an integer onto the stack, extending the stack if necessary. Handles
3718 'set' magic. See C<PUSHi>.
3724 Push a double onto the stack, extending the stack if necessary. Handles 'set'
3725 magic. See C<PUSHn>.
3731 Push a string onto the stack, extending the stack if necessary. The C<len>
3732 indicates the length of the string. Handles 'set' magic. See C<PUSHp>.
3734 XPUSHp(char *c, int len)
3738 Push an SV onto the stack, extending the stack if necessary. Does not
3739 handle 'set' magic. See C<PUSHs>.
3745 Push an unsigned integer onto the stack, extending the stack if
3746 necessary. See C<PUSHu>.
3750 Macro to declare an XSUB and its C parameter list. This is handled by
3755 Return from XSUB, indicating number of items on the stack. This is usually
3756 handled by C<xsubpp>.
3760 =item XSRETURN_EMPTY
3762 Return an empty list from an XSUB immediately.
3768 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
3774 Return C<&PL_sv_no> from an XSUB immediately. Uses C<XST_mNO>.
3780 Return an double from an XSUB immediately. Uses C<XST_mNV>.
3786 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
3788 XSRETURN_PV(char *v)
3790 =item XSRETURN_UNDEF
3792 Return C<&PL_sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
3798 Return C<&PL_sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
3804 Place an integer into the specified position C<i> on the stack. The value is
3805 stored in a new mortal SV.
3807 XST_mIV( int i, IV v )
3811 Place a double into the specified position C<i> on the stack. The value is
3812 stored in a new mortal SV.
3814 XST_mNV( int i, NV v )
3818 Place C<&PL_sv_no> into the specified position C<i> on the stack.
3824 Place a copy of a string into the specified position C<i> on the stack. The
3825 value is stored in a new mortal SV.
3827 XST_mPV( int i, char *v )
3831 Place C<&PL_sv_undef> into the specified position C<i> on the stack.
3837 Place C<&PL_sv_yes> into the specified position C<i> on the stack.
3843 The version identifier for an XS module. This is usually handled
3844 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
3846 =item XS_VERSION_BOOTCHECK
3848 Macro to verify that a PM module's $VERSION variable matches the XS module's
3849 C<XS_VERSION> variable. This is usually handled automatically by
3850 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
3854 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
3855 destination, C<n> is the number of items, and C<t> is the type.
3857 void Zero( d, n, t )
3863 Until May 1997, this document was maintained by Jeff Okamoto
3864 <okamoto@corp.hp.com>. It is now maintained as part of Perl itself.
3866 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
3867 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
3868 Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
3869 Stephen McCamant, and Gurusamy Sarathy.
3871 API Listing originally by Dean Roehrich <roehrich@cray.com>.