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1 | =head1 NAME |
2 | ||
8e07c86e | 3 | perlxs - XS language reference manual |
a0d0e21e LW |
4 | |
5 | =head1 DESCRIPTION | |
6 | ||
7 | =head2 Introduction | |
8 | ||
9 | XS is a language used to create an extension interface | |
10 | between Perl and some C library which one wishes to use with | |
11 | Perl. The XS interface is combined with the library to | |
12 | create a new library which can be linked to Perl. An B<XSUB> | |
13 | is a function in the XS language and is the core component | |
14 | of the Perl application interface. | |
15 | ||
16 | The XS compiler is called B<xsubpp>. This compiler will embed | |
17 | the constructs necessary to let an XSUB, which is really a C | |
18 | function in disguise, manipulate Perl values and creates the | |
19 | glue necessary to let Perl access the XSUB. The compiler | |
20 | uses B<typemaps> to determine how to map C function parameters | |
21 | and variables to Perl values. The default typemap handles | |
22 | many common C types. A supplement typemap must be created | |
23 | to handle special structures and types for the library being | |
24 | linked. | |
25 | ||
cb1a09d0 | 26 | See L<perlxstut> for a tutorial on the whole extension creation process. |
8e07c86e | 27 | |
7b8d334a GS |
28 | Note: For many extensions, Dave Beazley's SWIG system provides a |
29 | significantly more convenient mechanism for creating the XS glue | |
30 | code. See L<http://www.cs.utah.edu/~beazley/SWIG> for more | |
31 | information. | |
32 | ||
8e07c86e AD |
33 | =head2 On The Road |
34 | ||
a5f75d66 AD |
35 | Many of the examples which follow will concentrate on creating an interface |
36 | between Perl and the ONC+ RPC bind library functions. The rpcb_gettime() | |
37 | function is used to demonstrate many features of the XS language. This | |
38 | function has two parameters; the first is an input parameter and the second | |
39 | is an output parameter. The function also returns a status value. | |
a0d0e21e LW |
40 | |
41 | bool_t rpcb_gettime(const char *host, time_t *timep); | |
42 | ||
43 | From C this function will be called with the following | |
44 | statements. | |
45 | ||
46 | #include <rpc/rpc.h> | |
47 | bool_t status; | |
48 | time_t timep; | |
49 | status = rpcb_gettime( "localhost", &timep ); | |
50 | ||
51 | If an XSUB is created to offer a direct translation between this function | |
52 | and Perl, then this XSUB will be used from Perl with the following code. | |
53 | The $status and $timep variables will contain the output of the function. | |
54 | ||
55 | use RPC; | |
56 | $status = rpcb_gettime( "localhost", $timep ); | |
57 | ||
58 | The following XS file shows an XS subroutine, or XSUB, which | |
59 | demonstrates one possible interface to the rpcb_gettime() | |
60 | function. This XSUB represents a direct translation between | |
61 | C and Perl and so preserves the interface even from Perl. | |
62 | This XSUB will be invoked from Perl with the usage shown | |
63 | above. Note that the first three #include statements, for | |
64 | C<EXTERN.h>, C<perl.h>, and C<XSUB.h>, will always be present at the | |
65 | beginning of an XS file. This approach and others will be | |
66 | expanded later in this document. | |
67 | ||
68 | #include "EXTERN.h" | |
69 | #include "perl.h" | |
70 | #include "XSUB.h" | |
71 | #include <rpc/rpc.h> | |
72 | ||
73 | MODULE = RPC PACKAGE = RPC | |
74 | ||
75 | bool_t | |
76 | rpcb_gettime(host,timep) | |
8e07c86e AD |
77 | char *host |
78 | time_t &timep | |
a0d0e21e LW |
79 | OUTPUT: |
80 | timep | |
81 | ||
82 | Any extension to Perl, including those containing XSUBs, | |
83 | should have a Perl module to serve as the bootstrap which | |
84 | pulls the extension into Perl. This module will export the | |
85 | extension's functions and variables to the Perl program and | |
86 | will cause the extension's XSUBs to be linked into Perl. | |
87 | The following module will be used for most of the examples | |
88 | in this document and should be used from Perl with the C<use> | |
89 | command as shown earlier. Perl modules are explained in | |
90 | more detail later in this document. | |
91 | ||
92 | package RPC; | |
93 | ||
94 | require Exporter; | |
95 | require DynaLoader; | |
96 | @ISA = qw(Exporter DynaLoader); | |
97 | @EXPORT = qw( rpcb_gettime ); | |
98 | ||
99 | bootstrap RPC; | |
100 | 1; | |
101 | ||
102 | Throughout this document a variety of interfaces to the rpcb_gettime() | |
103 | XSUB will be explored. The XSUBs will take their parameters in different | |
104 | orders or will take different numbers of parameters. In each case the | |
105 | XSUB is an abstraction between Perl and the real C rpcb_gettime() | |
106 | function, and the XSUB must always ensure that the real rpcb_gettime() | |
107 | function is called with the correct parameters. This abstraction will | |
108 | allow the programmer to create a more Perl-like interface to the C | |
109 | function. | |
110 | ||
111 | =head2 The Anatomy of an XSUB | |
112 | ||
8e07c86e AD |
113 | The following XSUB allows a Perl program to access a C library function |
114 | called sin(). The XSUB will imitate the C function which takes a single | |
115 | argument and returns a single value. | |
a0d0e21e LW |
116 | |
117 | double | |
118 | sin(x) | |
8e07c86e | 119 | double x |
a0d0e21e | 120 | |
8e07c86e AD |
121 | When using C pointers the indirection operator C<*> should be considered |
122 | part of the type and the address operator C<&> should be considered part of | |
123 | the variable, as is demonstrated in the rpcb_gettime() function above. See | |
124 | the section on typemaps for more about handling qualifiers and unary | |
125 | operators in C types. | |
a0d0e21e | 126 | |
a0d0e21e LW |
127 | The function name and the return type must be placed on |
128 | separate lines. | |
129 | ||
130 | INCORRECT CORRECT | |
131 | ||
132 | double sin(x) double | |
8e07c86e AD |
133 | double x sin(x) |
134 | double x | |
a0d0e21e | 135 | |
c07a80fd | 136 | The function body may be indented or left-adjusted. The following example |
137 | shows a function with its body left-adjusted. Most examples in this | |
138 | document will indent the body. | |
139 | ||
140 | CORRECT | |
141 | ||
142 | double | |
143 | sin(x) | |
144 | double x | |
145 | ||
a0d0e21e LW |
146 | =head2 The Argument Stack |
147 | ||
148 | The argument stack is used to store the values which are | |
149 | sent as parameters to the XSUB and to store the XSUB's | |
150 | return value. In reality all Perl functions keep their | |
151 | values on this stack at the same time, each limited to its | |
152 | own range of positions on the stack. In this document the | |
153 | first position on that stack which belongs to the active | |
154 | function will be referred to as position 0 for that function. | |
155 | ||
8e07c86e AD |
156 | XSUBs refer to their stack arguments with the macro B<ST(x)>, where I<x> |
157 | refers to a position in this XSUB's part of the stack. Position 0 for that | |
a0d0e21e LW |
158 | function would be known to the XSUB as ST(0). The XSUB's incoming |
159 | parameters and outgoing return values always begin at ST(0). For many | |
160 | simple cases the B<xsubpp> compiler will generate the code necessary to | |
161 | handle the argument stack by embedding code fragments found in the | |
162 | typemaps. In more complex cases the programmer must supply the code. | |
163 | ||
164 | =head2 The RETVAL Variable | |
165 | ||
166 | The RETVAL variable is a magic variable which always matches | |
167 | the return type of the C library function. The B<xsubpp> compiler will | |
168 | supply this variable in each XSUB and by default will use it to hold the | |
169 | return value of the C library function being called. In simple cases the | |
170 | value of RETVAL will be placed in ST(0) of the argument stack where it can | |
171 | be received by Perl as the return value of the XSUB. | |
172 | ||
173 | If the XSUB has a return type of C<void> then the compiler will | |
174 | not supply a RETVAL variable for that function. When using | |
e7ea3e70 IZ |
175 | the PPCODE: directive the RETVAL variable is not needed, unless used |
176 | explicitly. | |
177 | ||
178 | If PPCODE: directive is not used, C<void> return value should be used | |
179 | only for subroutines which do not return a value, I<even if> CODE: | |
54310121 | 180 | directive is used which sets ST(0) explicitly. |
e7ea3e70 IZ |
181 | |
182 | Older versions of this document recommended to use C<void> return | |
183 | value in such cases. It was discovered that this could lead to | |
184 | segfaults in cases when XSUB was I<truely> C<void>. This practice is | |
185 | now deprecated, and may be not supported at some future version. Use | |
186 | the return value C<SV *> in such cases. (Currently C<xsubpp> contains | |
187 | some heuristic code which tries to disambiguate between "truely-void" | |
188 | and "old-practice-declared-as-void" functions. Hence your code is at | |
189 | mercy of this heuristics unless you use C<SV *> as return value.) | |
a0d0e21e LW |
190 | |
191 | =head2 The MODULE Keyword | |
192 | ||
193 | The MODULE keyword is used to start the XS code and to | |
194 | specify the package of the functions which are being | |
195 | defined. All text preceding the first MODULE keyword is | |
196 | considered C code and is passed through to the output | |
197 | untouched. Every XS module will have a bootstrap function | |
198 | which is used to hook the XSUBs into Perl. The package name | |
199 | of this bootstrap function will match the value of the last | |
200 | MODULE statement in the XS source files. The value of | |
201 | MODULE should always remain constant within the same XS | |
202 | file, though this is not required. | |
203 | ||
204 | The following example will start the XS code and will place | |
205 | all functions in a package named RPC. | |
206 | ||
207 | MODULE = RPC | |
208 | ||
209 | =head2 The PACKAGE Keyword | |
210 | ||
211 | When functions within an XS source file must be separated into packages | |
212 | the PACKAGE keyword should be used. This keyword is used with the MODULE | |
213 | keyword and must follow immediately after it when used. | |
214 | ||
215 | MODULE = RPC PACKAGE = RPC | |
216 | ||
217 | [ XS code in package RPC ] | |
218 | ||
219 | MODULE = RPC PACKAGE = RPCB | |
220 | ||
221 | [ XS code in package RPCB ] | |
222 | ||
223 | MODULE = RPC PACKAGE = RPC | |
224 | ||
225 | [ XS code in package RPC ] | |
226 | ||
227 | Although this keyword is optional and in some cases provides redundant | |
228 | information it should always be used. This keyword will ensure that the | |
229 | XSUBs appear in the desired package. | |
230 | ||
231 | =head2 The PREFIX Keyword | |
232 | ||
233 | The PREFIX keyword designates prefixes which should be | |
234 | removed from the Perl function names. If the C function is | |
235 | C<rpcb_gettime()> and the PREFIX value is C<rpcb_> then Perl will | |
236 | see this function as C<gettime()>. | |
237 | ||
238 | This keyword should follow the PACKAGE keyword when used. | |
239 | If PACKAGE is not used then PREFIX should follow the MODULE | |
240 | keyword. | |
241 | ||
242 | MODULE = RPC PREFIX = rpc_ | |
243 | ||
244 | MODULE = RPC PACKAGE = RPCB PREFIX = rpcb_ | |
245 | ||
246 | =head2 The OUTPUT: Keyword | |
247 | ||
248 | The OUTPUT: keyword indicates that certain function parameters should be | |
249 | updated (new values made visible to Perl) when the XSUB terminates or that | |
250 | certain values should be returned to the calling Perl function. For | |
251 | simple functions, such as the sin() function above, the RETVAL variable is | |
252 | automatically designated as an output value. In more complex functions | |
253 | the B<xsubpp> compiler will need help to determine which variables are output | |
254 | variables. | |
255 | ||
256 | This keyword will normally be used to complement the CODE: keyword. | |
257 | The RETVAL variable is not recognized as an output variable when the | |
258 | CODE: keyword is present. The OUTPUT: keyword is used in this | |
259 | situation to tell the compiler that RETVAL really is an output | |
260 | variable. | |
261 | ||
262 | The OUTPUT: keyword can also be used to indicate that function parameters | |
263 | are output variables. This may be necessary when a parameter has been | |
264 | modified within the function and the programmer would like the update to | |
8e07c86e | 265 | be seen by Perl. |
a0d0e21e LW |
266 | |
267 | bool_t | |
268 | rpcb_gettime(host,timep) | |
8e07c86e AD |
269 | char *host |
270 | time_t &timep | |
a0d0e21e LW |
271 | OUTPUT: |
272 | timep | |
273 | ||
274 | The OUTPUT: keyword will also allow an output parameter to | |
275 | be mapped to a matching piece of code rather than to a | |
ef50df4b | 276 | typemap. |
a0d0e21e LW |
277 | |
278 | bool_t | |
279 | rpcb_gettime(host,timep) | |
8e07c86e AD |
280 | char *host |
281 | time_t &timep | |
a0d0e21e | 282 | OUTPUT: |
ef50df4b GS |
283 | timep sv_setnv(ST(1), (double)timep); |
284 | ||
285 | B<xsubpp> emits an automatic C<SvSETMAGIC()> for all parameters in the | |
286 | OUTPUT section of the XSUB, except RETVAL. This is the usually desired | |
287 | behavior, as it takes care of properly invoking 'set' magic on output | |
288 | parameters (needed for hash or array element parameters that must be | |
289 | created if they didn't exist). If for some reason, this behavior is | |
290 | not desired, the OUTPUT section may contain a C<SETMAGIC: DISABLE> line | |
291 | to disable it for the remainder of the parameters in the OUTPUT section. | |
292 | Likewise, C<SETMAGIC: ENABLE> can be used to reenable it for the | |
293 | remainder of the OUTPUT section. See L<perlguts> for more details | |
294 | about 'set' magic. | |
a0d0e21e LW |
295 | |
296 | =head2 The CODE: Keyword | |
297 | ||
298 | This keyword is used in more complicated XSUBs which require | |
299 | special handling for the C function. The RETVAL variable is | |
300 | available but will not be returned unless it is specified | |
301 | under the OUTPUT: keyword. | |
302 | ||
303 | The following XSUB is for a C function which requires special handling of | |
304 | its parameters. The Perl usage is given first. | |
305 | ||
306 | $status = rpcb_gettime( "localhost", $timep ); | |
307 | ||
54310121 | 308 | The XSUB follows. |
a0d0e21e | 309 | |
d1b91892 AD |
310 | bool_t |
311 | rpcb_gettime(host,timep) | |
8e07c86e AD |
312 | char *host |
313 | time_t timep | |
a0d0e21e LW |
314 | CODE: |
315 | RETVAL = rpcb_gettime( host, &timep ); | |
316 | OUTPUT: | |
317 | timep | |
318 | RETVAL | |
319 | ||
c07a80fd | 320 | =head2 The INIT: Keyword |
321 | ||
322 | The INIT: keyword allows initialization to be inserted into the XSUB before | |
323 | the compiler generates the call to the C function. Unlike the CODE: keyword | |
324 | above, this keyword does not affect the way the compiler handles RETVAL. | |
325 | ||
326 | bool_t | |
327 | rpcb_gettime(host,timep) | |
328 | char *host | |
329 | time_t &timep | |
330 | INIT: | |
331 | printf("# Host is %s\n", host ); | |
332 | OUTPUT: | |
333 | timep | |
a0d0e21e LW |
334 | |
335 | =head2 The NO_INIT Keyword | |
336 | ||
337 | The NO_INIT keyword is used to indicate that a function | |
54310121 | 338 | parameter is being used only as an output value. The B<xsubpp> |
a0d0e21e LW |
339 | compiler will normally generate code to read the values of |
340 | all function parameters from the argument stack and assign | |
341 | them to C variables upon entry to the function. NO_INIT | |
342 | will tell the compiler that some parameters will be used for | |
343 | output rather than for input and that they will be handled | |
344 | before the function terminates. | |
345 | ||
346 | The following example shows a variation of the rpcb_gettime() function. | |
54310121 | 347 | This function uses the timep variable only as an output variable and does |
a0d0e21e LW |
348 | not care about its initial contents. |
349 | ||
350 | bool_t | |
351 | rpcb_gettime(host,timep) | |
8e07c86e AD |
352 | char *host |
353 | time_t &timep = NO_INIT | |
a0d0e21e LW |
354 | OUTPUT: |
355 | timep | |
356 | ||
357 | =head2 Initializing Function Parameters | |
358 | ||
359 | Function parameters are normally initialized with their | |
360 | values from the argument stack. The typemaps contain the | |
361 | code segments which are used to transfer the Perl values to | |
362 | the C parameters. The programmer, however, is allowed to | |
7ad6fb0b TM |
363 | override the typemaps and supply alternate (or additional) |
364 | initialization code. | |
a0d0e21e LW |
365 | |
366 | The following code demonstrates how to supply initialization code for | |
7ad6fb0b TM |
367 | function parameters. The initialization code is eval'd within double |
368 | quotes by the compiler before it is added to the output so anything | |
369 | which should be interpreted literally [mainly C<$>, C<@>, or C<\\>] | |
370 | must be protected with backslashes. The variables C<$var>, C<$arg>, | |
371 | and C<$type> can be used as in typemaps. | |
a0d0e21e LW |
372 | |
373 | bool_t | |
374 | rpcb_gettime(host,timep) | |
9cde0e7f | 375 | char *host = (char *)SvPV($arg,PL_na); |
8e07c86e | 376 | time_t &timep = 0; |
a0d0e21e LW |
377 | OUTPUT: |
378 | timep | |
379 | ||
380 | This should not be used to supply default values for parameters. One | |
381 | would normally use this when a function parameter must be processed by | |
382 | another library function before it can be used. Default parameters are | |
383 | covered in the next section. | |
384 | ||
7ad6fb0b TM |
385 | If the initialization begins with C<=>, then it is output on |
386 | the same line where the input variable is declared. If the | |
387 | initialization begins with C<;> or C<+>, then it is output after | |
388 | all of the input variables have been declared. The C<=> and C<;> | |
389 | cases replace the initialization normally supplied from the typemap. | |
390 | For the C<+> case, the initialization from the typemap will preceed | |
391 | the initialization code included after the C<+>. A global | |
392 | variable, C<%v>, is available for the truely rare case where | |
393 | information from one initialization is needed in another | |
394 | initialization. | |
395 | ||
396 | bool_t | |
397 | rpcb_gettime(host,timep) | |
398 | time_t &timep ; /*\$v{time}=@{[$v{time}=$arg]}*/ | |
9cde0e7f | 399 | char *host + SvOK($v{time}) ? SvPV($arg,PL_na) : NULL; |
7ad6fb0b TM |
400 | OUTPUT: |
401 | timep | |
402 | ||
a0d0e21e LW |
403 | =head2 Default Parameter Values |
404 | ||
405 | Default values can be specified for function parameters by | |
406 | placing an assignment statement in the parameter list. The | |
407 | default value may be a number or a string. Defaults should | |
408 | always be used on the right-most parameters only. | |
409 | ||
410 | To allow the XSUB for rpcb_gettime() to have a default host | |
411 | value the parameters to the XSUB could be rearranged. The | |
412 | XSUB will then call the real rpcb_gettime() function with | |
413 | the parameters in the correct order. Perl will call this | |
414 | XSUB with either of the following statements. | |
415 | ||
416 | $status = rpcb_gettime( $timep, $host ); | |
417 | ||
418 | $status = rpcb_gettime( $timep ); | |
419 | ||
420 | The XSUB will look like the code which follows. A CODE: | |
421 | block is used to call the real rpcb_gettime() function with | |
422 | the parameters in the correct order for that function. | |
423 | ||
424 | bool_t | |
425 | rpcb_gettime(timep,host="localhost") | |
8e07c86e AD |
426 | char *host |
427 | time_t timep = NO_INIT | |
a0d0e21e LW |
428 | CODE: |
429 | RETVAL = rpcb_gettime( host, &timep ); | |
430 | OUTPUT: | |
431 | timep | |
432 | RETVAL | |
433 | ||
c07a80fd | 434 | =head2 The PREINIT: Keyword |
435 | ||
436 | The PREINIT: keyword allows extra variables to be declared before the | |
437 | typemaps are expanded. If a variable is declared in a CODE: block then that | |
438 | variable will follow any typemap code. This may result in a C syntax | |
439 | error. To force the variable to be declared before the typemap code, place | |
440 | it into a PREINIT: block. The PREINIT: keyword may be used one or more | |
441 | times within an XSUB. | |
442 | ||
443 | The following examples are equivalent, but if the code is using complex | |
444 | typemaps then the first example is safer. | |
445 | ||
446 | bool_t | |
447 | rpcb_gettime(timep) | |
448 | time_t timep = NO_INIT | |
449 | PREINIT: | |
450 | char *host = "localhost"; | |
451 | CODE: | |
452 | RETVAL = rpcb_gettime( host, &timep ); | |
453 | OUTPUT: | |
454 | timep | |
455 | RETVAL | |
456 | ||
457 | A correct, but error-prone example. | |
458 | ||
459 | bool_t | |
460 | rpcb_gettime(timep) | |
461 | time_t timep = NO_INIT | |
462 | CODE: | |
463 | char *host = "localhost"; | |
464 | RETVAL = rpcb_gettime( host, &timep ); | |
465 | OUTPUT: | |
466 | timep | |
467 | RETVAL | |
468 | ||
84287afe | 469 | =head2 The SCOPE: Keyword |
470 | ||
471 | The SCOPE: keyword allows scoping to be enabled for a particular XSUB. If | |
472 | enabled, the XSUB will invoke ENTER and LEAVE automatically. | |
473 | ||
474 | To support potentially complex type mappings, if a typemap entry used | |
475 | by this XSUB contains a comment like C</*scope*/> then scoping will | |
476 | automatically be enabled for that XSUB. | |
477 | ||
478 | To enable scoping: | |
479 | ||
480 | SCOPE: ENABLE | |
481 | ||
482 | To disable scoping: | |
483 | ||
484 | SCOPE: DISABLE | |
485 | ||
c07a80fd | 486 | =head2 The INPUT: Keyword |
487 | ||
488 | The XSUB's parameters are usually evaluated immediately after entering the | |
489 | XSUB. The INPUT: keyword can be used to force those parameters to be | |
490 | evaluated a little later. The INPUT: keyword can be used multiple times | |
491 | within an XSUB and can be used to list one or more input variables. This | |
492 | keyword is used with the PREINIT: keyword. | |
493 | ||
494 | The following example shows how the input parameter C<timep> can be | |
495 | evaluated late, after a PREINIT. | |
496 | ||
497 | bool_t | |
498 | rpcb_gettime(host,timep) | |
499 | char *host | |
500 | PREINIT: | |
501 | time_t tt; | |
502 | INPUT: | |
503 | time_t timep | |
504 | CODE: | |
505 | RETVAL = rpcb_gettime( host, &tt ); | |
506 | timep = tt; | |
507 | OUTPUT: | |
508 | timep | |
509 | RETVAL | |
510 | ||
511 | The next example shows each input parameter evaluated late. | |
512 | ||
513 | bool_t | |
514 | rpcb_gettime(host,timep) | |
515 | PREINIT: | |
516 | time_t tt; | |
517 | INPUT: | |
518 | char *host | |
519 | PREINIT: | |
520 | char *h; | |
521 | INPUT: | |
522 | time_t timep | |
523 | CODE: | |
524 | h = host; | |
525 | RETVAL = rpcb_gettime( h, &tt ); | |
526 | timep = tt; | |
527 | OUTPUT: | |
528 | timep | |
529 | RETVAL | |
530 | ||
a0d0e21e LW |
531 | =head2 Variable-length Parameter Lists |
532 | ||
533 | XSUBs can have variable-length parameter lists by specifying an ellipsis | |
534 | C<(...)> in the parameter list. This use of the ellipsis is similar to that | |
535 | found in ANSI C. The programmer is able to determine the number of | |
536 | arguments passed to the XSUB by examining the C<items> variable which the | |
537 | B<xsubpp> compiler supplies for all XSUBs. By using this mechanism one can | |
538 | create an XSUB which accepts a list of parameters of unknown length. | |
539 | ||
540 | The I<host> parameter for the rpcb_gettime() XSUB can be | |
541 | optional so the ellipsis can be used to indicate that the | |
542 | XSUB will take a variable number of parameters. Perl should | |
d1b91892 | 543 | be able to call this XSUB with either of the following statements. |
a0d0e21e LW |
544 | |
545 | $status = rpcb_gettime( $timep, $host ); | |
546 | ||
547 | $status = rpcb_gettime( $timep ); | |
548 | ||
549 | The XS code, with ellipsis, follows. | |
550 | ||
551 | bool_t | |
552 | rpcb_gettime(timep, ...) | |
8e07c86e | 553 | time_t timep = NO_INIT |
c07a80fd | 554 | PREINIT: |
a0d0e21e | 555 | char *host = "localhost"; |
c07a80fd | 556 | CODE: |
557 | if( items > 1 ) | |
9cde0e7f | 558 | host = (char *)SvPV(ST(1), PL_na); |
c07a80fd | 559 | RETVAL = rpcb_gettime( host, &timep ); |
a0d0e21e LW |
560 | OUTPUT: |
561 | timep | |
562 | RETVAL | |
563 | ||
cfc02341 IZ |
564 | =head2 The C_ARGS: Keyword |
565 | ||
566 | The C_ARGS: keyword allows creating of XSUBS which have different | |
567 | calling sequence from Perl than from C, without a need to write | |
568 | CODE: or CPPCODE: section. The contents of the C_ARGS: paragraph is | |
569 | put as the argument to the called C function without any change. | |
570 | ||
571 | For example, suppose that C function is declared as | |
572 | ||
573 | symbolic nth_derivative(int n, symbolic function, int flags); | |
574 | ||
575 | and that the default flags are kept in a global C variable | |
576 | C<default_flags>. Suppose that you want to create an interface which | |
577 | is called as | |
578 | ||
579 | $second_deriv = $function->nth_derivative(2); | |
580 | ||
581 | To do this, declare the XSUB as | |
582 | ||
583 | symbolic | |
584 | nth_derivative(function, n) | |
585 | symbolic function | |
586 | int n | |
587 | C_ARGS: | |
588 | n, function, default_flags | |
589 | ||
a0d0e21e LW |
590 | =head2 The PPCODE: Keyword |
591 | ||
592 | The PPCODE: keyword is an alternate form of the CODE: keyword and is used | |
593 | to tell the B<xsubpp> compiler that the programmer is supplying the code to | |
d1b91892 | 594 | control the argument stack for the XSUBs return values. Occasionally one |
a0d0e21e LW |
595 | will want an XSUB to return a list of values rather than a single value. |
596 | In these cases one must use PPCODE: and then explicitly push the list of | |
597 | values on the stack. The PPCODE: and CODE: keywords are not used | |
598 | together within the same XSUB. | |
599 | ||
600 | The following XSUB will call the C rpcb_gettime() function | |
601 | and will return its two output values, timep and status, to | |
602 | Perl as a single list. | |
603 | ||
d1b91892 AD |
604 | void |
605 | rpcb_gettime(host) | |
8e07c86e | 606 | char *host |
c07a80fd | 607 | PREINIT: |
a0d0e21e LW |
608 | time_t timep; |
609 | bool_t status; | |
c07a80fd | 610 | PPCODE: |
a0d0e21e | 611 | status = rpcb_gettime( host, &timep ); |
924508f0 | 612 | EXTEND(SP, 2); |
cb1a09d0 AD |
613 | PUSHs(sv_2mortal(newSViv(status))); |
614 | PUSHs(sv_2mortal(newSViv(timep))); | |
a0d0e21e LW |
615 | |
616 | Notice that the programmer must supply the C code necessary | |
617 | to have the real rpcb_gettime() function called and to have | |
618 | the return values properly placed on the argument stack. | |
619 | ||
620 | The C<void> return type for this function tells the B<xsubpp> compiler that | |
621 | the RETVAL variable is not needed or used and that it should not be created. | |
622 | In most scenarios the void return type should be used with the PPCODE: | |
623 | directive. | |
624 | ||
625 | The EXTEND() macro is used to make room on the argument | |
626 | stack for 2 return values. The PPCODE: directive causes the | |
924508f0 | 627 | B<xsubpp> compiler to create a stack pointer available as C<SP>, and it |
a0d0e21e LW |
628 | is this pointer which is being used in the EXTEND() macro. |
629 | The values are then pushed onto the stack with the PUSHs() | |
630 | macro. | |
631 | ||
632 | Now the rpcb_gettime() function can be used from Perl with | |
633 | the following statement. | |
634 | ||
635 | ($status, $timep) = rpcb_gettime("localhost"); | |
636 | ||
ef50df4b GS |
637 | When handling output parameters with a PPCODE section, be sure to handle |
638 | 'set' magic properly. See L<perlguts> for details about 'set' magic. | |
639 | ||
a0d0e21e LW |
640 | =head2 Returning Undef And Empty Lists |
641 | ||
5f05dabc | 642 | Occasionally the programmer will want to return simply |
a0d0e21e LW |
643 | C<undef> or an empty list if a function fails rather than a |
644 | separate status value. The rpcb_gettime() function offers | |
645 | just this situation. If the function succeeds we would like | |
646 | to have it return the time and if it fails we would like to | |
647 | have undef returned. In the following Perl code the value | |
648 | of $timep will either be undef or it will be a valid time. | |
649 | ||
650 | $timep = rpcb_gettime( "localhost" ); | |
651 | ||
7b8d334a | 652 | The following XSUB uses the C<SV *> return type as a mnemonic only, |
e7ea3e70 | 653 | and uses a CODE: block to indicate to the compiler |
a0d0e21e LW |
654 | that the programmer has supplied all the necessary code. The |
655 | sv_newmortal() call will initialize the return value to undef, making that | |
656 | the default return value. | |
657 | ||
e7ea3e70 | 658 | SV * |
a0d0e21e LW |
659 | rpcb_gettime(host) |
660 | char * host | |
c07a80fd | 661 | PREINIT: |
a0d0e21e LW |
662 | time_t timep; |
663 | bool_t x; | |
c07a80fd | 664 | CODE: |
a0d0e21e LW |
665 | ST(0) = sv_newmortal(); |
666 | if( rpcb_gettime( host, &timep ) ) | |
667 | sv_setnv( ST(0), (double)timep); | |
a0d0e21e LW |
668 | |
669 | The next example demonstrates how one would place an explicit undef in the | |
670 | return value, should the need arise. | |
671 | ||
e7ea3e70 | 672 | SV * |
a0d0e21e LW |
673 | rpcb_gettime(host) |
674 | char * host | |
c07a80fd | 675 | PREINIT: |
a0d0e21e LW |
676 | time_t timep; |
677 | bool_t x; | |
c07a80fd | 678 | CODE: |
a0d0e21e LW |
679 | ST(0) = sv_newmortal(); |
680 | if( rpcb_gettime( host, &timep ) ){ | |
681 | sv_setnv( ST(0), (double)timep); | |
682 | } | |
683 | else{ | |
9cde0e7f | 684 | ST(0) = &PL_sv_undef; |
a0d0e21e | 685 | } |
a0d0e21e LW |
686 | |
687 | To return an empty list one must use a PPCODE: block and | |
688 | then not push return values on the stack. | |
689 | ||
690 | void | |
691 | rpcb_gettime(host) | |
8e07c86e | 692 | char *host |
c07a80fd | 693 | PREINIT: |
a0d0e21e | 694 | time_t timep; |
c07a80fd | 695 | PPCODE: |
a0d0e21e | 696 | if( rpcb_gettime( host, &timep ) ) |
cb1a09d0 | 697 | PUSHs(sv_2mortal(newSViv(timep))); |
a0d0e21e LW |
698 | else{ |
699 | /* Nothing pushed on stack, so an empty */ | |
700 | /* list is implicitly returned. */ | |
701 | } | |
a0d0e21e | 702 | |
f27cfbbe | 703 | Some people may be inclined to include an explicit C<return> in the above |
704 | XSUB, rather than letting control fall through to the end. In those | |
705 | situations C<XSRETURN_EMPTY> should be used, instead. This will ensure that | |
706 | the XSUB stack is properly adjusted. Consult L<perlguts/"API LISTING"> for | |
707 | other C<XSRETURN> macros. | |
708 | ||
4633a7c4 LW |
709 | =head2 The REQUIRE: Keyword |
710 | ||
711 | The REQUIRE: keyword is used to indicate the minimum version of the | |
712 | B<xsubpp> compiler needed to compile the XS module. An XS module which | |
5f05dabc | 713 | contains the following statement will compile with only B<xsubpp> version |
4633a7c4 LW |
714 | 1.922 or greater: |
715 | ||
716 | REQUIRE: 1.922 | |
717 | ||
a0d0e21e LW |
718 | =head2 The CLEANUP: Keyword |
719 | ||
720 | This keyword can be used when an XSUB requires special cleanup procedures | |
721 | before it terminates. When the CLEANUP: keyword is used it must follow | |
722 | any CODE:, PPCODE:, or OUTPUT: blocks which are present in the XSUB. The | |
723 | code specified for the cleanup block will be added as the last statements | |
724 | in the XSUB. | |
725 | ||
726 | =head2 The BOOT: Keyword | |
727 | ||
728 | The BOOT: keyword is used to add code to the extension's bootstrap | |
729 | function. The bootstrap function is generated by the B<xsubpp> compiler and | |
730 | normally holds the statements necessary to register any XSUBs with Perl. | |
731 | With the BOOT: keyword the programmer can tell the compiler to add extra | |
732 | statements to the bootstrap function. | |
733 | ||
734 | This keyword may be used any time after the first MODULE keyword and should | |
735 | appear on a line by itself. The first blank line after the keyword will | |
736 | terminate the code block. | |
737 | ||
738 | BOOT: | |
739 | # The following message will be printed when the | |
740 | # bootstrap function executes. | |
741 | printf("Hello from the bootstrap!\n"); | |
742 | ||
c07a80fd | 743 | =head2 The VERSIONCHECK: Keyword |
744 | ||
745 | The VERSIONCHECK: keyword corresponds to B<xsubpp>'s C<-versioncheck> and | |
5f05dabc | 746 | C<-noversioncheck> options. This keyword overrides the command line |
c07a80fd | 747 | options. Version checking is enabled by default. When version checking is |
748 | enabled the XS module will attempt to verify that its version matches the | |
749 | version of the PM module. | |
750 | ||
751 | To enable version checking: | |
752 | ||
753 | VERSIONCHECK: ENABLE | |
754 | ||
755 | To disable version checking: | |
756 | ||
757 | VERSIONCHECK: DISABLE | |
758 | ||
759 | =head2 The PROTOTYPES: Keyword | |
760 | ||
761 | The PROTOTYPES: keyword corresponds to B<xsubpp>'s C<-prototypes> and | |
54310121 | 762 | C<-noprototypes> options. This keyword overrides the command line options. |
c07a80fd | 763 | Prototypes are enabled by default. When prototypes are enabled XSUBs will |
764 | be given Perl prototypes. This keyword may be used multiple times in an XS | |
765 | module to enable and disable prototypes for different parts of the module. | |
766 | ||
767 | To enable prototypes: | |
768 | ||
769 | PROTOTYPES: ENABLE | |
770 | ||
771 | To disable prototypes: | |
772 | ||
773 | PROTOTYPES: DISABLE | |
774 | ||
775 | =head2 The PROTOTYPE: Keyword | |
776 | ||
777 | This keyword is similar to the PROTOTYPES: keyword above but can be used to | |
778 | force B<xsubpp> to use a specific prototype for the XSUB. This keyword | |
779 | overrides all other prototype options and keywords but affects only the | |
780 | current XSUB. Consult L<perlsub/Prototypes> for information about Perl | |
781 | prototypes. | |
782 | ||
783 | bool_t | |
784 | rpcb_gettime(timep, ...) | |
785 | time_t timep = NO_INIT | |
786 | PROTOTYPE: $;$ | |
787 | PREINIT: | |
788 | char *host = "localhost"; | |
789 | CODE: | |
790 | if( items > 1 ) | |
9cde0e7f | 791 | host = (char *)SvPV(ST(1), PL_na); |
c07a80fd | 792 | RETVAL = rpcb_gettime( host, &timep ); |
793 | OUTPUT: | |
794 | timep | |
795 | RETVAL | |
796 | ||
797 | =head2 The ALIAS: Keyword | |
798 | ||
cfc02341 | 799 | The ALIAS: keyword allows an XSUB to have two or more unique Perl names |
c07a80fd | 800 | and to know which of those names was used when it was invoked. The Perl |
801 | names may be fully-qualified with package names. Each alias is given an | |
802 | index. The compiler will setup a variable called C<ix> which contain the | |
803 | index of the alias which was used. When the XSUB is called with its | |
804 | declared name C<ix> will be 0. | |
805 | ||
806 | The following example will create aliases C<FOO::gettime()> and | |
807 | C<BAR::getit()> for this function. | |
808 | ||
809 | bool_t | |
810 | rpcb_gettime(host,timep) | |
811 | char *host | |
812 | time_t &timep | |
813 | ALIAS: | |
814 | FOO::gettime = 1 | |
815 | BAR::getit = 2 | |
816 | INIT: | |
817 | printf("# ix = %d\n", ix ); | |
818 | OUTPUT: | |
819 | timep | |
820 | ||
cfc02341 IZ |
821 | =head2 The INTERFACE: Keyword |
822 | ||
823 | This keyword declares the current XSUB as a keeper of the given | |
824 | calling signature. If some text follows this keyword, it is | |
825 | considered as a list of functions which have this signature, and | |
826 | should be attached to XSUBs. | |
827 | ||
828 | Say, if you have 4 functions multiply(), divide(), add(), subtract() all | |
829 | having the signature | |
830 | ||
831 | symbolic f(symbolic, symbolic); | |
832 | ||
833 | you code them all by using XSUB | |
834 | ||
835 | symbolic | |
836 | interface_s_ss(arg1, arg2) | |
837 | symbolic arg1 | |
838 | symbolic arg2 | |
839 | INTERFACE: | |
840 | multiply divide | |
841 | add subtract | |
842 | ||
843 | The advantage of this approach comparing to ALIAS: keyword is that one | |
844 | can attach an extra function remainder() at runtime by using | |
845 | ||
846 | CV *mycv = newXSproto("Symbolic::remainder", | |
847 | XS_Symbolic_interface_s_ss, __FILE__, "$$"); | |
848 | XSINTERFACE_FUNC_SET(mycv, remainder); | |
849 | ||
850 | (This example supposes that there was no INTERFACE_MACRO: section, | |
851 | otherwise one needs to use something else instead of | |
852 | C<XSINTERFACE_FUNC_SET>.) | |
853 | ||
854 | =head2 The INTERFACE_MACRO: Keyword | |
855 | ||
856 | This keyword allows one to define an INTERFACE using a different way | |
857 | to extract a function pointer from an XSUB. The text which follows | |
858 | this keyword should give the name of macros which would extract/set a | |
859 | function pointer. The extractor macro is given return type, C<CV*>, | |
860 | and C<XSANY.any_dptr> for this C<CV*>. The setter macro is given cv, | |
861 | and the function pointer. | |
862 | ||
863 | The default value is C<XSINTERFACE_FUNC> and C<XSINTERFACE_FUNC_SET>. | |
864 | An INTERFACE keyword with an empty list of functions can be omitted if | |
865 | INTERFACE_MACRO keyword is used. | |
866 | ||
867 | Suppose that in the previous example functions pointers for | |
868 | multiply(), divide(), add(), subtract() are kept in a global C array | |
869 | C<fp[]> with offsets being C<multiply_off>, C<divide_off>, C<add_off>, | |
870 | C<subtract_off>. Then one can use | |
871 | ||
872 | #define XSINTERFACE_FUNC_BYOFFSET(ret,cv,f) \ | |
873 | ((XSINTERFACE_CVT(ret,))fp[CvXSUBANY(cv).any_i32]) | |
874 | #define XSINTERFACE_FUNC_BYOFFSET_set(cv,f) \ | |
875 | CvXSUBANY(cv).any_i32 = CAT2( f, _off ) | |
876 | ||
877 | in C section, | |
878 | ||
879 | symbolic | |
880 | interface_s_ss(arg1, arg2) | |
881 | symbolic arg1 | |
882 | symbolic arg2 | |
883 | INTERFACE_MACRO: | |
884 | XSINTERFACE_FUNC_BYOFFSET | |
885 | XSINTERFACE_FUNC_BYOFFSET_set | |
886 | INTERFACE: | |
887 | multiply divide | |
888 | add subtract | |
889 | ||
890 | in XSUB section. | |
891 | ||
c07a80fd | 892 | =head2 The INCLUDE: Keyword |
893 | ||
894 | This keyword can be used to pull other files into the XS module. The other | |
895 | files may have XS code. INCLUDE: can also be used to run a command to | |
896 | generate the XS code to be pulled into the module. | |
897 | ||
898 | The file F<Rpcb1.xsh> contains our C<rpcb_gettime()> function: | |
899 | ||
900 | bool_t | |
901 | rpcb_gettime(host,timep) | |
902 | char *host | |
903 | time_t &timep | |
904 | OUTPUT: | |
905 | timep | |
906 | ||
907 | The XS module can use INCLUDE: to pull that file into it. | |
908 | ||
909 | INCLUDE: Rpcb1.xsh | |
910 | ||
911 | If the parameters to the INCLUDE: keyword are followed by a pipe (C<|>) then | |
912 | the compiler will interpret the parameters as a command. | |
913 | ||
914 | INCLUDE: cat Rpcb1.xsh | | |
915 | ||
916 | =head2 The CASE: Keyword | |
917 | ||
918 | The CASE: keyword allows an XSUB to have multiple distinct parts with each | |
919 | part acting as a virtual XSUB. CASE: is greedy and if it is used then all | |
920 | other XS keywords must be contained within a CASE:. This means nothing may | |
921 | precede the first CASE: in the XSUB and anything following the last CASE: is | |
922 | included in that case. | |
923 | ||
924 | A CASE: might switch via a parameter of the XSUB, via the C<ix> ALIAS: | |
925 | variable (see L<"The ALIAS: Keyword">), or maybe via the C<items> variable | |
926 | (see L<"Variable-length Parameter Lists">). The last CASE: becomes the | |
927 | B<default> case if it is not associated with a conditional. The following | |
928 | example shows CASE switched via C<ix> with a function C<rpcb_gettime()> | |
929 | having an alias C<x_gettime()>. When the function is called as | |
b772cb6e | 930 | C<rpcb_gettime()> its parameters are the usual C<(char *host, time_t *timep)>, |
931 | but when the function is called as C<x_gettime()> its parameters are | |
c07a80fd | 932 | reversed, C<(time_t *timep, char *host)>. |
933 | ||
934 | long | |
935 | rpcb_gettime(a,b) | |
936 | CASE: ix == 1 | |
937 | ALIAS: | |
938 | x_gettime = 1 | |
939 | INPUT: | |
940 | # 'a' is timep, 'b' is host | |
941 | char *b | |
942 | time_t a = NO_INIT | |
943 | CODE: | |
944 | RETVAL = rpcb_gettime( b, &a ); | |
945 | OUTPUT: | |
946 | a | |
947 | RETVAL | |
948 | CASE: | |
949 | # 'a' is host, 'b' is timep | |
950 | char *a | |
951 | time_t &b = NO_INIT | |
952 | OUTPUT: | |
953 | b | |
954 | RETVAL | |
955 | ||
956 | That function can be called with either of the following statements. Note | |
957 | the different argument lists. | |
958 | ||
959 | $status = rpcb_gettime( $host, $timep ); | |
960 | ||
961 | $status = x_gettime( $timep, $host ); | |
962 | ||
963 | =head2 The & Unary Operator | |
964 | ||
965 | The & unary operator is used to tell the compiler that it should dereference | |
966 | the object when it calls the C function. This is used when a CODE: block is | |
967 | not used and the object is a not a pointer type (the object is an C<int> or | |
968 | C<long> but not a C<int*> or C<long*>). | |
969 | ||
970 | The following XSUB will generate incorrect C code. The xsubpp compiler will | |
971 | turn this into code which calls C<rpcb_gettime()> with parameters C<(char | |
972 | *host, time_t timep)>, but the real C<rpcb_gettime()> wants the C<timep> | |
973 | parameter to be of type C<time_t*> rather than C<time_t>. | |
974 | ||
975 | bool_t | |
976 | rpcb_gettime(host,timep) | |
977 | char *host | |
978 | time_t timep | |
979 | OUTPUT: | |
980 | timep | |
981 | ||
982 | That problem is corrected by using the C<&> operator. The xsubpp compiler | |
983 | will now turn this into code which calls C<rpcb_gettime()> correctly with | |
984 | parameters C<(char *host, time_t *timep)>. It does this by carrying the | |
985 | C<&> through, so the function call looks like C<rpcb_gettime(host, &timep)>. | |
986 | ||
987 | bool_t | |
988 | rpcb_gettime(host,timep) | |
989 | char *host | |
990 | time_t &timep | |
991 | OUTPUT: | |
992 | timep | |
993 | ||
a0d0e21e LW |
994 | =head2 Inserting Comments and C Preprocessor Directives |
995 | ||
f27cfbbe | 996 | C preprocessor directives are allowed within BOOT:, PREINIT: INIT:, |
5f05dabc | 997 | CODE:, PPCODE:, and CLEANUP: blocks, as well as outside the functions. |
f27cfbbe | 998 | Comments are allowed anywhere after the MODULE keyword. The compiler |
999 | will pass the preprocessor directives through untouched and will remove | |
1000 | the commented lines. | |
b772cb6e | 1001 | |
f27cfbbe | 1002 | Comments can be added to XSUBs by placing a C<#> as the first |
1003 | non-whitespace of a line. Care should be taken to avoid making the | |
1004 | comment look like a C preprocessor directive, lest it be interpreted as | |
1005 | such. The simplest way to prevent this is to put whitespace in front of | |
1006 | the C<#>. | |
1007 | ||
f27cfbbe | 1008 | If you use preprocessor directives to choose one of two |
1009 | versions of a function, use | |
1010 | ||
1011 | #if ... version1 | |
1012 | #else /* ... version2 */ | |
1013 | #endif | |
1014 | ||
1015 | and not | |
1016 | ||
1017 | #if ... version1 | |
1018 | #endif | |
1019 | #if ... version2 | |
1020 | #endif | |
1021 | ||
1022 | because otherwise xsubpp will believe that you made a duplicate | |
1023 | definition of the function. Also, put a blank line before the | |
1024 | #else/#endif so it will not be seen as part of the function body. | |
a0d0e21e LW |
1025 | |
1026 | =head2 Using XS With C++ | |
1027 | ||
1028 | If a function is defined as a C++ method then it will assume | |
1029 | its first argument is an object pointer. The object pointer | |
1030 | will be stored in a variable called THIS. The object should | |
1031 | have been created by C++ with the new() function and should | |
cb1a09d0 AD |
1032 | be blessed by Perl with the sv_setref_pv() macro. The |
1033 | blessing of the object by Perl can be handled by a typemap. An example | |
1034 | typemap is shown at the end of this section. | |
a0d0e21e LW |
1035 | |
1036 | If the method is defined as static it will call the C++ | |
1037 | function using the class::method() syntax. If the method is not static | |
f27cfbbe | 1038 | the function will be called using the THIS-E<gt>method() syntax. |
a0d0e21e | 1039 | |
cb1a09d0 | 1040 | The next examples will use the following C++ class. |
a0d0e21e | 1041 | |
a5f75d66 | 1042 | class color { |
cb1a09d0 | 1043 | public: |
a5f75d66 AD |
1044 | color(); |
1045 | ~color(); | |
cb1a09d0 AD |
1046 | int blue(); |
1047 | void set_blue( int ); | |
1048 | ||
1049 | private: | |
1050 | int c_blue; | |
1051 | }; | |
1052 | ||
1053 | The XSUBs for the blue() and set_blue() methods are defined with the class | |
1054 | name but the parameter for the object (THIS, or "self") is implicit and is | |
1055 | not listed. | |
1056 | ||
1057 | int | |
1058 | color::blue() | |
a0d0e21e LW |
1059 | |
1060 | void | |
cb1a09d0 AD |
1061 | color::set_blue( val ) |
1062 | int val | |
a0d0e21e | 1063 | |
cb1a09d0 AD |
1064 | Both functions will expect an object as the first parameter. The xsubpp |
1065 | compiler will call that object C<THIS> and will use it to call the specified | |
1066 | method. So in the C++ code the blue() and set_blue() methods will be called | |
1067 | in the following manner. | |
a0d0e21e | 1068 | |
cb1a09d0 | 1069 | RETVAL = THIS->blue(); |
a0d0e21e | 1070 | |
cb1a09d0 | 1071 | THIS->set_blue( val ); |
a0d0e21e | 1072 | |
cb1a09d0 AD |
1073 | If the function's name is B<DESTROY> then the C++ C<delete> function will be |
1074 | called and C<THIS> will be given as its parameter. | |
a0d0e21e | 1075 | |
d1b91892 | 1076 | void |
cb1a09d0 AD |
1077 | color::DESTROY() |
1078 | ||
1079 | The C++ code will call C<delete>. | |
1080 | ||
1081 | delete THIS; | |
a0d0e21e | 1082 | |
cb1a09d0 AD |
1083 | If the function's name is B<new> then the C++ C<new> function will be called |
1084 | to create a dynamic C++ object. The XSUB will expect the class name, which | |
1085 | will be kept in a variable called C<CLASS>, to be given as the first | |
1086 | argument. | |
a0d0e21e | 1087 | |
cb1a09d0 AD |
1088 | color * |
1089 | color::new() | |
a0d0e21e | 1090 | |
cb1a09d0 | 1091 | The C++ code will call C<new>. |
a0d0e21e | 1092 | |
cb1a09d0 AD |
1093 | RETVAL = new color(); |
1094 | ||
1095 | The following is an example of a typemap that could be used for this C++ | |
1096 | example. | |
1097 | ||
1098 | TYPEMAP | |
1099 | color * O_OBJECT | |
1100 | ||
1101 | OUTPUT | |
1102 | # The Perl object is blessed into 'CLASS', which should be a | |
1103 | # char* having the name of the package for the blessing. | |
1104 | O_OBJECT | |
1105 | sv_setref_pv( $arg, CLASS, (void*)$var ); | |
a6006777 | 1106 | |
cb1a09d0 AD |
1107 | INPUT |
1108 | O_OBJECT | |
1109 | if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) ) | |
1110 | $var = ($type)SvIV((SV*)SvRV( $arg )); | |
1111 | else{ | |
1112 | warn( \"${Package}::$func_name() -- $var is not a blessed SV reference\" ); | |
1113 | XSRETURN_UNDEF; | |
1114 | } | |
a0d0e21e | 1115 | |
d1b91892 | 1116 | =head2 Interface Strategy |
a0d0e21e LW |
1117 | |
1118 | When designing an interface between Perl and a C library a straight | |
1119 | translation from C to XS is often sufficient. The interface will often be | |
1120 | very C-like and occasionally nonintuitive, especially when the C function | |
1121 | modifies one of its parameters. In cases where the programmer wishes to | |
1122 | create a more Perl-like interface the following strategy may help to | |
1123 | identify the more critical parts of the interface. | |
1124 | ||
1125 | Identify the C functions which modify their parameters. The XSUBs for | |
1126 | these functions may be able to return lists to Perl, or may be | |
1127 | candidates to return undef or an empty list in case of failure. | |
1128 | ||
d1b91892 | 1129 | Identify which values are used by only the C and XSUB functions |
a0d0e21e LW |
1130 | themselves. If Perl does not need to access the contents of the value |
1131 | then it may not be necessary to provide a translation for that value | |
1132 | from C to Perl. | |
1133 | ||
1134 | Identify the pointers in the C function parameter lists and return | |
1135 | values. Some pointers can be handled in XS with the & unary operator on | |
1136 | the variable name while others will require the use of the * operator on | |
1137 | the type name. In general it is easier to work with the & operator. | |
1138 | ||
1139 | Identify the structures used by the C functions. In many | |
1140 | cases it may be helpful to use the T_PTROBJ typemap for | |
1141 | these structures so they can be manipulated by Perl as | |
1142 | blessed objects. | |
1143 | ||
a0d0e21e LW |
1144 | =head2 Perl Objects And C Structures |
1145 | ||
1146 | When dealing with C structures one should select either | |
1147 | B<T_PTROBJ> or B<T_PTRREF> for the XS type. Both types are | |
1148 | designed to handle pointers to complex objects. The | |
1149 | T_PTRREF type will allow the Perl object to be unblessed | |
1150 | while the T_PTROBJ type requires that the object be blessed. | |
1151 | By using T_PTROBJ one can achieve a form of type-checking | |
d1b91892 | 1152 | because the XSUB will attempt to verify that the Perl object |
a0d0e21e LW |
1153 | is of the expected type. |
1154 | ||
1155 | The following XS code shows the getnetconfigent() function which is used | |
8e07c86e | 1156 | with ONC+ TIRPC. The getnetconfigent() function will return a pointer to a |
a0d0e21e LW |
1157 | C structure and has the C prototype shown below. The example will |
1158 | demonstrate how the C pointer will become a Perl reference. Perl will | |
1159 | consider this reference to be a pointer to a blessed object and will | |
1160 | attempt to call a destructor for the object. A destructor will be | |
1161 | provided in the XS source to free the memory used by getnetconfigent(). | |
1162 | Destructors in XS can be created by specifying an XSUB function whose name | |
1163 | ends with the word B<DESTROY>. XS destructors can be used to free memory | |
1164 | which may have been malloc'd by another XSUB. | |
1165 | ||
1166 | struct netconfig *getnetconfigent(const char *netid); | |
1167 | ||
1168 | A C<typedef> will be created for C<struct netconfig>. The Perl | |
1169 | object will be blessed in a class matching the name of the C | |
1170 | type, with the tag C<Ptr> appended, and the name should not | |
1171 | have embedded spaces if it will be a Perl package name. The | |
1172 | destructor will be placed in a class corresponding to the | |
1173 | class of the object and the PREFIX keyword will be used to | |
1174 | trim the name to the word DESTROY as Perl will expect. | |
1175 | ||
1176 | typedef struct netconfig Netconfig; | |
1177 | ||
1178 | MODULE = RPC PACKAGE = RPC | |
1179 | ||
1180 | Netconfig * | |
1181 | getnetconfigent(netid) | |
8e07c86e | 1182 | char *netid |
a0d0e21e LW |
1183 | |
1184 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ | |
1185 | ||
1186 | void | |
1187 | rpcb_DESTROY(netconf) | |
8e07c86e | 1188 | Netconfig *netconf |
a0d0e21e LW |
1189 | CODE: |
1190 | printf("Now in NetconfigPtr::DESTROY\n"); | |
1191 | free( netconf ); | |
1192 | ||
1193 | This example requires the following typemap entry. Consult the typemap | |
1194 | section for more information about adding new typemaps for an extension. | |
1195 | ||
1196 | TYPEMAP | |
1197 | Netconfig * T_PTROBJ | |
1198 | ||
1199 | This example will be used with the following Perl statements. | |
1200 | ||
1201 | use RPC; | |
1202 | $netconf = getnetconfigent("udp"); | |
1203 | ||
1204 | When Perl destroys the object referenced by $netconf it will send the | |
1205 | object to the supplied XSUB DESTROY function. Perl cannot determine, and | |
1206 | does not care, that this object is a C struct and not a Perl object. In | |
1207 | this sense, there is no difference between the object created by the | |
1208 | getnetconfigent() XSUB and an object created by a normal Perl subroutine. | |
1209 | ||
a0d0e21e LW |
1210 | =head2 The Typemap |
1211 | ||
1212 | The typemap is a collection of code fragments which are used by the B<xsubpp> | |
1213 | compiler to map C function parameters and values to Perl values. The | |
1214 | typemap file may consist of three sections labeled C<TYPEMAP>, C<INPUT>, and | |
b56ec344 JH |
1215 | C<OUTPUT>. Any unlabelled initial section is assumed to be a C<TYPEMAP> |
1216 | section if a name is not explicitly specified. The INPUT section tells | |
1217 | the compiler how to translate Perl values | |
a0d0e21e LW |
1218 | into variables of certain C types. The OUTPUT section tells the compiler |
1219 | how to translate the values from certain C types into values Perl can | |
1220 | understand. The TYPEMAP section tells the compiler which of the INPUT and | |
1221 | OUTPUT code fragments should be used to map a given C type to a Perl value. | |
b56ec344 JH |
1222 | The section labels C<TYPEMAP>, C<INPUT>, or C<OUTPUT> must begin |
1223 | in the first column on a line by themselves, and must be in uppercase. | |
a0d0e21e LW |
1224 | |
1225 | The default typemap in the C<ext> directory of the Perl source contains many | |
1226 | useful types which can be used by Perl extensions. Some extensions define | |
1227 | additional typemaps which they keep in their own directory. These | |
1228 | additional typemaps may reference INPUT and OUTPUT maps in the main | |
1229 | typemap. The B<xsubpp> compiler will allow the extension's own typemap to | |
1230 | override any mappings which are in the default typemap. | |
1231 | ||
1232 | Most extensions which require a custom typemap will need only the TYPEMAP | |
1233 | section of the typemap file. The custom typemap used in the | |
1234 | getnetconfigent() example shown earlier demonstrates what may be the typical | |
1235 | use of extension typemaps. That typemap is used to equate a C structure | |
1236 | with the T_PTROBJ typemap. The typemap used by getnetconfigent() is shown | |
1237 | here. Note that the C type is separated from the XS type with a tab and | |
1238 | that the C unary operator C<*> is considered to be a part of the C type name. | |
1239 | ||
1240 | TYPEMAP | |
1241 | Netconfig *<tab>T_PTROBJ | |
1242 | ||
1748e8dd RS |
1243 | Here's a more complicated example: suppose that you wanted C<struct |
1244 | netconfig> to be blessed into the class C<Net::Config>. One way to do | |
1245 | this is to use underscores (_) to separate package names, as follows: | |
1246 | ||
1247 | typedef struct netconfig * Net_Config; | |
1248 | ||
1249 | And then provide a typemap entry C<T_PTROBJ_SPECIAL> that maps underscores to | |
1250 | double-colons (::), and declare C<Net_Config> to be of that type: | |
1251 | ||
1252 | ||
1253 | TYPEMAP | |
1254 | Net_Config T_PTROBJ_SPECIAL | |
1255 | ||
1256 | INPUT | |
1257 | T_PTROBJ_SPECIAL | |
1258 | if (sv_derived_from($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")) { | |
1259 | IV tmp = SvIV((SV*)SvRV($arg)); | |
1260 | $var = ($type) tmp; | |
1261 | } | |
1262 | else | |
1263 | croak(\"$var is not of type ${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\") | |
1264 | ||
1265 | OUTPUT | |
1266 | T_PTROBJ_SPECIAL | |
1267 | sv_setref_pv($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\", | |
1268 | (void*)$var); | |
1269 | ||
1270 | The INPUT and OUTPUT sections substitute underscores for double-colons | |
1271 | on the fly, giving the desired effect. This example demonstrates some | |
1272 | of the power and versatility of the typemap facility. | |
1273 | ||
a0d0e21e LW |
1274 | =head1 EXAMPLES |
1275 | ||
1276 | File C<RPC.xs>: Interface to some ONC+ RPC bind library functions. | |
1277 | ||
1278 | #include "EXTERN.h" | |
1279 | #include "perl.h" | |
1280 | #include "XSUB.h" | |
1281 | ||
1282 | #include <rpc/rpc.h> | |
1283 | ||
1284 | typedef struct netconfig Netconfig; | |
1285 | ||
1286 | MODULE = RPC PACKAGE = RPC | |
1287 | ||
e7ea3e70 | 1288 | SV * |
a0d0e21e | 1289 | rpcb_gettime(host="localhost") |
8e07c86e | 1290 | char *host |
c07a80fd | 1291 | PREINIT: |
a0d0e21e | 1292 | time_t timep; |
c07a80fd | 1293 | CODE: |
a0d0e21e LW |
1294 | ST(0) = sv_newmortal(); |
1295 | if( rpcb_gettime( host, &timep ) ) | |
1296 | sv_setnv( ST(0), (double)timep ); | |
a0d0e21e LW |
1297 | |
1298 | Netconfig * | |
1299 | getnetconfigent(netid="udp") | |
8e07c86e | 1300 | char *netid |
a0d0e21e LW |
1301 | |
1302 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ | |
1303 | ||
1304 | void | |
1305 | rpcb_DESTROY(netconf) | |
8e07c86e | 1306 | Netconfig *netconf |
a0d0e21e LW |
1307 | CODE: |
1308 | printf("NetconfigPtr::DESTROY\n"); | |
1309 | free( netconf ); | |
1310 | ||
1311 | File C<typemap>: Custom typemap for RPC.xs. | |
1312 | ||
1313 | TYPEMAP | |
1314 | Netconfig * T_PTROBJ | |
1315 | ||
1316 | File C<RPC.pm>: Perl module for the RPC extension. | |
1317 | ||
1318 | package RPC; | |
1319 | ||
1320 | require Exporter; | |
1321 | require DynaLoader; | |
1322 | @ISA = qw(Exporter DynaLoader); | |
1323 | @EXPORT = qw(rpcb_gettime getnetconfigent); | |
1324 | ||
1325 | bootstrap RPC; | |
1326 | 1; | |
1327 | ||
1328 | File C<rpctest.pl>: Perl test program for the RPC extension. | |
1329 | ||
1330 | use RPC; | |
1331 | ||
1332 | $netconf = getnetconfigent(); | |
1333 | $a = rpcb_gettime(); | |
1334 | print "time = $a\n"; | |
1335 | print "netconf = $netconf\n"; | |
1336 | ||
1337 | $netconf = getnetconfigent("tcp"); | |
1338 | $a = rpcb_gettime("poplar"); | |
1339 | print "time = $a\n"; | |
1340 | print "netconf = $netconf\n"; | |
1341 | ||
1342 | ||
c07a80fd | 1343 | =head1 XS VERSION |
1344 | ||
f27cfbbe | 1345 | This document covers features supported by C<xsubpp> 1.935. |
c07a80fd | 1346 | |
a0d0e21e LW |
1347 | =head1 AUTHOR |
1348 | ||
9607fc9c | 1349 | Dean Roehrich <F<roehrich@cray.com>> |
b772cb6e | 1350 | Jul 8, 1996 |