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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
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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.
a0d0e21e
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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:
a0d0e21e
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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
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623
624Scalar variables normally contain only one type of value, an integer,
625double, pointer, or reference. Perl will automatically convert the
626actual scalar data from the stored type into the requested type.
627
628Some scalar variables contain more than one type of scalar data. For
629example, the variable C<$!> contains either the numeric value of C<errno>
630or its string equivalent from either C<strerror> or C<sys_errlist[]>.
631
632To force multiple data values into an SV, you must do two things: use the
633C<sv_set*v> routines to add the additional scalar type, then set a flag
634so that Perl will believe it contains more than one type of data. The
635four macros to set the flags are:
636
637 SvIOK_on
638 SvNOK_on
639 SvPOK_on
640 SvROK_on
641
642The particular macro you must use depends on which C<sv_set*v> routine
643you called first. This is because every C<sv_set*v> routine turns on
644only the bit for the particular type of data being set, and turns off
645all the rest.
646
647For example, to create a new Perl variable called "dberror" that contains
648both the numeric and descriptive string error values, you could use the
649following code:
650
651 extern int dberror;
652 extern char *dberror_list;
653
654 SV* sv = perl_get_sv("dberror", TRUE);
655 sv_setiv(sv, (IV) dberror);
656 sv_setpv(sv, dberror_list[dberror]);
657 SvIOK_on(sv);
658
659If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
660macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
661
662=head2 Magic Variables
a0d0e21e 663
d1b91892
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664[This section still under construction. Ignore everything here. Post no
665bills. Everything not permitted is forbidden.]
666
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667Any SV may be magical, that is, it has special features that a normal
668SV does not have. These features are stored in the SV structure in a
5f05dabc 669linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
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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
d1b91892
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698associated with an SV.
699
54310121
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700The C<name> and C<namlen> arguments are used to associate a string with
701the magic, typically the name of a variable. C<namlen> is stored in the
702C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
d1b91892
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703copy of the name is stored in C<mg_ptr> field.
704
705The sv_magic function uses C<how> to determine which, if any, predefined
706"Magic Virtual Table" should be assigned to the C<mg_virtual> field.
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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
07fa94a1 768 mg_type MGVTBL Type of magical
5f05dabc 769 ------- ------ ----------------------------
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AD
770 \0 vtbl_sv Regexp???
771 A vtbl_amagic Operator Overloading
772 a vtbl_amagicelem Operator Overloading
773 c 0 Used in Operator Overloading
774 B vtbl_bm Boyer-Moore???
775 E vtbl_env %ENV hash
776 e vtbl_envelem %ENV hash element
777 g vtbl_mglob Regexp /g flag???
778 I vtbl_isa @ISA array
779 i vtbl_isaelem @ISA array element
780 L 0 (but sets RMAGICAL) Perl Module/Debugger???
781 l vtbl_dbline Debugger?
44a8e56a 782 o vtbl_collxfrm Locale transformation
d1b91892
AD
783 P vtbl_pack Tied Array or Hash
784 p vtbl_packelem Tied Array or Hash element
785 q vtbl_packelem Tied Scalar or Handle
786 S vtbl_sig Signal Hash
787 s vtbl_sigelem Signal Hash element
788 t vtbl_taint Taintedness
789 U vtbl_uvar ???
790 v vtbl_vec Vector
791 x vtbl_substr Substring???
e616eb7b 792 y vtbl_itervar Shadow "foreach" iterator variable
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AD
793 * vtbl_glob GV???
794 # vtbl_arylen Array Length
795 . vtbl_pos $. scalar variable
5f05dabc 796 ~ None Used by certain extensions
d1b91892 797
68dc0745
PP
798When an uppercase and lowercase letter both exist in the table, then the
799uppercase letter is used to represent some kind of composite type (a list
800or a hash), and the lowercase letter is used to represent an element of
d1b91892
AD
801that composite type.
802
5f05dabc
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803The '~' magic type is defined specifically for use by extensions and
804will not be used by perl itself. Extensions can use ~ magic to 'attach'
805private information to variables (typically objects). This is especially
806useful because there is no way for normal perl code to corrupt this
807private information (unlike using extra elements of a hash object).
808
809Note that because multiple extensions may be using ~ magic it is
810important for extensions to take extra care with it. Typically only
811using it on objects blessed into the same class as the extension
812is sufficient. It may also be appropriate to add an I32 'signature'
813at the top of the private data area and check that.
814
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AD
815=head2 Finding Magic
816
817 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
818
819This routine returns a pointer to the C<MAGIC> structure stored in the SV.
820If the SV does not have that magical feature, C<NULL> is returned. Also,
54310121 821if the SV is not of type SVt_PVMG, Perl may core dump.
d1b91892
AD
822
823 int mg_copy(SV* sv, SV* nsv, char* key, STRLEN klen);
824
825This routine checks to see what types of magic C<sv> has. If the mg_type
68dc0745
PP
826field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
827the mg_type field is changed to be the lowercase letter.
a0d0e21e 828
04343c6d
GS
829=head2 Understanding the Magic of Tied Hashes and Arrays
830
831Tied hashes and arrays are magical beasts of the 'P' magic type.
9edb2b46
GS
832
833WARNING: As of the 5.004 release, proper usage of the array and hash
834access functions requires understanding a few caveats. Some
835of these caveats are actually considered bugs in the API, to be fixed
836in later releases, and are bracketed with [MAYCHANGE] below. If
837you find yourself actually applying such information in this section, be
838aware that the behavior may change in the future, umm, without warning.
04343c6d
GS
839
840The C<av_store> function, when given a tied array argument, merely
841copies the magic of the array onto the value to be "stored", using
842C<mg_copy>. It may also return NULL, indicating that the value did not
9edb2b46
GS
843actually need to be stored in the array. [MAYCHANGE] After a call to
844C<av_store> on a tied array, the caller will usually need to call
845C<mg_set(val)> to actually invoke the perl level "STORE" method on the
846TIEARRAY object. If C<av_store> did return NULL, a call to
847C<SvREFCNT_dec(val)> will also be usually necessary to avoid a memory
848leak. [/MAYCHANGE]
04343c6d
GS
849
850The previous paragraph is applicable verbatim to tied hash access using the
851C<hv_store> and C<hv_store_ent> functions as well.
852
853C<av_fetch> and the corresponding hash functions C<hv_fetch> and
854C<hv_fetch_ent> actually return an undefined mortal value whose magic
855has been initialized using C<mg_copy>. Note the value so returned does not
9edb2b46
GS
856need to be deallocated, as it is already mortal. [MAYCHANGE] But you will
857need to call C<mg_get()> on the returned value in order to actually invoke
858the perl level "FETCH" method on the underlying TIE object. Similarly,
04343c6d
GS
859you may also call C<mg_set()> on the return value after possibly assigning
860a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
9edb2b46 861method on the TIE object. [/MAYCHANGE]
04343c6d 862
9edb2b46 863[MAYCHANGE]
04343c6d
GS
864In other words, the array or hash fetch/store functions don't really
865fetch and store actual values in the case of tied arrays and hashes. They
866merely call C<mg_copy> to attach magic to the values that were meant to be
867"stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
868do the job of invoking the TIE methods on the underlying objects. Thus
9edb2b46 869the magic mechanism currently implements a kind of lazy access to arrays
04343c6d
GS
870and hashes.
871
872Currently (as of perl version 5.004), use of the hash and array access
873functions requires the user to be aware of whether they are operating on
9edb2b46
GS
874"normal" hashes and arrays, or on their tied variants. The API may be
875changed to provide more transparent access to both tied and normal data
876types in future versions.
877[/MAYCHANGE]
04343c6d
GS
878
879You would do well to understand that the TIEARRAY and TIEHASH interfaces
880are mere sugar to invoke some perl method calls while using the uniform hash
881and array syntax. The use of this sugar imposes some overhead (typically
882about two to four extra opcodes per FETCH/STORE operation, in addition to
883the creation of all the mortal variables required to invoke the methods).
884This overhead will be comparatively small if the TIE methods are themselves
885substantial, but if they are only a few statements long, the overhead
886will not be insignificant.
887
0a753a76 888=head1 Subroutines
a0d0e21e 889
68dc0745 890=head2 XSUBs and the Argument Stack
5f05dabc
PP
891
892The XSUB mechanism is a simple way for Perl programs to access C subroutines.
893An XSUB routine will have a stack that contains the arguments from the Perl
894program, and a way to map from the Perl data structures to a C equivalent.
895
896The stack arguments are accessible through the C<ST(n)> macro, which returns
897the C<n>'th stack argument. Argument 0 is the first argument passed in the
898Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
899an C<SV*> is used.
900
901Most of the time, output from the C routine can be handled through use of
902the RETVAL and OUTPUT directives. However, there are some cases where the
903argument stack is not already long enough to handle all the return values.
904An example is the POSIX tzname() call, which takes no arguments, but returns
905two, the local time zone's standard and summer time abbreviations.
906
907To handle this situation, the PPCODE directive is used and the stack is
908extended using the macro:
909
910 EXTEND(sp, num);
911
912where C<sp> is the stack pointer, and C<num> is the number of elements the
913stack should be extended by.
914
915Now that there is room on the stack, values can be pushed on it using the
54310121 916macros to push IVs, doubles, strings, and SV pointers respectively:
5f05dabc
PP
917
918 PUSHi(IV)
919 PUSHn(double)
920 PUSHp(char*, I32)
921 PUSHs(SV*)
922
923And now the Perl program calling C<tzname>, the two values will be assigned
924as in:
925
926 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
927
928An alternate (and possibly simpler) method to pushing values on the stack is
929to use the macros:
930
931 XPUSHi(IV)
932 XPUSHn(double)
933 XPUSHp(char*, I32)
934 XPUSHs(SV*)
935
936These macros automatically adjust the stack for you, if needed. Thus, you
937do not need to call C<EXTEND> to extend the stack.
938
939For more information, consult L<perlxs> and L<perlxstut>.
940
941=head2 Calling Perl Routines from within C Programs
a0d0e21e
LW
942
943There are four routines that can be used to call a Perl subroutine from
944within a C program. These four are:
945
946 I32 perl_call_sv(SV*, I32);
947 I32 perl_call_pv(char*, I32);
948 I32 perl_call_method(char*, I32);
949 I32 perl_call_argv(char*, I32, register char**);
950
d1b91892
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951The routine most often used is C<perl_call_sv>. The C<SV*> argument
952contains either the name of the Perl subroutine to be called, or a
953reference to the subroutine. The second argument consists of flags
954that control the context in which the subroutine is called, whether
955or not the subroutine is being passed arguments, how errors should be
956trapped, and how to treat return values.
a0d0e21e
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957
958All four routines return the number of arguments that the subroutine returned
959on the Perl stack.
960
d1b91892
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961When using any of these routines (except C<perl_call_argv>), the programmer
962must manipulate the Perl stack. These include the following macros and
963functions:
a0d0e21e
LW
964
965 dSP
966 PUSHMARK()
967 PUTBACK
968 SPAGAIN
969 ENTER
970 SAVETMPS
971 FREETMPS
972 LEAVE
973 XPUSH*()
cb1a09d0 974 POP*()
a0d0e21e 975
5f05dabc
PP
976For a detailed description of calling conventions from C to Perl,
977consult L<perlcall>.
a0d0e21e 978
5f05dabc 979=head2 Memory Allocation
a0d0e21e 980
5f05dabc
PP
981It is suggested that you use the version of malloc that is distributed
982with Perl. It keeps pools of various sizes of unallocated memory in
07fa94a1
JO
983order to satisfy allocation requests more quickly. However, on some
984platforms, it may cause spurious malloc or free errors.
d1b91892
AD
985
986 New(x, pointer, number, type);
987 Newc(x, pointer, number, type, cast);
988 Newz(x, pointer, number, type);
989
07fa94a1 990These three macros are used to initially allocate memory.
5f05dabc
PP
991
992The first argument C<x> was a "magic cookie" that was used to keep track
993of who called the macro, to help when debugging memory problems. However,
07fa94a1
JO
994the current code makes no use of this feature (most Perl developers now
995use run-time memory checkers), so this argument can be any number.
5f05dabc
PP
996
997The second argument C<pointer> should be the name of a variable that will
998point to the newly allocated memory.
d1b91892 999
d1b91892
AD
1000The third and fourth arguments C<number> and C<type> specify how many of
1001the specified type of data structure should be allocated. The argument
1002C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
1003should be used if the C<pointer> argument is different from the C<type>
1004argument.
1005
1006Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
1007to zero out all the newly allocated memory.
1008
1009 Renew(pointer, number, type);
1010 Renewc(pointer, number, type, cast);
1011 Safefree(pointer)
1012
1013These three macros are used to change a memory buffer size or to free a
1014piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1015match those of C<New> and C<Newc> with the exception of not needing the
1016"magic cookie" argument.
1017
1018 Move(source, dest, number, type);
1019 Copy(source, dest, number, type);
1020 Zero(dest, number, type);
1021
1022These three macros are used to move, copy, or zero out previously allocated
1023memory. The C<source> and C<dest> arguments point to the source and
1024destination starting points. Perl will move, copy, or zero out C<number>
1025instances of the size of the C<type> data structure (using the C<sizeof>
1026function).
a0d0e21e 1027
5f05dabc 1028=head2 PerlIO
ce3d39e2 1029
5f05dabc
PP
1030The most recent development releases of Perl has been experimenting with
1031removing Perl's dependency on the "normal" standard I/O suite and allowing
1032other stdio implementations to be used. This involves creating a new
1033abstraction layer that then calls whichever implementation of stdio Perl
68dc0745 1034was compiled with. All XSUBs should now use the functions in the PerlIO
5f05dabc
PP
1035abstraction layer and not make any assumptions about what kind of stdio
1036is being used.
1037
1038For a complete description of the PerlIO abstraction, consult L<perlapio>.
1039
8ebc5c01 1040=head2 Putting a C value on Perl stack
ce3d39e2
IZ
1041
1042A lot of opcodes (this is an elementary operation in the internal perl
1043stack machine) put an SV* on the stack. However, as an optimization
1044the corresponding SV is (usually) not recreated each time. The opcodes
1045reuse specially assigned SVs (I<target>s) which are (as a corollary)
1046not constantly freed/created.
1047
0a753a76 1048Each of the targets is created only once (but see
ce3d39e2
IZ
1049L<Scratchpads and recursion> below), and when an opcode needs to put
1050an integer, a double, or a string on stack, it just sets the
1051corresponding parts of its I<target> and puts the I<target> on stack.
1052
1053The macro to put this target on stack is C<PUSHTARG>, and it is
1054directly used in some opcodes, as well as indirectly in zillions of
1055others, which use it via C<(X)PUSH[pni]>.
1056
8ebc5c01 1057=head2 Scratchpads
ce3d39e2 1058
54310121 1059The question remains on when the SVs which are I<target>s for opcodes
5f05dabc
PP
1060are created. The answer is that they are created when the current unit --
1061a subroutine or a file (for opcodes for statements outside of
1062subroutines) -- is compiled. During this time a special anonymous Perl
ce3d39e2
IZ
1063array is created, which is called a scratchpad for the current
1064unit.
1065
54310121 1066A scratchpad keeps SVs which are lexicals for the current unit and are
ce3d39e2
IZ
1067targets for opcodes. One can deduce that an SV lives on a scratchpad
1068by looking on its flags: lexicals have C<SVs_PADMY> set, and
1069I<target>s have C<SVs_PADTMP> set.
1070
54310121
PP
1071The correspondence between OPs and I<target>s is not 1-to-1. Different
1072OPs in the compile tree of the unit can use the same target, if this
ce3d39e2
IZ
1073would not conflict with the expected life of the temporary.
1074
2ae324a7 1075=head2 Scratchpads and recursion
ce3d39e2
IZ
1076
1077In fact it is not 100% true that a compiled unit contains a pointer to
1078the scratchpad AV. In fact it contains a pointer to an AV of
1079(initially) one element, and this element is the scratchpad AV. Why do
1080we need an extra level of indirection?
1081
1082The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1083these can create several execution pointers going into the same
1084subroutine. For the subroutine-child not write over the temporaries
1085for the subroutine-parent (lifespan of which covers the call to the
1086child), the parent and the child should have different
1087scratchpads. (I<And> the lexicals should be separate anyway!)
1088
5f05dabc
PP
1089So each subroutine is born with an array of scratchpads (of length 1).
1090On each entry to the subroutine it is checked that the current
ce3d39e2
IZ
1091depth of the recursion is not more than the length of this array, and
1092if it is, new scratchpad is created and pushed into the array.
1093
1094The I<target>s on this scratchpad are C<undef>s, but they are already
1095marked with correct flags.
1096
0a753a76
PP
1097=head1 Compiled code
1098
1099=head2 Code tree
1100
1101Here we describe the internal form your code is converted to by
1102Perl. Start with a simple example:
1103
1104 $a = $b + $c;
1105
1106This is converted to a tree similar to this one:
1107
1108 assign-to
1109 / \
1110 + $a
1111 / \
1112 $b $c
1113
1114(but slightly more complicated). This tree reflect the way Perl
1115parsed your code, but has nothing to do with the execution order.
1116There is an additional "thread" going through the nodes of the tree
1117which shows the order of execution of the nodes. In our simplified
1118example above it looks like:
1119
1120 $b ---> $c ---> + ---> $a ---> assign-to
1121
1122But with the actual compile tree for C<$a = $b + $c> it is different:
1123some nodes I<optimized away>. As a corollary, though the actual tree
1124contains more nodes than our simplified example, the execution order
1125is the same as in our example.
1126
1127=head2 Examining the tree
1128
1129If you have your perl compiled for debugging (usually done with C<-D
1130optimize=-g> on C<Configure> command line), you may examine the
1131compiled tree by specifying C<-Dx> on the Perl command line. The
1132output takes several lines per node, and for C<$b+$c> it looks like
1133this:
1134
1135 5 TYPE = add ===> 6
1136 TARG = 1
1137 FLAGS = (SCALAR,KIDS)
1138 {
1139 TYPE = null ===> (4)
1140 (was rv2sv)
1141 FLAGS = (SCALAR,KIDS)
1142 {
1143 3 TYPE = gvsv ===> 4
1144 FLAGS = (SCALAR)
1145 GV = main::b
1146 }
1147 }
1148 {
1149 TYPE = null ===> (5)
1150 (was rv2sv)
1151 FLAGS = (SCALAR,KIDS)
1152 {
1153 4 TYPE = gvsv ===> 5
1154 FLAGS = (SCALAR)
1155 GV = main::c
1156 }
1157 }
1158
1159This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1160not optimized away (one per number in the left column). The immediate
1161children of the given node correspond to C<{}> pairs on the same level
1162of indentation, thus this listing corresponds to the tree:
1163
1164 add
1165 / \
1166 null null
1167 | |
1168 gvsv gvsv
1169
1170The execution order is indicated by C<===E<gt>> marks, thus it is C<3
11714 5 6> (node C<6> is not included into above listing), i.e.,
1172C<gvsv gvsv add whatever>.
1173
1174=head2 Compile pass 1: check routines
1175
1176The tree is created by the I<pseudo-compiler> while yacc code feeds it
1177the constructions it recognizes. Since yacc works bottom-up, so does
1178the first pass of perl compilation.
1179
1180What makes this pass interesting for perl developers is that some
1181optimization may be performed on this pass. This is optimization by
1182so-called I<check routines>. The correspondence between node names
1183and corresponding check routines is described in F<opcode.pl> (do not
1184forget to run C<make regen_headers> if you modify this file).
1185
1186A check routine is called when the node is fully constructed except
1187for the execution-order thread. Since at this time there is no
1188back-links to the currently constructed node, one can do most any
1189operation to the top-level node, including freeing it and/or creating
1190new nodes above/below it.
1191
1192The check routine returns the node which should be inserted into the
1193tree (if the top-level node was not modified, check routine returns
1194its argument).
1195
1196By convention, check routines have names C<ck_*>. They are usually
1197called from C<new*OP> subroutines (or C<convert>) (which in turn are
1198called from F<perly.y>).
1199
1200=head2 Compile pass 1a: constant folding
1201
1202Immediately after the check routine is called the returned node is
1203checked for being compile-time executable. If it is (the value is
1204judged to be constant) it is immediately executed, and a I<constant>
1205node with the "return value" of the corresponding subtree is
1206substituted instead. The subtree is deleted.
1207
1208If constant folding was not performed, the execution-order thread is
1209created.
1210
1211=head2 Compile pass 2: context propagation
1212
1213When a context for a part of compile tree is known, it is propagated
1214down through the tree. Aat this time the context can have 5 values
1215(instead of 2 for runtime context): void, boolean, scalar, list, and
1216lvalue. In contrast with the pass 1 this pass is processed from top
1217to bottom: a node's context determines the context for its children.
1218
1219Additional context-dependent optimizations are performed at this time.
1220Since at this moment the compile tree contains back-references (via
1221"thread" pointers), nodes cannot be free()d now. To allow
1222optimized-away nodes at this stage, such nodes are null()ified instead
1223of free()ing (i.e. their type is changed to OP_NULL).
1224
1225=head2 Compile pass 3: peephole optimization
1226
1227After the compile tree for a subroutine (or for an C<eval> or a file)
1228is created, an additional pass over the code is performed. This pass
1229is neither top-down or bottom-up, but in the execution order (with
1230additional compilications for conditionals). These optimizations are
1231done in the subroutine peep(). Optimizations performed at this stage
1232are subject to the same restrictions as in the pass 2.
1233
1234=head1 API LISTING
a0d0e21e 1235
cb1a09d0
AD
1236This is a listing of functions, macros, flags, and variables that may be
1237useful to extension writers or that may be found while reading other
1238extensions.
a0d0e21e 1239
cb1a09d0 1240=over 8
a0d0e21e 1241
cb1a09d0
AD
1242=item AvFILL
1243
1244See C<av_len>.
1245
1246=item av_clear
1247
0146554f
GA
1248Clears an array, making it empty. Does not free the memory used by the
1249array itself.
cb1a09d0
AD
1250
1251 void av_clear _((AV* ar));
1252
1253=item av_extend
1254
1255Pre-extend an array. The C<key> is the index to which the array should be
1256extended.
1257
1258 void av_extend _((AV* ar, I32 key));
1259
1260=item av_fetch
1261
1262Returns the SV at the specified index in the array. The C<key> is the
1263index. If C<lval> is set then the fetch will be part of a store. Check
1264that the return value is non-null before dereferencing it to a C<SV*>.
1265
04343c6d
GS
1266See L<Understanding the Magic of Tied Hashes and Arrays> for more
1267information on how to use this function on tied arrays.
1268
cb1a09d0
AD
1269 SV** av_fetch _((AV* ar, I32 key, I32 lval));
1270
1271=item av_len
1272
1273Returns the highest index in the array. Returns -1 if the array is empty.
1274
1275 I32 av_len _((AV* ar));
1276
1277=item av_make
1278
5fb8527f
PP
1279Creates a new AV and populates it with a list of SVs. The SVs are copied
1280into the array, so they may be freed after the call to av_make. The new AV
5f05dabc 1281will have a reference count of 1.
cb1a09d0
AD
1282
1283 AV* av_make _((I32 size, SV** svp));
1284
1285=item av_pop
1286
1287Pops an SV off the end of the array. Returns C<&sv_undef> if the array is
1288empty.
1289
1290 SV* av_pop _((AV* ar));
1291
1292=item av_push
1293
5fb8527f
PP
1294Pushes an SV onto the end of the array. The array will grow automatically
1295to accommodate the addition.
cb1a09d0
AD
1296
1297 void av_push _((AV* ar, SV* val));
1298
1299=item av_shift
1300
1301Shifts an SV off the beginning of the array.
1302
1303 SV* av_shift _((AV* ar));
1304
1305=item av_store
1306
1307Stores an SV in an array. The array index is specified as C<key>. The
04343c6d
GS
1308return value will be NULL if the operation failed or if the value did not
1309need to be actually stored within the array (as in the case of tied arrays).
1310Otherwise it can be dereferenced to get the original C<SV*>. Note that the
1311caller is responsible for suitably incrementing the reference count of C<val>
1312before the call, and decrementing it if the function returned NULL.
1313
1314See L<Understanding the Magic of Tied Hashes and Arrays> for more
1315information on how to use this function on tied arrays.
cb1a09d0
AD
1316
1317 SV** av_store _((AV* ar, I32 key, SV* val));
1318
1319=item av_undef
1320
0146554f 1321Undefines the array. Frees the memory used by the array itself.
cb1a09d0
AD
1322
1323 void av_undef _((AV* ar));
1324
1325=item av_unshift
1326
0146554f
GA
1327Unshift the given number of C<undef> values onto the beginning of the
1328array. The array will grow automatically to accommodate the addition.
1329You must then use C<av_store> to assign values to these new elements.
cb1a09d0
AD
1330
1331 void av_unshift _((AV* ar, I32 num));
1332
1333=item CLASS
1334
1335Variable which is setup by C<xsubpp> to indicate the class name for a C++ XS
5fb8527f
PP
1336constructor. This is always a C<char*>. See C<THIS> and
1337L<perlxs/"Using XS With C++">.
cb1a09d0
AD
1338
1339=item Copy
1340
1341The XSUB-writer's interface to the C C<memcpy> function. The C<s> is the
1342source, C<d> is the destination, C<n> is the number of items, and C<t> is
0146554f 1343the type. May fail on overlapping copies. See also C<Move>.
cb1a09d0
AD
1344
1345 (void) Copy( s, d, n, t );
1346
1347=item croak
1348
1349This is the XSUB-writer's interface to Perl's C<die> function. Use this
1350function the same way you use the C C<printf> function. See C<warn>.
1351
1352=item CvSTASH
1353
1354Returns the stash of the CV.
1355
1356 HV * CvSTASH( SV* sv )
1357
1358=item DBsingle
1359
1360When Perl is run in debugging mode, with the B<-d> switch, this SV is a
1361boolean which indicates whether subs are being single-stepped.
5fb8527f
PP
1362Single-stepping is automatically turned on after every step. This is the C
1363variable which corresponds to Perl's $DB::single variable. See C<DBsub>.
cb1a09d0
AD
1364
1365=item DBsub
1366
1367When Perl is run in debugging mode, with the B<-d> switch, this GV contains
5fb8527f
PP
1368the SV which holds the name of the sub being debugged. This is the C
1369variable which corresponds to Perl's $DB::sub variable. See C<DBsingle>.
cb1a09d0
AD
1370The sub name can be found by
1371
1372 SvPV( GvSV( DBsub ), na )
1373
5fb8527f
PP
1374=item DBtrace
1375
1376Trace variable used when Perl is run in debugging mode, with the B<-d>
1377switch. This is the C variable which corresponds to Perl's $DB::trace
1378variable. See C<DBsingle>.
1379
cb1a09d0
AD
1380=item dMARK
1381
5fb8527f
PP
1382Declare a stack marker variable, C<mark>, for the XSUB. See C<MARK> and
1383C<dORIGMARK>.
cb1a09d0
AD
1384
1385=item dORIGMARK
1386
1387Saves the original stack mark for the XSUB. See C<ORIGMARK>.
1388
5fb8527f
PP
1389=item dowarn
1390
1391The C variable which corresponds to Perl's $^W warning variable.
1392
cb1a09d0
AD
1393=item dSP
1394
5fb8527f 1395Declares a stack pointer variable, C<sp>, for the XSUB. See C<SP>.
cb1a09d0
AD
1396
1397=item dXSARGS
1398
1399Sets up stack and mark pointers for an XSUB, calling dSP and dMARK. This is
1400usually handled automatically by C<xsubpp>. Declares the C<items> variable
1401to indicate the number of items on the stack.
1402
5fb8527f
PP
1403=item dXSI32
1404
1405Sets up the C<ix> variable for an XSUB which has aliases. This is usually
1406handled automatically by C<xsubpp>.
1407
cb1a09d0
AD
1408=item ENTER
1409
1410Opening bracket on a callback. See C<LEAVE> and L<perlcall>.
1411
1412 ENTER;
1413
1414=item EXTEND
1415
1416Used to extend the argument stack for an XSUB's return values.
1417
1418 EXTEND( sp, int x );
1419
1420=item FREETMPS
1421
1422Closing bracket for temporaries on a callback. See C<SAVETMPS> and
1423L<perlcall>.
1424
1425 FREETMPS;
1426
1427=item G_ARRAY
1428
54310121 1429Used to indicate array context. See C<GIMME_V>, C<GIMME> and L<perlcall>.
cb1a09d0
AD
1430
1431=item G_DISCARD
1432
1433Indicates that arguments returned from a callback should be discarded. See
1434L<perlcall>.
1435
1436=item G_EVAL
1437
1438Used to force a Perl C<eval> wrapper around a callback. See L<perlcall>.
1439
1440=item GIMME
1441
54310121
PP
1442A backward-compatible version of C<GIMME_V> which can only return
1443C<G_SCALAR> or C<G_ARRAY>; in a void context, it returns C<G_SCALAR>.
1444
1445=item GIMME_V
1446
1447The XSUB-writer's equivalent to Perl's C<wantarray>. Returns
1448C<G_VOID>, C<G_SCALAR> or C<G_ARRAY> for void, scalar or array
1449context, respectively.
cb1a09d0
AD
1450
1451=item G_NOARGS
1452
1453Indicates that no arguments are being sent to a callback. See L<perlcall>.
1454
1455=item G_SCALAR
1456
54310121
PP
1457Used to indicate scalar context. See C<GIMME_V>, C<GIMME>, and L<perlcall>.
1458
1459=item G_VOID
1460
1461Used to indicate void context. See C<GIMME_V> and L<perlcall>.
cb1a09d0 1462
faed5253
JO
1463=item gv_fetchmeth
1464
1465Returns the glob with the given C<name> and a defined subroutine or
9607fc9c
PP
1466C<NULL>. The glob lives in the given C<stash>, or in the stashes
1467accessable via @ISA and @<UNIVERSAL>.
faed5253 1468
9607fc9c 1469The argument C<level> should be either 0 or -1. If C<level==0>, as a
0a753a76
PP
1470side-effect creates a glob with the given C<name> in the given
1471C<stash> which in the case of success contains an alias for the
1472subroutine, and sets up caching info for this glob. Similarly for all
1473the searched stashes.
1474
9607fc9c
PP
1475This function grants C<"SUPER"> token as a postfix of the stash name.
1476
0a753a76
PP
1477The GV returned from C<gv_fetchmeth> may be a method cache entry,
1478which is not visible to Perl code. So when calling C<perl_call_sv>,
1479you should not use the GV directly; instead, you should use the
1480method's CV, which can be obtained from the GV with the C<GvCV> macro.
faed5253
JO
1481
1482 GV* gv_fetchmeth _((HV* stash, char* name, STRLEN len, I32 level));
1483
1484=item gv_fetchmethod
1485
dc848c6f
PP
1486=item gv_fetchmethod_autoload
1487
faed5253 1488Returns the glob which contains the subroutine to call to invoke the
dc848c6f
PP
1489method on the C<stash>. In fact in the presense of autoloading this may
1490be the glob for "AUTOLOAD". In this case the corresponding variable
faed5253
JO
1491$AUTOLOAD is already setup.
1492
dc848c6f
PP
1493The third parameter of C<gv_fetchmethod_autoload> determines whether AUTOLOAD
1494lookup is performed if the given method is not present: non-zero means
1495yes, look for AUTOLOAD; zero means no, don't look for AUTOLOAD. Calling
1496C<gv_fetchmethod> is equivalent to calling C<gv_fetchmethod_autoload> with a
1497non-zero C<autoload> parameter.
1498
1499These functions grant C<"SUPER"> token as a prefix of the method name.
1500
1501Note that if you want to keep the returned glob for a long time, you
1502need to check for it being "AUTOLOAD", since at the later time the call
faed5253
JO
1503may load a different subroutine due to $AUTOLOAD changing its value.
1504Use the glob created via a side effect to do this.
1505
dc848c6f
PP
1506These functions have the same side-effects and as C<gv_fetchmeth> with
1507C<level==0>. C<name> should be writable if contains C<':'> or C<'\''>.
0a753a76 1508The warning against passing the GV returned by C<gv_fetchmeth> to
dc848c6f 1509C<perl_call_sv> apply equally to these functions.
faed5253
JO
1510
1511 GV* gv_fetchmethod _((HV* stash, char* name));
dc848c6f
PP
1512 GV* gv_fetchmethod_autoload _((HV* stash, char* name,
1513 I32 autoload));
faed5253 1514
cb1a09d0
AD
1515=item gv_stashpv
1516
1517Returns a pointer to the stash for a specified package. If C<create> is set
1518then the package will be created if it does not already exist. If C<create>
1519is not set and the package does not exist then NULL is returned.
1520
1521 HV* gv_stashpv _((char* name, I32 create));
1522
1523=item gv_stashsv
1524
1525Returns a pointer to the stash for a specified package. See C<gv_stashpv>.
1526
1527 HV* gv_stashsv _((SV* sv, I32 create));
1528
e5581bf4 1529=item GvSV
cb1a09d0 1530
e5581bf4 1531Return the SV from the GV.
44a8e56a 1532
1e422769
PP
1533=item HEf_SVKEY
1534
1535This flag, used in the length slot of hash entries and magic
1536structures, specifies the structure contains a C<SV*> pointer where a
1537C<char*> pointer is to be expected. (For information only--not to be used).
1538
1e422769
PP
1539=item HeHASH
1540
1541Returns the computed hash (type C<U32>) stored in the hash entry.
1542
1543 HeHASH(HE* he)
1544
1545=item HeKEY
1546
1547Returns the actual pointer stored in the key slot of the hash entry.
1548The pointer may be either C<char*> or C<SV*>, depending on the value of
1549C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
1550are usually preferable for finding the value of a key.
1551
1552 HeKEY(HE* he)
1553
1554=item HeKLEN
1555
1556If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
1557holds an C<SV*> key. Otherwise, holds the actual length of the key.
1558Can be assigned to. The C<HePV()> macro is usually preferable for finding
1559key lengths.
1560
1561 HeKLEN(HE* he)
1562
1563=item HePV
1564
1565Returns the key slot of the hash entry as a C<char*> value, doing any
1566necessary dereferencing of possibly C<SV*> keys. The length of
1567the string is placed in C<len> (this is a macro, so do I<not> use
1568C<&len>). If you do not care about what the length of the key is,
1569you may use the global variable C<na>. Remember though, that hash
1570keys in perl are free to contain embedded nulls, so using C<strlen()>
1571or similar is not a good way to find the length of hash keys.
1572This is very similar to the C<SvPV()> macro described elsewhere in
1573this document.
1574
1575 HePV(HE* he, STRLEN len)
1576
1577=item HeSVKEY
1578
1579Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
1580does not contain an C<SV*> key.
1581
1582 HeSVKEY(HE* he)
1583
1584=item HeSVKEY_force
1585
1586Returns the key as an C<SV*>. Will create and return a temporary
1587mortal C<SV*> if the hash entry contains only a C<char*> key.
1588
1589 HeSVKEY_force(HE* he)
1590
1591=item HeSVKEY_set
1592
1593Sets the key to a given C<SV*>, taking care to set the appropriate flags
1594to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
1595
1596 HeSVKEY_set(HE* he, SV* sv)
1597
1598=item HeVAL
1599
1600Returns the value slot (type C<SV*>) stored in the hash entry.
1601
1602 HeVAL(HE* he)
1603
cb1a09d0
AD
1604=item hv_clear
1605
1606Clears a hash, making it empty.
1607
1608 void hv_clear _((HV* tb));
1609
68dc0745
PP
1610=item hv_delayfree_ent
1611
1612Releases a hash entry, such as while iterating though the hash, but
1613delays actual freeing of key and value until the end of the current
1614statement (or thereabouts) with C<sv_2mortal>. See C<hv_iternext>
1615and C<hv_free_ent>.
1616
1617 void hv_delayfree_ent _((HV* hv, HE* entry));
1618
cb1a09d0
AD
1619=item hv_delete
1620
1621Deletes a key/value pair in the hash. The value SV is removed from the hash
5fb8527f 1622and returned to the caller. The C<klen> is the length of the key. The
04343c6d 1623C<flags> value will normally be zero; if set to G_DISCARD then NULL will be
cb1a09d0
AD
1624returned.
1625
1626 SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
1627
1e422769
PP
1628=item hv_delete_ent
1629
1630Deletes a key/value pair in the hash. The value SV is removed from the hash
1631and returned to the caller. The C<flags> value will normally be zero; if set
04343c6d 1632to G_DISCARD then NULL will be returned. C<hash> can be a valid precomputed
1e422769
PP
1633hash value, or 0 to ask for it to be computed.
1634
1635 SV* hv_delete_ent _((HV* tb, SV* key, I32 flags, U32 hash));
1636
cb1a09d0
AD
1637=item hv_exists
1638
1639Returns a boolean indicating whether the specified hash key exists. The
5fb8527f 1640C<klen> is the length of the key.
cb1a09d0
AD
1641
1642 bool hv_exists _((HV* tb, char* key, U32 klen));
1643
1e422769
PP
1644=item hv_exists_ent
1645
1646Returns a boolean indicating whether the specified hash key exists. C<hash>
54310121 1647can be a valid precomputed hash value, or 0 to ask for it to be computed.
1e422769
PP
1648
1649 bool hv_exists_ent _((HV* tb, SV* key, U32 hash));
1650
cb1a09d0
AD
1651=item hv_fetch
1652
1653Returns the SV which corresponds to the specified key in the hash. The
5fb8527f 1654C<klen> is the length of the key. If C<lval> is set then the fetch will be
cb1a09d0
AD
1655part of a store. Check that the return value is non-null before
1656dereferencing it to a C<SV*>.
1657
04343c6d
GS
1658See L<Understanding the Magic of Tied Hashes and Arrays> for more
1659information on how to use this function on tied hashes.
1660
cb1a09d0
AD
1661 SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
1662
1e422769
PP
1663=item hv_fetch_ent
1664
1665Returns the hash entry which corresponds to the specified key in the hash.
54310121 1666C<hash> must be a valid precomputed hash number for the given C<key>, or
1e422769
PP
16670 if you want the function to compute it. IF C<lval> is set then the
1668fetch will be part of a store. Make sure the return value is non-null
1669before accessing it. The return value when C<tb> is a tied hash
1670is a pointer to a static location, so be sure to make a copy of the
1671structure if you need to store it somewhere.
1672
04343c6d
GS
1673See L<Understanding the Magic of Tied Hashes and Arrays> for more
1674information on how to use this function on tied hashes.
1675
1e422769
PP
1676 HE* hv_fetch_ent _((HV* tb, SV* key, I32 lval, U32 hash));
1677
68dc0745
PP
1678=item hv_free_ent
1679
1680Releases a hash entry, such as while iterating though the hash. See
1681C<hv_iternext> and C<hv_delayfree_ent>.
1682
1683 void hv_free_ent _((HV* hv, HE* entry));
1684
cb1a09d0
AD
1685=item hv_iterinit
1686
1687Prepares a starting point to traverse a hash table.
1688
1689 I32 hv_iterinit _((HV* tb));
1690
1691=item hv_iterkey
1692
1693Returns the key from the current position of the hash iterator. See
1694C<hv_iterinit>.
1695
1696 char* hv_iterkey _((HE* entry, I32* retlen));
1697
1e422769 1698=item hv_iterkeysv
3fe9a6f1 1699
1e422769
PP
1700Returns the key as an C<SV*> from the current position of the hash
1701iterator. The return value will always be a mortal copy of the
1702key. Also see C<hv_iterinit>.
1703
1704 SV* hv_iterkeysv _((HE* entry));
1705
cb1a09d0
AD
1706=item hv_iternext
1707
1708Returns entries from a hash iterator. See C<hv_iterinit>.
1709
1710 HE* hv_iternext _((HV* tb));
1711
1712=item hv_iternextsv
1713
1714Performs an C<hv_iternext>, C<hv_iterkey>, and C<hv_iterval> in one
1715operation.
1716
1717 SV * hv_iternextsv _((HV* hv, char** key, I32* retlen));
1718
1719=item hv_iterval
1720
1721Returns the value from the current position of the hash iterator. See
1722C<hv_iterkey>.
1723
1724 SV* hv_iterval _((HV* tb, HE* entry));
1725
1726=item hv_magic
1727
1728Adds magic to a hash. See C<sv_magic>.
1729
1730 void hv_magic _((HV* hv, GV* gv, int how));
1731
1732=item HvNAME
1733
1734Returns the package name of a stash. See C<SvSTASH>, C<CvSTASH>.
1735
1736 char *HvNAME (HV* stash)
1737
1738=item hv_store
1739
1740Stores an SV in a hash. The hash key is specified as C<key> and C<klen> is
54310121 1741the length of the key. The C<hash> parameter is the precomputed hash
cb1a09d0 1742value; if it is zero then Perl will compute it. The return value will be
04343c6d
GS
1743NULL if the operation failed or if the value did not need to be actually
1744stored within the hash (as in the case of tied hashes). Otherwise it can
1745be dereferenced to get the original C<SV*>. Note that the caller is
1746responsible for suitably incrementing the reference count of C<val>
1747before the call, and decrementing it if the function returned NULL.
1748
1749See L<Understanding the Magic of Tied Hashes and Arrays> for more
1750information on how to use this function on tied hashes.
cb1a09d0
AD
1751
1752 SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
1753
1e422769
PP
1754=item hv_store_ent
1755
1756Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
54310121 1757parameter is the precomputed hash value; if it is zero then Perl will
1e422769 1758compute it. The return value is the new hash entry so created. It will be
04343c6d
GS
1759NULL if the operation failed or if the value did not need to be actually
1760stored within the hash (as in the case of tied hashes). Otherwise the
1761contents of the return value can be accessed using the C<He???> macros
1762described here. Note that the caller is responsible for suitably
1763incrementing the reference count of C<val> before the call, and decrementing
1764it if the function returned NULL.
1765
1766See L<Understanding the Magic of Tied Hashes and Arrays> for more
1767information on how to use this function on tied hashes.
1e422769
PP
1768
1769 HE* hv_store_ent _((HV* tb, SV* key, SV* val, U32 hash));
1770
cb1a09d0
AD
1771=item hv_undef
1772
1773Undefines the hash.
1774
1775 void hv_undef _((HV* tb));
1776
1777=item isALNUM
1778
1779Returns a boolean indicating whether the C C<char> is an ascii alphanumeric
5f05dabc 1780character or digit.
cb1a09d0
AD
1781
1782 int isALNUM (char c)
1783
1784=item isALPHA
1785
5fb8527f 1786Returns a boolean indicating whether the C C<char> is an ascii alphabetic
cb1a09d0
AD
1787character.
1788
1789 int isALPHA (char c)
1790
1791=item isDIGIT
1792
1793Returns a boolean indicating whether the C C<char> is an ascii digit.
1794
1795 int isDIGIT (char c)
1796
1797=item isLOWER
1798
1799Returns a boolean indicating whether the C C<char> is a lowercase character.
1800
1801 int isLOWER (char c)
1802
1803=item isSPACE
1804
1805Returns a boolean indicating whether the C C<char> is whitespace.
1806
1807 int isSPACE (char c)
1808
1809=item isUPPER
1810
1811Returns a boolean indicating whether the C C<char> is an uppercase character.
1812
1813 int isUPPER (char c)
1814
1815=item items
1816
1817Variable which is setup by C<xsubpp> to indicate the number of items on the
5fb8527f
PP
1818stack. See L<perlxs/"Variable-length Parameter Lists">.
1819
1820=item ix
1821
1822Variable which is setup by C<xsubpp> to indicate which of an XSUB's aliases
1823was used to invoke it. See L<perlxs/"The ALIAS: Keyword">.
cb1a09d0
AD
1824
1825=item LEAVE
1826
1827Closing bracket on a callback. See C<ENTER> and L<perlcall>.
1828
1829 LEAVE;
1830
1831=item MARK
1832
5fb8527f 1833Stack marker variable for the XSUB. See C<dMARK>.
cb1a09d0
AD
1834
1835=item mg_clear
1836
1837Clear something magical that the SV represents. See C<sv_magic>.
1838
1839 int mg_clear _((SV* sv));
1840
1841=item mg_copy
1842
1843Copies the magic from one SV to another. See C<sv_magic>.
1844
1845 int mg_copy _((SV *, SV *, char *, STRLEN));
1846
1847=item mg_find
1848
1849Finds the magic pointer for type matching the SV. See C<sv_magic>.
1850
1851 MAGIC* mg_find _((SV* sv, int type));
1852
1853=item mg_free
1854
1855Free any magic storage used by the SV. See C<sv_magic>.
1856
1857 int mg_free _((SV* sv));
1858
1859=item mg_get
1860
1861Do magic after a value is retrieved from the SV. See C<sv_magic>.
1862
1863 int mg_get _((SV* sv));
1864
1865=item mg_len
1866
1867Report on the SV's length. See C<sv_magic>.
1868
1869 U32 mg_len _((SV* sv));
1870
1871=item mg_magical
1872
1873Turns on the magical status of an SV. See C<sv_magic>.
1874
1875 void mg_magical _((SV* sv));
1876
1877=item mg_set
1878
1879Do magic after a value is assigned to the SV. See C<sv_magic>.
1880
1881 int mg_set _((SV* sv));
1882
1883=item Move
1884
1885The XSUB-writer's interface to the C C<memmove> function. The C<s> is the
1886source, C<d> is the destination, C<n> is the number of items, and C<t> is
0146554f 1887the type. Can do overlapping moves. See also C<Copy>.
cb1a09d0
AD
1888
1889 (void) Move( s, d, n, t );
1890
1891=item na
1892
1893A variable which may be used with C<SvPV> to tell Perl to calculate the
1894string length.
1895
1896=item New
1897
1898The XSUB-writer's interface to the C C<malloc> function.
1899
1900 void * New( x, void *ptr, int size, type )
1901
1902=item Newc
1903
1904The XSUB-writer's interface to the C C<malloc> function, with cast.
1905
1906 void * Newc( x, void *ptr, int size, type, cast )
1907
1908=item Newz
1909
1910The XSUB-writer's interface to the C C<malloc> function. The allocated
1911memory is zeroed with C<memzero>.
1912
1913 void * Newz( x, void *ptr, int size, type )
1914
1915=item newAV
1916
5f05dabc 1917Creates a new AV. The reference count is set to 1.
cb1a09d0
AD
1918
1919 AV* newAV _((void));
1920
1921=item newHV
1922
5f05dabc 1923Creates a new HV. The reference count is set to 1.
cb1a09d0
AD
1924
1925 HV* newHV _((void));
1926
5f05dabc 1927=item newRV_inc
cb1a09d0 1928
5f05dabc 1929Creates an RV wrapper for an SV. The reference count for the original SV is
cb1a09d0
AD
1930incremented.
1931
5f05dabc
PP
1932 SV* newRV_inc _((SV* ref));
1933
1934For historical reasons, "newRV" is a synonym for "newRV_inc".
1935
1936=item newRV_noinc
1937
1938Creates an RV wrapper for an SV. The reference count for the original
1939SV is B<not> incremented.
1940
07fa94a1 1941 SV* newRV_noinc _((SV* ref));
cb1a09d0
AD
1942
1943=item newSV
1944
1945Creates a new SV. The C<len> parameter indicates the number of bytes of
68dc0745 1946preallocated string space the SV should have. The reference count for the
07fa94a1 1947new SV is set to 1.
cb1a09d0
AD
1948
1949 SV* newSV _((STRLEN len));
1950
1951=item newSViv
1952
07fa94a1
JO
1953Creates a new SV and copies an integer into it. The reference count for the
1954SV is set to 1.
cb1a09d0
AD
1955
1956 SV* newSViv _((IV i));
1957
1958=item newSVnv
1959
07fa94a1
JO
1960Creates a new SV and copies a double into it. The reference count for the
1961SV is set to 1.
cb1a09d0
AD
1962
1963 SV* newSVnv _((NV i));
1964
1965=item newSVpv
1966
07fa94a1
JO
1967Creates a new SV and copies a string into it. The reference count for the
1968SV is set to 1. If C<len> is zero then Perl will compute the length.
cb1a09d0
AD
1969
1970 SV* newSVpv _((char* s, STRLEN len));
1971
1972=item newSVrv
1973
1974Creates a new SV for the RV, C<rv>, to point to. If C<rv> is not an RV then
5fb8527f 1975it will be upgraded to one. If C<classname> is non-null then the new SV will
cb1a09d0 1976be blessed in the specified package. The new SV is returned and its
5f05dabc 1977reference count is 1.
8ebc5c01 1978
cb1a09d0
AD
1979 SV* newSVrv _((SV* rv, char* classname));
1980
1981=item newSVsv
1982
5fb8527f 1983Creates a new SV which is an exact duplicate of the original SV.
cb1a09d0
AD
1984
1985 SV* newSVsv _((SV* old));
1986
1987=item newXS
1988
1989Used by C<xsubpp> to hook up XSUBs as Perl subs.
1990
1991=item newXSproto
1992
1993Used by C<xsubpp> to hook up XSUBs as Perl subs. Adds Perl prototypes to
1994the subs.
1995
1996=item Nullav
1997
1998Null AV pointer.
1999
2000=item Nullch
2001
2002Null character pointer.
2003
2004=item Nullcv
2005
2006Null CV pointer.
2007
2008=item Nullhv
2009
2010Null HV pointer.
2011
2012=item Nullsv
2013
2014Null SV pointer.
2015
2016=item ORIGMARK
2017
2018The original stack mark for the XSUB. See C<dORIGMARK>.
2019
2020=item perl_alloc
2021
2022Allocates a new Perl interpreter. See L<perlembed>.
2023
2024=item perl_call_argv
2025
2026Performs a callback to the specified Perl sub. See L<perlcall>.
2027
2028 I32 perl_call_argv _((char* subname, I32 flags, char** argv));
2029
2030=item perl_call_method
2031
2032Performs a callback to the specified Perl method. The blessed object must
2033be on the stack. See L<perlcall>.
2034
2035 I32 perl_call_method _((char* methname, I32 flags));
2036
2037=item perl_call_pv
2038
2039Performs a callback to the specified Perl sub. See L<perlcall>.
2040
2041 I32 perl_call_pv _((char* subname, I32 flags));
2042
2043=item perl_call_sv
2044
2045Performs a callback to the Perl sub whose name is in the SV. See
2046L<perlcall>.
2047
2048 I32 perl_call_sv _((SV* sv, I32 flags));
2049
2050=item perl_construct
2051
2052Initializes a new Perl interpreter. See L<perlembed>.
2053
2054=item perl_destruct
2055
2056Shuts down a Perl interpreter. See L<perlembed>.
2057
2058=item perl_eval_sv
2059
2060Tells Perl to C<eval> the string in the SV.
2061
2062 I32 perl_eval_sv _((SV* sv, I32 flags));
2063
137443ea
PP
2064=item perl_eval_pv
2065
2066Tells Perl to C<eval> the given string and return an SV* result.
2067
2068 SV* perl_eval_pv _((char* p, I32 croak_on_error));
2069
cb1a09d0
AD
2070=item perl_free
2071
2072Releases a Perl interpreter. See L<perlembed>.
2073
2074=item perl_get_av
2075
2076Returns the AV of the specified Perl array. If C<create> is set and the
2077Perl variable does not exist then it will be created. If C<create> is not
04343c6d 2078set and the variable does not exist then NULL is returned.
cb1a09d0
AD
2079
2080 AV* perl_get_av _((char* name, I32 create));
2081
2082=item perl_get_cv
2083
2084Returns the CV of the specified Perl sub. If C<create> is set and the Perl
2085variable does not exist then it will be created. If C<create> is not
04343c6d 2086set and the variable does not exist then NULL is returned.
cb1a09d0
AD
2087
2088 CV* perl_get_cv _((char* name, I32 create));
2089
2090=item perl_get_hv
2091
2092Returns the HV of the specified Perl hash. If C<create> is set and the Perl
2093variable does not exist then it will be created. If C<create> is not
04343c6d 2094set and the variable does not exist then NULL is returned.
cb1a09d0
AD
2095
2096 HV* perl_get_hv _((char* name, I32 create));
2097
2098=item perl_get_sv
2099
2100Returns the SV of the specified Perl scalar. If C<create> is set and the
2101Perl variable does not exist then it will be created. If C<create> is not
04343c6d 2102set and the variable does not exist then NULL is returned.
cb1a09d0
AD
2103
2104 SV* perl_get_sv _((char* name, I32 create));
2105
2106=item perl_parse
2107
2108Tells a Perl interpreter to parse a Perl script. See L<perlembed>.
2109
2110=item perl_require_pv
2111
2112Tells Perl to C<require> a module.
2113
2114 void perl_require_pv _((char* pv));
2115
2116=item perl_run
2117
2118Tells a Perl interpreter to run. See L<perlembed>.
2119
2120=item POPi
2121
2122Pops an integer off the stack.
2123
2124 int POPi();
2125
2126=item POPl
2127
2128Pops a long off the stack.
2129
2130 long POPl();
2131
2132=item POPp
2133
2134Pops a string off the stack.
2135
2136 char * POPp();
2137
2138=item POPn
2139
2140Pops a double off the stack.
2141
2142 double POPn();
2143
2144=item POPs
2145
2146Pops an SV off the stack.
2147
2148 SV* POPs();
2149
2150=item PUSHMARK
2151
2152Opening bracket for arguments on a callback. See C<PUTBACK> and L<perlcall>.
2153
2154 PUSHMARK(p)
2155
2156=item PUSHi
2157
2158Push an integer onto the stack. The stack must have room for this element.
2159See C<XPUSHi>.
2160
2161 PUSHi(int d)
2162
2163=item PUSHn
2164
2165Push a double onto the stack. The stack must have room for this element.
2166See C<XPUSHn>.
2167
2168 PUSHn(double d)
2169
2170=item PUSHp
2171
2172Push a string onto the stack. The stack must have room for this element.
2173The C<len> indicates the length of the string. See C<XPUSHp>.
2174
2175 PUSHp(char *c, int len )
2176
2177=item PUSHs
2178
2179Push an SV onto the stack. The stack must have room for this element. See
2180C<XPUSHs>.
2181
2182 PUSHs(sv)
2183
2184=item PUTBACK
2185
2186Closing bracket for XSUB arguments. This is usually handled by C<xsubpp>.
2187See C<PUSHMARK> and L<perlcall> for other uses.
2188
2189 PUTBACK;
2190
2191=item Renew
2192
2193The XSUB-writer's interface to the C C<realloc> function.
2194
2195 void * Renew( void *ptr, int size, type )
2196
2197=item Renewc
2198
2199The XSUB-writer's interface to the C C<realloc> function, with cast.
2200
2201 void * Renewc( void *ptr, int size, type, cast )
2202
2203=item RETVAL
2204
2205Variable which is setup by C<xsubpp> to hold the return value for an XSUB.
5fb8527f
PP
2206This is always the proper type for the XSUB.
2207See L<perlxs/"The RETVAL Variable">.
cb1a09d0
AD
2208
2209=item safefree
2210
2211The XSUB-writer's interface to the C C<free> function.
2212
2213=item safemalloc
2214
2215The XSUB-writer's interface to the C C<malloc> function.
2216
2217=item saferealloc
2218
2219The XSUB-writer's interface to the C C<realloc> function.
2220
2221=item savepv
2222
2223Copy a string to a safe spot. This does not use an SV.
2224
2225 char* savepv _((char* sv));
2226
2227=item savepvn
2228
2229Copy a string to a safe spot. The C<len> indicates number of bytes to
2230copy. This does not use an SV.
2231
2232 char* savepvn _((char* sv, I32 len));
2233
2234=item SAVETMPS
2235
2236Opening bracket for temporaries on a callback. See C<FREETMPS> and
2237L<perlcall>.
2238
2239 SAVETMPS;
2240
2241=item SP
2242
2243Stack pointer. This is usually handled by C<xsubpp>. See C<dSP> and
2244C<SPAGAIN>.
2245
2246=item SPAGAIN
2247
54310121 2248Refetch the stack pointer. Used after a callback. See L<perlcall>.
cb1a09d0
AD
2249
2250 SPAGAIN;
2251
2252=item ST
2253
2254Used to access elements on the XSUB's stack.
2255
2256 SV* ST(int x)
2257
2258=item strEQ
2259
2260Test two strings to see if they are equal. Returns true or false.
2261
2262 int strEQ( char *s1, char *s2 )
2263
2264=item strGE
2265
2266Test two strings to see if the first, C<s1>, is greater than or equal to the
2267second, C<s2>. Returns true or false.
2268
2269 int strGE( char *s1, char *s2 )
2270
2271=item strGT
2272
2273Test two strings to see if the first, C<s1>, is greater than the second,
2274C<s2>. Returns true or false.
2275
2276 int strGT( char *s1, char *s2 )
2277
2278=item strLE
2279
2280Test two strings to see if the first, C<s1>, is less than or equal to the
2281second, C<s2>. Returns true or false.
2282
2283 int strLE( char *s1, char *s2 )
2284
2285=item strLT
2286
2287Test two strings to see if the first, C<s1>, is less than the second,
2288C<s2>. Returns true or false.
2289
2290 int strLT( char *s1, char *s2 )
2291
2292=item strNE
2293
2294Test two strings to see if they are different. Returns true or false.
2295
2296 int strNE( char *s1, char *s2 )
2297
2298=item strnEQ
2299
2300Test two strings to see if they are equal. The C<len> parameter indicates
2301the number of bytes to compare. Returns true or false.
2302
2303 int strnEQ( char *s1, char *s2 )
2304
2305=item strnNE
2306
2307Test two strings to see if they are different. The C<len> parameter
2308indicates the number of bytes to compare. Returns true or false.
2309
2310 int strnNE( char *s1, char *s2, int len )
2311
2312=item sv_2mortal
2313
2314Marks an SV as mortal. The SV will be destroyed when the current context
2315ends.
2316
2317 SV* sv_2mortal _((SV* sv));
2318
2319=item sv_bless
2320
2321Blesses an SV into a specified package. The SV must be an RV. The package
07fa94a1
JO
2322must be designated by its stash (see C<gv_stashpv()>). The reference count
2323of the SV is unaffected.
cb1a09d0
AD
2324
2325 SV* sv_bless _((SV* sv, HV* stash));
2326
2327=item sv_catpv
2328
2329Concatenates the string onto the end of the string which is in the SV.
2330
2331 void sv_catpv _((SV* sv, char* ptr));
2332
2333=item sv_catpvn
2334
2335Concatenates the string onto the end of the string which is in the SV. The
2336C<len> indicates number of bytes to copy.
2337
2338 void sv_catpvn _((SV* sv, char* ptr, STRLEN len));
2339
46fc3d4c
PP
2340=item sv_catpvf
2341
2342Processes its arguments like C<sprintf> and appends the formatted output
2343to an SV.
2344
2345 void sv_catpvf _((SV* sv, const char* pat, ...));
2346
cb1a09d0
AD
2347=item sv_catsv
2348
5fb8527f 2349Concatenates the string from SV C<ssv> onto the end of the string in SV
cb1a09d0
AD
2350C<dsv>.
2351
2352 void sv_catsv _((SV* dsv, SV* ssv));
2353
5fb8527f
PP
2354=item sv_cmp
2355
2356Compares the strings in two SVs. Returns -1, 0, or 1 indicating whether the
2357string in C<sv1> is less than, equal to, or greater than the string in
2358C<sv2>.
2359
2360 I32 sv_cmp _((SV* sv1, SV* sv2));
2361
cb1a09d0
AD
2362=item SvCUR
2363
2364Returns the length of the string which is in the SV. See C<SvLEN>.
2365
2366 int SvCUR (SV* sv)
2367
2368=item SvCUR_set
2369
2370Set the length of the string which is in the SV. See C<SvCUR>.
2371
2372 SvCUR_set (SV* sv, int val )
2373
5fb8527f
PP
2374=item sv_dec
2375
5f05dabc 2376Auto-decrement of the value in the SV.
5fb8527f
PP
2377
2378 void sv_dec _((SV* sv));
2379
cb1a09d0
AD
2380=item SvEND
2381
2382Returns a pointer to the last character in the string which is in the SV.
2383See C<SvCUR>. Access the character as
2384
2385 *SvEND(sv)
2386
5fb8527f
PP
2387=item sv_eq
2388
2389Returns a boolean indicating whether the strings in the two SVs are
2390identical.
2391
2392 I32 sv_eq _((SV* sv1, SV* sv2));
2393
cb1a09d0
AD
2394=item SvGROW
2395
5fb8527f
PP
2396Expands the character buffer in the SV. Calls C<sv_grow> to perform the
2397expansion if necessary. Returns a pointer to the character buffer.
cb1a09d0
AD
2398
2399 char * SvGROW( SV* sv, int len )
2400
5fb8527f
PP
2401=item sv_grow
2402
2403Expands the character buffer in the SV. This will use C<sv_unref> and will
2404upgrade the SV to C<SVt_PV>. Returns a pointer to the character buffer.
2405Use C<SvGROW>.
2406
2407=item sv_inc
2408
07fa94a1 2409Auto-increment of the value in the SV.
5fb8527f
PP
2410
2411 void sv_inc _((SV* sv));
2412
cb1a09d0
AD
2413=item SvIOK
2414
2415Returns a boolean indicating whether the SV contains an integer.
2416
2417 int SvIOK (SV* SV)
2418
2419=item SvIOK_off
2420
2421Unsets the IV status of an SV.
2422
2423 SvIOK_off (SV* sv)
2424
2425=item SvIOK_on
2426
2427Tells an SV that it is an integer.
2428
2429 SvIOK_on (SV* sv)
2430
5fb8527f
PP
2431=item SvIOK_only
2432
2433Tells an SV that it is an integer and disables all other OK bits.
2434
2435 SvIOK_on (SV* sv)
2436
cb1a09d0
AD
2437=item SvIOKp
2438
2439Returns a boolean indicating whether the SV contains an integer. Checks the
2440B<private> setting. Use C<SvIOK>.
2441
2442 int SvIOKp (SV* SV)
2443
2444=item sv_isa
2445
2446Returns a boolean indicating whether the SV is blessed into the specified
2447class. This does not know how to check for subtype, so it doesn't work in
2448an inheritance relationship.
2449
2450 int sv_isa _((SV* sv, char* name));
2451
2452=item SvIV
2453
2454Returns the integer which is in the SV.
2455
2456 int SvIV (SV* sv)
2457
2458=item sv_isobject
2459
2460Returns a boolean indicating whether the SV is an RV pointing to a blessed
2461object. If the SV is not an RV, or if the object is not blessed, then this
2462will return false.
2463
2464 int sv_isobject _((SV* sv));
2465
2466=item SvIVX
2467
2468Returns the integer which is stored in the SV.
2469
2470 int SvIVX (SV* sv);
2471
2472=item SvLEN
2473
2474Returns the size of the string buffer in the SV. See C<SvCUR>.
2475
2476 int SvLEN (SV* sv)
2477
5fb8527f
PP
2478=item sv_len
2479
2480Returns the length of the string in the SV. Use C<SvCUR>.
2481
2482 STRLEN sv_len _((SV* sv));
2483
cb1a09d0
AD
2484=item sv_magic
2485
2486Adds magic to an SV.
2487
2488 void sv_magic _((SV* sv, SV* obj, int how, char* name, I32 namlen));
2489
2490=item sv_mortalcopy
2491
2492Creates a new SV which is a copy of the original SV. The new SV is marked
5f05dabc 2493as mortal.
cb1a09d0
AD
2494
2495 SV* sv_mortalcopy _((SV* oldsv));
2496
2497=item SvOK
2498
2499Returns a boolean indicating whether the value is an SV.
2500
2501 int SvOK (SV* sv)
2502
2503=item sv_newmortal
2504
5f05dabc 2505Creates a new SV which is mortal. The reference count of the SV is set to 1.
cb1a09d0
AD
2506
2507 SV* sv_newmortal _((void));
2508
2509=item sv_no
2510
2511This is the C<false> SV. See C<sv_yes>. Always refer to this as C<&sv_no>.
2512
2513=item SvNIOK
2514
2515Returns a boolean indicating whether the SV contains a number, integer or
2516double.
2517
2518 int SvNIOK (SV* SV)
2519
2520=item SvNIOK_off
2521
2522Unsets the NV/IV status of an SV.
2523
2524 SvNIOK_off (SV* sv)
2525
2526=item SvNIOKp
2527
2528Returns a boolean indicating whether the SV contains a number, integer or
2529double. Checks the B<private> setting. Use C<SvNIOK>.
2530
2531 int SvNIOKp (SV* SV)
2532
2533=item SvNOK
2534
2535Returns a boolean indicating whether the SV contains a double.
2536
2537 int SvNOK (SV* SV)
2538
2539=item SvNOK_off
2540
2541Unsets the NV status of an SV.
2542
2543 SvNOK_off (SV* sv)
2544
2545=item SvNOK_on
2546
2547Tells an SV that it is a double.
2548
2549 SvNOK_on (SV* sv)
2550
5fb8527f
PP
2551=item SvNOK_only
2552
2553Tells an SV that it is a double and disables all other OK bits.
2554
2555 SvNOK_on (SV* sv)
2556
cb1a09d0
AD
2557=item SvNOKp
2558
2559Returns a boolean indicating whether the SV contains a double. Checks the
2560B<private> setting. Use C<SvNOK>.
2561
2562 int SvNOKp (SV* SV)
2563
2564=item SvNV
2565
2566Returns the double which is stored in the SV.
2567
2568 double SvNV (SV* sv);
2569
2570=item SvNVX
2571
2572Returns the double which is stored in the SV.
2573
2574 double SvNVX (SV* sv);
2575
2576=item SvPOK
2577
2578Returns a boolean indicating whether the SV contains a character string.
2579
2580 int SvPOK (SV* SV)
2581
2582=item SvPOK_off
2583
2584Unsets the PV status of an SV.
2585
2586 SvPOK_off (SV* sv)
2587
2588=item SvPOK_on
2589
2590Tells an SV that it is a string.
2591
2592 SvPOK_on (SV* sv)
2593
5fb8527f
PP
2594=item SvPOK_only
2595
2596Tells an SV that it is a string and disables all other OK bits.
2597
2598 SvPOK_on (SV* sv)
2599
cb1a09d0
AD
2600=item SvPOKp
2601
2602Returns a boolean indicating whether the SV contains a character string.
2603Checks the B<private> setting. Use C<SvPOK>.
2604
2605 int SvPOKp (SV* SV)
2606
2607=item SvPV
2608
2609Returns a pointer to the string in the SV, or a stringified form of the SV
2610if the SV does not contain a string. If C<len> is C<na> then Perl will
2611handle the length on its own.
2612
2613 char * SvPV (SV* sv, int len )
2614
2615=item SvPVX
2616
2617Returns a pointer to the string in the SV. The SV must contain a string.
2618
2619 char * SvPVX (SV* sv)
2620
2621=item SvREFCNT
2622
5f05dabc 2623Returns the value of the object's reference count.
cb1a09d0
AD
2624
2625 int SvREFCNT (SV* sv);
2626
2627=item SvREFCNT_dec
2628
5f05dabc 2629Decrements the reference count of the given SV.
cb1a09d0
AD
2630
2631 void SvREFCNT_dec (SV* sv)
2632
2633=item SvREFCNT_inc
2634
5f05dabc 2635Increments the reference count of the given SV.
cb1a09d0
AD
2636
2637 void SvREFCNT_inc (SV* sv)
2638
2639=item SvROK
2640
2641Tests if the SV is an RV.
2642
2643 int SvROK (SV* sv)
2644
2645=item SvROK_off
2646
2647Unsets the RV status of an SV.
2648
2649 SvROK_off (SV* sv)
2650
2651=item SvROK_on
2652
2653Tells an SV that it is an RV.
2654
2655 SvROK_on (SV* sv)
2656
2657=item SvRV
2658
2659Dereferences an RV to return the SV.
2660
2661 SV* SvRV (SV* sv);
2662
2663=item sv_setiv
2664
2665Copies an integer into the given SV.
2666
2667 void sv_setiv _((SV* sv, IV num));
2668
2669=item sv_setnv
2670
2671Copies a double into the given SV.
2672
2673 void sv_setnv _((SV* sv, double num));
2674
2675=item sv_setpv
2676
2677Copies a string into an SV. The string must be null-terminated.
2678
2679 void sv_setpv _((SV* sv, char* ptr));
2680
2681=item sv_setpvn
2682
2683Copies a string into an SV. The C<len> parameter indicates the number of
2684bytes to be copied.
2685
2686 void sv_setpvn _((SV* sv, char* ptr, STRLEN len));
2687
46fc3d4c
PP
2688=item sv_setpvf
2689
2690Processes its arguments like C<sprintf> and sets an SV to the formatted
2691output.
2692
2693 void sv_setpvf _((SV* sv, const char* pat, ...));
2694
cb1a09d0
AD
2695=item sv_setref_iv
2696
5fb8527f
PP
2697Copies an integer into a new SV, optionally blessing the SV. The C<rv>
2698argument will be upgraded to an RV. That RV will be modified to point to
2699the new SV. The C<classname> argument indicates the package for the
2700blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
5f05dabc 2701will be returned and will have a reference count of 1.
cb1a09d0
AD
2702
2703 SV* sv_setref_iv _((SV *rv, char *classname, IV iv));
2704
2705=item sv_setref_nv
2706
5fb8527f
PP
2707Copies a double into a new SV, optionally blessing the SV. The C<rv>
2708argument will be upgraded to an RV. That RV will be modified to point to
2709the new SV. The C<classname> argument indicates the package for the
2710blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
5f05dabc 2711will be returned and will have a reference count of 1.
cb1a09d0
AD
2712
2713 SV* sv_setref_nv _((SV *rv, char *classname, double nv));
2714
2715=item sv_setref_pv
2716
5fb8527f
PP
2717Copies a pointer into a new SV, optionally blessing the SV. The C<rv>
2718argument will be upgraded to an RV. That RV will be modified to point to
2719the new SV. If the C<pv> argument is NULL then C<sv_undef> will be placed
2720into the SV. The C<classname> argument indicates the package for the
2721blessing. Set C<classname> to C<Nullch> to avoid the blessing. The new SV
5f05dabc 2722will be returned and will have a reference count of 1.
cb1a09d0
AD
2723
2724 SV* sv_setref_pv _((SV *rv, char *classname, void* pv));
2725
2726Do not use with integral Perl types such as HV, AV, SV, CV, because those
2727objects will become corrupted by the pointer copy process.
2728
2729Note that C<sv_setref_pvn> copies the string while this copies the pointer.
2730
2731=item sv_setref_pvn
2732
5fb8527f
PP
2733Copies a string into a new SV, optionally blessing the SV. The length of the
2734string must be specified with C<n>. The C<rv> argument will be upgraded to
2735an RV. That RV will be modified to point to the new SV. The C<classname>
cb1a09d0
AD
2736argument indicates the package for the blessing. Set C<classname> to
2737C<Nullch> to avoid the blessing. The new SV will be returned and will have
5f05dabc 2738a reference count of 1.
cb1a09d0
AD
2739
2740 SV* sv_setref_pvn _((SV *rv, char *classname, char* pv, I32 n));
2741
2742Note that C<sv_setref_pv> copies the pointer while this copies the string.
2743
2744=item sv_setsv
2745
2746Copies the contents of the source SV C<ssv> into the destination SV C<dsv>.
5f05dabc 2747The source SV may be destroyed if it is mortal.
cb1a09d0
AD
2748
2749 void sv_setsv _((SV* dsv, SV* ssv));
2750
2751=item SvSTASH
2752
2753Returns the stash of the SV.
2754
2755 HV * SvSTASH (SV* sv)
2756
2757=item SVt_IV
2758
2759Integer type flag for scalars. See C<svtype>.
2760
2761=item SVt_PV
2762
2763Pointer type flag for scalars. See C<svtype>.
2764
2765=item SVt_PVAV
2766
2767Type flag for arrays. See C<svtype>.
2768
2769=item SVt_PVCV
2770
2771Type flag for code refs. See C<svtype>.
2772
2773=item SVt_PVHV
2774
2775Type flag for hashes. See C<svtype>.
2776
2777=item SVt_PVMG
2778
2779Type flag for blessed scalars. See C<svtype>.
2780
2781=item SVt_NV
2782
2783Double type flag for scalars. See C<svtype>.
2784
2785=item SvTRUE
2786
2787Returns a boolean indicating whether Perl would evaluate the SV as true or
2788false, defined or undefined.
2789
2790 int SvTRUE (SV* sv)
2791
2792=item SvTYPE
2793
2794Returns the type of the SV. See C<svtype>.
2795
2796 svtype SvTYPE (SV* sv)
2797
2798=item svtype
2799
2800An enum of flags for Perl types. These are found in the file B<sv.h> in the
2801C<svtype> enum. Test these flags with the C<SvTYPE> macro.
2802
2803=item SvUPGRADE
2804
5fb8527f
PP
2805Used to upgrade an SV to a more complex form. Uses C<sv_upgrade> to perform
2806the upgrade if necessary. See C<svtype>.
2807
2808 bool SvUPGRADE _((SV* sv, svtype mt));
2809
2810=item sv_upgrade
2811
2812Upgrade an SV to a more complex form. Use C<SvUPGRADE>. See C<svtype>.
cb1a09d0
AD
2813
2814=item sv_undef
2815
2816This is the C<undef> SV. Always refer to this as C<&sv_undef>.
2817
5fb8527f
PP
2818=item sv_unref
2819
07fa94a1
JO
2820Unsets the RV status of the SV, and decrements the reference count of
2821whatever was being referenced by the RV. This can almost be thought of
2822as a reversal of C<newSVrv>. See C<SvROK_off>.
5fb8527f
PP
2823
2824 void sv_unref _((SV* sv));
2825
cb1a09d0
AD
2826=item sv_usepvn
2827
2828Tells an SV to use C<ptr> to find its string value. Normally the string is
5fb8527f
PP
2829stored inside the SV but sv_usepvn allows the SV to use an outside string.
2830The C<ptr> should point to memory that was allocated by C<malloc>. The
cb1a09d0
AD
2831string length, C<len>, must be supplied. This function will realloc the
2832memory pointed to by C<ptr>, so that pointer should not be freed or used by
2833the programmer after giving it to sv_usepvn.
2834
2835 void sv_usepvn _((SV* sv, char* ptr, STRLEN len));
2836
2837=item sv_yes
2838
2839This is the C<true> SV. See C<sv_no>. Always refer to this as C<&sv_yes>.
2840
2841=item THIS
2842
2843Variable which is setup by C<xsubpp> to designate the object in a C++ XSUB.
2844This is always the proper type for the C++ object. See C<CLASS> and
5fb8527f 2845L<perlxs/"Using XS With C++">.
cb1a09d0
AD
2846
2847=item toLOWER
2848
2849Converts the specified character to lowercase.
2850
2851 int toLOWER (char c)
2852
2853=item toUPPER
2854
2855Converts the specified character to uppercase.
2856
2857 int toUPPER (char c)
2858
2859=item warn
2860
2861This is the XSUB-writer's interface to Perl's C<warn> function. Use this
2862function the same way you use the C C<printf> function. See C<croak()>.
2863
2864=item XPUSHi
2865
2866Push an integer onto the stack, extending the stack if necessary. See
2867C<PUSHi>.
2868
2869 XPUSHi(int d)
2870
2871=item XPUSHn
2872
2873Push a double onto the stack, extending the stack if necessary. See
2874C<PUSHn>.
2875
2876 XPUSHn(double d)
2877
2878=item XPUSHp
2879
2880Push a string onto the stack, extending the stack if necessary. The C<len>
2881indicates the length of the string. See C<PUSHp>.
2882
2883 XPUSHp(char *c, int len)
2884
2885=item XPUSHs
2886
2887Push an SV onto the stack, extending the stack if necessary. See C<PUSHs>.
2888
2889 XPUSHs(sv)
2890
5fb8527f
PP
2891=item XS
2892
2893Macro to declare an XSUB and its C parameter list. This is handled by
2894C<xsubpp>.
2895
cb1a09d0
AD
2896=item XSRETURN
2897
2898Return from XSUB, indicating number of items on the stack. This is usually
2899handled by C<xsubpp>.
2900
5fb8527f 2901 XSRETURN(int x);
cb1a09d0
AD
2902
2903=item XSRETURN_EMPTY
2904
5fb8527f 2905Return an empty list from an XSUB immediately.
cb1a09d0
AD
2906
2907 XSRETURN_EMPTY;
2908
5fb8527f
PP
2909=item XSRETURN_IV
2910
2911Return an integer from an XSUB immediately. Uses C<XST_mIV>.
2912
2913 XSRETURN_IV(IV v);
2914
cb1a09d0
AD
2915=item XSRETURN_NO
2916
5fb8527f 2917Return C<&sv_no> from an XSUB immediately. Uses C<XST_mNO>.
cb1a09d0
AD
2918
2919 XSRETURN_NO;
2920
5fb8527f
PP
2921=item XSRETURN_NV
2922
2923Return an double from an XSUB immediately. Uses C<XST_mNV>.
2924
2925 XSRETURN_NV(NV v);
2926
2927=item XSRETURN_PV
2928
2929Return a copy of a string from an XSUB immediately. Uses C<XST_mPV>.
2930
2931 XSRETURN_PV(char *v);
2932
cb1a09d0
AD
2933=item XSRETURN_UNDEF
2934
5fb8527f 2935Return C<&sv_undef> from an XSUB immediately. Uses C<XST_mUNDEF>.
cb1a09d0
AD
2936
2937 XSRETURN_UNDEF;
2938
2939=item XSRETURN_YES
2940
5fb8527f 2941Return C<&sv_yes> from an XSUB immediately. Uses C<XST_mYES>.
cb1a09d0
AD
2942
2943 XSRETURN_YES;
2944
5fb8527f
PP
2945=item XST_mIV
2946
2947Place an integer into the specified position C<i> on the stack. The value is
2948stored in a new mortal SV.
2949
2950 XST_mIV( int i, IV v );
2951
2952=item XST_mNV
2953
2954Place a double into the specified position C<i> on the stack. The value is
2955stored in a new mortal SV.
2956
2957 XST_mNV( int i, NV v );
2958
2959=item XST_mNO
2960
2961Place C<&sv_no> into the specified position C<i> on the stack.
2962
2963 XST_mNO( int i );
2964
2965=item XST_mPV
2966
2967Place a copy of a string into the specified position C<i> on the stack. The
2968value is stored in a new mortal SV.
2969
2970 XST_mPV( int i, char *v );
2971
2972=item XST_mUNDEF
2973
2974Place C<&sv_undef> into the specified position C<i> on the stack.
2975
2976 XST_mUNDEF( int i );
2977
2978=item XST_mYES
2979
2980Place C<&sv_yes> into the specified position C<i> on the stack.
2981
2982 XST_mYES( int i );
2983
2984=item XS_VERSION
2985
2986The version identifier for an XS module. This is usually handled
2987automatically by C<ExtUtils::MakeMaker>. See C<XS_VERSION_BOOTCHECK>.
2988
2989=item XS_VERSION_BOOTCHECK
2990
2991Macro to verify that a PM module's $VERSION variable matches the XS module's
2992C<XS_VERSION> variable. This is usually handled automatically by
2993C<xsubpp>. See L<perlxs/"The VERSIONCHECK: Keyword">.
2994
cb1a09d0
AD
2995=item Zero
2996
2997The XSUB-writer's interface to the C C<memzero> function. The C<d> is the
2998destination, C<n> is the number of items, and C<t> is the type.
2999
3000 (void) Zero( d, n, t );
3001
3002=back
3003
5f05dabc 3004=head1 EDITOR
cb1a09d0 3005
9607fc9c 3006Jeff Okamoto <F<okamoto@corp.hp.com>>
cb1a09d0
AD
3007
3008With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
3009Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
55497cff 3010Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
cb1a09d0 3011
9607fc9c 3012API Listing by Dean Roehrich <F<roehrich@cray.com>>.
cb1a09d0
AD
3013
3014=head1 DATE
3015
04343c6d 3016Version 31.8: 1997/5/17