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(char*, int);
42 SV* newSVpvn(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*, char*);
52 void sv_setpvn(SV*, 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 untrustworty (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:
93 which will automatically coerce the actual scalar type into an IV, double,
96 In the C<SvPV> macro, the length of the string returned is placed into the
97 variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
98 care what the length of the data is, use the global variable C<na>. Remember,
99 however, that Perl allows arbitrary strings of data that may both contain
100 NULs and might not be terminated by a NUL.
102 If you want to know if the scalar value is TRUE, you can use:
106 Although Perl will automatically grow strings for you, if you need to force
107 Perl to allocate more memory for your SV, you can use the macro
109 SvGROW(SV*, STRLEN newlen)
111 which will determine if more memory needs to be allocated. If so, it will
112 call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
113 decrease, the allocated memory of an SV and that it does not automatically
114 add a byte for the a trailing NUL (perl's own string functions typically do
115 C<SvGROW(sv, len + 1)>).
117 If you have an SV and want to know what kind of data Perl thinks is stored
118 in it, you can use the following macros to check the type of SV you have.
124 You can get and set the current length of the string stored in an SV with
125 the following macros:
128 SvCUR_set(SV*, I32 val)
130 You can also get a pointer to the end of the string stored in the SV
135 But note that these last three macros are valid only if C<SvPOK()> is true.
137 If you want to append something to the end of string stored in an C<SV*>,
138 you can use the following functions:
140 void sv_catpv(SV*, char*);
141 void sv_catpvn(SV*, char*, int);
142 void sv_catpvf(SV*, const char*, ...);
143 void sv_catpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
144 void sv_catsv(SV*, SV*);
146 The first function calculates the length of the string to be appended by
147 using C<strlen>. In the second, you specify the length of the string
148 yourself. The third function processes its arguments like C<sprintf> and
149 appends the formatted output. The fourth function works like C<vsprintf>.
150 You can specify the address and length of an array of SVs instead of the
151 va_list argument. The fifth function extends the string stored in the first
152 SV with the string stored in the second SV. It also forces the second SV
153 to be interpreted as a string.
155 The C<sv_cat*()> functions are not generic enough to operate on values that
156 have "magic". See L<Magic Virtual Tables> later in this document.
158 If you know the name of a scalar variable, you can get a pointer to its SV
159 by using the following:
161 SV* perl_get_sv("package::varname", FALSE);
163 This returns NULL if the variable does not exist.
165 If you want to know if this variable (or any other SV) is actually C<defined>,
170 The scalar C<undef> value is stored in an SV instance called C<sv_undef>. Its
171 address can be used whenever an C<SV*> is needed.
173 There are also the two values C<sv_yes> and C<sv_no>, which contain Boolean
174 TRUE and FALSE values, respectively. Like C<sv_undef>, their addresses can
175 be used whenever an C<SV*> is needed.
177 Do not be fooled into thinking that C<(SV *) 0> is the same as C<&sv_undef>.
181 if (I-am-to-return-a-real-value) {
182 sv = sv_2mortal(newSViv(42));
186 This code tries to return a new SV (which contains the value 42) if it should
187 return a real value, or undef otherwise. Instead it has returned a NULL
188 pointer which, somewhere down the line, will cause a segmentation violation,
189 bus error, or just weird results. Change the zero to C<&sv_undef> in the first
190 line and all will be well.
192 To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
193 call is not necessary (see L<Reference Counts and Mortality>).
195 =head2 What's Really Stored in an SV?
197 Recall that the usual method of determining the type of scalar you have is
198 to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
199 usually these macros will always return TRUE and calling the C<Sv*V>
200 macros will do the appropriate conversion of string to integer/double or
201 integer/double to string.
203 If you I<really> need to know if you have an integer, double, or string
204 pointer in an SV, you can use the following three macros instead:
210 These will tell you if you truly have an integer, double, or string pointer
211 stored in your SV. The "p" stands for private.
213 In general, though, it's best to use the C<Sv*V> macros.
215 =head2 Working with AVs
217 There are two ways to create and load an AV. The first method creates an
222 The second method both creates the AV and initially populates it with SVs:
224 AV* av_make(I32 num, SV **ptr);
226 The second argument points to an array containing C<num> C<SV*>'s. Once the
227 AV has been created, the SVs can be destroyed, if so desired.
229 Once the AV has been created, the following operations are possible on AVs:
231 void av_push(AV*, SV*);
234 void av_unshift(AV*, I32 num);
236 These should be familiar operations, with the exception of C<av_unshift>.
237 This routine adds C<num> elements at the front of the array with the C<undef>
238 value. You must then use C<av_store> (described below) to assign values
239 to these new elements.
241 Here are some other functions:
244 SV** av_fetch(AV*, I32 key, I32 lval);
245 SV** av_store(AV*, I32 key, SV* val);
247 The C<av_len> function returns the highest index value in array (just
248 like $#array in Perl). If the array is empty, -1 is returned. The
249 C<av_fetch> function returns the value at index C<key>, but if C<lval>
250 is non-zero, then C<av_fetch> will store an undef value at that index.
251 The C<av_store> function stores the value C<val> at index C<key>, and does
252 not increment the reference count of C<val>. Thus the caller is responsible
253 for taking care of that, and if C<av_store> returns NULL, the caller will
254 have to decrement the reference count to avoid a memory leak. Note that
255 C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s as their
260 void av_extend(AV*, I32 key);
262 The C<av_clear> function deletes all the elements in the AV* array, but
263 does not actually delete the array itself. The C<av_undef> function will
264 delete all the elements in the array plus the array itself. The
265 C<av_extend> function extends the array so that it contains C<key>
266 elements. If C<key> is less than the current length of the array, then
269 If you know the name of an array variable, you can get a pointer to its AV
270 by using the following:
272 AV* perl_get_av("package::varname", FALSE);
274 This returns NULL if the variable does not exist.
276 See L<Understanding the Magic of Tied Hashes and Arrays> for more
277 information on how to use the array access functions on tied arrays.
279 =head2 Working with HVs
281 To create an HV, you use the following routine:
285 Once the HV has been created, the following operations are possible on HVs:
287 SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
288 SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
290 The C<klen> parameter is the length of the key being passed in (Note that
291 you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
292 length of the key). The C<val> argument contains the SV pointer to the
293 scalar being stored, and C<hash> is the precomputed hash value (zero if
294 you want C<hv_store> to calculate it for you). The C<lval> parameter
295 indicates whether this fetch is actually a part of a store operation, in
296 which case a new undefined value will be added to the HV with the supplied
297 key and C<hv_fetch> will return as if the value had already existed.
299 Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
300 C<SV*>. To access the scalar value, you must first dereference the return
301 value. However, you should check to make sure that the return value is
302 not NULL before dereferencing it.
304 These two functions check if a hash table entry exists, and deletes it.
306 bool hv_exists(HV*, char* key, U32 klen);
307 SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
309 If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
310 create and return a mortal copy of the deleted value.
312 And more miscellaneous functions:
317 Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
318 table but does not actually delete the hash table. The C<hv_undef> deletes
319 both the entries and the hash table itself.
321 Perl keeps the actual data in linked list of structures with a typedef of HE.
322 These contain the actual key and value pointers (plus extra administrative
323 overhead). The key is a string pointer; the value is an C<SV*>. However,
324 once you have an C<HE*>, to get the actual key and value, use the routines
327 I32 hv_iterinit(HV*);
328 /* Prepares starting point to traverse hash table */
329 HE* hv_iternext(HV*);
330 /* Get the next entry, and return a pointer to a
331 structure that has both the key and value */
332 char* hv_iterkey(HE* entry, I32* retlen);
333 /* Get the key from an HE structure and also return
334 the length of the key string */
335 SV* hv_iterval(HV*, HE* entry);
336 /* Return a SV pointer to the value of the HE
338 SV* hv_iternextsv(HV*, char** key, I32* retlen);
339 /* This convenience routine combines hv_iternext,
340 hv_iterkey, and hv_iterval. The key and retlen
341 arguments are return values for the key and its
342 length. The value is returned in the SV* argument */
344 If you know the name of a hash variable, you can get a pointer to its HV
345 by using the following:
347 HV* perl_get_hv("package::varname", FALSE);
349 This returns NULL if the variable does not exist.
351 The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
357 hash = hash * 33 + *s++;
359 See L<Understanding the Magic of Tied Hashes and Arrays> for more
360 information on how to use the hash access functions on tied hashes.
362 =head2 Hash API Extensions
364 Beginning with version 5.004, the following functions are also supported:
366 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
367 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
369 bool hv_exists_ent (HV* tb, SV* key, U32 hash);
370 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
372 SV* hv_iterkeysv (HE* entry);
374 Note that these functions take C<SV*> keys, which simplifies writing
375 of extension code that deals with hash structures. These functions
376 also allow passing of C<SV*> keys to C<tie> functions without forcing
377 you to stringify the keys (unlike the previous set of functions).
379 They also return and accept whole hash entries (C<HE*>), making their
380 use more efficient (since the hash number for a particular string
381 doesn't have to be recomputed every time). See L<API LISTING> later in
382 this document for detailed descriptions.
384 The following macros must always be used to access the contents of hash
385 entries. Note that the arguments to these macros must be simple
386 variables, since they may get evaluated more than once. See
387 L<API LISTING> later in this document for detailed descriptions of these
390 HePV(HE* he, STRLEN len)
394 HeSVKEY_force(HE* he)
395 HeSVKEY_set(HE* he, SV* sv)
397 These two lower level macros are defined, but must only be used when
398 dealing with keys that are not C<SV*>s:
403 Note that both C<hv_store> and C<hv_store_ent> do not increment the
404 reference count of the stored C<val>, which is the caller's responsibility.
405 If these functions return a NULL value, the caller will usually have to
406 decrement the reference count of C<val> to avoid a memory leak.
410 References are a special type of scalar that point to other data types
411 (including references).
413 To create a reference, use either of the following functions:
415 SV* newRV_inc((SV*) thing);
416 SV* newRV_noinc((SV*) thing);
418 The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
419 functions are identical except that C<newRV_inc> increments the reference
420 count of the C<thing>, while C<newRV_noinc> does not. For historical
421 reasons, C<newRV> is a synonym for C<newRV_inc>.
423 Once you have a reference, you can use the following macro to dereference
428 then call the appropriate routines, casting the returned C<SV*> to either an
429 C<AV*> or C<HV*>, if required.
431 To determine if an SV is a reference, you can use the following macro:
435 To discover what type of value the reference refers to, use the following
436 macro and then check the return value.
440 The most useful types that will be returned are:
449 SVt_PVGV Glob (possible a file handle)
450 SVt_PVMG Blessed or Magical Scalar
452 See the sv.h header file for more details.
454 =head2 Blessed References and Class Objects
456 References are also used to support object-oriented programming. In the
457 OO lexicon, an object is simply a reference that has been blessed into a
458 package (or class). Once blessed, the programmer may now use the reference
459 to access the various methods in the class.
461 A reference can be blessed into a package with the following function:
463 SV* sv_bless(SV* sv, HV* stash);
465 The C<sv> argument must be a reference. The C<stash> argument specifies
466 which class the reference will belong to. See
467 L<Stashes and Globs> for information on converting class names into stashes.
469 /* Still under construction */
471 Upgrades rv to reference if not already one. Creates new SV for rv to
472 point to. If C<classname> is non-null, the SV is blessed into the specified
473 class. SV is returned.
475 SV* newSVrv(SV* rv, char* classname);
477 Copies integer or double into an SV whose reference is C<rv>. SV is blessed
478 if C<classname> is non-null.
480 SV* sv_setref_iv(SV* rv, char* classname, IV iv);
481 SV* sv_setref_nv(SV* rv, char* classname, NV iv);
483 Copies the pointer value (I<the address, not the string!>) into an SV whose
484 reference is rv. SV is blessed if C<classname> is non-null.
486 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
488 Copies string into an SV whose reference is C<rv>. Set length to 0 to let
489 Perl calculate the string length. SV is blessed if C<classname> is non-null.
491 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
493 Tests whether the SV is blessed into the specified class. It does not
494 check inheritance relationships.
496 int sv_isa(SV* sv, char* name);
498 Tests whether the SV is a reference to a blessed object.
500 int sv_isobject(SV* sv);
502 Tests whether the SV is derived from the specified class. SV can be either
503 a reference to a blessed object or a string containing a class name. This
504 is the function implementing the C<UNIVERSAL::isa> functionality.
506 bool sv_derived_from(SV* sv, char* name);
508 To check if you've got an object derived from a specific class you have
511 if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... }
513 =head2 Creating New Variables
515 To create a new Perl variable with an undef value which can be accessed from
516 your Perl script, use the following routines, depending on the variable type.
518 SV* perl_get_sv("package::varname", TRUE);
519 AV* perl_get_av("package::varname", TRUE);
520 HV* perl_get_hv("package::varname", TRUE);
522 Notice the use of TRUE as the second parameter. The new variable can now
523 be set, using the routines appropriate to the data type.
525 There are additional macros whose values may be bitwise OR'ed with the
526 C<TRUE> argument to enable certain extra features. Those bits are:
528 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
529 "Name <varname> used only once: possible typo" warning.
530 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
531 the variable did not exist before the function was called.
533 If you do not specify a package name, the variable is created in the current
536 =head2 Reference Counts and Mortality
538 Perl uses an reference count-driven garbage collection mechanism. SVs,
539 AVs, or HVs (xV for short in the following) start their life with a
540 reference count of 1. If the reference count of an xV ever drops to 0,
541 then it will be destroyed and its memory made available for reuse.
543 This normally doesn't happen at the Perl level unless a variable is
544 undef'ed or the last variable holding a reference to it is changed or
545 overwritten. At the internal level, however, reference counts can be
546 manipulated with the following macros:
548 int SvREFCNT(SV* sv);
549 SV* SvREFCNT_inc(SV* sv);
550 void SvREFCNT_dec(SV* sv);
552 However, there is one other function which manipulates the reference
553 count of its argument. The C<newRV_inc> function, you will recall,
554 creates a reference to the specified argument. As a side effect,
555 it increments the argument's reference count. If this is not what
556 you want, use C<newRV_noinc> instead.
558 For example, imagine you want to return a reference from an XSUB function.
559 Inside the XSUB routine, you create an SV which initially has a reference
560 count of one. Then you call C<newRV_inc>, passing it the just-created SV.
561 This returns the reference as a new SV, but the reference count of the
562 SV you passed to C<newRV_inc> has been incremented to two. Now you
563 return the reference from the XSUB routine and forget about the SV.
564 But Perl hasn't! Whenever the returned reference is destroyed, the
565 reference count of the original SV is decreased to one and nothing happens.
566 The SV will hang around without any way to access it until Perl itself
567 terminates. This is a memory leak.
569 The correct procedure, then, is to use C<newRV_noinc> instead of
570 C<newRV_inc>. Then, if and when the last reference is destroyed,
571 the reference count of the SV will go to zero and it will be destroyed,
572 stopping any memory leak.
574 There are some convenience functions available that can help with the
575 destruction of xVs. These functions introduce the concept of "mortality".
576 An xV that is mortal has had its reference count marked to be decremented,
577 but not actually decremented, until "a short time later". Generally the
578 term "short time later" means a single Perl statement, such as a call to
579 an XSUB function. The actual determinant for when mortal xVs have their
580 reference count decremented depends on two macros, SAVETMPS and FREETMPS.
581 See L<perlcall> and L<perlxs> for more details on these macros.
583 "Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
584 However, if you mortalize a variable twice, the reference count will
585 later be decremented twice.
587 You should be careful about creating mortal variables. Strange things
588 can happen if you make the same value mortal within multiple contexts,
589 or if you make a variable mortal multiple times.
591 To create a mortal variable, use the functions:
595 SV* sv_mortalcopy(SV*)
597 The first call creates a mortal SV, the second converts an existing
598 SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
599 third creates a mortal copy of an existing SV.
601 The mortal routines are not just for SVs -- AVs and HVs can be
602 made mortal by passing their address (type-casted to C<SV*>) to the
603 C<sv_2mortal> or C<sv_mortalcopy> routines.
605 =head2 Stashes and Globs
607 A "stash" is a hash that contains all of the different objects that
608 are contained within a package. Each key of the stash is a symbol
609 name (shared by all the different types of objects that have the same
610 name), and each value in the hash table is a GV (Glob Value). This GV
611 in turn contains references to the various objects of that name,
612 including (but not limited to) the following:
621 There is a single stash called "defstash" that holds the items that exist
622 in the "main" package. To get at the items in other packages, append the
623 string "::" to the package name. The items in the "Foo" package are in
624 the stash "Foo::" in defstash. The items in the "Bar::Baz" package are
625 in the stash "Baz::" in "Bar::"'s stash.
627 To get the stash pointer for a particular package, use the function:
629 HV* gv_stashpv(char* name, I32 create)
630 HV* gv_stashsv(SV*, I32 create)
632 The first function takes a literal string, the second uses the string stored
633 in the SV. Remember that a stash is just a hash table, so you get back an
634 C<HV*>. The C<create> flag will create a new package if it is set.
636 The name that C<gv_stash*v> wants is the name of the package whose symbol table
637 you want. The default package is called C<main>. If you have multiply nested
638 packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
641 Alternately, if you have an SV that is a blessed reference, you can find
642 out the stash pointer by using:
644 HV* SvSTASH(SvRV(SV*));
646 then use the following to get the package name itself:
648 char* HvNAME(HV* stash);
650 If you need to bless or re-bless an object you can use the following
653 SV* sv_bless(SV*, HV* stash)
655 where the first argument, an C<SV*>, must be a reference, and the second
656 argument is a stash. The returned C<SV*> can now be used in the same way
659 For more information on references and blessings, consult L<perlref>.
661 =head2 Double-Typed SVs
663 Scalar variables normally contain only one type of value, an integer,
664 double, pointer, or reference. Perl will automatically convert the
665 actual scalar data from the stored type into the requested type.
667 Some scalar variables contain more than one type of scalar data. For
668 example, the variable C<$!> contains either the numeric value of C<errno>
669 or its string equivalent from either C<strerror> or C<sys_errlist[]>.
671 To force multiple data values into an SV, you must do two things: use the
672 C<sv_set*v> routines to add the additional scalar type, then set a flag
673 so that Perl will believe it contains more than one type of data. The
674 four macros to set the flags are:
681 The particular macro you must use depends on which C<sv_set*v> routine
682 you called first. This is because every C<sv_set*v> routine turns on
683 only the bit for the particular type of data being set, and turns off
686 For example, to create a new Perl variable called "dberror" that contains
687 both the numeric and descriptive string error values, you could use the
691 extern char *dberror_list;
693 SV* sv = perl_get_sv("dberror", TRUE);
694 sv_setiv(sv, (IV) dberror);
695 sv_setpv(sv, dberror_list[dberror]);
698 If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
699 macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
701 =head2 Magic Variables
703 [This section still under construction. Ignore everything here. Post no
704 bills. Everything not permitted is forbidden.]
706 Any SV may be magical, that is, it has special features that a normal
707 SV does not have. These features are stored in the SV structure in a
708 linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
721 Note this is current as of patchlevel 0, and could change at any time.
723 =head2 Assigning Magic
725 Perl adds magic to an SV using the sv_magic function:
727 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
729 The C<sv> argument is a pointer to the SV that is to acquire a new magical
732 If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
733 set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
734 it to the beginning of the linked list of magical features. Any prior
735 entry of the same type of magic is deleted. Note that this can be
736 overridden, and multiple instances of the same type of magic can be
737 associated with an SV.
739 The C<name> and C<namlen> arguments are used to associate a string with
740 the magic, typically the name of a variable. C<namlen> is stored in the
741 C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
742 copy of the name is stored in C<mg_ptr> field.
744 The sv_magic function uses C<how> to determine which, if any, predefined
745 "Magic Virtual Table" should be assigned to the C<mg_virtual> field.
746 See the "Magic Virtual Table" section below. The C<how> argument is also
747 stored in the C<mg_type> field.
749 The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
750 structure. If it is not the same as the C<sv> argument, the reference
751 count of the C<obj> object is incremented. If it is the same, or if
752 the C<how> argument is "#", or if it is a NULL pointer, then C<obj> is
753 merely stored, without the reference count being incremented.
755 There is also a function to add magic to an C<HV>:
757 void hv_magic(HV *hv, GV *gv, int how);
759 This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
761 To remove the magic from an SV, call the function sv_unmagic:
763 void sv_unmagic(SV *sv, int type);
765 The C<type> argument should be equal to the C<how> value when the C<SV>
766 was initially made magical.
768 =head2 Magic Virtual Tables
770 The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
771 C<MGVTBL>, which is a structure of function pointers and stands for
772 "Magic Virtual Table" to handle the various operations that might be
773 applied to that variable.
775 The C<MGVTBL> has five pointers to the following routine types:
777 int (*svt_get)(SV* sv, MAGIC* mg);
778 int (*svt_set)(SV* sv, MAGIC* mg);
779 U32 (*svt_len)(SV* sv, MAGIC* mg);
780 int (*svt_clear)(SV* sv, MAGIC* mg);
781 int (*svt_free)(SV* sv, MAGIC* mg);
783 This MGVTBL structure is set at compile-time in C<perl.h> and there are
784 currently 19 types (or 21 with overloading turned on). These different
785 structures contain pointers to various routines that perform additional
786 actions depending on which function is being called.
788 Function pointer Action taken
789 ---------------- ------------
790 svt_get Do something after the value of the SV is retrieved.
791 svt_set Do something after the SV is assigned a value.
792 svt_len Report on the SV's length.
793 svt_clear Clear something the SV represents.
794 svt_free Free any extra storage associated with the SV.
796 For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
797 to an C<mg_type> of '\0') contains:
799 { magic_get, magic_set, magic_len, 0, 0 }
801 Thus, when an SV is determined to be magical and of type '\0', if a get
802 operation is being performed, the routine C<magic_get> is called. All
803 the various routines for the various magical types begin with C<magic_>.
805 The current kinds of Magic Virtual Tables are:
807 mg_type MGVTBL Type of magic
808 ------- ------ ----------------------------
809 \0 vtbl_sv Special scalar variable
810 A vtbl_amagic %OVERLOAD hash
811 a vtbl_amagicelem %OVERLOAD hash element
812 c (none) Holds overload table (AMT) on stash
813 B vtbl_bm Boyer-Moore (fast string search)
815 e vtbl_envelem %ENV hash element
816 f vtbl_fm Formline ('compiled' format)
817 g vtbl_mglob m//g target / study()ed string
818 I vtbl_isa @ISA array
819 i vtbl_isaelem @ISA array element
820 k vtbl_nkeys scalar(keys()) lvalue
821 L (none) Debugger %_<filename
822 l vtbl_dbline Debugger %_<filename element
823 o vtbl_collxfrm Locale transformation
824 P vtbl_pack Tied array or hash
825 p vtbl_packelem Tied array or hash element
826 q vtbl_packelem Tied scalar or handle
828 s vtbl_sigelem %SIG hash element
829 t vtbl_taint Taintedness
830 U vtbl_uvar Available for use by extensions
831 v vtbl_vec vec() lvalue
832 x vtbl_substr substr() lvalue
833 y vtbl_defelem Shadow "foreach" iterator variable /
834 smart parameter vivification
835 * vtbl_glob GV (typeglob)
836 # vtbl_arylen Array length ($#ary)
837 . vtbl_pos pos() lvalue
838 ~ (none) Available for use by extensions
840 When an uppercase and lowercase letter both exist in the table, then the
841 uppercase letter is used to represent some kind of composite type (a list
842 or a hash), and the lowercase letter is used to represent an element of
845 The '~' and 'U' magic types are defined specifically for use by
846 extensions and will not be used by perl itself. Extensions can use
847 '~' magic to 'attach' private information to variables (typically
848 objects). This is especially useful because there is no way for
849 normal perl code to corrupt this private information (unlike using
850 extra elements of a hash object).
852 Similarly, 'U' magic can be used much like tie() to call a C function
853 any time a scalar's value is used or changed. The C<MAGIC>'s
854 C<mg_ptr> field points to a C<ufuncs> structure:
857 I32 (*uf_val)(IV, SV*);
858 I32 (*uf_set)(IV, SV*);
862 When the SV is read from or written to, the C<uf_val> or C<uf_set>
863 function will be called with C<uf_index> as the first arg and a
864 pointer to the SV as the second.
866 Note that because multiple extensions may be using '~' or 'U' magic,
867 it is important for extensions to take extra care to avoid conflict.
868 Typically only using the magic on objects blessed into the same class
869 as the extension is sufficient. For '~' magic, it may also be
870 appropriate to add an I32 'signature' at the top of the private data
873 Also note that the C<sv_set*()> and C<sv_cat*()> functions described
874 earlier do B<not> invoke 'set' magic on their targets. This must
875 be done by the user either by calling the C<SvSETMAGIC()> macro after
876 calling these functions, or by using one of the C<sv_set*_mg()> or
877 C<sv_cat*_mg()> functions. Similarly, generic C code must call the
878 C<SvGETMAGIC()> macro to invoke any 'get' magic if they use an SV
879 obtained from external sources in functions that don't handle magic.
880 L<API LISTING> later in this document identifies such functions.
881 For example, calls to the C<sv_cat*()> functions typically need to be
882 followed by C<SvSETMAGIC()>, but they don't need a prior C<SvGETMAGIC()>
883 since their implementation handles 'get' magic.
887 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
889 This routine returns a pointer to the C<MAGIC> structure stored in the SV.
890 If the SV does not have that magical feature, C<NULL> is returned. Also,
891 if the SV is not of type SVt_PVMG, Perl may core dump.
893 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
895 This routine checks to see what types of magic C<sv> has. If the mg_type
896 field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
897 the mg_type field is changed to be the lowercase letter.
899 =head2 Understanding the Magic of Tied Hashes and Arrays
901 Tied hashes and arrays are magical beasts of the 'P' magic type.
903 WARNING: As of the 5.004 release, proper usage of the array and hash
904 access functions requires understanding a few caveats. Some
905 of these caveats are actually considered bugs in the API, to be fixed
906 in later releases, and are bracketed with [MAYCHANGE] below. If
907 you find yourself actually applying such information in this section, be
908 aware that the behavior may change in the future, umm, without warning.
910 The C<av_store> function, when given a tied array argument, merely
911 copies the magic of the array onto the value to be "stored", using
912 C<mg_copy>. It may also return NULL, indicating that the value did not
913 actually need to be stored in the array. [MAYCHANGE] After a call to
914 C<av_store> on a tied array, the caller will usually need to call
915 C<mg_set(val)> to actually invoke the perl level "STORE" method on the
916 TIEARRAY object. If C<av_store> did return NULL, a call to
917 C<SvREFCNT_dec(val)> will also be usually necessary to avoid a memory
920 The previous paragraph is applicable verbatim to tied hash access using the
921 C<hv_store> and C<hv_store_ent> functions as well.
923 C<av_fetch> and the corresponding hash functions C<hv_fetch> and
924 C<hv_fetch_ent> actually return an undefined mortal value whose magic
925 has been initialized using C<mg_copy>. Note the value so returned does not
926 need to be deallocated, as it is already mortal. [MAYCHANGE] But you will
927 need to call C<mg_get()> on the returned value in order to actually invoke
928 the perl level "FETCH" method on the underlying TIE object. Similarly,
929 you may also call C<mg_set()> on the return value after possibly assigning
930 a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
931 method on the TIE object. [/MAYCHANGE]
934 In other words, the array or hash fetch/store functions don't really
935 fetch and store actual values in the case of tied arrays and hashes. They
936 merely call C<mg_copy> to attach magic to the values that were meant to be
937 "stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
938 do the job of invoking the TIE methods on the underlying objects. Thus
939 the magic mechanism currently implements a kind of lazy access to arrays
942 Currently (as of perl version 5.004), use of the hash and array access
943 functions requires the user to be aware of whether they are operating on
944 "normal" hashes and arrays, or on their tied variants. The API may be
945 changed to provide more transparent access to both tied and normal data
946 types in future versions.
949 You would do well to understand that the TIEARRAY and TIEHASH interfaces
950 are mere sugar to invoke some perl method calls while using the uniform hash
951 and array syntax. The use of this sugar imposes some overhead (typically
952 about two to four extra opcodes per FETCH/STORE operation, in addition to
953 the creation of all the mortal variables required to invoke the methods).
954 This overhead will be comparatively small if the TIE methods are themselves
955 substantial, but if they are only a few statements long, the overhead
956 will not be insignificant.
958 =head2 Localizing changes
960 Perl has a very handy construction
967 This construction is I<approximately> equivalent to
976 The biggest difference is that the first construction would
977 reinstate the initial value of $var, irrespective of how control exits
978 the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
979 more efficient as well.
981 There is a way to achieve a similar task from C via Perl API: create a
982 I<pseudo-block>, and arrange for some changes to be automatically
983 undone at the end of it, either explicit, or via a non-local exit (via
984 die()). A I<block>-like construct is created by a pair of
985 C<ENTER>/C<LEAVE> macros (see L<perlcall/EXAMPLE/"Returning a
986 Scalar">). Such a construct may be created specially for some
987 important localized task, or an existing one (like boundaries of
988 enclosing Perl subroutine/block, or an existing pair for freeing TMPs)
989 may be used. (In the second case the overhead of additional
990 localization must be almost negligible.) Note that any XSUB is
991 automatically enclosed in an C<ENTER>/C<LEAVE> pair.
993 Inside such a I<pseudo-block> the following service is available:
997 =item C<SAVEINT(int i)>
999 =item C<SAVEIV(IV i)>
1001 =item C<SAVEI32(I32 i)>
1003 =item C<SAVELONG(long i)>
1005 These macros arrange things to restore the value of integer variable
1006 C<i> at the end of enclosing I<pseudo-block>.
1008 =item C<SAVESPTR(s)>
1010 =item C<SAVEPPTR(p)>
1012 These macros arrange things to restore the value of pointers C<s> and
1013 C<p>. C<s> must be a pointer of a type which survives conversion to
1014 C<SV*> and back, C<p> should be able to survive conversion to C<char*>
1017 =item C<SAVEFREESV(SV *sv)>
1019 The refcount of C<sv> would be decremented at the end of
1020 I<pseudo-block>. This is similar to C<sv_2mortal>, which should (?) be
1023 =item C<SAVEFREEOP(OP *op)>
1025 The C<OP *> is op_free()ed at the end of I<pseudo-block>.
1027 =item C<SAVEFREEPV(p)>
1029 The chunk of memory which is pointed to by C<p> is Safefree()ed at the
1030 end of I<pseudo-block>.
1032 =item C<SAVECLEARSV(SV *sv)>
1034 Clears a slot in the current scratchpad which corresponds to C<sv> at
1035 the end of I<pseudo-block>.
1037 =item C<SAVEDELETE(HV *hv, char *key, I32 length)>
1039 The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
1040 string pointed to by C<key> is Safefree()ed. If one has a I<key> in
1041 short-lived storage, the corresponding string may be reallocated like
1044 SAVEDELETE(defstash, savepv(tmpbuf), strlen(tmpbuf));
1046 =item C<SAVEDESTRUCTOR(f,p)>
1048 At the end of I<pseudo-block> the function C<f> is called with the
1049 only argument (of type C<void*>) C<p>.
1051 =item C<SAVESTACK_POS()>
1053 The current offset on the Perl internal stack (cf. C<SP>) is restored
1054 at the end of I<pseudo-block>.
1058 The following API list contains functions, thus one needs to
1059 provide pointers to the modifiable data explicitly (either C pointers,
1060 or Perlish C<GV *>s). Where the above macros take C<int>, a similar
1061 function takes C<int *>.
1065 =item C<SV* save_scalar(GV *gv)>
1067 Equivalent to Perl code C<local $gv>.
1069 =item C<AV* save_ary(GV *gv)>
1071 =item C<HV* save_hash(GV *gv)>
1073 Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
1075 =item C<void save_item(SV *item)>
1077 Duplicates the current value of C<SV>, on the exit from the current
1078 C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
1079 using the stored value.
1081 =item C<void save_list(SV **sarg, I32 maxsarg)>
1083 A variant of C<save_item> which takes multiple arguments via an array
1084 C<sarg> of C<SV*> of length C<maxsarg>.
1086 =item C<SV* save_svref(SV **sptr)>
1088 Similar to C<save_scalar>, but will reinstate a C<SV *>.
1090 =item C<void save_aptr(AV **aptr)>
1092 =item C<void save_hptr(HV **hptr)>
1094 Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
1098 The C<Alias> module implements localization of the basic types within the
1099 I<caller's scope>. People who are interested in how to localize things in
1100 the containing scope should take a look there too.
1104 =head2 XSUBs and the Argument Stack
1106 The XSUB mechanism is a simple way for Perl programs to access C subroutines.
1107 An XSUB routine will have a stack that contains the arguments from the Perl
1108 program, and a way to map from the Perl data structures to a C equivalent.
1110 The stack arguments are accessible through the C<ST(n)> macro, which returns
1111 the C<n>'th stack argument. Argument 0 is the first argument passed in the
1112 Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
1115 Most of the time, output from the C routine can be handled through use of
1116 the RETVAL and OUTPUT directives. However, there are some cases where the
1117 argument stack is not already long enough to handle all the return values.
1118 An example is the POSIX tzname() call, which takes no arguments, but returns
1119 two, the local time zone's standard and summer time abbreviations.
1121 To handle this situation, the PPCODE directive is used and the stack is
1122 extended using the macro:
1126 where C<SP> is the macro that represents the local copy of the stack pointer,
1127 and C<num> is the number of elements the stack should be extended by.
1129 Now that there is room on the stack, values can be pushed on it using the
1130 macros to push IVs, doubles, strings, and SV pointers respectively:
1137 And now the Perl program calling C<tzname>, the two values will be assigned
1140 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
1142 An alternate (and possibly simpler) method to pushing values on the stack is
1150 These macros automatically adjust the stack for you, if needed. Thus, you
1151 do not need to call C<EXTEND> to extend the stack.
1153 For more information, consult L<perlxs> and L<perlxstut>.
1155 =head2 Calling Perl Routines from within C Programs
1157 There are four routines that can be used to call a Perl subroutine from
1158 within a C program. These four are:
1160 I32 perl_call_sv(SV*, I32);
1161 I32 perl_call_pv(char*, I32);
1162 I32 perl_call_method(char*, I32);
1163 I32 perl_call_argv(char*, I32, register char**);
1165 The routine most often used is C<perl_call_sv>. The C<SV*> argument
1166 contains either the name of the Perl subroutine to be called, or a
1167 reference to the subroutine. The second argument consists of flags
1168 that control the context in which the subroutine is called, whether
1169 or not the subroutine is being passed arguments, how errors should be
1170 trapped, and how to treat return values.
1172 All four routines return the number of arguments that the subroutine returned
1175 When using any of these routines (except C<perl_call_argv>), the programmer
1176 must manipulate the Perl stack. These include the following macros and
1191 For a detailed description of calling conventions from C to Perl,
1192 consult L<perlcall>.
1194 =head2 Memory Allocation
1196 It is suggested that you use the version of malloc that is distributed
1197 with Perl. It keeps pools of various sizes of unallocated memory in
1198 order to satisfy allocation requests more quickly. However, on some
1199 platforms, it may cause spurious malloc or free errors.
1201 New(x, pointer, number, type);
1202 Newc(x, pointer, number, type, cast);
1203 Newz(x, pointer, number, type);
1205 These three macros are used to initially allocate memory.
1207 The first argument C<x> was a "magic cookie" that was used to keep track
1208 of who called the macro, to help when debugging memory problems. However,
1209 the current code makes no use of this feature (most Perl developers now
1210 use run-time memory checkers), so this argument can be any number.
1212 The second argument C<pointer> should be the name of a variable that will
1213 point to the newly allocated memory.
1215 The third and fourth arguments C<number> and C<type> specify how many of
1216 the specified type of data structure should be allocated. The argument
1217 C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
1218 should be used if the C<pointer> argument is different from the C<type>
1221 Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
1222 to zero out all the newly allocated memory.
1224 Renew(pointer, number, type);
1225 Renewc(pointer, number, type, cast);
1228 These three macros are used to change a memory buffer size or to free a
1229 piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1230 match those of C<New> and C<Newc> with the exception of not needing the
1231 "magic cookie" argument.
1233 Move(source, dest, number, type);
1234 Copy(source, dest, number, type);
1235 Zero(dest, number, type);
1237 These three macros are used to move, copy, or zero out previously allocated
1238 memory. The C<source> and C<dest> arguments point to the source and
1239 destination starting points. Perl will move, copy, or zero out C<number>
1240 instances of the size of the C<type> data structure (using the C<sizeof>
1245 The most recent development releases of Perl has been experimenting with
1246 removing Perl's dependency on the "normal" standard I/O suite and allowing
1247 other stdio implementations to be used. This involves creating a new
1248 abstraction layer that then calls whichever implementation of stdio Perl
1249 was compiled with. All XSUBs should now use the functions in the PerlIO
1250 abstraction layer and not make any assumptions about what kind of stdio
1253 For a complete description of the PerlIO abstraction, consult L<perlapio>.
1255 =head2 Putting a C value on Perl stack
1257 A lot of opcodes (this is an elementary operation in the internal perl
1258 stack machine) put an SV* on the stack. However, as an optimization
1259 the corresponding SV is (usually) not recreated each time. The opcodes
1260 reuse specially assigned SVs (I<target>s) which are (as a corollary)
1261 not constantly freed/created.
1263 Each of the targets is created only once (but see
1264 L<Scratchpads and recursion> below), and when an opcode needs to put
1265 an integer, a double, or a string on stack, it just sets the
1266 corresponding parts of its I<target> and puts the I<target> on stack.
1268 The macro to put this target on stack is C<PUSHTARG>, and it is
1269 directly used in some opcodes, as well as indirectly in zillions of
1270 others, which use it via C<(X)PUSH[pni]>.
1274 The question remains on when the SVs which are I<target>s for opcodes
1275 are created. The answer is that they are created when the current unit --
1276 a subroutine or a file (for opcodes for statements outside of
1277 subroutines) -- is compiled. During this time a special anonymous Perl
1278 array is created, which is called a scratchpad for the current
1281 A scratchpad keeps SVs which are lexicals for the current unit and are
1282 targets for opcodes. One can deduce that an SV lives on a scratchpad
1283 by looking on its flags: lexicals have C<SVs_PADMY> set, and
1284 I<target>s have C<SVs_PADTMP> set.
1286 The correspondence between OPs and I<target>s is not 1-to-1. Different
1287 OPs in the compile tree of the unit can use the same target, if this
1288 would not conflict with the expected life of the temporary.
1290 =head2 Scratchpads and recursion
1292 In fact it is not 100% true that a compiled unit contains a pointer to
1293 the scratchpad AV. In fact it contains a pointer to an AV of
1294 (initially) one element, and this element is the scratchpad AV. Why do
1295 we need an extra level of indirection?
1297 The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1298 these can create several execution pointers going into the same
1299 subroutine. For the subroutine-child not write over the temporaries
1300 for the subroutine-parent (lifespan of which covers the call to the
1301 child), the parent and the child should have different
1302 scratchpads. (I<And> the lexicals should be separate anyway!)
1304 So each subroutine is born with an array of scratchpads (of length 1).
1305 On each entry to the subroutine it is checked that the current
1306 depth of the recursion is not more than the length of this array, and
1307 if it is, new scratchpad is created and pushed into the array.
1309 The I<target>s on this scratchpad are C<undef>s, but they are already
1310 marked with correct flags.
1312 =head1 Compiled code
1316 Here we describe the internal form your code is converted to by
1317 Perl. Start with a simple example:
1321 This is converted to a tree similar to this one:
1329 (but slightly more complicated). This tree reflects the way Perl
1330 parsed your code, but has nothing to do with the execution order.
1331 There is an additional "thread" going through the nodes of the tree
1332 which shows the order of execution of the nodes. In our simplified
1333 example above it looks like:
1335 $b ---> $c ---> + ---> $a ---> assign-to
1337 But with the actual compile tree for C<$a = $b + $c> it is different:
1338 some nodes I<optimized away>. As a corollary, though the actual tree
1339 contains more nodes than our simplified example, the execution order
1340 is the same as in our example.
1342 =head2 Examining the tree
1344 If you have your perl compiled for debugging (usually done with C<-D
1345 optimize=-g> on C<Configure> command line), you may examine the
1346 compiled tree by specifying C<-Dx> on the Perl command line. The
1347 output takes several lines per node, and for C<$b+$c> it looks like
1352 FLAGS = (SCALAR,KIDS)
1354 TYPE = null ===> (4)
1356 FLAGS = (SCALAR,KIDS)
1358 3 TYPE = gvsv ===> 4
1364 TYPE = null ===> (5)
1366 FLAGS = (SCALAR,KIDS)
1368 4 TYPE = gvsv ===> 5
1374 This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1375 not optimized away (one per number in the left column). The immediate
1376 children of the given node correspond to C<{}> pairs on the same level
1377 of indentation, thus this listing corresponds to the tree:
1385 The execution order is indicated by C<===E<gt>> marks, thus it is C<3
1386 4 5 6> (node C<6> is not included into above listing), i.e.,
1387 C<gvsv gvsv add whatever>.
1389 =head2 Compile pass 1: check routines
1391 The tree is created by the I<pseudo-compiler> while yacc code feeds it
1392 the constructions it recognizes. Since yacc works bottom-up, so does
1393 the first pass of perl compilation.
1395 What makes this pass interesting for perl developers is that some
1396 optimization may be performed on this pass. This is optimization by
1397 so-called I<check routines>. The correspondence between node names
1398 and corresponding check routines is described in F<opcode.pl> (do not
1399 forget to run C<make regen_headers> if you modify this file).
1401 A check routine is called when the node is fully constructed except
1402 for the execution-order thread. Since at this time there are no
1403 back-links to the currently constructed node, one can do most any
1404 operation to the top-level node, including freeing it and/or creating
1405 new nodes above/below it.
1407 The check routine returns the node which should be inserted into the
1408 tree (if the top-level node was not modified, check routine returns
1411 By convention, check routines have names C<ck_*>. They are usually
1412 called from C<new*OP> subroutines (or C<convert>) (which in turn are
1413 called from F<perly.y>).
1415 =head2 Compile pass 1a: constant folding
1417 Immediately after the check routine is called the returned node is
1418 checked for being compile-time executable. If it is (the value is
1419 judged to be constant) it is immediately executed, and a I<constant>
1420 node with the "return value" of the corresponding subtree is
1421 substituted instead. The subtree is deleted.
1423 If constant folding was not performed, the execution-order thread is
1426 =head2 Compile pass 2: context propagation
1428 When a context for a part of compile tree is known, it is propagated
1429 down through the tree. At this time the context can have 5 values
1430 (instead of 2 for runtime context): void, boolean, scalar, list, and
1431 lvalue. In contrast with the pass 1 this pass is processed from top
1432 to bottom: a node's context determines the context for its children.
1434 Additional context-dependent optimizations are performed at this time.
1435 Since at this moment the compile tree contains back-references (via
1436 "thread" pointers), nodes cannot be free()d now. To allow
1437 optimized-away nodes at this stage, such nodes are null()ified instead
1438 of free()ing (i.e. their type is changed to OP_NULL).
1440 =head2 Compile pass 3: peephole optimization
1442 After the compile tree for a subroutine (or for an C<eval> or a file)
1443 is created, an additional pass over the code is performed. This pass
1444 is neither top-down or bottom-up, but in the execution order (with
1445 additional complications for conditionals). These optimizations are
1446 done in the subroutine peep(). Optimizations performed at this stage
1447 are subject to the same restrictions as in the pass 2.
1451 This is a listing of functions, macros, flags, and variables that may be
1452 useful to extension writers or that may be found while reading other
1454 The sort order of the listing is case insensitive, with any
1455 occurrences of '_' ignored for the the purpose of sorting.
1461 Clears an array, making it empty. Does not free the memory used by the
1464 void av_clear (AV* ar)
1468 Pre-extend an array. The C<key> is the index to which the array should be
1471 void av_extend (AV* ar, I32 key)
1475 Returns the SV at the specified index in the array. The C<key> is the
1476 index. If C<lval> is set then the fetch will be part of a store. Check
1477 that the return value is non-null before dereferencing it to a C<SV*>.
1479 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1480 information on how to use this function on tied arrays.
1482 SV** av_fetch (AV* ar, I32 key, I32 lval)
1486 Same as C<av_len()>. Deprecated, use C<av_len()> instead.
1490 Returns the highest index in the array. Returns -1 if the array is empty.
1496 Creates a new AV and populates it with a list of SVs. The SVs are copied
1497 into the array, so they may be freed after the call to av_make. The new AV
1498 will have a reference count of 1.
1500 AV* av_make (I32 size, SV** svp)
1504 Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1511 Pushes an SV onto the end of the array. The array will grow automatically
1512 to accommodate the addition.
1514 void av_push (AV* ar, SV* val)
1518 Shifts an SV off the beginning of the array.
1520 SV* av_shift (AV* ar)
1524 Stores an SV in an array. The array index is specified as C<key>. The
1525 return value will be NULL if the operation failed or if the value did not
1526 need to be actually stored within the array (as in the case of tied arrays).
1527 Otherwise it can be dereferenced to get the original C<SV*>. Note that the
1528 caller is responsible for suitably incrementing the reference count of C<val>
1529 before the call, and decrementing it if the function returned NULL.
1531 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1532 information on how to use this function on tied arrays.
1534 SV** av_store (AV* ar, I32 key, SV* val)
1538 Undefines the array. Frees the memory used by the array itself.
1540 void av_undef (AV* ar)
1544 Unshift the given number of C<undef> values onto the beginning of the
1545 array. The array will grow automatically to accommodate the addition.
1546 You must then use C<av_store> to assign values to these new elements.
1548 void av_unshift (AV* ar, I32 num)
1552 Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
1553 constructor. This is always a C<char*>. See C<THIS> and
1554 L<perlxs/"Using XS With C++">.
1558 The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1559 source, C<d> is the destination, C<n> is the number of items, and C<t> is
1560 the type. May fail on overlapping copies. See also C<Move>.
1562 void Copy( s, d, n, t )
1566 This is the XSUB-writer's interface to Perl's C<die> function. Use this
1567 function the same way you use the C C<printf> function. See C<warn>.
1571 Returns the stash of the CV.
1573 HV* CvSTASH( SV* sv )
1577 When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1578 boolean which indicates whether subs are being single-stepped.
1579 Single-stepping is automatically turned on after every step. This is the C
1580 variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
1584 When Perl is run in debugging mode, with the B<-d> switch, this GV contains
1585 the SV which holds the name of the sub being debugged. This is the C
1586 variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
1587 The sub name can be found by
1589 SvPV( GvSV( DBsub ), na )
1593 Trace variable used when Perl is run in debugging mode, with the B<-d>
1594 switch. This is the C variable which corresponds to Perl's $DB::trace
1595 variable. See C<DBsingle>.
1599 Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1604 Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1608 The C variable which corresponds to Perl's $^W warning variable.
1612 Declares a local copy of perl's stack pointer for the XSUB, available via
1613 the C<SP> macro. See C<SP>.
1617 Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1618 usually handled automatically by C<xsubpp>. Declares the C<items> variable
1619 to indicate the number of items on the stack.
1623 Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1624 handled automatically by C<xsubpp>.
1628 Switches filehandle to binmode. C<iotype> is what C<IoTYPE(io)> would
1631 do_binmode(fp, iotype, TRUE);
1635 Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1641 Used to extend the argument stack for an XSUB's return values.
1647 Analyses the string in order to make fast searches on it using fbm_instr() --
1648 the Boyer-Moore algorithm.
1650 void fbm_compile(SV* sv, U32 flags)
1654 Returns the location of the SV in the string delimited by C<str> and
1655 C<strend>. It returns C<Nullch> if the string can't be found. The
1656 C<sv> does not have to be fbm_compiled, but the search will not be as
1659 char* fbm_instr(char *str, char *strend, SV *sv, U32 flags)
1663 Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1670 Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
1674 Indicates that arguments returned from a callback should be discarded. See
1679 Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1683 A backward-compatible version of C<GIMME_V> which can only return
1684 C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
1688 The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
1689 C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
1690 context, respectively.
1694 Indicates that no arguments are being sent to a callback. See L<perlcall>.
1698 Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
1702 Returns the glob with the given C<name> and a defined subroutine or
1703 C<NULL>. The glob lives in the given C<stash>, or in the stashes
1704 accessible via @ISA and @UNIVERSAL.
1706 The argument C<level> should be either 0 or -1. If C<level==0>, as a
1707 side-effect creates a glob with the given C<name> in the given
1708 C<stash> which in the case of success contains an alias for the
1709 subroutine, and sets up caching info for this glob. Similarly for all
1710 the searched stashes.
1712 This function grants C<"SUPER"> token as a postfix of the stash name.
1714 The GV returned from C<gv_fetchmeth> may be a method cache entry,
1715 which is not visible to Perl code. So when calling C<perl_call_sv>,
1716 you should not use the GV directly; instead, you should use the
1717 method's CV, which can be obtained from the GV with the C<GvCV> macro.
1719 GV* gv_fetchmeth (HV* stash, char* name, STRLEN len, I32 level)
1721 =item gv_fetchmethod
1723 =item gv_fetchmethod_autoload
1725 Returns the glob which contains the subroutine to call to invoke the
1726 method on the C<stash>. In fact in the presense of autoloading this may
1727 be the glob for "AUTOLOAD". In this case the corresponding variable
1728 $AUTOLOAD is already setup.
1730 The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
1731 lookup is performed if the given method is not present: non-zero means
1732 yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
1733 C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
1734 non-zero C<autoload> parameter.
1736 These functions grant C<"SUPER"> token as a prefix of the method name.
1738 Note that if you want to keep the returned glob for a long time, you
1739 need to check for it being "AUTOLOAD", since at the later time the call
1740 may load a different subroutine due to $AUTOLOAD changing its value.
1741 Use the glob created via a side effect to do this.
1743 These functions have the same side-effects and as C<gv_fetchmeth> with
1744 C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
1745 The warning against passing the GV returned by C<gv_fetchmeth> to
1746 C<perl_call_sv> apply equally to these functions.
1748 GV* gv_fetchmethod (HV* stash, char* name)
1749 GV* gv_fetchmethod_autoload (HV* stash, char* name, I32 autoload)
1753 Used to indicate void context. See C<GIMME_V> and L<perlcall>.
1757 Returns a pointer to the stash for a specified package. If C<create> is set
1758 then the package will be created if it does not already exist. If C<create>
1759 is not set and the package does not exist then NULL is returned.
1761 HV* gv_stashpv (char* name, I32 create)
1765 Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1767 HV* gv_stashsv (SV* sv, I32 create)
1771 Return the SV from the GV.
1775 This flag, used in the length slot of hash entries and magic
1776 structures, specifies the structure contains a C<SV*> pointer where a
1777 C<char*> pointer is to be expected. (For information only--not to be used).
1781 Returns the computed hash stored in the hash entry.
1787 Returns the actual pointer stored in the key slot of the hash entry.
1788 The pointer may be either C<char*> or C<SV*>, depending on the value of
1789 C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
1790 are usually preferable for finding the value of a key.
1796 If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
1797 holds an C<SV*> key. Otherwise, holds the actual length of the key.
1798 Can be assigned to. The C<HePV()> macro is usually preferable for finding
1805 Returns the key slot of the hash entry as a C<char*> value, doing any
1806 necessary dereferencing of possibly C<SV*> keys. The length of
1807 the string is placed in C<len> (this is a macro, so do I<not> use
1808 C<&len>). If you do not care about what the length of the key is,
1809 you may use the global variable C<na>. Remember though, that hash
1810 keys in perl are free to contain embedded nulls, so using C<strlen()>
1811 or similar is not a good way to find the length of hash keys.
1812 This is very similar to the C<SvPV()> macro described elsewhere in
1815 char* HePV(HE* he, STRLEN len)
1819 Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
1820 does not contain an C<SV*> key.
1826 Returns the key as an C<SV*>. Will create and return a temporary
1827 mortal C<SV*> if the hash entry contains only a C<char*> key.
1829 HeSVKEY_force(HE* he)
1833 Sets the key to a given C<SV*>, taking care to set the appropriate flags
1834 to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
1836 HeSVKEY_set(HE* he, SV* sv)
1840 Returns the value slot (type C<SV*>) stored in the hash entry.
1846 Clears a hash, making it empty.
1848 void hv_clear (HV* tb)
1850 =item hv_delayfree_ent
1852 Releases a hash entry, such as while iterating though the hash, but
1853 delays actual freeing of key and value until the end of the current
1854 statement (or thereabouts) with C<sv_2mortal>. See C<hv_iternext>
1857 void hv_delayfree_ent (HV* hv, HE* entry)
1861 Deletes a key/value pair in the hash. The value SV is removed from the hash
1862 and returned to the caller. The C<klen> is the length of the key. The
1863 C<flags> value will normally be zero; if set to G_DISCARD then NULL will be
1866 SV* hv_delete (HV* tb, char* key, U32 klen, I32 flags)
1870 Deletes a key/value pair in the hash. The value SV is removed from the hash
1871 and returned to the caller. The C<flags> value will normally be zero; if set
1872 to G_DISCARD then NULL will be returned. C<hash> can be a valid precomputed
1873 hash value, or 0 to ask for it to be computed.
1875 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash)
1879 Returns a boolean indicating whether the specified hash key exists. The
1880 C<klen> is the length of the key.
1882 bool hv_exists (HV* tb, char* key, U32 klen)
1886 Returns a boolean indicating whether the specified hash key exists. C<hash>
1887 can be a valid precomputed hash value, or 0 to ask for it to be computed.
1889 bool hv_exists_ent (HV* tb, SV* key, U32 hash)
1893 Returns the SV which corresponds to the specified key in the hash. The
1894 C<klen> is the length of the key. If C<lval> is set then the fetch will be
1895 part of a store. Check that the return value is non-null before
1896 dereferencing it to a C<SV*>.
1898 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1899 information on how to use this function on tied hashes.
1901 SV** hv_fetch (HV* tb, char* key, U32 klen, I32 lval)
1905 Returns the hash entry which corresponds to the specified key in the hash.
1906 C<hash> must be a valid precomputed hash number for the given C<key>, or
1907 0 if you want the function to compute it. IF C<lval> is set then the
1908 fetch will be part of a store. Make sure the return value is non-null
1909 before accessing it. The return value when C<tb> is a tied hash
1910 is a pointer to a static location, so be sure to make a copy of the
1911 structure if you need to store it somewhere.
1913 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1914 information on how to use this function on tied hashes.
1916 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash)
1920 Releases a hash entry, such as while iterating though the hash. See
1921 C<hv_iternext> and C<hv_delayfree_ent>.
1923 void hv_free_ent (HV* hv, HE* entry)
1927 Prepares a starting point to traverse a hash table.
1929 I32 hv_iterinit (HV* tb)
1931 Returns the number of keys in the hash (i.e. the same as C<HvKEYS(tb)>).
1932 The return value is currently only meaningful for hashes without tie
1935 NOTE: Before version 5.004_65, C<hv_iterinit> used to return the number
1936 of hash buckets that happen to be in use. If you still need that
1937 esoteric value, you can get it through the macro C<HvFILL(tb)>.
1941 Returns the key from the current position of the hash iterator. See
1944 char* hv_iterkey (HE* entry, I32* retlen)
1948 Returns the key as an C<SV*> from the current position of the hash
1949 iterator. The return value will always be a mortal copy of the
1950 key. Also see C<hv_iterinit>.
1952 SV* hv_iterkeysv (HE* entry)
1956 Returns entries from a hash iterator. See C<hv_iterinit>.
1958 HE* hv_iternext (HV* tb)
1962 Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1965 SV* hv_iternextsv (HV* hv, char** key, I32* retlen)
1969 Returns the value from the current position of the hash iterator. See
1972 SV* hv_iterval (HV* tb, HE* entry)
1976 Adds magic to a hash. See C<sv_magic>.
1978 void hv_magic (HV* hv, GV* gv, int how)
1982 Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1984 char* HvNAME (HV* stash)
1988 Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
1989 the length of the key. The C<hash> parameter is the precomputed hash
1990 value; if it is zero then Perl will compute it. The return value will be
1991 NULL if the operation failed or if the value did not need to be actually
1992 stored within the hash (as in the case of tied hashes). Otherwise it can
1993 be dereferenced to get the original C<SV*>. Note that the caller is
1994 responsible for suitably incrementing the reference count of C<val>
1995 before the call, and decrementing it if the function returned NULL.
1997 See L<Understanding the Magic of Tied Hashes and Arrays> for more
1998 information on how to use this function on tied hashes.
2000 SV** hv_store (HV* tb, char* key, U32 klen, SV* val, U32 hash)
2004 Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
2005 parameter is the precomputed hash value; if it is zero then Perl will
2006 compute it. The return value is the new hash entry so created. It will be
2007 NULL if the operation failed or if the value did not need to be actually
2008 stored within the hash (as in the case of tied hashes). Otherwise the
2009 contents of the return value can be accessed using the C<He???> macros
2010 described here. Note that the caller is responsible for suitably
2011 incrementing the reference count of C<val> before the call, and decrementing
2012 it if the function returned NULL.
2014 See L<Understanding the Magic of Tied Hashes and Arrays> for more
2015 information on how to use this function on tied hashes.
2017 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash)
2023 void hv_undef (HV* tb)
2027 Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
2030 int isALNUM (char c)
2034 Returns a boolean indicating whether the C C<char> is an ascii alphabetic
2037 int isALPHA (char c)
2041 Returns a boolean indicating whether the C C<char> is an ascii digit.
2043 int isDIGIT (char c)
2047 Returns a boolean indicating whether the C C<char> is a lowercase character.
2049 int isLOWER (char c)
2053 Returns a boolean indicating whether the C C<char> is whitespace.
2055 int isSPACE (char c)
2059 Returns a boolean indicating whether the C C<char> is an uppercase character.
2061 int isUPPER (char c)
2065 Variable which is setup by C<xsubpp> to indicate the number of items on the
2066 stack. See L<perlxs/"Variable-length Parameter Lists">.
2070 Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
2071 was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
2075 Closing bracket on a callback. See C<ENTER> and L<perlcall>.
2079 =item looks_like_number
2081 Test if an the content of an SV looks like a number (or is a number).
2083 int looks_like_number(SV*)
2088 Stack marker variable for the XSUB. See C<dMARK>.
2092 Clear something magical that the SV represents. See C<sv_magic>.
2094 int mg_clear (SV* sv)
2098 Copies the magic from one SV to another. See C<sv_magic>.
2100 int mg_copy (SV *, SV *, char *, STRLEN)
2104 Finds the magic pointer for type matching the SV. See C<sv_magic>.
2106 MAGIC* mg_find (SV* sv, int type)
2110 Free any magic storage used by the SV. See C<sv_magic>.
2112 int mg_free (SV* sv)
2116 Do magic after a value is retrieved from the SV. See C<sv_magic>.
2122 Report on the SV's length. See C<sv_magic>.
2128 Turns on the magical status of an SV. See C<sv_magic>.
2130 void mg_magical (SV* sv)
2134 Do magic after a value is assigned to the SV. See C<sv_magic>.
2140 The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
2141 source, C<d> is the destination, C<n> is the number of items, and C<t> is
2142 the type. Can do overlapping moves. See also C<Copy>.
2144 void Move( s, d, n, t )
2148 A variable which may be used with C<SvPV> to tell Perl to calculate the
2153 The XSUB-writer's interface to the C C<malloc> function.
2155 void* New( x, void *ptr, int size, type )
2159 Creates a new AV. The reference count is set to 1.
2165 The XSUB-writer's interface to the C C<malloc> function, with cast.
2167 void* Newc( x, void *ptr, int size, type, cast )
2171 Creates a constant sub equivalent to Perl C<sub FOO () { 123 }>
2172 which is eligible for inlining at compile-time.
2174 void newCONSTSUB(HV* stash, char* name, SV* sv)
2178 Creates a new HV. The reference count is set to 1.
2184 Creates an RV wrapper for an SV. The reference count for the original SV is
2187 SV* newRV_inc (SV* ref)
2189 For historical reasons, "newRV" is a synonym for "newRV_inc".
2193 Creates an RV wrapper for an SV. The reference count for the original
2194 SV is B<not> incremented.
2196 SV* newRV_noinc (SV* ref)
2200 Creates a new SV. A non-zero C<len> parameter indicates the number of
2201 bytes of preallocated string space the SV should have. An extra byte
2202 for a tailing NUL is also reserved. (SvPOK is not set for the SV even
2203 if string space is allocated.) The reference count for the new SV is
2204 set to 1. C<id> is an integer id between 0 and 1299 (used to identify
2207 SV* NEWSV (int id, STRLEN len)
2211 Creates a new SV and copies an integer into it. The reference count for the
2218 Creates a new SV and copies a double into it. The reference count for the
2225 Creates a new SV and copies a string into it. The reference count for the
2226 SV is set to 1. If C<len> is zero then Perl will compute the length.
2228 SV* newSVpv (char* s, STRLEN len)
2232 Creates a new SV an initialize it with the string formatted like
2235 SV* newSVpvf(const char* pat, ...);
2239 Creates a new SV and copies a string into it. The reference count for the
2240 SV is set to 1. If C<len> is zero then Perl will create a zero length
2243 SV* newSVpvn (char* s, STRLEN len)
2247 Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
2248 it will be upgraded to one. If C<classname> is non-null then the new SV will
2249 be blessed in the specified package. The new SV is returned and its
2250 reference count is 1.
2252 SV* newSVrv (SV* rv, char* classname)
2256 Creates a new SV which is an exact duplicate of the original SV.
2258 SV* newSVsv (SV* old)
2262 Used by C<xsubpp> to hook up XSUBs as Perl subs.
2266 Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
2271 The XSUB-writer's interface to the C C<malloc> function. The allocated
2272 memory is zeroed with C<memzero>.
2274 void* Newz( x, void *ptr, int size, type )
2282 Null character pointer.
2298 The original stack mark for the XSUB. See C<dORIGMARK>.
2302 Allocates a new Perl interpreter. See L<perlembed>.
2304 =item perl_call_argv
2306 Performs a callback to the specified Perl sub. See L<perlcall>.
2308 I32 perl_call_argv (char* subname, I32 flags, char** argv)
2310 =item perl_call_method
2312 Performs a callback to the specified Perl method. The blessed object must
2313 be on the stack. See L<perlcall>.
2315 I32 perl_call_method (char* methname, I32 flags)
2319 Performs a callback to the specified Perl sub. See L<perlcall>.
2321 I32 perl_call_pv (char* subname, I32 flags)
2325 Performs a callback to the Perl sub whose name is in the SV. See
2328 I32 perl_call_sv (SV* sv, I32 flags)
2330 =item perl_construct
2332 Initializes a new Perl interpreter. See L<perlembed>.
2336 Shuts down a Perl interpreter. See L<perlembed>.
2340 Tells Perl to C<eval> the string in the SV.
2342 I32 perl_eval_sv (SV* sv, I32 flags)
2346 Tells Perl to C<eval> the given string and return an SV* result.
2348 SV* perl_eval_pv (char* p, I32 croak_on_error)
2352 Releases a Perl interpreter. See L<perlembed>.
2356 Returns the AV of the specified Perl array. If C<create> is set and the
2357 Perl variable does not exist then it will be created. If C<create> is not
2358 set and the variable does not exist then NULL is returned.
2360 AV* perl_get_av (char* name, I32 create)
2364 Returns the CV of the specified Perl sub. If C<create> is set and the Perl
2365 variable does not exist then it will be created. If C<create> is not
2366 set and the variable does not exist then NULL is returned.
2368 CV* perl_get_cv (char* name, I32 create)
2372 Returns the HV of the specified Perl hash. If C<create> is set and the Perl
2373 variable does not exist then it will be created. If C<create> is not
2374 set and the variable does not exist then NULL is returned.
2376 HV* perl_get_hv (char* name, I32 create)
2380 Returns the SV of the specified Perl scalar. If C<create> is set and the
2381 Perl variable does not exist then it will be created. If C<create> is not
2382 set and the variable does not exist then NULL is returned.
2384 SV* perl_get_sv (char* name, I32 create)
2388 Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
2390 =item perl_require_pv
2392 Tells Perl to C<require> a module.
2394 void perl_require_pv (char* pv)
2398 Tells a Perl interpreter to run. See L<perlembed>.
2402 Pops an integer off the stack.
2408 Pops a long off the stack.
2414 Pops a string off the stack.
2420 Pops a double off the stack.
2426 Pops an SV off the stack.
2432 Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2438 Push an integer onto the stack. The stack must have room for this element.
2439 Handles 'set' magic. See C<XPUSHi>.
2445 Push a double onto the stack. The stack must have room for this element.
2446 Handles 'set' magic. See C<XPUSHn>.
2448 void PUSHn(double d)
2452 Push a string onto the stack. The stack must have room for this element.
2453 The C<len> indicates the length of the string. Handles 'set' magic. See
2456 void PUSHp(char *c, int len )
2460 Push an SV onto the stack. The stack must have room for this element. Does
2461 not handle 'set' magic. See C<XPUSHs>.
2467 Push an unsigned integer onto the stack. The stack must have room for
2468 this element. See C<XPUSHu>.
2470 void PUSHu(unsigned int d)
2475 Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2476 See C<PUSHMARK> and L<perlcall> for other uses.
2482 The XSUB-writer's interface to the C C<realloc> function.
2484 void* Renew( void *ptr, int size, type )
2488 The XSUB-writer's interface to the C C<realloc> function, with cast.
2490 void* Renewc( void *ptr, int size, type, cast )
2494 Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
2495 This is always the proper type for the XSUB.
2496 See L<perlxs/"The RETVAL Variable">.
2500 The XSUB-writer's interface to the C C<free> function.
2504 The XSUB-writer's interface to the C C<malloc> function.
2508 The XSUB-writer's interface to the C C<realloc> function.
2512 Copy a string to a safe spot. This does not use an SV.
2514 char* savepv (char* sv)
2518 Copy a string to a safe spot. The C<len> indicates number of bytes to
2519 copy. This does not use an SV.
2521 char* savepvn (char* sv, I32 len)
2525 Opening bracket for temporaries on a callback. See C<FREETMPS> and
2532 Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2537 Refetch the stack pointer. Used after a callback. See L<perlcall>.
2543 Used to access elements on the XSUB's stack.
2549 Test two strings to see if they are equal. Returns true or false.
2551 int strEQ( char *s1, char *s2 )
2555 Test two strings to see if the first, C<s1>, is greater than or equal to the
2556 second, C<s2>. Returns true or false.
2558 int strGE( char *s1, char *s2 )
2562 Test two strings to see if the first, C<s1>, is greater than the second,
2563 C<s2>. Returns true or false.
2565 int strGT( char *s1, char *s2 )
2569 Test two strings to see if the first, C<s1>, is less than or equal to the
2570 second, C<s2>. Returns true or false.
2572 int strLE( char *s1, char *s2 )
2576 Test two strings to see if the first, C<s1>, is less than the second,
2577 C<s2>. Returns true or false.
2579 int strLT( char *s1, char *s2 )
2583 Test two strings to see if they are different. Returns true or false.
2585 int strNE( char *s1, char *s2 )
2589 Test two strings to see if they are equal. The C<len> parameter indicates
2590 the number of bytes to compare. Returns true or false.
2592 int strnEQ( char *s1, char *s2 )
2596 Test two strings to see if they are different. The C<len> parameter
2597 indicates the number of bytes to compare. Returns true or false.
2599 int strnNE( char *s1, char *s2, int len )
2603 Marks an SV as mortal. The SV will be destroyed when the current context
2606 SV* sv_2mortal (SV* sv)
2610 Blesses an SV into a specified package. The SV must be an RV. The package
2611 must be designated by its stash (see C<gv_stashpv()>). The reference count
2612 of the SV is unaffected.
2614 SV* sv_bless (SV* sv, HV* stash)
2618 Concatenates the string onto the end of the string which is in the SV.
2619 Handles 'get' magic, but not 'set' magic. See C<sv_catpv_mg>.
2621 void sv_catpv (SV* sv, char* ptr)
2625 Like C<sv_catpv>, but also handles 'set' magic.
2627 void sv_catpvn (SV* sv, char* ptr)
2631 Concatenates the string onto the end of the string which is in the SV. The
2632 C<len> indicates number of bytes to copy. Handles 'get' magic, but not
2633 'set' magic. See C<sv_catpvn_mg>.
2635 void sv_catpvn (SV* sv, char* ptr, STRLEN len)
2639 Like C<sv_catpvn>, but also handles 'set' magic.
2641 void sv_catpvn_mg (SV* sv, char* ptr, STRLEN len)
2645 Processes its arguments like C<sprintf> and appends the formatted output
2646 to an SV. Handles 'get' magic, but not 'set' magic. C<SvSETMAGIC()> must
2647 typically be called after calling this function to handle 'set' magic.
2649 void sv_catpvf (SV* sv, const char* pat, ...)
2653 Like C<sv_catpvf>, but also handles 'set' magic.
2655 void sv_catpvf_mg (SV* sv, const char* pat, ...)
2659 Concatenates the string from SV C<ssv> onto the end of the string in SV
2660 C<dsv>. Handles 'get' magic, but not 'set' magic. See C<sv_catsv_mg>.
2662 void sv_catsv (SV* dsv, SV* ssv)
2666 Like C<sv_catsv>, but also handles 'set' magic.
2668 void sv_catsv_mg (SV* dsv, SV* ssv)
2672 Efficient removal of characters from the beginning of the string
2673 buffer. SvPOK(sv) must be true and the C<ptr> must be a pointer to
2674 somewhere inside the string buffer. The C<ptr> becomes the first
2675 character of the adjusted string.
2677 void sv_chop(SV* sv, char *ptr)
2682 Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2683 string in C<sv1> is less than, equal to, or greater than the string in
2686 I32 sv_cmp (SV* sv1, SV* sv2)
2690 Returns the length of the string which is in the SV. See C<SvLEN>.
2696 Set the length of the string which is in the SV. See C<SvCUR>.
2698 void SvCUR_set (SV* sv, int val )
2702 Auto-decrement of the value in the SV.
2704 void sv_dec (SV* sv)
2706 =item sv_derived_from
2708 Returns a boolean indicating whether the SV is a subclass of the
2711 int sv_derived_from(SV* sv, char* class)
2713 =item sv_derived_from
2715 Returns a boolean indicating whether the SV is derived from the specified
2716 class. This is the function that implements C<UNIVERSAL::isa>. It works
2717 for class names as well as for objects.
2719 bool sv_derived_from _((SV* sv, char* name));
2723 Returns a pointer to the last character in the string which is in the SV.
2724 See C<SvCUR>. Access the character as
2730 Returns a boolean indicating whether the strings in the two SVs are
2733 I32 sv_eq (SV* sv1, SV* sv2)
2737 Invokes C<mg_get> on an SV if it has 'get' magic. This macro evaluates
2738 its argument more than once.
2740 void SvGETMAGIC( SV *sv )
2744 Expands the character buffer in the SV so that it has room for the
2745 indicated number of bytes (remember to reserve space for an extra
2746 trailing NUL character). Calls C<sv_grow> to perform the expansion if
2747 necessary. Returns a pointer to the character buffer.
2749 char* SvGROW( SV* sv, int len )
2753 Expands the character buffer in the SV. This will use C<sv_unref> and will
2754 upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2759 Auto-increment of the value in the SV.
2761 void sv_inc (SV* sv)
2765 Inserts a string at the specified offset/length within the SV.
2766 Similar to the Perl substr() function.
2768 void sv_insert(SV *sv, STRLEN offset, STRLEN len,
2769 char *str, STRLEN strlen)
2773 Returns a boolean indicating whether the SV contains an integer.
2779 Unsets the IV status of an SV.
2781 void SvIOK_off (SV* sv)
2785 Tells an SV that it is an integer.
2787 void SvIOK_on (SV* sv)
2791 Tells an SV that it is an integer and disables all other OK bits.
2793 void SvIOK_only (SV* sv)
2797 Returns a boolean indicating whether the SV contains an integer. Checks the
2798 B<private> setting. Use C<SvIOK>.
2804 Returns a boolean indicating whether the SV is blessed into the specified
2805 class. This does not check for subtypes; use C<sv_derived_from> to verify
2806 an inheritance relationship.
2808 int sv_isa (SV* sv, char* name)
2812 Returns a boolean indicating whether the SV is an RV pointing to a blessed
2813 object. If the SV is not an RV, or if the object is not blessed, then this
2816 int sv_isobject (SV* sv)
2820 Returns the integer which is in the SV.
2826 Returns the integer which is stored in the SV.
2832 Returns the size of the string buffer in the SV. See C<SvCUR>.
2838 Returns the length of the string in the SV. Use C<SvCUR>.
2840 STRLEN sv_len (SV* sv)
2844 Adds magic to an SV.
2846 void sv_magic (SV* sv, SV* obj, int how, char* name, I32 namlen)
2850 Creates a new SV which is a copy of the original SV. The new SV is marked
2853 SV* sv_mortalcopy (SV* oldsv)
2857 Creates a new SV which is mortal. The reference count of the SV is set to 1.
2859 SV* sv_newmortal (void)
2863 Returns a boolean indicating whether the SV contains a number, integer or
2870 Unsets the NV/IV status of an SV.
2872 void SvNIOK_off (SV* sv)
2876 Returns a boolean indicating whether the SV contains a number, integer or
2877 double. Checks the B<private> setting. Use C<SvNIOK>.
2879 int SvNIOKp (SV* SV)
2883 This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2887 Returns a boolean indicating whether the SV contains a double.
2893 Unsets the NV status of an SV.
2895 void SvNOK_off (SV* sv)
2899 Tells an SV that it is a double.
2901 void SvNOK_on (SV* sv)
2905 Tells an SV that it is a double and disables all other OK bits.
2907 void SvNOK_only (SV* sv)
2911 Returns a boolean indicating whether the SV contains a double. Checks the
2912 B<private> setting. Use C<SvNOK>.
2918 Returns the double which is stored in the SV.
2920 double SvNV (SV* sv)
2924 Returns the double which is stored in the SV.
2926 double SvNVX (SV* sv)
2930 Returns a boolean indicating whether the value is an SV.
2936 Returns a boolean indicating whether the SvIVX is a valid offset value
2937 for the SvPVX. This hack is used internally to speed up removal of
2938 characters from the beginning of a SvPV. When SvOOK is true, then the
2939 start of the allocated string buffer is really (SvPVX - SvIVX).
2945 Returns a boolean indicating whether the SV contains a character string.
2951 Unsets the PV status of an SV.
2953 void SvPOK_off (SV* sv)
2957 Tells an SV that it is a string.
2959 void SvPOK_on (SV* sv)
2963 Tells an SV that it is a string and disables all other OK bits.
2965 void SvPOK_only (SV* sv)
2969 Returns a boolean indicating whether the SV contains a character string.
2970 Checks the B<private> setting. Use C<SvPOK>.
2976 Returns a pointer to the string in the SV, or a stringified form of the SV
2977 if the SV does not contain a string. If C<len> is C<na> then Perl will
2978 handle the length on its own. Handles 'get' magic.
2980 char* SvPV (SV* sv, int len )
2984 Like <SvPV> but will force the SV into becoming a string (SvPOK). You
2985 want force if you are going to update the SvPVX directly.
2987 char* SvPV_force(SV* sv, int len)
2992 Returns a pointer to the string in the SV. The SV must contain a string.
2994 char* SvPVX (SV* sv)
2998 Returns the value of the object's reference count.
3000 int SvREFCNT (SV* sv)
3004 Decrements the reference count of the given SV.
3006 void SvREFCNT_dec (SV* sv)
3010 Increments the reference count of the given SV.
3012 void SvREFCNT_inc (SV* sv)
3016 Tests if the SV is an RV.
3022 Unsets the RV status of an SV.
3024 void SvROK_off (SV* sv)
3028 Tells an SV that it is an RV.
3030 void SvROK_on (SV* sv)
3034 Dereferences an RV to return the SV.
3040 Invokes C<mg_set> on an SV if it has 'set' magic. This macro evaluates
3041 its argument more than once.
3043 void SvSETMAGIC( SV *sv )
3047 Copies an integer into the given SV. Does not handle 'set' magic.
3050 void sv_setiv (SV* sv, IV num)
3054 Like C<sv_setiv>, but also handles 'set' magic.
3056 void sv_setiv_mg (SV* sv, IV num)
3060 Copies a double into the given SV. Does not handle 'set' magic.
3063 void sv_setnv (SV* sv, double num)
3067 Like C<sv_setnv>, but also handles 'set' magic.
3069 void sv_setnv_mg (SV* sv, double num)
3073 Copies a string into an SV. The string must be null-terminated.
3074 Does not handle 'set' magic. See C<sv_setpv_mg>.
3076 void sv_setpv (SV* sv, char* ptr)
3080 Like C<sv_setpv>, but also handles 'set' magic.
3082 void sv_setpv_mg (SV* sv, char* ptr)
3086 Copies an integer into the given SV, also updating its string value.
3087 Does not handle 'set' magic. See C<sv_setpviv_mg>.
3089 void sv_setpviv (SV* sv, IV num)
3093 Like C<sv_setpviv>, but also handles 'set' magic.
3095 void sv_setpviv_mg (SV* sv, IV num)
3099 Copies a string into an SV. The C<len> parameter indicates the number of
3100 bytes to be copied. Does not handle 'set' magic. See C<sv_setpvn_mg>.
3102 void sv_setpvn (SV* sv, char* ptr, STRLEN len)
3106 Like C<sv_setpvn>, but also handles 'set' magic.
3108 void sv_setpvn_mg (SV* sv, char* ptr, STRLEN len)
3112 Processes its arguments like C<sprintf> and sets an SV to the formatted
3113 output. Does not handle 'set' magic. See C<sv_setpvf_mg>.
3115 void sv_setpvf (SV* sv, const char* pat, ...)
3119 Like C<sv_setpvf>, but also handles 'set' magic.
3121 void sv_setpvf_mg (SV* sv, const char* pat, ...)
3125 Copies an integer into a new SV, optionally blessing the SV. The C<rv>
3126 argument will be upgraded to an RV. That RV will be modified to point to
3127 the new SV. The C<classname> argument indicates the package for the
3128 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3129 will be returned and will have a reference count of 1.
3131 SV* sv_setref_iv (SV *rv, char *classname, IV iv)
3135 Copies a double into a new SV, optionally blessing the SV. The C<rv>
3136 argument will be upgraded to an RV. That RV will be modified to point to
3137 the new SV. The C<classname> argument indicates the package for the
3138 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3139 will be returned and will have a reference count of 1.
3141 SV* sv_setref_nv (SV *rv, char *classname, double nv)
3145 Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
3146 argument will be upgraded to an RV. That RV will be modified to point to
3147 the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
3148 into the SV. The C<classname> argument indicates the package for the
3149 blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
3150 will be returned and will have a reference count of 1.
3152 SV* sv_setref_pv (SV *rv, char *classname, void* pv)
3154 Do not use with integral Perl types such as HV, AV, SV, CV, because those
3155 objects will become corrupted by the pointer copy process.
3157 Note that C<sv_setref_pvn> copies the string while this copies the pointer.
3161 Copies a string into a new SV, optionally blessing the SV. The length of the
3162 string must be specified with C<n>. The C<rv> argument will be upgraded to
3163 an RV. That RV will be modified to point to the new SV. The C<classname>
3164 argument indicates the package for the blessing. Set C<classname> to
3165 C<Nullch> to avoid the blessing. The new SV will be returned and will have
3166 a reference count of 1.
3168 SV* sv_setref_pvn (SV *rv, char *classname, char* pv, I32 n)
3170 Note that C<sv_setref_pv> copies the pointer while this copies the string.
3174 Calls C<sv_setsv> if dsv is not the same as ssv. May evaluate arguments
3177 void SvSetSV (SV* dsv, SV* ssv)
3179 =item SvSetSV_nosteal
3181 Calls a non-destructive version of C<sv_setsv> if dsv is not the same as ssv.
3182 May evaluate arguments more than once.
3184 void SvSetSV_nosteal (SV* dsv, SV* ssv)
3188 Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
3189 The source SV may be destroyed if it is mortal. Does not handle 'set' magic.
3190 See the macro forms C<SvSetSV>, C<SvSetSV_nosteal> and C<sv_setsv_mg>.
3192 void sv_setsv (SV* dsv, SV* ssv)
3196 Like C<sv_setsv>, but also handles 'set' magic.
3198 void sv_setsv_mg (SV* dsv, SV* ssv)
3202 Copies an unsigned integer into the given SV. Does not handle 'set' magic.
3205 void sv_setuv (SV* sv, UV num)
3209 Like C<sv_setuv>, but also handles 'set' magic.
3211 void sv_setuv_mg (SV* sv, UV num)
3215 Returns the stash of the SV.
3217 HV* SvSTASH (SV* sv)
3221 Taints an SV if tainting is enabled
3223 void SvTAINT (SV* sv)
3227 Checks to see if an SV is tainted. Returns TRUE if it is, FALSE if not.
3229 int SvTAINTED (SV* sv)
3233 Untaints an SV. Be I<very> careful with this routine, as it short-circuits
3234 some of Perl's fundamental security features. XS module authors should
3235 not use this function unless they fully understand all the implications
3236 of unconditionally untainting the value. Untainting should be done in
3237 the standard perl fashion, via a carefully crafted regexp, rather than
3238 directly untainting variables.
3240 void SvTAINTED_off (SV* sv)
3244 Marks an SV as tainted.
3246 void SvTAINTED_on (SV* sv)
3250 Integer type flag for scalars. See C<svtype>.
3254 Pointer type flag for scalars. See C<svtype>.
3258 Type flag for arrays. See C<svtype>.
3262 Type flag for code refs. See C<svtype>.
3266 Type flag for hashes. See C<svtype>.
3270 Type flag for blessed scalars. See C<svtype>.
3274 Double type flag for scalars. See C<svtype>.
3278 Returns a boolean indicating whether Perl would evaluate the SV as true or
3279 false, defined or undefined. Does not handle 'get' magic.
3285 Returns the type of the SV. See C<svtype>.
3287 svtype SvTYPE (SV* sv)
3291 An enum of flags for Perl types. These are found in the file B<sv.h> in the
3292 C<svtype> enum. Test these flags with the C<SvTYPE> macro.
3296 This is the C<undef> SV. Always refer to this as C<&sv_undef>.
3300 Unsets the RV status of the SV, and decrements the reference count of
3301 whatever was being referenced by the RV. This can almost be thought of
3302 as a reversal of C<newSVrv>. See C<SvROK_off>.
3304 void sv_unref (SV* sv)
3308 Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
3309 the upgrade if necessary. See C<svtype>.
3311 bool SvUPGRADE (SV* sv, svtype mt)
3315 Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
3319 Tells an SV to use C<ptr> to find its string value. Normally the string is
3320 stored inside the SV but sv_usepvn allows the SV to use an outside string.
3321 The C<ptr> should point to memory that was allocated by C<malloc>. The
3322 string length, C<len>, must be supplied. This function will realloc the
3323 memory pointed to by C<ptr>, so that pointer should not be freed or used by
3324 the programmer after giving it to sv_usepvn. Does not handle 'set' magic.
3325 See C<sv_usepvn_mg>.
3327 void sv_usepvn (SV* sv, char* ptr, STRLEN len)
3331 Like C<sv_usepvn>, but also handles 'set' magic.
3333 void sv_usepvn_mg (SV* sv, char* ptr, STRLEN len)
3335 =item sv_vcatpvfn(sv, pat, patlen, args, svargs, svmax, used_locale)
3337 Processes its arguments like C<vsprintf> and appends the formatted output
3338 to an SV. Uses an array of SVs if the C style variable argument list is
3339 missing (NULL). Indicates if locale information has been used for formatting.
3341 void sv_catpvfn _((SV* sv, const char* pat, STRLEN patlen,
3342 va_list *args, SV **svargs, I32 svmax,
3343 bool *used_locale));
3345 =item sv_vsetpvfn(sv, pat, patlen, args, svargs, svmax, used_locale)
3347 Works like C<vcatpvfn> but copies the text into the SV instead of
3350 void sv_setpvfn _((SV* sv, const char* pat, STRLEN patlen,
3351 va_list *args, SV **svargs, I32 svmax,
3352 bool *used_locale));
3356 Returns the unsigned integer which is in the SV.
3362 Returns the unsigned integer which is stored in the SV.
3368 This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
3372 Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
3373 This is always the proper type for the C++ object. See C<CLASS> and
3374 L<perlxs/"Using XS With C++">.
3378 Converts the specified character to lowercase.
3380 int toLOWER (char c)
3384 Converts the specified character to uppercase.
3386 int toUPPER (char c)
3390 This is the XSUB-writer's interface to Perl's C<warn> function. Use this
3391 function the same way you use the C C<printf> function. See C<croak()>.
3395 Push an integer onto the stack, extending the stack if necessary. Handles
3396 'set' magic. See C<PUSHi>.
3402 Push a double onto the stack, extending the stack if necessary. Handles 'set'
3403 magic. See C<PUSHn>.
3409 Push a string onto the stack, extending the stack if necessary. The C<len>
3410 indicates the length of the string. Handles 'set' magic. See C<PUSHp>.
3412 XPUSHp(char *c, int len)
3416 Push an SV onto the stack, extending the stack if necessary. Does not
3417 handle 'set' magic. See C<PUSHs>.
3423 Push an unsigned integer onto the stack, extending the stack if
3424 necessary. See C<PUSHu>.
3428 Macro to declare an XSUB and its C parameter list. This is handled by
3433 Return from XSUB, indicating number of items on the stack. This is usually
3434 handled by C<xsubpp>.
3438 =item XSRETURN_EMPTY
3440 Return an empty list from an XSUB immediately.
3446 Return an integer from an XSUB immediately. Uses C<XST_mIV>.
3452 Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
3458 Return an double from an XSUB immediately. Uses C<XST_mNV>.
3464 Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
3466 XSRETURN_PV(char *v)
3468 =item XSRETURN_UNDEF
3470 Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
3476 Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
3482 Place an integer into the specified position C<i> on the stack. The value is
3483 stored in a new mortal SV.
3485 XST_mIV( int i, IV v )
3489 Place a double into the specified position C<i> on the stack. The value is
3490 stored in a new mortal SV.
3492 XST_mNV( int i, NV v )
3496 Place C<&sv_no> into the specified position C<i> on the stack.
3502 Place a copy of a string into the specified position C<i> on the stack. The
3503 value is stored in a new mortal SV.
3505 XST_mPV( int i, char *v )
3509 Place C<&sv_undef> into the specified position C<i> on the stack.
3515 Place C<&sv_yes> into the specified position C<i> on the stack.
3521 The version identifier for an XS module. This is usually handled
3522 automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
3524 =item XS_VERSION_BOOTCHECK
3526 Macro to verify that a PM module's $VERSION variable matches the XS module's
3527 C<XS_VERSION> variable. This is usually handled automatically by
3528 C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
3532 The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
3533 destination, C<n> is the number of items, and C<t> is the type.
3535 void Zero( d, n, t )
3541 Until May 1997, this document was maintained by Jeff Okamoto
3542 <okamoto@corp.hp.com>. It is now maintained as part of Perl itself.
3544 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
3545 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
3546 Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
3547 Stephen McCamant, and Gurusamy Sarathy.
3549 API Listing originally by Dean Roehrich <roehrich@cray.com>.