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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 | |
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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 | |
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33 | =head2 On The Road |
34 | |
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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. |
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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) |
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77 | char *host |
78 | time_t &timep |
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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 | |
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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. |
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116 | |
117 | double |
118 | sin(x) |
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119 | double x |
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120 | |
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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. |
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126 | |
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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 |
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133 | double x sin(x) |
134 | double x |
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135 | |
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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 | |
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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 | |
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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 |
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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 |
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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: |
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180 | directive is used which sets ST(0) explicitly. |
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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.) |
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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 |
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265 | be seen by Perl. |
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266 | |
267 | bool_t |
268 | rpcb_gettime(host,timep) |
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269 | char *host |
270 | time_t &timep |
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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 |
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276 | typemap. |
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277 | |
278 | bool_t |
279 | rpcb_gettime(host,timep) |
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280 | char *host |
281 | time_t &timep |
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282 | OUTPUT: |
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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. |
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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 | |
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308 | The XSUB follows. |
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309 | |
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310 | bool_t |
311 | rpcb_gettime(host,timep) |
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312 | char *host |
313 | time_t timep |
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314 | CODE: |
315 | RETVAL = rpcb_gettime( host, &timep ); |
316 | OUTPUT: |
317 | timep |
318 | RETVAL |
319 | |
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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 |
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334 | |
335 | =head2 The NO_INIT Keyword |
336 | |
337 | The NO_INIT keyword is used to indicate that a function |
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338 | parameter is being used only as an output value. The B<xsubpp> |
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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. |
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347 | This function uses the timep variable only as an output variable and does |
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348 | not care about its initial contents. |
349 | |
350 | bool_t |
351 | rpcb_gettime(host,timep) |
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352 | char *host |
353 | time_t &timep = NO_INIT |
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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 |
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363 | override the typemaps and supply alternate (or additional) |
364 | initialization code. |
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365 | |
366 | The following code demonstrates how to supply initialization code for |
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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<$type> can be used as in typemaps. |
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372 | |
373 | bool_t |
374 | rpcb_gettime(host,timep) |
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375 | char *host = (char *)SvPV($arg,PL_na); |
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376 | time_t &timep = 0; |
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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 | |
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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]}*/ |
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399 | char *host + SvOK($v{time}) ? SvPV($arg,PL_na) : NULL; |
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400 | OUTPUT: |
401 | timep |
402 | |
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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") |
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426 | char *host |
427 | time_t timep = NO_INIT |
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428 | CODE: |
429 | RETVAL = rpcb_gettime( host, &timep ); |
430 | OUTPUT: |
431 | timep |
432 | RETVAL |
433 | |
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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 | |
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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 | |
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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 | |
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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 |
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543 | be able to call this XSUB with either of the following statements. |
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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, ...) |
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553 | time_t timep = NO_INIT |
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554 | PREINIT: |
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555 | char *host = "localhost"; |
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556 | STRLEN n_a; |
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557 | CODE: |
558 | if( items > 1 ) |
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559 | host = (char *)SvPV(ST(1), n_a); |
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560 | RETVAL = rpcb_gettime( host, &timep ); |
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561 | OUTPUT: |
562 | timep |
563 | RETVAL |
564 | |
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565 | =head2 The C_ARGS: Keyword |
566 | |
567 | The C_ARGS: keyword allows creating of XSUBS which have different |
568 | calling sequence from Perl than from C, without a need to write |
569 | CODE: or CPPCODE: section. The contents of the C_ARGS: paragraph is |
570 | put as the argument to the called C function without any change. |
571 | |
572 | For example, suppose that C function is declared as |
573 | |
574 | symbolic nth_derivative(int n, symbolic function, int flags); |
575 | |
576 | and that the default flags are kept in a global C variable |
577 | C<default_flags>. Suppose that you want to create an interface which |
578 | is called as |
579 | |
580 | $second_deriv = $function->nth_derivative(2); |
581 | |
582 | To do this, declare the XSUB as |
583 | |
584 | symbolic |
585 | nth_derivative(function, n) |
586 | symbolic function |
587 | int n |
588 | C_ARGS: |
589 | n, function, default_flags |
590 | |
a0d0e21e |
591 | =head2 The PPCODE: Keyword |
592 | |
593 | The PPCODE: keyword is an alternate form of the CODE: keyword and is used |
594 | to tell the B<xsubpp> compiler that the programmer is supplying the code to |
d1b91892 |
595 | control the argument stack for the XSUBs return values. Occasionally one |
a0d0e21e |
596 | will want an XSUB to return a list of values rather than a single value. |
597 | In these cases one must use PPCODE: and then explicitly push the list of |
598 | values on the stack. The PPCODE: and CODE: keywords are not used |
599 | together within the same XSUB. |
600 | |
601 | The following XSUB will call the C rpcb_gettime() function |
602 | and will return its two output values, timep and status, to |
603 | Perl as a single list. |
604 | |
d1b91892 |
605 | void |
606 | rpcb_gettime(host) |
8e07c86e |
607 | char *host |
c07a80fd |
608 | PREINIT: |
a0d0e21e |
609 | time_t timep; |
610 | bool_t status; |
c07a80fd |
611 | PPCODE: |
a0d0e21e |
612 | status = rpcb_gettime( host, &timep ); |
924508f0 |
613 | EXTEND(SP, 2); |
cb1a09d0 |
614 | PUSHs(sv_2mortal(newSViv(status))); |
615 | PUSHs(sv_2mortal(newSViv(timep))); |
a0d0e21e |
616 | |
617 | Notice that the programmer must supply the C code necessary |
618 | to have the real rpcb_gettime() function called and to have |
619 | the return values properly placed on the argument stack. |
620 | |
621 | The C<void> return type for this function tells the B<xsubpp> compiler that |
622 | the RETVAL variable is not needed or used and that it should not be created. |
623 | In most scenarios the void return type should be used with the PPCODE: |
624 | directive. |
625 | |
626 | The EXTEND() macro is used to make room on the argument |
627 | stack for 2 return values. The PPCODE: directive causes the |
924508f0 |
628 | B<xsubpp> compiler to create a stack pointer available as C<SP>, and it |
a0d0e21e |
629 | is this pointer which is being used in the EXTEND() macro. |
630 | The values are then pushed onto the stack with the PUSHs() |
631 | macro. |
632 | |
633 | Now the rpcb_gettime() function can be used from Perl with |
634 | the following statement. |
635 | |
636 | ($status, $timep) = rpcb_gettime("localhost"); |
637 | |
ef50df4b |
638 | When handling output parameters with a PPCODE section, be sure to handle |
639 | 'set' magic properly. See L<perlguts> for details about 'set' magic. |
640 | |
a0d0e21e |
641 | =head2 Returning Undef And Empty Lists |
642 | |
5f05dabc |
643 | Occasionally the programmer will want to return simply |
a0d0e21e |
644 | C<undef> or an empty list if a function fails rather than a |
645 | separate status value. The rpcb_gettime() function offers |
646 | just this situation. If the function succeeds we would like |
647 | to have it return the time and if it fails we would like to |
648 | have undef returned. In the following Perl code the value |
649 | of $timep will either be undef or it will be a valid time. |
650 | |
651 | $timep = rpcb_gettime( "localhost" ); |
652 | |
7b8d334a |
653 | The following XSUB uses the C<SV *> return type as a mnemonic only, |
e7ea3e70 |
654 | and uses a CODE: block to indicate to the compiler |
a0d0e21e |
655 | that the programmer has supplied all the necessary code. The |
656 | sv_newmortal() call will initialize the return value to undef, making that |
657 | the default return value. |
658 | |
e7ea3e70 |
659 | SV * |
a0d0e21e |
660 | rpcb_gettime(host) |
661 | char * host |
c07a80fd |
662 | PREINIT: |
a0d0e21e |
663 | time_t timep; |
664 | bool_t x; |
c07a80fd |
665 | CODE: |
a0d0e21e |
666 | ST(0) = sv_newmortal(); |
667 | if( rpcb_gettime( host, &timep ) ) |
668 | sv_setnv( ST(0), (double)timep); |
a0d0e21e |
669 | |
670 | The next example demonstrates how one would place an explicit undef in the |
671 | return value, should the need arise. |
672 | |
e7ea3e70 |
673 | SV * |
a0d0e21e |
674 | rpcb_gettime(host) |
675 | char * host |
c07a80fd |
676 | PREINIT: |
a0d0e21e |
677 | time_t timep; |
678 | bool_t x; |
c07a80fd |
679 | CODE: |
a0d0e21e |
680 | ST(0) = sv_newmortal(); |
681 | if( rpcb_gettime( host, &timep ) ){ |
682 | sv_setnv( ST(0), (double)timep); |
683 | } |
684 | else{ |
9cde0e7f |
685 | ST(0) = &PL_sv_undef; |
a0d0e21e |
686 | } |
a0d0e21e |
687 | |
688 | To return an empty list one must use a PPCODE: block and |
689 | then not push return values on the stack. |
690 | |
691 | void |
692 | rpcb_gettime(host) |
8e07c86e |
693 | char *host |
c07a80fd |
694 | PREINIT: |
a0d0e21e |
695 | time_t timep; |
c07a80fd |
696 | PPCODE: |
a0d0e21e |
697 | if( rpcb_gettime( host, &timep ) ) |
cb1a09d0 |
698 | PUSHs(sv_2mortal(newSViv(timep))); |
a0d0e21e |
699 | else{ |
700 | /* Nothing pushed on stack, so an empty */ |
701 | /* list is implicitly returned. */ |
702 | } |
a0d0e21e |
703 | |
f27cfbbe |
704 | Some people may be inclined to include an explicit C<return> in the above |
705 | XSUB, rather than letting control fall through to the end. In those |
706 | situations C<XSRETURN_EMPTY> should be used, instead. This will ensure that |
707 | the XSUB stack is properly adjusted. Consult L<perlguts/"API LISTING"> for |
708 | other C<XSRETURN> macros. |
709 | |
4633a7c4 |
710 | =head2 The REQUIRE: Keyword |
711 | |
712 | The REQUIRE: keyword is used to indicate the minimum version of the |
713 | B<xsubpp> compiler needed to compile the XS module. An XS module which |
5f05dabc |
714 | contains the following statement will compile with only B<xsubpp> version |
4633a7c4 |
715 | 1.922 or greater: |
716 | |
717 | REQUIRE: 1.922 |
718 | |
a0d0e21e |
719 | =head2 The CLEANUP: Keyword |
720 | |
721 | This keyword can be used when an XSUB requires special cleanup procedures |
722 | before it terminates. When the CLEANUP: keyword is used it must follow |
723 | any CODE:, PPCODE:, or OUTPUT: blocks which are present in the XSUB. The |
724 | code specified for the cleanup block will be added as the last statements |
725 | in the XSUB. |
726 | |
727 | =head2 The BOOT: Keyword |
728 | |
729 | The BOOT: keyword is used to add code to the extension's bootstrap |
730 | function. The bootstrap function is generated by the B<xsubpp> compiler and |
731 | normally holds the statements necessary to register any XSUBs with Perl. |
732 | With the BOOT: keyword the programmer can tell the compiler to add extra |
733 | statements to the bootstrap function. |
734 | |
735 | This keyword may be used any time after the first MODULE keyword and should |
736 | appear on a line by itself. The first blank line after the keyword will |
737 | terminate the code block. |
738 | |
739 | BOOT: |
740 | # The following message will be printed when the |
741 | # bootstrap function executes. |
742 | printf("Hello from the bootstrap!\n"); |
743 | |
c07a80fd |
744 | =head2 The VERSIONCHECK: Keyword |
745 | |
746 | The VERSIONCHECK: keyword corresponds to B<xsubpp>'s C<-versioncheck> and |
5f05dabc |
747 | C<-noversioncheck> options. This keyword overrides the command line |
c07a80fd |
748 | options. Version checking is enabled by default. When version checking is |
749 | enabled the XS module will attempt to verify that its version matches the |
750 | version of the PM module. |
751 | |
752 | To enable version checking: |
753 | |
754 | VERSIONCHECK: ENABLE |
755 | |
756 | To disable version checking: |
757 | |
758 | VERSIONCHECK: DISABLE |
759 | |
760 | =head2 The PROTOTYPES: Keyword |
761 | |
762 | The PROTOTYPES: keyword corresponds to B<xsubpp>'s C<-prototypes> and |
54310121 |
763 | C<-noprototypes> options. This keyword overrides the command line options. |
c07a80fd |
764 | Prototypes are enabled by default. When prototypes are enabled XSUBs will |
765 | be given Perl prototypes. This keyword may be used multiple times in an XS |
766 | module to enable and disable prototypes for different parts of the module. |
767 | |
768 | To enable prototypes: |
769 | |
770 | PROTOTYPES: ENABLE |
771 | |
772 | To disable prototypes: |
773 | |
774 | PROTOTYPES: DISABLE |
775 | |
776 | =head2 The PROTOTYPE: Keyword |
777 | |
778 | This keyword is similar to the PROTOTYPES: keyword above but can be used to |
779 | force B<xsubpp> to use a specific prototype for the XSUB. This keyword |
780 | overrides all other prototype options and keywords but affects only the |
781 | current XSUB. Consult L<perlsub/Prototypes> for information about Perl |
782 | prototypes. |
783 | |
784 | bool_t |
785 | rpcb_gettime(timep, ...) |
786 | time_t timep = NO_INIT |
787 | PROTOTYPE: $;$ |
788 | PREINIT: |
789 | char *host = "localhost"; |
2d8e6c8d |
790 | STRLEN n_a; |
c07a80fd |
791 | CODE: |
792 | if( items > 1 ) |
2d8e6c8d |
793 | host = (char *)SvPV(ST(1), n_a); |
c07a80fd |
794 | RETVAL = rpcb_gettime( host, &timep ); |
795 | OUTPUT: |
796 | timep |
797 | RETVAL |
798 | |
799 | =head2 The ALIAS: Keyword |
800 | |
cfc02341 |
801 | The ALIAS: keyword allows an XSUB to have two or more unique Perl names |
c07a80fd |
802 | and to know which of those names was used when it was invoked. The Perl |
803 | names may be fully-qualified with package names. Each alias is given an |
804 | index. The compiler will setup a variable called C<ix> which contain the |
805 | index of the alias which was used. When the XSUB is called with its |
806 | declared name C<ix> will be 0. |
807 | |
808 | The following example will create aliases C<FOO::gettime()> and |
809 | C<BAR::getit()> for this function. |
810 | |
811 | bool_t |
812 | rpcb_gettime(host,timep) |
813 | char *host |
814 | time_t &timep |
815 | ALIAS: |
816 | FOO::gettime = 1 |
817 | BAR::getit = 2 |
818 | INIT: |
819 | printf("# ix = %d\n", ix ); |
820 | OUTPUT: |
821 | timep |
822 | |
cfc02341 |
823 | =head2 The INTERFACE: Keyword |
824 | |
825 | This keyword declares the current XSUB as a keeper of the given |
826 | calling signature. If some text follows this keyword, it is |
827 | considered as a list of functions which have this signature, and |
828 | should be attached to XSUBs. |
829 | |
830 | Say, if you have 4 functions multiply(), divide(), add(), subtract() all |
831 | having the signature |
832 | |
833 | symbolic f(symbolic, symbolic); |
834 | |
835 | you code them all by using XSUB |
836 | |
837 | symbolic |
838 | interface_s_ss(arg1, arg2) |
839 | symbolic arg1 |
840 | symbolic arg2 |
841 | INTERFACE: |
842 | multiply divide |
843 | add subtract |
844 | |
845 | The advantage of this approach comparing to ALIAS: keyword is that one |
846 | can attach an extra function remainder() at runtime by using |
847 | |
848 | CV *mycv = newXSproto("Symbolic::remainder", |
849 | XS_Symbolic_interface_s_ss, __FILE__, "$$"); |
850 | XSINTERFACE_FUNC_SET(mycv, remainder); |
851 | |
852 | (This example supposes that there was no INTERFACE_MACRO: section, |
853 | otherwise one needs to use something else instead of |
854 | C<XSINTERFACE_FUNC_SET>.) |
855 | |
856 | =head2 The INTERFACE_MACRO: Keyword |
857 | |
858 | This keyword allows one to define an INTERFACE using a different way |
859 | to extract a function pointer from an XSUB. The text which follows |
860 | this keyword should give the name of macros which would extract/set a |
861 | function pointer. The extractor macro is given return type, C<CV*>, |
862 | and C<XSANY.any_dptr> for this C<CV*>. The setter macro is given cv, |
863 | and the function pointer. |
864 | |
865 | The default value is C<XSINTERFACE_FUNC> and C<XSINTERFACE_FUNC_SET>. |
866 | An INTERFACE keyword with an empty list of functions can be omitted if |
867 | INTERFACE_MACRO keyword is used. |
868 | |
869 | Suppose that in the previous example functions pointers for |
870 | multiply(), divide(), add(), subtract() are kept in a global C array |
871 | C<fp[]> with offsets being C<multiply_off>, C<divide_off>, C<add_off>, |
872 | C<subtract_off>. Then one can use |
873 | |
874 | #define XSINTERFACE_FUNC_BYOFFSET(ret,cv,f) \ |
875 | ((XSINTERFACE_CVT(ret,))fp[CvXSUBANY(cv).any_i32]) |
876 | #define XSINTERFACE_FUNC_BYOFFSET_set(cv,f) \ |
877 | CvXSUBANY(cv).any_i32 = CAT2( f, _off ) |
878 | |
879 | in C section, |
880 | |
881 | symbolic |
882 | interface_s_ss(arg1, arg2) |
883 | symbolic arg1 |
884 | symbolic arg2 |
885 | INTERFACE_MACRO: |
886 | XSINTERFACE_FUNC_BYOFFSET |
887 | XSINTERFACE_FUNC_BYOFFSET_set |
888 | INTERFACE: |
889 | multiply divide |
890 | add subtract |
891 | |
892 | in XSUB section. |
893 | |
c07a80fd |
894 | =head2 The INCLUDE: Keyword |
895 | |
896 | This keyword can be used to pull other files into the XS module. The other |
897 | files may have XS code. INCLUDE: can also be used to run a command to |
898 | generate the XS code to be pulled into the module. |
899 | |
900 | The file F<Rpcb1.xsh> contains our C<rpcb_gettime()> function: |
901 | |
902 | bool_t |
903 | rpcb_gettime(host,timep) |
904 | char *host |
905 | time_t &timep |
906 | OUTPUT: |
907 | timep |
908 | |
909 | The XS module can use INCLUDE: to pull that file into it. |
910 | |
911 | INCLUDE: Rpcb1.xsh |
912 | |
913 | If the parameters to the INCLUDE: keyword are followed by a pipe (C<|>) then |
914 | the compiler will interpret the parameters as a command. |
915 | |
916 | INCLUDE: cat Rpcb1.xsh | |
917 | |
918 | =head2 The CASE: Keyword |
919 | |
920 | The CASE: keyword allows an XSUB to have multiple distinct parts with each |
921 | part acting as a virtual XSUB. CASE: is greedy and if it is used then all |
922 | other XS keywords must be contained within a CASE:. This means nothing may |
923 | precede the first CASE: in the XSUB and anything following the last CASE: is |
924 | included in that case. |
925 | |
926 | A CASE: might switch via a parameter of the XSUB, via the C<ix> ALIAS: |
927 | variable (see L<"The ALIAS: Keyword">), or maybe via the C<items> variable |
928 | (see L<"Variable-length Parameter Lists">). The last CASE: becomes the |
929 | B<default> case if it is not associated with a conditional. The following |
930 | example shows CASE switched via C<ix> with a function C<rpcb_gettime()> |
931 | having an alias C<x_gettime()>. When the function is called as |
b772cb6e |
932 | C<rpcb_gettime()> its parameters are the usual C<(char *host, time_t *timep)>, |
933 | but when the function is called as C<x_gettime()> its parameters are |
c07a80fd |
934 | reversed, C<(time_t *timep, char *host)>. |
935 | |
936 | long |
937 | rpcb_gettime(a,b) |
938 | CASE: ix == 1 |
939 | ALIAS: |
940 | x_gettime = 1 |
941 | INPUT: |
942 | # 'a' is timep, 'b' is host |
943 | char *b |
944 | time_t a = NO_INIT |
945 | CODE: |
946 | RETVAL = rpcb_gettime( b, &a ); |
947 | OUTPUT: |
948 | a |
949 | RETVAL |
950 | CASE: |
951 | # 'a' is host, 'b' is timep |
952 | char *a |
953 | time_t &b = NO_INIT |
954 | OUTPUT: |
955 | b |
956 | RETVAL |
957 | |
958 | That function can be called with either of the following statements. Note |
959 | the different argument lists. |
960 | |
961 | $status = rpcb_gettime( $host, $timep ); |
962 | |
963 | $status = x_gettime( $timep, $host ); |
964 | |
965 | =head2 The & Unary Operator |
966 | |
967 | The & unary operator is used to tell the compiler that it should dereference |
968 | the object when it calls the C function. This is used when a CODE: block is |
969 | not used and the object is a not a pointer type (the object is an C<int> or |
970 | C<long> but not a C<int*> or C<long*>). |
971 | |
972 | The following XSUB will generate incorrect C code. The xsubpp compiler will |
973 | turn this into code which calls C<rpcb_gettime()> with parameters C<(char |
974 | *host, time_t timep)>, but the real C<rpcb_gettime()> wants the C<timep> |
975 | parameter to be of type C<time_t*> rather than C<time_t>. |
976 | |
977 | bool_t |
978 | rpcb_gettime(host,timep) |
979 | char *host |
980 | time_t timep |
981 | OUTPUT: |
982 | timep |
983 | |
984 | That problem is corrected by using the C<&> operator. The xsubpp compiler |
985 | will now turn this into code which calls C<rpcb_gettime()> correctly with |
986 | parameters C<(char *host, time_t *timep)>. It does this by carrying the |
987 | C<&> through, so the function call looks like C<rpcb_gettime(host, &timep)>. |
988 | |
989 | bool_t |
990 | rpcb_gettime(host,timep) |
991 | char *host |
992 | time_t &timep |
993 | OUTPUT: |
994 | timep |
995 | |
a0d0e21e |
996 | =head2 Inserting Comments and C Preprocessor Directives |
997 | |
f27cfbbe |
998 | C preprocessor directives are allowed within BOOT:, PREINIT: INIT:, |
5f05dabc |
999 | CODE:, PPCODE:, and CLEANUP: blocks, as well as outside the functions. |
f27cfbbe |
1000 | Comments are allowed anywhere after the MODULE keyword. The compiler |
1001 | will pass the preprocessor directives through untouched and will remove |
1002 | the commented lines. |
b772cb6e |
1003 | |
f27cfbbe |
1004 | Comments can be added to XSUBs by placing a C<#> as the first |
1005 | non-whitespace of a line. Care should be taken to avoid making the |
1006 | comment look like a C preprocessor directive, lest it be interpreted as |
1007 | such. The simplest way to prevent this is to put whitespace in front of |
1008 | the C<#>. |
1009 | |
f27cfbbe |
1010 | If you use preprocessor directives to choose one of two |
1011 | versions of a function, use |
1012 | |
1013 | #if ... version1 |
1014 | #else /* ... version2 */ |
1015 | #endif |
1016 | |
1017 | and not |
1018 | |
1019 | #if ... version1 |
1020 | #endif |
1021 | #if ... version2 |
1022 | #endif |
1023 | |
1024 | because otherwise xsubpp will believe that you made a duplicate |
1025 | definition of the function. Also, put a blank line before the |
1026 | #else/#endif so it will not be seen as part of the function body. |
a0d0e21e |
1027 | |
1028 | =head2 Using XS With C++ |
1029 | |
1030 | If a function is defined as a C++ method then it will assume |
1031 | its first argument is an object pointer. The object pointer |
1032 | will be stored in a variable called THIS. The object should |
1033 | have been created by C++ with the new() function and should |
cb1a09d0 |
1034 | be blessed by Perl with the sv_setref_pv() macro. The |
1035 | blessing of the object by Perl can be handled by a typemap. An example |
1036 | typemap is shown at the end of this section. |
a0d0e21e |
1037 | |
1038 | If the method is defined as static it will call the C++ |
1039 | function using the class::method() syntax. If the method is not static |
f27cfbbe |
1040 | the function will be called using the THIS-E<gt>method() syntax. |
a0d0e21e |
1041 | |
cb1a09d0 |
1042 | The next examples will use the following C++ class. |
a0d0e21e |
1043 | |
a5f75d66 |
1044 | class color { |
cb1a09d0 |
1045 | public: |
a5f75d66 |
1046 | color(); |
1047 | ~color(); |
cb1a09d0 |
1048 | int blue(); |
1049 | void set_blue( int ); |
1050 | |
1051 | private: |
1052 | int c_blue; |
1053 | }; |
1054 | |
1055 | The XSUBs for the blue() and set_blue() methods are defined with the class |
1056 | name but the parameter for the object (THIS, or "self") is implicit and is |
1057 | not listed. |
1058 | |
1059 | int |
1060 | color::blue() |
a0d0e21e |
1061 | |
1062 | void |
cb1a09d0 |
1063 | color::set_blue( val ) |
1064 | int val |
a0d0e21e |
1065 | |
cb1a09d0 |
1066 | Both functions will expect an object as the first parameter. The xsubpp |
1067 | compiler will call that object C<THIS> and will use it to call the specified |
1068 | method. So in the C++ code the blue() and set_blue() methods will be called |
1069 | in the following manner. |
a0d0e21e |
1070 | |
cb1a09d0 |
1071 | RETVAL = THIS->blue(); |
a0d0e21e |
1072 | |
cb1a09d0 |
1073 | THIS->set_blue( val ); |
a0d0e21e |
1074 | |
cb1a09d0 |
1075 | If the function's name is B<DESTROY> then the C++ C<delete> function will be |
1076 | called and C<THIS> will be given as its parameter. |
a0d0e21e |
1077 | |
d1b91892 |
1078 | void |
cb1a09d0 |
1079 | color::DESTROY() |
1080 | |
1081 | The C++ code will call C<delete>. |
1082 | |
1083 | delete THIS; |
a0d0e21e |
1084 | |
cb1a09d0 |
1085 | If the function's name is B<new> then the C++ C<new> function will be called |
1086 | to create a dynamic C++ object. The XSUB will expect the class name, which |
1087 | will be kept in a variable called C<CLASS>, to be given as the first |
1088 | argument. |
a0d0e21e |
1089 | |
cb1a09d0 |
1090 | color * |
1091 | color::new() |
a0d0e21e |
1092 | |
cb1a09d0 |
1093 | The C++ code will call C<new>. |
a0d0e21e |
1094 | |
cb1a09d0 |
1095 | RETVAL = new color(); |
1096 | |
1097 | The following is an example of a typemap that could be used for this C++ |
1098 | example. |
1099 | |
1100 | TYPEMAP |
1101 | color * O_OBJECT |
1102 | |
1103 | OUTPUT |
1104 | # The Perl object is blessed into 'CLASS', which should be a |
1105 | # char* having the name of the package for the blessing. |
1106 | O_OBJECT |
1107 | sv_setref_pv( $arg, CLASS, (void*)$var ); |
a6006777 |
1108 | |
cb1a09d0 |
1109 | INPUT |
1110 | O_OBJECT |
1111 | if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) ) |
1112 | $var = ($type)SvIV((SV*)SvRV( $arg )); |
1113 | else{ |
1114 | warn( \"${Package}::$func_name() -- $var is not a blessed SV reference\" ); |
1115 | XSRETURN_UNDEF; |
1116 | } |
a0d0e21e |
1117 | |
d1b91892 |
1118 | =head2 Interface Strategy |
a0d0e21e |
1119 | |
1120 | When designing an interface between Perl and a C library a straight |
1121 | translation from C to XS is often sufficient. The interface will often be |
1122 | very C-like and occasionally nonintuitive, especially when the C function |
1123 | modifies one of its parameters. In cases where the programmer wishes to |
1124 | create a more Perl-like interface the following strategy may help to |
1125 | identify the more critical parts of the interface. |
1126 | |
1127 | Identify the C functions which modify their parameters. The XSUBs for |
1128 | these functions may be able to return lists to Perl, or may be |
1129 | candidates to return undef or an empty list in case of failure. |
1130 | |
d1b91892 |
1131 | Identify which values are used by only the C and XSUB functions |
a0d0e21e |
1132 | themselves. If Perl does not need to access the contents of the value |
1133 | then it may not be necessary to provide a translation for that value |
1134 | from C to Perl. |
1135 | |
1136 | Identify the pointers in the C function parameter lists and return |
1137 | values. Some pointers can be handled in XS with the & unary operator on |
1138 | the variable name while others will require the use of the * operator on |
1139 | the type name. In general it is easier to work with the & operator. |
1140 | |
1141 | Identify the structures used by the C functions. In many |
1142 | cases it may be helpful to use the T_PTROBJ typemap for |
1143 | these structures so they can be manipulated by Perl as |
1144 | blessed objects. |
1145 | |
a0d0e21e |
1146 | =head2 Perl Objects And C Structures |
1147 | |
1148 | When dealing with C structures one should select either |
1149 | B<T_PTROBJ> or B<T_PTRREF> for the XS type. Both types are |
1150 | designed to handle pointers to complex objects. The |
1151 | T_PTRREF type will allow the Perl object to be unblessed |
1152 | while the T_PTROBJ type requires that the object be blessed. |
1153 | By using T_PTROBJ one can achieve a form of type-checking |
d1b91892 |
1154 | because the XSUB will attempt to verify that the Perl object |
a0d0e21e |
1155 | is of the expected type. |
1156 | |
1157 | The following XS code shows the getnetconfigent() function which is used |
8e07c86e |
1158 | with ONC+ TIRPC. The getnetconfigent() function will return a pointer to a |
a0d0e21e |
1159 | C structure and has the C prototype shown below. The example will |
1160 | demonstrate how the C pointer will become a Perl reference. Perl will |
1161 | consider this reference to be a pointer to a blessed object and will |
1162 | attempt to call a destructor for the object. A destructor will be |
1163 | provided in the XS source to free the memory used by getnetconfigent(). |
1164 | Destructors in XS can be created by specifying an XSUB function whose name |
1165 | ends with the word B<DESTROY>. XS destructors can be used to free memory |
1166 | which may have been malloc'd by another XSUB. |
1167 | |
1168 | struct netconfig *getnetconfigent(const char *netid); |
1169 | |
1170 | A C<typedef> will be created for C<struct netconfig>. The Perl |
1171 | object will be blessed in a class matching the name of the C |
1172 | type, with the tag C<Ptr> appended, and the name should not |
1173 | have embedded spaces if it will be a Perl package name. The |
1174 | destructor will be placed in a class corresponding to the |
1175 | class of the object and the PREFIX keyword will be used to |
1176 | trim the name to the word DESTROY as Perl will expect. |
1177 | |
1178 | typedef struct netconfig Netconfig; |
1179 | |
1180 | MODULE = RPC PACKAGE = RPC |
1181 | |
1182 | Netconfig * |
1183 | getnetconfigent(netid) |
8e07c86e |
1184 | char *netid |
a0d0e21e |
1185 | |
1186 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ |
1187 | |
1188 | void |
1189 | rpcb_DESTROY(netconf) |
8e07c86e |
1190 | Netconfig *netconf |
a0d0e21e |
1191 | CODE: |
1192 | printf("Now in NetconfigPtr::DESTROY\n"); |
1193 | free( netconf ); |
1194 | |
1195 | This example requires the following typemap entry. Consult the typemap |
1196 | section for more information about adding new typemaps for an extension. |
1197 | |
1198 | TYPEMAP |
1199 | Netconfig * T_PTROBJ |
1200 | |
1201 | This example will be used with the following Perl statements. |
1202 | |
1203 | use RPC; |
1204 | $netconf = getnetconfigent("udp"); |
1205 | |
1206 | When Perl destroys the object referenced by $netconf it will send the |
1207 | object to the supplied XSUB DESTROY function. Perl cannot determine, and |
1208 | does not care, that this object is a C struct and not a Perl object. In |
1209 | this sense, there is no difference between the object created by the |
1210 | getnetconfigent() XSUB and an object created by a normal Perl subroutine. |
1211 | |
a0d0e21e |
1212 | =head2 The Typemap |
1213 | |
1214 | The typemap is a collection of code fragments which are used by the B<xsubpp> |
1215 | compiler to map C function parameters and values to Perl values. The |
1216 | typemap file may consist of three sections labeled C<TYPEMAP>, C<INPUT>, and |
7e9d670d |
1217 | C<OUTPUT>. Any unlabelled initial section is assumed to be a C<TYPEMAP> |
1218 | section if a name is not explicitly specified. The INPUT section tells |
1219 | the compiler how to translate Perl values |
a0d0e21e |
1220 | into variables of certain C types. The OUTPUT section tells the compiler |
1221 | how to translate the values from certain C types into values Perl can |
1222 | understand. The TYPEMAP section tells the compiler which of the INPUT and |
1223 | OUTPUT code fragments should be used to map a given C type to a Perl value. |
7e9d670d |
1224 | The section labels C<TYPEMAP>, C<INPUT>, or C<OUTPUT> must begin |
1225 | in the first column on a line by themselves, and must be in uppercase. |
a0d0e21e |
1226 | |
1227 | The default typemap in the C<ext> directory of the Perl source contains many |
1228 | useful types which can be used by Perl extensions. Some extensions define |
1229 | additional typemaps which they keep in their own directory. These |
1230 | additional typemaps may reference INPUT and OUTPUT maps in the main |
1231 | typemap. The B<xsubpp> compiler will allow the extension's own typemap to |
1232 | override any mappings which are in the default typemap. |
1233 | |
1234 | Most extensions which require a custom typemap will need only the TYPEMAP |
1235 | section of the typemap file. The custom typemap used in the |
1236 | getnetconfigent() example shown earlier demonstrates what may be the typical |
1237 | use of extension typemaps. That typemap is used to equate a C structure |
1238 | with the T_PTROBJ typemap. The typemap used by getnetconfigent() is shown |
1239 | here. Note that the C type is separated from the XS type with a tab and |
1240 | that the C unary operator C<*> is considered to be a part of the C type name. |
1241 | |
1242 | TYPEMAP |
1243 | Netconfig *<tab>T_PTROBJ |
1244 | |
1748e8dd |
1245 | Here's a more complicated example: suppose that you wanted C<struct |
1246 | netconfig> to be blessed into the class C<Net::Config>. One way to do |
1247 | this is to use underscores (_) to separate package names, as follows: |
1248 | |
1249 | typedef struct netconfig * Net_Config; |
1250 | |
1251 | And then provide a typemap entry C<T_PTROBJ_SPECIAL> that maps underscores to |
1252 | double-colons (::), and declare C<Net_Config> to be of that type: |
1253 | |
1254 | |
1255 | TYPEMAP |
1256 | Net_Config T_PTROBJ_SPECIAL |
1257 | |
1258 | INPUT |
1259 | T_PTROBJ_SPECIAL |
1260 | if (sv_derived_from($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")) { |
1261 | IV tmp = SvIV((SV*)SvRV($arg)); |
1262 | $var = ($type) tmp; |
1263 | } |
1264 | else |
1265 | croak(\"$var is not of type ${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\") |
1266 | |
1267 | OUTPUT |
1268 | T_PTROBJ_SPECIAL |
1269 | sv_setref_pv($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\", |
1270 | (void*)$var); |
1271 | |
1272 | The INPUT and OUTPUT sections substitute underscores for double-colons |
1273 | on the fly, giving the desired effect. This example demonstrates some |
1274 | of the power and versatility of the typemap facility. |
1275 | |
a0d0e21e |
1276 | =head1 EXAMPLES |
1277 | |
1278 | File C<RPC.xs>: Interface to some ONC+ RPC bind library functions. |
1279 | |
1280 | #include "EXTERN.h" |
1281 | #include "perl.h" |
1282 | #include "XSUB.h" |
1283 | |
1284 | #include <rpc/rpc.h> |
1285 | |
1286 | typedef struct netconfig Netconfig; |
1287 | |
1288 | MODULE = RPC PACKAGE = RPC |
1289 | |
e7ea3e70 |
1290 | SV * |
a0d0e21e |
1291 | rpcb_gettime(host="localhost") |
8e07c86e |
1292 | char *host |
c07a80fd |
1293 | PREINIT: |
a0d0e21e |
1294 | time_t timep; |
c07a80fd |
1295 | CODE: |
a0d0e21e |
1296 | ST(0) = sv_newmortal(); |
1297 | if( rpcb_gettime( host, &timep ) ) |
1298 | sv_setnv( ST(0), (double)timep ); |
a0d0e21e |
1299 | |
1300 | Netconfig * |
1301 | getnetconfigent(netid="udp") |
8e07c86e |
1302 | char *netid |
a0d0e21e |
1303 | |
1304 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ |
1305 | |
1306 | void |
1307 | rpcb_DESTROY(netconf) |
8e07c86e |
1308 | Netconfig *netconf |
a0d0e21e |
1309 | CODE: |
1310 | printf("NetconfigPtr::DESTROY\n"); |
1311 | free( netconf ); |
1312 | |
1313 | File C<typemap>: Custom typemap for RPC.xs. |
1314 | |
1315 | TYPEMAP |
1316 | Netconfig * T_PTROBJ |
1317 | |
1318 | File C<RPC.pm>: Perl module for the RPC extension. |
1319 | |
1320 | package RPC; |
1321 | |
1322 | require Exporter; |
1323 | require DynaLoader; |
1324 | @ISA = qw(Exporter DynaLoader); |
1325 | @EXPORT = qw(rpcb_gettime getnetconfigent); |
1326 | |
1327 | bootstrap RPC; |
1328 | 1; |
1329 | |
1330 | File C<rpctest.pl>: Perl test program for the RPC extension. |
1331 | |
1332 | use RPC; |
1333 | |
1334 | $netconf = getnetconfigent(); |
1335 | $a = rpcb_gettime(); |
1336 | print "time = $a\n"; |
1337 | print "netconf = $netconf\n"; |
1338 | |
1339 | $netconf = getnetconfigent("tcp"); |
1340 | $a = rpcb_gettime("poplar"); |
1341 | print "time = $a\n"; |
1342 | print "netconf = $netconf\n"; |
1343 | |
1344 | |
c07a80fd |
1345 | =head1 XS VERSION |
1346 | |
f27cfbbe |
1347 | This document covers features supported by C<xsubpp> 1.935. |
c07a80fd |
1348 | |
a0d0e21e |
1349 | =head1 AUTHOR |
1350 | |
9607fc9c |
1351 | Dean Roehrich <F<roehrich@cray.com>> |
b772cb6e |
1352 | Jul 8, 1996 |