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1=head1 NAME
2
954c1994 3perlguts - Introduction to the Perl API
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4
5=head1 DESCRIPTION
6
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7This document attempts to describe how to use the Perl API, as well as
8containing some info on the basic workings of the Perl core. It is far
9from complete and probably contains many errors. Please refer any
10questions or comments to the author below.
a0d0e21e 11
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12=head1 Variables
13
5f05dabc 14=head2 Datatypes
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15
16Perl has three typedefs that handle Perl's three main data types:
17
18 SV Scalar Value
19 AV Array Value
20 HV Hash Value
21
d1b91892 22Each typedef has specific routines that manipulate the various data types.
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23
24=head2 What is an "IV"?
25
954c1994 26Perl uses a special typedef IV which is a simple signed integer type that is
5f05dabc 27guaranteed to be large enough to hold a pointer (as well as an integer).
954c1994 28Additionally, there is the UV, which is simply an unsigned IV.
a0d0e21e 29
d1b91892 30Perl also uses two special typedefs, I32 and I16, which will always be at
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31least 32-bits and 16-bits long, respectively. (Again, there are U32 and U16,
32as well.)
a0d0e21e 33
54310121 34=head2 Working with SVs
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35
36An SV can be created and loaded with one command. There are four types of
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37values that can be loaded: an integer value (IV), a double (NV),
38a string (PV), and another scalar (SV).
a0d0e21e 39
9da1e3b5 40The six routines are:
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41
42 SV* newSViv(IV);
43 SV* newSVnv(double);
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44 SV* newSVpv(const char*, int);
45 SV* newSVpvn(const char*, int);
46fc3d4c 46 SV* newSVpvf(const char*, ...);
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47 SV* newSVsv(SV*);
48
deb3007b 49To change the value of an *already-existing* SV, there are seven routines:
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50
51 void sv_setiv(SV*, IV);
deb3007b 52 void sv_setuv(SV*, UV);
a0d0e21e 53 void sv_setnv(SV*, double);
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54 void sv_setpv(SV*, const char*);
55 void sv_setpvn(SV*, const char*, int)
46fc3d4c 56 void sv_setpvf(SV*, const char*, ...);
9abd00ed 57 void sv_setpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
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58 void sv_setsv(SV*, SV*);
59
60Notice that you can choose to specify the length of the string to be
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61assigned by using C<sv_setpvn>, C<newSVpvn>, or C<newSVpv>, or you may
62allow Perl to calculate the length by using C<sv_setpv> or by specifying
630 as the second argument to C<newSVpv>. Be warned, though, that Perl will
64determine the string's length by using C<strlen>, which depends on the
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65string terminating with a NUL character.
66
67The arguments of C<sv_setpvf> are processed like C<sprintf>, and the
68formatted output becomes the value.
69
70C<sv_setpvfn> is an analogue of C<vsprintf>, but it allows you to specify
71either a pointer to a variable argument list or the address and length of
72an array of SVs. The last argument points to a boolean; on return, if that
73boolean is true, then locale-specific information has been used to format
c2611fb3 74the string, and the string's contents are therefore untrustworthy (see
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75L<perlsec>). This pointer may be NULL if that information is not
76important. Note that this function requires you to specify the length of
77the format.
78
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79STRLEN is an integer type (Size_t, usually defined as size_t in
80config.h) guaranteed to be large enough to represent the size of
81any string that perl can handle.
82
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83The C<sv_set*()> functions are not generic enough to operate on values
84that have "magic". See L<Magic Virtual Tables> later in this document.
a0d0e21e 85
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86All SVs that contain strings should be terminated with a NUL character.
87If it is not NUL-terminated there is a risk of
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88core dumps and corruptions from code which passes the string to C
89functions or system calls which expect a NUL-terminated string.
90Perl's own functions typically add a trailing NUL for this reason.
91Nevertheless, you should be very careful when you pass a string stored
92in an SV to a C function or system call.
93
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94To access the actual value that an SV points to, you can use the macros:
95
96 SvIV(SV*)
954c1994 97 SvUV(SV*)
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98 SvNV(SV*)
99 SvPV(SV*, STRLEN len)
1fa8b10d 100 SvPV_nolen(SV*)
a0d0e21e 101
954c1994 102which will automatically coerce the actual scalar type into an IV, UV, double,
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103or string.
104
105In the C<SvPV> macro, the length of the string returned is placed into the
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106variable C<len> (this is a macro, so you do I<not> use C<&len>). If you do
107not care what the length of the data is, use the C<SvPV_nolen> macro.
108Historically the C<SvPV> macro with the global variable C<PL_na> has been
109used in this case. But that can be quite inefficient because C<PL_na> must
110be accessed in thread-local storage in threaded Perl. In any case, remember
111that Perl allows arbitrary strings of data that may both contain NULs and
112might not be terminated by a NUL.
a0d0e21e 113
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114Also remember that C doesn't allow you to safely say C<foo(SvPV(s, len),
115len);>. It might work with your compiler, but it won't work for everyone.
116Break this sort of statement up into separate assignments:
117
b2f5ed49 118 SV *s;
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119 STRLEN len;
120 char * ptr;
b2f5ed49 121 ptr = SvPV(s, len);
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122 foo(ptr, len);
123
07fa94a1 124If you want to know if the scalar value is TRUE, you can use:
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125
126 SvTRUE(SV*)
127
128Although Perl will automatically grow strings for you, if you need to force
129Perl to allocate more memory for your SV, you can use the macro
130
131 SvGROW(SV*, STRLEN newlen)
132
133which will determine if more memory needs to be allocated. If so, it will
134call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
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135decrease, the allocated memory of an SV and that it does not automatically
136add a byte for the a trailing NUL (perl's own string functions typically do
8ebc5c01 137C<SvGROW(sv, len + 1)>).
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138
139If you have an SV and want to know what kind of data Perl thinks is stored
140in it, you can use the following macros to check the type of SV you have.
141
142 SvIOK(SV*)
143 SvNOK(SV*)
144 SvPOK(SV*)
145
146You can get and set the current length of the string stored in an SV with
147the following macros:
148
149 SvCUR(SV*)
150 SvCUR_set(SV*, I32 val)
151
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152You can also get a pointer to the end of the string stored in the SV
153with the macro:
154
155 SvEND(SV*)
156
157But note that these last three macros are valid only if C<SvPOK()> is true.
a0d0e21e 158
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159If you want to append something to the end of string stored in an C<SV*>,
160you can use the following functions:
161
08105a92 162 void sv_catpv(SV*, const char*);
e65f3abd 163 void sv_catpvn(SV*, const char*, STRLEN);
46fc3d4c 164 void sv_catpvf(SV*, const char*, ...);
9abd00ed 165 void sv_catpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
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166 void sv_catsv(SV*, SV*);
167
168The first function calculates the length of the string to be appended by
169using C<strlen>. In the second, you specify the length of the string
46fc3d4c 170yourself. The third function processes its arguments like C<sprintf> and
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171appends the formatted output. The fourth function works like C<vsprintf>.
172You can specify the address and length of an array of SVs instead of the
173va_list argument. The fifth function extends the string stored in the first
174SV with the string stored in the second SV. It also forces the second SV
175to be interpreted as a string.
176
177The C<sv_cat*()> functions are not generic enough to operate on values that
178have "magic". See L<Magic Virtual Tables> later in this document.
d1b91892 179
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180If you know the name of a scalar variable, you can get a pointer to its SV
181by using the following:
182
4929bf7b 183 SV* get_sv("package::varname", FALSE);
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184
185This returns NULL if the variable does not exist.
186
d1b91892 187If you want to know if this variable (or any other SV) is actually C<defined>,
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188you can call:
189
190 SvOK(SV*)
191
9cde0e7f 192The scalar C<undef> value is stored in an SV instance called C<PL_sv_undef>. Its
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193address can be used whenever an C<SV*> is needed.
194
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195There are also the two values C<PL_sv_yes> and C<PL_sv_no>, which contain Boolean
196TRUE and FALSE values, respectively. Like C<PL_sv_undef>, their addresses can
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197be used whenever an C<SV*> is needed.
198
9cde0e7f 199Do not be fooled into thinking that C<(SV *) 0> is the same as C<&PL_sv_undef>.
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200Take this code:
201
202 SV* sv = (SV*) 0;
203 if (I-am-to-return-a-real-value) {
204 sv = sv_2mortal(newSViv(42));
205 }
206 sv_setsv(ST(0), sv);
207
208This code tries to return a new SV (which contains the value 42) if it should
04343c6d 209return a real value, or undef otherwise. Instead it has returned a NULL
a0d0e21e 210pointer which, somewhere down the line, will cause a segmentation violation,
9cde0e7f 211bus error, or just weird results. Change the zero to C<&PL_sv_undef> in the first
5f05dabc 212line and all will be well.
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213
214To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
3fe9a6f1 215call is not necessary (see L<Reference Counts and Mortality>).
a0d0e21e 216
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217=head2 Offsets
218
219Perl provides the function C<sv_chop> to efficiently remove characters
220from the beginning of a string; you give it an SV and a pointer to
221somewhere inside the the PV, and it discards everything before the
222pointer. The efficiency comes by means of a little hack: instead of
223actually removing the characters, C<sv_chop> sets the flag C<OOK>
224(offset OK) to signal to other functions that the offset hack is in
225effect, and it puts the number of bytes chopped off into the IV field
226of the SV. It then moves the PV pointer (called C<SvPVX>) forward that
227many bytes, and adjusts C<SvCUR> and C<SvLEN>.
228
229Hence, at this point, the start of the buffer that we allocated lives
230at C<SvPVX(sv) - SvIV(sv)> in memory and the PV pointer is pointing
231into the middle of this allocated storage.
232
233This is best demonstrated by example:
234
235 % ./perl -Ilib -MDevel::Peek -le '$a="12345"; $a=~s/.//; Dump($a)'
236 SV = PVIV(0x8128450) at 0x81340f0
237 REFCNT = 1
238 FLAGS = (POK,OOK,pPOK)
239 IV = 1 (OFFSET)
240 PV = 0x8135781 ( "1" . ) "2345"\0
241 CUR = 4
242 LEN = 5
243
244Here the number of bytes chopped off (1) is put into IV, and
245C<Devel::Peek::Dump> helpfully reminds us that this is an offset. The
246portion of the string between the "real" and the "fake" beginnings is
247shown in parentheses, and the values of C<SvCUR> and C<SvLEN> reflect
248the fake beginning, not the real one.
249
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250Something similar to the offset hack is perfomed on AVs to enable
251efficient shifting and splicing off the beginning of the array; while
252C<AvARRAY> points to the first element in the array that is visible from
253Perl, C<AvALLOC> points to the real start of the C array. These are
254usually the same, but a C<shift> operation can be carried out by
255increasing C<AvARRAY> by one and decreasing C<AvFILL> and C<AvLEN>.
256Again, the location of the real start of the C array only comes into
257play when freeing the array. See C<av_shift> in F<av.c>.
258
d1b91892 259=head2 What's Really Stored in an SV?
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260
261Recall that the usual method of determining the type of scalar you have is
5f05dabc 262to use C<Sv*OK> macros. Because a scalar can be both a number and a string,
d1b91892 263usually these macros will always return TRUE and calling the C<Sv*V>
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264macros will do the appropriate conversion of string to integer/double or
265integer/double to string.
266
267If you I<really> need to know if you have an integer, double, or string
268pointer in an SV, you can use the following three macros instead:
269
270 SvIOKp(SV*)
271 SvNOKp(SV*)
272 SvPOKp(SV*)
273
274These will tell you if you truly have an integer, double, or string pointer
d1b91892 275stored in your SV. The "p" stands for private.
a0d0e21e 276
07fa94a1 277In general, though, it's best to use the C<Sv*V> macros.
a0d0e21e 278
54310121 279=head2 Working with AVs
a0d0e21e 280
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281There are two ways to create and load an AV. The first method creates an
282empty AV:
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283
284 AV* newAV();
285
54310121 286The second method both creates the AV and initially populates it with SVs:
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287
288 AV* av_make(I32 num, SV **ptr);
289
5f05dabc 290The second argument points to an array containing C<num> C<SV*>'s. Once the
54310121 291AV has been created, the SVs can be destroyed, if so desired.
a0d0e21e 292
54310121 293Once the AV has been created, the following operations are possible on AVs:
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294
295 void av_push(AV*, SV*);
296 SV* av_pop(AV*);
297 SV* av_shift(AV*);
298 void av_unshift(AV*, I32 num);
299
300These should be familiar operations, with the exception of C<av_unshift>.
301This routine adds C<num> elements at the front of the array with the C<undef>
302value. You must then use C<av_store> (described below) to assign values
303to these new elements.
304
305Here are some other functions:
306
5f05dabc 307 I32 av_len(AV*);
a0d0e21e 308 SV** av_fetch(AV*, I32 key, I32 lval);
a0d0e21e 309 SV** av_store(AV*, I32 key, SV* val);
a0d0e21e 310
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311The C<av_len> function returns the highest index value in array (just
312like $#array in Perl). If the array is empty, -1 is returned. The
313C<av_fetch> function returns the value at index C<key>, but if C<lval>
314is non-zero, then C<av_fetch> will store an undef value at that index.
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315The C<av_store> function stores the value C<val> at index C<key>, and does
316not increment the reference count of C<val>. Thus the caller is responsible
317for taking care of that, and if C<av_store> returns NULL, the caller will
318have to decrement the reference count to avoid a memory leak. Note that
319C<av_fetch> and C<av_store> both return C<SV**>'s, not C<SV*>'s as their
320return value.
d1b91892 321
a0d0e21e 322 void av_clear(AV*);
a0d0e21e 323 void av_undef(AV*);
cb1a09d0 324 void av_extend(AV*, I32 key);
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325
326The C<av_clear> function deletes all the elements in the AV* array, but
327does not actually delete the array itself. The C<av_undef> function will
328delete all the elements in the array plus the array itself. The
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329C<av_extend> function extends the array so that it contains at least C<key+1>
330elements. If C<key+1> is less than the currently allocated length of the array,
331then nothing is done.
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332
333If you know the name of an array variable, you can get a pointer to its AV
334by using the following:
335
4929bf7b 336 AV* get_av("package::varname", FALSE);
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337
338This returns NULL if the variable does not exist.
339
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340See L<Understanding the Magic of Tied Hashes and Arrays> for more
341information on how to use the array access functions on tied arrays.
342
54310121 343=head2 Working with HVs
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344
345To create an HV, you use the following routine:
346
347 HV* newHV();
348
54310121 349Once the HV has been created, the following operations are possible on HVs:
a0d0e21e 350
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351 SV** hv_store(HV*, const char* key, U32 klen, SV* val, U32 hash);
352 SV** hv_fetch(HV*, const char* key, U32 klen, I32 lval);
a0d0e21e 353
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354The C<klen> parameter is the length of the key being passed in (Note that
355you cannot pass 0 in as a value of C<klen> to tell Perl to measure the
356length of the key). The C<val> argument contains the SV pointer to the
54310121 357scalar being stored, and C<hash> is the precomputed hash value (zero if
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358you want C<hv_store> to calculate it for you). The C<lval> parameter
359indicates whether this fetch is actually a part of a store operation, in
360which case a new undefined value will be added to the HV with the supplied
361key and C<hv_fetch> will return as if the value had already existed.
a0d0e21e 362
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363Remember that C<hv_store> and C<hv_fetch> return C<SV**>'s and not just
364C<SV*>. To access the scalar value, you must first dereference the return
365value. However, you should check to make sure that the return value is
366not NULL before dereferencing it.
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367
368These two functions check if a hash table entry exists, and deletes it.
369
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370 bool hv_exists(HV*, const char* key, U32 klen);
371 SV* hv_delete(HV*, const char* key, U32 klen, I32 flags);
a0d0e21e 372
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373If C<flags> does not include the C<G_DISCARD> flag then C<hv_delete> will
374create and return a mortal copy of the deleted value.
375
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376And more miscellaneous functions:
377
378 void hv_clear(HV*);
a0d0e21e 379 void hv_undef(HV*);
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380
381Like their AV counterparts, C<hv_clear> deletes all the entries in the hash
382table but does not actually delete the hash table. The C<hv_undef> deletes
383both the entries and the hash table itself.
a0d0e21e 384
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385Perl keeps the actual data in linked list of structures with a typedef of HE.
386These contain the actual key and value pointers (plus extra administrative
387overhead). The key is a string pointer; the value is an C<SV*>. However,
388once you have an C<HE*>, to get the actual key and value, use the routines
389specified below.
390
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391 I32 hv_iterinit(HV*);
392 /* Prepares starting point to traverse hash table */
393 HE* hv_iternext(HV*);
394 /* Get the next entry, and return a pointer to a
395 structure that has both the key and value */
396 char* hv_iterkey(HE* entry, I32* retlen);
397 /* Get the key from an HE structure and also return
398 the length of the key string */
cb1a09d0 399 SV* hv_iterval(HV*, HE* entry);
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400 /* Return a SV pointer to the value of the HE
401 structure */
cb1a09d0 402 SV* hv_iternextsv(HV*, char** key, I32* retlen);
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403 /* This convenience routine combines hv_iternext,
404 hv_iterkey, and hv_iterval. The key and retlen
405 arguments are return values for the key and its
406 length. The value is returned in the SV* argument */
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407
408If you know the name of a hash variable, you can get a pointer to its HV
409by using the following:
410
4929bf7b 411 HV* get_hv("package::varname", FALSE);
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412
413This returns NULL if the variable does not exist.
414
8ebc5c01 415The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
a0d0e21e 416
a0d0e21e 417 hash = 0;
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418 while (klen--)
419 hash = (hash * 33) + *key++;
87275199 420 hash = hash + (hash >> 5); /* after 5.6 */
ab192400 421
87275199 422The last step was added in version 5.6 to improve distribution of
ab192400 423lower bits in the resulting hash value.
a0d0e21e 424
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425See L<Understanding the Magic of Tied Hashes and Arrays> for more
426information on how to use the hash access functions on tied hashes.
427
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428=head2 Hash API Extensions
429
430Beginning with version 5.004, the following functions are also supported:
431
432 HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
433 HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
c47ff5f1 434
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435 bool hv_exists_ent (HV* tb, SV* key, U32 hash);
436 SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
c47ff5f1 437
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438 SV* hv_iterkeysv (HE* entry);
439
440Note that these functions take C<SV*> keys, which simplifies writing
441of extension code that deals with hash structures. These functions
442also allow passing of C<SV*> keys to C<tie> functions without forcing
443you to stringify the keys (unlike the previous set of functions).
444
445They also return and accept whole hash entries (C<HE*>), making their
446use more efficient (since the hash number for a particular string
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447doesn't have to be recomputed every time). See L<perlapi> for detailed
448descriptions.
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449
450The following macros must always be used to access the contents of hash
451entries. Note that the arguments to these macros must be simple
452variables, since they may get evaluated more than once. See
4a4eefd0 453L<perlapi> for detailed descriptions of these macros.
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454
455 HePV(HE* he, STRLEN len)
456 HeVAL(HE* he)
457 HeHASH(HE* he)
458 HeSVKEY(HE* he)
459 HeSVKEY_force(HE* he)
460 HeSVKEY_set(HE* he, SV* sv)
461
462These two lower level macros are defined, but must only be used when
463dealing with keys that are not C<SV*>s:
464
465 HeKEY(HE* he)
466 HeKLEN(HE* he)
467
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468Note that both C<hv_store> and C<hv_store_ent> do not increment the
469reference count of the stored C<val>, which is the caller's responsibility.
470If these functions return a NULL value, the caller will usually have to
471decrement the reference count of C<val> to avoid a memory leak.
1e422769 472
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473=head2 References
474
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475References are a special type of scalar that point to other data types
476(including references).
a0d0e21e 477
07fa94a1 478To create a reference, use either of the following functions:
a0d0e21e 479
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480 SV* newRV_inc((SV*) thing);
481 SV* newRV_noinc((SV*) thing);
a0d0e21e 482
5f05dabc 483The C<thing> argument can be any of an C<SV*>, C<AV*>, or C<HV*>. The
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484functions are identical except that C<newRV_inc> increments the reference
485count of the C<thing>, while C<newRV_noinc> does not. For historical
486reasons, C<newRV> is a synonym for C<newRV_inc>.
487
488Once you have a reference, you can use the following macro to dereference
489the reference:
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490
491 SvRV(SV*)
492
493then call the appropriate routines, casting the returned C<SV*> to either an
d1b91892 494C<AV*> or C<HV*>, if required.
a0d0e21e 495
d1b91892 496To determine if an SV is a reference, you can use the following macro:
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497
498 SvROK(SV*)
499
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500To discover what type of value the reference refers to, use the following
501macro and then check the return value.
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502
503 SvTYPE(SvRV(SV*))
504
505The most useful types that will be returned are:
506
507 SVt_IV Scalar
508 SVt_NV Scalar
509 SVt_PV Scalar
5f05dabc 510 SVt_RV Scalar
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511 SVt_PVAV Array
512 SVt_PVHV Hash
513 SVt_PVCV Code
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514 SVt_PVGV Glob (possible a file handle)
515 SVt_PVMG Blessed or Magical Scalar
516
517 See the sv.h header file for more details.
d1b91892 518
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519=head2 Blessed References and Class Objects
520
521References are also used to support object-oriented programming. In the
522OO lexicon, an object is simply a reference that has been blessed into a
523package (or class). Once blessed, the programmer may now use the reference
524to access the various methods in the class.
525
526A reference can be blessed into a package with the following function:
527
528 SV* sv_bless(SV* sv, HV* stash);
529
530The C<sv> argument must be a reference. The C<stash> argument specifies
3fe9a6f1 531which class the reference will belong to. See
2ae324a7 532L<Stashes and Globs> for information on converting class names into stashes.
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533
534/* Still under construction */
535
536Upgrades rv to reference if not already one. Creates new SV for rv to
8ebc5c01
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537point to. If C<classname> is non-null, the SV is blessed into the specified
538class. SV is returned.
cb1a09d0 539
08105a92 540 SV* newSVrv(SV* rv, const char* classname);
cb1a09d0 541
e1c57cef 542Copies integer, unsigned integer or double into an SV whose reference is C<rv>. SV is blessed
8ebc5c01 543if C<classname> is non-null.
cb1a09d0 544
08105a92 545 SV* sv_setref_iv(SV* rv, const char* classname, IV iv);
e1c57cef 546 SV* sv_setref_uv(SV* rv, const char* classname, UV uv);
08105a92 547 SV* sv_setref_nv(SV* rv, const char* classname, NV iv);
cb1a09d0 548
5f05dabc 549Copies the pointer value (I<the address, not the string!>) into an SV whose
8ebc5c01 550reference is rv. SV is blessed if C<classname> is non-null.
cb1a09d0 551
08105a92 552 SV* sv_setref_pv(SV* rv, const char* classname, PV iv);
cb1a09d0 553
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554Copies string into an SV whose reference is C<rv>. Set length to 0 to let
555Perl calculate the string length. SV is blessed if C<classname> is non-null.
cb1a09d0 556
e65f3abd 557 SV* sv_setref_pvn(SV* rv, const char* classname, PV iv, STRLEN length);
cb1a09d0 558
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559Tests whether the SV is blessed into the specified class. It does not
560check inheritance relationships.
561
08105a92 562 int sv_isa(SV* sv, const char* name);
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563
564Tests whether the SV is a reference to a blessed object.
565
566 int sv_isobject(SV* sv);
567
568Tests whether the SV is derived from the specified class. SV can be either
569a reference to a blessed object or a string containing a class name. This
570is the function implementing the C<UNIVERSAL::isa> functionality.
571
08105a92 572 bool sv_derived_from(SV* sv, const char* name);
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573
574To check if you've got an object derived from a specific class you have
575to write:
576
577 if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... }
cb1a09d0 578
5f05dabc 579=head2 Creating New Variables
cb1a09d0 580
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581To create a new Perl variable with an undef value which can be accessed from
582your Perl script, use the following routines, depending on the variable type.
cb1a09d0 583
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584 SV* get_sv("package::varname", TRUE);
585 AV* get_av("package::varname", TRUE);
586 HV* get_hv("package::varname", TRUE);
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587
588Notice the use of TRUE as the second parameter. The new variable can now
589be set, using the routines appropriate to the data type.
590
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591There are additional macros whose values may be bitwise OR'ed with the
592C<TRUE> argument to enable certain extra features. Those bits are:
cb1a09d0 593
5f05dabc 594 GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
54310121 595 "Name <varname> used only once: possible typo" warning.
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596 GV_ADDWARN Issues the warning "Had to create <varname> unexpectedly" if
597 the variable did not exist before the function was called.
cb1a09d0 598
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599If you do not specify a package name, the variable is created in the current
600package.
cb1a09d0 601
5f05dabc 602=head2 Reference Counts and Mortality
a0d0e21e 603
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604Perl uses an reference count-driven garbage collection mechanism. SVs,
605AVs, or HVs (xV for short in the following) start their life with a
55497cff 606reference count of 1. If the reference count of an xV ever drops to 0,
07fa94a1 607then it will be destroyed and its memory made available for reuse.
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608
609This normally doesn't happen at the Perl level unless a variable is
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610undef'ed or the last variable holding a reference to it is changed or
611overwritten. At the internal level, however, reference counts can be
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612manipulated with the following macros:
613
614 int SvREFCNT(SV* sv);
5f05dabc 615 SV* SvREFCNT_inc(SV* sv);
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616 void SvREFCNT_dec(SV* sv);
617
618However, there is one other function which manipulates the reference
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619count of its argument. The C<newRV_inc> function, you will recall,
620creates a reference to the specified argument. As a side effect,
621it increments the argument's reference count. If this is not what
622you want, use C<newRV_noinc> instead.
623
624For example, imagine you want to return a reference from an XSUB function.
625Inside the XSUB routine, you create an SV which initially has a reference
626count of one. Then you call C<newRV_inc>, passing it the just-created SV.
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627This returns the reference as a new SV, but the reference count of the
628SV you passed to C<newRV_inc> has been incremented to two. Now you
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629return the reference from the XSUB routine and forget about the SV.
630But Perl hasn't! Whenever the returned reference is destroyed, the
631reference count of the original SV is decreased to one and nothing happens.
632The SV will hang around without any way to access it until Perl itself
633terminates. This is a memory leak.
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634
635The correct procedure, then, is to use C<newRV_noinc> instead of
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636C<newRV_inc>. Then, if and when the last reference is destroyed,
637the reference count of the SV will go to zero and it will be destroyed,
07fa94a1 638stopping any memory leak.
55497cff 639
5f05dabc 640There are some convenience functions available that can help with the
54310121 641destruction of xVs. These functions introduce the concept of "mortality".
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642An xV that is mortal has had its reference count marked to be decremented,
643but not actually decremented, until "a short time later". Generally the
644term "short time later" means a single Perl statement, such as a call to
54310121 645an XSUB function. The actual determinant for when mortal xVs have their
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646reference count decremented depends on two macros, SAVETMPS and FREETMPS.
647See L<perlcall> and L<perlxs> for more details on these macros.
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648
649"Mortalization" then is at its simplest a deferred C<SvREFCNT_dec>.
650However, if you mortalize a variable twice, the reference count will
651later be decremented twice.
652
653You should be careful about creating mortal variables. Strange things
654can happen if you make the same value mortal within multiple contexts,
5f05dabc 655or if you make a variable mortal multiple times.
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656
657To create a mortal variable, use the functions:
658
659 SV* sv_newmortal()
660 SV* sv_2mortal(SV*)
661 SV* sv_mortalcopy(SV*)
662
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663The first call creates a mortal SV, the second converts an existing
664SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
665third creates a mortal copy of an existing SV.
a0d0e21e 666
54310121 667The mortal routines are not just for SVs -- AVs and HVs can be
faed5253 668made mortal by passing their address (type-casted to C<SV*>) to the
07fa94a1 669C<sv_2mortal> or C<sv_mortalcopy> routines.
a0d0e21e 670
5f05dabc 671=head2 Stashes and Globs
a0d0e21e 672
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673A "stash" is a hash that contains all of the different objects that
674are contained within a package. Each key of the stash is a symbol
675name (shared by all the different types of objects that have the same
676name), and each value in the hash table is a GV (Glob Value). This GV
677in turn contains references to the various objects of that name,
678including (but not limited to) the following:
cb1a09d0 679
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680 Scalar Value
681 Array Value
682 Hash Value
a3cb178b 683 I/O Handle
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684 Format
685 Subroutine
686
9cde0e7f 687There is a single stash called "PL_defstash" that holds the items that exist
5f05dabc
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688in the "main" package. To get at the items in other packages, append the
689string "::" to the package name. The items in the "Foo" package are in
9cde0e7f 690the stash "Foo::" in PL_defstash. The items in the "Bar::Baz" package are
5f05dabc 691in the stash "Baz::" in "Bar::"'s stash.
a0d0e21e 692
d1b91892 693To get the stash pointer for a particular package, use the function:
a0d0e21e 694
08105a92 695 HV* gv_stashpv(const char* name, I32 create)
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696 HV* gv_stashsv(SV*, I32 create)
697
698The first function takes a literal string, the second uses the string stored
d1b91892 699in the SV. Remember that a stash is just a hash table, so you get back an
cb1a09d0 700C<HV*>. The C<create> flag will create a new package if it is set.
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701
702The name that C<gv_stash*v> wants is the name of the package whose symbol table
703you want. The default package is called C<main>. If you have multiply nested
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704packages, pass their names to C<gv_stash*v>, separated by C<::> as in the Perl
705language itself.
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706
707Alternately, if you have an SV that is a blessed reference, you can find
708out the stash pointer by using:
709
710 HV* SvSTASH(SvRV(SV*));
711
712then use the following to get the package name itself:
713
714 char* HvNAME(HV* stash);
715
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716If you need to bless or re-bless an object you can use the following
717function:
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718
719 SV* sv_bless(SV*, HV* stash)
720
721where the first argument, an C<SV*>, must be a reference, and the second
722argument is a stash. The returned C<SV*> can now be used in the same way
723as any other SV.
724
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725For more information on references and blessings, consult L<perlref>.
726
54310121 727=head2 Double-Typed SVs
0a753a76
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728
729Scalar variables normally contain only one type of value, an integer,
730double, pointer, or reference. Perl will automatically convert the
731actual scalar data from the stored type into the requested type.
732
733Some scalar variables contain more than one type of scalar data. For
734example, the variable C<$!> contains either the numeric value of C<errno>
735or its string equivalent from either C<strerror> or C<sys_errlist[]>.
736
737To force multiple data values into an SV, you must do two things: use the
738C<sv_set*v> routines to add the additional scalar type, then set a flag
739so that Perl will believe it contains more than one type of data. The
740four macros to set the flags are:
741
742 SvIOK_on
743 SvNOK_on
744 SvPOK_on
745 SvROK_on
746
747The particular macro you must use depends on which C<sv_set*v> routine
748you called first. This is because every C<sv_set*v> routine turns on
749only the bit for the particular type of data being set, and turns off
750all the rest.
751
752For example, to create a new Perl variable called "dberror" that contains
753both the numeric and descriptive string error values, you could use the
754following code:
755
756 extern int dberror;
757 extern char *dberror_list;
758
4929bf7b 759 SV* sv = get_sv("dberror", TRUE);
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760 sv_setiv(sv, (IV) dberror);
761 sv_setpv(sv, dberror_list[dberror]);
762 SvIOK_on(sv);
763
764If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
765macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
766
767=head2 Magic Variables
a0d0e21e 768
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769[This section still under construction. Ignore everything here. Post no
770bills. Everything not permitted is forbidden.]
771
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772Any SV may be magical, that is, it has special features that a normal
773SV does not have. These features are stored in the SV structure in a
5f05dabc 774linked list of C<struct magic>'s, typedef'ed to C<MAGIC>.
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775
776 struct magic {
777 MAGIC* mg_moremagic;
778 MGVTBL* mg_virtual;
779 U16 mg_private;
780 char mg_type;
781 U8 mg_flags;
782 SV* mg_obj;
783 char* mg_ptr;
784 I32 mg_len;
785 };
786
787Note this is current as of patchlevel 0, and could change at any time.
788
789=head2 Assigning Magic
790
791Perl adds magic to an SV using the sv_magic function:
792
08105a92 793 void sv_magic(SV* sv, SV* obj, int how, const char* name, I32 namlen);
d1b91892
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794
795The C<sv> argument is a pointer to the SV that is to acquire a new magical
796feature.
797
798If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
799set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
800it to the beginning of the linked list of magical features. Any prior
801entry of the same type of magic is deleted. Note that this can be
5fb8527f 802overridden, and multiple instances of the same type of magic can be
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803associated with an SV.
804
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805The C<name> and C<namlen> arguments are used to associate a string with
806the magic, typically the name of a variable. C<namlen> is stored in the
807C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
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808copy of the name is stored in C<mg_ptr> field.
809
810The sv_magic function uses C<how> to determine which, if any, predefined
811"Magic Virtual Table" should be assigned to the C<mg_virtual> field.
cb1a09d0 812See the "Magic Virtual Table" section below. The C<how> argument is also
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813stored in the C<mg_type> field. The value of C<how> should be chosen
814from the set of macros C<PERL_MAGIC_foo> found perl.h. Note that before
815these macros were added, perl internals used to directly use character
816literals, so you may occasionally come across old code or documentation
817referrring to 'U' magic rather than C<PERL_MAGIC_uvar> for example.
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818
819The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
820structure. If it is not the same as the C<sv> argument, the reference
821count of the C<obj> object is incremented. If it is the same, or if
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822the C<how> argument is C<PERL_MAGIC_arylen>", or if it is a NULL pointer,
823then C<obj> is merely stored, without the reference count being incremented.
d1b91892 824
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825There is also a function to add magic to an C<HV>:
826
827 void hv_magic(HV *hv, GV *gv, int how);
828
829This simply calls C<sv_magic> and coerces the C<gv> argument into an C<SV>.
830
831To remove the magic from an SV, call the function sv_unmagic:
832
833 void sv_unmagic(SV *sv, int type);
834
835The C<type> argument should be equal to the C<how> value when the C<SV>
836was initially made magical.
837
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838=head2 Magic Virtual Tables
839
840The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
841C<MGVTBL>, which is a structure of function pointers and stands for
842"Magic Virtual Table" to handle the various operations that might be
843applied to that variable.
844
845The C<MGVTBL> has five pointers to the following routine types:
846
847 int (*svt_get)(SV* sv, MAGIC* mg);
848 int (*svt_set)(SV* sv, MAGIC* mg);
849 U32 (*svt_len)(SV* sv, MAGIC* mg);
850 int (*svt_clear)(SV* sv, MAGIC* mg);
851 int (*svt_free)(SV* sv, MAGIC* mg);
852
853This MGVTBL structure is set at compile-time in C<perl.h> and there are
854currently 19 types (or 21 with overloading turned on). These different
855structures contain pointers to various routines that perform additional
856actions depending on which function is being called.
857
858 Function pointer Action taken
859 ---------------- ------------
860 svt_get Do something after the value of the SV is retrieved.
861 svt_set Do something after the SV is assigned a value.
862 svt_len Report on the SV's length.
863 svt_clear Clear something the SV represents.
864 svt_free Free any extra storage associated with the SV.
865
866For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
14befaf4 867to an C<mg_type> of C<PERL_MAGIC_sv>) contains:
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868
869 { magic_get, magic_set, magic_len, 0, 0 }
870
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871Thus, when an SV is determined to be magical and of type C<PERL_MAGIC_sv>,
872if a get operation is being performed, the routine C<magic_get> is
873called. All the various routines for the various magical types begin
874with C<magic_>. NOTE: the magic routines are not considered part of
875the Perl API, and may not be exported by the Perl library.
d1b91892
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876
877The current kinds of Magic Virtual Tables are:
878
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879 mg_type
880 (old-style char and macro) MGVTBL Type of magic
881 -------------------------- ------ ----------------------------
882 \0 PERL_MAGIC_sv vtbl_sv Special scalar variable
883 A PERL_MAGIC_overload vtbl_amagic %OVERLOAD hash
884 a PERL_MAGIC_overload_elem vtbl_amagicelem %OVERLOAD hash element
885 c PERL_MAGIC_overload_table (none) Holds overload table (AMT)
886 on stash
887 B PERL_MAGIC_bm vtbl_bm Boyer-Moore (fast string search)
888 D PERL_MAGIC_regdata vtbl_regdata Regex match position data
889 (@+ and @- vars)
890 d PERL_MAGIC_regdatum vtbl_regdatum Regex match position data
891 element
892 E PERL_MAGIC_env vtbl_env %ENV hash
893 e PERL_MAGIC_envelem vtbl_envelem %ENV hash element
894 f PERL_MAGIC_fm vtbl_fm Formline ('compiled' format)
895 g PERL_MAGIC_regex_global vtbl_mglob m//g target / study()ed string
896 I PERL_MAGIC_isa vtbl_isa @ISA array
897 i PERL_MAGIC_isaelem vtbl_isaelem @ISA array element
898 k PERL_MAGIC_nkeys vtbl_nkeys scalar(keys()) lvalue
899 L PERL_MAGIC_dbfile (none) Debugger %_<filename
900 l PERL_MAGIC_dbline vtbl_dbline Debugger %_<filename element
901 m PERL_MAGIC_mutex vtbl_mutex ???
902 o PERL_MAGIC_collxfrm vtbl_collxfrm Locale transformation
903 P PERL_MAGIC_tied vtbl_pack Tied array or hash
904 p PERL_MAGIC_tiedelem vtbl_packelem Tied array or hash element
905 q PERL_MAGIC_tiedscalar vtbl_packelem Tied scalar or handle
906 r PERL_MAGIC_qr vtbl_qr precompiled qr// regex
907 S PERL_MAGIC_sig vtbl_sig %SIG hash
908 s PERL_MAGIC_sigelem vtbl_sigelem %SIG hash element
909 t PERL_MAGIC_taint vtbl_taint Taintedness
910 U PERL_MAGIC_uvar vtbl_uvar Available for use by extensions
911 v PERL_MAGIC_vec vtbl_vec vec() lvalue
912 x PERL_MAGIC_substr vtbl_substr substr() lvalue
913 y PERL_MAGIC_defelem vtbl_defelem Shadow "foreach" iterator
914 variable / smart parameter
915 vivification
916 * PERL_MAGIC_glob vtbl_glob GV (typeglob)
917 # PERL_MAGIC_arylen vtbl_arylen Array length ($#ary)
918 . PERL_MAGIC_pos vtbl_pos pos() lvalue
919 < PERL_MAGIC_backref vtbl_backref ???
920 ~ PERL_MAGIC_ext (none) Available for use by extensions
d1b91892 921
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922When an uppercase and lowercase letter both exist in the table, then the
923uppercase letter is used to represent some kind of composite type (a list
924or a hash), and the lowercase letter is used to represent an element of
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925that composite type. Some internals code makes use of this case
926relationship.
927
928The C<PERL_MAGIC_ext> and C<PERL_MAGIC_uvar> magic types are defined
929specifically for use by extensions and will not be used by perl itself.
930Extensions can use C<PERL_MAGIC_ext> magic to 'attach' private information
931to variables (typically objects). This is especially useful because
932there is no way for normal perl code to corrupt this private information
933(unlike using extra elements of a hash object).
934
935Similarly, C<PERL_MAGIC_uvar> magic can be used much like tie() to call a
936C function any time a scalar's value is used or changed. The C<MAGIC>'s
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937C<mg_ptr> field points to a C<ufuncs> structure:
938
939 struct ufuncs {
940 I32 (*uf_val)(IV, SV*);
941 I32 (*uf_set)(IV, SV*);
942 IV uf_index;
943 };
944
945When the SV is read from or written to, the C<uf_val> or C<uf_set>
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946function will be called with C<uf_index> as the first arg and a pointer to
947the SV as the second. A simple example of how to add C<PERL_MAGIC_uvar>
1526ead6
AB
948magic is shown below. Note that the ufuncs structure is copied by
949sv_magic, so you can safely allocate it on the stack.
950
951 void
952 Umagic(sv)
953 SV *sv;
954 PREINIT:
955 struct ufuncs uf;
956 CODE:
957 uf.uf_val = &my_get_fn;
958 uf.uf_set = &my_set_fn;
959 uf.uf_index = 0;
14befaf4 960 sv_magic(sv, 0, PERL_MAGIC_uvar, (char*)&uf, sizeof(uf));
5f05dabc 961
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962Note that because multiple extensions may be using C<PERL_MAGIC_ext>
963or C<PERL_MAGIC_uvar> magic, it is important for extensions to take
964extra care to avoid conflict. Typically only using the magic on
965objects blessed into the same class as the extension is sufficient.
966For C<PERL_MAGIC_ext> magic, it may also be appropriate to add an I32
967'signature' at the top of the private data area and check that.
5f05dabc 968
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969Also note that the C<sv_set*()> and C<sv_cat*()> functions described
970earlier do B<not> invoke 'set' magic on their targets. This must
971be done by the user either by calling the C<SvSETMAGIC()> macro after
972calling these functions, or by using one of the C<sv_set*_mg()> or
973C<sv_cat*_mg()> functions. Similarly, generic C code must call the
974C<SvGETMAGIC()> macro to invoke any 'get' magic if they use an SV
975obtained from external sources in functions that don't handle magic.
4a4eefd0 976See L<perlapi> for a description of these functions.
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977For example, calls to the C<sv_cat*()> functions typically need to be
978followed by C<SvSETMAGIC()>, but they don't need a prior C<SvGETMAGIC()>
979since their implementation handles 'get' magic.
980
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981=head2 Finding Magic
982
983 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */
984
985This routine returns a pointer to the C<MAGIC> structure stored in the SV.
986If the SV does not have that magical feature, C<NULL> is returned. Also,
54310121 987if the SV is not of type SVt_PVMG, Perl may core dump.
d1b91892 988
08105a92 989 int mg_copy(SV* sv, SV* nsv, const char* key, STRLEN klen);
d1b91892
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990
991This routine checks to see what types of magic C<sv> has. If the mg_type
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PP
992field is an uppercase letter, then the mg_obj is copied to C<nsv>, but
993the mg_type field is changed to be the lowercase letter.
a0d0e21e 994
04343c6d
GS
995=head2 Understanding the Magic of Tied Hashes and Arrays
996
14befaf4
DM
997Tied hashes and arrays are magical beasts of the C<PERL_MAGIC_tied>
998magic type.
9edb2b46
GS
999
1000WARNING: As of the 5.004 release, proper usage of the array and hash
1001access functions requires understanding a few caveats. Some
1002of these caveats are actually considered bugs in the API, to be fixed
1003in later releases, and are bracketed with [MAYCHANGE] below. If
1004you find yourself actually applying such information in this section, be
1005aware that the behavior may change in the future, umm, without warning.
04343c6d 1006
1526ead6
AB
1007The perl tie function associates a variable with an object that implements
1008the various GET, SET etc methods. To perform the equivalent of the perl
1009tie function from an XSUB, you must mimic this behaviour. The code below
1010carries out the necessary steps - firstly it creates a new hash, and then
1011creates a second hash which it blesses into the class which will implement
1012the tie methods. Lastly it ties the two hashes together, and returns a
1013reference to the new tied hash. Note that the code below does NOT call the
1014TIEHASH method in the MyTie class -
1015see L<Calling Perl Routines from within C Programs> for details on how
1016to do this.
1017
1018 SV*
1019 mytie()
1020 PREINIT:
1021 HV *hash;
1022 HV *stash;
1023 SV *tie;
1024 CODE:
1025 hash = newHV();
1026 tie = newRV_noinc((SV*)newHV());
1027 stash = gv_stashpv("MyTie", TRUE);
1028 sv_bless(tie, stash);
14befaf4 1029 hv_magic(hash, tie, PERL_MAGIC_tied);
1526ead6
AB
1030 RETVAL = newRV_noinc(hash);
1031 OUTPUT:
1032 RETVAL
1033
04343c6d
GS
1034The C<av_store> function, when given a tied array argument, merely
1035copies the magic of the array onto the value to be "stored", using
1036C<mg_copy>. It may also return NULL, indicating that the value did not
9edb2b46
GS
1037actually need to be stored in the array. [MAYCHANGE] After a call to
1038C<av_store> on a tied array, the caller will usually need to call
1039C<mg_set(val)> to actually invoke the perl level "STORE" method on the
1040TIEARRAY object. If C<av_store> did return NULL, a call to
1041C<SvREFCNT_dec(val)> will also be usually necessary to avoid a memory
1042leak. [/MAYCHANGE]
04343c6d
GS
1043
1044The previous paragraph is applicable verbatim to tied hash access using the
1045C<hv_store> and C<hv_store_ent> functions as well.
1046
1047C<av_fetch> and the corresponding hash functions C<hv_fetch> and
1048C<hv_fetch_ent> actually return an undefined mortal value whose magic
1049has been initialized using C<mg_copy>. Note the value so returned does not
9edb2b46
GS
1050need to be deallocated, as it is already mortal. [MAYCHANGE] But you will
1051need to call C<mg_get()> on the returned value in order to actually invoke
1052the perl level "FETCH" method on the underlying TIE object. Similarly,
04343c6d
GS
1053you may also call C<mg_set()> on the return value after possibly assigning
1054a suitable value to it using C<sv_setsv>, which will invoke the "STORE"
9edb2b46 1055method on the TIE object. [/MAYCHANGE]
04343c6d 1056
9edb2b46 1057[MAYCHANGE]
04343c6d
GS
1058In other words, the array or hash fetch/store functions don't really
1059fetch and store actual values in the case of tied arrays and hashes. They
1060merely call C<mg_copy> to attach magic to the values that were meant to be
1061"stored" or "fetched". Later calls to C<mg_get> and C<mg_set> actually
1062do the job of invoking the TIE methods on the underlying objects. Thus
9edb2b46 1063the magic mechanism currently implements a kind of lazy access to arrays
04343c6d
GS
1064and hashes.
1065
1066Currently (as of perl version 5.004), use of the hash and array access
1067functions requires the user to be aware of whether they are operating on
9edb2b46
GS
1068"normal" hashes and arrays, or on their tied variants. The API may be
1069changed to provide more transparent access to both tied and normal data
1070types in future versions.
1071[/MAYCHANGE]
04343c6d
GS
1072
1073You would do well to understand that the TIEARRAY and TIEHASH interfaces
1074are mere sugar to invoke some perl method calls while using the uniform hash
1075and array syntax. The use of this sugar imposes some overhead (typically
1076about two to four extra opcodes per FETCH/STORE operation, in addition to
1077the creation of all the mortal variables required to invoke the methods).
1078This overhead will be comparatively small if the TIE methods are themselves
1079substantial, but if they are only a few statements long, the overhead
1080will not be insignificant.
1081
d1c897a1
IZ
1082=head2 Localizing changes
1083
1084Perl has a very handy construction
1085
1086 {
1087 local $var = 2;
1088 ...
1089 }
1090
1091This construction is I<approximately> equivalent to
1092
1093 {
1094 my $oldvar = $var;
1095 $var = 2;
1096 ...
1097 $var = $oldvar;
1098 }
1099
1100The biggest difference is that the first construction would
1101reinstate the initial value of $var, irrespective of how control exits
1102the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
1103more efficient as well.
1104
1105There is a way to achieve a similar task from C via Perl API: create a
1106I<pseudo-block>, and arrange for some changes to be automatically
1107undone at the end of it, either explicit, or via a non-local exit (via
1108die()). A I<block>-like construct is created by a pair of
b687b08b
TC
1109C<ENTER>/C<LEAVE> macros (see L<perlcall/"Returning a Scalar">).
1110Such a construct may be created specially for some important localized
1111task, or an existing one (like boundaries of enclosing Perl
1112subroutine/block, or an existing pair for freeing TMPs) may be
1113used. (In the second case the overhead of additional localization must
1114be almost negligible.) Note that any XSUB is automatically enclosed in
1115an C<ENTER>/C<LEAVE> pair.
d1c897a1
IZ
1116
1117Inside such a I<pseudo-block> the following service is available:
1118
13a2d996 1119=over 4
d1c897a1
IZ
1120
1121=item C<SAVEINT(int i)>
1122
1123=item C<SAVEIV(IV i)>
1124
1125=item C<SAVEI32(I32 i)>
1126
1127=item C<SAVELONG(long i)>
1128
1129These macros arrange things to restore the value of integer variable
1130C<i> at the end of enclosing I<pseudo-block>.
1131
1132=item C<SAVESPTR(s)>
1133
1134=item C<SAVEPPTR(p)>
1135
1136These macros arrange things to restore the value of pointers C<s> and
1137C<p>. C<s> must be a pointer of a type which survives conversion to
1138C<SV*> and back, C<p> should be able to survive conversion to C<char*>
1139and back.
1140
1141=item C<SAVEFREESV(SV *sv)>
1142
1143The refcount of C<sv> would be decremented at the end of
26d9b02f
JH
1144I<pseudo-block>. This is similar to C<sv_2mortal> in that it is also a
1145mechanism for doing a delayed C<SvREFCNT_dec>. However, while C<sv_2mortal>
1146extends the lifetime of C<sv> until the beginning of the next statement,
1147C<SAVEFREESV> extends it until the end of the enclosing scope. These
1148lifetimes can be wildly different.
1149
1150Also compare C<SAVEMORTALIZESV>.
1151
1152=item C<SAVEMORTALIZESV(SV *sv)>
1153
1154Just like C<SAVEFREESV>, but mortalizes C<sv> at the end of the current
1155scope instead of decrementing its reference count. This usually has the
1156effect of keeping C<sv> alive until the statement that called the currently
1157live scope has finished executing.
d1c897a1
IZ
1158
1159=item C<SAVEFREEOP(OP *op)>
1160
1161The C<OP *> is op_free()ed at the end of I<pseudo-block>.
1162
1163=item C<SAVEFREEPV(p)>
1164
1165The chunk of memory which is pointed to by C<p> is Safefree()ed at the
1166end of I<pseudo-block>.
1167
1168=item C<SAVECLEARSV(SV *sv)>
1169
1170Clears a slot in the current scratchpad which corresponds to C<sv> at
1171the end of I<pseudo-block>.
1172
1173=item C<SAVEDELETE(HV *hv, char *key, I32 length)>
1174
1175The key C<key> of C<hv> is deleted at the end of I<pseudo-block>. The
1176string pointed to by C<key> is Safefree()ed. If one has a I<key> in
1177short-lived storage, the corresponding string may be reallocated like
1178this:
1179
9cde0e7f 1180 SAVEDELETE(PL_defstash, savepv(tmpbuf), strlen(tmpbuf));
d1c897a1 1181
c76ac1ee 1182=item C<SAVEDESTRUCTOR(DESTRUCTORFUNC_NOCONTEXT_t f, void *p)>
d1c897a1
IZ
1183
1184At the end of I<pseudo-block> the function C<f> is called with the
c76ac1ee
GS
1185only argument C<p>.
1186
1187=item C<SAVEDESTRUCTOR_X(DESTRUCTORFUNC_t f, void *p)>
1188
1189At the end of I<pseudo-block> the function C<f> is called with the
1190implicit context argument (if any), and C<p>.
d1c897a1
IZ
1191
1192=item C<SAVESTACK_POS()>
1193
1194The current offset on the Perl internal stack (cf. C<SP>) is restored
1195at the end of I<pseudo-block>.
1196
1197=back
1198
1199The following API list contains functions, thus one needs to
1200provide pointers to the modifiable data explicitly (either C pointers,
1201or Perlish C<GV *>s). Where the above macros take C<int>, a similar
1202function takes C<int *>.
1203
13a2d996 1204=over 4
d1c897a1
IZ
1205
1206=item C<SV* save_scalar(GV *gv)>
1207
1208Equivalent to Perl code C<local $gv>.
1209
1210=item C<AV* save_ary(GV *gv)>
1211
1212=item C<HV* save_hash(GV *gv)>
1213
1214Similar to C<save_scalar>, but localize C<@gv> and C<%gv>.
1215
1216=item C<void save_item(SV *item)>
1217
1218Duplicates the current value of C<SV>, on the exit from the current
1219C<ENTER>/C<LEAVE> I<pseudo-block> will restore the value of C<SV>
1220using the stored value.
1221
1222=item C<void save_list(SV **sarg, I32 maxsarg)>
1223
1224A variant of C<save_item> which takes multiple arguments via an array
1225C<sarg> of C<SV*> of length C<maxsarg>.
1226
1227=item C<SV* save_svref(SV **sptr)>
1228
1229Similar to C<save_scalar>, but will reinstate a C<SV *>.
1230
1231=item C<void save_aptr(AV **aptr)>
1232
1233=item C<void save_hptr(HV **hptr)>
1234
1235Similar to C<save_svref>, but localize C<AV *> and C<HV *>.
1236
1237=back
1238
1239The C<Alias> module implements localization of the basic types within the
1240I<caller's scope>. People who are interested in how to localize things in
1241the containing scope should take a look there too.
1242
0a753a76 1243=head1 Subroutines
a0d0e21e 1244
68dc0745 1245=head2 XSUBs and the Argument Stack
5f05dabc
PP
1246
1247The XSUB mechanism is a simple way for Perl programs to access C subroutines.
1248An XSUB routine will have a stack that contains the arguments from the Perl
1249program, and a way to map from the Perl data structures to a C equivalent.
1250
1251The stack arguments are accessible through the C<ST(n)> macro, which returns
1252the C<n>'th stack argument. Argument 0 is the first argument passed in the
1253Perl subroutine call. These arguments are C<SV*>, and can be used anywhere
1254an C<SV*> is used.
1255
1256Most of the time, output from the C routine can be handled through use of
1257the RETVAL and OUTPUT directives. However, there are some cases where the
1258argument stack is not already long enough to handle all the return values.
1259An example is the POSIX tzname() call, which takes no arguments, but returns
1260two, the local time zone's standard and summer time abbreviations.
1261
1262To handle this situation, the PPCODE directive is used and the stack is
1263extended using the macro:
1264
924508f0 1265 EXTEND(SP, num);
5f05dabc 1266
924508f0
GS
1267where C<SP> is the macro that represents the local copy of the stack pointer,
1268and C<num> is the number of elements the stack should be extended by.
5f05dabc
PP
1269
1270Now that there is room on the stack, values can be pushed on it using the
54310121 1271macros to push IVs, doubles, strings, and SV pointers respectively:
5f05dabc
PP
1272
1273 PUSHi(IV)
1274 PUSHn(double)
1275 PUSHp(char*, I32)
1276 PUSHs(SV*)
1277
1278And now the Perl program calling C<tzname>, the two values will be assigned
1279as in:
1280
1281 ($standard_abbrev, $summer_abbrev) = POSIX::tzname;
1282
1283An alternate (and possibly simpler) method to pushing values on the stack is
1284to use the macros:
1285
1286 XPUSHi(IV)
1287 XPUSHn(double)
1288 XPUSHp(char*, I32)
1289 XPUSHs(SV*)
1290
1291These macros automatically adjust the stack for you, if needed. Thus, you
1292do not need to call C<EXTEND> to extend the stack.
1bd1c0d5 1293However, see L</Putting a C value on Perl stack>
5f05dabc
PP
1294
1295For more information, consult L<perlxs> and L<perlxstut>.
1296
1297=head2 Calling Perl Routines from within C Programs
a0d0e21e
LW
1298
1299There are four routines that can be used to call a Perl subroutine from
1300within a C program. These four are:
1301
954c1994
GS
1302 I32 call_sv(SV*, I32);
1303 I32 call_pv(const char*, I32);
1304 I32 call_method(const char*, I32);
1305 I32 call_argv(const char*, I32, register char**);
a0d0e21e 1306
954c1994 1307The routine most often used is C<call_sv>. The C<SV*> argument
d1b91892
AD
1308contains either the name of the Perl subroutine to be called, or a
1309reference to the subroutine. The second argument consists of flags
1310that control the context in which the subroutine is called, whether
1311or not the subroutine is being passed arguments, how errors should be
1312trapped, and how to treat return values.
a0d0e21e
LW
1313
1314All four routines return the number of arguments that the subroutine returned
1315on the Perl stack.
1316
954c1994
GS
1317These routines used to be called C<perl_call_sv> etc., before Perl v5.6.0,
1318but those names are now deprecated; macros of the same name are provided for
1319compatibility.
1320
1321When using any of these routines (except C<call_argv>), the programmer
d1b91892
AD
1322must manipulate the Perl stack. These include the following macros and
1323functions:
a0d0e21e
LW
1324
1325 dSP
924508f0 1326 SP
a0d0e21e
LW
1327 PUSHMARK()
1328 PUTBACK
1329 SPAGAIN
1330 ENTER
1331 SAVETMPS
1332 FREETMPS
1333 LEAVE
1334 XPUSH*()
cb1a09d0 1335 POP*()
a0d0e21e 1336
5f05dabc
PP
1337For a detailed description of calling conventions from C to Perl,
1338consult L<perlcall>.
a0d0e21e 1339
5f05dabc 1340=head2 Memory Allocation
a0d0e21e 1341
86058a2d
GS
1342All memory meant to be used with the Perl API functions should be manipulated
1343using the macros described in this section. The macros provide the necessary
1344transparency between differences in the actual malloc implementation that is
1345used within perl.
1346
1347It is suggested that you enable the version of malloc that is distributed
5f05dabc 1348with Perl. It keeps pools of various sizes of unallocated memory in
07fa94a1
JO
1349order to satisfy allocation requests more quickly. However, on some
1350platforms, it may cause spurious malloc or free errors.
d1b91892
AD
1351
1352 New(x, pointer, number, type);
1353 Newc(x, pointer, number, type, cast);
1354 Newz(x, pointer, number, type);
1355
07fa94a1 1356These three macros are used to initially allocate memory.
5f05dabc
PP
1357
1358The first argument C<x> was a "magic cookie" that was used to keep track
1359of who called the macro, to help when debugging memory problems. However,
07fa94a1
JO
1360the current code makes no use of this feature (most Perl developers now
1361use run-time memory checkers), so this argument can be any number.
5f05dabc
PP
1362
1363The second argument C<pointer> should be the name of a variable that will
1364point to the newly allocated memory.
d1b91892 1365
d1b91892
AD
1366The third and fourth arguments C<number> and C<type> specify how many of
1367the specified type of data structure should be allocated. The argument
1368C<type> is passed to C<sizeof>. The final argument to C<Newc>, C<cast>,
1369should be used if the C<pointer> argument is different from the C<type>
1370argument.
1371
1372Unlike the C<New> and C<Newc> macros, the C<Newz> macro calls C<memzero>
1373to zero out all the newly allocated memory.
1374
1375 Renew(pointer, number, type);
1376 Renewc(pointer, number, type, cast);
1377 Safefree(pointer)
1378
1379These three macros are used to change a memory buffer size or to free a
1380piece of memory no longer needed. The arguments to C<Renew> and C<Renewc>
1381match those of C<New> and C<Newc> with the exception of not needing the
1382"magic cookie" argument.
1383
1384 Move(source, dest, number, type);
1385 Copy(source, dest, number, type);
1386 Zero(dest, number, type);
1387
1388These three macros are used to move, copy, or zero out previously allocated
1389memory. The C<source> and C<dest> arguments point to the source and
1390destination starting points. Perl will move, copy, or zero out C<number>
1391instances of the size of the C<type> data structure (using the C<sizeof>
1392function).
a0d0e21e 1393
5f05dabc 1394=head2 PerlIO
ce3d39e2 1395
5f05dabc
PP
1396The most recent development releases of Perl has been experimenting with
1397removing Perl's dependency on the "normal" standard I/O suite and allowing
1398other stdio implementations to be used. This involves creating a new
1399abstraction layer that then calls whichever implementation of stdio Perl
68dc0745 1400was compiled with. All XSUBs should now use the functions in the PerlIO
5f05dabc
PP
1401abstraction layer and not make any assumptions about what kind of stdio
1402is being used.
1403
1404For a complete description of the PerlIO abstraction, consult L<perlapio>.
1405
8ebc5c01 1406=head2 Putting a C value on Perl stack
ce3d39e2
IZ
1407
1408A lot of opcodes (this is an elementary operation in the internal perl
1409stack machine) put an SV* on the stack. However, as an optimization
1410the corresponding SV is (usually) not recreated each time. The opcodes
1411reuse specially assigned SVs (I<target>s) which are (as a corollary)
1412not constantly freed/created.
1413
0a753a76 1414Each of the targets is created only once (but see
ce3d39e2
IZ
1415L<Scratchpads and recursion> below), and when an opcode needs to put
1416an integer, a double, or a string on stack, it just sets the
1417corresponding parts of its I<target> and puts the I<target> on stack.
1418
1419The macro to put this target on stack is C<PUSHTARG>, and it is
1420directly used in some opcodes, as well as indirectly in zillions of
1421others, which use it via C<(X)PUSH[pni]>.
1422
1bd1c0d5
SC
1423Because the target is reused, you must be careful when pushing multiple
1424values on the stack. The following code will not do what you think:
1425
1426 XPUSHi(10);
1427 XPUSHi(20);
1428
1429This translates as "set C<TARG> to 10, push a pointer to C<TARG> onto
1430the stack; set C<TARG> to 20, push a pointer to C<TARG> onto the stack".
1431At the end of the operation, the stack does not contain the values 10
1432and 20, but actually contains two pointers to C<TARG>, which we have set
1433to 20. If you need to push multiple different values, use C<XPUSHs>,
1434which bypasses C<TARG>.
1435
1436On a related note, if you do use C<(X)PUSH[npi]>, then you're going to
1437need a C<dTARG> in your variable declarations so that the C<*PUSH*>
1438macros can make use of the local variable C<TARG>.
1439
8ebc5c01 1440=head2 Scratchpads
ce3d39e2 1441
54310121 1442The question remains on when the SVs which are I<target>s for opcodes
5f05dabc
PP
1443are created. The answer is that they are created when the current unit --
1444a subroutine or a file (for opcodes for statements outside of
1445subroutines) -- is compiled. During this time a special anonymous Perl
ce3d39e2
IZ
1446array is created, which is called a scratchpad for the current
1447unit.
1448
54310121 1449A scratchpad keeps SVs which are lexicals for the current unit and are
ce3d39e2
IZ
1450targets for opcodes. One can deduce that an SV lives on a scratchpad
1451by looking on its flags: lexicals have C<SVs_PADMY> set, and
1452I<target>s have C<SVs_PADTMP> set.
1453
54310121
PP
1454The correspondence between OPs and I<target>s is not 1-to-1. Different
1455OPs in the compile tree of the unit can use the same target, if this
ce3d39e2
IZ
1456would not conflict with the expected life of the temporary.
1457
2ae324a7 1458=head2 Scratchpads and recursion
ce3d39e2
IZ
1459
1460In fact it is not 100% true that a compiled unit contains a pointer to
1461the scratchpad AV. In fact it contains a pointer to an AV of
1462(initially) one element, and this element is the scratchpad AV. Why do
1463we need an extra level of indirection?
1464
1465The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
1466these can create several execution pointers going into the same
1467subroutine. For the subroutine-child not write over the temporaries
1468for the subroutine-parent (lifespan of which covers the call to the
1469child), the parent and the child should have different
1470scratchpads. (I<And> the lexicals should be separate anyway!)
1471
5f05dabc
PP
1472So each subroutine is born with an array of scratchpads (of length 1).
1473On each entry to the subroutine it is checked that the current
ce3d39e2
IZ
1474depth of the recursion is not more than the length of this array, and
1475if it is, new scratchpad is created and pushed into the array.
1476
1477The I<target>s on this scratchpad are C<undef>s, but they are already
1478marked with correct flags.
1479
0a753a76
PP
1480=head1 Compiled code
1481
1482=head2 Code tree
1483
1484Here we describe the internal form your code is converted to by
1485Perl. Start with a simple example:
1486
1487 $a = $b + $c;
1488
1489This is converted to a tree similar to this one:
1490
1491 assign-to
1492 / \
1493 + $a
1494 / \
1495 $b $c
1496
7b8d334a 1497(but slightly more complicated). This tree reflects the way Perl
0a753a76
PP
1498parsed your code, but has nothing to do with the execution order.
1499There is an additional "thread" going through the nodes of the tree
1500which shows the order of execution of the nodes. In our simplified
1501example above it looks like:
1502
1503 $b ---> $c ---> + ---> $a ---> assign-to
1504
1505But with the actual compile tree for C<$a = $b + $c> it is different:
1506some nodes I<optimized away>. As a corollary, though the actual tree
1507contains more nodes than our simplified example, the execution order
1508is the same as in our example.
1509
1510=head2 Examining the tree
1511
1512If you have your perl compiled for debugging (usually done with C<-D
1513optimize=-g> on C<Configure> command line), you may examine the
1514compiled tree by specifying C<-Dx> on the Perl command line. The
1515output takes several lines per node, and for C<$b+$c> it looks like
1516this:
1517
1518 5 TYPE = add ===> 6
1519 TARG = 1
1520 FLAGS = (SCALAR,KIDS)
1521 {
1522 TYPE = null ===> (4)
1523 (was rv2sv)
1524 FLAGS = (SCALAR,KIDS)
1525 {
1526 3 TYPE = gvsv ===> 4
1527 FLAGS = (SCALAR)
1528 GV = main::b
1529 }
1530 }
1531 {
1532 TYPE = null ===> (5)
1533 (was rv2sv)
1534 FLAGS = (SCALAR,KIDS)
1535 {
1536 4 TYPE = gvsv ===> 5
1537 FLAGS = (SCALAR)
1538 GV = main::c
1539 }
1540 }
1541
1542This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
1543not optimized away (one per number in the left column). The immediate
1544children of the given node correspond to C<{}> pairs on the same level
1545of indentation, thus this listing corresponds to the tree:
1546
1547 add
1548 / \
1549 null null
1550 | |
1551 gvsv gvsv
1552
1553The execution order is indicated by C<===E<gt>> marks, thus it is C<3
15544 5 6> (node C<6> is not included into above listing), i.e.,
1555C<gvsv gvsv add whatever>.
1556
9afa14e3
SC
1557Each of these nodes represents an op, a fundamental operation inside the
1558Perl core. The code which implements each operation can be found in the
1559F<pp*.c> files; the function which implements the op with type C<gvsv>
1560is C<pp_gvsv>, and so on. As the tree above shows, different ops have
1561different numbers of children: C<add> is a binary operator, as one would
1562expect, and so has two children. To accommodate the various different
1563numbers of children, there are various types of op data structure, and
1564they link together in different ways.
1565
1566The simplest type of op structure is C<OP>: this has no children. Unary
1567operators, C<UNOP>s, have one child, and this is pointed to by the
1568C<op_first> field. Binary operators (C<BINOP>s) have not only an
1569C<op_first> field but also an C<op_last> field. The most complex type of
1570op is a C<LISTOP>, which has any number of children. In this case, the
1571first child is pointed to by C<op_first> and the last child by
1572C<op_last>. The children in between can be found by iteratively
1573following the C<op_sibling> pointer from the first child to the last.
1574
1575There are also two other op types: a C<PMOP> holds a regular expression,
1576and has no children, and a C<LOOP> may or may not have children. If the
1577C<op_children> field is non-zero, it behaves like a C<LISTOP>. To
1578complicate matters, if a C<UNOP> is actually a C<null> op after
1579optimization (see L</Compile pass 2: context propagation>) it will still
1580have children in accordance with its former type.
1581
0a753a76
PP
1582=head2 Compile pass 1: check routines
1583
8870b5c7
GS
1584The tree is created by the compiler while I<yacc> code feeds it
1585the constructions it recognizes. Since I<yacc> works bottom-up, so does
0a753a76
PP
1586the first pass of perl compilation.
1587
1588What makes this pass interesting for perl developers is that some
1589optimization may be performed on this pass. This is optimization by
8870b5c7 1590so-called "check routines". The correspondence between node names
0a753a76
PP
1591and corresponding check routines is described in F<opcode.pl> (do not
1592forget to run C<make regen_headers> if you modify this file).
1593
1594A check routine is called when the node is fully constructed except
7b8d334a 1595for the execution-order thread. Since at this time there are no
0a753a76
PP
1596back-links to the currently constructed node, one can do most any
1597operation to the top-level node, including freeing it and/or creating
1598new nodes above/below it.
1599
1600The check routine returns the node which should be inserted into the
1601tree (if the top-level node was not modified, check routine returns
1602its argument).
1603
1604By convention, check routines have names C<ck_*>. They are usually
1605called from C<new*OP> subroutines (or C<convert>) (which in turn are
1606called from F<perly.y>).
1607
1608=head2 Compile pass 1a: constant folding
1609
1610Immediately after the check routine is called the returned node is
1611checked for being compile-time executable. If it is (the value is
1612judged to be constant) it is immediately executed, and a I<constant>
1613node with the "return value" of the corresponding subtree is
1614substituted instead. The subtree is deleted.
1615
1616If constant folding was not performed, the execution-order thread is
1617created.
1618
1619=head2 Compile pass 2: context propagation
1620
1621When a context for a part of compile tree is known, it is propagated
a3cb178b 1622down through the tree. At this time the context can have 5 values
0a753a76
PP
1623(instead of 2 for runtime context): void, boolean, scalar, list, and
1624lvalue. In contrast with the pass 1 this pass is processed from top
1625to bottom: a node's context determines the context for its children.
1626
1627Additional context-dependent optimizations are performed at this time.
1628Since at this moment the compile tree contains back-references (via
1629"thread" pointers), nodes cannot be free()d now. To allow
1630optimized-away nodes at this stage, such nodes are null()ified instead
1631of free()ing (i.e. their type is changed to OP_NULL).
1632
1633=head2 Compile pass 3: peephole optimization
1634
1635After the compile tree for a subroutine (or for an C<eval> or a file)
1636is created, an additional pass over the code is performed. This pass
1637is neither top-down or bottom-up, but in the execution order (with
7b8d334a 1638additional complications for conditionals). These optimizations are
0a753a76
PP
1639done in the subroutine peep(). Optimizations performed at this stage
1640are subject to the same restrictions as in the pass 2.
1641
9afa14e3
SC
1642=head1 Examining internal data structures with the C<dump> functions
1643
1644To aid debugging, the source file F<dump.c> contains a number of
1645functions which produce formatted output of internal data structures.
1646
1647The most commonly used of these functions is C<Perl_sv_dump>; it's used
1648for dumping SVs, AVs, HVs, and CVs. The C<Devel::Peek> module calls
1649C<sv_dump> to produce debugging output from Perl-space, so users of that
1650module should already be familiar with its format.
1651
1652C<Perl_op_dump> can be used to dump an C<OP> structure or any of its
1653derivatives, and produces output similiar to C<perl -Dx>; in fact,
1654C<Perl_dump_eval> will dump the main root of the code being evaluated,
1655exactly like C<-Dx>.
1656
1657Other useful functions are C<Perl_dump_sub>, which turns a C<GV> into an
1658op tree, C<Perl_dump_packsubs> which calls C<Perl_dump_sub> on all the
1659subroutines in a package like so: (Thankfully, these are all xsubs, so
1660there is no op tree)
1661
1662 (gdb) print Perl_dump_packsubs(PL_defstash)
1663
1664 SUB attributes::bootstrap = (xsub 0x811fedc 0)
1665
1666 SUB UNIVERSAL::can = (xsub 0x811f50c 0)
1667
1668 SUB UNIVERSAL::isa = (xsub 0x811f304 0)
1669
1670 SUB UNIVERSAL::VERSION = (xsub 0x811f7ac 0)
1671
1672 SUB DynaLoader::boot_DynaLoader = (xsub 0x805b188 0)
1673
1674and C<Perl_dump_all>, which dumps all the subroutines in the stash and
1675the op tree of the main root.
1676
954c1994 1677=head1 How multiple interpreters and concurrency are supported
ee072b34 1678
ee072b34
GS
1679=head2 Background and PERL_IMPLICIT_CONTEXT
1680
1681The Perl interpreter can be regarded as a closed box: it has an API
1682for feeding it code or otherwise making it do things, but it also has
1683functions for its own use. This smells a lot like an object, and
1684there are ways for you to build Perl so that you can have multiple
1685interpreters, with one interpreter represented either as a C++ object,
1686a C structure, or inside a thread. The thread, the C structure, or
1687the C++ object will contain all the context, the state of that
1688interpreter.
1689
54aff467
GS
1690Three macros control the major Perl build flavors: MULTIPLICITY,
1691USE_THREADS and PERL_OBJECT. The MULTIPLICITY build has a C structure
1692that packages all the interpreter state, there is a similar thread-specific
a7486cbb
JH
1693data structure under USE_THREADS, and the (now deprecated) PERL_OBJECT
1694build has a C++ class to maintain interpreter state. In all three cases,
54aff467
GS
1695PERL_IMPLICIT_CONTEXT is also normally defined, and enables the
1696support for passing in a "hidden" first argument that represents all three
651a3225 1697data structures.
54aff467
GS
1698
1699All this obviously requires a way for the Perl internal functions to be
ee072b34
GS
1700C++ methods, subroutines taking some kind of structure as the first
1701argument, or subroutines taking nothing as the first argument. To
1702enable these three very different ways of building the interpreter,
1703the Perl source (as it does in so many other situations) makes heavy
1704use of macros and subroutine naming conventions.
1705
54aff467 1706First problem: deciding which functions will be public API functions and
954c1994
GS
1707which will be private. All functions whose names begin C<S_> are private
1708(think "S" for "secret" or "static"). All other functions begin with
1709"Perl_", but just because a function begins with "Perl_" does not mean it is
a422fd2d
SC
1710part of the API. (See L</Internal Functions>.) The easiest way to be B<sure> a
1711function is part of the API is to find its entry in L<perlapi>.
1712If it exists in L<perlapi>, it's part of the API. If it doesn't, and you
1713think it should be (i.e., you need it for your extension), send mail via
1714L<perlbug> explaining why you think it should be.
ee072b34
GS
1715
1716Second problem: there must be a syntax so that the same subroutine
1717declarations and calls can pass a structure as their first argument,
1718or pass nothing. To solve this, the subroutines are named and
1719declared in a particular way. Here's a typical start of a static
1720function used within the Perl guts:
1721
1722 STATIC void
1723 S_incline(pTHX_ char *s)
1724
1725STATIC becomes "static" in C, and is #define'd to nothing in C++.
1726
651a3225
GS
1727A public function (i.e. part of the internal API, but not necessarily
1728sanctioned for use in extensions) begins like this:
ee072b34
GS
1729
1730 void
1731 Perl_sv_setsv(pTHX_ SV* dsv, SV* ssv)
1732
1733C<pTHX_> is one of a number of macros (in perl.h) that hide the
1734details of the interpreter's context. THX stands for "thread", "this",
1735or "thingy", as the case may be. (And no, George Lucas is not involved. :-)
1736The first character could be 'p' for a B<p>rototype, 'a' for B<a>rgument,
a7486cbb
JH
1737or 'd' for B<d>eclaration, so we have C<pTHX>, C<aTHX> and C<dTHX>, and
1738their variants.
ee072b34 1739
a7486cbb
JH
1740When Perl is built without options that set PERL_IMPLICIT_CONTEXT, there is no
1741first argument containing the interpreter's context. The trailing underscore
ee072b34
GS
1742in the pTHX_ macro indicates that the macro expansion needs a comma
1743after the context argument because other arguments follow it. If
1744PERL_IMPLICIT_CONTEXT is not defined, pTHX_ will be ignored, and the
54aff467
GS
1745subroutine is not prototyped to take the extra argument. The form of the
1746macro without the trailing underscore is used when there are no additional
ee072b34
GS
1747explicit arguments.
1748
54aff467 1749When a core function calls another, it must pass the context. This
a7486cbb 1750is normally hidden via macros. Consider C<sv_setsv>. It expands into
ee072b34
GS
1751something like this:
1752
1753 ifdef PERL_IMPLICIT_CONTEXT
c52f9dcd 1754 define sv_setsv(a,b) Perl_sv_setsv(aTHX_ a, b)
ee072b34
GS
1755 /* can't do this for vararg functions, see below */
1756 else
c52f9dcd 1757 define sv_setsv Perl_sv_setsv
ee072b34
GS
1758 endif
1759
1760This works well, and means that XS authors can gleefully write:
1761
1762 sv_setsv(foo, bar);
1763
1764and still have it work under all the modes Perl could have been
1765compiled with.
1766
1767Under PERL_OBJECT in the core, that will translate to either:
1768
1769 CPerlObj::Perl_sv_setsv(foo,bar); # in CPerlObj functions,
1770 # C++ takes care of 'this'
1771 or
1772
1773 pPerl->Perl_sv_setsv(foo,bar); # in truly static functions,
1774 # see objXSUB.h
1775
1776Under PERL_OBJECT in extensions (aka PERL_CAPI), or under
a7486cbb
JH
1777MULTIPLICITY/USE_THREADS with PERL_IMPLICIT_CONTEXT in both core
1778and extensions, it will become:
ee072b34
GS
1779
1780 Perl_sv_setsv(aTHX_ foo, bar); # the canonical Perl "API"
1781 # for all build flavors
1782
1783This doesn't work so cleanly for varargs functions, though, as macros
1784imply that the number of arguments is known in advance. Instead we
1785either need to spell them out fully, passing C<aTHX_> as the first
1786argument (the Perl core tends to do this with functions like
1787Perl_warner), or use a context-free version.
1788
1789The context-free version of Perl_warner is called
1790Perl_warner_nocontext, and does not take the extra argument. Instead
1791it does dTHX; to get the context from thread-local storage. We
1792C<#define warner Perl_warner_nocontext> so that extensions get source
1793compatibility at the expense of performance. (Passing an arg is
1794cheaper than grabbing it from thread-local storage.)
1795
1796You can ignore [pad]THX[xo] when browsing the Perl headers/sources.
1797Those are strictly for use within the core. Extensions and embedders
1798need only be aware of [pad]THX.
1799
a7486cbb
JH
1800=head2 So what happened to dTHR?
1801
1802C<dTHR> was introduced in perl 5.005 to support the older thread model.
1803The older thread model now uses the C<THX> mechanism to pass context
1804pointers around, so C<dTHR> is not useful any more. Perl 5.6.0 and
1805later still have it for backward source compatibility, but it is defined
1806to be a no-op.
1807
ee072b34
GS
1808=head2 How do I use all this in extensions?
1809
1810When Perl is built with PERL_IMPLICIT_CONTEXT, extensions that call
1811any functions in the Perl API will need to pass the initial context
1812argument somehow. The kicker is that you will need to write it in
1813such a way that the extension still compiles when Perl hasn't been
1814built with PERL_IMPLICIT_CONTEXT enabled.
1815
1816There are three ways to do this. First, the easy but inefficient way,
1817which is also the default, in order to maintain source compatibility
1818with extensions: whenever XSUB.h is #included, it redefines the aTHX
1819and aTHX_ macros to call a function that will return the context.
1820Thus, something like:
1821
1822 sv_setsv(asv, bsv);
1823
4375e838 1824in your extension will translate to this when PERL_IMPLICIT_CONTEXT is
54aff467 1825in effect:
ee072b34 1826
2fa86c13 1827 Perl_sv_setsv(Perl_get_context(), asv, bsv);
ee072b34 1828
54aff467 1829or to this otherwise:
ee072b34
GS
1830
1831 Perl_sv_setsv(asv, bsv);
1832
1833You have to do nothing new in your extension to get this; since
2fa86c13 1834the Perl library provides Perl_get_context(), it will all just
ee072b34
GS
1835work.
1836
1837The second, more efficient way is to use the following template for
1838your Foo.xs:
1839
c52f9dcd
JH
1840 #define PERL_NO_GET_CONTEXT /* we want efficiency */
1841 #include "EXTERN.h"
1842 #include "perl.h"
1843 #include "XSUB.h"
ee072b34
GS
1844
1845 static my_private_function(int arg1, int arg2);
1846
c52f9dcd
JH
1847 static SV *
1848 my_private_function(int arg1, int arg2)
1849 {
1850 dTHX; /* fetch context */
1851 ... call many Perl API functions ...
1852 }
ee072b34
GS
1853
1854 [... etc ...]
1855
c52f9dcd 1856 MODULE = Foo PACKAGE = Foo
ee072b34 1857
c52f9dcd 1858 /* typical XSUB */
ee072b34 1859
c52f9dcd
JH
1860 void
1861 my_xsub(arg)
1862 int arg
1863 CODE:
1864 my_private_function(arg, 10);
ee072b34
GS
1865
1866Note that the only two changes from the normal way of writing an
1867extension is the addition of a C<#define PERL_NO_GET_CONTEXT> before
1868including the Perl headers, followed by a C<dTHX;> declaration at
1869the start of every function that will call the Perl API. (You'll
1870know which functions need this, because the C compiler will complain
1871that there's an undeclared identifier in those functions.) No changes
1872are needed for the XSUBs themselves, because the XS() macro is
1873correctly defined to pass in the implicit context if needed.
1874
1875The third, even more efficient way is to ape how it is done within
1876the Perl guts:
1877
1878
c52f9dcd
JH
1879 #define PERL_NO_GET_CONTEXT /* we want efficiency */
1880 #include "EXTERN.h"
1881 #include "perl.h"
1882 #include "XSUB.h"
ee072b34
GS
1883
1884 /* pTHX_ only needed for functions that call Perl API */
1885 static my_private_function(pTHX_ int arg1, int arg2);
1886
c52f9dcd
JH
1887 static SV *
1888 my_private_function(pTHX_ int arg1, int arg2)
1889 {
1890 /* dTHX; not needed here, because THX is an argument */
1891 ... call Perl API functions ...
1892 }
ee072b34
GS
1893
1894 [... etc ...]
1895
c52f9dcd 1896 MODULE = Foo PACKAGE = Foo
ee072b34 1897
c52f9dcd 1898 /* typical XSUB */
ee072b34 1899
c52f9dcd
JH
1900 void
1901 my_xsub(arg)
1902 int arg
1903 CODE:
1904 my_private_function(aTHX_ arg, 10);
ee072b34
GS
1905
1906This implementation never has to fetch the context using a function
1907call, since it is always passed as an extra argument. Depending on
1908your needs for simplicity or efficiency, you may mix the previous
1909two approaches freely.
1910
651a3225
GS
1911Never add a comma after C<pTHX> yourself--always use the form of the
1912macro with the underscore for functions that take explicit arguments,
1913or the form without the argument for functions with no explicit arguments.
ee072b34 1914
a7486cbb
JH
1915=head2 Should I do anything special if I call perl from multiple threads?
1916
1917If you create interpreters in one thread and then proceed to call them in
1918another, you need to make sure perl's own Thread Local Storage (TLS) slot is
1919initialized correctly in each of those threads.
1920
1921The C<perl_alloc> and C<perl_clone> API functions will automatically set
1922the TLS slot to the interpreter they created, so that there is no need to do
1923anything special if the interpreter is always accessed in the same thread that
1924created it, and that thread did not create or call any other interpreters
1925afterwards. If that is not the case, you have to set the TLS slot of the
1926thread before calling any functions in the Perl API on that particular
1927interpreter. This is done by calling the C<PERL_SET_CONTEXT> macro in that
1928thread as the first thing you do:
1929
1930 /* do this before doing anything else with some_perl */
1931 PERL_SET_CONTEXT(some_perl);
1932
1933 ... other Perl API calls on some_perl go here ...
1934
ee072b34
GS
1935=head2 Future Plans and PERL_IMPLICIT_SYS
1936
1937Just as PERL_IMPLICIT_CONTEXT provides a way to bundle up everything
1938that the interpreter knows about itself and pass it around, so too are
1939there plans to allow the interpreter to bundle up everything it knows
1940about the environment it's running on. This is enabled with the
a7486cbb
JH
1941PERL_IMPLICIT_SYS macro. Currently it only works with PERL_OBJECT
1942and USE_THREADS on Windows (see inside iperlsys.h).
ee072b34
GS
1943
1944This allows the ability to provide an extra pointer (called the "host"
1945environment) for all the system calls. This makes it possible for
1946all the system stuff to maintain their own state, broken down into
1947seven C structures. These are thin wrappers around the usual system
1948calls (see win32/perllib.c) for the default perl executable, but for a
1949more ambitious host (like the one that would do fork() emulation) all
1950the extra work needed to pretend that different interpreters are
1951actually different "processes", would be done here.
1952
1953The Perl engine/interpreter and the host are orthogonal entities.
1954There could be one or more interpreters in a process, and one or
1955more "hosts", with free association between them.
1956
a422fd2d
SC
1957=head1 Internal Functions
1958
1959All of Perl's internal functions which will be exposed to the outside
1960world are be prefixed by C<Perl_> so that they will not conflict with XS
1961functions or functions used in a program in which Perl is embedded.
1962Similarly, all global variables begin with C<PL_>. (By convention,
1963static functions start with C<S_>)
1964
1965Inside the Perl core, you can get at the functions either with or
1966without the C<Perl_> prefix, thanks to a bunch of defines that live in
1967F<embed.h>. This header file is generated automatically from
1968F<embed.pl>. F<embed.pl> also creates the prototyping header files for
1969the internal functions, generates the documentation and a lot of other
1970bits and pieces. It's important that when you add a new function to the
1971core or change an existing one, you change the data in the table at the
1972end of F<embed.pl> as well. Here's a sample entry from that table:
1973
1974 Apd |SV** |av_fetch |AV* ar|I32 key|I32 lval
1975
1976The second column is the return type, the third column the name. Columns
1977after that are the arguments. The first column is a set of flags:
1978
1979=over 3
1980
1981=item A
1982
1983This function is a part of the public API.
1984
1985=item p
1986
1987This function has a C<Perl_> prefix; ie, it is defined as C<Perl_av_fetch>
1988
1989=item d
1990
1991This function has documentation using the C<apidoc> feature which we'll
1992look at in a second.
1993
1994=back
1995
1996Other available flags are:
1997
1998=over 3
1999
2000=item s
2001
a7486cbb
JH
2002This is a static function and is defined as C<S_whatever>, and usually
2003called within the sources as C<whatever(...)>.
a422fd2d
SC
2004
2005=item n
2006
2007This does not use C<aTHX_> and C<pTHX> to pass interpreter context. (See
2008L<perlguts/Background and PERL_IMPLICIT_CONTEXT>.)
2009
2010=item r
2011
2012This function never returns; C<croak>, C<exit> and friends.
2013
2014=item f
2015
2016This function takes a variable number of arguments, C<printf> style.
2017The argument list should end with C<...>, like this:
2018
2019 Afprd |void |croak |const char* pat|...
2020
a7486cbb 2021=item M
a422fd2d
SC
2022
2023This function is part of the experimental development API, and may change
2024or disappear without notice.
2025
2026=item o
2027
2028This function should not have a compatibility macro to define, say,
2029C<Perl_parse> to C<parse>. It must be called as C<Perl_parse>.
2030
2031=item j
2032
2033This function is not a member of C<CPerlObj>. If you don't know
2034what this means, don't use it.
2035
2036=item x
2037
2038This function isn't exported out of the Perl core.
2039
2040=back
2041
2042If you edit F<embed.pl>, you will need to run C<make regen_headers> to
2043force a rebuild of F<embed.h> and other auto-generated files.
2044
6b4667fc 2045=head2 Formatted Printing of IVs, UVs, and NVs
9dd9db0b 2046
6b4667fc
A
2047If you are printing IVs, UVs, or NVS instead of the stdio(3) style
2048formatting codes like C<%d>, C<%ld>, C<%f>, you should use the
2049following macros for portability
9dd9db0b 2050
c52f9dcd
JH
2051 IVdf IV in decimal
2052 UVuf UV in decimal
2053 UVof UV in octal
2054 UVxf UV in hexadecimal
2055 NVef NV %e-like
2056 NVff NV %f-like
2057 NVgf NV %g-like
9dd9db0b 2058
6b4667fc
A
2059These will take care of 64-bit integers and long doubles.
2060For example:
2061
c52f9dcd 2062 printf("IV is %"IVdf"\n", iv);
6b4667fc
A
2063
2064The IVdf will expand to whatever is the correct format for the IVs.
9dd9db0b 2065
8908e76d
JH
2066If you are printing addresses of pointers, use UVxf combined
2067with PTR2UV(), do not use %lx or %p.
2068
2069=head2 Pointer-To-Integer and Integer-To-Pointer
2070
2071Because pointer size does not necessarily equal integer size,
2072use the follow macros to do it right.
2073
c52f9dcd
JH
2074 PTR2UV(pointer)
2075 PTR2IV(pointer)
2076 PTR2NV(pointer)
2077 INT2PTR(pointertotype, integer)
8908e76d
JH
2078
2079For example:
2080
c52f9dcd
JH
2081 IV iv = ...;
2082 SV *sv = INT2PTR(SV*, iv);
8908e76d
JH
2083
2084and
2085
c52f9dcd
JH
2086 AV *av = ...;
2087 UV uv = PTR2UV(av);
8908e76d 2088
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2089=head2 Source Documentation
2090
2091There's an effort going on to document the internal functions and
2092automatically produce reference manuals from them - L<perlapi> is one
2093such manual which details all the functions which are available to XS
2094writers. L<perlintern> is the autogenerated manual for the functions
2095which are not part of the API and are supposedly for internal use only.
2096
2097Source documentation is created by putting POD comments into the C
2098source, like this:
2099
2100 /*
2101 =for apidoc sv_setiv
2102
2103 Copies an integer into the given SV. Does not handle 'set' magic. See
2104 C<sv_setiv_mg>.
2105
2106 =cut
2107 */
2108
2109Please try and supply some documentation if you add functions to the
2110Perl core.
2111
2112=head1 Unicode Support
2113
2114Perl 5.6.0 introduced Unicode support. It's important for porters and XS
2115writers to understand this support and make sure that the code they
2116write does not corrupt Unicode data.
2117
2118=head2 What B<is> Unicode, anyway?
2119
2120In the olden, less enlightened times, we all used to use ASCII. Most of
2121us did, anyway. The big problem with ASCII is that it's American. Well,
2122no, that's not actually the problem; the problem is that it's not
2123particularly useful for people who don't use the Roman alphabet. What
2124used to happen was that particular languages would stick their own
2125alphabet in the upper range of the sequence, between 128 and 255. Of
2126course, we then ended up with plenty of variants that weren't quite
2127ASCII, and the whole point of it being a standard was lost.
2128
2129Worse still, if you've got a language like Chinese or
2130Japanese that has hundreds or thousands of characters, then you really
2131can't fit them into a mere 256, so they had to forget about ASCII
2132altogether, and build their own systems using pairs of numbers to refer
2133to one character.
2134
2135To fix this, some people formed Unicode, Inc. and
2136produced a new character set containing all the characters you can
2137possibly think of and more. There are several ways of representing these
2138characters, and the one Perl uses is called UTF8. UTF8 uses
2139a variable number of bytes to represent a character, instead of just
b3b6085d 2140one. You can learn more about Unicode at http://www.unicode.org/
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2141
2142=head2 How can I recognise a UTF8 string?
2143
2144You can't. This is because UTF8 data is stored in bytes just like
2145non-UTF8 data. The Unicode character 200, (C<0xC8> for you hex types)
2146capital E with a grave accent, is represented by the two bytes
2147C<v196.172>. Unfortunately, the non-Unicode string C<chr(196).chr(172)>
2148has that byte sequence as well. So you can't tell just by looking - this
2149is what makes Unicode input an interesting problem.
2150
2151The API function C<is_utf8_string> can help; it'll tell you if a string
2152contains only valid UTF8 characters. However, it can't do the work for
2153you. On a character-by-character basis, C<is_utf8_char> will tell you
2154whether the current character in a string is valid UTF8.
2155
2156=head2 How does UTF8 represent Unicode characters?
2157
2158As mentioned above, UTF8 uses a variable number of bytes to store a
2159character. Characters with values 1...128 are stored in one byte, just
2160like good ol' ASCII. Character 129 is stored as C<v194.129>; this
a31a806a 2161continues up to character 191, which is C<v194.191>. Now we've run out of
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2162bits (191 is binary C<10111111>) so we move on; 192 is C<v195.128>. And
2163so it goes on, moving to three bytes at character 2048.
2164
2165Assuming you know you're dealing with a UTF8 string, you can find out
2166how long the first character in it is with the C<UTF8SKIP> macro:
2167
2168 char *utf = "\305\233\340\240\201";
2169 I32 len;
2170
2171 len = UTF8SKIP(utf); /* len is 2 here */
2172 utf += len;
2173 len = UTF8SKIP(utf); /* len is 3 here */
2174
2175Another way to skip over characters in a UTF8 string is to use
2176C<utf8_hop>, which takes a string and a number of characters to skip
2177over. You're on your own about bounds checking, though, so don't use it
2178lightly.
2179
2180All bytes in a multi-byte UTF8 character will have the high bit set, so
2181you can test if you need to do something special with this character
2182like this:
2183
2184 UV uv;
2185
2186 if (utf & 0x80)
2187 /* Must treat this as UTF8 */
2188 uv = utf8_to_uv(utf);
2189 else
2190 /* OK to treat this character as a byte */
2191 uv = *utf;
2192
2193You can also see in that example that we use C<utf8_to_uv> to get the
2194value of the character; the inverse function C<uv_to_utf8> is available
2195for putting a UV into UTF8:
2196
2197 if (uv > 0x80)
2198 /* Must treat this as UTF8 */
2199 utf8 = uv_to_utf8(utf8, uv);
2200 else
2201 /* OK to treat this character as a byte */
2202 *utf8++ = uv;
2203
2204You B<must> convert characters to UVs using the above functions if
2205you're ever in a situation where you have to match UTF8 and non-UTF8
2206characters. You may not skip over UTF8 characters in this case. If you
2207do this, you'll lose the ability to match hi-bit non-UTF8 characters;
2208for instance, if your UTF8 string contains C<v196.172>, and you skip
2209that character, you can never match a C<chr(200)> in a non-UTF8 string.
2210So don't do that!
2211
2212=head2 How does Perl store UTF8 strings?
2213
2214Currently, Perl deals with Unicode strings and non-Unicode strings
2215slightly differently. If a string has been identified as being UTF-8
2216encoded, Perl will set a flag in the SV, C<SVf_UTF8>. You can check and
2217manipulate this flag with the following macros:
2218
2219 SvUTF8(sv)
2220 SvUTF8_on(sv)
2221 SvUTF8_off(sv)
2222
2223This flag has an important effect on Perl's treatment of the string: if
2224Unicode data is not properly distinguished, regular expressions,
2225C<length>, C<substr> and other string handling operations will have
2226undesirable results.
2227
2228The problem comes when you have, for instance, a string that isn't
2229flagged is UTF8, and contains a byte sequence that could be UTF8 -
2230especially when combining non-UTF8 and UTF8 strings.
2231
2232Never forget that the C<SVf_UTF8> flag is separate to the PV value; you
2233need be sure you don't accidentally knock it off while you're
2234manipulating SVs. More specifically, you cannot expect to do this:
2235
2236 SV *sv;
2237 SV *nsv;
2238 STRLEN len;
2239 char *p;
2240
2241 p = SvPV(sv, len);
2242 frobnicate(p);
2243 nsv = newSVpvn(p, len);
2244
2245The C<char*> string does not tell you the whole story, and you can't
2246copy or reconstruct an SV just by copying the string value. Check if the
2247old SV has the UTF8 flag set, and act accordingly:
2248
2249 p = SvPV(sv, len);
2250 frobnicate(p);
2251 nsv = newSVpvn(p, len);
2252 if (SvUTF8(sv))
2253 SvUTF8_on(nsv);
2254
2255In fact, your C<frobnicate> function should be made aware of whether or
2256not it's dealing with UTF8 data, so that it can handle the string
2257appropriately.
2258
2259=head2 How do I convert a string to UTF8?
2260
2261If you're mixing UTF8 and non-UTF8 strings, you might find it necessary
2262to upgrade one of the strings to UTF8. If you've got an SV, the easiest
2263way to do this is:
2264
2265 sv_utf8_upgrade(sv);
2266
2267However, you must not do this, for example:
2268
2269 if (!SvUTF8(left))
2270 sv_utf8_upgrade(left);
2271
2272If you do this in a binary operator, you will actually change one of the
b1866b2d 2273strings that came into the operator, and, while it shouldn't be noticeable
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2274by the end user, it can cause problems.
2275
2276Instead, C<bytes_to_utf8> will give you a UTF8-encoded B<copy> of its
2277string argument. This is useful for having the data available for
b1866b2d 2278comparisons and so on, without harming the original SV. There's also
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2279C<utf8_to_bytes> to go the other way, but naturally, this will fail if
2280the string contains any characters above 255 that can't be represented
2281in a single byte.
2282
2283=head2 Is there anything else I need to know?
2284
2285Not really. Just remember these things:
2286
2287=over 3
2288
2289=item *
2290
2291There's no way to tell if a string is UTF8 or not. You can tell if an SV
2292is UTF8 by looking at is C<SvUTF8> flag. Don't forget to set the flag if
2293something should be UTF8. Treat the flag as part of the PV, even though
2294it's not - if you pass on the PV to somewhere, pass on the flag too.
2295
2296=item *
2297
2298If a string is UTF8, B<always> use C<utf8_to_uv> to get at the value,
2299unless C<!(*s & 0x80)> in which case you can use C<*s>.
2300
2301=item *
2302
2303When writing to a UTF8 string, B<always> use C<uv_to_utf8>, unless
2304C<uv < 0x80> in which case you can use C<*s = uv>.
2305
2306=item *
2307
2308Mixing UTF8 and non-UTF8 strings is tricky. Use C<bytes_to_utf8> to get
2309a new string which is UTF8 encoded. There are tricks you can use to
2310delay deciding whether you need to use a UTF8 string until you get to a
2311high character - C<HALF_UPGRADE> is one of those.
2312
2313=back
2314
954c1994 2315=head1 AUTHORS
e89caa19 2316
954c1994
GS
2317Until May 1997, this document was maintained by Jeff Okamoto
2318<okamoto@corp.hp.com>. It is now maintained as part of Perl itself
2319by the Perl 5 Porters <perl5-porters@perl.org>.
cb1a09d0 2320
954c1994
GS
2321With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
2322Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
2323Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
2324Stephen McCamant, and Gurusamy Sarathy.
cb1a09d0 2325
954c1994 2326API Listing originally by Dean Roehrich <roehrich@cray.com>.
cb1a09d0 2327
954c1994
GS
2328Modifications to autogenerate the API listing (L<perlapi>) by Benjamin
2329Stuhl.
cb1a09d0 2330
954c1994 2331=head1 SEE ALSO
cb1a09d0 2332
954c1994 2333perlapi(1), perlintern(1), perlxs(1), perlembed(1)