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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
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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
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540reference count decremented depends on two macros, SAVETMPS and FREETMPS.
541See L<perlcall> and L<perlxs> for more details on these macros.
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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
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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
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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
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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.
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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.
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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
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611If you need to bless or re-bless an object you can use the following
612function:
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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
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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>.
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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
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698associated with an SV.
699
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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
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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.
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707See the "Magic Virtual Table" section below. The C<how> argument is also
708stored in the C<mg_type> field.
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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
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714merely stored, without the reference count being incremented.
715
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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
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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
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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
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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
0a753a76 907=head1 Subroutines
a0d0e21e 908
68dc0745 909=head2 XSUBs and the Argument Stack
5f05dabc
PP
910
911The XSUB mechanism is a simple way for Perl programs to access C subroutines.
912An XSUB routine will have a stack that contains the arguments from the Perl
913program, and a way to map from the Perl data structures to a C equivalent.
914
915The stack arguments are accessible through the C<ST(n)> macro, which returns
916the C<n>'th stack argument. Argument 0 is the first argument passed in the
917Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
918an C<SV*> is used.
919
920Most of the time, output from the C routine can be handled through use of
921the RETVAL and OUTPUT directives. However, there are some cases where the
922argument stack is not already long enough to handle all the return values.
923An example is the POSIX tzname() call, which takes no arguments, but returns
924two, the local time zone's standard and summer time abbreviations.
925
926To handle this situation, the PPCODE directive is used and the stack is
927extended using the macro:
928
929 EXTEND(sp, num);
930
931where C<sp> is the stack pointer, and C<num> is the number of elements the
932stack should be extended by.
933
934Now that there is room on the stack, values can be pushed on it using the
54310121 935macros to push IVs, doubles, strings, and SV pointers respectively:
5f05dabc
PP
936
937 PUSHi(IV)
938 PUSHn(double)
939 PUSHp(char*, I32)
940 PUSHs(SV*)
941
942And now the Perl program calling C<tzname>, the two values will be assigned
943as in:
944
945 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
946
947An alternate (and possibly simpler) method to pushing values on the stack is
948to use the macros:
949
950 XPUSHi(IV)
951 XPUSHn(double)
952 XPUSHp(char*, I32)
953 XPUSHs(SV*)
954
955These macros automatically adjust the stack for you, if needed. Thus, you
956do not need to call C<EXTEND> to extend the stack.
957
958For more information, consult L<perlxs> and L<perlxstut>.
959
960=head2 Calling Perl Routines from within C Programs
a0d0e21e
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961
962There are four routines that can be used to call a Perl subroutine from
963within a C program. These four are:
964
965 I32 perl_call_sv(SV*, I32);
966 I32 perl_call_pv(char*, I32);
967 I32 perl_call_method(char*, I32);
968 I32 perl_call_argv(char*, I32, register char**);
969
d1b91892
AD
970The routine most often used is C<perl_call_sv>. The C<SV*> argument
971contains either the name of the Perl subroutine to be called, or a
972reference to the subroutine. The second argument consists of flags
973that control the context in which the subroutine is called, whether
974or not the subroutine is being passed arguments, how errors should be
975trapped, and how to treat return values.
a0d0e21e
LW
976
977All four routines return the number of arguments that the subroutine returned
978on the Perl stack.
979
d1b91892
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980When using any of these routines (except C<perl_call_argv>), the programmer
981must manipulate the Perl stack. These include the following macros and
982functions:
a0d0e21e
LW
983
984 dSP
985 PUSHMARK()
986 PUTBACK
987 SPAGAIN
988 ENTER
989 SAVETMPS
990 FREETMPS
991 LEAVE
992 XPUSH*()
cb1a09d0 993 POP*()
a0d0e21e 994
5f05dabc
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995For a detailed description of calling conventions from C to Perl,
996consult L<perlcall>.
a0d0e21e 997
5f05dabc 998=head2 Memory Allocation
a0d0e21e 999
5f05dabc
PP
1000It is suggested that you use the version of malloc that is distributed
1001with Perl. It keeps pools of various sizes of unallocated memory in
07fa94a1
JO
1002order to satisfy allocation requests more quickly. However, on some
1003platforms, it may cause spurious malloc or free errors.
d1b91892
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1004
1005 New(x, pointer, number, type);
1006 Newc(x, pointer, number, type, cast);
1007 Newz(x, pointer, number, type);
1008
07fa94a1 1009These three macros are used to initially allocate memory.
5f05dabc
PP
1010
1011The first argument C<x> was a "magic cookie" that was used to keep track
1012of who called the macro, to help when debugging memory problems. However,
07fa94a1
JO
1013the current code makes no use of this feature (most Perl developers now
1014use run-time memory checkers), so this argument can be any number.
5f05dabc
PP
1015
1016The second argument C<pointer> should be the name of a variable that will
1017point to the newly allocated memory.
d1b91892 1018
d1b91892
AD
1019The third and fourth arguments C<number> and C<type> specify how many of
1020the specified type of data structure should be allocated. The argument
1021C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
1022should be used if the C<pointer> argument is different from the C<type>
1023argument.
1024
1025Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
1026to zero out all the newly allocated memory.
1027
1028 Renew(pointer, number, type);
1029 Renewc(pointer, number, type, cast);
1030 Safefree(pointer)
1031
1032These three macros are used to change a memory buffer size or to free a
1033piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1034match those of C<New> and C<Newc> with the exception of not needing the
1035"magic cookie" argument.
1036
1037 Move(source, dest, number, type);
1038 Copy(source, dest, number, type);
1039 Zero(dest, number, type);
1040
1041These three macros are used to move, copy, or zero out previously allocated
1042memory. The C<source> and C<dest> arguments point to the source and
1043destination starting points. Perl will move, copy, or zero out C<number>
1044instances of the size of the C<type> data structure (using the C<sizeof>
1045function).
a0d0e21e 1046
5f05dabc 1047=head2 PerlIO
ce3d39e2 1048
5f05dabc
PP
1049The most recent development releases of Perl has been experimenting with
1050removing Perl's dependency on the "normal" standard I/O suite and allowing
1051other stdio implementations to be used. This involves creating a new
1052abstraction layer that then calls whichever implementation of stdio Perl
68dc0745 1053was compiled with. All XSUBs should now use the functions in the PerlIO
5f05dabc
PP
1054abstraction layer and not make any assumptions about what kind of stdio
1055is being used.
1056
1057For a complete description of the PerlIO abstraction, consult L<perlapio>.
1058
8ebc5c01 1059=head2 Putting a C value on Perl stack
ce3d39e2
IZ
1060
1061A lot of opcodes (this is an elementary operation in the internal perl
1062stack machine) put an SV* on the stack. However, as an optimization
1063the corresponding SV is (usually) not recreated each time. The opcodes
1064reuse specially assigned SVs (I<target>s) which are (as a corollary)
1065not constantly freed/created.
1066
0a753a76 1067Each of the targets is created only once (but see
ce3d39e2
IZ
1068L<Scratchpads and recursion> below), and when an opcode needs to put
1069an integer, a double, or a string on stack, it just sets the
1070corresponding parts of its I<target> and puts the I<target> on stack.
1071
1072The macro to put this target on stack is C<PUSHTARG>, and it is
1073directly used in some opcodes, as well as indirectly in zillions of
1074others, which use it via C<(X)PUSH[pni]>.
1075
8ebc5c01 1076=head2 Scratchpads
ce3d39e2 1077
54310121 1078The question remains on when the SVs which are I<target>s for opcodes
5f05dabc
PP
1079are created. The answer is that they are created when the current unit --
1080a subroutine or a file (for opcodes for statements outside of
1081subroutines) -- is compiled. During this time a special anonymous Perl
ce3d39e2
IZ
1082array is created, which is called a scratchpad for the current
1083unit.
1084
54310121 1085A scratchpad keeps SVs which are lexicals for the current unit and are
ce3d39e2
IZ
1086targets for opcodes. One can deduce that an SV lives on a scratchpad
1087by looking on its flags: lexicals have C<SVs_PADMY> set, and
1088I<target>s have C<SVs_PADTMP> set.
1089
54310121
PP
1090The correspondence between OPs and I<target>s is not 1-to-1. Different
1091OPs in the compile tree of the unit can use the same target, if this
ce3d39e2
IZ
1092would not conflict with the expected life of the temporary.
1093
2ae324a7 1094=head2 Scratchpads and recursion
ce3d39e2
IZ
1095
1096In fact it is not 100% true that a compiled unit contains a pointer to
1097the scratchpad AV. In fact it contains a pointer to an AV of
1098(initially) one element, and this element is the scratchpad AV. Why do
1099we need an extra level of indirection?
1100
1101The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1102these can create several execution pointers going into the same
1103subroutine. For the subroutine-child not write over the temporaries
1104for the subroutine-parent (lifespan of which covers the call to the
1105child), the parent and the child should have different
1106scratchpads. (I<And> the lexicals should be separate anyway!)
1107
5f05dabc
PP
1108So each subroutine is born with an array of scratchpads (of length 1).
1109On each entry to the subroutine it is checked that the current
ce3d39e2
IZ
1110depth of the recursion is not more than the length of this array, and
1111if it is, new scratchpad is created and pushed into the array.
1112
1113The I<target>s on this scratchpad are C<undef>s, but they are already
1114marked with correct flags.
1115
0a753a76
PP
1116=head1 Compiled code
1117
1118=head2 Code tree
1119
1120Here we describe the internal form your code is converted to by
1121Perl. Start with a simple example:
1122
1123 $a = $b + $c;
1124
1125This is converted to a tree similar to this one:
1126
1127 assign-to
1128 / \
1129 + $a
1130 / \
1131 $b $c
1132
1133(but slightly more complicated). This tree reflect the way Perl
1134parsed your code, but has nothing to do with the execution order.
1135There is an additional "thread" going through the nodes of the tree
1136which shows the order of execution of the nodes. In our simplified
1137example above it looks like:
1138
1139 $b ---> $c ---> + ---> $a ---> assign-to
1140
1141But with the actual compile tree for C<$a = $b + $c> it is different:
1142some nodes I<optimized away>. As a corollary, though the actual tree
1143contains more nodes than our simplified example, the execution order
1144is the same as in our example.
1145
1146=head2 Examining the tree
1147
1148If you have your perl compiled for debugging (usually done with C<-D
1149optimize=-g> on C<Configure> command line), you may examine the
1150compiled tree by specifying C<-Dx> on the Perl command line. The
1151output takes several lines per node, and for C<$b+$c> it looks like
1152this:
1153
1154 5 TYPE = add ===> 6
1155 TARG = 1
1156 FLAGS = (SCALAR,KIDS)
1157 {
1158 TYPE = null ===> (4)
1159 (was rv2sv)
1160 FLAGS = (SCALAR,KIDS)
1161 {
1162 3 TYPE = gvsv ===> 4
1163 FLAGS = (SCALAR)
1164 GV = main::b
1165 }
1166 }
1167 {
1168 TYPE = null ===> (5)
1169 (was rv2sv)
1170 FLAGS = (SCALAR,KIDS)
1171 {
1172 4 TYPE = gvsv ===> 5
1173 FLAGS = (SCALAR)
1174 GV = main::c
1175 }
1176 }
1177
1178This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1179not optimized away (one per number in the left column). The immediate
1180children of the given node correspond to C<{}> pairs on the same level
1181of indentation, thus this listing corresponds to the tree:
1182
1183 add
1184 / \
1185 null null
1186 | |
1187 gvsv gvsv
1188
1189The execution order is indicated by C<===E<gt>> marks, thus it is C<3
11904 5 6> (node C<6> is not included into above listing), i.e.,
1191C<gvsv gvsv add whatever>.
1192
1193=head2 Compile pass 1: check routines
1194
1195The tree is created by the I<pseudo-compiler> while yacc code feeds it
1196the constructions it recognizes. Since yacc works bottom-up, so does
1197the first pass of perl compilation.
1198
1199What makes this pass interesting for perl developers is that some
1200optimization may be performed on this pass. This is optimization by
1201so-called I<check routines>. The correspondence between node names
1202and corresponding check routines is described in F<opcode.pl> (do not
1203forget to run C<make regen_headers> if you modify this file).
1204
1205A check routine is called when the node is fully constructed except
1206for the execution-order thread. Since at this time there is no
1207back-links to the currently constructed node, one can do most any
1208operation to the top-level node, including freeing it and/or creating
1209new nodes above/below it.
1210
1211The check routine returns the node which should be inserted into the
1212tree (if the top-level node was not modified, check routine returns
1213its argument).
1214
1215By convention, check routines have names C<ck_*>. They are usually
1216called from C<new*OP> subroutines (or C<convert>) (which in turn are
1217called from F<perly.y>).
1218
1219=head2 Compile pass 1a: constant folding
1220
1221Immediately after the check routine is called the returned node is
1222checked for being compile-time executable. If it is (the value is
1223judged to be constant) it is immediately executed, and a I<constant>
1224node with the "return value" of the corresponding subtree is
1225substituted instead. The subtree is deleted.
1226
1227If constant folding was not performed, the execution-order thread is
1228created.
1229
1230=head2 Compile pass 2: context propagation
1231
1232When a context for a part of compile tree is known, it is propagated
1233down through the tree. Aat this time the context can have 5 values
1234(instead of 2 for runtime context): void, boolean, scalar, list, and
1235lvalue. In contrast with the pass 1 this pass is processed from top
1236to bottom: a node's context determines the context for its children.
1237
1238Additional context-dependent optimizations are performed at this time.
1239Since at this moment the compile tree contains back-references (via
1240"thread" pointers), nodes cannot be free()d now. To allow
1241optimized-away nodes at this stage, such nodes are null()ified instead
1242of free()ing (i.e. their type is changed to OP_NULL).
1243
1244=head2 Compile pass 3: peephole optimization
1245
1246After the compile tree for a subroutine (or for an C<eval> or a file)
1247is created, an additional pass over the code is performed. This pass
1248is neither top-down or bottom-up, but in the execution order (with
1249additional compilications for conditionals). These optimizations are
1250done in the subroutine peep(). Optimizations performed at this stage
1251are subject to the same restrictions as in the pass 2.
1252
1253=head1 API LISTING
a0d0e21e 1254
cb1a09d0
AD
1255This is a listing of functions, macros, flags, and variables that may be
1256useful to extension writers or that may be found while reading other
1257extensions.
a0d0e21e 1258
cb1a09d0 1259=over 8
a0d0e21e 1260
cb1a09d0
AD
1261=item AvFILL
1262
1263See C<av_len>.
1264
1265=item av_clear
1266
0146554f
GA
1267Clears an array, making it empty. Does not free the memory used by the
1268array itself.
cb1a09d0
AD
1269
1270 void av_clear _((AV* ar));
1271
1272=item av_extend
1273
1274Pre-extend an array. The C<key> is the index to which the array should be
1275extended.
1276
1277 void av_extend _((AV* ar, I32 key));
1278
1279=item av_fetch
1280
1281Returns the SV at the specified index in the array. The C<key> is the
1282index. If C<lval> is set then the fetch will be part of a store. Check
1283that the return value is non-null before dereferencing it to a C<SV*>.
1284
04343c6d
GS
1285See L<Understanding the Magic of Tied Hashes and Arrays> for more
1286information on how to use this function on tied arrays.
1287
cb1a09d0
AD
1288 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1289
1290=item av_len
1291
1292Returns the highest index in the array. Returns -1 if the array is empty.
1293
1294 I32 av_len _((AV* ar));
1295
1296=item av_make
1297
5fb8527f
PP
1298Creates a new AV and populates it with a list of SVs. The SVs are copied
1299into the array, so they may be freed after the call to av_make. The new AV
5f05dabc 1300will have a reference count of 1.
cb1a09d0
AD
1301
1302 AV* av_make _((I32 size, SV** svp));
1303
1304=item av_pop
1305
1306Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1307empty.
1308
1309 SV* av_pop _((AV* ar));
1310
1311=item av_push
1312
5fb8527f
PP
1313Pushes an SV onto the end of the array. The array will grow automatically
1314to accommodate the addition.
cb1a09d0
AD
1315
1316 void av_push _((AV* ar, SV* val));
1317
1318=item av_shift
1319
1320Shifts an SV off the beginning of the array.
1321
1322 SV* av_shift _((AV* ar));
1323
1324=item av_store
1325
1326Stores an SV in an array. The array index is specified as C<key>. The
04343c6d
GS
1327return value will be NULL if the operation failed or if the value did not
1328need to be actually stored within the array (as in the case of tied arrays).
1329Otherwise it can be dereferenced to get the original C<SV*>. Note that the
1330caller is responsible for suitably incrementing the reference count of C<val>
1331before the call, and decrementing it if the function returned NULL.
1332
1333See L<Understanding the Magic of Tied Hashes and Arrays> for more
1334information on how to use this function on tied arrays.
cb1a09d0
AD
1335
1336 SV** av_store _((AV* ar, I32 key, SV* val));
1337
1338=item av_undef
1339
0146554f 1340Undefines the array. Frees the memory used by the array itself.
cb1a09d0
AD
1341
1342 void av_undef _((AV* ar));
1343
1344=item av_unshift
1345
0146554f
GA
1346Unshift the given number of C<undef> values onto the beginning of the
1347array. The array will grow automatically to accommodate the addition.
1348You must then use C<av_store> to assign values to these new elements.
cb1a09d0
AD
1349
1350 void av_unshift _((AV* ar, I32 num));
1351
1352=item CLASS
1353
1354Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
5fb8527f
PP
1355constructor. This is always a C<char*>. See C<THIS> and
1356L<perlxs/"Using XS With C++">.
cb1a09d0
AD
1357
1358=item Copy
1359
1360The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1361source, C<d> is the destination, C<n> is the number of items, and C<t> is
0146554f 1362the type. May fail on overlapping copies. See also C<Move>.
cb1a09d0
AD
1363
1364 (void) Copy( s, d, n, t );
1365
1366=item croak
1367
1368This is the XSUB-writer's interface to Perl's C<die> function. Use this
1369function the same way you use the C C<printf> function. See C<warn>.
1370
1371=item CvSTASH
1372
1373Returns the stash of the CV.
1374
1375 HV * CvSTASH( SV* sv )
1376
1377=item DBsingle
1378
1379When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1380boolean which indicates whether subs are being single-stepped.
5fb8527f
PP
1381Single-stepping is automatically turned on after every step. This is the C
1382variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
cb1a09d0
AD
1383
1384=item DBsub
1385
1386When Perl is run in debugging mode, with the B<-d> switch, this GV contains
5fb8527f
PP
1387the SV which holds the name of the sub being debugged. This is the C
1388variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
cb1a09d0
AD
1389The sub name can be found by
1390
1391 SvPV( GvSV( DBsub ), na )
1392
5fb8527f
PP
1393=item DBtrace
1394
1395Trace variable used when Perl is run in debugging mode, with the B<-d>
1396switch. This is the C variable which corresponds to Perl's $DB::trace
1397variable. See C<DBsingle>.
1398
cb1a09d0
AD
1399=item dMARK
1400
5fb8527f
PP
1401Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1402C<dORIGMARK>.
cb1a09d0
AD
1403
1404=item dORIGMARK
1405
1406Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1407
5fb8527f
PP
1408=item dowarn
1409
1410The C variable which corresponds to Perl's $^W warning variable.
1411
cb1a09d0
AD
1412=item dSP
1413
5fb8527f 1414Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
cb1a09d0
AD
1415
1416=item dXSARGS
1417
1418Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1419usually handled automatically by C<xsubpp>. Declares the C<items> variable
1420to indicate the number of items on the stack.
1421
5fb8527f
PP
1422=item dXSI32
1423
1424Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1425handled automatically by C<xsubpp>.
1426
cb1a09d0
AD
1427=item ENTER
1428
1429Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1430
1431 ENTER;
1432
1433=item EXTEND
1434
1435Used to extend the argument stack for an XSUB's return values.
1436
1437 EXTEND( sp, int x );
1438
1439=item FREETMPS
1440
1441Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1442L<perlcall>.
1443
1444 FREETMPS;
1445
1446=item G_ARRAY
1447
54310121 1448Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
cb1a09d0
AD
1449
1450=item G_DISCARD
1451
1452Indicates that arguments returned from a callback should be discarded. See
1453L<perlcall>.
1454
1455=item G_EVAL
1456
1457Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1458
1459=item GIMME
1460
54310121
PP
1461A backward-compatible version of C<GIMME_V> which can only return
1462C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
1463
1464=item GIMME_V
1465
1466The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
1467C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
1468context, respectively.
cb1a09d0
AD
1469
1470=item G_NOARGS
1471
1472Indicates that no arguments are being sent to a callback. See L<perlcall>.
1473
1474=item G_SCALAR
1475
54310121
PP
1476Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
1477
1478=item G_VOID
1479
1480Used to indicate void context. See C<GIMME_V> and L<perlcall>.
cb1a09d0 1481
faed5253
JO
1482=item gv_fetchmeth
1483
1484Returns the glob with the given C<name> and a defined subroutine or
9607fc9c
PP
1485C<NULL>. The glob lives in the given C<stash>, or in the stashes
1486accessable via @ISA and @<UNIVERSAL>.
faed5253 1487
9607fc9c 1488The argument C<level> should be either 0 or -1. If C<level==0>, as a
0a753a76
PP
1489side-effect creates a glob with the given C<name> in the given
1490C<stash> which in the case of success contains an alias for the
1491subroutine, and sets up caching info for this glob. Similarly for all
1492the searched stashes.
1493
9607fc9c
PP
1494This function grants C<"SUPER"> token as a postfix of the stash name.
1495
0a753a76
PP
1496The GV returned from C<gv_fetchmeth> may be a method cache entry,
1497which is not visible to Perl code. So when calling C<perl_call_sv>,
1498you should not use the GV directly; instead, you should use the
1499method's CV, which can be obtained from the GV with the C<GvCV> macro.
faed5253
JO
1500
1501 GV* gv_fetchmeth _((HV* stash, char* name, STRLEN len, I32 level));
1502
1503=item gv_fetchmethod
1504
dc848c6f
PP
1505=item gv_fetchmethod_autoload
1506
faed5253 1507Returns the glob which contains the subroutine to call to invoke the
dc848c6f
PP
1508method on the C<stash>. In fact in the presense of autoloading this may
1509be the glob for "AUTOLOAD". In this case the corresponding variable
faed5253
JO
1510$AUTOLOAD is already setup.
1511
dc848c6f
PP
1512The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
1513lookup is performed if the given method is not present: non-zero means
1514yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
1515C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
1516non-zero C<autoload> parameter.
1517
1518These functions grant C<"SUPER"> token as a prefix of the method name.
1519
1520Note that if you want to keep the returned glob for a long time, you
1521need to check for it being "AUTOLOAD", since at the later time the call
faed5253
JO
1522may load a different subroutine due to $AUTOLOAD changing its value.
1523Use the glob created via a side effect to do this.
1524
dc848c6f
PP
1525These functions have the same side-effects and as C<gv_fetchmeth> with
1526C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
0a753a76 1527The warning against passing the GV returned by C<gv_fetchmeth> to
dc848c6f 1528C<perl_call_sv> apply equally to these functions.
faed5253
JO
1529
1530 GV* gv_fetchmethod _((HV* stash, char* name));
dc848c6f
PP
1531 GV* gv_fetchmethod_autoload _((HV* stash, char* name,
1532 I32 autoload));
faed5253 1533
cb1a09d0
AD
1534=item gv_stashpv
1535
1536Returns a pointer to the stash for a specified package. If C<create> is set
1537then the package will be created if it does not already exist. If C<create>
1538is not set and the package does not exist then NULL is returned.
1539
1540 HV* gv_stashpv _((char* name, I32 create));
1541
1542=item gv_stashsv
1543
1544Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1545
1546 HV* gv_stashsv _((SV* sv, I32 create));
1547
e5581bf4 1548=item GvSV
cb1a09d0 1549
e5581bf4 1550Return the SV from the GV.
44a8e56a 1551
1e422769
PP
1552=item HEf_SVKEY
1553
1554This flag, used in the length slot of hash entries and magic
1555structures, specifies the structure contains a C<SV*> pointer where a
1556C<char*> pointer is to be expected. (For information only--not to be used).
1557
1e422769
PP
1558=item HeHASH
1559
1560Returns the computed hash (type C<U32>) stored in the hash entry.
1561
1562 HeHASH(HE* he)
1563
1564=item HeKEY
1565
1566Returns the actual pointer stored in the key slot of the hash entry.
1567The pointer may be either C<char*> or C<SV*>, depending on the value of
1568C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
1569are usually preferable for finding the value of a key.
1570
1571 HeKEY(HE* he)
1572
1573=item HeKLEN
1574
1575If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
1576holds an C<SV*> key. Otherwise, holds the actual length of the key.
1577Can be assigned to. The C<HePV()> macro is usually preferable for finding
1578key lengths.
1579
1580 HeKLEN(HE* he)
1581
1582=item HePV
1583
1584Returns the key slot of the hash entry as a C<char*> value, doing any
1585necessary dereferencing of possibly C<SV*> keys. The length of
1586the string is placed in C<len> (this is a macro, so do I<not> use
1587C<&len>). If you do not care about what the length of the key is,
1588you may use the global variable C<na>. Remember though, that hash
1589keys in perl are free to contain embedded nulls, so using C<strlen()>
1590or similar is not a good way to find the length of hash keys.
1591This is very similar to the C<SvPV()> macro described elsewhere in
1592this document.
1593
1594 HePV(HE* he, STRLEN len)
1595
1596=item HeSVKEY
1597
1598Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
1599does not contain an C<SV*> key.
1600
1601 HeSVKEY(HE* he)
1602
1603=item HeSVKEY_force
1604
1605Returns the key as an C<SV*>. Will create and return a temporary
1606mortal C<SV*> if the hash entry contains only a C<char*> key.
1607
1608 HeSVKEY_force(HE* he)
1609
1610=item HeSVKEY_set
1611
1612Sets the key to a given C<SV*>, taking care to set the appropriate flags
1613to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
1614
1615 HeSVKEY_set(HE* he, SV* sv)
1616
1617=item HeVAL
1618
1619Returns the value slot (type C<SV*>) stored in the hash entry.
1620
1621 HeVAL(HE* he)
1622
cb1a09d0
AD
1623=item hv_clear
1624
1625Clears a hash, making it empty.
1626
1627 void hv_clear _((HV* tb));
1628
68dc0745
PP
1629=item hv_delayfree_ent
1630
1631Releases a hash entry, such as while iterating though the hash, but
1632delays actual freeing of key and value until the end of the current
1633statement (or thereabouts) with C<sv_2mortal>. See C<hv_iternext>
1634and C<hv_free_ent>.
1635
1636 void hv_delayfree_ent _((HV* hv, HE* entry));
1637
cb1a09d0
AD
1638=item hv_delete
1639
1640Deletes a key/value pair in the hash. The value SV is removed from the hash
5fb8527f 1641and returned to the caller. The C<klen> is the length of the key. The
04343c6d 1642C<flags> value will normally be zero; if set to G_DISCARD then NULL will be
cb1a09d0
AD
1643returned.
1644
1645 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1646
1e422769
PP
1647=item hv_delete_ent
1648
1649Deletes a key/value pair in the hash. The value SV is removed from the hash
1650and returned to the caller. The C<flags> value will normally be zero; if set
04343c6d 1651to G_DISCARD then NULL will be returned. C<hash> can be a valid precomputed
1e422769
PP
1652hash value, or 0 to ask for it to be computed.
1653
1654 SV* hv_delete_ent _((HV* tb, SV* key, I32 flags, U32 hash));
1655
cb1a09d0
AD
1656=item hv_exists
1657
1658Returns a boolean indicating whether the specified hash key exists. The
5fb8527f 1659C<klen> is the length of the key.
cb1a09d0
AD
1660
1661 bool hv_exists _((HV* tb, char* key, U32 klen));
1662
1e422769
PP
1663=item hv_exists_ent
1664
1665Returns a boolean indicating whether the specified hash key exists. C<hash>
54310121 1666can be a valid precomputed hash value, or 0 to ask for it to be computed.
1e422769
PP
1667
1668 bool hv_exists_ent _((HV* tb, SV* key, U32 hash));
1669
cb1a09d0
AD
1670=item hv_fetch
1671
1672Returns the SV which corresponds to the specified key in the hash. The
5fb8527f 1673C<klen> is the length of the key. If C<lval> is set then the fetch will be
cb1a09d0
AD
1674part of a store. Check that the return value is non-null before
1675dereferencing it to a C<SV*>.
1676
04343c6d
GS
1677See L<Understanding the Magic of Tied Hashes and Arrays> for more
1678information on how to use this function on tied hashes.
1679
cb1a09d0
AD
1680 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1681
1e422769
PP
1682=item hv_fetch_ent
1683
1684Returns the hash entry which corresponds to the specified key in the hash.
54310121 1685C<hash> must be a valid precomputed hash number for the given C<key>, or
1e422769
PP
16860 if you want the function to compute it. IF C<lval> is set then the
1687fetch will be part of a store. Make sure the return value is non-null
1688before accessing it. The return value when C<tb> is a tied hash
1689is a pointer to a static location, so be sure to make a copy of the
1690structure if you need to store it somewhere.
1691
04343c6d
GS
1692See L<Understanding the Magic of Tied Hashes and Arrays> for more
1693information on how to use this function on tied hashes.
1694
1e422769
PP
1695 HE* hv_fetch_ent _((HV* tb, SV* key, I32 lval, U32 hash));
1696
68dc0745
PP
1697=item hv_free_ent
1698
1699Releases a hash entry, such as while iterating though the hash. See
1700C<hv_iternext> and C<hv_delayfree_ent>.
1701
1702 void hv_free_ent _((HV* hv, HE* entry));
1703
cb1a09d0
AD
1704=item hv_iterinit
1705
1706Prepares a starting point to traverse a hash table.
1707
1708 I32 hv_iterinit _((HV* tb));
1709
1710=item hv_iterkey
1711
1712Returns the key from the current position of the hash iterator. See
1713C<hv_iterinit>.
1714
1715 char* hv_iterkey _((HE* entry, I32* retlen));
1716
1e422769 1717=item hv_iterkeysv
3fe9a6f1 1718
1e422769
PP
1719Returns the key as an C<SV*> from the current position of the hash
1720iterator. The return value will always be a mortal copy of the
1721key. Also see C<hv_iterinit>.
1722
1723 SV* hv_iterkeysv _((HE* entry));
1724
cb1a09d0
AD
1725=item hv_iternext
1726
1727Returns entries from a hash iterator. See C<hv_iterinit>.
1728
1729 HE* hv_iternext _((HV* tb));
1730
1731=item hv_iternextsv
1732
1733Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1734operation.
1735
1736 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1737
1738=item hv_iterval
1739
1740Returns the value from the current position of the hash iterator. See
1741C<hv_iterkey>.
1742
1743 SV* hv_iterval _((HV* tb, HE* entry));
1744
1745=item hv_magic
1746
1747Adds magic to a hash. See C<sv_magic>.
1748
1749 void hv_magic _((HV* hv, GV* gv, int how));
1750
1751=item HvNAME
1752
1753Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1754
1755 char *HvNAME (HV* stash)
1756
1757=item hv_store
1758
1759Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
54310121 1760the length of the key. The C<hash> parameter is the precomputed hash
cb1a09d0 1761value; if it is zero then Perl will compute it. The return value will be
04343c6d
GS
1762NULL if the operation failed or if the value did not need to be actually
1763stored within the hash (as in the case of tied hashes). Otherwise it can
1764be dereferenced to get the original C<SV*>. Note that the caller is
1765responsible for suitably incrementing the reference count of C<val>
1766before the call, and decrementing it if the function returned NULL.
1767
1768See L<Understanding the Magic of Tied Hashes and Arrays> for more
1769information on how to use this function on tied hashes.
cb1a09d0
AD
1770
1771 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1772
1e422769
PP
1773=item hv_store_ent
1774
1775Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
54310121 1776parameter is the precomputed hash value; if it is zero then Perl will
1e422769 1777compute it. The return value is the new hash entry so created. It will be
04343c6d
GS
1778NULL if the operation failed or if the value did not need to be actually
1779stored within the hash (as in the case of tied hashes). Otherwise the
1780contents of the return value can be accessed using the C<He???> macros
1781described here. Note that the caller is responsible for suitably
1782incrementing the reference count of C<val> before the call, and decrementing
1783it if the function returned NULL.
1784
1785See L<Understanding the Magic of Tied Hashes and Arrays> for more
1786information on how to use this function on tied hashes.
1e422769
PP
1787
1788 HE* hv_store_ent _((HV* tb, SV* key, SV* val, U32 hash));
1789
cb1a09d0
AD
1790=item hv_undef
1791
1792Undefines the hash.
1793
1794 void hv_undef _((HV* tb));
1795
1796=item isALNUM
1797
1798Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
5f05dabc 1799character or digit.
cb1a09d0
AD
1800
1801 int isALNUM (char c)
1802
1803=item isALPHA
1804
5fb8527f 1805Returns a boolean indicating whether the C C<char> is an ascii alphabetic
cb1a09d0
AD
1806character.
1807
1808 int isALPHA (char c)
1809
1810=item isDIGIT
1811
1812Returns a boolean indicating whether the C C<char> is an ascii digit.
1813
1814 int isDIGIT (char c)
1815
1816=item isLOWER
1817
1818Returns a boolean indicating whether the C C<char> is a lowercase character.
1819
1820 int isLOWER (char c)
1821
1822=item isSPACE
1823
1824Returns a boolean indicating whether the C C<char> is whitespace.
1825
1826 int isSPACE (char c)
1827
1828=item isUPPER
1829
1830Returns a boolean indicating whether the C C<char> is an uppercase character.
1831
1832 int isUPPER (char c)
1833
1834=item items
1835
1836Variable which is setup by C<xsubpp> to indicate the number of items on the
5fb8527f
PP
1837stack. See L<perlxs/"Variable-length Parameter Lists">.
1838
1839=item ix
1840
1841Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1842was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
cb1a09d0
AD
1843
1844=item LEAVE
1845
1846Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1847
1848 LEAVE;
1849
1850=item MARK
1851
5fb8527f 1852Stack marker variable for the XSUB. See C<dMARK>.
cb1a09d0
AD
1853
1854=item mg_clear
1855
1856Clear something magical that the SV represents. See C<sv_magic>.
1857
1858 int mg_clear _((SV* sv));
1859
1860=item mg_copy
1861
1862Copies the magic from one SV to another. See C<sv_magic>.
1863
1864 int mg_copy _((SV *, SV *, char *, STRLEN));
1865
1866=item mg_find
1867
1868Finds the magic pointer for type matching the SV. See C<sv_magic>.
1869
1870 MAGIC* mg_find _((SV* sv, int type));
1871
1872=item mg_free
1873
1874Free any magic storage used by the SV. See C<sv_magic>.
1875
1876 int mg_free _((SV* sv));
1877
1878=item mg_get
1879
1880Do magic after a value is retrieved from the SV. See C<sv_magic>.
1881
1882 int mg_get _((SV* sv));
1883
1884=item mg_len
1885
1886Report on the SV's length. See C<sv_magic>.
1887
1888 U32 mg_len _((SV* sv));
1889
1890=item mg_magical
1891
1892Turns on the magical status of an SV. See C<sv_magic>.
1893
1894 void mg_magical _((SV* sv));
1895
1896=item mg_set
1897
1898Do magic after a value is assigned to the SV. See C<sv_magic>.
1899
1900 int mg_set _((SV* sv));
1901
1902=item Move
1903
1904The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
1905source, C<d> is the destination, C<n> is the number of items, and C<t> is
0146554f 1906the type. Can do overlapping moves. See also C<Copy>.
cb1a09d0
AD
1907
1908 (void) Move( s, d, n, t );
1909
1910=item na
1911
1912A variable which may be used with C<SvPV> to tell Perl to calculate the
1913string length.
1914
1915=item New
1916
1917The XSUB-writer's interface to the C C<malloc> function.
1918
1919 void * New( x, void *ptr, int size, type )
1920
1921=item Newc
1922
1923The XSUB-writer's interface to the C C<malloc> function, with cast.
1924
1925 void * Newc( x, void *ptr, int size, type, cast )
1926
1927=item Newz
1928
1929The XSUB-writer's interface to the C C<malloc> function. The allocated
1930memory is zeroed with C<memzero>.
1931
1932 void * Newz( x, void *ptr, int size, type )
1933
1934=item newAV
1935
5f05dabc 1936Creates a new AV. The reference count is set to 1.
cb1a09d0
AD
1937
1938 AV* newAV _((void));
1939
1940=item newHV
1941
5f05dabc 1942Creates a new HV. The reference count is set to 1.
cb1a09d0
AD
1943
1944 HV* newHV _((void));
1945
5f05dabc 1946=item newRV_inc
cb1a09d0 1947
5f05dabc 1948Creates an RV wrapper for an SV. The reference count for the original SV is
cb1a09d0
AD
1949incremented.
1950
5f05dabc
PP
1951 SV* newRV_inc _((SV* ref));
1952
1953For historical reasons, "newRV" is a synonym for "newRV_inc".
1954
1955=item newRV_noinc
1956
1957Creates an RV wrapper for an SV. The reference count for the original
1958SV is B<not> incremented.
1959
07fa94a1 1960 SV* newRV_noinc _((SV* ref));
cb1a09d0
AD
1961
1962=item newSV
1963
1964Creates a new SV. The C<len> parameter indicates the number of bytes of
68dc0745 1965preallocated string space the SV should have. The reference count for the
07fa94a1 1966new SV is set to 1.
cb1a09d0
AD
1967
1968 SV* newSV _((STRLEN len));
1969
1970=item newSViv
1971
07fa94a1
JO
1972Creates a new SV and copies an integer into it. The reference count for the
1973SV is set to 1.
cb1a09d0
AD
1974
1975 SV* newSViv _((IV i));
1976
1977=item newSVnv
1978
07fa94a1
JO
1979Creates a new SV and copies a double into it. The reference count for the
1980SV is set to 1.
cb1a09d0
AD
1981
1982 SV* newSVnv _((NV i));
1983
1984=item newSVpv
1985
07fa94a1
JO
1986Creates a new SV and copies a string into it. The reference count for the
1987SV is set to 1. If C<len> is zero then Perl will compute the length.
cb1a09d0
AD
1988
1989 SV* newSVpv _((char* s, STRLEN len));
1990
1991=item newSVrv
1992
1993Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
5fb8527f 1994it will be upgraded to one. If C<classname> is non-null then the new SV will
cb1a09d0 1995be blessed in the specified package. The new SV is returned and its
5f05dabc 1996reference count is 1.
8ebc5c01 1997
cb1a09d0
AD
1998 SV* newSVrv _((SV* rv, char* classname));
1999
2000=item newSVsv
2001
5fb8527f 2002Creates a new SV which is an exact duplicate of the original SV.
cb1a09d0
AD
2003
2004 SV* newSVsv _((SV* old));
2005
2006=item newXS
2007
2008Used by C<xsubpp> to hook up XSUBs as Perl subs.
2009
2010=item newXSproto
2011
2012Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
2013the subs.
2014
2015=item Nullav
2016
2017Null AV pointer.
2018
2019=item Nullch
2020
2021Null character pointer.
2022
2023=item Nullcv
2024
2025Null CV pointer.
2026
2027=item Nullhv
2028
2029Null HV pointer.
2030
2031=item Nullsv
2032
2033Null SV pointer.
2034
2035=item ORIGMARK
2036
2037The original stack mark for the XSUB. See C<dORIGMARK>.
2038
2039=item perl_alloc
2040
2041Allocates a new Perl interpreter. See L<perlembed>.
2042
2043=item perl_call_argv
2044
2045Performs a callback to the specified Perl sub. See L<perlcall>.
2046
2047 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
2048
2049=item perl_call_method
2050
2051Performs a callback to the specified Perl method. The blessed object must
2052be on the stack. See L<perlcall>.
2053
2054 I32 perl_call_method _((char* methname, I32 flags));
2055
2056=item perl_call_pv
2057
2058Performs a callback to the specified Perl sub. See L<perlcall>.
2059
2060 I32 perl_call_pv _((char* subname, I32 flags));
2061
2062=item perl_call_sv
2063
2064Performs a callback to the Perl sub whose name is in the SV. See
2065L<perlcall>.
2066
2067 I32 perl_call_sv _((SV* sv, I32 flags));
2068
2069=item perl_construct
2070
2071Initializes a new Perl interpreter. See L<perlembed>.
2072
2073=item perl_destruct
2074
2075Shuts down a Perl interpreter. See L<perlembed>.
2076
2077=item perl_eval_sv
2078
2079Tells Perl to C<eval> the string in the SV.
2080
2081 I32 perl_eval_sv _((SV* sv, I32 flags));
2082
137443ea
PP
2083=item perl_eval_pv
2084
2085Tells Perl to C<eval> the given string and return an SV* result.
2086
2087 SV* perl_eval_pv _((char* p, I32 croak_on_error));
2088
cb1a09d0
AD
2089=item perl_free
2090
2091Releases a Perl interpreter. See L<perlembed>.
2092
2093=item perl_get_av
2094
2095Returns the AV of the specified Perl array. If C<create> is set and the
2096Perl variable does not exist then it will be created. If C<create> is not
04343c6d 2097set and the variable does not exist then NULL is returned.
cb1a09d0
AD
2098
2099 AV* perl_get_av _((char* name, I32 create));
2100
2101=item perl_get_cv
2102
2103Returns the CV of the specified Perl sub. If C<create> is set and the Perl
2104variable does not exist then it will be created. If C<create> is not
04343c6d 2105set and the variable does not exist then NULL is returned.
cb1a09d0
AD
2106
2107 CV* perl_get_cv _((char* name, I32 create));
2108
2109=item perl_get_hv
2110
2111Returns the HV of the specified Perl hash. If C<create> is set and the Perl
2112variable does not exist then it will be created. If C<create> is not
04343c6d 2113set and the variable does not exist then NULL is returned.
cb1a09d0
AD
2114
2115 HV* perl_get_hv _((char* name, I32 create));
2116
2117=item perl_get_sv
2118
2119Returns the SV of the specified Perl scalar. If C<create> is set and the
2120Perl variable does not exist then it will be created. If C<create> is not
04343c6d 2121set and the variable does not exist then NULL is returned.
cb1a09d0
AD
2122
2123 SV* perl_get_sv _((char* name, I32 create));
2124
2125=item perl_parse
2126
2127Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
2128
2129=item perl_require_pv
2130
2131Tells Perl to C<require> a module.
2132
2133 void perl_require_pv _((char* pv));
2134
2135=item perl_run
2136
2137Tells a Perl interpreter to run. See L<perlembed>.
2138
2139=item POPi
2140
2141Pops an integer off the stack.
2142
2143 int POPi();
2144
2145=item POPl
2146
2147Pops a long off the stack.
2148
2149 long POPl();
2150
2151=item POPp
2152
2153Pops a string off the stack.
2154
2155 char * POPp();
2156
2157=item POPn
2158
2159Pops a double off the stack.
2160
2161 double POPn();
2162
2163=item POPs
2164
2165Pops an SV off the stack.
2166
2167 SV* POPs();
2168
2169=item PUSHMARK
2170
2171Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2172
2173 PUSHMARK(p)
2174
2175=item PUSHi
2176
2177Push an integer onto the stack. The stack must have room for this element.
2178See C<XPUSHi>.
2179
2180 PUSHi(int d)
2181
2182=item PUSHn
2183
2184Push a double onto the stack. The stack must have room for this element.
2185See C<XPUSHn>.
2186
2187 PUSHn(double d)
2188
2189=item PUSHp
2190
2191Push a string onto the stack. The stack must have room for this element.
2192The C<len> indicates the length of the string. See C<XPUSHp>.
2193
2194 PUSHp(char *c, int len )
2195
2196=item PUSHs
2197
2198Push an SV onto the stack. The stack must have room for this element. See
2199C<XPUSHs>.
2200
2201 PUSHs(sv)
2202
2203=item PUTBACK
2204
2205Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2206See C<PUSHMARK> and L<perlcall> for other uses.
2207
2208 PUTBACK;
2209
2210=item Renew
2211
2212The XSUB-writer's interface to the C C<realloc> function.
2213
2214 void * Renew( void *ptr, int size, type )
2215
2216=item Renewc
2217
2218The XSUB-writer's interface to the C C<realloc> function, with cast.
2219
2220 void * Renewc( void *ptr, int size, type, cast )
2221
2222=item RETVAL
2223
2224Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
5fb8527f
PP
2225This is always the proper type for the XSUB.
2226See L<perlxs/"The RETVAL Variable">.
cb1a09d0
AD
2227
2228=item safefree
2229
2230The XSUB-writer's interface to the C C<free> function.
2231
2232=item safemalloc
2233
2234The XSUB-writer's interface to the C C<malloc> function.
2235
2236=item saferealloc
2237
2238The XSUB-writer's interface to the C C<realloc> function.
2239
2240=item savepv
2241
2242Copy a string to a safe spot. This does not use an SV.
2243
2244 char* savepv _((char* sv));
2245
2246=item savepvn
2247
2248Copy a string to a safe spot. The C<len> indicates number of bytes to
2249copy. This does not use an SV.
2250
2251 char* savepvn _((char* sv, I32 len));
2252
2253=item SAVETMPS
2254
2255Opening bracket for temporaries on a callback. See C<FREETMPS> and
2256L<perlcall>.
2257
2258 SAVETMPS;
2259
2260=item SP
2261
2262Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2263C<SPAGAIN>.
2264
2265=item SPAGAIN
2266
54310121 2267Refetch the stack pointer. Used after a callback. See L<perlcall>.
cb1a09d0
AD
2268
2269 SPAGAIN;
2270
2271=item ST
2272
2273Used to access elements on the XSUB's stack.
2274
2275 SV* ST(int x)
2276
2277=item strEQ
2278
2279Test two strings to see if they are equal. Returns true or false.
2280
2281 int strEQ( char *s1, char *s2 )
2282
2283=item strGE
2284
2285Test two strings to see if the first, C<s1>, is greater than or equal to the
2286second, C<s2>. Returns true or false.
2287
2288 int strGE( char *s1, char *s2 )
2289
2290=item strGT
2291
2292Test two strings to see if the first, C<s1>, is greater than the second,
2293C<s2>. Returns true or false.
2294
2295 int strGT( char *s1, char *s2 )
2296
2297=item strLE
2298
2299Test two strings to see if the first, C<s1>, is less than or equal to the
2300second, C<s2>. Returns true or false.
2301
2302 int strLE( char *s1, char *s2 )
2303
2304=item strLT
2305
2306Test two strings to see if the first, C<s1>, is less than the second,
2307C<s2>. Returns true or false.
2308
2309 int strLT( char *s1, char *s2 )
2310
2311=item strNE
2312
2313Test two strings to see if they are different. Returns true or false.
2314
2315 int strNE( char *s1, char *s2 )
2316
2317=item strnEQ
2318
2319Test two strings to see if they are equal. The C<len> parameter indicates
2320the number of bytes to compare. Returns true or false.
2321
2322 int strnEQ( char *s1, char *s2 )
2323
2324=item strnNE
2325
2326Test two strings to see if they are different. The C<len> parameter
2327indicates the number of bytes to compare. Returns true or false.
2328
2329 int strnNE( char *s1, char *s2, int len )
2330
2331=item sv_2mortal
2332
2333Marks an SV as mortal. The SV will be destroyed when the current context
2334ends.
2335
2336 SV* sv_2mortal _((SV* sv));
2337
2338=item sv_bless
2339
2340Blesses an SV into a specified package. The SV must be an RV. The package
07fa94a1
JO
2341must be designated by its stash (see C<gv_stashpv()>). The reference count
2342of the SV is unaffected.
cb1a09d0
AD
2343
2344 SV* sv_bless _((SV* sv, HV* stash));
2345
2346=item sv_catpv
2347
2348Concatenates the string onto the end of the string which is in the SV.
2349
2350 void sv_catpv _((SV* sv, char* ptr));
2351
2352=item sv_catpvn
2353
2354Concatenates the string onto the end of the string which is in the SV. The
2355C<len> indicates number of bytes to copy.
2356
2357 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
2358
46fc3d4c
PP
2359=item sv_catpvf
2360
2361Processes its arguments like C<sprintf> and appends the formatted output
2362to an SV.
2363
2364 void sv_catpvf _((SV* sv, const char* pat, ...));
2365
cb1a09d0
AD
2366=item sv_catsv
2367
5fb8527f 2368Concatenates the string from SV C<ssv> onto the end of the string in SV
cb1a09d0
AD
2369C<dsv>.
2370
2371 void sv_catsv _((SV* dsv, SV* ssv));
2372
5fb8527f
PP
2373=item sv_cmp
2374
2375Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2376string in C<sv1> is less than, equal to, or greater than the string in
2377C<sv2>.
2378
2379 I32 sv_cmp _((SV* sv1, SV* sv2));
2380
cb1a09d0
AD
2381=item SvCUR
2382
2383Returns the length of the string which is in the SV. See C<SvLEN>.
2384
2385 int SvCUR (SV* sv)
2386
2387=item SvCUR_set
2388
2389Set the length of the string which is in the SV. See C<SvCUR>.
2390
2391 SvCUR_set (SV* sv, int val )
2392
5fb8527f
PP
2393=item sv_dec
2394
5f05dabc 2395Auto-decrement of the value in the SV.
5fb8527f
PP
2396
2397 void sv_dec _((SV* sv));
2398
cb1a09d0
AD
2399=item SvEND
2400
2401Returns a pointer to the last character in the string which is in the SV.
2402See C<SvCUR>. Access the character as
2403
2404 *SvEND(sv)
2405
5fb8527f
PP
2406=item sv_eq
2407
2408Returns a boolean indicating whether the strings in the two SVs are
2409identical.
2410
2411 I32 sv_eq _((SV* sv1, SV* sv2));
2412
cb1a09d0
AD
2413=item SvGROW
2414
5fb8527f
PP
2415Expands the character buffer in the SV. Calls C<sv_grow> to perform the
2416expansion if necessary. Returns a pointer to the character buffer.
cb1a09d0
AD
2417
2418 char * SvGROW( SV* sv, int len )
2419
5fb8527f
PP
2420=item sv_grow
2421
2422Expands the character buffer in the SV. This will use C<sv_unref> and will
2423upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2424Use C<SvGROW>.
2425
2426=item sv_inc
2427
07fa94a1 2428Auto-increment of the value in the SV.
5fb8527f
PP
2429
2430 void sv_inc _((SV* sv));
2431
cb1a09d0
AD
2432=item SvIOK
2433
2434Returns a boolean indicating whether the SV contains an integer.
2435
2436 int SvIOK (SV* SV)
2437
2438=item SvIOK_off
2439
2440Unsets the IV status of an SV.
2441
2442 SvIOK_off (SV* sv)
2443
2444=item SvIOK_on
2445
2446Tells an SV that it is an integer.
2447
2448 SvIOK_on (SV* sv)
2449
5fb8527f
PP
2450=item SvIOK_only
2451
2452Tells an SV that it is an integer and disables all other OK bits.
2453
2454 SvIOK_on (SV* sv)
2455
cb1a09d0
AD
2456=item SvIOKp
2457
2458Returns a boolean indicating whether the SV contains an integer. Checks the
2459B<private> setting. Use C<SvIOK>.
2460
2461 int SvIOKp (SV* SV)
2462
2463=item sv_isa
2464
2465Returns a boolean indicating whether the SV is blessed into the specified
2466class. This does not know how to check for subtype, so it doesn't work in
2467an inheritance relationship.
2468
2469 int sv_isa _((SV* sv, char* name));
2470
2471=item SvIV
2472
2473Returns the integer which is in the SV.
2474
2475 int SvIV (SV* sv)
2476
2477=item sv_isobject
2478
2479Returns a boolean indicating whether the SV is an RV pointing to a blessed
2480object. If the SV is not an RV, or if the object is not blessed, then this
2481will return false.
2482
2483 int sv_isobject _((SV* sv));
2484
2485=item SvIVX
2486
2487Returns the integer which is stored in the SV.
2488
2489 int SvIVX (SV* sv);
2490
2491=item SvLEN
2492
2493Returns the size of the string buffer in the SV. See C<SvCUR>.
2494
2495 int SvLEN (SV* sv)
2496
5fb8527f
PP
2497=item sv_len
2498
2499Returns the length of the string in the SV. Use C<SvCUR>.
2500
2501 STRLEN sv_len _((SV* sv));
2502
cb1a09d0
AD
2503=item sv_magic
2504
2505Adds magic to an SV.
2506
2507 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2508
2509=item sv_mortalcopy
2510
2511Creates a new SV which is a copy of the original SV. The new SV is marked
5f05dabc 2512as mortal.
cb1a09d0
AD
2513
2514 SV* sv_mortalcopy _((SV* oldsv));
2515
2516=item SvOK
2517
2518Returns a boolean indicating whether the value is an SV.
2519
2520 int SvOK (SV* sv)
2521
2522=item sv_newmortal
2523
5f05dabc 2524Creates a new SV which is mortal. The reference count of the SV is set to 1.
cb1a09d0
AD
2525
2526 SV* sv_newmortal _((void));
2527
2528=item sv_no
2529
2530This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2531
2532=item SvNIOK
2533
2534Returns a boolean indicating whether the SV contains a number, integer or
2535double.
2536
2537 int SvNIOK (SV* SV)
2538
2539=item SvNIOK_off
2540
2541Unsets the NV/IV status of an SV.
2542
2543 SvNIOK_off (SV* sv)
2544
2545=item SvNIOKp
2546
2547Returns a boolean indicating whether the SV contains a number, integer or
2548double. Checks the B<private> setting. Use C<SvNIOK>.
2549
2550 int SvNIOKp (SV* SV)
2551
2552=item SvNOK
2553
2554Returns a boolean indicating whether the SV contains a double.
2555
2556 int SvNOK (SV* SV)
2557
2558=item SvNOK_off
2559
2560Unsets the NV status of an SV.
2561
2562 SvNOK_off (SV* sv)
2563
2564=item SvNOK_on
2565
2566Tells an SV that it is a double.
2567
2568 SvNOK_on (SV* sv)
2569
5fb8527f
PP
2570=item SvNOK_only
2571
2572Tells an SV that it is a double and disables all other OK bits.
2573
2574 SvNOK_on (SV* sv)
2575
cb1a09d0
AD
2576=item SvNOKp
2577
2578Returns a boolean indicating whether the SV contains a double. Checks the
2579B<private> setting. Use C<SvNOK>.
2580
2581 int SvNOKp (SV* SV)
2582
2583=item SvNV
2584
2585Returns the double which is stored in the SV.
2586
2587 double SvNV (SV* sv);
2588
2589=item SvNVX
2590
2591Returns the double which is stored in the SV.
2592
2593 double SvNVX (SV* sv);
2594
2595=item SvPOK
2596
2597Returns a boolean indicating whether the SV contains a character string.
2598
2599 int SvPOK (SV* SV)
2600
2601=item SvPOK_off
2602
2603Unsets the PV status of an SV.
2604
2605 SvPOK_off (SV* sv)
2606
2607=item SvPOK_on
2608
2609Tells an SV that it is a string.
2610
2611 SvPOK_on (SV* sv)
2612
5fb8527f
PP
2613=item SvPOK_only
2614
2615Tells an SV that it is a string and disables all other OK bits.
2616
2617 SvPOK_on (SV* sv)
2618
cb1a09d0
AD
2619=item SvPOKp
2620
2621Returns a boolean indicating whether the SV contains a character string.
2622Checks the B<private> setting. Use C<SvPOK>.
2623
2624 int SvPOKp (SV* SV)
2625
2626=item SvPV
2627
2628Returns a pointer to the string in the SV, or a stringified form of the SV
2629if the SV does not contain a string. If C<len> is C<na> then Perl will
2630handle the length on its own.
2631
2632 char * SvPV (SV* sv, int len )
2633
2634=item SvPVX
2635
2636Returns a pointer to the string in the SV. The SV must contain a string.
2637
2638 char * SvPVX (SV* sv)
2639
2640=item SvREFCNT
2641
5f05dabc 2642Returns the value of the object's reference count.
cb1a09d0
AD
2643
2644 int SvREFCNT (SV* sv);
2645
2646=item SvREFCNT_dec
2647
5f05dabc 2648Decrements the reference count of the given SV.
cb1a09d0
AD
2649
2650 void SvREFCNT_dec (SV* sv)
2651
2652=item SvREFCNT_inc
2653
5f05dabc 2654Increments the reference count of the given SV.
cb1a09d0
AD
2655
2656 void SvREFCNT_inc (SV* sv)
2657
2658=item SvROK
2659
2660Tests if the SV is an RV.
2661
2662 int SvROK (SV* sv)
2663
2664=item SvROK_off
2665
2666Unsets the RV status of an SV.
2667
2668 SvROK_off (SV* sv)
2669
2670=item SvROK_on
2671
2672Tells an SV that it is an RV.
2673
2674 SvROK_on (SV* sv)
2675
2676=item SvRV
2677
2678Dereferences an RV to return the SV.
2679
2680 SV* SvRV (SV* sv);
2681
2682=item sv_setiv
2683
2684Copies an integer into the given SV.
2685
2686 void sv_setiv _((SV* sv, IV num));
2687
2688=item sv_setnv
2689
2690Copies a double into the given SV.
2691
2692 void sv_setnv _((SV* sv, double num));
2693
2694=item sv_setpv
2695
2696Copies a string into an SV. The string must be null-terminated.
2697
2698 void sv_setpv _((SV* sv, char* ptr));
2699
2700=item sv_setpvn
2701
2702Copies a string into an SV. The C<len> parameter indicates the number of
2703bytes to be copied.
2704
2705 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2706
46fc3d4c
PP
2707=item sv_setpvf
2708
2709Processes its arguments like C<sprintf> and sets an SV to the formatted
2710output.
2711
2712 void sv_setpvf _((SV* sv, const char* pat, ...));
2713
cb1a09d0
AD
2714=item sv_setref_iv
2715
5fb8527f
PP
2716Copies an integer into a new SV, optionally blessing the SV. The C<rv>
2717argument will be upgraded to an RV. That RV will be modified to point to
2718the new SV. The C<classname> argument indicates the package for the
2719blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
5f05dabc 2720will be returned and will have a reference count of 1.
cb1a09d0
AD
2721
2722 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2723
2724=item sv_setref_nv
2725
5fb8527f
PP
2726Copies a double into a new SV, optionally blessing the SV. The C<rv>
2727argument will be upgraded to an RV. That RV will be modified to point to
2728the new SV. The C<classname> argument indicates the package for the
2729blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
5f05dabc 2730will be returned and will have a reference count of 1.
cb1a09d0
AD
2731
2732 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2733
2734=item sv_setref_pv
2735
5fb8527f
PP
2736Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
2737argument will be upgraded to an RV. That RV will be modified to point to
2738the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
2739into the SV. The C<classname> argument indicates the package for the
2740blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
5f05dabc 2741will be returned and will have a reference count of 1.
cb1a09d0
AD
2742
2743 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2744
2745Do not use with integral Perl types such as HV, AV, SV, CV, because those
2746objects will become corrupted by the pointer copy process.
2747
2748Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2749
2750=item sv_setref_pvn
2751
5fb8527f
PP
2752Copies a string into a new SV, optionally blessing the SV. The length of the
2753string must be specified with C<n>. The C<rv> argument will be upgraded to
2754an RV. That RV will be modified to point to the new SV. The C<classname>
cb1a09d0
AD
2755argument indicates the package for the blessing. Set C<classname> to
2756C<Nullch> to avoid the blessing. The new SV will be returned and will have
5f05dabc 2757a reference count of 1.
cb1a09d0
AD
2758
2759 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2760
2761Note that C<sv_setref_pv> copies the pointer while this copies the string.
2762
2763=item sv_setsv
2764
2765Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
5f05dabc 2766The source SV may be destroyed if it is mortal.
cb1a09d0
AD
2767
2768 void sv_setsv _((SV* dsv, SV* ssv));
2769
2770=item SvSTASH
2771
2772Returns the stash of the SV.
2773
2774 HV * SvSTASH (SV* sv)
2775
2776=item SVt_IV
2777
2778Integer type flag for scalars. See C<svtype>.
2779
2780=item SVt_PV
2781
2782Pointer type flag for scalars. See C<svtype>.
2783
2784=item SVt_PVAV
2785
2786Type flag for arrays. See C<svtype>.
2787
2788=item SVt_PVCV
2789
2790Type flag for code refs. See C<svtype>.
2791
2792=item SVt_PVHV
2793
2794Type flag for hashes. See C<svtype>.
2795
2796=item SVt_PVMG
2797
2798Type flag for blessed scalars. See C<svtype>.
2799
2800=item SVt_NV
2801
2802Double type flag for scalars. See C<svtype>.
2803
2804=item SvTRUE
2805
2806Returns a boolean indicating whether Perl would evaluate the SV as true or
2807false, defined or undefined.
2808
2809 int SvTRUE (SV* sv)
2810
2811=item SvTYPE
2812
2813Returns the type of the SV. See C<svtype>.
2814
2815 svtype SvTYPE (SV* sv)
2816
2817=item svtype
2818
2819An enum of flags for Perl types. These are found in the file B<sv.h> in the
2820C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2821
2822=item SvUPGRADE
2823
5fb8527f
PP
2824Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
2825the upgrade if necessary. See C<svtype>.
2826
2827 bool SvUPGRADE _((SV* sv, svtype mt));
2828
2829=item sv_upgrade
2830
2831Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
cb1a09d0
AD
2832
2833=item sv_undef
2834
2835This is the C<undef> SV. Always refer to this as C<&sv_undef>.
2836
5fb8527f
PP
2837=item sv_unref
2838
07fa94a1
JO
2839Unsets the RV status of the SV, and decrements the reference count of
2840whatever was being referenced by the RV. This can almost be thought of
2841as a reversal of C<newSVrv>. See C<SvROK_off>.
5fb8527f
PP
2842
2843 void sv_unref _((SV* sv));
2844
cb1a09d0
AD
2845=item sv_usepvn
2846
2847Tells an SV to use C<ptr> to find its string value. Normally the string is
5fb8527f
PP
2848stored inside the SV but sv_usepvn allows the SV to use an outside string.
2849The C<ptr> should point to memory that was allocated by C<malloc>. The
cb1a09d0
AD
2850string length, C<len>, must be supplied. This function will realloc the
2851memory pointed to by C<ptr>, so that pointer should not be freed or used by
2852the programmer after giving it to sv_usepvn.
2853
2854 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
2855
2856=item sv_yes
2857
2858This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
2859
2860=item THIS
2861
2862Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
2863This is always the proper type for the C++ object. See C<CLASS> and
5fb8527f 2864L<perlxs/"Using XS With C++">.
cb1a09d0
AD
2865
2866=item toLOWER
2867
2868Converts the specified character to lowercase.
2869
2870 int toLOWER (char c)
2871
2872=item toUPPER
2873
2874Converts the specified character to uppercase.
2875
2876 int toUPPER (char c)
2877
2878=item warn
2879
2880This is the XSUB-writer's interface to Perl's C<warn> function. Use this
2881function the same way you use the C C<printf> function. See C<croak()>.
2882
2883=item XPUSHi
2884
2885Push an integer onto the stack, extending the stack if necessary. See
2886C<PUSHi>.
2887
2888 XPUSHi(int d)
2889
2890=item XPUSHn
2891
2892Push a double onto the stack, extending the stack if necessary. See
2893C<PUSHn>.
2894
2895 XPUSHn(double d)
2896
2897=item XPUSHp
2898
2899Push a string onto the stack, extending the stack if necessary. The C<len>
2900indicates the length of the string. See C<PUSHp>.
2901
2902 XPUSHp(char *c, int len)
2903
2904=item XPUSHs
2905
2906Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
2907
2908 XPUSHs(sv)
2909
5fb8527f
PP
2910=item XS
2911
2912Macro to declare an XSUB and its C parameter list. This is handled by
2913C<xsubpp>.
2914
cb1a09d0
AD
2915=item XSRETURN
2916
2917Return from XSUB, indicating number of items on the stack. This is usually
2918handled by C<xsubpp>.
2919
5fb8527f 2920 XSRETURN(int x);
cb1a09d0
AD
2921
2922=item XSRETURN_EMPTY
2923
5fb8527f 2924Return an empty list from an XSUB immediately.
cb1a09d0
AD
2925
2926 XSRETURN_EMPTY;
2927
5fb8527f
PP
2928=item XSRETURN_IV
2929
2930Return an integer from an XSUB immediately. Uses C<XST_mIV>.
2931
2932 XSRETURN_IV(IV v);
2933
cb1a09d0
AD
2934=item XSRETURN_NO
2935
5fb8527f 2936Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
cb1a09d0
AD
2937
2938 XSRETURN_NO;
2939
5fb8527f
PP
2940=item XSRETURN_NV
2941
2942Return an double from an XSUB immediately. Uses C<XST_mNV>.
2943
2944 XSRETURN_NV(NV v);
2945
2946=item XSRETURN_PV
2947
2948Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
2949
2950 XSRETURN_PV(char *v);
2951
cb1a09d0
AD
2952=item XSRETURN_UNDEF
2953
5fb8527f 2954Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
cb1a09d0
AD
2955
2956 XSRETURN_UNDEF;
2957
2958=item XSRETURN_YES
2959
5fb8527f 2960Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
cb1a09d0
AD
2961
2962 XSRETURN_YES;
2963
5fb8527f
PP
2964=item XST_mIV
2965
2966Place an integer into the specified position C<i> on the stack. The value is
2967stored in a new mortal SV.
2968
2969 XST_mIV( int i, IV v );
2970
2971=item XST_mNV
2972
2973Place a double into the specified position C<i> on the stack. The value is
2974stored in a new mortal SV.
2975
2976 XST_mNV( int i, NV v );
2977
2978=item XST_mNO
2979
2980Place C<&sv_no> into the specified position C<i> on the stack.
2981
2982 XST_mNO( int i );
2983
2984=item XST_mPV
2985
2986Place a copy of a string into the specified position C<i> on the stack. The
2987value is stored in a new mortal SV.
2988
2989 XST_mPV( int i, char *v );
2990
2991=item XST_mUNDEF
2992
2993Place C<&sv_undef> into the specified position C<i> on the stack.
2994
2995 XST_mUNDEF( int i );
2996
2997=item XST_mYES
2998
2999Place C<&sv_yes> into the specified position C<i> on the stack.
3000
3001 XST_mYES( int i );
3002
3003=item XS_VERSION
3004
3005The version identifier for an XS module. This is usually handled
3006automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
3007
3008=item XS_VERSION_BOOTCHECK
3009
3010Macro to verify that a PM module's $VERSION variable matches the XS module's
3011C<XS_VERSION> variable. This is usually handled automatically by
3012C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
3013
cb1a09d0
AD
3014=item Zero
3015
3016The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
3017destination, C<n> is the number of items, and C<t> is the type.
3018
3019 (void) Zero( d, n, t );
3020
3021=back
3022
5f05dabc 3023=head1 EDITOR
cb1a09d0 3024
9607fc9c 3025Jeff Okamoto <F<okamoto@corp.hp.com>>
cb1a09d0
AD
3026
3027With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
3028Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
bdbeb323
SM
3029Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer, and
3030Stephen McCamant.
cb1a09d0 3031
9607fc9c 3032API Listing by Dean Roehrich <F<roehrich@cray.com>>.
cb1a09d0
AD
3033
3034=head1 DATE
3035
04343c6d 3036Version 31.8: 1997/5/17