Commit | Line | Data |
---|---|---|
a0d0e21e LW |
1 | =head1 NAME |
2 | ||
8e07c86e | 3 | perlxs - XS language reference manual |
a0d0e21e LW |
4 | |
5 | =head1 DESCRIPTION | |
6 | ||
7 | =head2 Introduction | |
8 | ||
beb31b0b GS |
9 | XS is an interface description file format used to create an extension |
10 | interface between Perl and C code (or a C library) which one wishes | |
11 | to use with Perl. The XS interface is combined with the library to | |
12 | create a new library which can then be either dynamically loaded | |
13 | or statically linked into perl. The XS interface description is | |
14 | written in the XS language and is the core component of the Perl | |
15 | extension interface. | |
16 | ||
17 | An B<XSUB> forms the basic unit of the XS interface. After compilation | |
18 | by the B<xsubpp> compiler, each XSUB amounts to a C function definition | |
19 | which will provide the glue between Perl calling conventions and C | |
20 | calling conventions. | |
21 | ||
22 | The glue code pulls the arguments from the Perl stack, converts these | |
23 | Perl values to the formats expected by a C function, call this C function, | |
24 | transfers the return values of the C function back to Perl. | |
25 | Return values here may be a conventional C return value or any C | |
26 | function arguments that may serve as output parameters. These return | |
27 | values may be passed back to Perl either by putting them on the | |
28 | Perl stack, or by modifying the arguments supplied from the Perl side. | |
29 | ||
30 | The above is a somewhat simplified view of what really happens. Since | |
31 | Perl allows more flexible calling conventions than C, XSUBs may do much | |
32 | more in practice, such as checking input parameters for validity, | |
33 | throwing exceptions (or returning undef/empty list) if the return value | |
34 | from the C function indicates failure, calling different C functions | |
35 | based on numbers and types of the arguments, providing an object-oriented | |
36 | interface, etc. | |
37 | ||
38 | Of course, one could write such glue code directly in C. However, this | |
39 | would be a tedious task, especially if one needs to write glue for | |
40 | multiple C functions, and/or one is not familiar enough with the Perl | |
41 | stack discipline and other such arcana. XS comes to the rescue here: | |
42 | instead of writing this glue C code in long-hand, one can write | |
43 | a more concise short-hand I<description> of what should be done by | |
44 | the glue, and let the XS compiler B<xsubpp> handle the rest. | |
45 | ||
46 | The XS language allows one to describe the mapping between how the C | |
47 | routine is used, and how the corresponding Perl routine is used. It | |
48 | also allows creation of Perl routines which are directly translated to | |
49 | C code and which are not related to a pre-existing C function. In cases | |
50 | when the C interface coincides with the Perl interface, the XSUB | |
51 | declaration is almost identical to a declaration of a C function (in K&R | |
52 | style). In such circumstances, there is another tool called C<h2xs> | |
53 | that is able to translate an entire C header file into a corresponding | |
54 | XS file that will provide glue to the functions/macros described in | |
55 | the header file. | |
56 | ||
57 | The XS compiler is called B<xsubpp>. This compiler creates | |
58 | the constructs necessary to let an XSUB manipulate Perl values, and | |
59 | creates the glue necessary to let Perl call the XSUB. The compiler | |
a0d0e21e | 60 | uses B<typemaps> to determine how to map C function parameters |
beb31b0b GS |
61 | and output values to Perl values and back. The default typemap |
62 | (which comes with Perl) handles many common C types. A supplementary | |
63 | typemap may also be needed to handle any special structures and types | |
64 | for the library being linked. | |
65 | ||
66 | A file in XS format starts with a C language section which goes until the | |
67 | first C<MODULE =Z<>> directive. Other XS directives and XSUB definitions | |
68 | may follow this line. The "language" used in this part of the file | |
69 | is usually referred to as the XS language. | |
a0d0e21e | 70 | |
cb1a09d0 | 71 | See L<perlxstut> for a tutorial on the whole extension creation process. |
8e07c86e | 72 | |
beb31b0b GS |
73 | Note: For some extensions, Dave Beazley's SWIG system may provide a |
74 | significantly more convenient mechanism for creating the extension glue | |
6cecdcac | 75 | code. See L<http://www.swig.org> for more |
7b8d334a GS |
76 | information. |
77 | ||
8e07c86e AD |
78 | =head2 On The Road |
79 | ||
a5f75d66 AD |
80 | Many of the examples which follow will concentrate on creating an interface |
81 | between Perl and the ONC+ RPC bind library functions. The rpcb_gettime() | |
82 | function is used to demonstrate many features of the XS language. This | |
83 | function has two parameters; the first is an input parameter and the second | |
84 | is an output parameter. The function also returns a status value. | |
a0d0e21e LW |
85 | |
86 | bool_t rpcb_gettime(const char *host, time_t *timep); | |
87 | ||
88 | From C this function will be called with the following | |
89 | statements. | |
90 | ||
91 | #include <rpc/rpc.h> | |
92 | bool_t status; | |
93 | time_t timep; | |
94 | status = rpcb_gettime( "localhost", &timep ); | |
95 | ||
96 | If an XSUB is created to offer a direct translation between this function | |
97 | and Perl, then this XSUB will be used from Perl with the following code. | |
98 | The $status and $timep variables will contain the output of the function. | |
99 | ||
100 | use RPC; | |
101 | $status = rpcb_gettime( "localhost", $timep ); | |
102 | ||
103 | The following XS file shows an XS subroutine, or XSUB, which | |
104 | demonstrates one possible interface to the rpcb_gettime() | |
105 | function. This XSUB represents a direct translation between | |
106 | C and Perl and so preserves the interface even from Perl. | |
107 | This XSUB will be invoked from Perl with the usage shown | |
108 | above. Note that the first three #include statements, for | |
109 | C<EXTERN.h>, C<perl.h>, and C<XSUB.h>, will always be present at the | |
110 | beginning of an XS file. This approach and others will be | |
111 | expanded later in this document. | |
112 | ||
113 | #include "EXTERN.h" | |
114 | #include "perl.h" | |
115 | #include "XSUB.h" | |
116 | #include <rpc/rpc.h> | |
117 | ||
118 | MODULE = RPC PACKAGE = RPC | |
119 | ||
120 | bool_t | |
121 | rpcb_gettime(host,timep) | |
8e07c86e AD |
122 | char *host |
123 | time_t &timep | |
beb31b0b | 124 | OUTPUT: |
a0d0e21e LW |
125 | timep |
126 | ||
127 | Any extension to Perl, including those containing XSUBs, | |
128 | should have a Perl module to serve as the bootstrap which | |
129 | pulls the extension into Perl. This module will export the | |
130 | extension's functions and variables to the Perl program and | |
131 | will cause the extension's XSUBs to be linked into Perl. | |
132 | The following module will be used for most of the examples | |
133 | in this document and should be used from Perl with the C<use> | |
134 | command as shown earlier. Perl modules are explained in | |
135 | more detail later in this document. | |
136 | ||
137 | package RPC; | |
138 | ||
139 | require Exporter; | |
140 | require DynaLoader; | |
141 | @ISA = qw(Exporter DynaLoader); | |
142 | @EXPORT = qw( rpcb_gettime ); | |
143 | ||
144 | bootstrap RPC; | |
145 | 1; | |
146 | ||
147 | Throughout this document a variety of interfaces to the rpcb_gettime() | |
148 | XSUB will be explored. The XSUBs will take their parameters in different | |
149 | orders or will take different numbers of parameters. In each case the | |
150 | XSUB is an abstraction between Perl and the real C rpcb_gettime() | |
151 | function, and the XSUB must always ensure that the real rpcb_gettime() | |
152 | function is called with the correct parameters. This abstraction will | |
153 | allow the programmer to create a more Perl-like interface to the C | |
154 | function. | |
155 | ||
156 | =head2 The Anatomy of an XSUB | |
157 | ||
beb31b0b GS |
158 | The simplest XSUBs consist of 3 parts: a description of the return |
159 | value, the name of the XSUB routine and the names of its arguments, | |
160 | and a description of types or formats of the arguments. | |
161 | ||
8e07c86e AD |
162 | The following XSUB allows a Perl program to access a C library function |
163 | called sin(). The XSUB will imitate the C function which takes a single | |
164 | argument and returns a single value. | |
a0d0e21e LW |
165 | |
166 | double | |
167 | sin(x) | |
8e07c86e | 168 | double x |
a0d0e21e | 169 | |
beb31b0b GS |
170 | When using parameters with C pointer types, as in |
171 | ||
172 | double string_to_double(char *s); | |
173 | ||
174 | there may be two ways to describe this argument to B<xsubpp>: | |
175 | ||
176 | char * s | |
177 | char &s | |
178 | ||
179 | Both these XS declarations correspond to the C<char*> C type, but they have | |
180 | different semantics. It is convenient to think that the indirection operator | |
181 | C<*> should be considered as a part of the type and the address operator C<&> | |
182 | should be considered part of the variable. See L<"The Typemap"> and | |
183 | L<"The & Unary Operator"> for more info about handling qualifiers and unary | |
8e07c86e | 184 | operators in C types. |
a0d0e21e | 185 | |
a0d0e21e | 186 | The function name and the return type must be placed on |
beb31b0b | 187 | separate lines and should be flush left-adjusted. |
a0d0e21e LW |
188 | |
189 | INCORRECT CORRECT | |
190 | ||
191 | double sin(x) double | |
8e07c86e AD |
192 | double x sin(x) |
193 | double x | |
a0d0e21e | 194 | |
c07a80fd | 195 | The function body may be indented or left-adjusted. The following example |
196 | shows a function with its body left-adjusted. Most examples in this | |
beb31b0b | 197 | document will indent the body for better readability. |
c07a80fd | 198 | |
199 | CORRECT | |
200 | ||
201 | double | |
202 | sin(x) | |
203 | double x | |
204 | ||
beb31b0b GS |
205 | More complicated XSUBs may contain many other sections. Each section of |
206 | an XSUB starts with the corresponding keyword, such as INIT: or CLEANUP:. | |
207 | However, the first two lines of an XSUB always contain the same data: | |
208 | descriptions of the return type and the names of the function and its | |
209 | parameters. Whatever immediately follows these is considered to be | |
210 | an INPUT: section unless explicitly marked with another keyword. | |
211 | (See L<The INPUT: Keyword>.) | |
212 | ||
213 | An XSUB section continues until another section-start keyword is found. | |
214 | ||
a0d0e21e LW |
215 | =head2 The Argument Stack |
216 | ||
beb31b0b | 217 | The Perl argument stack is used to store the values which are |
a0d0e21e | 218 | sent as parameters to the XSUB and to store the XSUB's |
beb31b0b GS |
219 | return value(s). In reality all Perl functions (including non-XSUB |
220 | ones) keep their values on this stack all the same time, each limited | |
221 | to its own range of positions on the stack. In this document the | |
a0d0e21e LW |
222 | first position on that stack which belongs to the active |
223 | function will be referred to as position 0 for that function. | |
224 | ||
8e07c86e AD |
225 | XSUBs refer to their stack arguments with the macro B<ST(x)>, where I<x> |
226 | refers to a position in this XSUB's part of the stack. Position 0 for that | |
a0d0e21e LW |
227 | function would be known to the XSUB as ST(0). The XSUB's incoming |
228 | parameters and outgoing return values always begin at ST(0). For many | |
229 | simple cases the B<xsubpp> compiler will generate the code necessary to | |
230 | handle the argument stack by embedding code fragments found in the | |
231 | typemaps. In more complex cases the programmer must supply the code. | |
232 | ||
233 | =head2 The RETVAL Variable | |
234 | ||
beb31b0b GS |
235 | The RETVAL variable is a special C variable that is declared automatically |
236 | for you. The C type of RETVAL matches the return type of the C library | |
237 | function. The B<xsubpp> compiler will declare this variable in each XSUB | |
238 | with non-C<void> return type. By default the generated C function | |
239 | will use RETVAL to hold the return value of the C library function being | |
240 | called. In simple cases the value of RETVAL will be placed in ST(0) of | |
241 | the argument stack where it can be received by Perl as the return value | |
242 | of the XSUB. | |
a0d0e21e LW |
243 | |
244 | If the XSUB has a return type of C<void> then the compiler will | |
beb31b0b GS |
245 | not declare a RETVAL variable for that function. When using |
246 | a PPCODE: section no manipulation of the RETVAL variable is required, the | |
247 | section may use direct stack manipulation to place output values on the stack. | |
e7ea3e70 IZ |
248 | |
249 | If PPCODE: directive is not used, C<void> return value should be used | |
250 | only for subroutines which do not return a value, I<even if> CODE: | |
54310121 | 251 | directive is used which sets ST(0) explicitly. |
e7ea3e70 IZ |
252 | |
253 | Older versions of this document recommended to use C<void> return | |
254 | value in such cases. It was discovered that this could lead to | |
c2611fb3 | 255 | segfaults in cases when XSUB was I<truly> C<void>. This practice is |
e7ea3e70 IZ |
256 | now deprecated, and may be not supported at some future version. Use |
257 | the return value C<SV *> in such cases. (Currently C<xsubpp> contains | |
c2611fb3 | 258 | some heuristic code which tries to disambiguate between "truly-void" |
e7ea3e70 IZ |
259 | and "old-practice-declared-as-void" functions. Hence your code is at |
260 | mercy of this heuristics unless you use C<SV *> as return value.) | |
a0d0e21e LW |
261 | |
262 | =head2 The MODULE Keyword | |
263 | ||
264 | The MODULE keyword is used to start the XS code and to | |
265 | specify the package of the functions which are being | |
266 | defined. All text preceding the first MODULE keyword is | |
267 | considered C code and is passed through to the output | |
268 | untouched. Every XS module will have a bootstrap function | |
269 | which is used to hook the XSUBs into Perl. The package name | |
270 | of this bootstrap function will match the value of the last | |
271 | MODULE statement in the XS source files. The value of | |
272 | MODULE should always remain constant within the same XS | |
273 | file, though this is not required. | |
274 | ||
275 | The following example will start the XS code and will place | |
276 | all functions in a package named RPC. | |
277 | ||
278 | MODULE = RPC | |
279 | ||
280 | =head2 The PACKAGE Keyword | |
281 | ||
282 | When functions within an XS source file must be separated into packages | |
283 | the PACKAGE keyword should be used. This keyword is used with the MODULE | |
284 | keyword and must follow immediately after it when used. | |
285 | ||
286 | MODULE = RPC PACKAGE = RPC | |
287 | ||
288 | [ XS code in package RPC ] | |
289 | ||
290 | MODULE = RPC PACKAGE = RPCB | |
291 | ||
292 | [ XS code in package RPCB ] | |
293 | ||
294 | MODULE = RPC PACKAGE = RPC | |
295 | ||
296 | [ XS code in package RPC ] | |
297 | ||
298 | Although this keyword is optional and in some cases provides redundant | |
299 | information it should always be used. This keyword will ensure that the | |
300 | XSUBs appear in the desired package. | |
301 | ||
302 | =head2 The PREFIX Keyword | |
303 | ||
304 | The PREFIX keyword designates prefixes which should be | |
305 | removed from the Perl function names. If the C function is | |
306 | C<rpcb_gettime()> and the PREFIX value is C<rpcb_> then Perl will | |
307 | see this function as C<gettime()>. | |
308 | ||
309 | This keyword should follow the PACKAGE keyword when used. | |
310 | If PACKAGE is not used then PREFIX should follow the MODULE | |
311 | keyword. | |
312 | ||
313 | MODULE = RPC PREFIX = rpc_ | |
314 | ||
315 | MODULE = RPC PACKAGE = RPCB PREFIX = rpcb_ | |
316 | ||
317 | =head2 The OUTPUT: Keyword | |
318 | ||
319 | The OUTPUT: keyword indicates that certain function parameters should be | |
320 | updated (new values made visible to Perl) when the XSUB terminates or that | |
321 | certain values should be returned to the calling Perl function. For | |
beb31b0b GS |
322 | simple functions which have no CODE: or PPCODE: section, |
323 | such as the sin() function above, the RETVAL variable is | |
324 | automatically designated as an output value. For more complex functions | |
a0d0e21e LW |
325 | the B<xsubpp> compiler will need help to determine which variables are output |
326 | variables. | |
327 | ||
328 | This keyword will normally be used to complement the CODE: keyword. | |
329 | The RETVAL variable is not recognized as an output variable when the | |
330 | CODE: keyword is present. The OUTPUT: keyword is used in this | |
331 | situation to tell the compiler that RETVAL really is an output | |
332 | variable. | |
333 | ||
334 | The OUTPUT: keyword can also be used to indicate that function parameters | |
335 | are output variables. This may be necessary when a parameter has been | |
336 | modified within the function and the programmer would like the update to | |
8e07c86e | 337 | be seen by Perl. |
a0d0e21e LW |
338 | |
339 | bool_t | |
340 | rpcb_gettime(host,timep) | |
8e07c86e AD |
341 | char *host |
342 | time_t &timep | |
beb31b0b | 343 | OUTPUT: |
a0d0e21e LW |
344 | timep |
345 | ||
346 | The OUTPUT: keyword will also allow an output parameter to | |
347 | be mapped to a matching piece of code rather than to a | |
ef50df4b | 348 | typemap. |
a0d0e21e LW |
349 | |
350 | bool_t | |
351 | rpcb_gettime(host,timep) | |
8e07c86e AD |
352 | char *host |
353 | time_t &timep | |
beb31b0b | 354 | OUTPUT: |
ef50df4b GS |
355 | timep sv_setnv(ST(1), (double)timep); |
356 | ||
357 | B<xsubpp> emits an automatic C<SvSETMAGIC()> for all parameters in the | |
358 | OUTPUT section of the XSUB, except RETVAL. This is the usually desired | |
359 | behavior, as it takes care of properly invoking 'set' magic on output | |
360 | parameters (needed for hash or array element parameters that must be | |
361 | created if they didn't exist). If for some reason, this behavior is | |
362 | not desired, the OUTPUT section may contain a C<SETMAGIC: DISABLE> line | |
363 | to disable it for the remainder of the parameters in the OUTPUT section. | |
364 | Likewise, C<SETMAGIC: ENABLE> can be used to reenable it for the | |
365 | remainder of the OUTPUT section. See L<perlguts> for more details | |
366 | about 'set' magic. | |
a0d0e21e LW |
367 | |
368 | =head2 The CODE: Keyword | |
369 | ||
370 | This keyword is used in more complicated XSUBs which require | |
371 | special handling for the C function. The RETVAL variable is | |
beb31b0b GS |
372 | still declared, but it will not be returned unless it is specified |
373 | in the OUTPUT: section. | |
a0d0e21e LW |
374 | |
375 | The following XSUB is for a C function which requires special handling of | |
376 | its parameters. The Perl usage is given first. | |
377 | ||
378 | $status = rpcb_gettime( "localhost", $timep ); | |
379 | ||
54310121 | 380 | The XSUB follows. |
a0d0e21e | 381 | |
d1b91892 AD |
382 | bool_t |
383 | rpcb_gettime(host,timep) | |
8e07c86e AD |
384 | char *host |
385 | time_t timep | |
beb31b0b | 386 | CODE: |
a0d0e21e | 387 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b | 388 | OUTPUT: |
a0d0e21e LW |
389 | timep |
390 | RETVAL | |
391 | ||
c07a80fd | 392 | =head2 The INIT: Keyword |
393 | ||
394 | The INIT: keyword allows initialization to be inserted into the XSUB before | |
395 | the compiler generates the call to the C function. Unlike the CODE: keyword | |
396 | above, this keyword does not affect the way the compiler handles RETVAL. | |
397 | ||
398 | bool_t | |
399 | rpcb_gettime(host,timep) | |
400 | char *host | |
401 | time_t &timep | |
beb31b0b | 402 | INIT: |
c07a80fd | 403 | printf("# Host is %s\n", host ); |
beb31b0b | 404 | OUTPUT: |
c07a80fd | 405 | timep |
a0d0e21e | 406 | |
beb31b0b GS |
407 | Another use for the INIT: section is to check for preconditions before |
408 | making a call to the C function: | |
409 | ||
410 | long long | |
411 | lldiv(a,b) | |
412 | long long a | |
413 | long long b | |
414 | INIT: | |
415 | if (a == 0 && b == 0) | |
416 | XSRETURN_UNDEF; | |
417 | if (b == 0) | |
418 | croak("lldiv: cannot divide by 0"); | |
419 | ||
a0d0e21e LW |
420 | =head2 The NO_INIT Keyword |
421 | ||
422 | The NO_INIT keyword is used to indicate that a function | |
54310121 | 423 | parameter is being used only as an output value. The B<xsubpp> |
a0d0e21e LW |
424 | compiler will normally generate code to read the values of |
425 | all function parameters from the argument stack and assign | |
426 | them to C variables upon entry to the function. NO_INIT | |
427 | will tell the compiler that some parameters will be used for | |
428 | output rather than for input and that they will be handled | |
429 | before the function terminates. | |
430 | ||
431 | The following example shows a variation of the rpcb_gettime() function. | |
54310121 | 432 | This function uses the timep variable only as an output variable and does |
a0d0e21e LW |
433 | not care about its initial contents. |
434 | ||
435 | bool_t | |
436 | rpcb_gettime(host,timep) | |
8e07c86e AD |
437 | char *host |
438 | time_t &timep = NO_INIT | |
beb31b0b | 439 | OUTPUT: |
a0d0e21e LW |
440 | timep |
441 | ||
442 | =head2 Initializing Function Parameters | |
443 | ||
beb31b0b GS |
444 | C function parameters are normally initialized with their values from |
445 | the argument stack (which in turn contains the parameters that were | |
446 | passed to the XSUB from Perl). The typemaps contain the | |
447 | code segments which are used to translate the Perl values to | |
a0d0e21e | 448 | the C parameters. The programmer, however, is allowed to |
7ad6fb0b | 449 | override the typemaps and supply alternate (or additional) |
beb31b0b GS |
450 | initialization code. Initialization code starts with the first |
451 | C<=>, C<;> or C<+> on a line in the INPUT: section. The only | |
452 | exception happens if this C<;> terminates the line, then this C<;> | |
453 | is quietly ignored. | |
a0d0e21e LW |
454 | |
455 | The following code demonstrates how to supply initialization code for | |
7ad6fb0b TM |
456 | function parameters. The initialization code is eval'd within double |
457 | quotes by the compiler before it is added to the output so anything | |
458 | which should be interpreted literally [mainly C<$>, C<@>, or C<\\>] | |
19799a22 GS |
459 | must be protected with backslashes. The variables $var, $arg, |
460 | and $type can be used as in typemaps. | |
a0d0e21e LW |
461 | |
462 | bool_t | |
463 | rpcb_gettime(host,timep) | |
9cde0e7f | 464 | char *host = (char *)SvPV($arg,PL_na); |
8e07c86e | 465 | time_t &timep = 0; |
beb31b0b | 466 | OUTPUT: |
a0d0e21e LW |
467 | timep |
468 | ||
469 | This should not be used to supply default values for parameters. One | |
470 | would normally use this when a function parameter must be processed by | |
471 | another library function before it can be used. Default parameters are | |
472 | covered in the next section. | |
473 | ||
beb31b0b GS |
474 | If the initialization begins with C<=>, then it is output in |
475 | the declaration for the input variable, replacing the initialization | |
476 | supplied by the typemap. If the initialization | |
477 | begins with C<;> or C<+>, then it is performed after | |
478 | all of the input variables have been declared. In the C<;> | |
479 | case the initialization normally supplied by the typemap is not performed. | |
480 | For the C<+> case, the declaration for the variable will include the | |
481 | initialization from the typemap. A global | |
c2611fb3 | 482 | variable, C<%v>, is available for the truly rare case where |
7ad6fb0b TM |
483 | information from one initialization is needed in another |
484 | initialization. | |
485 | ||
beb31b0b GS |
486 | Here's a truly obscure example: |
487 | ||
7ad6fb0b TM |
488 | bool_t |
489 | rpcb_gettime(host,timep) | |
beb31b0b GS |
490 | time_t &timep ; /* \$v{timep}=@{[$v{timep}=$arg]} */ |
491 | char *host + SvOK($v{timep}) ? SvPV($arg,PL_na) : NULL; | |
492 | OUTPUT: | |
7ad6fb0b TM |
493 | timep |
494 | ||
beb31b0b GS |
495 | The construct C<\$v{timep}=@{[$v{timep}=$arg]}> used in the above |
496 | example has a two-fold purpose: first, when this line is processed by | |
497 | B<xsubpp>, the Perl snippet C<$v{timep}=$arg> is evaluated. Second, | |
498 | the text of the evaluated snippet is output into the generated C file | |
499 | (inside a C comment)! During the processing of C<char *host> line, | |
500 | $arg will evaluate to C<ST(0)>, and C<$v{timep}> will evaluate to | |
501 | C<ST(1)>. | |
502 | ||
a0d0e21e LW |
503 | =head2 Default Parameter Values |
504 | ||
4628e4f8 GS |
505 | Default values for XSUB arguments can be specified by placing an |
506 | assignment statement in the parameter list. The default value may | |
a104f515 | 507 | be a number, a string or the special string C<NO_INIT>. Defaults should |
a0d0e21e LW |
508 | always be used on the right-most parameters only. |
509 | ||
510 | To allow the XSUB for rpcb_gettime() to have a default host | |
511 | value the parameters to the XSUB could be rearranged. The | |
512 | XSUB will then call the real rpcb_gettime() function with | |
beb31b0b GS |
513 | the parameters in the correct order. This XSUB can be called |
514 | from Perl with either of the following statements: | |
a0d0e21e LW |
515 | |
516 | $status = rpcb_gettime( $timep, $host ); | |
517 | ||
518 | $status = rpcb_gettime( $timep ); | |
519 | ||
520 | The XSUB will look like the code which follows. A CODE: | |
521 | block is used to call the real rpcb_gettime() function with | |
522 | the parameters in the correct order for that function. | |
523 | ||
524 | bool_t | |
525 | rpcb_gettime(timep,host="localhost") | |
8e07c86e AD |
526 | char *host |
527 | time_t timep = NO_INIT | |
beb31b0b | 528 | CODE: |
a0d0e21e | 529 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b | 530 | OUTPUT: |
a0d0e21e LW |
531 | timep |
532 | RETVAL | |
533 | ||
c07a80fd | 534 | =head2 The PREINIT: Keyword |
535 | ||
beb31b0b | 536 | The PREINIT: keyword allows extra variables to be declared immediately |
a2293a43 | 537 | before or after the declarations of the parameters from the INPUT: section |
beb31b0b GS |
538 | are emitted. |
539 | ||
540 | If a variable is declared inside a CODE: section it will follow any typemap | |
541 | code that is emitted for the input parameters. This may result in the | |
542 | declaration ending up after C code, which is C syntax error. Similar | |
543 | errors may happen with an explicit C<;>-type or C<+>-type initialization of | |
544 | parameters is used (see L<"Initializing Function Parameters">). Declaring | |
545 | these variables in an INIT: section will not help. | |
546 | ||
547 | In such cases, to force an additional variable to be declared together | |
548 | with declarations of other variables, place the declaration into a | |
549 | PREINIT: section. The PREINIT: keyword may be used one or more times | |
550 | within an XSUB. | |
c07a80fd | 551 | |
552 | The following examples are equivalent, but if the code is using complex | |
553 | typemaps then the first example is safer. | |
554 | ||
555 | bool_t | |
556 | rpcb_gettime(timep) | |
557 | time_t timep = NO_INIT | |
beb31b0b | 558 | PREINIT: |
c07a80fd | 559 | char *host = "localhost"; |
beb31b0b | 560 | CODE: |
c07a80fd | 561 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b | 562 | OUTPUT: |
c07a80fd | 563 | timep |
564 | RETVAL | |
565 | ||
beb31b0b GS |
566 | For this particular case an INIT: keyword would generate the |
567 | same C code as the PREINIT: keyword. Another correct, but error-prone example: | |
c07a80fd | 568 | |
569 | bool_t | |
570 | rpcb_gettime(timep) | |
571 | time_t timep = NO_INIT | |
beb31b0b | 572 | CODE: |
c07a80fd | 573 | char *host = "localhost"; |
574 | RETVAL = rpcb_gettime( host, &timep ); | |
beb31b0b GS |
575 | OUTPUT: |
576 | timep | |
577 | RETVAL | |
578 | ||
579 | Another way to declare C<host> is to use a C block in the CODE: section: | |
580 | ||
581 | bool_t | |
582 | rpcb_gettime(timep) | |
583 | time_t timep = NO_INIT | |
584 | CODE: | |
585 | { | |
586 | char *host = "localhost"; | |
587 | RETVAL = rpcb_gettime( host, &timep ); | |
588 | } | |
589 | OUTPUT: | |
590 | timep | |
591 | RETVAL | |
592 | ||
593 | The ability to put additional declarations before the typemap entries are | |
594 | processed is very handy in the cases when typemap conversions manipulate | |
595 | some global state: | |
596 | ||
597 | MyObject | |
598 | mutate(o) | |
599 | PREINIT: | |
600 | MyState st = global_state; | |
601 | INPUT: | |
602 | MyObject o; | |
603 | CLEANUP: | |
604 | reset_to(global_state, st); | |
605 | ||
606 | Here we suppose that conversion to C<MyObject> in the INPUT: section and from | |
607 | MyObject when processing RETVAL will modify a global variable C<global_state>. | |
608 | After these conversions are performed, we restore the old value of | |
609 | C<global_state> (to avoid memory leaks, for example). | |
610 | ||
611 | There is another way to trade clarity for compactness: INPUT sections allow | |
612 | declaration of C variables which do not appear in the parameter list of | |
613 | a subroutine. Thus the above code for mutate() can be rewritten as | |
614 | ||
615 | MyObject | |
616 | mutate(o) | |
617 | MyState st = global_state; | |
618 | MyObject o; | |
619 | CLEANUP: | |
620 | reset_to(global_state, st); | |
621 | ||
622 | and the code for rpcb_gettime() can be rewritten as | |
623 | ||
624 | bool_t | |
625 | rpcb_gettime(timep) | |
626 | time_t timep = NO_INIT | |
627 | char *host = "localhost"; | |
628 | C_ARGS: | |
629 | host, &timep | |
630 | OUTPUT: | |
c07a80fd | 631 | timep |
632 | RETVAL | |
633 | ||
84287afe | 634 | =head2 The SCOPE: Keyword |
635 | ||
636 | The SCOPE: keyword allows scoping to be enabled for a particular XSUB. If | |
637 | enabled, the XSUB will invoke ENTER and LEAVE automatically. | |
638 | ||
639 | To support potentially complex type mappings, if a typemap entry used | |
beb31b0b GS |
640 | by an XSUB contains a comment like C</*scope*/> then scoping will |
641 | be automatically enabled for that XSUB. | |
84287afe | 642 | |
643 | To enable scoping: | |
644 | ||
645 | SCOPE: ENABLE | |
646 | ||
647 | To disable scoping: | |
648 | ||
649 | SCOPE: DISABLE | |
650 | ||
c07a80fd | 651 | =head2 The INPUT: Keyword |
652 | ||
653 | The XSUB's parameters are usually evaluated immediately after entering the | |
654 | XSUB. The INPUT: keyword can be used to force those parameters to be | |
655 | evaluated a little later. The INPUT: keyword can be used multiple times | |
656 | within an XSUB and can be used to list one or more input variables. This | |
657 | keyword is used with the PREINIT: keyword. | |
658 | ||
659 | The following example shows how the input parameter C<timep> can be | |
660 | evaluated late, after a PREINIT. | |
661 | ||
662 | bool_t | |
663 | rpcb_gettime(host,timep) | |
664 | char *host | |
beb31b0b | 665 | PREINIT: |
c07a80fd | 666 | time_t tt; |
beb31b0b | 667 | INPUT: |
c07a80fd | 668 | time_t timep |
beb31b0b | 669 | CODE: |
c07a80fd | 670 | RETVAL = rpcb_gettime( host, &tt ); |
671 | timep = tt; | |
beb31b0b | 672 | OUTPUT: |
c07a80fd | 673 | timep |
674 | RETVAL | |
675 | ||
676 | The next example shows each input parameter evaluated late. | |
677 | ||
678 | bool_t | |
679 | rpcb_gettime(host,timep) | |
beb31b0b | 680 | PREINIT: |
c07a80fd | 681 | time_t tt; |
beb31b0b | 682 | INPUT: |
c07a80fd | 683 | char *host |
beb31b0b | 684 | PREINIT: |
c07a80fd | 685 | char *h; |
beb31b0b | 686 | INPUT: |
c07a80fd | 687 | time_t timep |
beb31b0b | 688 | CODE: |
c07a80fd | 689 | h = host; |
690 | RETVAL = rpcb_gettime( h, &tt ); | |
691 | timep = tt; | |
beb31b0b GS |
692 | OUTPUT: |
693 | timep | |
694 | RETVAL | |
695 | ||
696 | Since INPUT sections allow declaration of C variables which do not appear | |
697 | in the parameter list of a subroutine, this may be shortened to: | |
698 | ||
699 | bool_t | |
700 | rpcb_gettime(host,timep) | |
701 | time_t tt; | |
702 | char *host; | |
703 | char *h = host; | |
704 | time_t timep; | |
705 | CODE: | |
706 | RETVAL = rpcb_gettime( h, &tt ); | |
707 | timep = tt; | |
708 | OUTPUT: | |
c07a80fd | 709 | timep |
710 | RETVAL | |
711 | ||
beb31b0b GS |
712 | (We used our knowledge that input conversion for C<char *> is a "simple" one, |
713 | thus C<host> is initialized on the declaration line, and our assignment | |
714 | C<h = host> is not performed too early. Otherwise one would need to have the | |
715 | assignment C<h = host> in a CODE: or INIT: section.) | |
716 | ||
a0d0e21e LW |
717 | =head2 Variable-length Parameter Lists |
718 | ||
719 | XSUBs can have variable-length parameter lists by specifying an ellipsis | |
720 | C<(...)> in the parameter list. This use of the ellipsis is similar to that | |
721 | found in ANSI C. The programmer is able to determine the number of | |
722 | arguments passed to the XSUB by examining the C<items> variable which the | |
723 | B<xsubpp> compiler supplies for all XSUBs. By using this mechanism one can | |
724 | create an XSUB which accepts a list of parameters of unknown length. | |
725 | ||
726 | The I<host> parameter for the rpcb_gettime() XSUB can be | |
727 | optional so the ellipsis can be used to indicate that the | |
728 | XSUB will take a variable number of parameters. Perl should | |
d1b91892 | 729 | be able to call this XSUB with either of the following statements. |
a0d0e21e LW |
730 | |
731 | $status = rpcb_gettime( $timep, $host ); | |
732 | ||
733 | $status = rpcb_gettime( $timep ); | |
734 | ||
735 | The XS code, with ellipsis, follows. | |
736 | ||
737 | bool_t | |
738 | rpcb_gettime(timep, ...) | |
8e07c86e | 739 | time_t timep = NO_INIT |
beb31b0b | 740 | PREINIT: |
a0d0e21e | 741 | char *host = "localhost"; |
2d8e6c8d | 742 | STRLEN n_a; |
beb31b0b GS |
743 | CODE: |
744 | if( items > 1 ) | |
745 | host = (char *)SvPV(ST(1), n_a); | |
746 | RETVAL = rpcb_gettime( host, &timep ); | |
747 | OUTPUT: | |
a0d0e21e LW |
748 | timep |
749 | RETVAL | |
750 | ||
cfc02341 IZ |
751 | =head2 The C_ARGS: Keyword |
752 | ||
753 | The C_ARGS: keyword allows creating of XSUBS which have different | |
754 | calling sequence from Perl than from C, without a need to write | |
beb31b0b | 755 | CODE: or PPCODE: section. The contents of the C_ARGS: paragraph is |
cfc02341 IZ |
756 | put as the argument to the called C function without any change. |
757 | ||
beb31b0b | 758 | For example, suppose that a C function is declared as |
cfc02341 IZ |
759 | |
760 | symbolic nth_derivative(int n, symbolic function, int flags); | |
761 | ||
762 | and that the default flags are kept in a global C variable | |
763 | C<default_flags>. Suppose that you want to create an interface which | |
764 | is called as | |
765 | ||
766 | $second_deriv = $function->nth_derivative(2); | |
767 | ||
768 | To do this, declare the XSUB as | |
769 | ||
770 | symbolic | |
771 | nth_derivative(function, n) | |
772 | symbolic function | |
773 | int n | |
beb31b0b | 774 | C_ARGS: |
cfc02341 IZ |
775 | n, function, default_flags |
776 | ||
a0d0e21e LW |
777 | =head2 The PPCODE: Keyword |
778 | ||
779 | The PPCODE: keyword is an alternate form of the CODE: keyword and is used | |
780 | to tell the B<xsubpp> compiler that the programmer is supplying the code to | |
d1b91892 | 781 | control the argument stack for the XSUBs return values. Occasionally one |
a0d0e21e LW |
782 | will want an XSUB to return a list of values rather than a single value. |
783 | In these cases one must use PPCODE: and then explicitly push the list of | |
beb31b0b | 784 | values on the stack. The PPCODE: and CODE: keywords should not be used |
a0d0e21e LW |
785 | together within the same XSUB. |
786 | ||
beb31b0b GS |
787 | The actual difference between PPCODE: and CODE: sections is in the |
788 | initialization of C<SP> macro (which stands for the I<current> Perl | |
789 | stack pointer), and in the handling of data on the stack when returning | |
790 | from an XSUB. In CODE: sections SP preserves the value which was on | |
791 | entry to the XSUB: SP is on the function pointer (which follows the | |
792 | last parameter). In PPCODE: sections SP is moved backward to the | |
793 | beginning of the parameter list, which allows C<PUSH*()> macros | |
794 | to place output values in the place Perl expects them to be when | |
795 | the XSUB returns back to Perl. | |
796 | ||
797 | The generated trailer for a CODE: section ensures that the number of return | |
798 | values Perl will see is either 0 or 1 (depending on the C<void>ness of the | |
799 | return value of the C function, and heuristics mentioned in | |
800 | L<"The RETVAL Variable">). The trailer generated for a PPCODE: section | |
801 | is based on the number of return values and on the number of times | |
802 | C<SP> was updated by C<[X]PUSH*()> macros. | |
803 | ||
804 | Note that macros C<ST(i)>, C<XST_m*()> and C<XSRETURN*()> work equally | |
805 | well in CODE: sections and PPCODE: sections. | |
806 | ||
a0d0e21e LW |
807 | The following XSUB will call the C rpcb_gettime() function |
808 | and will return its two output values, timep and status, to | |
809 | Perl as a single list. | |
810 | ||
d1b91892 AD |
811 | void |
812 | rpcb_gettime(host) | |
8e07c86e | 813 | char *host |
beb31b0b | 814 | PREINIT: |
a0d0e21e LW |
815 | time_t timep; |
816 | bool_t status; | |
beb31b0b | 817 | PPCODE: |
a0d0e21e | 818 | status = rpcb_gettime( host, &timep ); |
924508f0 | 819 | EXTEND(SP, 2); |
cb1a09d0 AD |
820 | PUSHs(sv_2mortal(newSViv(status))); |
821 | PUSHs(sv_2mortal(newSViv(timep))); | |
a0d0e21e LW |
822 | |
823 | Notice that the programmer must supply the C code necessary | |
824 | to have the real rpcb_gettime() function called and to have | |
825 | the return values properly placed on the argument stack. | |
826 | ||
827 | The C<void> return type for this function tells the B<xsubpp> compiler that | |
828 | the RETVAL variable is not needed or used and that it should not be created. | |
829 | In most scenarios the void return type should be used with the PPCODE: | |
830 | directive. | |
831 | ||
832 | The EXTEND() macro is used to make room on the argument | |
833 | stack for 2 return values. The PPCODE: directive causes the | |
924508f0 | 834 | B<xsubpp> compiler to create a stack pointer available as C<SP>, and it |
a0d0e21e LW |
835 | is this pointer which is being used in the EXTEND() macro. |
836 | The values are then pushed onto the stack with the PUSHs() | |
837 | macro. | |
838 | ||
839 | Now the rpcb_gettime() function can be used from Perl with | |
840 | the following statement. | |
841 | ||
842 | ($status, $timep) = rpcb_gettime("localhost"); | |
843 | ||
ef50df4b GS |
844 | When handling output parameters with a PPCODE section, be sure to handle |
845 | 'set' magic properly. See L<perlguts> for details about 'set' magic. | |
846 | ||
a0d0e21e LW |
847 | =head2 Returning Undef And Empty Lists |
848 | ||
5f05dabc | 849 | Occasionally the programmer will want to return simply |
a0d0e21e LW |
850 | C<undef> or an empty list if a function fails rather than a |
851 | separate status value. The rpcb_gettime() function offers | |
852 | just this situation. If the function succeeds we would like | |
853 | to have it return the time and if it fails we would like to | |
854 | have undef returned. In the following Perl code the value | |
855 | of $timep will either be undef or it will be a valid time. | |
856 | ||
857 | $timep = rpcb_gettime( "localhost" ); | |
858 | ||
7b8d334a | 859 | The following XSUB uses the C<SV *> return type as a mnemonic only, |
e7ea3e70 | 860 | and uses a CODE: block to indicate to the compiler |
a0d0e21e LW |
861 | that the programmer has supplied all the necessary code. The |
862 | sv_newmortal() call will initialize the return value to undef, making that | |
863 | the default return value. | |
864 | ||
e7ea3e70 | 865 | SV * |
a0d0e21e LW |
866 | rpcb_gettime(host) |
867 | char * host | |
beb31b0b | 868 | PREINIT: |
a0d0e21e LW |
869 | time_t timep; |
870 | bool_t x; | |
beb31b0b | 871 | CODE: |
a0d0e21e LW |
872 | ST(0) = sv_newmortal(); |
873 | if( rpcb_gettime( host, &timep ) ) | |
874 | sv_setnv( ST(0), (double)timep); | |
a0d0e21e LW |
875 | |
876 | The next example demonstrates how one would place an explicit undef in the | |
877 | return value, should the need arise. | |
878 | ||
e7ea3e70 | 879 | SV * |
a0d0e21e LW |
880 | rpcb_gettime(host) |
881 | char * host | |
beb31b0b | 882 | PREINIT: |
a0d0e21e LW |
883 | time_t timep; |
884 | bool_t x; | |
beb31b0b | 885 | CODE: |
a0d0e21e LW |
886 | ST(0) = sv_newmortal(); |
887 | if( rpcb_gettime( host, &timep ) ){ | |
888 | sv_setnv( ST(0), (double)timep); | |
889 | } | |
890 | else{ | |
9cde0e7f | 891 | ST(0) = &PL_sv_undef; |
a0d0e21e | 892 | } |
a0d0e21e LW |
893 | |
894 | To return an empty list one must use a PPCODE: block and | |
895 | then not push return values on the stack. | |
896 | ||
897 | void | |
898 | rpcb_gettime(host) | |
8e07c86e | 899 | char *host |
beb31b0b | 900 | PREINIT: |
a0d0e21e | 901 | time_t timep; |
beb31b0b | 902 | PPCODE: |
a0d0e21e | 903 | if( rpcb_gettime( host, &timep ) ) |
cb1a09d0 | 904 | PUSHs(sv_2mortal(newSViv(timep))); |
a0d0e21e | 905 | else{ |
beb31b0b GS |
906 | /* Nothing pushed on stack, so an empty |
907 | * list is implicitly returned. */ | |
a0d0e21e | 908 | } |
a0d0e21e | 909 | |
f27cfbbe | 910 | Some people may be inclined to include an explicit C<return> in the above |
911 | XSUB, rather than letting control fall through to the end. In those | |
912 | situations C<XSRETURN_EMPTY> should be used, instead. This will ensure that | |
913 | the XSUB stack is properly adjusted. Consult L<perlguts/"API LISTING"> for | |
914 | other C<XSRETURN> macros. | |
915 | ||
beb31b0b GS |
916 | Since C<XSRETURN_*> macros can be used with CODE blocks as well, one can |
917 | rewrite this example as: | |
918 | ||
919 | int | |
920 | rpcb_gettime(host) | |
921 | char *host | |
922 | PREINIT: | |
923 | time_t timep; | |
924 | CODE: | |
925 | RETVAL = rpcb_gettime( host, &timep ); | |
926 | if (RETVAL == 0) | |
927 | XSRETURN_UNDEF; | |
928 | OUTPUT: | |
929 | RETVAL | |
930 | ||
931 | In fact, one can put this check into a CLEANUP: section as well. Together | |
932 | with PREINIT: simplifications, this leads to: | |
933 | ||
934 | int | |
935 | rpcb_gettime(host) | |
936 | char *host | |
937 | time_t timep; | |
938 | CLEANUP: | |
939 | if (RETVAL == 0) | |
940 | XSRETURN_UNDEF; | |
941 | ||
4633a7c4 LW |
942 | =head2 The REQUIRE: Keyword |
943 | ||
944 | The REQUIRE: keyword is used to indicate the minimum version of the | |
945 | B<xsubpp> compiler needed to compile the XS module. An XS module which | |
5f05dabc | 946 | contains the following statement will compile with only B<xsubpp> version |
4633a7c4 LW |
947 | 1.922 or greater: |
948 | ||
949 | REQUIRE: 1.922 | |
950 | ||
a0d0e21e LW |
951 | =head2 The CLEANUP: Keyword |
952 | ||
953 | This keyword can be used when an XSUB requires special cleanup procedures | |
954 | before it terminates. When the CLEANUP: keyword is used it must follow | |
955 | any CODE:, PPCODE:, or OUTPUT: blocks which are present in the XSUB. The | |
956 | code specified for the cleanup block will be added as the last statements | |
957 | in the XSUB. | |
958 | ||
959 | =head2 The BOOT: Keyword | |
960 | ||
961 | The BOOT: keyword is used to add code to the extension's bootstrap | |
962 | function. The bootstrap function is generated by the B<xsubpp> compiler and | |
963 | normally holds the statements necessary to register any XSUBs with Perl. | |
964 | With the BOOT: keyword the programmer can tell the compiler to add extra | |
965 | statements to the bootstrap function. | |
966 | ||
967 | This keyword may be used any time after the first MODULE keyword and should | |
968 | appear on a line by itself. The first blank line after the keyword will | |
969 | terminate the code block. | |
970 | ||
971 | BOOT: | |
972 | # The following message will be printed when the | |
973 | # bootstrap function executes. | |
974 | printf("Hello from the bootstrap!\n"); | |
975 | ||
c07a80fd | 976 | =head2 The VERSIONCHECK: Keyword |
977 | ||
978 | The VERSIONCHECK: keyword corresponds to B<xsubpp>'s C<-versioncheck> and | |
5f05dabc | 979 | C<-noversioncheck> options. This keyword overrides the command line |
c07a80fd | 980 | options. Version checking is enabled by default. When version checking is |
981 | enabled the XS module will attempt to verify that its version matches the | |
982 | version of the PM module. | |
983 | ||
984 | To enable version checking: | |
985 | ||
986 | VERSIONCHECK: ENABLE | |
987 | ||
988 | To disable version checking: | |
989 | ||
990 | VERSIONCHECK: DISABLE | |
991 | ||
992 | =head2 The PROTOTYPES: Keyword | |
993 | ||
994 | The PROTOTYPES: keyword corresponds to B<xsubpp>'s C<-prototypes> and | |
54310121 | 995 | C<-noprototypes> options. This keyword overrides the command line options. |
c07a80fd | 996 | Prototypes are enabled by default. When prototypes are enabled XSUBs will |
997 | be given Perl prototypes. This keyword may be used multiple times in an XS | |
998 | module to enable and disable prototypes for different parts of the module. | |
999 | ||
1000 | To enable prototypes: | |
1001 | ||
1002 | PROTOTYPES: ENABLE | |
1003 | ||
1004 | To disable prototypes: | |
1005 | ||
1006 | PROTOTYPES: DISABLE | |
1007 | ||
1008 | =head2 The PROTOTYPE: Keyword | |
1009 | ||
1010 | This keyword is similar to the PROTOTYPES: keyword above but can be used to | |
1011 | force B<xsubpp> to use a specific prototype for the XSUB. This keyword | |
1012 | overrides all other prototype options and keywords but affects only the | |
1013 | current XSUB. Consult L<perlsub/Prototypes> for information about Perl | |
1014 | prototypes. | |
1015 | ||
1016 | bool_t | |
1017 | rpcb_gettime(timep, ...) | |
1018 | time_t timep = NO_INIT | |
beb31b0b GS |
1019 | PROTOTYPE: $;$ |
1020 | PREINIT: | |
c07a80fd | 1021 | char *host = "localhost"; |
2d8e6c8d | 1022 | STRLEN n_a; |
beb31b0b | 1023 | CODE: |
c07a80fd | 1024 | if( items > 1 ) |
2d8e6c8d | 1025 | host = (char *)SvPV(ST(1), n_a); |
c07a80fd | 1026 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b | 1027 | OUTPUT: |
c07a80fd | 1028 | timep |
1029 | RETVAL | |
1030 | ||
1031 | =head2 The ALIAS: Keyword | |
1032 | ||
cfc02341 | 1033 | The ALIAS: keyword allows an XSUB to have two or more unique Perl names |
c07a80fd | 1034 | and to know which of those names was used when it was invoked. The Perl |
1035 | names may be fully-qualified with package names. Each alias is given an | |
1036 | index. The compiler will setup a variable called C<ix> which contain the | |
1037 | index of the alias which was used. When the XSUB is called with its | |
1038 | declared name C<ix> will be 0. | |
1039 | ||
1040 | The following example will create aliases C<FOO::gettime()> and | |
1041 | C<BAR::getit()> for this function. | |
1042 | ||
1043 | bool_t | |
1044 | rpcb_gettime(host,timep) | |
1045 | char *host | |
1046 | time_t &timep | |
beb31b0b | 1047 | ALIAS: |
c07a80fd | 1048 | FOO::gettime = 1 |
1049 | BAR::getit = 2 | |
beb31b0b | 1050 | INIT: |
c07a80fd | 1051 | printf("# ix = %d\n", ix ); |
beb31b0b | 1052 | OUTPUT: |
c07a80fd | 1053 | timep |
1054 | ||
cfc02341 IZ |
1055 | =head2 The INTERFACE: Keyword |
1056 | ||
1057 | This keyword declares the current XSUB as a keeper of the given | |
1058 | calling signature. If some text follows this keyword, it is | |
1059 | considered as a list of functions which have this signature, and | |
beb31b0b | 1060 | should be attached to the current XSUB. |
cfc02341 | 1061 | |
beb31b0b GS |
1062 | For example, if you have 4 C functions multiply(), divide(), add(), |
1063 | subtract() all having the signature: | |
cfc02341 IZ |
1064 | |
1065 | symbolic f(symbolic, symbolic); | |
1066 | ||
beb31b0b | 1067 | you can make them all to use the same XSUB using this: |
cfc02341 IZ |
1068 | |
1069 | symbolic | |
1070 | interface_s_ss(arg1, arg2) | |
1071 | symbolic arg1 | |
1072 | symbolic arg2 | |
1073 | INTERFACE: | |
1074 | multiply divide | |
1075 | add subtract | |
1076 | ||
beb31b0b GS |
1077 | (This is the complete XSUB code for 4 Perl functions!) Four generated |
1078 | Perl function share names with corresponding C functions. | |
1079 | ||
1080 | The advantage of this approach comparing to ALIAS: keyword is that there | |
1081 | is no need to code a switch statement, each Perl function (which shares | |
1082 | the same XSUB) knows which C function it should call. Additionally, one | |
cfc02341 | 1083 | can attach an extra function remainder() at runtime by using |
beb31b0b | 1084 | |
cfc02341 IZ |
1085 | CV *mycv = newXSproto("Symbolic::remainder", |
1086 | XS_Symbolic_interface_s_ss, __FILE__, "$$"); | |
1087 | XSINTERFACE_FUNC_SET(mycv, remainder); | |
1088 | ||
beb31b0b GS |
1089 | say, from another XSUB. (This example supposes that there was no |
1090 | INTERFACE_MACRO: section, otherwise one needs to use something else instead of | |
1091 | C<XSINTERFACE_FUNC_SET>, see the next section.) | |
cfc02341 IZ |
1092 | |
1093 | =head2 The INTERFACE_MACRO: Keyword | |
1094 | ||
1095 | This keyword allows one to define an INTERFACE using a different way | |
1096 | to extract a function pointer from an XSUB. The text which follows | |
1097 | this keyword should give the name of macros which would extract/set a | |
1098 | function pointer. The extractor macro is given return type, C<CV*>, | |
1099 | and C<XSANY.any_dptr> for this C<CV*>. The setter macro is given cv, | |
1100 | and the function pointer. | |
1101 | ||
1102 | The default value is C<XSINTERFACE_FUNC> and C<XSINTERFACE_FUNC_SET>. | |
1103 | An INTERFACE keyword with an empty list of functions can be omitted if | |
1104 | INTERFACE_MACRO keyword is used. | |
1105 | ||
1106 | Suppose that in the previous example functions pointers for | |
1107 | multiply(), divide(), add(), subtract() are kept in a global C array | |
1108 | C<fp[]> with offsets being C<multiply_off>, C<divide_off>, C<add_off>, | |
1109 | C<subtract_off>. Then one can use | |
1110 | ||
1111 | #define XSINTERFACE_FUNC_BYOFFSET(ret,cv,f) \ | |
1112 | ((XSINTERFACE_CVT(ret,))fp[CvXSUBANY(cv).any_i32]) | |
1113 | #define XSINTERFACE_FUNC_BYOFFSET_set(cv,f) \ | |
1114 | CvXSUBANY(cv).any_i32 = CAT2( f, _off ) | |
1115 | ||
1116 | in C section, | |
1117 | ||
1118 | symbolic | |
1119 | interface_s_ss(arg1, arg2) | |
1120 | symbolic arg1 | |
1121 | symbolic arg2 | |
beb31b0b | 1122 | INTERFACE_MACRO: |
cfc02341 IZ |
1123 | XSINTERFACE_FUNC_BYOFFSET |
1124 | XSINTERFACE_FUNC_BYOFFSET_set | |
beb31b0b | 1125 | INTERFACE: |
cfc02341 IZ |
1126 | multiply divide |
1127 | add subtract | |
1128 | ||
1129 | in XSUB section. | |
1130 | ||
c07a80fd | 1131 | =head2 The INCLUDE: Keyword |
1132 | ||
1133 | This keyword can be used to pull other files into the XS module. The other | |
1134 | files may have XS code. INCLUDE: can also be used to run a command to | |
1135 | generate the XS code to be pulled into the module. | |
1136 | ||
1137 | The file F<Rpcb1.xsh> contains our C<rpcb_gettime()> function: | |
1138 | ||
1139 | bool_t | |
1140 | rpcb_gettime(host,timep) | |
1141 | char *host | |
1142 | time_t &timep | |
beb31b0b | 1143 | OUTPUT: |
c07a80fd | 1144 | timep |
1145 | ||
1146 | The XS module can use INCLUDE: to pull that file into it. | |
1147 | ||
1148 | INCLUDE: Rpcb1.xsh | |
1149 | ||
1150 | If the parameters to the INCLUDE: keyword are followed by a pipe (C<|>) then | |
1151 | the compiler will interpret the parameters as a command. | |
1152 | ||
1153 | INCLUDE: cat Rpcb1.xsh | | |
1154 | ||
1155 | =head2 The CASE: Keyword | |
1156 | ||
1157 | The CASE: keyword allows an XSUB to have multiple distinct parts with each | |
1158 | part acting as a virtual XSUB. CASE: is greedy and if it is used then all | |
1159 | other XS keywords must be contained within a CASE:. This means nothing may | |
1160 | precede the first CASE: in the XSUB and anything following the last CASE: is | |
1161 | included in that case. | |
1162 | ||
1163 | A CASE: might switch via a parameter of the XSUB, via the C<ix> ALIAS: | |
1164 | variable (see L<"The ALIAS: Keyword">), or maybe via the C<items> variable | |
1165 | (see L<"Variable-length Parameter Lists">). The last CASE: becomes the | |
1166 | B<default> case if it is not associated with a conditional. The following | |
1167 | example shows CASE switched via C<ix> with a function C<rpcb_gettime()> | |
1168 | having an alias C<x_gettime()>. When the function is called as | |
b772cb6e | 1169 | C<rpcb_gettime()> its parameters are the usual C<(char *host, time_t *timep)>, |
1170 | but when the function is called as C<x_gettime()> its parameters are | |
c07a80fd | 1171 | reversed, C<(time_t *timep, char *host)>. |
1172 | ||
1173 | long | |
1174 | rpcb_gettime(a,b) | |
1175 | CASE: ix == 1 | |
beb31b0b | 1176 | ALIAS: |
c07a80fd | 1177 | x_gettime = 1 |
beb31b0b | 1178 | INPUT: |
c07a80fd | 1179 | # 'a' is timep, 'b' is host |
1180 | char *b | |
1181 | time_t a = NO_INIT | |
beb31b0b | 1182 | CODE: |
c07a80fd | 1183 | RETVAL = rpcb_gettime( b, &a ); |
beb31b0b | 1184 | OUTPUT: |
c07a80fd | 1185 | a |
1186 | RETVAL | |
1187 | CASE: | |
1188 | # 'a' is host, 'b' is timep | |
1189 | char *a | |
1190 | time_t &b = NO_INIT | |
beb31b0b | 1191 | OUTPUT: |
c07a80fd | 1192 | b |
1193 | RETVAL | |
1194 | ||
1195 | That function can be called with either of the following statements. Note | |
1196 | the different argument lists. | |
1197 | ||
1198 | $status = rpcb_gettime( $host, $timep ); | |
1199 | ||
1200 | $status = x_gettime( $timep, $host ); | |
1201 | ||
1202 | =head2 The & Unary Operator | |
1203 | ||
beb31b0b GS |
1204 | The C<&> unary operator in the INPUT: section is used to tell B<xsubpp> |
1205 | that it should convert a Perl value to/from C using the C type to the left | |
1206 | of C<&>, but provide a pointer to this value when the C function is called. | |
1207 | ||
1208 | This is useful to avoid a CODE: block for a C function which takes a parameter | |
1209 | by reference. Typically, the parameter should be not a pointer type (an | |
1210 | C<int> or C<long> but not a C<int*> or C<long*>). | |
c07a80fd | 1211 | |
beb31b0b | 1212 | The following XSUB will generate incorrect C code. The B<xsubpp> compiler will |
c07a80fd | 1213 | turn this into code which calls C<rpcb_gettime()> with parameters C<(char |
1214 | *host, time_t timep)>, but the real C<rpcb_gettime()> wants the C<timep> | |
1215 | parameter to be of type C<time_t*> rather than C<time_t>. | |
1216 | ||
1217 | bool_t | |
1218 | rpcb_gettime(host,timep) | |
1219 | char *host | |
1220 | time_t timep | |
beb31b0b | 1221 | OUTPUT: |
c07a80fd | 1222 | timep |
1223 | ||
beb31b0b | 1224 | That problem is corrected by using the C<&> operator. The B<xsubpp> compiler |
c07a80fd | 1225 | will now turn this into code which calls C<rpcb_gettime()> correctly with |
1226 | parameters C<(char *host, time_t *timep)>. It does this by carrying the | |
1227 | C<&> through, so the function call looks like C<rpcb_gettime(host, &timep)>. | |
1228 | ||
1229 | bool_t | |
1230 | rpcb_gettime(host,timep) | |
1231 | char *host | |
1232 | time_t &timep | |
beb31b0b | 1233 | OUTPUT: |
c07a80fd | 1234 | timep |
1235 | ||
a0d0e21e LW |
1236 | =head2 Inserting Comments and C Preprocessor Directives |
1237 | ||
f27cfbbe | 1238 | C preprocessor directives are allowed within BOOT:, PREINIT: INIT:, |
5f05dabc | 1239 | CODE:, PPCODE:, and CLEANUP: blocks, as well as outside the functions. |
f27cfbbe | 1240 | Comments are allowed anywhere after the MODULE keyword. The compiler |
1241 | will pass the preprocessor directives through untouched and will remove | |
1242 | the commented lines. | |
b772cb6e | 1243 | |
f27cfbbe | 1244 | Comments can be added to XSUBs by placing a C<#> as the first |
1245 | non-whitespace of a line. Care should be taken to avoid making the | |
1246 | comment look like a C preprocessor directive, lest it be interpreted as | |
1247 | such. The simplest way to prevent this is to put whitespace in front of | |
1248 | the C<#>. | |
1249 | ||
f27cfbbe | 1250 | If you use preprocessor directives to choose one of two |
1251 | versions of a function, use | |
1252 | ||
1253 | #if ... version1 | |
1254 | #else /* ... version2 */ | |
1255 | #endif | |
1256 | ||
1257 | and not | |
1258 | ||
1259 | #if ... version1 | |
1260 | #endif | |
1261 | #if ... version2 | |
1262 | #endif | |
1263 | ||
beb31b0b | 1264 | because otherwise B<xsubpp> will believe that you made a duplicate |
f27cfbbe | 1265 | definition of the function. Also, put a blank line before the |
1266 | #else/#endif so it will not be seen as part of the function body. | |
a0d0e21e LW |
1267 | |
1268 | =head2 Using XS With C++ | |
1269 | ||
beb31b0b GS |
1270 | If an XSUB name contains C<::>, it is considered to be a C++ method. |
1271 | The generated Perl function will assume that | |
a0d0e21e LW |
1272 | its first argument is an object pointer. The object pointer |
1273 | will be stored in a variable called THIS. The object should | |
1274 | have been created by C++ with the new() function and should | |
cb1a09d0 AD |
1275 | be blessed by Perl with the sv_setref_pv() macro. The |
1276 | blessing of the object by Perl can be handled by a typemap. An example | |
1277 | typemap is shown at the end of this section. | |
a0d0e21e | 1278 | |
beb31b0b GS |
1279 | If the return type of the XSUB includes C<static>, the method is considered |
1280 | to be a static method. It will call the C++ | |
a0d0e21e | 1281 | function using the class::method() syntax. If the method is not static |
f27cfbbe | 1282 | the function will be called using the THIS-E<gt>method() syntax. |
a0d0e21e | 1283 | |
cb1a09d0 | 1284 | The next examples will use the following C++ class. |
a0d0e21e | 1285 | |
a5f75d66 | 1286 | class color { |
cb1a09d0 | 1287 | public: |
a5f75d66 AD |
1288 | color(); |
1289 | ~color(); | |
cb1a09d0 AD |
1290 | int blue(); |
1291 | void set_blue( int ); | |
1292 | ||
1293 | private: | |
1294 | int c_blue; | |
1295 | }; | |
1296 | ||
1297 | The XSUBs for the blue() and set_blue() methods are defined with the class | |
1298 | name but the parameter for the object (THIS, or "self") is implicit and is | |
1299 | not listed. | |
1300 | ||
1301 | int | |
1302 | color::blue() | |
a0d0e21e LW |
1303 | |
1304 | void | |
cb1a09d0 AD |
1305 | color::set_blue( val ) |
1306 | int val | |
a0d0e21e | 1307 | |
beb31b0b GS |
1308 | Both Perl functions will expect an object as the first parameter. In the |
1309 | generated C++ code the object is called C<THIS>, and the method call will | |
1310 | be performed on this object. So in the C++ code the blue() and set_blue() | |
1311 | methods will be called as this: | |
a0d0e21e | 1312 | |
cb1a09d0 | 1313 | RETVAL = THIS->blue(); |
a0d0e21e | 1314 | |
cb1a09d0 | 1315 | THIS->set_blue( val ); |
a0d0e21e | 1316 | |
4628e4f8 GS |
1317 | You could also write a single get/set method using an optional argument: |
1318 | ||
1319 | int | |
a104f515 | 1320 | color::blue( val = NO_INIT ) |
4628e4f8 GS |
1321 | int val |
1322 | PROTOTYPE $;$ | |
1323 | CODE: | |
1324 | if (items > 1) | |
1325 | THIS->set_blue( val ); | |
1326 | RETVAL = THIS->blue(); | |
1327 | OUTPUT: | |
1328 | RETVAL | |
1329 | ||
cb1a09d0 | 1330 | If the function's name is B<DESTROY> then the C++ C<delete> function will be |
beb31b0b | 1331 | called and C<THIS> will be given as its parameter. The generated C++ code for |
a0d0e21e | 1332 | |
d1b91892 | 1333 | void |
cb1a09d0 AD |
1334 | color::DESTROY() |
1335 | ||
beb31b0b GS |
1336 | will look like this: |
1337 | ||
1338 | color *THIS = ...; // Initialized as in typemap | |
cb1a09d0 AD |
1339 | |
1340 | delete THIS; | |
a0d0e21e | 1341 | |
cb1a09d0 AD |
1342 | If the function's name is B<new> then the C++ C<new> function will be called |
1343 | to create a dynamic C++ object. The XSUB will expect the class name, which | |
1344 | will be kept in a variable called C<CLASS>, to be given as the first | |
1345 | argument. | |
a0d0e21e | 1346 | |
cb1a09d0 AD |
1347 | color * |
1348 | color::new() | |
a0d0e21e | 1349 | |
beb31b0b | 1350 | The generated C++ code will call C<new>. |
a0d0e21e | 1351 | |
beb31b0b | 1352 | RETVAL = new color(); |
cb1a09d0 AD |
1353 | |
1354 | The following is an example of a typemap that could be used for this C++ | |
1355 | example. | |
1356 | ||
1357 | TYPEMAP | |
1358 | color * O_OBJECT | |
1359 | ||
1360 | OUTPUT | |
1361 | # The Perl object is blessed into 'CLASS', which should be a | |
1362 | # char* having the name of the package for the blessing. | |
1363 | O_OBJECT | |
1364 | sv_setref_pv( $arg, CLASS, (void*)$var ); | |
a6006777 | 1365 | |
cb1a09d0 AD |
1366 | INPUT |
1367 | O_OBJECT | |
1368 | if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) ) | |
1369 | $var = ($type)SvIV((SV*)SvRV( $arg )); | |
1370 | else{ | |
1371 | warn( \"${Package}::$func_name() -- $var is not a blessed SV reference\" ); | |
1372 | XSRETURN_UNDEF; | |
1373 | } | |
a0d0e21e | 1374 | |
d1b91892 | 1375 | =head2 Interface Strategy |
a0d0e21e LW |
1376 | |
1377 | When designing an interface between Perl and a C library a straight | |
beb31b0b GS |
1378 | translation from C to XS (such as created by C<h2xs -x>) is often sufficient. |
1379 | However, sometimes the interface will look | |
a0d0e21e | 1380 | very C-like and occasionally nonintuitive, especially when the C function |
beb31b0b GS |
1381 | modifies one of its parameters, or returns failure inband (as in "negative |
1382 | return values mean failure"). In cases where the programmer wishes to | |
a0d0e21e LW |
1383 | create a more Perl-like interface the following strategy may help to |
1384 | identify the more critical parts of the interface. | |
1385 | ||
beb31b0b GS |
1386 | Identify the C functions with input/output or output parameters. The XSUBs for |
1387 | these functions may be able to return lists to Perl. | |
1388 | ||
1389 | Identify the C functions which use some inband info as an indication | |
1390 | of failure. They may be | |
1391 | candidates to return undef or an empty list in case of failure. If the | |
1392 | failure may be detected without a call to the C function, you may want to use | |
1393 | an INIT: section to report the failure. For failures detectable after the C | |
1394 | function returns one may want to use a CLEANUP: section to process the | |
1395 | failure. In more complicated cases use CODE: or PPCODE: sections. | |
1396 | ||
1397 | If many functions use the same failure indication based on the return value, | |
1398 | you may want to create a special typedef to handle this situation. Put | |
1399 | ||
1400 | typedef int negative_is_failure; | |
1401 | ||
1402 | near the beginning of XS file, and create an OUTPUT typemap entry | |
1403 | for C<negative_is_failure> which converts negative values to C<undef>, or | |
1404 | maybe croak()s. After this the return value of type C<negative_is_failure> | |
1405 | will create more Perl-like interface. | |
a0d0e21e | 1406 | |
d1b91892 | 1407 | Identify which values are used by only the C and XSUB functions |
beb31b0b GS |
1408 | themselves, say, when a parameter to a function should be a contents of a |
1409 | global variable. If Perl does not need to access the contents of the value | |
a0d0e21e LW |
1410 | then it may not be necessary to provide a translation for that value |
1411 | from C to Perl. | |
1412 | ||
1413 | Identify the pointers in the C function parameter lists and return | |
beb31b0b GS |
1414 | values. Some pointers may be used to implement input/output or |
1415 | output parameters, they can be handled in XS with the C<&> unary operator, | |
1416 | and, possibly, using the NO_INIT keyword. | |
1417 | Some others will require handling of types like C<int *>, and one needs | |
1418 | to decide what a useful Perl translation will do in such a case. When | |
1419 | the semantic is clear, it is advisable to put the translation into a typemap | |
1420 | file. | |
a0d0e21e LW |
1421 | |
1422 | Identify the structures used by the C functions. In many | |
1423 | cases it may be helpful to use the T_PTROBJ typemap for | |
1424 | these structures so they can be manipulated by Perl as | |
beb31b0b GS |
1425 | blessed objects. (This is handled automatically by C<h2xs -x>.) |
1426 | ||
1427 | If the same C type is used in several different contexts which require | |
1428 | different translations, C<typedef> several new types mapped to this C type, | |
1429 | and create separate F<typemap> entries for these new types. Use these | |
1430 | types in declarations of return type and parameters to XSUBs. | |
a0d0e21e | 1431 | |
a0d0e21e LW |
1432 | =head2 Perl Objects And C Structures |
1433 | ||
1434 | When dealing with C structures one should select either | |
1435 | B<T_PTROBJ> or B<T_PTRREF> for the XS type. Both types are | |
1436 | designed to handle pointers to complex objects. The | |
1437 | T_PTRREF type will allow the Perl object to be unblessed | |
1438 | while the T_PTROBJ type requires that the object be blessed. | |
1439 | By using T_PTROBJ one can achieve a form of type-checking | |
d1b91892 | 1440 | because the XSUB will attempt to verify that the Perl object |
a0d0e21e LW |
1441 | is of the expected type. |
1442 | ||
1443 | The following XS code shows the getnetconfigent() function which is used | |
8e07c86e | 1444 | with ONC+ TIRPC. The getnetconfigent() function will return a pointer to a |
a0d0e21e LW |
1445 | C structure and has the C prototype shown below. The example will |
1446 | demonstrate how the C pointer will become a Perl reference. Perl will | |
1447 | consider this reference to be a pointer to a blessed object and will | |
1448 | attempt to call a destructor for the object. A destructor will be | |
1449 | provided in the XS source to free the memory used by getnetconfigent(). | |
1450 | Destructors in XS can be created by specifying an XSUB function whose name | |
1451 | ends with the word B<DESTROY>. XS destructors can be used to free memory | |
1452 | which may have been malloc'd by another XSUB. | |
1453 | ||
1454 | struct netconfig *getnetconfigent(const char *netid); | |
1455 | ||
1456 | A C<typedef> will be created for C<struct netconfig>. The Perl | |
1457 | object will be blessed in a class matching the name of the C | |
1458 | type, with the tag C<Ptr> appended, and the name should not | |
1459 | have embedded spaces if it will be a Perl package name. The | |
1460 | destructor will be placed in a class corresponding to the | |
1461 | class of the object and the PREFIX keyword will be used to | |
1462 | trim the name to the word DESTROY as Perl will expect. | |
1463 | ||
1464 | typedef struct netconfig Netconfig; | |
1465 | ||
1466 | MODULE = RPC PACKAGE = RPC | |
1467 | ||
1468 | Netconfig * | |
1469 | getnetconfigent(netid) | |
8e07c86e | 1470 | char *netid |
a0d0e21e LW |
1471 | |
1472 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ | |
1473 | ||
1474 | void | |
1475 | rpcb_DESTROY(netconf) | |
8e07c86e | 1476 | Netconfig *netconf |
beb31b0b | 1477 | CODE: |
a0d0e21e LW |
1478 | printf("Now in NetconfigPtr::DESTROY\n"); |
1479 | free( netconf ); | |
1480 | ||
1481 | This example requires the following typemap entry. Consult the typemap | |
1482 | section for more information about adding new typemaps for an extension. | |
1483 | ||
1484 | TYPEMAP | |
1485 | Netconfig * T_PTROBJ | |
1486 | ||
1487 | This example will be used with the following Perl statements. | |
1488 | ||
1489 | use RPC; | |
1490 | $netconf = getnetconfigent("udp"); | |
1491 | ||
1492 | When Perl destroys the object referenced by $netconf it will send the | |
1493 | object to the supplied XSUB DESTROY function. Perl cannot determine, and | |
1494 | does not care, that this object is a C struct and not a Perl object. In | |
1495 | this sense, there is no difference between the object created by the | |
1496 | getnetconfigent() XSUB and an object created by a normal Perl subroutine. | |
1497 | ||
a0d0e21e LW |
1498 | =head2 The Typemap |
1499 | ||
1500 | The typemap is a collection of code fragments which are used by the B<xsubpp> | |
1501 | compiler to map C function parameters and values to Perl values. The | |
1502 | typemap file may consist of three sections labeled C<TYPEMAP>, C<INPUT>, and | |
beb31b0b GS |
1503 | C<OUTPUT>. An unlabelled initial section is assumed to be a C<TYPEMAP> |
1504 | section. The INPUT section tells | |
7e9d670d | 1505 | the compiler how to translate Perl values |
a0d0e21e LW |
1506 | into variables of certain C types. The OUTPUT section tells the compiler |
1507 | how to translate the values from certain C types into values Perl can | |
1508 | understand. The TYPEMAP section tells the compiler which of the INPUT and | |
1509 | OUTPUT code fragments should be used to map a given C type to a Perl value. | |
7e9d670d GS |
1510 | The section labels C<TYPEMAP>, C<INPUT>, or C<OUTPUT> must begin |
1511 | in the first column on a line by themselves, and must be in uppercase. | |
a0d0e21e LW |
1512 | |
1513 | The default typemap in the C<ext> directory of the Perl source contains many | |
1514 | useful types which can be used by Perl extensions. Some extensions define | |
1515 | additional typemaps which they keep in their own directory. These | |
1516 | additional typemaps may reference INPUT and OUTPUT maps in the main | |
1517 | typemap. The B<xsubpp> compiler will allow the extension's own typemap to | |
1518 | override any mappings which are in the default typemap. | |
1519 | ||
1520 | Most extensions which require a custom typemap will need only the TYPEMAP | |
1521 | section of the typemap file. The custom typemap used in the | |
1522 | getnetconfigent() example shown earlier demonstrates what may be the typical | |
1523 | use of extension typemaps. That typemap is used to equate a C structure | |
1524 | with the T_PTROBJ typemap. The typemap used by getnetconfigent() is shown | |
1525 | here. Note that the C type is separated from the XS type with a tab and | |
1526 | that the C unary operator C<*> is considered to be a part of the C type name. | |
1527 | ||
beb31b0b GS |
1528 | TYPEMAP |
1529 | Netconfig *<tab>T_PTROBJ | |
a0d0e21e | 1530 | |
1748e8dd RS |
1531 | Here's a more complicated example: suppose that you wanted C<struct |
1532 | netconfig> to be blessed into the class C<Net::Config>. One way to do | |
1533 | this is to use underscores (_) to separate package names, as follows: | |
1534 | ||
1535 | typedef struct netconfig * Net_Config; | |
1536 | ||
1537 | And then provide a typemap entry C<T_PTROBJ_SPECIAL> that maps underscores to | |
1538 | double-colons (::), and declare C<Net_Config> to be of that type: | |
1539 | ||
1540 | ||
1541 | TYPEMAP | |
1542 | Net_Config T_PTROBJ_SPECIAL | |
1543 | ||
1544 | INPUT | |
1545 | T_PTROBJ_SPECIAL | |
1546 | if (sv_derived_from($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")) { | |
1547 | IV tmp = SvIV((SV*)SvRV($arg)); | |
1548 | $var = ($type) tmp; | |
1549 | } | |
1550 | else | |
1551 | croak(\"$var is not of type ${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\") | |
1552 | ||
1553 | OUTPUT | |
1554 | T_PTROBJ_SPECIAL | |
1555 | sv_setref_pv($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\", | |
1556 | (void*)$var); | |
1557 | ||
1558 | The INPUT and OUTPUT sections substitute underscores for double-colons | |
1559 | on the fly, giving the desired effect. This example demonstrates some | |
1560 | of the power and versatility of the typemap facility. | |
1561 | ||
a0d0e21e LW |
1562 | =head1 EXAMPLES |
1563 | ||
1564 | File C<RPC.xs>: Interface to some ONC+ RPC bind library functions. | |
1565 | ||
1566 | #include "EXTERN.h" | |
1567 | #include "perl.h" | |
1568 | #include "XSUB.h" | |
1569 | ||
1570 | #include <rpc/rpc.h> | |
1571 | ||
1572 | typedef struct netconfig Netconfig; | |
1573 | ||
1574 | MODULE = RPC PACKAGE = RPC | |
1575 | ||
e7ea3e70 | 1576 | SV * |
a0d0e21e | 1577 | rpcb_gettime(host="localhost") |
8e07c86e | 1578 | char *host |
beb31b0b | 1579 | PREINIT: |
a0d0e21e | 1580 | time_t timep; |
beb31b0b | 1581 | CODE: |
a0d0e21e LW |
1582 | ST(0) = sv_newmortal(); |
1583 | if( rpcb_gettime( host, &timep ) ) | |
1584 | sv_setnv( ST(0), (double)timep ); | |
a0d0e21e LW |
1585 | |
1586 | Netconfig * | |
1587 | getnetconfigent(netid="udp") | |
8e07c86e | 1588 | char *netid |
a0d0e21e LW |
1589 | |
1590 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ | |
1591 | ||
1592 | void | |
1593 | rpcb_DESTROY(netconf) | |
8e07c86e | 1594 | Netconfig *netconf |
beb31b0b | 1595 | CODE: |
a0d0e21e LW |
1596 | printf("NetconfigPtr::DESTROY\n"); |
1597 | free( netconf ); | |
1598 | ||
1599 | File C<typemap>: Custom typemap for RPC.xs. | |
1600 | ||
1601 | TYPEMAP | |
1602 | Netconfig * T_PTROBJ | |
1603 | ||
1604 | File C<RPC.pm>: Perl module for the RPC extension. | |
1605 | ||
1606 | package RPC; | |
1607 | ||
1608 | require Exporter; | |
1609 | require DynaLoader; | |
1610 | @ISA = qw(Exporter DynaLoader); | |
1611 | @EXPORT = qw(rpcb_gettime getnetconfigent); | |
1612 | ||
1613 | bootstrap RPC; | |
1614 | 1; | |
1615 | ||
1616 | File C<rpctest.pl>: Perl test program for the RPC extension. | |
1617 | ||
1618 | use RPC; | |
1619 | ||
1620 | $netconf = getnetconfigent(); | |
1621 | $a = rpcb_gettime(); | |
1622 | print "time = $a\n"; | |
1623 | print "netconf = $netconf\n"; | |
1624 | ||
1625 | $netconf = getnetconfigent("tcp"); | |
1626 | $a = rpcb_gettime("poplar"); | |
1627 | print "time = $a\n"; | |
1628 | print "netconf = $netconf\n"; | |
1629 | ||
1630 | ||
c07a80fd | 1631 | =head1 XS VERSION |
1632 | ||
f27cfbbe | 1633 | This document covers features supported by C<xsubpp> 1.935. |
c07a80fd | 1634 | |
a0d0e21e LW |
1635 | =head1 AUTHOR |
1636 | ||
beb31b0b GS |
1637 | Originally written by Dean Roehrich <F<roehrich@cray.com>>. |
1638 | ||
7f2de2d2 | 1639 | Maintained since 1996 by The Perl Porters <F<perlbug@perl.org>>. |