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1 | =head1 NAME |
2 | |
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3 | perlxs - XS language reference manual |
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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 | |
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26 | See L<perlxstut> for a tutorial on the whole extension creation process. |
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27 | |
28 | =head2 On The Road |
29 | |
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30 | Many of the examples which follow will concentrate on creating an interface |
31 | between Perl and the ONC+ RPC bind library functions. The rpcb_gettime() |
32 | function is used to demonstrate many features of the XS language. This |
33 | function has two parameters; the first is an input parameter and the second |
34 | is an output parameter. The function also returns a status value. |
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35 | |
36 | bool_t rpcb_gettime(const char *host, time_t *timep); |
37 | |
38 | From C this function will be called with the following |
39 | statements. |
40 | |
41 | #include <rpc/rpc.h> |
42 | bool_t status; |
43 | time_t timep; |
44 | status = rpcb_gettime( "localhost", &timep ); |
45 | |
46 | If an XSUB is created to offer a direct translation between this function |
47 | and Perl, then this XSUB will be used from Perl with the following code. |
48 | The $status and $timep variables will contain the output of the function. |
49 | |
50 | use RPC; |
51 | $status = rpcb_gettime( "localhost", $timep ); |
52 | |
53 | The following XS file shows an XS subroutine, or XSUB, which |
54 | demonstrates one possible interface to the rpcb_gettime() |
55 | function. This XSUB represents a direct translation between |
56 | C and Perl and so preserves the interface even from Perl. |
57 | This XSUB will be invoked from Perl with the usage shown |
58 | above. Note that the first three #include statements, for |
59 | C<EXTERN.h>, C<perl.h>, and C<XSUB.h>, will always be present at the |
60 | beginning of an XS file. This approach and others will be |
61 | expanded later in this document. |
62 | |
63 | #include "EXTERN.h" |
64 | #include "perl.h" |
65 | #include "XSUB.h" |
66 | #include <rpc/rpc.h> |
67 | |
68 | MODULE = RPC PACKAGE = RPC |
69 | |
70 | bool_t |
71 | rpcb_gettime(host,timep) |
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72 | char *host |
73 | time_t &timep |
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74 | OUTPUT: |
75 | timep |
76 | |
77 | Any extension to Perl, including those containing XSUBs, |
78 | should have a Perl module to serve as the bootstrap which |
79 | pulls the extension into Perl. This module will export the |
80 | extension's functions and variables to the Perl program and |
81 | will cause the extension's XSUBs to be linked into Perl. |
82 | The following module will be used for most of the examples |
83 | in this document and should be used from Perl with the C<use> |
84 | command as shown earlier. Perl modules are explained in |
85 | more detail later in this document. |
86 | |
87 | package RPC; |
88 | |
89 | require Exporter; |
90 | require DynaLoader; |
91 | @ISA = qw(Exporter DynaLoader); |
92 | @EXPORT = qw( rpcb_gettime ); |
93 | |
94 | bootstrap RPC; |
95 | 1; |
96 | |
97 | Throughout this document a variety of interfaces to the rpcb_gettime() |
98 | XSUB will be explored. The XSUBs will take their parameters in different |
99 | orders or will take different numbers of parameters. In each case the |
100 | XSUB is an abstraction between Perl and the real C rpcb_gettime() |
101 | function, and the XSUB must always ensure that the real rpcb_gettime() |
102 | function is called with the correct parameters. This abstraction will |
103 | allow the programmer to create a more Perl-like interface to the C |
104 | function. |
105 | |
106 | =head2 The Anatomy of an XSUB |
107 | |
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108 | The following XSUB allows a Perl program to access a C library function |
109 | called sin(). The XSUB will imitate the C function which takes a single |
110 | argument and returns a single value. |
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111 | |
112 | double |
113 | sin(x) |
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114 | double x |
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115 | |
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116 | When using C pointers the indirection operator C<*> should be considered |
117 | part of the type and the address operator C<&> should be considered part of |
118 | the variable, as is demonstrated in the rpcb_gettime() function above. See |
119 | the section on typemaps for more about handling qualifiers and unary |
120 | operators in C types. |
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121 | |
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122 | The function name and the return type must be placed on |
123 | separate lines. |
124 | |
125 | INCORRECT CORRECT |
126 | |
127 | double sin(x) double |
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128 | double x sin(x) |
129 | double x |
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130 | |
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131 | The function body may be indented or left-adjusted. The following example |
132 | shows a function with its body left-adjusted. Most examples in this |
133 | document will indent the body. |
134 | |
135 | CORRECT |
136 | |
137 | double |
138 | sin(x) |
139 | double x |
140 | |
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141 | =head2 The Argument Stack |
142 | |
143 | The argument stack is used to store the values which are |
144 | sent as parameters to the XSUB and to store the XSUB's |
145 | return value. In reality all Perl functions keep their |
146 | values on this stack at the same time, each limited to its |
147 | own range of positions on the stack. In this document the |
148 | first position on that stack which belongs to the active |
149 | function will be referred to as position 0 for that function. |
150 | |
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151 | XSUBs refer to their stack arguments with the macro B<ST(x)>, where I<x> |
152 | refers to a position in this XSUB's part of the stack. Position 0 for that |
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153 | function would be known to the XSUB as ST(0). The XSUB's incoming |
154 | parameters and outgoing return values always begin at ST(0). For many |
155 | simple cases the B<xsubpp> compiler will generate the code necessary to |
156 | handle the argument stack by embedding code fragments found in the |
157 | typemaps. In more complex cases the programmer must supply the code. |
158 | |
159 | =head2 The RETVAL Variable |
160 | |
161 | The RETVAL variable is a magic variable which always matches |
162 | the return type of the C library function. The B<xsubpp> compiler will |
163 | supply this variable in each XSUB and by default will use it to hold the |
164 | return value of the C library function being called. In simple cases the |
165 | value of RETVAL will be placed in ST(0) of the argument stack where it can |
166 | be received by Perl as the return value of the XSUB. |
167 | |
168 | If the XSUB has a return type of C<void> then the compiler will |
169 | not supply a RETVAL variable for that function. When using |
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170 | the PPCODE: directive the RETVAL variable is not needed, unless used |
171 | explicitly. |
172 | |
173 | If PPCODE: directive is not used, C<void> return value should be used |
174 | only for subroutines which do not return a value, I<even if> CODE: |
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175 | directive is used which sets ST(0) explicitly. |
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176 | |
177 | Older versions of this document recommended to use C<void> return |
178 | value in such cases. It was discovered that this could lead to |
179 | segfaults in cases when XSUB was I<truely> C<void>. This practice is |
180 | now deprecated, and may be not supported at some future version. Use |
181 | the return value C<SV *> in such cases. (Currently C<xsubpp> contains |
182 | some heuristic code which tries to disambiguate between "truely-void" |
183 | and "old-practice-declared-as-void" functions. Hence your code is at |
184 | mercy of this heuristics unless you use C<SV *> as return value.) |
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185 | |
186 | =head2 The MODULE Keyword |
187 | |
188 | The MODULE keyword is used to start the XS code and to |
189 | specify the package of the functions which are being |
190 | defined. All text preceding the first MODULE keyword is |
191 | considered C code and is passed through to the output |
192 | untouched. Every XS module will have a bootstrap function |
193 | which is used to hook the XSUBs into Perl. The package name |
194 | of this bootstrap function will match the value of the last |
195 | MODULE statement in the XS source files. The value of |
196 | MODULE should always remain constant within the same XS |
197 | file, though this is not required. |
198 | |
199 | The following example will start the XS code and will place |
200 | all functions in a package named RPC. |
201 | |
202 | MODULE = RPC |
203 | |
204 | =head2 The PACKAGE Keyword |
205 | |
206 | When functions within an XS source file must be separated into packages |
207 | the PACKAGE keyword should be used. This keyword is used with the MODULE |
208 | keyword and must follow immediately after it when used. |
209 | |
210 | MODULE = RPC PACKAGE = RPC |
211 | |
212 | [ XS code in package RPC ] |
213 | |
214 | MODULE = RPC PACKAGE = RPCB |
215 | |
216 | [ XS code in package RPCB ] |
217 | |
218 | MODULE = RPC PACKAGE = RPC |
219 | |
220 | [ XS code in package RPC ] |
221 | |
222 | Although this keyword is optional and in some cases provides redundant |
223 | information it should always be used. This keyword will ensure that the |
224 | XSUBs appear in the desired package. |
225 | |
226 | =head2 The PREFIX Keyword |
227 | |
228 | The PREFIX keyword designates prefixes which should be |
229 | removed from the Perl function names. If the C function is |
230 | C<rpcb_gettime()> and the PREFIX value is C<rpcb_> then Perl will |
231 | see this function as C<gettime()>. |
232 | |
233 | This keyword should follow the PACKAGE keyword when used. |
234 | If PACKAGE is not used then PREFIX should follow the MODULE |
235 | keyword. |
236 | |
237 | MODULE = RPC PREFIX = rpc_ |
238 | |
239 | MODULE = RPC PACKAGE = RPCB PREFIX = rpcb_ |
240 | |
241 | =head2 The OUTPUT: Keyword |
242 | |
243 | The OUTPUT: keyword indicates that certain function parameters should be |
244 | updated (new values made visible to Perl) when the XSUB terminates or that |
245 | certain values should be returned to the calling Perl function. For |
246 | simple functions, such as the sin() function above, the RETVAL variable is |
247 | automatically designated as an output value. In more complex functions |
248 | the B<xsubpp> compiler will need help to determine which variables are output |
249 | variables. |
250 | |
251 | This keyword will normally be used to complement the CODE: keyword. |
252 | The RETVAL variable is not recognized as an output variable when the |
253 | CODE: keyword is present. The OUTPUT: keyword is used in this |
254 | situation to tell the compiler that RETVAL really is an output |
255 | variable. |
256 | |
257 | The OUTPUT: keyword can also be used to indicate that function parameters |
258 | are output variables. This may be necessary when a parameter has been |
259 | modified within the function and the programmer would like the update to |
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260 | be seen by Perl. |
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261 | |
262 | bool_t |
263 | rpcb_gettime(host,timep) |
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264 | char *host |
265 | time_t &timep |
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266 | OUTPUT: |
267 | timep |
268 | |
269 | The OUTPUT: keyword will also allow an output parameter to |
270 | be mapped to a matching piece of code rather than to a |
271 | typemap. |
272 | |
273 | bool_t |
274 | rpcb_gettime(host,timep) |
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275 | char *host |
276 | time_t &timep |
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277 | OUTPUT: |
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278 | timep sv_setnv(ST(1), (double)timep); |
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279 | |
280 | =head2 The CODE: Keyword |
281 | |
282 | This keyword is used in more complicated XSUBs which require |
283 | special handling for the C function. The RETVAL variable is |
284 | available but will not be returned unless it is specified |
285 | under the OUTPUT: keyword. |
286 | |
287 | The following XSUB is for a C function which requires special handling of |
288 | its parameters. The Perl usage is given first. |
289 | |
290 | $status = rpcb_gettime( "localhost", $timep ); |
291 | |
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292 | The XSUB follows. |
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293 | |
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294 | bool_t |
295 | rpcb_gettime(host,timep) |
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296 | char *host |
297 | time_t timep |
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298 | CODE: |
299 | RETVAL = rpcb_gettime( host, &timep ); |
300 | OUTPUT: |
301 | timep |
302 | RETVAL |
303 | |
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304 | =head2 The INIT: Keyword |
305 | |
306 | The INIT: keyword allows initialization to be inserted into the XSUB before |
307 | the compiler generates the call to the C function. Unlike the CODE: keyword |
308 | above, this keyword does not affect the way the compiler handles RETVAL. |
309 | |
310 | bool_t |
311 | rpcb_gettime(host,timep) |
312 | char *host |
313 | time_t &timep |
314 | INIT: |
315 | printf("# Host is %s\n", host ); |
316 | OUTPUT: |
317 | timep |
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318 | |
319 | =head2 The NO_INIT Keyword |
320 | |
321 | The NO_INIT keyword is used to indicate that a function |
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322 | parameter is being used only as an output value. The B<xsubpp> |
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323 | compiler will normally generate code to read the values of |
324 | all function parameters from the argument stack and assign |
325 | them to C variables upon entry to the function. NO_INIT |
326 | will tell the compiler that some parameters will be used for |
327 | output rather than for input and that they will be handled |
328 | before the function terminates. |
329 | |
330 | The following example shows a variation of the rpcb_gettime() function. |
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331 | This function uses the timep variable only as an output variable and does |
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332 | not care about its initial contents. |
333 | |
334 | bool_t |
335 | rpcb_gettime(host,timep) |
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336 | char *host |
337 | time_t &timep = NO_INIT |
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338 | OUTPUT: |
339 | timep |
340 | |
341 | =head2 Initializing Function Parameters |
342 | |
343 | Function parameters are normally initialized with their |
344 | values from the argument stack. The typemaps contain the |
345 | code segments which are used to transfer the Perl values to |
346 | the C parameters. The programmer, however, is allowed to |
347 | override the typemaps and supply alternate initialization |
348 | code. |
349 | |
350 | The following code demonstrates how to supply initialization code for |
351 | function parameters. The initialization code is eval'd by the compiler |
352 | before it is added to the output so anything which should be interpreted |
353 | literally, such as double quotes, must be protected with backslashes. |
354 | |
355 | bool_t |
356 | rpcb_gettime(host,timep) |
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357 | char *host = (char *)SvPV(ST(0),na); |
358 | time_t &timep = 0; |
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359 | OUTPUT: |
360 | timep |
361 | |
362 | This should not be used to supply default values for parameters. One |
363 | would normally use this when a function parameter must be processed by |
364 | another library function before it can be used. Default parameters are |
365 | covered in the next section. |
366 | |
367 | =head2 Default Parameter Values |
368 | |
369 | Default values can be specified for function parameters by |
370 | placing an assignment statement in the parameter list. The |
371 | default value may be a number or a string. Defaults should |
372 | always be used on the right-most parameters only. |
373 | |
374 | To allow the XSUB for rpcb_gettime() to have a default host |
375 | value the parameters to the XSUB could be rearranged. The |
376 | XSUB will then call the real rpcb_gettime() function with |
377 | the parameters in the correct order. Perl will call this |
378 | XSUB with either of the following statements. |
379 | |
380 | $status = rpcb_gettime( $timep, $host ); |
381 | |
382 | $status = rpcb_gettime( $timep ); |
383 | |
384 | The XSUB will look like the code which follows. A CODE: |
385 | block is used to call the real rpcb_gettime() function with |
386 | the parameters in the correct order for that function. |
387 | |
388 | bool_t |
389 | rpcb_gettime(timep,host="localhost") |
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390 | char *host |
391 | time_t timep = NO_INIT |
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392 | CODE: |
393 | RETVAL = rpcb_gettime( host, &timep ); |
394 | OUTPUT: |
395 | timep |
396 | RETVAL |
397 | |
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398 | =head2 The PREINIT: Keyword |
399 | |
400 | The PREINIT: keyword allows extra variables to be declared before the |
401 | typemaps are expanded. If a variable is declared in a CODE: block then that |
402 | variable will follow any typemap code. This may result in a C syntax |
403 | error. To force the variable to be declared before the typemap code, place |
404 | it into a PREINIT: block. The PREINIT: keyword may be used one or more |
405 | times within an XSUB. |
406 | |
407 | The following examples are equivalent, but if the code is using complex |
408 | typemaps then the first example is safer. |
409 | |
410 | bool_t |
411 | rpcb_gettime(timep) |
412 | time_t timep = NO_INIT |
413 | PREINIT: |
414 | char *host = "localhost"; |
415 | CODE: |
416 | RETVAL = rpcb_gettime( host, &timep ); |
417 | OUTPUT: |
418 | timep |
419 | RETVAL |
420 | |
421 | A correct, but error-prone example. |
422 | |
423 | bool_t |
424 | rpcb_gettime(timep) |
425 | time_t timep = NO_INIT |
426 | CODE: |
427 | char *host = "localhost"; |
428 | RETVAL = rpcb_gettime( host, &timep ); |
429 | OUTPUT: |
430 | timep |
431 | RETVAL |
432 | |
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433 | =head2 The SCOPE: Keyword |
434 | |
435 | The SCOPE: keyword allows scoping to be enabled for a particular XSUB. If |
436 | enabled, the XSUB will invoke ENTER and LEAVE automatically. |
437 | |
438 | To support potentially complex type mappings, if a typemap entry used |
439 | by this XSUB contains a comment like C</*scope*/> then scoping will |
440 | automatically be enabled for that XSUB. |
441 | |
442 | To enable scoping: |
443 | |
444 | SCOPE: ENABLE |
445 | |
446 | To disable scoping: |
447 | |
448 | SCOPE: DISABLE |
449 | |
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450 | =head2 The INPUT: Keyword |
451 | |
452 | The XSUB's parameters are usually evaluated immediately after entering the |
453 | XSUB. The INPUT: keyword can be used to force those parameters to be |
454 | evaluated a little later. The INPUT: keyword can be used multiple times |
455 | within an XSUB and can be used to list one or more input variables. This |
456 | keyword is used with the PREINIT: keyword. |
457 | |
458 | The following example shows how the input parameter C<timep> can be |
459 | evaluated late, after a PREINIT. |
460 | |
461 | bool_t |
462 | rpcb_gettime(host,timep) |
463 | char *host |
464 | PREINIT: |
465 | time_t tt; |
466 | INPUT: |
467 | time_t timep |
468 | CODE: |
469 | RETVAL = rpcb_gettime( host, &tt ); |
470 | timep = tt; |
471 | OUTPUT: |
472 | timep |
473 | RETVAL |
474 | |
475 | The next example shows each input parameter evaluated late. |
476 | |
477 | bool_t |
478 | rpcb_gettime(host,timep) |
479 | PREINIT: |
480 | time_t tt; |
481 | INPUT: |
482 | char *host |
483 | PREINIT: |
484 | char *h; |
485 | INPUT: |
486 | time_t timep |
487 | CODE: |
488 | h = host; |
489 | RETVAL = rpcb_gettime( h, &tt ); |
490 | timep = tt; |
491 | OUTPUT: |
492 | timep |
493 | RETVAL |
494 | |
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495 | =head2 Variable-length Parameter Lists |
496 | |
497 | XSUBs can have variable-length parameter lists by specifying an ellipsis |
498 | C<(...)> in the parameter list. This use of the ellipsis is similar to that |
499 | found in ANSI C. The programmer is able to determine the number of |
500 | arguments passed to the XSUB by examining the C<items> variable which the |
501 | B<xsubpp> compiler supplies for all XSUBs. By using this mechanism one can |
502 | create an XSUB which accepts a list of parameters of unknown length. |
503 | |
504 | The I<host> parameter for the rpcb_gettime() XSUB can be |
505 | optional so the ellipsis can be used to indicate that the |
506 | XSUB will take a variable number of parameters. Perl should |
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507 | be able to call this XSUB with either of the following statements. |
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508 | |
509 | $status = rpcb_gettime( $timep, $host ); |
510 | |
511 | $status = rpcb_gettime( $timep ); |
512 | |
513 | The XS code, with ellipsis, follows. |
514 | |
515 | bool_t |
516 | rpcb_gettime(timep, ...) |
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517 | time_t timep = NO_INIT |
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518 | PREINIT: |
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519 | char *host = "localhost"; |
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520 | CODE: |
521 | if( items > 1 ) |
522 | host = (char *)SvPV(ST(1), na); |
523 | RETVAL = rpcb_gettime( host, &timep ); |
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524 | OUTPUT: |
525 | timep |
526 | RETVAL |
527 | |
528 | =head2 The PPCODE: Keyword |
529 | |
530 | The PPCODE: keyword is an alternate form of the CODE: keyword and is used |
531 | to tell the B<xsubpp> compiler that the programmer is supplying the code to |
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532 | control the argument stack for the XSUBs return values. Occasionally one |
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533 | will want an XSUB to return a list of values rather than a single value. |
534 | In these cases one must use PPCODE: and then explicitly push the list of |
535 | values on the stack. The PPCODE: and CODE: keywords are not used |
536 | together within the same XSUB. |
537 | |
538 | The following XSUB will call the C rpcb_gettime() function |
539 | and will return its two output values, timep and status, to |
540 | Perl as a single list. |
541 | |
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542 | void |
543 | rpcb_gettime(host) |
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544 | char *host |
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545 | PREINIT: |
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546 | time_t timep; |
547 | bool_t status; |
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548 | PPCODE: |
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549 | status = rpcb_gettime( host, &timep ); |
550 | EXTEND(sp, 2); |
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551 | PUSHs(sv_2mortal(newSViv(status))); |
552 | PUSHs(sv_2mortal(newSViv(timep))); |
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553 | |
554 | Notice that the programmer must supply the C code necessary |
555 | to have the real rpcb_gettime() function called and to have |
556 | the return values properly placed on the argument stack. |
557 | |
558 | The C<void> return type for this function tells the B<xsubpp> compiler that |
559 | the RETVAL variable is not needed or used and that it should not be created. |
560 | In most scenarios the void return type should be used with the PPCODE: |
561 | directive. |
562 | |
563 | The EXTEND() macro is used to make room on the argument |
564 | stack for 2 return values. The PPCODE: directive causes the |
565 | B<xsubpp> compiler to create a stack pointer called C<sp>, and it |
566 | is this pointer which is being used in the EXTEND() macro. |
567 | The values are then pushed onto the stack with the PUSHs() |
568 | macro. |
569 | |
570 | Now the rpcb_gettime() function can be used from Perl with |
571 | the following statement. |
572 | |
573 | ($status, $timep) = rpcb_gettime("localhost"); |
574 | |
575 | =head2 Returning Undef And Empty Lists |
576 | |
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577 | Occasionally the programmer will want to return simply |
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578 | C<undef> or an empty list if a function fails rather than a |
579 | separate status value. The rpcb_gettime() function offers |
580 | just this situation. If the function succeeds we would like |
581 | to have it return the time and if it fails we would like to |
582 | have undef returned. In the following Perl code the value |
583 | of $timep will either be undef or it will be a valid time. |
584 | |
585 | $timep = rpcb_gettime( "localhost" ); |
586 | |
e7ea3e70 |
587 | The following XSUB uses the C<SV *> return type as a mneumonic only, |
588 | and uses a CODE: block to indicate to the compiler |
a0d0e21e |
589 | that the programmer has supplied all the necessary code. The |
590 | sv_newmortal() call will initialize the return value to undef, making that |
591 | the default return value. |
592 | |
e7ea3e70 |
593 | SV * |
a0d0e21e |
594 | rpcb_gettime(host) |
595 | char * host |
c07a80fd |
596 | PREINIT: |
a0d0e21e |
597 | time_t timep; |
598 | bool_t x; |
c07a80fd |
599 | CODE: |
a0d0e21e |
600 | ST(0) = sv_newmortal(); |
601 | if( rpcb_gettime( host, &timep ) ) |
602 | sv_setnv( ST(0), (double)timep); |
a0d0e21e |
603 | |
604 | The next example demonstrates how one would place an explicit undef in the |
605 | return value, should the need arise. |
606 | |
e7ea3e70 |
607 | SV * |
a0d0e21e |
608 | rpcb_gettime(host) |
609 | char * host |
c07a80fd |
610 | PREINIT: |
a0d0e21e |
611 | time_t timep; |
612 | bool_t x; |
c07a80fd |
613 | CODE: |
a0d0e21e |
614 | ST(0) = sv_newmortal(); |
615 | if( rpcb_gettime( host, &timep ) ){ |
616 | sv_setnv( ST(0), (double)timep); |
617 | } |
618 | else{ |
619 | ST(0) = &sv_undef; |
620 | } |
a0d0e21e |
621 | |
622 | To return an empty list one must use a PPCODE: block and |
623 | then not push return values on the stack. |
624 | |
625 | void |
626 | rpcb_gettime(host) |
8e07c86e |
627 | char *host |
c07a80fd |
628 | PREINIT: |
a0d0e21e |
629 | time_t timep; |
c07a80fd |
630 | PPCODE: |
a0d0e21e |
631 | if( rpcb_gettime( host, &timep ) ) |
cb1a09d0 |
632 | PUSHs(sv_2mortal(newSViv(timep))); |
a0d0e21e |
633 | else{ |
634 | /* Nothing pushed on stack, so an empty */ |
635 | /* list is implicitly returned. */ |
636 | } |
a0d0e21e |
637 | |
f27cfbbe |
638 | Some people may be inclined to include an explicit C<return> in the above |
639 | XSUB, rather than letting control fall through to the end. In those |
640 | situations C<XSRETURN_EMPTY> should be used, instead. This will ensure that |
641 | the XSUB stack is properly adjusted. Consult L<perlguts/"API LISTING"> for |
642 | other C<XSRETURN> macros. |
643 | |
4633a7c4 |
644 | =head2 The REQUIRE: Keyword |
645 | |
646 | The REQUIRE: keyword is used to indicate the minimum version of the |
647 | B<xsubpp> compiler needed to compile the XS module. An XS module which |
5f05dabc |
648 | contains the following statement will compile with only B<xsubpp> version |
4633a7c4 |
649 | 1.922 or greater: |
650 | |
651 | REQUIRE: 1.922 |
652 | |
a0d0e21e |
653 | =head2 The CLEANUP: Keyword |
654 | |
655 | This keyword can be used when an XSUB requires special cleanup procedures |
656 | before it terminates. When the CLEANUP: keyword is used it must follow |
657 | any CODE:, PPCODE:, or OUTPUT: blocks which are present in the XSUB. The |
658 | code specified for the cleanup block will be added as the last statements |
659 | in the XSUB. |
660 | |
661 | =head2 The BOOT: Keyword |
662 | |
663 | The BOOT: keyword is used to add code to the extension's bootstrap |
664 | function. The bootstrap function is generated by the B<xsubpp> compiler and |
665 | normally holds the statements necessary to register any XSUBs with Perl. |
666 | With the BOOT: keyword the programmer can tell the compiler to add extra |
667 | statements to the bootstrap function. |
668 | |
669 | This keyword may be used any time after the first MODULE keyword and should |
670 | appear on a line by itself. The first blank line after the keyword will |
671 | terminate the code block. |
672 | |
673 | BOOT: |
674 | # The following message will be printed when the |
675 | # bootstrap function executes. |
676 | printf("Hello from the bootstrap!\n"); |
677 | |
c07a80fd |
678 | =head2 The VERSIONCHECK: Keyword |
679 | |
680 | The VERSIONCHECK: keyword corresponds to B<xsubpp>'s C<-versioncheck> and |
5f05dabc |
681 | C<-noversioncheck> options. This keyword overrides the command line |
c07a80fd |
682 | options. Version checking is enabled by default. When version checking is |
683 | enabled the XS module will attempt to verify that its version matches the |
684 | version of the PM module. |
685 | |
686 | To enable version checking: |
687 | |
688 | VERSIONCHECK: ENABLE |
689 | |
690 | To disable version checking: |
691 | |
692 | VERSIONCHECK: DISABLE |
693 | |
694 | =head2 The PROTOTYPES: Keyword |
695 | |
696 | The PROTOTYPES: keyword corresponds to B<xsubpp>'s C<-prototypes> and |
54310121 |
697 | C<-noprototypes> options. This keyword overrides the command line options. |
c07a80fd |
698 | Prototypes are enabled by default. When prototypes are enabled XSUBs will |
699 | be given Perl prototypes. This keyword may be used multiple times in an XS |
700 | module to enable and disable prototypes for different parts of the module. |
701 | |
702 | To enable prototypes: |
703 | |
704 | PROTOTYPES: ENABLE |
705 | |
706 | To disable prototypes: |
707 | |
708 | PROTOTYPES: DISABLE |
709 | |
710 | =head2 The PROTOTYPE: Keyword |
711 | |
712 | This keyword is similar to the PROTOTYPES: keyword above but can be used to |
713 | force B<xsubpp> to use a specific prototype for the XSUB. This keyword |
714 | overrides all other prototype options and keywords but affects only the |
715 | current XSUB. Consult L<perlsub/Prototypes> for information about Perl |
716 | prototypes. |
717 | |
718 | bool_t |
719 | rpcb_gettime(timep, ...) |
720 | time_t timep = NO_INIT |
721 | PROTOTYPE: $;$ |
722 | PREINIT: |
723 | char *host = "localhost"; |
724 | CODE: |
725 | if( items > 1 ) |
726 | host = (char *)SvPV(ST(1), na); |
727 | RETVAL = rpcb_gettime( host, &timep ); |
728 | OUTPUT: |
729 | timep |
730 | RETVAL |
731 | |
732 | =head2 The ALIAS: Keyword |
733 | |
68dc0745 |
734 | The ALIAS: keyword allows an XSUB to have two more unique Perl names |
c07a80fd |
735 | and to know which of those names was used when it was invoked. The Perl |
736 | names may be fully-qualified with package names. Each alias is given an |
737 | index. The compiler will setup a variable called C<ix> which contain the |
738 | index of the alias which was used. When the XSUB is called with its |
739 | declared name C<ix> will be 0. |
740 | |
741 | The following example will create aliases C<FOO::gettime()> and |
742 | C<BAR::getit()> for this function. |
743 | |
744 | bool_t |
745 | rpcb_gettime(host,timep) |
746 | char *host |
747 | time_t &timep |
748 | ALIAS: |
749 | FOO::gettime = 1 |
750 | BAR::getit = 2 |
751 | INIT: |
752 | printf("# ix = %d\n", ix ); |
753 | OUTPUT: |
754 | timep |
755 | |
756 | =head2 The INCLUDE: Keyword |
757 | |
758 | This keyword can be used to pull other files into the XS module. The other |
759 | files may have XS code. INCLUDE: can also be used to run a command to |
760 | generate the XS code to be pulled into the module. |
761 | |
762 | The file F<Rpcb1.xsh> contains our C<rpcb_gettime()> function: |
763 | |
764 | bool_t |
765 | rpcb_gettime(host,timep) |
766 | char *host |
767 | time_t &timep |
768 | OUTPUT: |
769 | timep |
770 | |
771 | The XS module can use INCLUDE: to pull that file into it. |
772 | |
773 | INCLUDE: Rpcb1.xsh |
774 | |
775 | If the parameters to the INCLUDE: keyword are followed by a pipe (C<|>) then |
776 | the compiler will interpret the parameters as a command. |
777 | |
778 | INCLUDE: cat Rpcb1.xsh | |
779 | |
780 | =head2 The CASE: Keyword |
781 | |
782 | The CASE: keyword allows an XSUB to have multiple distinct parts with each |
783 | part acting as a virtual XSUB. CASE: is greedy and if it is used then all |
784 | other XS keywords must be contained within a CASE:. This means nothing may |
785 | precede the first CASE: in the XSUB and anything following the last CASE: is |
786 | included in that case. |
787 | |
788 | A CASE: might switch via a parameter of the XSUB, via the C<ix> ALIAS: |
789 | variable (see L<"The ALIAS: Keyword">), or maybe via the C<items> variable |
790 | (see L<"Variable-length Parameter Lists">). The last CASE: becomes the |
791 | B<default> case if it is not associated with a conditional. The following |
792 | example shows CASE switched via C<ix> with a function C<rpcb_gettime()> |
793 | having an alias C<x_gettime()>. When the function is called as |
b772cb6e |
794 | C<rpcb_gettime()> its parameters are the usual C<(char *host, time_t *timep)>, |
795 | but when the function is called as C<x_gettime()> its parameters are |
c07a80fd |
796 | reversed, C<(time_t *timep, char *host)>. |
797 | |
798 | long |
799 | rpcb_gettime(a,b) |
800 | CASE: ix == 1 |
801 | ALIAS: |
802 | x_gettime = 1 |
803 | INPUT: |
804 | # 'a' is timep, 'b' is host |
805 | char *b |
806 | time_t a = NO_INIT |
807 | CODE: |
808 | RETVAL = rpcb_gettime( b, &a ); |
809 | OUTPUT: |
810 | a |
811 | RETVAL |
812 | CASE: |
813 | # 'a' is host, 'b' is timep |
814 | char *a |
815 | time_t &b = NO_INIT |
816 | OUTPUT: |
817 | b |
818 | RETVAL |
819 | |
820 | That function can be called with either of the following statements. Note |
821 | the different argument lists. |
822 | |
823 | $status = rpcb_gettime( $host, $timep ); |
824 | |
825 | $status = x_gettime( $timep, $host ); |
826 | |
827 | =head2 The & Unary Operator |
828 | |
829 | The & unary operator is used to tell the compiler that it should dereference |
830 | the object when it calls the C function. This is used when a CODE: block is |
831 | not used and the object is a not a pointer type (the object is an C<int> or |
832 | C<long> but not a C<int*> or C<long*>). |
833 | |
834 | The following XSUB will generate incorrect C code. The xsubpp compiler will |
835 | turn this into code which calls C<rpcb_gettime()> with parameters C<(char |
836 | *host, time_t timep)>, but the real C<rpcb_gettime()> wants the C<timep> |
837 | parameter to be of type C<time_t*> rather than C<time_t>. |
838 | |
839 | bool_t |
840 | rpcb_gettime(host,timep) |
841 | char *host |
842 | time_t timep |
843 | OUTPUT: |
844 | timep |
845 | |
846 | That problem is corrected by using the C<&> operator. The xsubpp compiler |
847 | will now turn this into code which calls C<rpcb_gettime()> correctly with |
848 | parameters C<(char *host, time_t *timep)>. It does this by carrying the |
849 | C<&> through, so the function call looks like C<rpcb_gettime(host, &timep)>. |
850 | |
851 | bool_t |
852 | rpcb_gettime(host,timep) |
853 | char *host |
854 | time_t &timep |
855 | OUTPUT: |
856 | timep |
857 | |
a0d0e21e |
858 | =head2 Inserting Comments and C Preprocessor Directives |
859 | |
f27cfbbe |
860 | C preprocessor directives are allowed within BOOT:, PREINIT: INIT:, |
5f05dabc |
861 | CODE:, PPCODE:, and CLEANUP: blocks, as well as outside the functions. |
f27cfbbe |
862 | Comments are allowed anywhere after the MODULE keyword. The compiler |
863 | will pass the preprocessor directives through untouched and will remove |
864 | the commented lines. |
b772cb6e |
865 | |
f27cfbbe |
866 | Comments can be added to XSUBs by placing a C<#> as the first |
867 | non-whitespace of a line. Care should be taken to avoid making the |
868 | comment look like a C preprocessor directive, lest it be interpreted as |
869 | such. The simplest way to prevent this is to put whitespace in front of |
870 | the C<#>. |
871 | |
f27cfbbe |
872 | If you use preprocessor directives to choose one of two |
873 | versions of a function, use |
874 | |
875 | #if ... version1 |
876 | #else /* ... version2 */ |
877 | #endif |
878 | |
879 | and not |
880 | |
881 | #if ... version1 |
882 | #endif |
883 | #if ... version2 |
884 | #endif |
885 | |
886 | because otherwise xsubpp will believe that you made a duplicate |
887 | definition of the function. Also, put a blank line before the |
888 | #else/#endif so it will not be seen as part of the function body. |
a0d0e21e |
889 | |
890 | =head2 Using XS With C++ |
891 | |
892 | If a function is defined as a C++ method then it will assume |
893 | its first argument is an object pointer. The object pointer |
894 | will be stored in a variable called THIS. The object should |
895 | have been created by C++ with the new() function and should |
cb1a09d0 |
896 | be blessed by Perl with the sv_setref_pv() macro. The |
897 | blessing of the object by Perl can be handled by a typemap. An example |
898 | typemap is shown at the end of this section. |
a0d0e21e |
899 | |
900 | If the method is defined as static it will call the C++ |
901 | function using the class::method() syntax. If the method is not static |
f27cfbbe |
902 | the function will be called using the THIS-E<gt>method() syntax. |
a0d0e21e |
903 | |
cb1a09d0 |
904 | The next examples will use the following C++ class. |
a0d0e21e |
905 | |
a5f75d66 |
906 | class color { |
cb1a09d0 |
907 | public: |
a5f75d66 |
908 | color(); |
909 | ~color(); |
cb1a09d0 |
910 | int blue(); |
911 | void set_blue( int ); |
912 | |
913 | private: |
914 | int c_blue; |
915 | }; |
916 | |
917 | The XSUBs for the blue() and set_blue() methods are defined with the class |
918 | name but the parameter for the object (THIS, or "self") is implicit and is |
919 | not listed. |
920 | |
921 | int |
922 | color::blue() |
a0d0e21e |
923 | |
924 | void |
cb1a09d0 |
925 | color::set_blue( val ) |
926 | int val |
a0d0e21e |
927 | |
cb1a09d0 |
928 | Both functions will expect an object as the first parameter. The xsubpp |
929 | compiler will call that object C<THIS> and will use it to call the specified |
930 | method. So in the C++ code the blue() and set_blue() methods will be called |
931 | in the following manner. |
a0d0e21e |
932 | |
cb1a09d0 |
933 | RETVAL = THIS->blue(); |
a0d0e21e |
934 | |
cb1a09d0 |
935 | THIS->set_blue( val ); |
a0d0e21e |
936 | |
cb1a09d0 |
937 | If the function's name is B<DESTROY> then the C++ C<delete> function will be |
938 | called and C<THIS> will be given as its parameter. |
a0d0e21e |
939 | |
d1b91892 |
940 | void |
cb1a09d0 |
941 | color::DESTROY() |
942 | |
943 | The C++ code will call C<delete>. |
944 | |
945 | delete THIS; |
a0d0e21e |
946 | |
cb1a09d0 |
947 | If the function's name is B<new> then the C++ C<new> function will be called |
948 | to create a dynamic C++ object. The XSUB will expect the class name, which |
949 | will be kept in a variable called C<CLASS>, to be given as the first |
950 | argument. |
a0d0e21e |
951 | |
cb1a09d0 |
952 | color * |
953 | color::new() |
a0d0e21e |
954 | |
cb1a09d0 |
955 | The C++ code will call C<new>. |
a0d0e21e |
956 | |
cb1a09d0 |
957 | RETVAL = new color(); |
958 | |
959 | The following is an example of a typemap that could be used for this C++ |
960 | example. |
961 | |
962 | TYPEMAP |
963 | color * O_OBJECT |
964 | |
965 | OUTPUT |
966 | # The Perl object is blessed into 'CLASS', which should be a |
967 | # char* having the name of the package for the blessing. |
968 | O_OBJECT |
969 | sv_setref_pv( $arg, CLASS, (void*)$var ); |
a6006777 |
970 | |
cb1a09d0 |
971 | INPUT |
972 | O_OBJECT |
973 | if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) ) |
974 | $var = ($type)SvIV((SV*)SvRV( $arg )); |
975 | else{ |
976 | warn( \"${Package}::$func_name() -- $var is not a blessed SV reference\" ); |
977 | XSRETURN_UNDEF; |
978 | } |
a0d0e21e |
979 | |
d1b91892 |
980 | =head2 Interface Strategy |
a0d0e21e |
981 | |
982 | When designing an interface between Perl and a C library a straight |
983 | translation from C to XS is often sufficient. The interface will often be |
984 | very C-like and occasionally nonintuitive, especially when the C function |
985 | modifies one of its parameters. In cases where the programmer wishes to |
986 | create a more Perl-like interface the following strategy may help to |
987 | identify the more critical parts of the interface. |
988 | |
989 | Identify the C functions which modify their parameters. The XSUBs for |
990 | these functions may be able to return lists to Perl, or may be |
991 | candidates to return undef or an empty list in case of failure. |
992 | |
d1b91892 |
993 | Identify which values are used by only the C and XSUB functions |
a0d0e21e |
994 | themselves. If Perl does not need to access the contents of the value |
995 | then it may not be necessary to provide a translation for that value |
996 | from C to Perl. |
997 | |
998 | Identify the pointers in the C function parameter lists and return |
999 | values. Some pointers can be handled in XS with the & unary operator on |
1000 | the variable name while others will require the use of the * operator on |
1001 | the type name. In general it is easier to work with the & operator. |
1002 | |
1003 | Identify the structures used by the C functions. In many |
1004 | cases it may be helpful to use the T_PTROBJ typemap for |
1005 | these structures so they can be manipulated by Perl as |
1006 | blessed objects. |
1007 | |
a0d0e21e |
1008 | =head2 Perl Objects And C Structures |
1009 | |
1010 | When dealing with C structures one should select either |
1011 | B<T_PTROBJ> or B<T_PTRREF> for the XS type. Both types are |
1012 | designed to handle pointers to complex objects. The |
1013 | T_PTRREF type will allow the Perl object to be unblessed |
1014 | while the T_PTROBJ type requires that the object be blessed. |
1015 | By using T_PTROBJ one can achieve a form of type-checking |
d1b91892 |
1016 | because the XSUB will attempt to verify that the Perl object |
a0d0e21e |
1017 | is of the expected type. |
1018 | |
1019 | The following XS code shows the getnetconfigent() function which is used |
8e07c86e |
1020 | with ONC+ TIRPC. The getnetconfigent() function will return a pointer to a |
a0d0e21e |
1021 | C structure and has the C prototype shown below. The example will |
1022 | demonstrate how the C pointer will become a Perl reference. Perl will |
1023 | consider this reference to be a pointer to a blessed object and will |
1024 | attempt to call a destructor for the object. A destructor will be |
1025 | provided in the XS source to free the memory used by getnetconfigent(). |
1026 | Destructors in XS can be created by specifying an XSUB function whose name |
1027 | ends with the word B<DESTROY>. XS destructors can be used to free memory |
1028 | which may have been malloc'd by another XSUB. |
1029 | |
1030 | struct netconfig *getnetconfigent(const char *netid); |
1031 | |
1032 | A C<typedef> will be created for C<struct netconfig>. The Perl |
1033 | object will be blessed in a class matching the name of the C |
1034 | type, with the tag C<Ptr> appended, and the name should not |
1035 | have embedded spaces if it will be a Perl package name. The |
1036 | destructor will be placed in a class corresponding to the |
1037 | class of the object and the PREFIX keyword will be used to |
1038 | trim the name to the word DESTROY as Perl will expect. |
1039 | |
1040 | typedef struct netconfig Netconfig; |
1041 | |
1042 | MODULE = RPC PACKAGE = RPC |
1043 | |
1044 | Netconfig * |
1045 | getnetconfigent(netid) |
8e07c86e |
1046 | char *netid |
a0d0e21e |
1047 | |
1048 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ |
1049 | |
1050 | void |
1051 | rpcb_DESTROY(netconf) |
8e07c86e |
1052 | Netconfig *netconf |
a0d0e21e |
1053 | CODE: |
1054 | printf("Now in NetconfigPtr::DESTROY\n"); |
1055 | free( netconf ); |
1056 | |
1057 | This example requires the following typemap entry. Consult the typemap |
1058 | section for more information about adding new typemaps for an extension. |
1059 | |
1060 | TYPEMAP |
1061 | Netconfig * T_PTROBJ |
1062 | |
1063 | This example will be used with the following Perl statements. |
1064 | |
1065 | use RPC; |
1066 | $netconf = getnetconfigent("udp"); |
1067 | |
1068 | When Perl destroys the object referenced by $netconf it will send the |
1069 | object to the supplied XSUB DESTROY function. Perl cannot determine, and |
1070 | does not care, that this object is a C struct and not a Perl object. In |
1071 | this sense, there is no difference between the object created by the |
1072 | getnetconfigent() XSUB and an object created by a normal Perl subroutine. |
1073 | |
a0d0e21e |
1074 | =head2 The Typemap |
1075 | |
1076 | The typemap is a collection of code fragments which are used by the B<xsubpp> |
1077 | compiler to map C function parameters and values to Perl values. The |
1078 | typemap file may consist of three sections labeled C<TYPEMAP>, C<INPUT>, and |
1079 | C<OUTPUT>. The INPUT section tells the compiler how to translate Perl values |
1080 | into variables of certain C types. The OUTPUT section tells the compiler |
1081 | how to translate the values from certain C types into values Perl can |
1082 | understand. The TYPEMAP section tells the compiler which of the INPUT and |
1083 | OUTPUT code fragments should be used to map a given C type to a Perl value. |
1084 | Each of the sections of the typemap must be preceded by one of the TYPEMAP, |
1085 | INPUT, or OUTPUT keywords. |
1086 | |
1087 | The default typemap in the C<ext> directory of the Perl source contains many |
1088 | useful types which can be used by Perl extensions. Some extensions define |
1089 | additional typemaps which they keep in their own directory. These |
1090 | additional typemaps may reference INPUT and OUTPUT maps in the main |
1091 | typemap. The B<xsubpp> compiler will allow the extension's own typemap to |
1092 | override any mappings which are in the default typemap. |
1093 | |
1094 | Most extensions which require a custom typemap will need only the TYPEMAP |
1095 | section of the typemap file. The custom typemap used in the |
1096 | getnetconfigent() example shown earlier demonstrates what may be the typical |
1097 | use of extension typemaps. That typemap is used to equate a C structure |
1098 | with the T_PTROBJ typemap. The typemap used by getnetconfigent() is shown |
1099 | here. Note that the C type is separated from the XS type with a tab and |
1100 | that the C unary operator C<*> is considered to be a part of the C type name. |
1101 | |
1102 | TYPEMAP |
1103 | Netconfig *<tab>T_PTROBJ |
1104 | |
1105 | =head1 EXAMPLES |
1106 | |
1107 | File C<RPC.xs>: Interface to some ONC+ RPC bind library functions. |
1108 | |
1109 | #include "EXTERN.h" |
1110 | #include "perl.h" |
1111 | #include "XSUB.h" |
1112 | |
1113 | #include <rpc/rpc.h> |
1114 | |
1115 | typedef struct netconfig Netconfig; |
1116 | |
1117 | MODULE = RPC PACKAGE = RPC |
1118 | |
e7ea3e70 |
1119 | SV * |
a0d0e21e |
1120 | rpcb_gettime(host="localhost") |
8e07c86e |
1121 | char *host |
c07a80fd |
1122 | PREINIT: |
a0d0e21e |
1123 | time_t timep; |
c07a80fd |
1124 | CODE: |
a0d0e21e |
1125 | ST(0) = sv_newmortal(); |
1126 | if( rpcb_gettime( host, &timep ) ) |
1127 | sv_setnv( ST(0), (double)timep ); |
a0d0e21e |
1128 | |
1129 | Netconfig * |
1130 | getnetconfigent(netid="udp") |
8e07c86e |
1131 | char *netid |
a0d0e21e |
1132 | |
1133 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ |
1134 | |
1135 | void |
1136 | rpcb_DESTROY(netconf) |
8e07c86e |
1137 | Netconfig *netconf |
a0d0e21e |
1138 | CODE: |
1139 | printf("NetconfigPtr::DESTROY\n"); |
1140 | free( netconf ); |
1141 | |
1142 | File C<typemap>: Custom typemap for RPC.xs. |
1143 | |
1144 | TYPEMAP |
1145 | Netconfig * T_PTROBJ |
1146 | |
1147 | File C<RPC.pm>: Perl module for the RPC extension. |
1148 | |
1149 | package RPC; |
1150 | |
1151 | require Exporter; |
1152 | require DynaLoader; |
1153 | @ISA = qw(Exporter DynaLoader); |
1154 | @EXPORT = qw(rpcb_gettime getnetconfigent); |
1155 | |
1156 | bootstrap RPC; |
1157 | 1; |
1158 | |
1159 | File C<rpctest.pl>: Perl test program for the RPC extension. |
1160 | |
1161 | use RPC; |
1162 | |
1163 | $netconf = getnetconfigent(); |
1164 | $a = rpcb_gettime(); |
1165 | print "time = $a\n"; |
1166 | print "netconf = $netconf\n"; |
1167 | |
1168 | $netconf = getnetconfigent("tcp"); |
1169 | $a = rpcb_gettime("poplar"); |
1170 | print "time = $a\n"; |
1171 | print "netconf = $netconf\n"; |
1172 | |
1173 | |
c07a80fd |
1174 | =head1 XS VERSION |
1175 | |
f27cfbbe |
1176 | This document covers features supported by C<xsubpp> 1.935. |
c07a80fd |
1177 | |
a0d0e21e |
1178 | =head1 AUTHOR |
1179 | |
9607fc9c |
1180 | Dean Roehrich <F<roehrich@cray.com>> |
b772cb6e |
1181 | Jul 8, 1996 |