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1=head1 NAME
2
3perlguts - Perl's Internal Functions
4
5=head1 DESCRIPTION
6
7This document attempts to describe some of the internal functions of the
8Perl executable. It is far from complete and probably contains many errors.
9Please refer any questions or comments to the author below.
10
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11=head1 Variables
12
5f05dabc 13=head2 Datatypes
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14
15Perl has three typedefs that handle Perl's three main data types:
16
17 SV Scalar Value
18 AV Array Value
19 HV Hash Value
20
d1b91892 21Each typedef has specific routines that manipulate the various data types.
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22
23=head2 What is an "IV"?
24
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25Perl uses a special typedef IV which is a simple integer type that is
26guaranteed to be large enough to hold a pointer (as well as an integer).
a0d0e21e 27
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28Perl also uses two special typedefs, I32 and I16, which will always be at
29least 32-bits and 16-bits long, respectively.
a0d0e21e 30
54310121 31=head2 Working with SVs
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32
33An SV can be created and loaded with one command. There are four types of
34values that can be loaded: an integer value (IV), a double (NV), a string,
35(PV), and another scalar (SV).
36
46fc3d4c 37The five routines are:
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38
39 SV* newSViv(IV);
40 SV* newSVnv(double);
41 SV* newSVpv(char*, int);
46fc3d4c 42 SV* newSVpvf(const char*, ...);
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43 SV* newSVsv(SV*);
44
46fc3d4c 45To change the value of an *already-existing* SV, there are six routines:
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46
47 void sv_setiv(SV*, IV);
48 void sv_setnv(SV*, double);
a0d0e21e 49 void sv_setpv(SV*, char*);
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50 void sv_setpvn(SV*, char*, int)
51 void sv_setpvf(SV*, const char*, ...);
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52 void sv_setsv(SV*, SV*);
53
54Notice that you can choose to specify the length of the string to be
d1b91892 55assigned by using C<sv_setpvn> or C<newSVpv>, or you may allow Perl to
cb1a09d0 56calculate the length by using C<sv_setpv> or by specifying 0 as the second
d1b91892 57argument to C<newSVpv>. Be warned, though, that Perl will determine the
a0d0e21e 58string's length by using C<strlen>, which depends on the string terminating
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59with a NUL character. The arguments of C<sv_setpvf> are processed like
60C<sprintf>, and the formatted output becomes the value.
a0d0e21e 61
54310121 62All SVs that will contain strings should, but need not, be terminated
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63with a NUL character. If it is not NUL-terminated there is a risk of
64core dumps and corruptions from code which passes the string to C
65functions or system calls which expect a NUL-terminated string.
66Perl's own functions typically add a trailing NUL for this reason.
67Nevertheless, you should be very careful when you pass a string stored
68in an SV to a C function or system call.
69
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70To access the actual value that an SV points to, you can use the macros:
71
72 SvIV(SV*)
73 SvNV(SV*)
74 SvPV(SV*, STRLEN len)
75
76which will automatically coerce the actual scalar type into an IV, double,
77or string.
78
79In the C<SvPV> macro, the length of the string returned is placed into the
80variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do not
81care what the length of the data is, use the global variable C<na>. Remember,
82however, that Perl allows arbitrary strings of data that may both contain
54310121 83NULs and might not be terminated by a NUL.
a0d0e21e 84
07fa94a1 85If you want to know if the scalar value is TRUE, you can use:
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86
87 SvTRUE(SV*)
88
89Although Perl will automatically grow strings for you, if you need to force
90Perl to allocate more memory for your SV, you can use the macro
91
92 SvGROW(SV*, STRLEN newlen)
93
94which will determine if more memory needs to be allocated. If so, it will
95call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
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96decrease, the allocated memory of an SV and that it does not automatically
97add a byte for the a trailing NUL (perl's own string functions typically do
8ebc5c01 98C<SvGROW(sv, len + 1)>).
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99
100If you have an SV and want to know what kind of data Perl thinks is stored
101in it, you can use the following macros to check the type of SV you have.
102
103 SvIOK(SV*)
104 SvNOK(SV*)
105 SvPOK(SV*)
106
107You can get and set the current length of the string stored in an SV with
108the following macros:
109
110 SvCUR(SV*)
111 SvCUR_set(SV*, I32 val)
112
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113You can also get a pointer to the end of the string stored in the SV
114with the macro:
115
116 SvEND(SV*)
117
118But note that these last three macros are valid only if C<SvPOK()> is true.
a0d0e21e 119
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120If you want to append something to the end of string stored in an C<SV*>,
121you can use the following functions:
122
123 void sv_catpv(SV*, char*);
124 void sv_catpvn(SV*, char*, int);
46fc3d4c 125 void sv_catpvf(SV*, const char*, ...);
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126 void sv_catsv(SV*, SV*);
127
128The first function calculates the length of the string to be appended by
129using C<strlen>. In the second, you specify the length of the string
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130yourself. The third function processes its arguments like C<sprintf> and
131appends the formatted output. The fourth function extends the string
132stored in the first SV with the string stored in the second SV. It also
133forces the second SV to be interpreted as a string.
d1b91892 134
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135If you know the name of a scalar variable, you can get a pointer to its SV
136by using the following:
137
5f05dabc 138 SV* perl_get_sv("package::varname", FALSE);
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139
140This returns NULL if the variable does not exist.
141
d1b91892 142If you want to know if this variable (or any other SV) is actually C<defined>,
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143you can call:
144
145 SvOK(SV*)
146
147The scalar C<undef> value is stored in an SV instance called C<sv_undef>. Its
148address can be used whenever an C<SV*> is needed.
149
150There are also the two values C<sv_yes> and C<sv_no>, which contain Boolean
151TRUE and FALSE values, respectively. Like C<sv_undef>, their addresses can
152be used whenever an C<SV*> is needed.
153
154Do not be fooled into thinking that C<(SV *) 0> is the same as C<&sv_undef>.
155Take this code:
156
157 SV* sv = (SV*) 0;
158 if (I-am-to-return-a-real-value) {
159 sv = sv_2mortal(newSViv(42));
160 }
161 sv_setsv(ST(0), sv);
162
163This code tries to return a new SV (which contains the value 42) if it should
04343c6d 164return a real value, or undef otherwise. Instead it has returned a NULL
a0d0e21e 165pointer which, somewhere down the line, will cause a segmentation violation,
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166bus error, or just weird results. Change the zero to C<&sv_undef> in the first
167line and all will be well.
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168
169To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
3fe9a6f1 170call is not necessary (see L<Reference Counts and Mortality>).
a0d0e21e 171
d1b91892 172=head2 What's Really Stored in an SV?
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173
174Recall that the usual method of determining the type of scalar you have is
5f05dabc 175to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
d1b91892 176usually these macros will always return TRUE and calling the C<Sv*V>
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177macros will do the appropriate conversion of string to integer/double or
178integer/double to string.
179
180If you I<really> need to know if you have an integer, double, or string
181pointer in an SV, you can use the following three macros instead:
182
183 SvIOKp(SV*)
184 SvNOKp(SV*)
185 SvPOKp(SV*)
186
187These will tell you if you truly have an integer, double, or string pointer
d1b91892 188stored in your SV. The "p" stands for private.
a0d0e21e 189
07fa94a1 190In general, though, it's best to use the C<Sv*V> macros.
a0d0e21e 191
54310121 192=head2 Working with AVs
a0d0e21e 193
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194There are two ways to create and load an AV. The first method creates an
195empty AV:
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196
197 AV* newAV();
198
54310121 199The second method both creates the AV and initially populates it with SVs:
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200
201 AV* av_make(I32 num, SV **ptr);
202
5f05dabc 203The second argument points to an array containing C<num> C<SV*>'s. Once the
54310121 204AV has been created, the SVs can be destroyed, if so desired.
a0d0e21e 205
54310121 206Once the AV has been created, the following operations are possible on AVs:
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207
208 void av_push(AV*, SV*);
209 SV* av_pop(AV*);
210 SV* av_shift(AV*);
211 void av_unshift(AV*, I32 num);
212
213These should be familiar operations, with the exception of C<av_unshift>.
214This routine adds C<num> elements at the front of the array with the C<undef>
215value. You must then use C<av_store> (described below) to assign values
216to these new elements.
217
218Here are some other functions:
219
5f05dabc 220 I32 av_len(AV*);
a0d0e21e 221 SV** av_fetch(AV*, I32 key, I32 lval);
a0d0e21e 222 SV** av_store(AV*, I32 key, SV* val);
a0d0e21e 223
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224The C<av_len> function returns the highest index value in array (just
225like $#array in Perl). If the array is empty, -1 is returned. The
226C<av_fetch> function returns the value at index C<key>, but if C<lval>
227is non-zero, then C<av_fetch> will store an undef value at that index.
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228The C<av_store> function stores the value C<val> at index C<key>, and does
229not increment the reference count of C<val>. Thus the caller is responsible
230for taking care of that, and if C<av_store> returns NULL, the caller will
231have to decrement the reference count to avoid a memory leak. Note that
232C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s as their
233return value.
d1b91892 234
a0d0e21e 235 void av_clear(AV*);
a0d0e21e 236 void av_undef(AV*);
cb1a09d0 237 void av_extend(AV*, I32 key);
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238
239The C<av_clear> function deletes all the elements in the AV* array, but
240does not actually delete the array itself. The C<av_undef> function will
241delete all the elements in the array plus the array itself. The
242C<av_extend> function extends the array so that it contains C<key>
243elements. If C<key> is less than the current length of the array, then
244nothing is done.
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245
246If you know the name of an array variable, you can get a pointer to its AV
247by using the following:
248
5f05dabc 249 AV* perl_get_av("package::varname", FALSE);
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250
251This returns NULL if the variable does not exist.
252
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253See L<Understanding the Magic of Tied Hashes and Arrays> for more
254information on how to use the array access functions on tied arrays.
255
54310121 256=head2 Working with HVs
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257
258To create an HV, you use the following routine:
259
260 HV* newHV();
261
54310121 262Once the HV has been created, the following operations are possible on HVs:
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263
264 SV** hv_store(HV*, char* key, U32 klen, SV* val, U32 hash);
265 SV** hv_fetch(HV*, char* key, U32 klen, I32 lval);
266
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267The C<klen> parameter is the length of the key being passed in (Note that
268you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
269length of the key). The C<val> argument contains the SV pointer to the
54310121 270scalar being stored, and C<hash> is the precomputed hash value (zero if
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271you want C<hv_store> to calculate it for you). The C<lval> parameter
272indicates whether this fetch is actually a part of a store operation, in
273which case a new undefined value will be added to the HV with the supplied
274key and C<hv_fetch> will return as if the value had already existed.
a0d0e21e 275
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276Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
277C<SV*>. To access the scalar value, you must first dereference the return
278value. However, you should check to make sure that the return value is
279not NULL before dereferencing it.
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280
281These two functions check if a hash table entry exists, and deletes it.
282
283 bool hv_exists(HV*, char* key, U32 klen);
d1b91892 284 SV* hv_delete(HV*, char* key, U32 klen, I32 flags);
a0d0e21e 285
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286If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
287create and return a mortal copy of the deleted value.
288
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289And more miscellaneous functions:
290
291 void hv_clear(HV*);
a0d0e21e 292 void hv_undef(HV*);
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293
294Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
295table but does not actually delete the hash table. The C<hv_undef> deletes
296both the entries and the hash table itself.
a0d0e21e 297
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298Perl keeps the actual data in linked list of structures with a typedef of HE.
299These contain the actual key and value pointers (plus extra administrative
300overhead). The key is a string pointer; the value is an C<SV*>. However,
301once you have an C<HE*>, to get the actual key and value, use the routines
302specified below.
303
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304 I32 hv_iterinit(HV*);
305 /* Prepares starting point to traverse hash table */
306 HE* hv_iternext(HV*);
307 /* Get the next entry, and return a pointer to a
308 structure that has both the key and value */
309 char* hv_iterkey(HE* entry, I32* retlen);
310 /* Get the key from an HE structure and also return
311 the length of the key string */
cb1a09d0 312 SV* hv_iterval(HV*, HE* entry);
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313 /* Return a SV pointer to the value of the HE
314 structure */
cb1a09d0 315 SV* hv_iternextsv(HV*, char** key, I32* retlen);
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316 /* This convenience routine combines hv_iternext,
317 hv_iterkey, and hv_iterval. The key and retlen
318 arguments are return values for the key and its
319 length. The value is returned in the SV* argument */
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320
321If you know the name of a hash variable, you can get a pointer to its HV
322by using the following:
323
5f05dabc 324 HV* perl_get_hv("package::varname", FALSE);
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325
326This returns NULL if the variable does not exist.
327
8ebc5c01 328The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
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329
330 i = klen;
331 hash = 0;
332 s = key;
333 while (i--)
334 hash = hash * 33 + *s++;
335
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336See L<Understanding the Magic of Tied Hashes and Arrays> for more
337information on how to use the hash access functions on tied hashes.
338
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339=head2 Hash API Extensions
340
341Beginning with version 5.004, the following functions are also supported:
342
343 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
344 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
345
346 bool hv_exists_ent (HV* tb, SV* key, U32 hash);
347 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
348
349 SV* hv_iterkeysv (HE* entry);
350
351Note that these functions take C<SV*> keys, which simplifies writing
352of extension code that deals with hash structures. These functions
353also allow passing of C<SV*> keys to C<tie> functions without forcing
354you to stringify the keys (unlike the previous set of functions).
355
356They also return and accept whole hash entries (C<HE*>), making their
357use more efficient (since the hash number for a particular string
358doesn't have to be recomputed every time). See L<API LISTING> later in
359this document for detailed descriptions.
360
361The following macros must always be used to access the contents of hash
362entries. Note that the arguments to these macros must be simple
363variables, since they may get evaluated more than once. See
364L<API LISTING> later in this document for detailed descriptions of these
365macros.
366
367 HePV(HE* he, STRLEN len)
368 HeVAL(HE* he)
369 HeHASH(HE* he)
370 HeSVKEY(HE* he)
371 HeSVKEY_force(HE* he)
372 HeSVKEY_set(HE* he, SV* sv)
373
374These two lower level macros are defined, but must only be used when
375dealing with keys that are not C<SV*>s:
376
377 HeKEY(HE* he)
378 HeKLEN(HE* he)
379
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380Note that both C<hv_store> and C<hv_store_ent> do not increment the
381reference count of the stored C<val>, which is the caller's responsibility.
382If these functions return a NULL value, the caller will usually have to
383decrement the reference count of C<val> to avoid a memory leak.
1e422769 384
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385=head2 References
386
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387References are a special type of scalar that point to other data types
388(including references).
a0d0e21e 389
07fa94a1 390To create a reference, use either of the following functions:
a0d0e21e 391
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392 SV* newRV_inc((SV*) thing);
393 SV* newRV_noinc((SV*) thing);
a0d0e21e 394
5f05dabc 395The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
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396functions are identical except that C<newRV_inc> increments the reference
397count of the C<thing>, while C<newRV_noinc> does not. For historical
398reasons, C<newRV> is a synonym for C<newRV_inc>.
399
400Once you have a reference, you can use the following macro to dereference
401the reference:
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402
403 SvRV(SV*)
404
405then call the appropriate routines, casting the returned C<SV*> to either an
d1b91892 406C<AV*> or C<HV*>, if required.
a0d0e21e 407
d1b91892 408To determine if an SV is a reference, you can use the following macro:
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409
410 SvROK(SV*)
411
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412To discover what type of value the reference refers to, use the following
413macro and then check the return value.
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414
415 SvTYPE(SvRV(SV*))
416
417The most useful types that will be returned are:
418
419 SVt_IV Scalar
420 SVt_NV Scalar
421 SVt_PV Scalar
5f05dabc 422 SVt_RV Scalar
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423 SVt_PVAV Array
424 SVt_PVHV Hash
425 SVt_PVCV Code
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426 SVt_PVGV Glob (possible a file handle)
427 SVt_PVMG Blessed or Magical Scalar
428
429 See the sv.h header file for more details.
d1b91892 430
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431=head2 Blessed References and Class Objects
432
433References are also used to support object-oriented programming. In the
434OO lexicon, an object is simply a reference that has been blessed into a
435package (or class). Once blessed, the programmer may now use the reference
436to access the various methods in the class.
437
438A reference can be blessed into a package with the following function:
439
440 SV* sv_bless(SV* sv, HV* stash);
441
442The C<sv> argument must be a reference. The C<stash> argument specifies
3fe9a6f1 443which class the reference will belong to. See
2ae324a7 444L<Stashes and Globs> for information on converting class names into stashes.
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445
446/* Still under construction */
447
448Upgrades rv to reference if not already one. Creates new SV for rv to
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449point to. If C<classname> is non-null, the SV is blessed into the specified
450class. SV is returned.
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451
452 SV* newSVrv(SV* rv, char* classname);
453
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454Copies integer or double into an SV whose reference is C<rv>. SV is blessed
455if C<classname> is non-null.
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456
457 SV* sv_setref_iv(SV* rv, char* classname, IV iv);
458 SV* sv_setref_nv(SV* rv, char* classname, NV iv);
459
5f05dabc 460Copies the pointer value (I<the address, not the string!>) into an SV whose
8ebc5c01 461reference is rv. SV is blessed if C<classname> is non-null.
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462
463 SV* sv_setref_pv(SV* rv, char* classname, PV iv);
464
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465Copies string into an SV whose reference is C<rv>. Set length to 0 to let
466Perl calculate the string length. SV is blessed if C<classname> is non-null.
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467
468 SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
469
470 int sv_isa(SV* sv, char* name);
471 int sv_isobject(SV* sv);
472
5f05dabc 473=head2 Creating New Variables
cb1a09d0 474
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475To create a new Perl variable with an undef value which can be accessed from
476your Perl script, use the following routines, depending on the variable type.
cb1a09d0 477
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478 SV* perl_get_sv("package::varname", TRUE);
479 AV* perl_get_av("package::varname", TRUE);
480 HV* perl_get_hv("package::varname", TRUE);
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481
482Notice the use of TRUE as the second parameter. The new variable can now
483be set, using the routines appropriate to the data type.
484
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485There are additional macros whose values may be bitwise OR'ed with the
486C<TRUE> argument to enable certain extra features. Those bits are:
cb1a09d0 487
5f05dabc 488 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
54310121 489 "Name <varname> used only once: possible typo" warning.
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490 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
491 the variable did not exist before the function was called.
cb1a09d0 492
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493If you do not specify a package name, the variable is created in the current
494package.
cb1a09d0 495
5f05dabc 496=head2 Reference Counts and Mortality
a0d0e21e 497
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498Perl uses an reference count-driven garbage collection mechanism. SVs,
499AVs, or HVs (xV for short in the following) start their life with a
55497cff 500reference count of 1. If the reference count of an xV ever drops to 0,
07fa94a1 501then it will be destroyed and its memory made available for reuse.
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502
503This normally doesn't happen at the Perl level unless a variable is
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504undef'ed or the last variable holding a reference to it is changed or
505overwritten. At the internal level, however, reference counts can be
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506manipulated with the following macros:
507
508 int SvREFCNT(SV* sv);
5f05dabc 509 SV* SvREFCNT_inc(SV* sv);
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510 void SvREFCNT_dec(SV* sv);
511
512However, there is one other function which manipulates the reference
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513count of its argument. The C<newRV_inc> function, you will recall,
514creates a reference to the specified argument. As a side effect,
515it increments the argument's reference count. If this is not what
516you want, use C<newRV_noinc> instead.
517
518For example, imagine you want to return a reference from an XSUB function.
519Inside the XSUB routine, you create an SV which initially has a reference
520count of one. Then you call C<newRV_inc>, passing it the just-created SV.
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521This returns the reference as a new SV, but the reference count of the
522SV you passed to C<newRV_inc> has been incremented to two. Now you
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523return the reference from the XSUB routine and forget about the SV.
524But Perl hasn't! Whenever the returned reference is destroyed, the
525reference count of the original SV is decreased to one and nothing happens.
526The SV will hang around without any way to access it until Perl itself
527terminates. This is a memory leak.
5f05dabc
PP
528
529The correct procedure, then, is to use C<newRV_noinc> instead of
faed5253
JO
530C<newRV_inc>. Then, if and when the last reference is destroyed,
531the reference count of the SV will go to zero and it will be destroyed,
07fa94a1 532stopping any memory leak.
55497cff 533
5f05dabc 534There are some convenience functions available that can help with the
54310121 535destruction of xVs. These functions introduce the concept of "mortality".
07fa94a1
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536An xV that is mortal has had its reference count marked to be decremented,
537but not actually decremented, until "a short time later". Generally the
538term "short time later" means a single Perl statement, such as a call to
54310121 539an XSUB function. The actual determinant for when mortal xVs have their
07fa94a1
JO
540reference count decremented depends on two macros, SAVETMPS and FREETMPS.
541See L<perlcall> and L<perlxs> for more details on these macros.
55497cff
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542
543"Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
544However, if you mortalize a variable twice, the reference count will
545later be decremented twice.
546
547You should be careful about creating mortal variables. Strange things
548can happen if you make the same value mortal within multiple contexts,
5f05dabc 549or if you make a variable mortal multiple times.
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550
551To create a mortal variable, use the functions:
552
553 SV* sv_newmortal()
554 SV* sv_2mortal(SV*)
555 SV* sv_mortalcopy(SV*)
556
5f05dabc
PP
557The first call creates a mortal SV, the second converts an existing
558SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
559third creates a mortal copy of an existing SV.
a0d0e21e 560
54310121 561The mortal routines are not just for SVs -- AVs and HVs can be
faed5253 562made mortal by passing their address (type-casted to C<SV*>) to the
07fa94a1 563C<sv_2mortal> or C<sv_mortalcopy> routines.
a0d0e21e 564
5f05dabc 565=head2 Stashes and Globs
a0d0e21e 566
aa689395
PP
567A "stash" is a hash that contains all of the different objects that
568are contained within a package. Each key of the stash is a symbol
569name (shared by all the different types of objects that have the same
570name), and each value in the hash table is a GV (Glob Value). This GV
571in turn contains references to the various objects of that name,
572including (but not limited to) the following:
cb1a09d0 573
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574 Scalar Value
575 Array Value
576 Hash Value
577 File Handle
578 Directory Handle
579 Format
580 Subroutine
581
5f05dabc
PP
582There is a single stash called "defstash" that holds the items that exist
583in the "main" package. To get at the items in other packages, append the
584string "::" to the package name. The items in the "Foo" package are in
585the stash "Foo::" in defstash. The items in the "Bar::Baz" package are
586in the stash "Baz::" in "Bar::"'s stash.
a0d0e21e 587
d1b91892 588To get the stash pointer for a particular package, use the function:
a0d0e21e
LW
589
590 HV* gv_stashpv(char* name, I32 create)
591 HV* gv_stashsv(SV*, I32 create)
592
593The first function takes a literal string, the second uses the string stored
d1b91892 594in the SV. Remember that a stash is just a hash table, so you get back an
cb1a09d0 595C<HV*>. The C<create> flag will create a new package if it is set.
a0d0e21e
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596
597The name that C<gv_stash*v> wants is the name of the package whose symbol table
598you want. The default package is called C<main>. If you have multiply nested
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599packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
600language itself.
a0d0e21e
LW
601
602Alternately, if you have an SV that is a blessed reference, you can find
603out the stash pointer by using:
604
605 HV* SvSTASH(SvRV(SV*));
606
607then use the following to get the package name itself:
608
609 char* HvNAME(HV* stash);
610
5f05dabc
PP
611If you need to bless or re-bless an object you can use the following
612function:
a0d0e21e
LW
613
614 SV* sv_bless(SV*, HV* stash)
615
616where the first argument, an C<SV*>, must be a reference, and the second
617argument is a stash. The returned C<SV*> can now be used in the same way
618as any other SV.
619
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620For more information on references and blessings, consult L<perlref>.
621
54310121 622=head2 Double-Typed SVs
0a753a76
PP
623
624Scalar variables normally contain only one type of value, an integer,
625double, pointer, or reference. Perl will automatically convert the
626actual scalar data from the stored type into the requested type.
627
628Some scalar variables contain more than one type of scalar data. For
629example, the variable C<$!> contains either the numeric value of C<errno>
630or its string equivalent from either C<strerror> or C<sys_errlist[]>.
631
632To force multiple data values into an SV, you must do two things: use the
633C<sv_set*v> routines to add the additional scalar type, then set a flag
634so that Perl will believe it contains more than one type of data. The
635four macros to set the flags are:
636
637 SvIOK_on
638 SvNOK_on
639 SvPOK_on
640 SvROK_on
641
642The particular macro you must use depends on which C<sv_set*v> routine
643you called first. This is because every C<sv_set*v> routine turns on
644only the bit for the particular type of data being set, and turns off
645all the rest.
646
647For example, to create a new Perl variable called "dberror" that contains
648both the numeric and descriptive string error values, you could use the
649following code:
650
651 extern int dberror;
652 extern char *dberror_list;
653
654 SV* sv = perl_get_sv("dberror", TRUE);
655 sv_setiv(sv, (IV) dberror);
656 sv_setpv(sv, dberror_list[dberror]);
657 SvIOK_on(sv);
658
659If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
660macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
661
662=head2 Magic Variables
a0d0e21e 663
d1b91892
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664[This section still under construction. Ignore everything here. Post no
665bills. Everything not permitted is forbidden.]
666
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667Any SV may be magical, that is, it has special features that a normal
668SV does not have. These features are stored in the SV structure in a
5f05dabc 669linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
d1b91892
AD
670
671 struct magic {
672 MAGIC* mg_moremagic;
673 MGVTBL* mg_virtual;
674 U16 mg_private;
675 char mg_type;
676 U8 mg_flags;
677 SV* mg_obj;
678 char* mg_ptr;
679 I32 mg_len;
680 };
681
682Note this is current as of patchlevel 0, and could change at any time.
683
684=head2 Assigning Magic
685
686Perl adds magic to an SV using the sv_magic function:
687
688 void sv_magic(SV* sv, SV* obj, int how, char* name, I32 namlen);
689
690The C<sv> argument is a pointer to the SV that is to acquire a new magical
691feature.
692
693If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
694set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
695it to the beginning of the linked list of magical features. Any prior
696entry of the same type of magic is deleted. Note that this can be
5fb8527f 697overridden, and multiple instances of the same type of magic can be
d1b91892
AD
698associated with an SV.
699
54310121
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700The C<name> and C<namlen> arguments are used to associate a string with
701the magic, typically the name of a variable. C<namlen> is stored in the
702C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
d1b91892
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703copy of the name is stored in C<mg_ptr> field.
704
705The sv_magic function uses C<how> to determine which, if any, predefined
706"Magic Virtual Table" should be assigned to the C<mg_virtual> field.
cb1a09d0
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707See the "Magic Virtual Table" section below. The C<how> argument is also
708stored in the C<mg_type> field.
d1b91892
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709
710The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
711structure. If it is not the same as the C<sv> argument, the reference
712count of the C<obj> object is incremented. If it is the same, or if
04343c6d 713the C<how> argument is "#", or if it is a NULL pointer, then C<obj> is
d1b91892
AD
714merely stored, without the reference count being incremented.
715
cb1a09d0
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716There is also a function to add magic to an C<HV>:
717
718 void hv_magic(HV *hv, GV *gv, int how);
719
720This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
721
722To remove the magic from an SV, call the function sv_unmagic:
723
724 void sv_unmagic(SV *sv, int type);
725
726The C<type> argument should be equal to the C<how> value when the C<SV>
727was initially made magical.
728
d1b91892
AD
729=head2 Magic Virtual Tables
730
731The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
732C<MGVTBL>, which is a structure of function pointers and stands for
733"Magic Virtual Table" to handle the various operations that might be
734applied to that variable.
735
736The C<MGVTBL> has five pointers to the following routine types:
737
738 int (*svt_get)(SV* sv, MAGIC* mg);
739 int (*svt_set)(SV* sv, MAGIC* mg);
740 U32 (*svt_len)(SV* sv, MAGIC* mg);
741 int (*svt_clear)(SV* sv, MAGIC* mg);
742 int (*svt_free)(SV* sv, MAGIC* mg);
743
744This MGVTBL structure is set at compile-time in C<perl.h> and there are
745currently 19 types (or 21 with overloading turned on). These different
746structures contain pointers to various routines that perform additional
747actions depending on which function is being called.
748
749 Function pointer Action taken
750 ---------------- ------------
751 svt_get Do something after the value of the SV is retrieved.
752 svt_set Do something after the SV is assigned a value.
753 svt_len Report on the SV's length.
754 svt_clear Clear something the SV represents.
755 svt_free Free any extra storage associated with the SV.
756
757For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
758to an C<mg_type> of '\0') contains:
759
760 { magic_get, magic_set, magic_len, 0, 0 }
761
762Thus, when an SV is determined to be magical and of type '\0', if a get
763operation is being performed, the routine C<magic_get> is called. All
764the various routines for the various magical types begin with C<magic_>.
765
766The current kinds of Magic Virtual Tables are:
767
bdbeb323 768 mg_type MGVTBL Type of magic
5f05dabc 769 ------- ------ ----------------------------
bdbeb323
SM
770 \0 vtbl_sv Special scalar variable
771 A vtbl_amagic %OVERLOAD hash
772 a vtbl_amagicelem %OVERLOAD hash element
773 c (none) Holds overload table (AMT) on stash
774 B vtbl_bm Boyer-Moore (fast string search)
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AD
775 E vtbl_env %ENV hash
776 e vtbl_envelem %ENV hash element
bdbeb323
SM
777 f vtbl_fm Formline ('compiled' format)
778 g vtbl_mglob m//g target / study()ed string
d1b91892
AD
779 I vtbl_isa @ISA array
780 i vtbl_isaelem @ISA array element
bdbeb323
SM
781 k vtbl_nkeys scalar(keys()) lvalue
782 L (none) Debugger %_<filename
783 l vtbl_dbline Debugger %_<filename element
44a8e56a 784 o vtbl_collxfrm Locale transformation
bdbeb323
SM
785 P vtbl_pack Tied array or hash
786 p vtbl_packelem Tied array or hash element
787 q vtbl_packelem Tied scalar or handle
788 S vtbl_sig %SIG hash
789 s vtbl_sigelem %SIG hash element
d1b91892 790 t vtbl_taint Taintedness
bdbeb323
SM
791 U vtbl_uvar Available for use by extensions
792 v vtbl_vec vec() lvalue
793 x vtbl_substr substr() lvalue
794 y vtbl_defelem Shadow "foreach" iterator variable /
795 smart parameter vivification
796 * vtbl_glob GV (typeglob)
797 # vtbl_arylen Array length ($#ary)
798 . vtbl_pos pos() lvalue
799 ~ (none) Available for use by extensions
d1b91892 800
68dc0745
PP
801When an uppercase and lowercase letter both exist in the table, then the
802uppercase letter is used to represent some kind of composite type (a list
803or a hash), and the lowercase letter is used to represent an element of
d1b91892
AD
804that composite type.
805
bdbeb323
SM
806The '~' and 'U' magic types are defined specifically for use by
807extensions and will not be used by perl itself. Extensions can use
808'~' magic to 'attach' private information to variables (typically
809objects). This is especially useful because there is no way for
810normal perl code to corrupt this private information (unlike using
811extra elements of a hash object).
812
813Similarly, 'U' magic can be used much like tie() to call a C function
814any time a scalar's value is used or changed. The C<MAGIC>'s
815C<mg_ptr> field points to a C<ufuncs> structure:
816
817 struct ufuncs {
818 I32 (*uf_val)(IV, SV*);
819 I32 (*uf_set)(IV, SV*);
820 IV uf_index;
821 };
822
823When the SV is read from or written to, the C<uf_val> or C<uf_set>
824function will be called with C<uf_index> as the first arg and a
825pointer to the SV as the second.
5f05dabc 826
bdbeb323
SM
827Note that because multiple extensions may be using '~' or 'U' magic,
828it is important for extensions to take extra care to avoid conflict.
829Typically only using the magic on objects blessed into the same class
830as the extension is sufficient. For '~' magic, it may also be
831appropriate to add an I32 'signature' at the top of the private data
832area and check that.
5f05dabc 833
d1b91892
AD
834=head2 Finding Magic
835
836 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
837
838This routine returns a pointer to the C<MAGIC> structure stored in the SV.
839If the SV does not have that magical feature, C<NULL> is returned. Also,
54310121 840if the SV is not of type SVt_PVMG, Perl may core dump.
d1b91892
AD
841
842 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
843
844This routine checks to see what types of magic C<sv> has. If the mg_type
68dc0745
PP
845field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
846the mg_type field is changed to be the lowercase letter.
a0d0e21e 847
04343c6d
GS
848=head2 Understanding the Magic of Tied Hashes and Arrays
849
850Tied hashes and arrays are magical beasts of the 'P' magic type.
9edb2b46
GS
851
852WARNING: As of the 5.004 release, proper usage of the array and hash
853access functions requires understanding a few caveats. Some
854of these caveats are actually considered bugs in the API, to be fixed
855in later releases, and are bracketed with [MAYCHANGE] below. If
856you find yourself actually applying such information in this section, be
857aware that the behavior may change in the future, umm, without warning.
04343c6d
GS
858
859The C<av_store> function, when given a tied array argument, merely
860copies the magic of the array onto the value to be "stored", using
861C<mg_copy>. It may also return NULL, indicating that the value did not
9edb2b46
GS
862actually need to be stored in the array. [MAYCHANGE] After a call to
863C<av_store> on a tied array, the caller will usually need to call
864C<mg_set(val)> to actually invoke the perl level "STORE" method on the
865TIEARRAY object. If C<av_store> did return NULL, a call to
866C<SvREFCNT_dec(val)> will also be usually necessary to avoid a memory
867leak. [/MAYCHANGE]
04343c6d
GS
868
869The previous paragraph is applicable verbatim to tied hash access using the
870C<hv_store> and C<hv_store_ent> functions as well.
871
872C<av_fetch> and the corresponding hash functions C<hv_fetch> and
873C<hv_fetch_ent> actually return an undefined mortal value whose magic
874has been initialized using C<mg_copy>. Note the value so returned does not
9edb2b46
GS
875need to be deallocated, as it is already mortal. [MAYCHANGE] But you will
876need to call C<mg_get()> on the returned value in order to actually invoke
877the perl level "FETCH" method on the underlying TIE object. Similarly,
04343c6d
GS
878you may also call C<mg_set()> on the return value after possibly assigning
879a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
9edb2b46 880method on the TIE object. [/MAYCHANGE]
04343c6d 881
9edb2b46 882[MAYCHANGE]
04343c6d
GS
883In other words, the array or hash fetch/store functions don't really
884fetch and store actual values in the case of tied arrays and hashes. They
885merely call C<mg_copy> to attach magic to the values that were meant to be
886"stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
887do the job of invoking the TIE methods on the underlying objects. Thus
9edb2b46 888the magic mechanism currently implements a kind of lazy access to arrays
04343c6d
GS
889and hashes.
890
891Currently (as of perl version 5.004), use of the hash and array access
892functions requires the user to be aware of whether they are operating on
9edb2b46
GS
893"normal" hashes and arrays, or on their tied variants. The API may be
894changed to provide more transparent access to both tied and normal data
895types in future versions.
896[/MAYCHANGE]
04343c6d
GS
897
898You would do well to understand that the TIEARRAY and TIEHASH interfaces
899are mere sugar to invoke some perl method calls while using the uniform hash
900and array syntax. The use of this sugar imposes some overhead (typically
901about two to four extra opcodes per FETCH/STORE operation, in addition to
902the creation of all the mortal variables required to invoke the methods).
903This overhead will be comparatively small if the TIE methods are themselves
904substantial, but if they are only a few statements long, the overhead
905will not be insignificant.
906
d1c897a1
IZ
907=head2 Localizing changes
908
909Perl has a very handy construction
910
911 {
912 local $var = 2;
913 ...
914 }
915
916This construction is I<approximately> equivalent to
917
918 {
919 my $oldvar = $var;
920 $var = 2;
921 ...
922 $var = $oldvar;
923 }
924
925The biggest difference is that the first construction would
926reinstate the initial value of $var, irrespective of how control exits
927the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
928more efficient as well.
929
930There is a way to achieve a similar task from C via Perl API: create a
931I<pseudo-block>, and arrange for some changes to be automatically
932undone at the end of it, either explicit, or via a non-local exit (via
933die()). A I<block>-like construct is created by a pair of
934C<ENTER>/C<LEAVE> macros (see L<perlcall/EXAMPLE/"Returning a
935Scalar">). Such a construct may be created specially for some
936important localized task, or an existing one (like boundaries of
937enclosing Perl subroutine/block, or an existing pair for freeing TMPs)
938may be used. (In the second case the overhead of additional
939localization must be almost negligible.) Note that any XSUB is
940automatically enclosed in an C<ENTER>/C<LEAVE> pair.
941
942Inside such a I<pseudo-block> the following service is available:
943
944=over
945
946=item C<SAVEINT(int i)>
947
948=item C<SAVEIV(IV i)>
949
950=item C<SAVEI32(I32 i)>
951
952=item C<SAVELONG(long i)>
953
954These macros arrange things to restore the value of integer variable
955C<i> at the end of enclosing I<pseudo-block>.
956
957=item C<SAVESPTR(s)>
958
959=item C<SAVEPPTR(p)>
960
961These macros arrange things to restore the value of pointers C<s> and
962C<p>. C<s> must be a pointer of a type which survives conversion to
963C<SV*> and back, C<p> should be able to survive conversion to C<char*>
964and back.
965
966=item C<SAVEFREESV(SV *sv)>
967
968The refcount of C<sv> would be decremented at the end of
969I<pseudo-block>. This is similar to C<sv_2mortal>, which should (?) be
970used instead.
971
972=item C<SAVEFREEOP(OP *op)>
973
974The C<OP *> is op_free()ed at the end of I<pseudo-block>.
975
976=item C<SAVEFREEPV(p)>
977
978The chunk of memory which is pointed to by C<p> is Safefree()ed at the
979end of I<pseudo-block>.
980
981=item C<SAVECLEARSV(SV *sv)>
982
983Clears a slot in the current scratchpad which corresponds to C<sv> at
984the end of I<pseudo-block>.
985
986=item C<SAVEDELETE(HV *hv, char *key, I32 length)>
987
988The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
989string pointed to by C<key> is Safefree()ed. If one has a I<key> in
990short-lived storage, the corresponding string may be reallocated like
991this:
992
993 SAVEDELETE(defstash, savepv(tmpbuf), strlen(tmpbuf));
994
995=item C<SAVEDESTRUCTOR(f,p)>
996
997At the end of I<pseudo-block> the function C<f> is called with the
998only argument (of type C<void*>) C<p>.
999
1000=item C<SAVESTACK_POS()>
1001
1002The current offset on the Perl internal stack (cf. C<SP>) is restored
1003at the end of I<pseudo-block>.
1004
1005=back
1006
1007The following API list contains functions, thus one needs to
1008provide pointers to the modifiable data explicitly (either C pointers,
1009or Perlish C<GV *>s). Where the above macros take C<int>, a similar
1010function takes C<int *>.
1011
1012=over
1013
1014=item C<SV* save_scalar(GV *gv)>
1015
1016Equivalent to Perl code C<local $gv>.
1017
1018=item C<AV* save_ary(GV *gv)>
1019
1020=item C<HV* save_hash(GV *gv)>
1021
1022Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
1023
1024=item C<void save_item(SV *item)>
1025
1026Duplicates the current value of C<SV>, on the exit from the current
1027C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
1028using the stored value.
1029
1030=item C<void save_list(SV **sarg, I32 maxsarg)>
1031
1032A variant of C<save_item> which takes multiple arguments via an array
1033C<sarg> of C<SV*> of length C<maxsarg>.
1034
1035=item C<SV* save_svref(SV **sptr)>
1036
1037Similar to C<save_scalar>, but will reinstate a C<SV *>.
1038
1039=item C<void save_aptr(AV **aptr)>
1040
1041=item C<void save_hptr(HV **hptr)>
1042
1043Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
1044
1045=back
1046
1047The C<Alias> module implements localization of the basic types within the
1048I<caller's scope>. People who are interested in how to localize things in
1049the containing scope should take a look there too.
1050
0a753a76 1051=head1 Subroutines
a0d0e21e 1052
68dc0745 1053=head2 XSUBs and the Argument Stack
5f05dabc
PP
1054
1055The XSUB mechanism is a simple way for Perl programs to access C subroutines.
1056An XSUB routine will have a stack that contains the arguments from the Perl
1057program, and a way to map from the Perl data structures to a C equivalent.
1058
1059The stack arguments are accessible through the C<ST(n)> macro, which returns
1060the C<n>'th stack argument. Argument 0 is the first argument passed in the
1061Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
1062an C<SV*> is used.
1063
1064Most of the time, output from the C routine can be handled through use of
1065the RETVAL and OUTPUT directives. However, there are some cases where the
1066argument stack is not already long enough to handle all the return values.
1067An example is the POSIX tzname() call, which takes no arguments, but returns
1068two, the local time zone's standard and summer time abbreviations.
1069
1070To handle this situation, the PPCODE directive is used and the stack is
1071extended using the macro:
1072
1073 EXTEND(sp, num);
1074
1075where C<sp> is the stack pointer, and C<num> is the number of elements the
1076stack should be extended by.
1077
1078Now that there is room on the stack, values can be pushed on it using the
54310121 1079macros to push IVs, doubles, strings, and SV pointers respectively:
5f05dabc
PP
1080
1081 PUSHi(IV)
1082 PUSHn(double)
1083 PUSHp(char*, I32)
1084 PUSHs(SV*)
1085
1086And now the Perl program calling C<tzname>, the two values will be assigned
1087as in:
1088
1089 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
1090
1091An alternate (and possibly simpler) method to pushing values on the stack is
1092to use the macros:
1093
1094 XPUSHi(IV)
1095 XPUSHn(double)
1096 XPUSHp(char*, I32)
1097 XPUSHs(SV*)
1098
1099These macros automatically adjust the stack for you, if needed. Thus, you
1100do not need to call C<EXTEND> to extend the stack.
1101
1102For more information, consult L<perlxs> and L<perlxstut>.
1103
1104=head2 Calling Perl Routines from within C Programs
a0d0e21e
LW
1105
1106There are four routines that can be used to call a Perl subroutine from
1107within a C program. These four are:
1108
1109 I32 perl_call_sv(SV*, I32);
1110 I32 perl_call_pv(char*, I32);
1111 I32 perl_call_method(char*, I32);
1112 I32 perl_call_argv(char*, I32, register char**);
1113
d1b91892
AD
1114The routine most often used is C<perl_call_sv>. The C<SV*> argument
1115contains either the name of the Perl subroutine to be called, or a
1116reference to the subroutine. The second argument consists of flags
1117that control the context in which the subroutine is called, whether
1118or not the subroutine is being passed arguments, how errors should be
1119trapped, and how to treat return values.
a0d0e21e
LW
1120
1121All four routines return the number of arguments that the subroutine returned
1122on the Perl stack.
1123
d1b91892
AD
1124When using any of these routines (except C<perl_call_argv>), the programmer
1125must manipulate the Perl stack. These include the following macros and
1126functions:
a0d0e21e
LW
1127
1128 dSP
1129 PUSHMARK()
1130 PUTBACK
1131 SPAGAIN
1132 ENTER
1133 SAVETMPS
1134 FREETMPS
1135 LEAVE
1136 XPUSH*()
cb1a09d0 1137 POP*()
a0d0e21e 1138
5f05dabc
PP
1139For a detailed description of calling conventions from C to Perl,
1140consult L<perlcall>.
a0d0e21e 1141
5f05dabc 1142=head2 Memory Allocation
a0d0e21e 1143
5f05dabc
PP
1144It is suggested that you use the version of malloc that is distributed
1145with Perl. It keeps pools of various sizes of unallocated memory in
07fa94a1
JO
1146order to satisfy allocation requests more quickly. However, on some
1147platforms, it may cause spurious malloc or free errors.
d1b91892
AD
1148
1149 New(x, pointer, number, type);
1150 Newc(x, pointer, number, type, cast);
1151 Newz(x, pointer, number, type);
1152
07fa94a1 1153These three macros are used to initially allocate memory.
5f05dabc
PP
1154
1155The first argument C<x> was a "magic cookie" that was used to keep track
1156of who called the macro, to help when debugging memory problems. However,
07fa94a1
JO
1157the current code makes no use of this feature (most Perl developers now
1158use run-time memory checkers), so this argument can be any number.
5f05dabc
PP
1159
1160The second argument C<pointer> should be the name of a variable that will
1161point to the newly allocated memory.
d1b91892 1162
d1b91892
AD
1163The third and fourth arguments C<number> and C<type> specify how many of
1164the specified type of data structure should be allocated. The argument
1165C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
1166should be used if the C<pointer> argument is different from the C<type>
1167argument.
1168
1169Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
1170to zero out all the newly allocated memory.
1171
1172 Renew(pointer, number, type);
1173 Renewc(pointer, number, type, cast);
1174 Safefree(pointer)
1175
1176These three macros are used to change a memory buffer size or to free a
1177piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1178match those of C<New> and C<Newc> with the exception of not needing the
1179"magic cookie" argument.
1180
1181 Move(source, dest, number, type);
1182 Copy(source, dest, number, type);
1183 Zero(dest, number, type);
1184
1185These three macros are used to move, copy, or zero out previously allocated
1186memory. The C<source> and C<dest> arguments point to the source and
1187destination starting points. Perl will move, copy, or zero out C<number>
1188instances of the size of the C<type> data structure (using the C<sizeof>
1189function).
a0d0e21e 1190
5f05dabc 1191=head2 PerlIO
ce3d39e2 1192
5f05dabc
PP
1193The most recent development releases of Perl has been experimenting with
1194removing Perl's dependency on the "normal" standard I/O suite and allowing
1195other stdio implementations to be used. This involves creating a new
1196abstraction layer that then calls whichever implementation of stdio Perl
68dc0745 1197was compiled with. All XSUBs should now use the functions in the PerlIO
5f05dabc
PP
1198abstraction layer and not make any assumptions about what kind of stdio
1199is being used.
1200
1201For a complete description of the PerlIO abstraction, consult L<perlapio>.
1202
8ebc5c01 1203=head2 Putting a C value on Perl stack
ce3d39e2
IZ
1204
1205A lot of opcodes (this is an elementary operation in the internal perl
1206stack machine) put an SV* on the stack. However, as an optimization
1207the corresponding SV is (usually) not recreated each time. The opcodes
1208reuse specially assigned SVs (I<target>s) which are (as a corollary)
1209not constantly freed/created.
1210
0a753a76 1211Each of the targets is created only once (but see
ce3d39e2
IZ
1212L<Scratchpads and recursion> below), and when an opcode needs to put
1213an integer, a double, or a string on stack, it just sets the
1214corresponding parts of its I<target> and puts the I<target> on stack.
1215
1216The macro to put this target on stack is C<PUSHTARG>, and it is
1217directly used in some opcodes, as well as indirectly in zillions of
1218others, which use it via C<(X)PUSH[pni]>.
1219
8ebc5c01 1220=head2 Scratchpads
ce3d39e2 1221
54310121 1222The question remains on when the SVs which are I<target>s for opcodes
5f05dabc
PP
1223are created. The answer is that they are created when the current unit --
1224a subroutine or a file (for opcodes for statements outside of
1225subroutines) -- is compiled. During this time a special anonymous Perl
ce3d39e2
IZ
1226array is created, which is called a scratchpad for the current
1227unit.
1228
54310121 1229A scratchpad keeps SVs which are lexicals for the current unit and are
ce3d39e2
IZ
1230targets for opcodes. One can deduce that an SV lives on a scratchpad
1231by looking on its flags: lexicals have C<SVs_PADMY> set, and
1232I<target>s have C<SVs_PADTMP> set.
1233
54310121
PP
1234The correspondence between OPs and I<target>s is not 1-to-1. Different
1235OPs in the compile tree of the unit can use the same target, if this
ce3d39e2
IZ
1236would not conflict with the expected life of the temporary.
1237
2ae324a7 1238=head2 Scratchpads and recursion
ce3d39e2
IZ
1239
1240In fact it is not 100% true that a compiled unit contains a pointer to
1241the scratchpad AV. In fact it contains a pointer to an AV of
1242(initially) one element, and this element is the scratchpad AV. Why do
1243we need an extra level of indirection?
1244
1245The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1246these can create several execution pointers going into the same
1247subroutine. For the subroutine-child not write over the temporaries
1248for the subroutine-parent (lifespan of which covers the call to the
1249child), the parent and the child should have different
1250scratchpads. (I<And> the lexicals should be separate anyway!)
1251
5f05dabc
PP
1252So each subroutine is born with an array of scratchpads (of length 1).
1253On each entry to the subroutine it is checked that the current
ce3d39e2
IZ
1254depth of the recursion is not more than the length of this array, and
1255if it is, new scratchpad is created and pushed into the array.
1256
1257The I<target>s on this scratchpad are C<undef>s, but they are already
1258marked with correct flags.
1259
0a753a76
PP
1260=head1 Compiled code
1261
1262=head2 Code tree
1263
1264Here we describe the internal form your code is converted to by
1265Perl. Start with a simple example:
1266
1267 $a = $b + $c;
1268
1269This is converted to a tree similar to this one:
1270
1271 assign-to
1272 / \
1273 + $a
1274 / \
1275 $b $c
1276
1277(but slightly more complicated). This tree reflect the way Perl
1278parsed your code, but has nothing to do with the execution order.
1279There is an additional "thread" going through the nodes of the tree
1280which shows the order of execution of the nodes. In our simplified
1281example above it looks like:
1282
1283 $b ---> $c ---> + ---> $a ---> assign-to
1284
1285But with the actual compile tree for C<$a = $b + $c> it is different:
1286some nodes I<optimized away>. As a corollary, though the actual tree
1287contains more nodes than our simplified example, the execution order
1288is the same as in our example.
1289
1290=head2 Examining the tree
1291
1292If you have your perl compiled for debugging (usually done with C<-D
1293optimize=-g> on C<Configure> command line), you may examine the
1294compiled tree by specifying C<-Dx> on the Perl command line. The
1295output takes several lines per node, and for C<$b+$c> it looks like
1296this:
1297
1298 5 TYPE = add ===> 6
1299 TARG = 1
1300 FLAGS = (SCALAR,KIDS)
1301 {
1302 TYPE = null ===> (4)
1303 (was rv2sv)
1304 FLAGS = (SCALAR,KIDS)
1305 {
1306 3 TYPE = gvsv ===> 4
1307 FLAGS = (SCALAR)
1308 GV = main::b
1309 }
1310 }
1311 {
1312 TYPE = null ===> (5)
1313 (was rv2sv)
1314 FLAGS = (SCALAR,KIDS)
1315 {
1316 4 TYPE = gvsv ===> 5
1317 FLAGS = (SCALAR)
1318 GV = main::c
1319 }
1320 }
1321
1322This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1323not optimized away (one per number in the left column). The immediate
1324children of the given node correspond to C<{}> pairs on the same level
1325of indentation, thus this listing corresponds to the tree:
1326
1327 add
1328 / \
1329 null null
1330 | |
1331 gvsv gvsv
1332
1333The execution order is indicated by C<===E<gt>> marks, thus it is C<3
13344 5 6> (node C<6> is not included into above listing), i.e.,
1335C<gvsv gvsv add whatever>.
1336
1337=head2 Compile pass 1: check routines
1338
1339The tree is created by the I<pseudo-compiler> while yacc code feeds it
1340the constructions it recognizes. Since yacc works bottom-up, so does
1341the first pass of perl compilation.
1342
1343What makes this pass interesting for perl developers is that some
1344optimization may be performed on this pass. This is optimization by
1345so-called I<check routines>. The correspondence between node names
1346and corresponding check routines is described in F<opcode.pl> (do not
1347forget to run C<make regen_headers> if you modify this file).
1348
1349A check routine is called when the node is fully constructed except
1350for the execution-order thread. Since at this time there is no
1351back-links to the currently constructed node, one can do most any
1352operation to the top-level node, including freeing it and/or creating
1353new nodes above/below it.
1354
1355The check routine returns the node which should be inserted into the
1356tree (if the top-level node was not modified, check routine returns
1357its argument).
1358
1359By convention, check routines have names C<ck_*>. They are usually
1360called from C<new*OP> subroutines (or C<convert>) (which in turn are
1361called from F<perly.y>).
1362
1363=head2 Compile pass 1a: constant folding
1364
1365Immediately after the check routine is called the returned node is
1366checked for being compile-time executable. If it is (the value is
1367judged to be constant) it is immediately executed, and a I<constant>
1368node with the "return value" of the corresponding subtree is
1369substituted instead. The subtree is deleted.
1370
1371If constant folding was not performed, the execution-order thread is
1372created.
1373
1374=head2 Compile pass 2: context propagation
1375
1376When a context for a part of compile tree is known, it is propagated
1377down through the tree. Aat this time the context can have 5 values
1378(instead of 2 for runtime context): void, boolean, scalar, list, and
1379lvalue. In contrast with the pass 1 this pass is processed from top
1380to bottom: a node's context determines the context for its children.
1381
1382Additional context-dependent optimizations are performed at this time.
1383Since at this moment the compile tree contains back-references (via
1384"thread" pointers), nodes cannot be free()d now. To allow
1385optimized-away nodes at this stage, such nodes are null()ified instead
1386of free()ing (i.e. their type is changed to OP_NULL).
1387
1388=head2 Compile pass 3: peephole optimization
1389
1390After the compile tree for a subroutine (or for an C<eval> or a file)
1391is created, an additional pass over the code is performed. This pass
1392is neither top-down or bottom-up, but in the execution order (with
1393additional compilications for conditionals). These optimizations are
1394done in the subroutine peep(). Optimizations performed at this stage
1395are subject to the same restrictions as in the pass 2.
1396
1397=head1 API LISTING
a0d0e21e 1398
cb1a09d0
AD
1399This is a listing of functions, macros, flags, and variables that may be
1400useful to extension writers or that may be found while reading other
1401extensions.
a0d0e21e 1402
cb1a09d0 1403=over 8
a0d0e21e 1404
cb1a09d0
AD
1405=item AvFILL
1406
fb73857a 1407Same as C<av_len>.
cb1a09d0
AD
1408
1409=item av_clear
1410
0146554f
GA
1411Clears an array, making it empty. Does not free the memory used by the
1412array itself.
cb1a09d0
AD
1413
1414 void av_clear _((AV* ar));
1415
1416=item av_extend
1417
1418Pre-extend an array. The C<key> is the index to which the array should be
1419extended.
1420
1421 void av_extend _((AV* ar, I32 key));
1422
1423=item av_fetch
1424
1425Returns the SV at the specified index in the array. The C<key> is the
1426index. If C<lval> is set then the fetch will be part of a store. Check
1427that the return value is non-null before dereferencing it to a C<SV*>.
1428
04343c6d
GS
1429See L<Understanding the Magic of Tied Hashes and Arrays> for more
1430information on how to use this function on tied arrays.
1431
cb1a09d0
AD
1432 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1433
1434=item av_len
1435
1436Returns the highest index in the array. Returns -1 if the array is empty.
1437
1438 I32 av_len _((AV* ar));
1439
1440=item av_make
1441
5fb8527f
PP
1442Creates a new AV and populates it with a list of SVs. The SVs are copied
1443into the array, so they may be freed after the call to av_make. The new AV
5f05dabc 1444will have a reference count of 1.
cb1a09d0
AD
1445
1446 AV* av_make _((I32 size, SV** svp));
1447
1448=item av_pop
1449
1450Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1451empty.
1452
1453 SV* av_pop _((AV* ar));
1454
1455=item av_push
1456
5fb8527f
PP
1457Pushes an SV onto the end of the array. The array will grow automatically
1458to accommodate the addition.
cb1a09d0
AD
1459
1460 void av_push _((AV* ar, SV* val));
1461
1462=item av_shift
1463
1464Shifts an SV off the beginning of the array.
1465
1466 SV* av_shift _((AV* ar));
1467
1468=item av_store
1469
1470Stores an SV in an array. The array index is specified as C<key>. The
04343c6d
GS
1471return value will be NULL if the operation failed or if the value did not
1472need to be actually stored within the array (as in the case of tied arrays).
1473Otherwise it can be dereferenced to get the original C<SV*>. Note that the
1474caller is responsible for suitably incrementing the reference count of C<val>
1475before the call, and decrementing it if the function returned NULL.
1476
1477See L<Understanding the Magic of Tied Hashes and Arrays> for more
1478information on how to use this function on tied arrays.
cb1a09d0
AD
1479
1480 SV** av_store _((AV* ar, I32 key, SV* val));
1481
1482=item av_undef
1483
0146554f 1484Undefines the array. Frees the memory used by the array itself.
cb1a09d0
AD
1485
1486 void av_undef _((AV* ar));
1487
1488=item av_unshift
1489
0146554f
GA
1490Unshift the given number of C<undef> values onto the beginning of the
1491array. The array will grow automatically to accommodate the addition.
1492You must then use C<av_store> to assign values to these new elements.
cb1a09d0
AD
1493
1494 void av_unshift _((AV* ar, I32 num));
1495
1496=item CLASS
1497
1498Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
5fb8527f
PP
1499constructor. This is always a C<char*>. See C<THIS> and
1500L<perlxs/"Using XS With C++">.
cb1a09d0
AD
1501
1502=item Copy
1503
1504The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1505source, C<d> is the destination, C<n> is the number of items, and C<t> is
0146554f 1506the type. May fail on overlapping copies. See also C<Move>.
cb1a09d0
AD
1507
1508 (void) Copy( s, d, n, t );
1509
1510=item croak
1511
1512This is the XSUB-writer's interface to Perl's C<die> function. Use this
1513function the same way you use the C C<printf> function. See C<warn>.
1514
1515=item CvSTASH
1516
1517Returns the stash of the CV.
1518
1519 HV * CvSTASH( SV* sv )
1520
1521=item DBsingle
1522
1523When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1524boolean which indicates whether subs are being single-stepped.
5fb8527f
PP
1525Single-stepping is automatically turned on after every step. This is the C
1526variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
cb1a09d0
AD
1527
1528=item DBsub
1529
1530When Perl is run in debugging mode, with the B<-d> switch, this GV contains
5fb8527f
PP
1531the SV which holds the name of the sub being debugged. This is the C
1532variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
cb1a09d0
AD
1533The sub name can be found by
1534
1535 SvPV( GvSV( DBsub ), na )
1536
5fb8527f
PP
1537=item DBtrace
1538
1539Trace variable used when Perl is run in debugging mode, with the B<-d>
1540switch. This is the C variable which corresponds to Perl's $DB::trace
1541variable. See C<DBsingle>.
1542
cb1a09d0
AD
1543=item dMARK
1544
5fb8527f
PP
1545Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1546C<dORIGMARK>.
cb1a09d0
AD
1547
1548=item dORIGMARK
1549
1550Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1551
5fb8527f
PP
1552=item dowarn
1553
1554The C variable which corresponds to Perl's $^W warning variable.
1555
cb1a09d0
AD
1556=item dSP
1557
5fb8527f 1558Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
cb1a09d0
AD
1559
1560=item dXSARGS
1561
1562Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1563usually handled automatically by C<xsubpp>. Declares the C<items> variable
1564to indicate the number of items on the stack.
1565
5fb8527f
PP
1566=item dXSI32
1567
1568Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1569handled automatically by C<xsubpp>.
1570
cb1a09d0
AD
1571=item ENTER
1572
1573Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1574
1575 ENTER;
1576
1577=item EXTEND
1578
1579Used to extend the argument stack for an XSUB's return values.
1580
1581 EXTEND( sp, int x );
1582
1583=item FREETMPS
1584
1585Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1586L<perlcall>.
1587
1588 FREETMPS;
1589
1590=item G_ARRAY
1591
54310121 1592Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
cb1a09d0
AD
1593
1594=item G_DISCARD
1595
1596Indicates that arguments returned from a callback should be discarded. See
1597L<perlcall>.
1598
1599=item G_EVAL
1600
1601Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1602
1603=item GIMME
1604
54310121
PP
1605A backward-compatible version of C<GIMME_V> which can only return
1606C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
1607
1608=item GIMME_V
1609
1610The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
1611C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
1612context, respectively.
cb1a09d0
AD
1613
1614=item G_NOARGS
1615
1616Indicates that no arguments are being sent to a callback. See L<perlcall>.
1617
1618=item G_SCALAR
1619
54310121
PP
1620Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
1621
1622=item G_VOID
1623
1624Used to indicate void context. See C<GIMME_V> and L<perlcall>.
cb1a09d0 1625
faed5253
JO
1626=item gv_fetchmeth
1627
1628Returns the glob with the given C<name> and a defined subroutine or
9607fc9c
PP
1629C<NULL>. The glob lives in the given C<stash>, or in the stashes
1630accessable via @ISA and @<UNIVERSAL>.
faed5253 1631
9607fc9c 1632The argument C<level> should be either 0 or -1. If C<level==0>, as a
0a753a76
PP
1633side-effect creates a glob with the given C<name> in the given
1634C<stash> which in the case of success contains an alias for the
1635subroutine, and sets up caching info for this glob. Similarly for all
1636the searched stashes.
1637
9607fc9c
PP
1638This function grants C<"SUPER"> token as a postfix of the stash name.
1639
0a753a76
PP
1640The GV returned from C<gv_fetchmeth> may be a method cache entry,
1641which is not visible to Perl code. So when calling C<perl_call_sv>,
1642you should not use the GV directly; instead, you should use the
1643method's CV, which can be obtained from the GV with the C<GvCV> macro.
faed5253
JO
1644
1645 GV* gv_fetchmeth _((HV* stash, char* name, STRLEN len, I32 level));
1646
1647=item gv_fetchmethod
1648
dc848c6f
PP
1649=item gv_fetchmethod_autoload
1650
faed5253 1651Returns the glob which contains the subroutine to call to invoke the
dc848c6f
PP
1652method on the C<stash>. In fact in the presense of autoloading this may
1653be the glob for "AUTOLOAD". In this case the corresponding variable
faed5253
JO
1654$AUTOLOAD is already setup.
1655
dc848c6f
PP
1656The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
1657lookup is performed if the given method is not present: non-zero means
1658yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
1659C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
1660non-zero C<autoload> parameter.
1661
1662These functions grant C<"SUPER"> token as a prefix of the method name.
1663
1664Note that if you want to keep the returned glob for a long time, you
1665need to check for it being "AUTOLOAD", since at the later time the call
faed5253
JO
1666may load a different subroutine due to $AUTOLOAD changing its value.
1667Use the glob created via a side effect to do this.
1668
dc848c6f
PP
1669These functions have the same side-effects and as C<gv_fetchmeth> with
1670C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
0a753a76 1671The warning against passing the GV returned by C<gv_fetchmeth> to
dc848c6f 1672C<perl_call_sv> apply equally to these functions.
faed5253
JO
1673
1674 GV* gv_fetchmethod _((HV* stash, char* name));
dc848c6f
PP
1675 GV* gv_fetchmethod_autoload _((HV* stash, char* name,
1676 I32 autoload));
faed5253 1677
cb1a09d0
AD
1678=item gv_stashpv
1679
1680Returns a pointer to the stash for a specified package. If C<create> is set
1681then the package will be created if it does not already exist. If C<create>
1682is not set and the package does not exist then NULL is returned.
1683
1684 HV* gv_stashpv _((char* name, I32 create));
1685
1686=item gv_stashsv
1687
1688Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1689
1690 HV* gv_stashsv _((SV* sv, I32 create));
1691
e5581bf4 1692=item GvSV
cb1a09d0 1693
e5581bf4 1694Return the SV from the GV.
44a8e56a 1695
1e422769
PP
1696=item HEf_SVKEY
1697
1698This flag, used in the length slot of hash entries and magic
1699structures, specifies the structure contains a C<SV*> pointer where a
1700C<char*> pointer is to be expected. (For information only--not to be used).
1701
1e422769
PP
1702=item HeHASH
1703
1704Returns the computed hash (type C<U32>) stored in the hash entry.
1705
1706 HeHASH(HE* he)
1707
1708=item HeKEY
1709
1710Returns the actual pointer stored in the key slot of the hash entry.
1711The pointer may be either C<char*> or C<SV*>, depending on the value of
1712C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
1713are usually preferable for finding the value of a key.
1714
1715 HeKEY(HE* he)
1716
1717=item HeKLEN
1718
1719If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
1720holds an C<SV*> key. Otherwise, holds the actual length of the key.
1721Can be assigned to. The C<HePV()> macro is usually preferable for finding
1722key lengths.
1723
1724 HeKLEN(HE* he)
1725
1726=item HePV
1727
1728Returns the key slot of the hash entry as a C<char*> value, doing any
1729necessary dereferencing of possibly C<SV*> keys. The length of
1730the string is placed in C<len> (this is a macro, so do I<not> use
1731C<&len>). If you do not care about what the length of the key is,
1732you may use the global variable C<na>. Remember though, that hash
1733keys in perl are free to contain embedded nulls, so using C<strlen()>
1734or similar is not a good way to find the length of hash keys.
1735This is very similar to the C<SvPV()> macro described elsewhere in
1736this document.
1737
1738 HePV(HE* he, STRLEN len)
1739
1740=item HeSVKEY
1741
1742Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
1743does not contain an C<SV*> key.
1744
1745 HeSVKEY(HE* he)
1746
1747=item HeSVKEY_force
1748
1749Returns the key as an C<SV*>. Will create and return a temporary
1750mortal C<SV*> if the hash entry contains only a C<char*> key.
1751
1752 HeSVKEY_force(HE* he)
1753
1754=item HeSVKEY_set
1755
1756Sets the key to a given C<SV*>, taking care to set the appropriate flags
1757to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
1758
1759 HeSVKEY_set(HE* he, SV* sv)
1760
1761=item HeVAL
1762
1763Returns the value slot (type C<SV*>) stored in the hash entry.
1764
1765 HeVAL(HE* he)
1766
cb1a09d0
AD
1767=item hv_clear
1768
1769Clears a hash, making it empty.
1770
1771 void hv_clear _((HV* tb));
1772
68dc0745
PP
1773=item hv_delayfree_ent
1774
1775Releases a hash entry, such as while iterating though the hash, but
1776delays actual freeing of key and value until the end of the current
1777statement (or thereabouts) with C<sv_2mortal>. See C<hv_iternext>
1778and C<hv_free_ent>.
1779
1780 void hv_delayfree_ent _((HV* hv, HE* entry));
1781
cb1a09d0
AD
1782=item hv_delete
1783
1784Deletes a key/value pair in the hash. The value SV is removed from the hash
5fb8527f 1785and returned to the caller. The C<klen> is the length of the key. The
04343c6d 1786C<flags> value will normally be zero; if set to G_DISCARD then NULL will be
cb1a09d0
AD
1787returned.
1788
1789 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1790
1e422769
PP
1791=item hv_delete_ent
1792
1793Deletes a key/value pair in the hash. The value SV is removed from the hash
1794and returned to the caller. The C<flags> value will normally be zero; if set
04343c6d 1795to G_DISCARD then NULL will be returned. C<hash> can be a valid precomputed
1e422769
PP
1796hash value, or 0 to ask for it to be computed.
1797
1798 SV* hv_delete_ent _((HV* tb, SV* key, I32 flags, U32 hash));
1799
cb1a09d0
AD
1800=item hv_exists
1801
1802Returns a boolean indicating whether the specified hash key exists. The
5fb8527f 1803C<klen> is the length of the key.
cb1a09d0
AD
1804
1805 bool hv_exists _((HV* tb, char* key, U32 klen));
1806
1e422769
PP
1807=item hv_exists_ent
1808
1809Returns a boolean indicating whether the specified hash key exists. C<hash>
54310121 1810can be a valid precomputed hash value, or 0 to ask for it to be computed.
1e422769
PP
1811
1812 bool hv_exists_ent _((HV* tb, SV* key, U32 hash));
1813
cb1a09d0
AD
1814=item hv_fetch
1815
1816Returns the SV which corresponds to the specified key in the hash. The
5fb8527f 1817C<klen> is the length of the key. If C<lval> is set then the fetch will be
cb1a09d0
AD
1818part of a store. Check that the return value is non-null before
1819dereferencing it to a C<SV*>.
1820
04343c6d
GS
1821See L<Understanding the Magic of Tied Hashes and Arrays> for more
1822information on how to use this function on tied hashes.
1823
cb1a09d0
AD
1824 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1825
1e422769
PP
1826=item hv_fetch_ent
1827
1828Returns the hash entry which corresponds to the specified key in the hash.
54310121 1829C<hash> must be a valid precomputed hash number for the given C<key>, or
1e422769
PP
18300 if you want the function to compute it. IF C<lval> is set then the
1831fetch will be part of a store. Make sure the return value is non-null
1832before accessing it. The return value when C<tb> is a tied hash
1833is a pointer to a static location, so be sure to make a copy of the
1834structure if you need to store it somewhere.
1835
04343c6d
GS
1836See L<Understanding the Magic of Tied Hashes and Arrays> for more
1837information on how to use this function on tied hashes.
1838
1e422769
PP
1839 HE* hv_fetch_ent _((HV* tb, SV* key, I32 lval, U32 hash));
1840
68dc0745
PP
1841=item hv_free_ent
1842
1843Releases a hash entry, such as while iterating though the hash. See
1844C<hv_iternext> and C<hv_delayfree_ent>.
1845
1846 void hv_free_ent _((HV* hv, HE* entry));
1847
cb1a09d0
AD
1848=item hv_iterinit
1849
1850Prepares a starting point to traverse a hash table.
1851
1852 I32 hv_iterinit _((HV* tb));
1853
fb73857a
PP
1854Note that hv_iterinit I<currently> returns the number of I<buckets> in
1855the hash and I<not> the number of keys (as indicated in the Advanced
1856Perl Programming book). This may change in future. Use the HvKEYS(hv)
1857macro to find the number of keys in a hash.
1858
cb1a09d0
AD
1859=item hv_iterkey
1860
1861Returns the key from the current position of the hash iterator. See
1862C<hv_iterinit>.
1863
1864 char* hv_iterkey _((HE* entry, I32* retlen));
1865
1e422769 1866=item hv_iterkeysv
3fe9a6f1 1867
1e422769
PP
1868Returns the key as an C<SV*> from the current position of the hash
1869iterator. The return value will always be a mortal copy of the
1870key. Also see C<hv_iterinit>.
1871
1872 SV* hv_iterkeysv _((HE* entry));
1873
cb1a09d0
AD
1874=item hv_iternext
1875
1876Returns entries from a hash iterator. See C<hv_iterinit>.
1877
1878 HE* hv_iternext _((HV* tb));
1879
1880=item hv_iternextsv
1881
1882Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1883operation.
1884
1885 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1886
1887=item hv_iterval
1888
1889Returns the value from the current position of the hash iterator. See
1890C<hv_iterkey>.
1891
1892 SV* hv_iterval _((HV* tb, HE* entry));
1893
1894=item hv_magic
1895
1896Adds magic to a hash. See C<sv_magic>.
1897
1898 void hv_magic _((HV* hv, GV* gv, int how));
1899
1900=item HvNAME
1901
1902Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1903
1904 char *HvNAME (HV* stash)
1905
1906=item hv_store
1907
1908Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
54310121 1909the length of the key. The C<hash> parameter is the precomputed hash
cb1a09d0 1910value; if it is zero then Perl will compute it. The return value will be
04343c6d
GS
1911NULL if the operation failed or if the value did not need to be actually
1912stored within the hash (as in the case of tied hashes). Otherwise it can
1913be dereferenced to get the original C<SV*>. Note that the caller is
1914responsible for suitably incrementing the reference count of C<val>
1915before the call, and decrementing it if the function returned NULL.
1916
1917See L<Understanding the Magic of Tied Hashes and Arrays> for more
1918information on how to use this function on tied hashes.
cb1a09d0
AD
1919
1920 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1921
1e422769
PP
1922=item hv_store_ent
1923
1924Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
54310121 1925parameter is the precomputed hash value; if it is zero then Perl will
1e422769 1926compute it. The return value is the new hash entry so created. It will be
04343c6d
GS
1927NULL if the operation failed or if the value did not need to be actually
1928stored within the hash (as in the case of tied hashes). Otherwise the
1929contents of the return value can be accessed using the C<He???> macros
1930described here. Note that the caller is responsible for suitably
1931incrementing the reference count of C<val> before the call, and decrementing
1932it if the function returned NULL.
1933
1934See L<Understanding the Magic of Tied Hashes and Arrays> for more
1935information on how to use this function on tied hashes.
1e422769
PP
1936
1937 HE* hv_store_ent _((HV* tb, SV* key, SV* val, U32 hash));
1938
cb1a09d0
AD
1939=item hv_undef
1940
1941Undefines the hash.
1942
1943 void hv_undef _((HV* tb));
1944
1945=item isALNUM
1946
1947Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
5f05dabc 1948character or digit.
cb1a09d0
AD
1949
1950 int isALNUM (char c)
1951
1952=item isALPHA
1953
5fb8527f 1954Returns a boolean indicating whether the C C<char> is an ascii alphabetic
cb1a09d0
AD
1955character.
1956
1957 int isALPHA (char c)
1958
1959=item isDIGIT
1960
1961Returns a boolean indicating whether the C C<char> is an ascii digit.
1962
1963 int isDIGIT (char c)
1964
1965=item isLOWER
1966
1967Returns a boolean indicating whether the C C<char> is a lowercase character.
1968
1969 int isLOWER (char c)
1970
1971=item isSPACE
1972
1973Returns a boolean indicating whether the C C<char> is whitespace.
1974
1975 int isSPACE (char c)
1976
1977=item isUPPER
1978
1979Returns a boolean indicating whether the C C<char> is an uppercase character.
1980
1981 int isUPPER (char c)
1982
1983=item items
1984
1985Variable which is setup by C<xsubpp> to indicate the number of items on the
5fb8527f
PP
1986stack. See L<perlxs/"Variable-length Parameter Lists">.
1987
1988=item ix
1989
1990Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1991was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
cb1a09d0
AD
1992
1993=item LEAVE
1994
1995Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1996
1997 LEAVE;
1998
1999=item MARK
2000
5fb8527f 2001Stack marker variable for the XSUB. See C<dMARK>.
cb1a09d0
AD
2002
2003=item mg_clear
2004
2005Clear something magical that the SV represents. See C<sv_magic>.
2006
2007 int mg_clear _((SV* sv));
2008
2009=item mg_copy
2010
2011Copies the magic from one SV to another. See C<sv_magic>.
2012
2013 int mg_copy _((SV *, SV *, char *, STRLEN));
2014
2015=item mg_find
2016
2017Finds the magic pointer for type matching the SV. See C<sv_magic>.
2018
2019 MAGIC* mg_find _((SV* sv, int type));
2020
2021=item mg_free
2022
2023Free any magic storage used by the SV. See C<sv_magic>.
2024
2025 int mg_free _((SV* sv));
2026
2027=item mg_get
2028
2029Do magic after a value is retrieved from the SV. See C<sv_magic>.
2030
2031 int mg_get _((SV* sv));
2032
2033=item mg_len
2034
2035Report on the SV's length. See C<sv_magic>.
2036
2037 U32 mg_len _((SV* sv));
2038
2039=item mg_magical
2040
2041Turns on the magical status of an SV. See C<sv_magic>.
2042
2043 void mg_magical _((SV* sv));
2044
2045=item mg_set
2046
2047Do magic after a value is assigned to the SV. See C<sv_magic>.
2048
2049 int mg_set _((SV* sv));
2050
2051=item Move
2052
2053The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
2054source, C<d> is the destination, C<n> is the number of items, and C<t> is
0146554f 2055the type. Can do overlapping moves. See also C<Copy>.
cb1a09d0
AD
2056
2057 (void) Move( s, d, n, t );
2058
2059=item na
2060
2061A variable which may be used with C<SvPV> to tell Perl to calculate the
2062string length.
2063
2064=item New
2065
2066The XSUB-writer's interface to the C C<malloc> function.
2067
2068 void * New( x, void *ptr, int size, type )
2069
2070=item Newc
2071
2072The XSUB-writer's interface to the C C<malloc> function, with cast.
2073
2074 void * Newc( x, void *ptr, int size, type, cast )
2075
2076=item Newz
2077
2078The XSUB-writer's interface to the C C<malloc> function. The allocated
2079memory is zeroed with C<memzero>.
2080
2081 void * Newz( x, void *ptr, int size, type )
2082
2083=item newAV
2084
5f05dabc 2085Creates a new AV. The reference count is set to 1.
cb1a09d0
AD
2086
2087 AV* newAV _((void));
2088
2089=item newHV
2090
5f05dabc 2091Creates a new HV. The reference count is set to 1.
cb1a09d0
AD
2092
2093 HV* newHV _((void));
2094
5f05dabc 2095=item newRV_inc
cb1a09d0 2096
5f05dabc 2097Creates an RV wrapper for an SV. The reference count for the original SV is
cb1a09d0
AD
2098incremented.
2099
5f05dabc
PP
2100 SV* newRV_inc _((SV* ref));
2101
2102For historical reasons, "newRV" is a synonym for "newRV_inc".
2103
2104=item newRV_noinc
2105
2106Creates an RV wrapper for an SV. The reference count for the original
2107SV is B<not> incremented.
2108
07fa94a1 2109 SV* newRV_noinc _((SV* ref));
cb1a09d0
AD
2110
2111=item newSV
2112
2113Creates a new SV. The C<len> parameter indicates the number of bytes of
68dc0745 2114preallocated string space the SV should have. The reference count for the
07fa94a1 2115new SV is set to 1.
cb1a09d0
AD
2116
2117 SV* newSV _((STRLEN len));
2118
2119=item newSViv
2120
07fa94a1
JO
2121Creates a new SV and copies an integer into it. The reference count for the
2122SV is set to 1.
cb1a09d0
AD
2123
2124 SV* newSViv _((IV i));
2125
2126=item newSVnv
2127
07fa94a1
JO
2128Creates a new SV and copies a double into it. The reference count for the
2129SV is set to 1.
cb1a09d0
AD
2130
2131 SV* newSVnv _((NV i));
2132
2133=item newSVpv
2134
07fa94a1
JO
2135Creates a new SV and copies a string into it. The reference count for the
2136SV is set to 1. If C<len> is zero then Perl will compute the length.
cb1a09d0
AD
2137
2138 SV* newSVpv _((char* s, STRLEN len));
2139
2140=item newSVrv
2141
2142Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
5fb8527f 2143it will be upgraded to one. If C<classname> is non-null then the new SV will
cb1a09d0 2144be blessed in the specified package. The new SV is returned and its
5f05dabc 2145reference count is 1.
8ebc5c01 2146
cb1a09d0
AD
2147 SV* newSVrv _((SV* rv, char* classname));
2148
2149=item newSVsv
2150
5fb8527f 2151Creates a new SV which is an exact duplicate of the original SV.
cb1a09d0
AD
2152
2153 SV* newSVsv _((SV* old));
2154
2155=item newXS
2156
2157Used by C<xsubpp> to hook up XSUBs as Perl subs.
2158
2159=item newXSproto
2160
2161Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
2162the subs.
2163
2164=item Nullav
2165
2166Null AV pointer.
2167
2168=item Nullch
2169
2170Null character pointer.
2171
2172=item Nullcv
2173
2174Null CV pointer.
2175
2176=item Nullhv
2177
2178Null HV pointer.
2179
2180=item Nullsv
2181
2182Null SV pointer.
2183
2184=item ORIGMARK
2185
2186The original stack mark for the XSUB. See C<dORIGMARK>.
2187
2188=item perl_alloc
2189
2190Allocates a new Perl interpreter. See L<perlembed>.
2191
2192=item perl_call_argv
2193
2194Performs a callback to the specified Perl sub. See L<perlcall>.
2195
2196 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
2197
2198=item perl_call_method
2199
2200Performs a callback to the specified Perl method. The blessed object must
2201be on the stack. See L<perlcall>.
2202
2203 I32 perl_call_method _((char* methname, I32 flags));
2204
2205=item perl_call_pv
2206
2207Performs a callback to the specified Perl sub. See L<perlcall>.
2208
2209 I32 perl_call_pv _((char* subname, I32 flags));
2210
2211=item perl_call_sv
2212
2213Performs a callback to the Perl sub whose name is in the SV. See
2214L<perlcall>.
2215
2216 I32 perl_call_sv _((SV* sv, I32 flags));
2217
2218=item perl_construct
2219
2220Initializes a new Perl interpreter. See L<perlembed>.
2221
2222=item perl_destruct
2223
2224Shuts down a Perl interpreter. See L<perlembed>.
2225
2226=item perl_eval_sv
2227
2228Tells Perl to C<eval> the string in the SV.
2229
2230 I32 perl_eval_sv _((SV* sv, I32 flags));
2231
137443ea
PP
2232=item perl_eval_pv
2233
2234Tells Perl to C<eval> the given string and return an SV* result.
2235
2236 SV* perl_eval_pv _((char* p, I32 croak_on_error));
2237
cb1a09d0
AD
2238=item perl_free
2239
2240Releases a Perl interpreter. See L<perlembed>.
2241
2242=item perl_get_av
2243
2244Returns the AV of the specified Perl array. If C<create> is set and the
2245Perl variable does not exist then it will be created. If C<create> is not
04343c6d 2246set and the variable does not exist then NULL is returned.
cb1a09d0
AD
2247
2248 AV* perl_get_av _((char* name, I32 create));
2249
2250=item perl_get_cv
2251
2252Returns the CV of the specified Perl sub. If C<create> is set and the Perl
2253variable does not exist then it will be created. If C<create> is not
04343c6d 2254set and the variable does not exist then NULL is returned.
cb1a09d0
AD
2255
2256 CV* perl_get_cv _((char* name, I32 create));
2257
2258=item perl_get_hv
2259
2260Returns the HV of the specified Perl hash. If C<create> is set and the Perl
2261variable does not exist then it will be created. If C<create> is not
04343c6d 2262set and the variable does not exist then NULL is returned.
cb1a09d0
AD
2263
2264 HV* perl_get_hv _((char* name, I32 create));
2265
2266=item perl_get_sv
2267
2268Returns the SV of the specified Perl scalar. If C<create> is set and the
2269Perl variable does not exist then it will be created. If C<create> is not
04343c6d 2270set and the variable does not exist then NULL is returned.
cb1a09d0
AD
2271
2272 SV* perl_get_sv _((char* name, I32 create));
2273
2274=item perl_parse
2275
2276Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
2277
2278=item perl_require_pv
2279
2280Tells Perl to C<require> a module.
2281
2282 void perl_require_pv _((char* pv));
2283
2284=item perl_run
2285
2286Tells a Perl interpreter to run. See L<perlembed>.
2287
2288=item POPi
2289
2290Pops an integer off the stack.
2291
2292 int POPi();
2293
2294=item POPl
2295
2296Pops a long off the stack.
2297
2298 long POPl();
2299
2300=item POPp
2301
2302Pops a string off the stack.
2303
2304 char * POPp();
2305
2306=item POPn
2307
2308Pops a double off the stack.
2309
2310 double POPn();
2311
2312=item POPs
2313
2314Pops an SV off the stack.
2315
2316 SV* POPs();
2317
2318=item PUSHMARK
2319
2320Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2321
2322 PUSHMARK(p)
2323
2324=item PUSHi
2325
2326Push an integer onto the stack. The stack must have room for this element.
2327See C<XPUSHi>.
2328
2329 PUSHi(int d)
2330
2331=item PUSHn
2332
2333Push a double onto the stack. The stack must have room for this element.
2334See C<XPUSHn>.
2335
2336 PUSHn(double d)
2337
2338=item PUSHp
2339
2340Push a string onto the stack. The stack must have room for this element.
2341The C<len> indicates the length of the string. See C<XPUSHp>.
2342
2343 PUSHp(char *c, int len )
2344
2345=item PUSHs
2346
2347Push an SV onto the stack. The stack must have room for this element. See
2348C<XPUSHs>.
2349
2350 PUSHs(sv)
2351
2352=item PUTBACK
2353
2354Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2355See C<PUSHMARK> and L<perlcall> for other uses.
2356
2357 PUTBACK;
2358
2359=item Renew
2360
2361The XSUB-writer's interface to the C C<realloc> function.
2362
2363 void * Renew( void *ptr, int size, type )
2364
2365=item Renewc
2366
2367The XSUB-writer's interface to the C C<realloc> function, with cast.
2368
2369 void * Renewc( void *ptr, int size, type, cast )
2370
2371=item RETVAL
2372
2373Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
5fb8527f
PP
2374This is always the proper type for the XSUB.
2375See L<perlxs/"The RETVAL Variable">.
cb1a09d0
AD
2376
2377=item safefree
2378
2379The XSUB-writer's interface to the C C<free> function.
2380
2381=item safemalloc
2382
2383The XSUB-writer's interface to the C C<malloc> function.
2384
2385=item saferealloc
2386
2387The XSUB-writer's interface to the C C<realloc> function.
2388
2389=item savepv
2390
2391Copy a string to a safe spot. This does not use an SV.
2392
2393 char* savepv _((char* sv));
2394
2395=item savepvn
2396
2397Copy a string to a safe spot. The C<len> indicates number of bytes to
2398copy. This does not use an SV.
2399
2400 char* savepvn _((char* sv, I32 len));
2401
2402=item SAVETMPS
2403
2404Opening bracket for temporaries on a callback. See C<FREETMPS> and
2405L<perlcall>.
2406
2407 SAVETMPS;
2408
2409=item SP
2410
2411Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2412C<SPAGAIN>.
2413
2414=item SPAGAIN
2415
54310121 2416Refetch the stack pointer. Used after a callback. See L<perlcall>.
cb1a09d0
AD
2417
2418 SPAGAIN;
2419
2420=item ST
2421
2422Used to access elements on the XSUB's stack.
2423
2424 SV* ST(int x)
2425
2426=item strEQ
2427
2428Test two strings to see if they are equal. Returns true or false.
2429
2430 int strEQ( char *s1, char *s2 )
2431
2432=item strGE
2433
2434Test two strings to see if the first, C<s1>, is greater than or equal to the
2435second, C<s2>. Returns true or false.
2436
2437 int strGE( char *s1, char *s2 )
2438
2439=item strGT
2440
2441Test two strings to see if the first, C<s1>, is greater than the second,
2442C<s2>. Returns true or false.
2443
2444 int strGT( char *s1, char *s2 )
2445
2446=item strLE
2447
2448Test two strings to see if the first, C<s1>, is less than or equal to the
2449second, C<s2>. Returns true or false.
2450
2451 int strLE( char *s1, char *s2 )
2452
2453=item strLT
2454
2455Test two strings to see if the first, C<s1>, is less than the second,
2456C<s2>. Returns true or false.
2457
2458 int strLT( char *s1, char *s2 )
2459
2460=item strNE
2461
2462Test two strings to see if they are different. Returns true or false.
2463
2464 int strNE( char *s1, char *s2 )
2465
2466=item strnEQ
2467
2468Test two strings to see if they are equal. The C<len> parameter indicates
2469the number of bytes to compare. Returns true or false.
2470
2471 int strnEQ( char *s1, char *s2 )
2472
2473=item strnNE
2474
2475Test two strings to see if they are different. The C<len> parameter
2476indicates the number of bytes to compare. Returns true or false.
2477
2478 int strnNE( char *s1, char *s2, int len )
2479
2480=item sv_2mortal
2481
2482Marks an SV as mortal. The SV will be destroyed when the current context
2483ends.
2484
2485 SV* sv_2mortal _((SV* sv));
2486
2487=item sv_bless
2488
2489Blesses an SV into a specified package. The SV must be an RV. The package
07fa94a1
JO
2490must be designated by its stash (see C<gv_stashpv()>). The reference count
2491of the SV is unaffected.
cb1a09d0
AD
2492
2493 SV* sv_bless _((SV* sv, HV* stash));
2494
2495=item sv_catpv
2496
2497Concatenates the string onto the end of the string which is in the SV.
2498
2499 void sv_catpv _((SV* sv, char* ptr));
2500
2501=item sv_catpvn
2502
2503Concatenates the string onto the end of the string which is in the SV. The
2504C<len> indicates number of bytes to copy.
2505
2506 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
2507
46fc3d4c
PP
2508=item sv_catpvf
2509
2510Processes its arguments like C<sprintf> and appends the formatted output
2511to an SV.
2512
2513 void sv_catpvf _((SV* sv, const char* pat, ...));
2514
cb1a09d0
AD
2515=item sv_catsv
2516
5fb8527f 2517Concatenates the string from SV C<ssv> onto the end of the string in SV
cb1a09d0
AD
2518C<dsv>.
2519
2520 void sv_catsv _((SV* dsv, SV* ssv));
2521
5fb8527f
PP
2522=item sv_cmp
2523
2524Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2525string in C<sv1> is less than, equal to, or greater than the string in
2526C<sv2>.
2527
2528 I32 sv_cmp _((SV* sv1, SV* sv2));
2529
cb1a09d0
AD
2530=item SvCUR
2531
2532Returns the length of the string which is in the SV. See C<SvLEN>.
2533
2534 int SvCUR (SV* sv)
2535
2536=item SvCUR_set
2537
2538Set the length of the string which is in the SV. See C<SvCUR>.
2539
2540 SvCUR_set (SV* sv, int val )
2541
5fb8527f
PP
2542=item sv_dec
2543
5f05dabc 2544Auto-decrement of the value in the SV.
5fb8527f
PP
2545
2546 void sv_dec _((SV* sv));
2547
cb1a09d0
AD
2548=item SvEND
2549
2550Returns a pointer to the last character in the string which is in the SV.
2551See C<SvCUR>. Access the character as
2552
2553 *SvEND(sv)
2554
5fb8527f
PP
2555=item sv_eq
2556
2557Returns a boolean indicating whether the strings in the two SVs are
2558identical.
2559
2560 I32 sv_eq _((SV* sv1, SV* sv2));
2561
cb1a09d0
AD
2562=item SvGROW
2563
5fb8527f
PP
2564Expands the character buffer in the SV. Calls C<sv_grow> to perform the
2565expansion if necessary. Returns a pointer to the character buffer.
cb1a09d0
AD
2566
2567 char * SvGROW( SV* sv, int len )
2568
5fb8527f
PP
2569=item sv_grow
2570
2571Expands the character buffer in the SV. This will use C<sv_unref> and will
2572upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2573Use C<SvGROW>.
2574
2575=item sv_inc
2576
07fa94a1 2577Auto-increment of the value in the SV.
5fb8527f
PP
2578
2579 void sv_inc _((SV* sv));
2580
cb1a09d0
AD
2581=item SvIOK
2582
2583Returns a boolean indicating whether the SV contains an integer.
2584
2585 int SvIOK (SV* SV)
2586
2587=item SvIOK_off
2588
2589Unsets the IV status of an SV.
2590
2591 SvIOK_off (SV* sv)
2592
2593=item SvIOK_on
2594
2595Tells an SV that it is an integer.
2596
2597 SvIOK_on (SV* sv)
2598
5fb8527f
PP
2599=item SvIOK_only
2600
2601Tells an SV that it is an integer and disables all other OK bits.
2602
2603 SvIOK_on (SV* sv)
2604
cb1a09d0
AD
2605=item SvIOKp
2606
2607Returns a boolean indicating whether the SV contains an integer. Checks the
2608B<private> setting. Use C<SvIOK>.
2609
2610 int SvIOKp (SV* SV)
2611
2612=item sv_isa
2613
2614Returns a boolean indicating whether the SV is blessed into the specified
2615class. This does not know how to check for subtype, so it doesn't work in
2616an inheritance relationship.
2617
2618 int sv_isa _((SV* sv, char* name));
2619
2620=item SvIV
2621
2622Returns the integer which is in the SV.
2623
2624 int SvIV (SV* sv)
2625
2626=item sv_isobject
2627
2628Returns a boolean indicating whether the SV is an RV pointing to a blessed
2629object. If the SV is not an RV, or if the object is not blessed, then this
2630will return false.
2631
2632 int sv_isobject _((SV* sv));
2633
2634=item SvIVX
2635
2636Returns the integer which is stored in the SV.
2637
2638 int SvIVX (SV* sv);
2639
2640=item SvLEN
2641
2642Returns the size of the string buffer in the SV. See C<SvCUR>.
2643
2644 int SvLEN (SV* sv)
2645
5fb8527f
PP
2646=item sv_len
2647
2648Returns the length of the string in the SV. Use C<SvCUR>.
2649
2650 STRLEN sv_len _((SV* sv));
2651
cb1a09d0
AD
2652=item sv_magic
2653
2654Adds magic to an SV.
2655
2656 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2657
2658=item sv_mortalcopy
2659
2660Creates a new SV which is a copy of the original SV. The new SV is marked
5f05dabc 2661as mortal.
cb1a09d0
AD
2662
2663 SV* sv_mortalcopy _((SV* oldsv));
2664
2665=item SvOK
2666
2667Returns a boolean indicating whether the value is an SV.
2668
2669 int SvOK (SV* sv)
2670
2671=item sv_newmortal
2672
5f05dabc 2673Creates a new SV which is mortal. The reference count of the SV is set to 1.
cb1a09d0
AD
2674
2675 SV* sv_newmortal _((void));
2676
2677=item sv_no
2678
2679This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2680
2681=item SvNIOK
2682
2683Returns a boolean indicating whether the SV contains a number, integer or
2684double.
2685
2686 int SvNIOK (SV* SV)
2687
2688=item SvNIOK_off
2689
2690Unsets the NV/IV status of an SV.
2691
2692 SvNIOK_off (SV* sv)
2693
2694=item SvNIOKp
2695
2696Returns a boolean indicating whether the SV contains a number, integer or
2697double. Checks the B<private> setting. Use C<SvNIOK>.
2698
2699 int SvNIOKp (SV* SV)
2700
2701=item SvNOK
2702
2703Returns a boolean indicating whether the SV contains a double.
2704
2705 int SvNOK (SV* SV)
2706
2707=item SvNOK_off
2708
2709Unsets the NV status of an SV.
2710
2711 SvNOK_off (SV* sv)
2712
2713=item SvNOK_on
2714
2715Tells an SV that it is a double.
2716
2717 SvNOK_on (SV* sv)
2718
5fb8527f
PP
2719=item SvNOK_only
2720
2721Tells an SV that it is a double and disables all other OK bits.
2722
2723 SvNOK_on (SV* sv)
2724
cb1a09d0
AD
2725=item SvNOKp
2726
2727Returns a boolean indicating whether the SV contains a double. Checks the
2728B<private> setting. Use C<SvNOK>.
2729
2730 int SvNOKp (SV* SV)
2731
2732=item SvNV
2733
2734Returns the double which is stored in the SV.
2735
2736 double SvNV (SV* sv);
2737
2738=item SvNVX
2739
2740Returns the double which is stored in the SV.
2741
2742 double SvNVX (SV* sv);
2743
2744=item SvPOK
2745
2746Returns a boolean indicating whether the SV contains a character string.
2747
2748 int SvPOK (SV* SV)
2749
2750=item SvPOK_off
2751
2752Unsets the PV status of an SV.
2753
2754 SvPOK_off (SV* sv)
2755
2756=item SvPOK_on
2757
2758Tells an SV that it is a string.
2759
2760 SvPOK_on (SV* sv)
2761
5fb8527f
PP
2762=item SvPOK_only
2763
2764Tells an SV that it is a string and disables all other OK bits.
2765
2766 SvPOK_on (SV* sv)
2767
cb1a09d0
AD
2768=item SvPOKp
2769
2770Returns a boolean indicating whether the SV contains a character string.
2771Checks the B<private> setting. Use C<SvPOK>.
2772
2773 int SvPOKp (SV* SV)
2774
2775=item SvPV
2776
2777Returns a pointer to the string in the SV, or a stringified form of the SV
2778if the SV does not contain a string. If C<len> is C<na> then Perl will
2779handle the length on its own.
2780
2781 char * SvPV (SV* sv, int len )
2782
2783=item SvPVX
2784
2785Returns a pointer to the string in the SV. The SV must contain a string.
2786
2787 char * SvPVX (SV* sv)
2788
2789=item SvREFCNT
2790
5f05dabc 2791Returns the value of the object's reference count.
cb1a09d0
AD
2792
2793 int SvREFCNT (SV* sv);
2794
2795=item SvREFCNT_dec
2796
5f05dabc 2797Decrements the reference count of the given SV.
cb1a09d0
AD
2798
2799 void SvREFCNT_dec (SV* sv)
2800
2801=item SvREFCNT_inc
2802
5f05dabc 2803Increments the reference count of the given SV.
cb1a09d0
AD
2804
2805 void SvREFCNT_inc (SV* sv)
2806
2807=item SvROK
2808
2809Tests if the SV is an RV.
2810
2811 int SvROK (SV* sv)
2812
2813=item SvROK_off
2814
2815Unsets the RV status of an SV.
2816
2817 SvROK_off (SV* sv)
2818
2819=item SvROK_on
2820
2821Tells an SV that it is an RV.
2822
2823 SvROK_on (SV* sv)
2824
2825=item SvRV
2826
2827Dereferences an RV to return the SV.
2828
2829 SV* SvRV (SV* sv);
2830
fb73857a
PP
2831=item SvTAINT
2832
2833Taints an SV if tainting is enabled
2834
2835 SvTAINT (SV* sv);
2836
2837=item SvTAINTED
2838
2839Checks to see if an SV is tainted. Returns TRUE if it is, FALSE if not.
2840
2841 SvTAINTED (SV* sv);
2842
2843=item SvTAINTED_off
2844
2845Untaints an SV. Be I<very> careful with this routine, as it short-circuits
2846some of Perl's fundamental security features. XS module authors should
2847not use this function unless they fully understand all the implications
2848of unconditionally untainting the value. Untainting should be done in
2849the standard perl fashion, via a carefully crafted regexp, rather than
2850directly untainting variables.
2851
2852 SvTAINTED_off (SV* sv);
2853
2854=item SvTAINTED_on
2855
2856Marks an SV as tainted.
2857
2858 SvTAINTED_on (SV* sv);
2859
cb1a09d0
AD
2860=item sv_setiv
2861
2862Copies an integer into the given SV.
2863
2864 void sv_setiv _((SV* sv, IV num));
2865
2866=item sv_setnv
2867
2868Copies a double into the given SV.
2869
2870 void sv_setnv _((SV* sv, double num));
2871
2872=item sv_setpv
2873
2874Copies a string into an SV. The string must be null-terminated.
2875
2876 void sv_setpv _((SV* sv, char* ptr));
2877
2878=item sv_setpvn
2879
2880Copies a string into an SV. The C<len> parameter indicates the number of
2881bytes to be copied.
2882
2883 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2884
46fc3d4c
PP
2885=item sv_setpvf
2886
2887Processes its arguments like C<sprintf> and sets an SV to the formatted
2888output.
2889
2890 void sv_setpvf _((SV* sv, const char* pat, ...));
2891
cb1a09d0
AD
2892=item sv_setref_iv
2893
5fb8527f
PP
2894Copies an integer into a new SV, optionally blessing the SV. The C<rv>
2895argument will be upgraded to an RV. That RV will be modified to point to
2896the new SV. The C<classname> argument indicates the package for the
2897blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
5f05dabc 2898will be returned and will have a reference count of 1.
cb1a09d0
AD
2899
2900 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2901
2902=item sv_setref_nv
2903
5fb8527f
PP
2904Copies a double into a new SV, optionally blessing the SV. The C<rv>
2905argument will be upgraded to an RV. That RV will be modified to point to
2906the new SV. The C<classname> argument indicates the package for the
2907blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
5f05dabc 2908will be returned and will have a reference count of 1.
cb1a09d0
AD
2909
2910 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2911
2912=item sv_setref_pv
2913
5fb8527f
PP
2914Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
2915argument will be upgraded to an RV. That RV will be modified to point to
2916the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
2917into the SV. The C<classname> argument indicates the package for the
2918blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
5f05dabc 2919will be returned and will have a reference count of 1.
cb1a09d0
AD
2920
2921 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2922
2923Do not use with integral Perl types such as HV, AV, SV, CV, because those
2924objects will become corrupted by the pointer copy process.
2925
2926Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2927
2928=item sv_setref_pvn
2929
5fb8527f
PP
2930Copies a string into a new SV, optionally blessing the SV. The length of the
2931string must be specified with C<n>. The C<rv> argument will be upgraded to
2932an RV. That RV will be modified to point to the new SV. The C<classname>
cb1a09d0
AD
2933argument indicates the package for the blessing. Set C<classname> to
2934C<Nullch> to avoid the blessing. The new SV will be returned and will have
5f05dabc 2935a reference count of 1.
cb1a09d0
AD
2936
2937 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2938
2939Note that C<sv_setref_pv> copies the pointer while this copies the string.
2940
2941=item sv_setsv
2942
2943Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
5f05dabc 2944The source SV may be destroyed if it is mortal.
cb1a09d0
AD
2945
2946 void sv_setsv _((SV* dsv, SV* ssv));
2947
2948=item SvSTASH
2949
2950Returns the stash of the SV.
2951
2952 HV * SvSTASH (SV* sv)
2953
2954=item SVt_IV
2955
2956Integer type flag for scalars. See C<svtype>.
2957
2958=item SVt_PV
2959
2960Pointer type flag for scalars. See C<svtype>.
2961
2962=item SVt_PVAV
2963
2964Type flag for arrays. See C<svtype>.
2965
2966=item SVt_PVCV
2967
2968Type flag for code refs. See C<svtype>.
2969
2970=item SVt_PVHV
2971
2972Type flag for hashes. See C<svtype>.
2973
2974=item SVt_PVMG
2975
2976Type flag for blessed scalars. See C<svtype>.
2977
2978=item SVt_NV
2979
2980Double type flag for scalars. See C<svtype>.
2981
2982=item SvTRUE
2983
2984Returns a boolean indicating whether Perl would evaluate the SV as true or
2985false, defined or undefined.
2986
2987 int SvTRUE (SV* sv)
2988
2989=item SvTYPE
2990
2991Returns the type of the SV. See C<svtype>.
2992
2993 svtype SvTYPE (SV* sv)
2994
2995=item svtype
2996
2997An enum of flags for Perl types. These are found in the file B<sv.h> in the
2998C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2999
3000=item SvUPGRADE
3001
5fb8527f
PP
3002Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
3003the upgrade if necessary. See C<svtype>.
3004
3005 bool SvUPGRADE _((SV* sv, svtype mt));
3006
3007=item sv_upgrade
3008
3009Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
cb1a09d0
AD
3010
3011=item sv_undef
3012
3013This is the C<undef> SV. Always refer to this as C<&sv_undef>.
3014
5fb8527f
PP
3015=item sv_unref
3016
07fa94a1
JO
3017Unsets the RV status of the SV, and decrements the reference count of
3018whatever was being referenced by the RV. This can almost be thought of
3019as a reversal of C<newSVrv>. See C<SvROK_off>.
5fb8527f
PP
3020
3021 void sv_unref _((SV* sv));
3022
cb1a09d0
AD
3023=item sv_usepvn
3024
3025Tells an SV to use C<ptr> to find its string value. Normally the string is
5fb8527f
PP
3026stored inside the SV but sv_usepvn allows the SV to use an outside string.
3027The C<ptr> should point to memory that was allocated by C<malloc>. The
cb1a09d0
AD
3028string length, C<len>, must be supplied. This function will realloc the
3029memory pointed to by C<ptr>, so that pointer should not be freed or used by
3030the programmer after giving it to sv_usepvn.
3031
3032 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
3033
3034=item sv_yes
3035
3036This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
3037
3038=item THIS
3039
3040Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
3041This is always the proper type for the C++ object. See C<CLASS> and
5fb8527f 3042L<perlxs/"Using XS With C++">.
cb1a09d0
AD
3043
3044=item toLOWER
3045
3046Converts the specified character to lowercase.
3047
3048 int toLOWER (char c)
3049
3050=item toUPPER
3051
3052Converts the specified character to uppercase.
3053
3054 int toUPPER (char c)
3055
3056=item warn
3057
3058This is the XSUB-writer's interface to Perl's C<warn> function. Use this
3059function the same way you use the C C<printf> function. See C<croak()>.
3060
3061=item XPUSHi
3062
3063Push an integer onto the stack, extending the stack if necessary. See
3064C<PUSHi>.
3065
3066 XPUSHi(int d)
3067
3068=item XPUSHn
3069
3070Push a double onto the stack, extending the stack if necessary. See
3071C<PUSHn>.
3072
3073 XPUSHn(double d)
3074
3075=item XPUSHp
3076
3077Push a string onto the stack, extending the stack if necessary. The C<len>
3078indicates the length of the string. See C<PUSHp>.
3079
3080 XPUSHp(char *c, int len)
3081
3082=item XPUSHs
3083
3084Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
3085
3086 XPUSHs(sv)
3087
5fb8527f
PP
3088=item XS
3089
3090Macro to declare an XSUB and its C parameter list. This is handled by
3091C<xsubpp>.
3092
cb1a09d0
AD
3093=item XSRETURN
3094
3095Return from XSUB, indicating number of items on the stack. This is usually
3096handled by C<xsubpp>.
3097
5fb8527f 3098 XSRETURN(int x);
cb1a09d0
AD
3099
3100=item XSRETURN_EMPTY
3101
5fb8527f 3102Return an empty list from an XSUB immediately.
cb1a09d0
AD
3103
3104 XSRETURN_EMPTY;
3105
5fb8527f
PP
3106=item XSRETURN_IV
3107
3108Return an integer from an XSUB immediately. Uses C<XST_mIV>.
3109
3110 XSRETURN_IV(IV v);
3111
cb1a09d0
AD
3112=item XSRETURN_NO
3113
5fb8527f 3114Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
cb1a09d0
AD
3115
3116 XSRETURN_NO;
3117
5fb8527f
PP
3118=item XSRETURN_NV
3119
3120Return an double from an XSUB immediately. Uses C<XST_mNV>.
3121
3122 XSRETURN_NV(NV v);
3123
3124=item XSRETURN_PV
3125
3126Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
3127
3128 XSRETURN_PV(char *v);
3129
cb1a09d0
AD
3130=item XSRETURN_UNDEF
3131
5fb8527f 3132Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
cb1a09d0
AD
3133
3134 XSRETURN_UNDEF;
3135
3136=item XSRETURN_YES
3137
5fb8527f 3138Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
cb1a09d0
AD
3139
3140 XSRETURN_YES;
3141
5fb8527f
PP
3142=item XST_mIV
3143
3144Place an integer into the specified position C<i> on the stack. The value is
3145stored in a new mortal SV.
3146
3147 XST_mIV( int i, IV v );
3148
3149=item XST_mNV
3150
3151Place a double into the specified position C<i> on the stack. The value is
3152stored in a new mortal SV.
3153
3154 XST_mNV( int i, NV v );
3155
3156=item XST_mNO
3157
3158Place C<&sv_no> into the specified position C<i> on the stack.
3159
3160 XST_mNO( int i );
3161
3162=item XST_mPV
3163
3164Place a copy of a string into the specified position C<i> on the stack. The
3165value is stored in a new mortal SV.
3166
3167 XST_mPV( int i, char *v );
3168
3169=item XST_mUNDEF
3170
3171Place C<&sv_undef> into the specified position C<i> on the stack.
3172
3173 XST_mUNDEF( int i );
3174
3175=item XST_mYES
3176
3177Place C<&sv_yes> into the specified position C<i> on the stack.
3178
3179 XST_mYES( int i );
3180
3181=item XS_VERSION
3182
3183The version identifier for an XS module. This is usually handled
3184automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
3185
3186=item XS_VERSION_BOOTCHECK
3187
3188Macro to verify that a PM module's $VERSION variable matches the XS module's
3189C<XS_VERSION> variable. This is usually handled automatically by
3190C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
3191
cb1a09d0
AD
3192=item Zero
3193
3194The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
3195destination, C<n> is the number of items, and C<t> is the type.
3196
3197 (void) Zero( d, n, t );
3198
3199=back
3200
5f05dabc 3201=head1 EDITOR
cb1a09d0 3202
9607fc9c 3203Jeff Okamoto <F<okamoto@corp.hp.com>>
cb1a09d0
AD
3204
3205With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
3206Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
bdbeb323
SM
3207Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer, and
3208Stephen McCamant.
cb1a09d0 3209
9607fc9c 3210API Listing by Dean Roehrich <F<roehrich@cray.com>>.
cb1a09d0
AD
3211
3212=head1 DATE
3213
04343c6d 3214Version 31.8: 1997/5/17