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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 | |
7817ba4d NC |
69 | is usually referred to as the XS language. B<xsubpp> recognizes and |
70 | skips POD (see L<perlpod>) in both the C and XS language sections, which | |
71 | allows the XS file to contain embedded documentation. | |
a0d0e21e | 72 | |
cb1a09d0 | 73 | See L<perlxstut> for a tutorial on the whole extension creation process. |
8e07c86e | 74 | |
beb31b0b | 75 | Note: For some extensions, Dave Beazley's SWIG system may provide a |
b3b6085d PP |
76 | significantly more convenient mechanism for creating the extension |
77 | glue code. See http://www.swig.org/ for more information. | |
7b8d334a | 78 | |
8e07c86e AD |
79 | =head2 On The Road |
80 | ||
a5f75d66 AD |
81 | Many of the examples which follow will concentrate on creating an interface |
82 | between Perl and the ONC+ RPC bind library functions. The rpcb_gettime() | |
83 | function is used to demonstrate many features of the XS language. This | |
84 | function has two parameters; the first is an input parameter and the second | |
85 | is an output parameter. The function also returns a status value. | |
a0d0e21e LW |
86 | |
87 | bool_t rpcb_gettime(const char *host, time_t *timep); | |
88 | ||
89 | From C this function will be called with the following | |
90 | statements. | |
91 | ||
92 | #include <rpc/rpc.h> | |
93 | bool_t status; | |
94 | time_t timep; | |
95 | status = rpcb_gettime( "localhost", &timep ); | |
96 | ||
97 | If an XSUB is created to offer a direct translation between this function | |
98 | and Perl, then this XSUB will be used from Perl with the following code. | |
99 | The $status and $timep variables will contain the output of the function. | |
100 | ||
101 | use RPC; | |
102 | $status = rpcb_gettime( "localhost", $timep ); | |
103 | ||
104 | The following XS file shows an XS subroutine, or XSUB, which | |
105 | demonstrates one possible interface to the rpcb_gettime() | |
106 | function. This XSUB represents a direct translation between | |
107 | C and Perl and so preserves the interface even from Perl. | |
108 | This XSUB will be invoked from Perl with the usage shown | |
109 | above. Note that the first three #include statements, for | |
110 | C<EXTERN.h>, C<perl.h>, and C<XSUB.h>, will always be present at the | |
111 | beginning of an XS file. This approach and others will be | |
112 | expanded later in this document. | |
113 | ||
114 | #include "EXTERN.h" | |
115 | #include "perl.h" | |
116 | #include "XSUB.h" | |
117 | #include <rpc/rpc.h> | |
118 | ||
119 | MODULE = RPC PACKAGE = RPC | |
120 | ||
121 | bool_t | |
122 | rpcb_gettime(host,timep) | |
8e07c86e AD |
123 | char *host |
124 | time_t &timep | |
beb31b0b | 125 | OUTPUT: |
a0d0e21e LW |
126 | timep |
127 | ||
128 | Any extension to Perl, including those containing XSUBs, | |
129 | should have a Perl module to serve as the bootstrap which | |
130 | pulls the extension into Perl. This module will export the | |
131 | extension's functions and variables to the Perl program and | |
132 | will cause the extension's XSUBs to be linked into Perl. | |
133 | The following module will be used for most of the examples | |
134 | in this document and should be used from Perl with the C<use> | |
135 | command as shown earlier. Perl modules are explained in | |
136 | more detail later in this document. | |
137 | ||
138 | package RPC; | |
139 | ||
140 | require Exporter; | |
141 | require DynaLoader; | |
142 | @ISA = qw(Exporter DynaLoader); | |
143 | @EXPORT = qw( rpcb_gettime ); | |
144 | ||
145 | bootstrap RPC; | |
146 | 1; | |
147 | ||
148 | Throughout this document a variety of interfaces to the rpcb_gettime() | |
149 | XSUB will be explored. The XSUBs will take their parameters in different | |
150 | orders or will take different numbers of parameters. In each case the | |
151 | XSUB is an abstraction between Perl and the real C rpcb_gettime() | |
152 | function, and the XSUB must always ensure that the real rpcb_gettime() | |
153 | function is called with the correct parameters. This abstraction will | |
154 | allow the programmer to create a more Perl-like interface to the C | |
155 | function. | |
156 | ||
157 | =head2 The Anatomy of an XSUB | |
158 | ||
beb31b0b GS |
159 | The simplest XSUBs consist of 3 parts: a description of the return |
160 | value, the name of the XSUB routine and the names of its arguments, | |
161 | and a description of types or formats of the arguments. | |
162 | ||
8e07c86e AD |
163 | The following XSUB allows a Perl program to access a C library function |
164 | called sin(). The XSUB will imitate the C function which takes a single | |
165 | argument and returns a single value. | |
a0d0e21e LW |
166 | |
167 | double | |
168 | sin(x) | |
8e07c86e | 169 | double x |
a0d0e21e | 170 | |
9e24e6f2 IZ |
171 | Optionally, one can merge the description of types and the list of |
172 | argument names, rewriting this as | |
beb31b0b | 173 | |
9e24e6f2 IZ |
174 | double |
175 | sin(double x) | |
176 | ||
177 | This makes this XSUB look similar to an ANSI C declaration. An optional | |
178 | semicolon is allowed after the argument list, as in | |
179 | ||
180 | double | |
181 | sin(double x); | |
182 | ||
183 | Parameters with C pointer types can have different semantic: C functions | |
184 | with similar declarations | |
beb31b0b | 185 | |
9e24e6f2 IZ |
186 | bool string_looks_as_a_number(char *s); |
187 | bool make_char_uppercase(char *c); | |
188 | ||
189 | are used in absolutely incompatible manner. Parameters to these functions | |
190 | could be described B<xsubpp> like this: | |
beb31b0b GS |
191 | |
192 | char * s | |
9e24e6f2 | 193 | char &c |
beb31b0b GS |
194 | |
195 | Both these XS declarations correspond to the C<char*> C type, but they have | |
9e24e6f2 IZ |
196 | different semantics, see L<"The & Unary Operator">. |
197 | ||
198 | It is convenient to think that the indirection operator | |
beb31b0b | 199 | C<*> should be considered as a part of the type and the address operator C<&> |
9e24e6f2 IZ |
200 | should be considered part of the variable. See L<"The Typemap"> |
201 | for more info about handling qualifiers and unary operators in C types. | |
a0d0e21e | 202 | |
a0d0e21e | 203 | The function name and the return type must be placed on |
beb31b0b | 204 | separate lines and should be flush left-adjusted. |
a0d0e21e LW |
205 | |
206 | INCORRECT CORRECT | |
207 | ||
208 | double sin(x) double | |
8e07c86e AD |
209 | double x sin(x) |
210 | double x | |
a0d0e21e | 211 | |
7817ba4d NC |
212 | The rest of the function description may be indented or left-adjusted. The |
213 | following example shows a function with its body left-adjusted. Most | |
214 | examples in this document will indent the body for better readability. | |
c07a80fd | 215 | |
216 | CORRECT | |
217 | ||
218 | double | |
219 | sin(x) | |
220 | double x | |
221 | ||
beb31b0b GS |
222 | More complicated XSUBs may contain many other sections. Each section of |
223 | an XSUB starts with the corresponding keyword, such as INIT: or CLEANUP:. | |
224 | However, the first two lines of an XSUB always contain the same data: | |
225 | descriptions of the return type and the names of the function and its | |
226 | parameters. Whatever immediately follows these is considered to be | |
227 | an INPUT: section unless explicitly marked with another keyword. | |
228 | (See L<The INPUT: Keyword>.) | |
229 | ||
230 | An XSUB section continues until another section-start keyword is found. | |
231 | ||
a0d0e21e LW |
232 | =head2 The Argument Stack |
233 | ||
beb31b0b | 234 | The Perl argument stack is used to store the values which are |
a0d0e21e | 235 | sent as parameters to the XSUB and to store the XSUB's |
beb31b0b GS |
236 | return value(s). In reality all Perl functions (including non-XSUB |
237 | ones) keep their values on this stack all the same time, each limited | |
238 | to its own range of positions on the stack. In this document the | |
a0d0e21e LW |
239 | first position on that stack which belongs to the active |
240 | function will be referred to as position 0 for that function. | |
241 | ||
8e07c86e AD |
242 | XSUBs refer to their stack arguments with the macro B<ST(x)>, where I<x> |
243 | refers to a position in this XSUB's part of the stack. Position 0 for that | |
a0d0e21e LW |
244 | function would be known to the XSUB as ST(0). The XSUB's incoming |
245 | parameters and outgoing return values always begin at ST(0). For many | |
246 | simple cases the B<xsubpp> compiler will generate the code necessary to | |
247 | handle the argument stack by embedding code fragments found in the | |
248 | typemaps. In more complex cases the programmer must supply the code. | |
249 | ||
250 | =head2 The RETVAL Variable | |
251 | ||
beb31b0b GS |
252 | The RETVAL variable is a special C variable that is declared automatically |
253 | for you. The C type of RETVAL matches the return type of the C library | |
254 | function. The B<xsubpp> compiler will declare this variable in each XSUB | |
255 | with non-C<void> return type. By default the generated C function | |
256 | will use RETVAL to hold the return value of the C library function being | |
257 | called. In simple cases the value of RETVAL will be placed in ST(0) of | |
258 | the argument stack where it can be received by Perl as the return value | |
259 | of the XSUB. | |
a0d0e21e LW |
260 | |
261 | If the XSUB has a return type of C<void> then the compiler will | |
beb31b0b GS |
262 | not declare a RETVAL variable for that function. When using |
263 | a PPCODE: section no manipulation of the RETVAL variable is required, the | |
264 | section may use direct stack manipulation to place output values on the stack. | |
e7ea3e70 IZ |
265 | |
266 | If PPCODE: directive is not used, C<void> return value should be used | |
267 | only for subroutines which do not return a value, I<even if> CODE: | |
54310121 | 268 | directive is used which sets ST(0) explicitly. |
e7ea3e70 IZ |
269 | |
270 | Older versions of this document recommended to use C<void> return | |
271 | value in such cases. It was discovered that this could lead to | |
c2611fb3 | 272 | segfaults in cases when XSUB was I<truly> C<void>. This practice is |
e7ea3e70 IZ |
273 | now deprecated, and may be not supported at some future version. Use |
274 | the return value C<SV *> in such cases. (Currently C<xsubpp> contains | |
c2611fb3 | 275 | some heuristic code which tries to disambiguate between "truly-void" |
e7ea3e70 IZ |
276 | and "old-practice-declared-as-void" functions. Hence your code is at |
277 | mercy of this heuristics unless you use C<SV *> as return value.) | |
a0d0e21e LW |
278 | |
279 | =head2 The MODULE Keyword | |
280 | ||
7817ba4d NC |
281 | The MODULE keyword is used to start the XS code and to specify the package |
282 | of the functions which are being defined. All text preceding the first | |
283 | MODULE keyword is considered C code and is passed through to the output with | |
284 | POD stripped, but otherwise untouched. Every XS module will have a | |
285 | bootstrap function which is used to hook the XSUBs into Perl. The package | |
286 | name of this bootstrap function will match the value of the last MODULE | |
287 | statement in the XS source files. The value of MODULE should always remain | |
288 | constant within the same XS file, though this is not required. | |
a0d0e21e LW |
289 | |
290 | The following example will start the XS code and will place | |
291 | all functions in a package named RPC. | |
292 | ||
293 | MODULE = RPC | |
294 | ||
295 | =head2 The PACKAGE Keyword | |
296 | ||
297 | When functions within an XS source file must be separated into packages | |
298 | the PACKAGE keyword should be used. This keyword is used with the MODULE | |
299 | keyword and must follow immediately after it when used. | |
300 | ||
301 | MODULE = RPC PACKAGE = RPC | |
302 | ||
303 | [ XS code in package RPC ] | |
304 | ||
305 | MODULE = RPC PACKAGE = RPCB | |
306 | ||
307 | [ XS code in package RPCB ] | |
308 | ||
309 | MODULE = RPC PACKAGE = RPC | |
310 | ||
311 | [ XS code in package RPC ] | |
312 | ||
313 | Although this keyword is optional and in some cases provides redundant | |
314 | information it should always be used. This keyword will ensure that the | |
315 | XSUBs appear in the desired package. | |
316 | ||
317 | =head2 The PREFIX Keyword | |
318 | ||
319 | The PREFIX keyword designates prefixes which should be | |
320 | removed from the Perl function names. If the C function is | |
321 | C<rpcb_gettime()> and the PREFIX value is C<rpcb_> then Perl will | |
322 | see this function as C<gettime()>. | |
323 | ||
324 | This keyword should follow the PACKAGE keyword when used. | |
325 | If PACKAGE is not used then PREFIX should follow the MODULE | |
326 | keyword. | |
327 | ||
328 | MODULE = RPC PREFIX = rpc_ | |
329 | ||
330 | MODULE = RPC PACKAGE = RPCB PREFIX = rpcb_ | |
331 | ||
332 | =head2 The OUTPUT: Keyword | |
333 | ||
334 | The OUTPUT: keyword indicates that certain function parameters should be | |
335 | updated (new values made visible to Perl) when the XSUB terminates or that | |
336 | certain values should be returned to the calling Perl function. For | |
beb31b0b GS |
337 | simple functions which have no CODE: or PPCODE: section, |
338 | such as the sin() function above, the RETVAL variable is | |
339 | automatically designated as an output value. For more complex functions | |
a0d0e21e LW |
340 | the B<xsubpp> compiler will need help to determine which variables are output |
341 | variables. | |
342 | ||
343 | This keyword will normally be used to complement the CODE: keyword. | |
344 | The RETVAL variable is not recognized as an output variable when the | |
345 | CODE: keyword is present. The OUTPUT: keyword is used in this | |
346 | situation to tell the compiler that RETVAL really is an output | |
347 | variable. | |
348 | ||
349 | The OUTPUT: keyword can also be used to indicate that function parameters | |
350 | are output variables. This may be necessary when a parameter has been | |
351 | modified within the function and the programmer would like the update to | |
8e07c86e | 352 | be seen by Perl. |
a0d0e21e LW |
353 | |
354 | bool_t | |
355 | rpcb_gettime(host,timep) | |
8e07c86e AD |
356 | char *host |
357 | time_t &timep | |
beb31b0b | 358 | OUTPUT: |
a0d0e21e LW |
359 | timep |
360 | ||
361 | The OUTPUT: keyword will also allow an output parameter to | |
362 | be mapped to a matching piece of code rather than to a | |
ef50df4b | 363 | typemap. |
a0d0e21e LW |
364 | |
365 | bool_t | |
366 | rpcb_gettime(host,timep) | |
8e07c86e AD |
367 | char *host |
368 | time_t &timep | |
beb31b0b | 369 | OUTPUT: |
ef50df4b GS |
370 | timep sv_setnv(ST(1), (double)timep); |
371 | ||
372 | B<xsubpp> emits an automatic C<SvSETMAGIC()> for all parameters in the | |
373 | OUTPUT section of the XSUB, except RETVAL. This is the usually desired | |
374 | behavior, as it takes care of properly invoking 'set' magic on output | |
375 | parameters (needed for hash or array element parameters that must be | |
376 | created if they didn't exist). If for some reason, this behavior is | |
377 | not desired, the OUTPUT section may contain a C<SETMAGIC: DISABLE> line | |
378 | to disable it for the remainder of the parameters in the OUTPUT section. | |
379 | Likewise, C<SETMAGIC: ENABLE> can be used to reenable it for the | |
380 | remainder of the OUTPUT section. See L<perlguts> for more details | |
381 | about 'set' magic. | |
a0d0e21e | 382 | |
9e24e6f2 IZ |
383 | =head2 The NO_OUTPUT Keyword |
384 | ||
385 | The NO_OUTPUT can be placed as the first token of the XSUB. This keyword | |
386 | indicates that while the C subroutine we provide an interface to has | |
387 | a non-C<void> return type, the return value of this C subroutine should not | |
388 | be returned from the generated Perl subroutine. | |
389 | ||
390 | With this keyword present L<The RETVAL Variable> is created, and in the | |
391 | generated call to the subroutine this variable is assigned to, but the value | |
392 | of this variable is not going to be used in the auto-generated code. | |
393 | ||
394 | This keyword makes sense only if C<RETVAL> is going to be accessed by the | |
395 | user-supplied code. It is especially useful to make a function interface | |
396 | more Perl-like, especially when the C return value is just an error condition | |
397 | indicator. For example, | |
398 | ||
399 | NO_OUTPUT int | |
400 | delete_file(char *name) | |
401 | POST_CALL: | |
402 | if (RETVAL != 0) | |
403 | croak("Error %d while deleting file '%s'", RETVAL, name); | |
404 | ||
405 | Here the generated XS function returns nothing on success, and will die() | |
406 | with a meaningful error message on error. | |
407 | ||
a0d0e21e LW |
408 | =head2 The CODE: Keyword |
409 | ||
410 | This keyword is used in more complicated XSUBs which require | |
411 | special handling for the C function. The RETVAL variable is | |
beb31b0b GS |
412 | still declared, but it will not be returned unless it is specified |
413 | in the OUTPUT: section. | |
a0d0e21e LW |
414 | |
415 | The following XSUB is for a C function which requires special handling of | |
416 | its parameters. The Perl usage is given first. | |
417 | ||
418 | $status = rpcb_gettime( "localhost", $timep ); | |
419 | ||
54310121 | 420 | The XSUB follows. |
a0d0e21e | 421 | |
d1b91892 AD |
422 | bool_t |
423 | rpcb_gettime(host,timep) | |
8e07c86e AD |
424 | char *host |
425 | time_t timep | |
beb31b0b | 426 | CODE: |
a0d0e21e | 427 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b | 428 | OUTPUT: |
a0d0e21e LW |
429 | timep |
430 | RETVAL | |
431 | ||
c07a80fd | 432 | =head2 The INIT: Keyword |
433 | ||
434 | The INIT: keyword allows initialization to be inserted into the XSUB before | |
435 | the compiler generates the call to the C function. Unlike the CODE: keyword | |
436 | above, this keyword does not affect the way the compiler handles RETVAL. | |
437 | ||
438 | bool_t | |
439 | rpcb_gettime(host,timep) | |
440 | char *host | |
441 | time_t &timep | |
beb31b0b | 442 | INIT: |
c07a80fd | 443 | printf("# Host is %s\n", host ); |
beb31b0b | 444 | OUTPUT: |
c07a80fd | 445 | timep |
a0d0e21e | 446 | |
beb31b0b GS |
447 | Another use for the INIT: section is to check for preconditions before |
448 | making a call to the C function: | |
449 | ||
450 | long long | |
451 | lldiv(a,b) | |
452 | long long a | |
453 | long long b | |
454 | INIT: | |
455 | if (a == 0 && b == 0) | |
456 | XSRETURN_UNDEF; | |
457 | if (b == 0) | |
458 | croak("lldiv: cannot divide by 0"); | |
459 | ||
a0d0e21e LW |
460 | =head2 The NO_INIT Keyword |
461 | ||
462 | The NO_INIT keyword is used to indicate that a function | |
54310121 | 463 | parameter is being used only as an output value. The B<xsubpp> |
a0d0e21e LW |
464 | compiler will normally generate code to read the values of |
465 | all function parameters from the argument stack and assign | |
466 | them to C variables upon entry to the function. NO_INIT | |
467 | will tell the compiler that some parameters will be used for | |
468 | output rather than for input and that they will be handled | |
469 | before the function terminates. | |
470 | ||
471 | The following example shows a variation of the rpcb_gettime() function. | |
54310121 | 472 | This function uses the timep variable only as an output variable and does |
a0d0e21e LW |
473 | not care about its initial contents. |
474 | ||
475 | bool_t | |
476 | rpcb_gettime(host,timep) | |
8e07c86e AD |
477 | char *host |
478 | time_t &timep = NO_INIT | |
beb31b0b | 479 | OUTPUT: |
a0d0e21e LW |
480 | timep |
481 | ||
482 | =head2 Initializing Function Parameters | |
483 | ||
beb31b0b GS |
484 | C function parameters are normally initialized with their values from |
485 | the argument stack (which in turn contains the parameters that were | |
486 | passed to the XSUB from Perl). The typemaps contain the | |
487 | code segments which are used to translate the Perl values to | |
a0d0e21e | 488 | the C parameters. The programmer, however, is allowed to |
7ad6fb0b | 489 | override the typemaps and supply alternate (or additional) |
beb31b0b GS |
490 | initialization code. Initialization code starts with the first |
491 | C<=>, C<;> or C<+> on a line in the INPUT: section. The only | |
492 | exception happens if this C<;> terminates the line, then this C<;> | |
493 | is quietly ignored. | |
a0d0e21e LW |
494 | |
495 | The following code demonstrates how to supply initialization code for | |
7ad6fb0b TM |
496 | function parameters. The initialization code is eval'd within double |
497 | quotes by the compiler before it is added to the output so anything | |
498 | which should be interpreted literally [mainly C<$>, C<@>, or C<\\>] | |
19799a22 GS |
499 | must be protected with backslashes. The variables $var, $arg, |
500 | and $type can be used as in typemaps. | |
a0d0e21e LW |
501 | |
502 | bool_t | |
503 | rpcb_gettime(host,timep) | |
9cde0e7f | 504 | char *host = (char *)SvPV($arg,PL_na); |
8e07c86e | 505 | time_t &timep = 0; |
beb31b0b | 506 | OUTPUT: |
a0d0e21e LW |
507 | timep |
508 | ||
509 | This should not be used to supply default values for parameters. One | |
510 | would normally use this when a function parameter must be processed by | |
511 | another library function before it can be used. Default parameters are | |
512 | covered in the next section. | |
513 | ||
beb31b0b GS |
514 | If the initialization begins with C<=>, then it is output in |
515 | the declaration for the input variable, replacing the initialization | |
516 | supplied by the typemap. If the initialization | |
517 | begins with C<;> or C<+>, then it is performed after | |
518 | all of the input variables have been declared. In the C<;> | |
519 | case the initialization normally supplied by the typemap is not performed. | |
520 | For the C<+> case, the declaration for the variable will include the | |
521 | initialization from the typemap. A global | |
c2611fb3 | 522 | variable, C<%v>, is available for the truly rare case where |
7ad6fb0b TM |
523 | information from one initialization is needed in another |
524 | initialization. | |
525 | ||
beb31b0b GS |
526 | Here's a truly obscure example: |
527 | ||
7ad6fb0b TM |
528 | bool_t |
529 | rpcb_gettime(host,timep) | |
beb31b0b GS |
530 | time_t &timep ; /* \$v{timep}=@{[$v{timep}=$arg]} */ |
531 | char *host + SvOK($v{timep}) ? SvPV($arg,PL_na) : NULL; | |
532 | OUTPUT: | |
7ad6fb0b TM |
533 | timep |
534 | ||
beb31b0b GS |
535 | The construct C<\$v{timep}=@{[$v{timep}=$arg]}> used in the above |
536 | example has a two-fold purpose: first, when this line is processed by | |
537 | B<xsubpp>, the Perl snippet C<$v{timep}=$arg> is evaluated. Second, | |
538 | the text of the evaluated snippet is output into the generated C file | |
539 | (inside a C comment)! During the processing of C<char *host> line, | |
540 | $arg will evaluate to C<ST(0)>, and C<$v{timep}> will evaluate to | |
541 | C<ST(1)>. | |
542 | ||
a0d0e21e LW |
543 | =head2 Default Parameter Values |
544 | ||
4628e4f8 GS |
545 | Default values for XSUB arguments can be specified by placing an |
546 | assignment statement in the parameter list. The default value may | |
a104f515 | 547 | be a number, a string or the special string C<NO_INIT>. Defaults should |
a0d0e21e LW |
548 | always be used on the right-most parameters only. |
549 | ||
550 | To allow the XSUB for rpcb_gettime() to have a default host | |
551 | value the parameters to the XSUB could be rearranged. The | |
552 | XSUB will then call the real rpcb_gettime() function with | |
beb31b0b GS |
553 | the parameters in the correct order. This XSUB can be called |
554 | from Perl with either of the following statements: | |
a0d0e21e LW |
555 | |
556 | $status = rpcb_gettime( $timep, $host ); | |
557 | ||
558 | $status = rpcb_gettime( $timep ); | |
559 | ||
560 | The XSUB will look like the code which follows. A CODE: | |
561 | block is used to call the real rpcb_gettime() function with | |
562 | the parameters in the correct order for that function. | |
563 | ||
564 | bool_t | |
565 | rpcb_gettime(timep,host="localhost") | |
8e07c86e AD |
566 | char *host |
567 | time_t timep = NO_INIT | |
beb31b0b | 568 | CODE: |
a0d0e21e | 569 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b | 570 | OUTPUT: |
a0d0e21e LW |
571 | timep |
572 | RETVAL | |
573 | ||
c07a80fd | 574 | =head2 The PREINIT: Keyword |
575 | ||
beb31b0b | 576 | The PREINIT: keyword allows extra variables to be declared immediately |
a2293a43 | 577 | before or after the declarations of the parameters from the INPUT: section |
beb31b0b GS |
578 | are emitted. |
579 | ||
580 | If a variable is declared inside a CODE: section it will follow any typemap | |
581 | code that is emitted for the input parameters. This may result in the | |
582 | declaration ending up after C code, which is C syntax error. Similar | |
583 | errors may happen with an explicit C<;>-type or C<+>-type initialization of | |
584 | parameters is used (see L<"Initializing Function Parameters">). Declaring | |
585 | these variables in an INIT: section will not help. | |
586 | ||
587 | In such cases, to force an additional variable to be declared together | |
588 | with declarations of other variables, place the declaration into a | |
589 | PREINIT: section. The PREINIT: keyword may be used one or more times | |
590 | within an XSUB. | |
c07a80fd | 591 | |
592 | The following examples are equivalent, but if the code is using complex | |
593 | typemaps then the first example is safer. | |
594 | ||
595 | bool_t | |
596 | rpcb_gettime(timep) | |
597 | time_t timep = NO_INIT | |
beb31b0b | 598 | PREINIT: |
c07a80fd | 599 | char *host = "localhost"; |
beb31b0b | 600 | CODE: |
c07a80fd | 601 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b | 602 | OUTPUT: |
c07a80fd | 603 | timep |
604 | RETVAL | |
605 | ||
beb31b0b GS |
606 | For this particular case an INIT: keyword would generate the |
607 | same C code as the PREINIT: keyword. Another correct, but error-prone example: | |
c07a80fd | 608 | |
609 | bool_t | |
610 | rpcb_gettime(timep) | |
611 | time_t timep = NO_INIT | |
beb31b0b | 612 | CODE: |
c07a80fd | 613 | char *host = "localhost"; |
614 | RETVAL = rpcb_gettime( host, &timep ); | |
beb31b0b GS |
615 | OUTPUT: |
616 | timep | |
617 | RETVAL | |
618 | ||
619 | Another way to declare C<host> is to use a C block in the CODE: section: | |
620 | ||
621 | bool_t | |
622 | rpcb_gettime(timep) | |
623 | time_t timep = NO_INIT | |
624 | CODE: | |
625 | { | |
626 | char *host = "localhost"; | |
627 | RETVAL = rpcb_gettime( host, &timep ); | |
628 | } | |
629 | OUTPUT: | |
630 | timep | |
631 | RETVAL | |
632 | ||
633 | The ability to put additional declarations before the typemap entries are | |
634 | processed is very handy in the cases when typemap conversions manipulate | |
635 | some global state: | |
636 | ||
637 | MyObject | |
638 | mutate(o) | |
639 | PREINIT: | |
640 | MyState st = global_state; | |
641 | INPUT: | |
642 | MyObject o; | |
643 | CLEANUP: | |
644 | reset_to(global_state, st); | |
645 | ||
646 | Here we suppose that conversion to C<MyObject> in the INPUT: section and from | |
647 | MyObject when processing RETVAL will modify a global variable C<global_state>. | |
648 | After these conversions are performed, we restore the old value of | |
649 | C<global_state> (to avoid memory leaks, for example). | |
650 | ||
651 | There is another way to trade clarity for compactness: INPUT sections allow | |
652 | declaration of C variables which do not appear in the parameter list of | |
653 | a subroutine. Thus the above code for mutate() can be rewritten as | |
654 | ||
655 | MyObject | |
656 | mutate(o) | |
657 | MyState st = global_state; | |
658 | MyObject o; | |
659 | CLEANUP: | |
660 | reset_to(global_state, st); | |
661 | ||
662 | and the code for rpcb_gettime() can be rewritten as | |
663 | ||
664 | bool_t | |
665 | rpcb_gettime(timep) | |
666 | time_t timep = NO_INIT | |
667 | char *host = "localhost"; | |
668 | C_ARGS: | |
669 | host, &timep | |
670 | OUTPUT: | |
c07a80fd | 671 | timep |
672 | RETVAL | |
673 | ||
84287afe | 674 | =head2 The SCOPE: Keyword |
675 | ||
676 | The SCOPE: keyword allows scoping to be enabled for a particular XSUB. If | |
677 | enabled, the XSUB will invoke ENTER and LEAVE automatically. | |
678 | ||
679 | To support potentially complex type mappings, if a typemap entry used | |
beb31b0b GS |
680 | by an XSUB contains a comment like C</*scope*/> then scoping will |
681 | be automatically enabled for that XSUB. | |
84287afe | 682 | |
683 | To enable scoping: | |
684 | ||
685 | SCOPE: ENABLE | |
686 | ||
687 | To disable scoping: | |
688 | ||
689 | SCOPE: DISABLE | |
690 | ||
c07a80fd | 691 | =head2 The INPUT: Keyword |
692 | ||
693 | The XSUB's parameters are usually evaluated immediately after entering the | |
694 | XSUB. The INPUT: keyword can be used to force those parameters to be | |
695 | evaluated a little later. The INPUT: keyword can be used multiple times | |
696 | within an XSUB and can be used to list one or more input variables. This | |
697 | keyword is used with the PREINIT: keyword. | |
698 | ||
699 | The following example shows how the input parameter C<timep> can be | |
700 | evaluated late, after a PREINIT. | |
701 | ||
702 | bool_t | |
703 | rpcb_gettime(host,timep) | |
704 | char *host | |
beb31b0b | 705 | PREINIT: |
c07a80fd | 706 | time_t tt; |
beb31b0b | 707 | INPUT: |
c07a80fd | 708 | time_t timep |
beb31b0b | 709 | CODE: |
c07a80fd | 710 | RETVAL = rpcb_gettime( host, &tt ); |
711 | timep = tt; | |
beb31b0b | 712 | OUTPUT: |
c07a80fd | 713 | timep |
714 | RETVAL | |
715 | ||
716 | The next example shows each input parameter evaluated late. | |
717 | ||
718 | bool_t | |
719 | rpcb_gettime(host,timep) | |
beb31b0b | 720 | PREINIT: |
c07a80fd | 721 | time_t tt; |
beb31b0b | 722 | INPUT: |
c07a80fd | 723 | char *host |
beb31b0b | 724 | PREINIT: |
c07a80fd | 725 | char *h; |
beb31b0b | 726 | INPUT: |
c07a80fd | 727 | time_t timep |
beb31b0b | 728 | CODE: |
c07a80fd | 729 | h = host; |
730 | RETVAL = rpcb_gettime( h, &tt ); | |
731 | timep = tt; | |
beb31b0b GS |
732 | OUTPUT: |
733 | timep | |
734 | RETVAL | |
735 | ||
736 | Since INPUT sections allow declaration of C variables which do not appear | |
737 | in the parameter list of a subroutine, this may be shortened to: | |
738 | ||
739 | bool_t | |
740 | rpcb_gettime(host,timep) | |
741 | time_t tt; | |
742 | char *host; | |
743 | char *h = host; | |
744 | time_t timep; | |
745 | CODE: | |
746 | RETVAL = rpcb_gettime( h, &tt ); | |
747 | timep = tt; | |
748 | OUTPUT: | |
c07a80fd | 749 | timep |
750 | RETVAL | |
751 | ||
beb31b0b GS |
752 | (We used our knowledge that input conversion for C<char *> is a "simple" one, |
753 | thus C<host> is initialized on the declaration line, and our assignment | |
754 | C<h = host> is not performed too early. Otherwise one would need to have the | |
755 | assignment C<h = host> in a CODE: or INIT: section.) | |
756 | ||
9e24e6f2 IZ |
757 | =head2 The IN/OUTLIST/IN_OUTLIST Keywords |
758 | ||
759 | In the list of parameters for an XSUB, one can precede parameter names | |
760 | by the C<IN>/C<OUTLIST>/C<IN_OUTLIST> keywords. C<IN> keyword is a default, | |
761 | the other two keywords indicate how the Perl interface should differ from | |
762 | the C interface. | |
763 | ||
764 | Parameters preceded by C<OUTLIST>/C<IN_OUTLIST> keywords are considered to | |
765 | be used by the C subroutine I<via pointers>. C<OUTLIST> keyword indicates | |
766 | that the C subroutine does not inspect the memory pointed by this parameter, | |
767 | but will write through this pointer to provide additional return values. | |
768 | Such parameters do not appear in the usage signature of the generated Perl | |
769 | function. | |
770 | ||
771 | Parameters preceded by C<IN_OUTLIST> I<do> appear as parameters to the | |
772 | Perl function. These parameters are converted to the corresponding C type, | |
773 | then pointers to these data are given as arguments to the C function. It | |
774 | is expected that the C function will write through these pointers | |
775 | ||
776 | The return list of the generated Perl function consists of the C return value | |
777 | from the function (unless the XSUB is of C<void> return type or | |
778 | C<The NO_INIT Keyword> was used) followed by all the C<OUTLIST> | |
7817ba4d | 779 | and C<IN_OUTLIST> parameters (in the order of appearance). Say, an XSUB |
9e24e6f2 IZ |
780 | |
781 | void | |
782 | day_month(OUTLIST day, IN unix_time, OUTLIST month) | |
783 | int day | |
784 | int unix_time | |
785 | int month | |
786 | ||
787 | should be used from Perl as | |
788 | ||
789 | my ($day, $month) = day_month(time); | |
790 | ||
791 | The C signature of the corresponding function should be | |
792 | ||
793 | void day_month(int *day, int unix_time, int *month); | |
794 | ||
795 | The C<in>/C<OUTLIST>/C<IN_OUTLIST> keywords can be mixed with ANSI-style | |
796 | declarations, as in | |
797 | ||
798 | void | |
799 | day_month(OUTLIST int day, int unix_time, OUTLIST int month) | |
800 | ||
801 | (here the optional C<IN> keyword is omitted). | |
802 | ||
803 | The C<IN_OUTLIST> parameters are somewhat similar to parameters introduced | |
804 | with L<The & Unary Operator> and put into the C<OUTPUT:> section (see | |
805 | L<The OUTPUT: Keyword>). Say, the same C function can be interfaced with as | |
806 | ||
807 | void | |
808 | day_month(day, unix_time, month) | |
809 | int &day = NO_INIT | |
810 | int unix_time | |
811 | int &month = NO_INIT | |
812 | OUTPUT: | |
813 | day | |
814 | month | |
815 | ||
816 | However, the generated Perl function is called in very C-ish style: | |
817 | ||
818 | my ($day, $month); | |
819 | day_month($day, time, $month); | |
820 | ||
a0d0e21e LW |
821 | =head2 Variable-length Parameter Lists |
822 | ||
823 | XSUBs can have variable-length parameter lists by specifying an ellipsis | |
824 | C<(...)> in the parameter list. This use of the ellipsis is similar to that | |
825 | found in ANSI C. The programmer is able to determine the number of | |
826 | arguments passed to the XSUB by examining the C<items> variable which the | |
827 | B<xsubpp> compiler supplies for all XSUBs. By using this mechanism one can | |
828 | create an XSUB which accepts a list of parameters of unknown length. | |
829 | ||
830 | The I<host> parameter for the rpcb_gettime() XSUB can be | |
831 | optional so the ellipsis can be used to indicate that the | |
832 | XSUB will take a variable number of parameters. Perl should | |
d1b91892 | 833 | be able to call this XSUB with either of the following statements. |
a0d0e21e LW |
834 | |
835 | $status = rpcb_gettime( $timep, $host ); | |
836 | ||
837 | $status = rpcb_gettime( $timep ); | |
838 | ||
839 | The XS code, with ellipsis, follows. | |
840 | ||
841 | bool_t | |
842 | rpcb_gettime(timep, ...) | |
8e07c86e | 843 | time_t timep = NO_INIT |
beb31b0b | 844 | PREINIT: |
a0d0e21e | 845 | char *host = "localhost"; |
2d8e6c8d | 846 | STRLEN n_a; |
beb31b0b GS |
847 | CODE: |
848 | if( items > 1 ) | |
849 | host = (char *)SvPV(ST(1), n_a); | |
850 | RETVAL = rpcb_gettime( host, &timep ); | |
851 | OUTPUT: | |
a0d0e21e LW |
852 | timep |
853 | RETVAL | |
854 | ||
cfc02341 IZ |
855 | =head2 The C_ARGS: Keyword |
856 | ||
857 | The C_ARGS: keyword allows creating of XSUBS which have different | |
858 | calling sequence from Perl than from C, without a need to write | |
beb31b0b | 859 | CODE: or PPCODE: section. The contents of the C_ARGS: paragraph is |
cfc02341 IZ |
860 | put as the argument to the called C function without any change. |
861 | ||
beb31b0b | 862 | For example, suppose that a C function is declared as |
cfc02341 IZ |
863 | |
864 | symbolic nth_derivative(int n, symbolic function, int flags); | |
865 | ||
866 | and that the default flags are kept in a global C variable | |
867 | C<default_flags>. Suppose that you want to create an interface which | |
868 | is called as | |
869 | ||
870 | $second_deriv = $function->nth_derivative(2); | |
871 | ||
872 | To do this, declare the XSUB as | |
873 | ||
874 | symbolic | |
875 | nth_derivative(function, n) | |
876 | symbolic function | |
877 | int n | |
beb31b0b | 878 | C_ARGS: |
cfc02341 IZ |
879 | n, function, default_flags |
880 | ||
a0d0e21e LW |
881 | =head2 The PPCODE: Keyword |
882 | ||
883 | The PPCODE: keyword is an alternate form of the CODE: keyword and is used | |
884 | to tell the B<xsubpp> compiler that the programmer is supplying the code to | |
d1b91892 | 885 | control the argument stack for the XSUBs return values. Occasionally one |
a0d0e21e LW |
886 | will want an XSUB to return a list of values rather than a single value. |
887 | In these cases one must use PPCODE: and then explicitly push the list of | |
beb31b0b | 888 | values on the stack. The PPCODE: and CODE: keywords should not be used |
a0d0e21e LW |
889 | together within the same XSUB. |
890 | ||
beb31b0b GS |
891 | The actual difference between PPCODE: and CODE: sections is in the |
892 | initialization of C<SP> macro (which stands for the I<current> Perl | |
893 | stack pointer), and in the handling of data on the stack when returning | |
894 | from an XSUB. In CODE: sections SP preserves the value which was on | |
895 | entry to the XSUB: SP is on the function pointer (which follows the | |
896 | last parameter). In PPCODE: sections SP is moved backward to the | |
897 | beginning of the parameter list, which allows C<PUSH*()> macros | |
898 | to place output values in the place Perl expects them to be when | |
899 | the XSUB returns back to Perl. | |
900 | ||
901 | The generated trailer for a CODE: section ensures that the number of return | |
902 | values Perl will see is either 0 or 1 (depending on the C<void>ness of the | |
903 | return value of the C function, and heuristics mentioned in | |
904 | L<"The RETVAL Variable">). The trailer generated for a PPCODE: section | |
905 | is based on the number of return values and on the number of times | |
906 | C<SP> was updated by C<[X]PUSH*()> macros. | |
907 | ||
908 | Note that macros C<ST(i)>, C<XST_m*()> and C<XSRETURN*()> work equally | |
909 | well in CODE: sections and PPCODE: sections. | |
910 | ||
a0d0e21e LW |
911 | The following XSUB will call the C rpcb_gettime() function |
912 | and will return its two output values, timep and status, to | |
913 | Perl as a single list. | |
914 | ||
d1b91892 AD |
915 | void |
916 | rpcb_gettime(host) | |
8e07c86e | 917 | char *host |
beb31b0b | 918 | PREINIT: |
a0d0e21e LW |
919 | time_t timep; |
920 | bool_t status; | |
beb31b0b | 921 | PPCODE: |
a0d0e21e | 922 | status = rpcb_gettime( host, &timep ); |
924508f0 | 923 | EXTEND(SP, 2); |
cb1a09d0 AD |
924 | PUSHs(sv_2mortal(newSViv(status))); |
925 | PUSHs(sv_2mortal(newSViv(timep))); | |
a0d0e21e LW |
926 | |
927 | Notice that the programmer must supply the C code necessary | |
928 | to have the real rpcb_gettime() function called and to have | |
929 | the return values properly placed on the argument stack. | |
930 | ||
931 | The C<void> return type for this function tells the B<xsubpp> compiler that | |
932 | the RETVAL variable is not needed or used and that it should not be created. | |
933 | In most scenarios the void return type should be used with the PPCODE: | |
934 | directive. | |
935 | ||
936 | The EXTEND() macro is used to make room on the argument | |
937 | stack for 2 return values. The PPCODE: directive causes the | |
924508f0 | 938 | B<xsubpp> compiler to create a stack pointer available as C<SP>, and it |
a0d0e21e LW |
939 | is this pointer which is being used in the EXTEND() macro. |
940 | The values are then pushed onto the stack with the PUSHs() | |
941 | macro. | |
942 | ||
943 | Now the rpcb_gettime() function can be used from Perl with | |
944 | the following statement. | |
945 | ||
946 | ($status, $timep) = rpcb_gettime("localhost"); | |
947 | ||
ef50df4b GS |
948 | When handling output parameters with a PPCODE section, be sure to handle |
949 | 'set' magic properly. See L<perlguts> for details about 'set' magic. | |
950 | ||
a0d0e21e LW |
951 | =head2 Returning Undef And Empty Lists |
952 | ||
5f05dabc | 953 | Occasionally the programmer will want to return simply |
a0d0e21e LW |
954 | C<undef> or an empty list if a function fails rather than a |
955 | separate status value. The rpcb_gettime() function offers | |
956 | just this situation. If the function succeeds we would like | |
957 | to have it return the time and if it fails we would like to | |
958 | have undef returned. In the following Perl code the value | |
959 | of $timep will either be undef or it will be a valid time. | |
960 | ||
961 | $timep = rpcb_gettime( "localhost" ); | |
962 | ||
7b8d334a | 963 | The following XSUB uses the C<SV *> return type as a mnemonic only, |
e7ea3e70 | 964 | and uses a CODE: block to indicate to the compiler |
a0d0e21e LW |
965 | that the programmer has supplied all the necessary code. The |
966 | sv_newmortal() call will initialize the return value to undef, making that | |
967 | the default return value. | |
968 | ||
e7ea3e70 | 969 | SV * |
a0d0e21e LW |
970 | rpcb_gettime(host) |
971 | char * host | |
beb31b0b | 972 | PREINIT: |
a0d0e21e LW |
973 | time_t timep; |
974 | bool_t x; | |
beb31b0b | 975 | CODE: |
a0d0e21e LW |
976 | ST(0) = sv_newmortal(); |
977 | if( rpcb_gettime( host, &timep ) ) | |
978 | sv_setnv( ST(0), (double)timep); | |
a0d0e21e LW |
979 | |
980 | The next example demonstrates how one would place an explicit undef in the | |
981 | return value, should the need arise. | |
982 | ||
e7ea3e70 | 983 | SV * |
a0d0e21e LW |
984 | rpcb_gettime(host) |
985 | char * host | |
beb31b0b | 986 | PREINIT: |
a0d0e21e LW |
987 | time_t timep; |
988 | bool_t x; | |
beb31b0b | 989 | CODE: |
a0d0e21e LW |
990 | ST(0) = sv_newmortal(); |
991 | if( rpcb_gettime( host, &timep ) ){ | |
992 | sv_setnv( ST(0), (double)timep); | |
993 | } | |
994 | else{ | |
9cde0e7f | 995 | ST(0) = &PL_sv_undef; |
a0d0e21e | 996 | } |
a0d0e21e LW |
997 | |
998 | To return an empty list one must use a PPCODE: block and | |
999 | then not push return values on the stack. | |
1000 | ||
1001 | void | |
1002 | rpcb_gettime(host) | |
8e07c86e | 1003 | char *host |
beb31b0b | 1004 | PREINIT: |
a0d0e21e | 1005 | time_t timep; |
beb31b0b | 1006 | PPCODE: |
a0d0e21e | 1007 | if( rpcb_gettime( host, &timep ) ) |
cb1a09d0 | 1008 | PUSHs(sv_2mortal(newSViv(timep))); |
a0d0e21e | 1009 | else{ |
beb31b0b GS |
1010 | /* Nothing pushed on stack, so an empty |
1011 | * list is implicitly returned. */ | |
a0d0e21e | 1012 | } |
a0d0e21e | 1013 | |
f27cfbbe | 1014 | Some people may be inclined to include an explicit C<return> in the above |
1015 | XSUB, rather than letting control fall through to the end. In those | |
1016 | situations C<XSRETURN_EMPTY> should be used, instead. This will ensure that | |
1017 | the XSUB stack is properly adjusted. Consult L<perlguts/"API LISTING"> for | |
1018 | other C<XSRETURN> macros. | |
1019 | ||
beb31b0b GS |
1020 | Since C<XSRETURN_*> macros can be used with CODE blocks as well, one can |
1021 | rewrite this example as: | |
1022 | ||
1023 | int | |
1024 | rpcb_gettime(host) | |
1025 | char *host | |
1026 | PREINIT: | |
1027 | time_t timep; | |
1028 | CODE: | |
1029 | RETVAL = rpcb_gettime( host, &timep ); | |
1030 | if (RETVAL == 0) | |
1031 | XSRETURN_UNDEF; | |
1032 | OUTPUT: | |
1033 | RETVAL | |
1034 | ||
9e24e6f2 | 1035 | In fact, one can put this check into a POST_CALL: section as well. Together |
beb31b0b GS |
1036 | with PREINIT: simplifications, this leads to: |
1037 | ||
1038 | int | |
1039 | rpcb_gettime(host) | |
1040 | char *host | |
1041 | time_t timep; | |
9e24e6f2 | 1042 | POST_CALL: |
beb31b0b GS |
1043 | if (RETVAL == 0) |
1044 | XSRETURN_UNDEF; | |
1045 | ||
4633a7c4 LW |
1046 | =head2 The REQUIRE: Keyword |
1047 | ||
1048 | The REQUIRE: keyword is used to indicate the minimum version of the | |
1049 | B<xsubpp> compiler needed to compile the XS module. An XS module which | |
5f05dabc | 1050 | contains the following statement will compile with only B<xsubpp> version |
4633a7c4 LW |
1051 | 1.922 or greater: |
1052 | ||
1053 | REQUIRE: 1.922 | |
1054 | ||
a0d0e21e LW |
1055 | =head2 The CLEANUP: Keyword |
1056 | ||
1057 | This keyword can be used when an XSUB requires special cleanup procedures | |
1058 | before it terminates. When the CLEANUP: keyword is used it must follow | |
1059 | any CODE:, PPCODE:, or OUTPUT: blocks which are present in the XSUB. The | |
1060 | code specified for the cleanup block will be added as the last statements | |
1061 | in the XSUB. | |
1062 | ||
9e24e6f2 IZ |
1063 | =head2 The POST_CALL: Keyword |
1064 | ||
1065 | This keyword can be used when an XSUB requires special procedures | |
1066 | executed after the C subroutine call is performed. When the POST_CALL: | |
1067 | keyword is used it must precede OUTPUT: and CLEANUP: blocks which are | |
1068 | present in the XSUB. | |
1069 | ||
1070 | The POST_CALL: block does not make a lot of sense when the C subroutine | |
1071 | call is supplied by user by providing either CODE: or PPCODE: section. | |
1072 | ||
a0d0e21e LW |
1073 | =head2 The BOOT: Keyword |
1074 | ||
1075 | The BOOT: keyword is used to add code to the extension's bootstrap | |
1076 | function. The bootstrap function is generated by the B<xsubpp> compiler and | |
1077 | normally holds the statements necessary to register any XSUBs with Perl. | |
1078 | With the BOOT: keyword the programmer can tell the compiler to add extra | |
1079 | statements to the bootstrap function. | |
1080 | ||
1081 | This keyword may be used any time after the first MODULE keyword and should | |
1082 | appear on a line by itself. The first blank line after the keyword will | |
1083 | terminate the code block. | |
1084 | ||
1085 | BOOT: | |
1086 | # The following message will be printed when the | |
1087 | # bootstrap function executes. | |
1088 | printf("Hello from the bootstrap!\n"); | |
1089 | ||
c07a80fd | 1090 | =head2 The VERSIONCHECK: Keyword |
1091 | ||
1092 | The VERSIONCHECK: keyword corresponds to B<xsubpp>'s C<-versioncheck> and | |
5f05dabc | 1093 | C<-noversioncheck> options. This keyword overrides the command line |
c07a80fd | 1094 | options. Version checking is enabled by default. When version checking is |
1095 | enabled the XS module will attempt to verify that its version matches the | |
1096 | version of the PM module. | |
1097 | ||
1098 | To enable version checking: | |
1099 | ||
1100 | VERSIONCHECK: ENABLE | |
1101 | ||
1102 | To disable version checking: | |
1103 | ||
1104 | VERSIONCHECK: DISABLE | |
1105 | ||
1106 | =head2 The PROTOTYPES: Keyword | |
1107 | ||
1108 | The PROTOTYPES: keyword corresponds to B<xsubpp>'s C<-prototypes> and | |
54310121 | 1109 | C<-noprototypes> options. This keyword overrides the command line options. |
c07a80fd | 1110 | Prototypes are enabled by default. When prototypes are enabled XSUBs will |
1111 | be given Perl prototypes. This keyword may be used multiple times in an XS | |
1112 | module to enable and disable prototypes for different parts of the module. | |
1113 | ||
1114 | To enable prototypes: | |
1115 | ||
1116 | PROTOTYPES: ENABLE | |
1117 | ||
1118 | To disable prototypes: | |
1119 | ||
1120 | PROTOTYPES: DISABLE | |
1121 | ||
1122 | =head2 The PROTOTYPE: Keyword | |
1123 | ||
1124 | This keyword is similar to the PROTOTYPES: keyword above but can be used to | |
1125 | force B<xsubpp> to use a specific prototype for the XSUB. This keyword | |
1126 | overrides all other prototype options and keywords but affects only the | |
1127 | current XSUB. Consult L<perlsub/Prototypes> for information about Perl | |
1128 | prototypes. | |
1129 | ||
1130 | bool_t | |
1131 | rpcb_gettime(timep, ...) | |
1132 | time_t timep = NO_INIT | |
beb31b0b GS |
1133 | PROTOTYPE: $;$ |
1134 | PREINIT: | |
c07a80fd | 1135 | char *host = "localhost"; |
2d8e6c8d | 1136 | STRLEN n_a; |
beb31b0b | 1137 | CODE: |
c07a80fd | 1138 | if( items > 1 ) |
2d8e6c8d | 1139 | host = (char *)SvPV(ST(1), n_a); |
c07a80fd | 1140 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b | 1141 | OUTPUT: |
c07a80fd | 1142 | timep |
1143 | RETVAL | |
1144 | ||
1145 | =head2 The ALIAS: Keyword | |
1146 | ||
cfc02341 | 1147 | The ALIAS: keyword allows an XSUB to have two or more unique Perl names |
c07a80fd | 1148 | and to know which of those names was used when it was invoked. The Perl |
1149 | names may be fully-qualified with package names. Each alias is given an | |
1150 | index. The compiler will setup a variable called C<ix> which contain the | |
1151 | index of the alias which was used. When the XSUB is called with its | |
1152 | declared name C<ix> will be 0. | |
1153 | ||
1154 | The following example will create aliases C<FOO::gettime()> and | |
1155 | C<BAR::getit()> for this function. | |
1156 | ||
1157 | bool_t | |
1158 | rpcb_gettime(host,timep) | |
1159 | char *host | |
1160 | time_t &timep | |
beb31b0b | 1161 | ALIAS: |
c07a80fd | 1162 | FOO::gettime = 1 |
1163 | BAR::getit = 2 | |
beb31b0b | 1164 | INIT: |
c07a80fd | 1165 | printf("# ix = %d\n", ix ); |
beb31b0b | 1166 | OUTPUT: |
c07a80fd | 1167 | timep |
1168 | ||
cfc02341 IZ |
1169 | =head2 The INTERFACE: Keyword |
1170 | ||
1171 | This keyword declares the current XSUB as a keeper of the given | |
1172 | calling signature. If some text follows this keyword, it is | |
1173 | considered as a list of functions which have this signature, and | |
beb31b0b | 1174 | should be attached to the current XSUB. |
cfc02341 | 1175 | |
beb31b0b GS |
1176 | For example, if you have 4 C functions multiply(), divide(), add(), |
1177 | subtract() all having the signature: | |
cfc02341 IZ |
1178 | |
1179 | symbolic f(symbolic, symbolic); | |
1180 | ||
beb31b0b | 1181 | you can make them all to use the same XSUB using this: |
cfc02341 IZ |
1182 | |
1183 | symbolic | |
1184 | interface_s_ss(arg1, arg2) | |
1185 | symbolic arg1 | |
1186 | symbolic arg2 | |
1187 | INTERFACE: | |
1188 | multiply divide | |
1189 | add subtract | |
1190 | ||
beb31b0b GS |
1191 | (This is the complete XSUB code for 4 Perl functions!) Four generated |
1192 | Perl function share names with corresponding C functions. | |
1193 | ||
1194 | The advantage of this approach comparing to ALIAS: keyword is that there | |
1195 | is no need to code a switch statement, each Perl function (which shares | |
1196 | the same XSUB) knows which C function it should call. Additionally, one | |
cfc02341 | 1197 | can attach an extra function remainder() at runtime by using |
beb31b0b | 1198 | |
cfc02341 IZ |
1199 | CV *mycv = newXSproto("Symbolic::remainder", |
1200 | XS_Symbolic_interface_s_ss, __FILE__, "$$"); | |
1201 | XSINTERFACE_FUNC_SET(mycv, remainder); | |
1202 | ||
beb31b0b GS |
1203 | say, from another XSUB. (This example supposes that there was no |
1204 | INTERFACE_MACRO: section, otherwise one needs to use something else instead of | |
1205 | C<XSINTERFACE_FUNC_SET>, see the next section.) | |
cfc02341 IZ |
1206 | |
1207 | =head2 The INTERFACE_MACRO: Keyword | |
1208 | ||
1209 | This keyword allows one to define an INTERFACE using a different way | |
1210 | to extract a function pointer from an XSUB. The text which follows | |
1211 | this keyword should give the name of macros which would extract/set a | |
1212 | function pointer. The extractor macro is given return type, C<CV*>, | |
1213 | and C<XSANY.any_dptr> for this C<CV*>. The setter macro is given cv, | |
1214 | and the function pointer. | |
1215 | ||
1216 | The default value is C<XSINTERFACE_FUNC> and C<XSINTERFACE_FUNC_SET>. | |
1217 | An INTERFACE keyword with an empty list of functions can be omitted if | |
1218 | INTERFACE_MACRO keyword is used. | |
1219 | ||
1220 | Suppose that in the previous example functions pointers for | |
1221 | multiply(), divide(), add(), subtract() are kept in a global C array | |
1222 | C<fp[]> with offsets being C<multiply_off>, C<divide_off>, C<add_off>, | |
1223 | C<subtract_off>. Then one can use | |
1224 | ||
1225 | #define XSINTERFACE_FUNC_BYOFFSET(ret,cv,f) \ | |
1226 | ((XSINTERFACE_CVT(ret,))fp[CvXSUBANY(cv).any_i32]) | |
1227 | #define XSINTERFACE_FUNC_BYOFFSET_set(cv,f) \ | |
1228 | CvXSUBANY(cv).any_i32 = CAT2( f, _off ) | |
1229 | ||
1230 | in C section, | |
1231 | ||
1232 | symbolic | |
1233 | interface_s_ss(arg1, arg2) | |
1234 | symbolic arg1 | |
1235 | symbolic arg2 | |
beb31b0b | 1236 | INTERFACE_MACRO: |
cfc02341 IZ |
1237 | XSINTERFACE_FUNC_BYOFFSET |
1238 | XSINTERFACE_FUNC_BYOFFSET_set | |
beb31b0b | 1239 | INTERFACE: |
cfc02341 IZ |
1240 | multiply divide |
1241 | add subtract | |
1242 | ||
1243 | in XSUB section. | |
1244 | ||
c07a80fd | 1245 | =head2 The INCLUDE: Keyword |
1246 | ||
1247 | This keyword can be used to pull other files into the XS module. The other | |
1248 | files may have XS code. INCLUDE: can also be used to run a command to | |
1249 | generate the XS code to be pulled into the module. | |
1250 | ||
1251 | The file F<Rpcb1.xsh> contains our C<rpcb_gettime()> function: | |
1252 | ||
1253 | bool_t | |
1254 | rpcb_gettime(host,timep) | |
1255 | char *host | |
1256 | time_t &timep | |
beb31b0b | 1257 | OUTPUT: |
c07a80fd | 1258 | timep |
1259 | ||
1260 | The XS module can use INCLUDE: to pull that file into it. | |
1261 | ||
1262 | INCLUDE: Rpcb1.xsh | |
1263 | ||
1264 | If the parameters to the INCLUDE: keyword are followed by a pipe (C<|>) then | |
1265 | the compiler will interpret the parameters as a command. | |
1266 | ||
1267 | INCLUDE: cat Rpcb1.xsh | | |
1268 | ||
1269 | =head2 The CASE: Keyword | |
1270 | ||
1271 | The CASE: keyword allows an XSUB to have multiple distinct parts with each | |
1272 | part acting as a virtual XSUB. CASE: is greedy and if it is used then all | |
1273 | other XS keywords must be contained within a CASE:. This means nothing may | |
1274 | precede the first CASE: in the XSUB and anything following the last CASE: is | |
1275 | included in that case. | |
1276 | ||
1277 | A CASE: might switch via a parameter of the XSUB, via the C<ix> ALIAS: | |
1278 | variable (see L<"The ALIAS: Keyword">), or maybe via the C<items> variable | |
1279 | (see L<"Variable-length Parameter Lists">). The last CASE: becomes the | |
1280 | B<default> case if it is not associated with a conditional. The following | |
1281 | example shows CASE switched via C<ix> with a function C<rpcb_gettime()> | |
1282 | having an alias C<x_gettime()>. When the function is called as | |
b772cb6e | 1283 | C<rpcb_gettime()> its parameters are the usual C<(char *host, time_t *timep)>, |
1284 | but when the function is called as C<x_gettime()> its parameters are | |
c07a80fd | 1285 | reversed, C<(time_t *timep, char *host)>. |
1286 | ||
1287 | long | |
1288 | rpcb_gettime(a,b) | |
1289 | CASE: ix == 1 | |
beb31b0b | 1290 | ALIAS: |
c07a80fd | 1291 | x_gettime = 1 |
beb31b0b | 1292 | INPUT: |
c07a80fd | 1293 | # 'a' is timep, 'b' is host |
1294 | char *b | |
1295 | time_t a = NO_INIT | |
beb31b0b | 1296 | CODE: |
c07a80fd | 1297 | RETVAL = rpcb_gettime( b, &a ); |
beb31b0b | 1298 | OUTPUT: |
c07a80fd | 1299 | a |
1300 | RETVAL | |
1301 | CASE: | |
1302 | # 'a' is host, 'b' is timep | |
1303 | char *a | |
1304 | time_t &b = NO_INIT | |
beb31b0b | 1305 | OUTPUT: |
c07a80fd | 1306 | b |
1307 | RETVAL | |
1308 | ||
1309 | That function can be called with either of the following statements. Note | |
1310 | the different argument lists. | |
1311 | ||
1312 | $status = rpcb_gettime( $host, $timep ); | |
1313 | ||
1314 | $status = x_gettime( $timep, $host ); | |
1315 | ||
1316 | =head2 The & Unary Operator | |
1317 | ||
beb31b0b GS |
1318 | The C<&> unary operator in the INPUT: section is used to tell B<xsubpp> |
1319 | that it should convert a Perl value to/from C using the C type to the left | |
1320 | of C<&>, but provide a pointer to this value when the C function is called. | |
1321 | ||
1322 | This is useful to avoid a CODE: block for a C function which takes a parameter | |
1323 | by reference. Typically, the parameter should be not a pointer type (an | |
1324 | C<int> or C<long> but not a C<int*> or C<long*>). | |
c07a80fd | 1325 | |
beb31b0b | 1326 | The following XSUB will generate incorrect C code. The B<xsubpp> compiler will |
c07a80fd | 1327 | turn this into code which calls C<rpcb_gettime()> with parameters C<(char |
1328 | *host, time_t timep)>, but the real C<rpcb_gettime()> wants the C<timep> | |
1329 | parameter to be of type C<time_t*> rather than C<time_t>. | |
1330 | ||
1331 | bool_t | |
1332 | rpcb_gettime(host,timep) | |
1333 | char *host | |
1334 | time_t timep | |
beb31b0b | 1335 | OUTPUT: |
c07a80fd | 1336 | timep |
1337 | ||
beb31b0b | 1338 | That problem is corrected by using the C<&> operator. The B<xsubpp> compiler |
c07a80fd | 1339 | will now turn this into code which calls C<rpcb_gettime()> correctly with |
1340 | parameters C<(char *host, time_t *timep)>. It does this by carrying the | |
1341 | C<&> through, so the function call looks like C<rpcb_gettime(host, &timep)>. | |
1342 | ||
1343 | bool_t | |
1344 | rpcb_gettime(host,timep) | |
1345 | char *host | |
1346 | time_t &timep | |
beb31b0b | 1347 | OUTPUT: |
c07a80fd | 1348 | timep |
1349 | ||
7817ba4d | 1350 | =head2 Inserting POD, Comments and C Preprocessor Directives |
a0d0e21e | 1351 | |
7817ba4d NC |
1352 | C preprocessor directives are allowed within BOOT:, PREINIT: INIT:, CODE:, |
1353 | PPCODE:, POST_CALL:, and CLEANUP: blocks, as well as outside the functions. | |
1354 | Comments are allowed anywhere after the MODULE keyword. The compiler will | |
1355 | pass the preprocessor directives through untouched and will remove the | |
1356 | commented lines. POD documentation is allowed at any point, both in the | |
1357 | C and XS language sections. POD must be terminated with a C<=cut> command; | |
1358 | C<xsubpp> will exit with an error if it does not. It is very unlikely that | |
1359 | human generated C code will be mistaken for POD, as most indenting styles | |
1360 | result in whitespace in front of any line starting with C<=>. Machine | |
1361 | generated XS files may fall into this trap unless care is taken to | |
1362 | ensure that a space breaks the sequence "\n=". | |
b772cb6e | 1363 | |
f27cfbbe | 1364 | Comments can be added to XSUBs by placing a C<#> as the first |
1365 | non-whitespace of a line. Care should be taken to avoid making the | |
1366 | comment look like a C preprocessor directive, lest it be interpreted as | |
1367 | such. The simplest way to prevent this is to put whitespace in front of | |
1368 | the C<#>. | |
1369 | ||
f27cfbbe | 1370 | If you use preprocessor directives to choose one of two |
1371 | versions of a function, use | |
1372 | ||
1373 | #if ... version1 | |
1374 | #else /* ... version2 */ | |
1375 | #endif | |
1376 | ||
1377 | and not | |
1378 | ||
1379 | #if ... version1 | |
1380 | #endif | |
1381 | #if ... version2 | |
1382 | #endif | |
1383 | ||
beb31b0b | 1384 | because otherwise B<xsubpp> will believe that you made a duplicate |
f27cfbbe | 1385 | definition of the function. Also, put a blank line before the |
1386 | #else/#endif so it will not be seen as part of the function body. | |
a0d0e21e LW |
1387 | |
1388 | =head2 Using XS With C++ | |
1389 | ||
beb31b0b GS |
1390 | If an XSUB name contains C<::>, it is considered to be a C++ method. |
1391 | The generated Perl function will assume that | |
a0d0e21e LW |
1392 | its first argument is an object pointer. The object pointer |
1393 | will be stored in a variable called THIS. The object should | |
1394 | have been created by C++ with the new() function and should | |
cb1a09d0 AD |
1395 | be blessed by Perl with the sv_setref_pv() macro. The |
1396 | blessing of the object by Perl can be handled by a typemap. An example | |
1397 | typemap is shown at the end of this section. | |
a0d0e21e | 1398 | |
beb31b0b GS |
1399 | If the return type of the XSUB includes C<static>, the method is considered |
1400 | to be a static method. It will call the C++ | |
a0d0e21e | 1401 | function using the class::method() syntax. If the method is not static |
f27cfbbe | 1402 | the function will be called using the THIS-E<gt>method() syntax. |
a0d0e21e | 1403 | |
cb1a09d0 | 1404 | The next examples will use the following C++ class. |
a0d0e21e | 1405 | |
a5f75d66 | 1406 | class color { |
cb1a09d0 | 1407 | public: |
a5f75d66 AD |
1408 | color(); |
1409 | ~color(); | |
cb1a09d0 AD |
1410 | int blue(); |
1411 | void set_blue( int ); | |
1412 | ||
1413 | private: | |
1414 | int c_blue; | |
1415 | }; | |
1416 | ||
1417 | The XSUBs for the blue() and set_blue() methods are defined with the class | |
1418 | name but the parameter for the object (THIS, or "self") is implicit and is | |
1419 | not listed. | |
1420 | ||
1421 | int | |
1422 | color::blue() | |
a0d0e21e LW |
1423 | |
1424 | void | |
cb1a09d0 AD |
1425 | color::set_blue( val ) |
1426 | int val | |
a0d0e21e | 1427 | |
beb31b0b GS |
1428 | Both Perl functions will expect an object as the first parameter. In the |
1429 | generated C++ code the object is called C<THIS>, and the method call will | |
1430 | be performed on this object. So in the C++ code the blue() and set_blue() | |
1431 | methods will be called as this: | |
a0d0e21e | 1432 | |
cb1a09d0 | 1433 | RETVAL = THIS->blue(); |
a0d0e21e | 1434 | |
cb1a09d0 | 1435 | THIS->set_blue( val ); |
a0d0e21e | 1436 | |
4628e4f8 GS |
1437 | You could also write a single get/set method using an optional argument: |
1438 | ||
1439 | int | |
a104f515 | 1440 | color::blue( val = NO_INIT ) |
4628e4f8 GS |
1441 | int val |
1442 | PROTOTYPE $;$ | |
1443 | CODE: | |
1444 | if (items > 1) | |
1445 | THIS->set_blue( val ); | |
1446 | RETVAL = THIS->blue(); | |
1447 | OUTPUT: | |
1448 | RETVAL | |
1449 | ||
cb1a09d0 | 1450 | If the function's name is B<DESTROY> then the C++ C<delete> function will be |
beb31b0b | 1451 | called and C<THIS> will be given as its parameter. The generated C++ code for |
a0d0e21e | 1452 | |
d1b91892 | 1453 | void |
cb1a09d0 AD |
1454 | color::DESTROY() |
1455 | ||
beb31b0b GS |
1456 | will look like this: |
1457 | ||
1458 | color *THIS = ...; // Initialized as in typemap | |
cb1a09d0 AD |
1459 | |
1460 | delete THIS; | |
a0d0e21e | 1461 | |
cb1a09d0 AD |
1462 | If the function's name is B<new> then the C++ C<new> function will be called |
1463 | to create a dynamic C++ object. The XSUB will expect the class name, which | |
1464 | will be kept in a variable called C<CLASS>, to be given as the first | |
1465 | argument. | |
a0d0e21e | 1466 | |
cb1a09d0 AD |
1467 | color * |
1468 | color::new() | |
a0d0e21e | 1469 | |
beb31b0b | 1470 | The generated C++ code will call C<new>. |
a0d0e21e | 1471 | |
beb31b0b | 1472 | RETVAL = new color(); |
cb1a09d0 AD |
1473 | |
1474 | The following is an example of a typemap that could be used for this C++ | |
1475 | example. | |
1476 | ||
1477 | TYPEMAP | |
1478 | color * O_OBJECT | |
1479 | ||
1480 | OUTPUT | |
1481 | # The Perl object is blessed into 'CLASS', which should be a | |
1482 | # char* having the name of the package for the blessing. | |
1483 | O_OBJECT | |
1484 | sv_setref_pv( $arg, CLASS, (void*)$var ); | |
a6006777 | 1485 | |
cb1a09d0 AD |
1486 | INPUT |
1487 | O_OBJECT | |
1488 | if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) ) | |
1489 | $var = ($type)SvIV((SV*)SvRV( $arg )); | |
1490 | else{ | |
1491 | warn( \"${Package}::$func_name() -- $var is not a blessed SV reference\" ); | |
1492 | XSRETURN_UNDEF; | |
1493 | } | |
a0d0e21e | 1494 | |
d1b91892 | 1495 | =head2 Interface Strategy |
a0d0e21e LW |
1496 | |
1497 | When designing an interface between Perl and a C library a straight | |
beb31b0b GS |
1498 | translation from C to XS (such as created by C<h2xs -x>) is often sufficient. |
1499 | However, sometimes the interface will look | |
a0d0e21e | 1500 | very C-like and occasionally nonintuitive, especially when the C function |
beb31b0b GS |
1501 | modifies one of its parameters, or returns failure inband (as in "negative |
1502 | return values mean failure"). In cases where the programmer wishes to | |
a0d0e21e LW |
1503 | create a more Perl-like interface the following strategy may help to |
1504 | identify the more critical parts of the interface. | |
1505 | ||
beb31b0b GS |
1506 | Identify the C functions with input/output or output parameters. The XSUBs for |
1507 | these functions may be able to return lists to Perl. | |
1508 | ||
1509 | Identify the C functions which use some inband info as an indication | |
1510 | of failure. They may be | |
1511 | candidates to return undef or an empty list in case of failure. If the | |
1512 | failure may be detected without a call to the C function, you may want to use | |
1513 | an INIT: section to report the failure. For failures detectable after the C | |
9e24e6f2 | 1514 | function returns one may want to use a POST_CALL: section to process the |
beb31b0b GS |
1515 | failure. In more complicated cases use CODE: or PPCODE: sections. |
1516 | ||
1517 | If many functions use the same failure indication based on the return value, | |
1518 | you may want to create a special typedef to handle this situation. Put | |
1519 | ||
1520 | typedef int negative_is_failure; | |
1521 | ||
1522 | near the beginning of XS file, and create an OUTPUT typemap entry | |
1523 | for C<negative_is_failure> which converts negative values to C<undef>, or | |
1524 | maybe croak()s. After this the return value of type C<negative_is_failure> | |
1525 | will create more Perl-like interface. | |
a0d0e21e | 1526 | |
d1b91892 | 1527 | Identify which values are used by only the C and XSUB functions |
beb31b0b GS |
1528 | themselves, say, when a parameter to a function should be a contents of a |
1529 | global variable. If Perl does not need to access the contents of the value | |
a0d0e21e LW |
1530 | then it may not be necessary to provide a translation for that value |
1531 | from C to Perl. | |
1532 | ||
1533 | Identify the pointers in the C function parameter lists and return | |
beb31b0b GS |
1534 | values. Some pointers may be used to implement input/output or |
1535 | output parameters, they can be handled in XS with the C<&> unary operator, | |
1536 | and, possibly, using the NO_INIT keyword. | |
1537 | Some others will require handling of types like C<int *>, and one needs | |
1538 | to decide what a useful Perl translation will do in such a case. When | |
1539 | the semantic is clear, it is advisable to put the translation into a typemap | |
1540 | file. | |
a0d0e21e LW |
1541 | |
1542 | Identify the structures used by the C functions. In many | |
1543 | cases it may be helpful to use the T_PTROBJ typemap for | |
1544 | these structures so they can be manipulated by Perl as | |
beb31b0b GS |
1545 | blessed objects. (This is handled automatically by C<h2xs -x>.) |
1546 | ||
1547 | If the same C type is used in several different contexts which require | |
1548 | different translations, C<typedef> several new types mapped to this C type, | |
1549 | and create separate F<typemap> entries for these new types. Use these | |
1550 | types in declarations of return type and parameters to XSUBs. | |
a0d0e21e | 1551 | |
a0d0e21e LW |
1552 | =head2 Perl Objects And C Structures |
1553 | ||
1554 | When dealing with C structures one should select either | |
1555 | B<T_PTROBJ> or B<T_PTRREF> for the XS type. Both types are | |
1556 | designed to handle pointers to complex objects. The | |
1557 | T_PTRREF type will allow the Perl object to be unblessed | |
1558 | while the T_PTROBJ type requires that the object be blessed. | |
1559 | By using T_PTROBJ one can achieve a form of type-checking | |
d1b91892 | 1560 | because the XSUB will attempt to verify that the Perl object |
a0d0e21e LW |
1561 | is of the expected type. |
1562 | ||
1563 | The following XS code shows the getnetconfigent() function which is used | |
8e07c86e | 1564 | with ONC+ TIRPC. The getnetconfigent() function will return a pointer to a |
a0d0e21e LW |
1565 | C structure and has the C prototype shown below. The example will |
1566 | demonstrate how the C pointer will become a Perl reference. Perl will | |
1567 | consider this reference to be a pointer to a blessed object and will | |
1568 | attempt to call a destructor for the object. A destructor will be | |
1569 | provided in the XS source to free the memory used by getnetconfigent(). | |
1570 | Destructors in XS can be created by specifying an XSUB function whose name | |
1571 | ends with the word B<DESTROY>. XS destructors can be used to free memory | |
1572 | which may have been malloc'd by another XSUB. | |
1573 | ||
1574 | struct netconfig *getnetconfigent(const char *netid); | |
1575 | ||
1576 | A C<typedef> will be created for C<struct netconfig>. The Perl | |
1577 | object will be blessed in a class matching the name of the C | |
1578 | type, with the tag C<Ptr> appended, and the name should not | |
1579 | have embedded spaces if it will be a Perl package name. The | |
1580 | destructor will be placed in a class corresponding to the | |
1581 | class of the object and the PREFIX keyword will be used to | |
1582 | trim the name to the word DESTROY as Perl will expect. | |
1583 | ||
1584 | typedef struct netconfig Netconfig; | |
1585 | ||
1586 | MODULE = RPC PACKAGE = RPC | |
1587 | ||
1588 | Netconfig * | |
1589 | getnetconfigent(netid) | |
8e07c86e | 1590 | char *netid |
a0d0e21e LW |
1591 | |
1592 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ | |
1593 | ||
1594 | void | |
1595 | rpcb_DESTROY(netconf) | |
8e07c86e | 1596 | Netconfig *netconf |
beb31b0b | 1597 | CODE: |
a0d0e21e LW |
1598 | printf("Now in NetconfigPtr::DESTROY\n"); |
1599 | free( netconf ); | |
1600 | ||
1601 | This example requires the following typemap entry. Consult the typemap | |
1602 | section for more information about adding new typemaps for an extension. | |
1603 | ||
1604 | TYPEMAP | |
1605 | Netconfig * T_PTROBJ | |
1606 | ||
1607 | This example will be used with the following Perl statements. | |
1608 | ||
1609 | use RPC; | |
1610 | $netconf = getnetconfigent("udp"); | |
1611 | ||
1612 | When Perl destroys the object referenced by $netconf it will send the | |
1613 | object to the supplied XSUB DESTROY function. Perl cannot determine, and | |
1614 | does not care, that this object is a C struct and not a Perl object. In | |
1615 | this sense, there is no difference between the object created by the | |
1616 | getnetconfigent() XSUB and an object created by a normal Perl subroutine. | |
1617 | ||
a0d0e21e LW |
1618 | =head2 The Typemap |
1619 | ||
1620 | The typemap is a collection of code fragments which are used by the B<xsubpp> | |
1621 | compiler to map C function parameters and values to Perl values. The | |
7817ba4d | 1622 | typemap file may consist of three sections labelled C<TYPEMAP>, C<INPUT>, and |
beb31b0b GS |
1623 | C<OUTPUT>. An unlabelled initial section is assumed to be a C<TYPEMAP> |
1624 | section. The INPUT section tells | |
7e9d670d | 1625 | the compiler how to translate Perl values |
a0d0e21e LW |
1626 | into variables of certain C types. The OUTPUT section tells the compiler |
1627 | how to translate the values from certain C types into values Perl can | |
1628 | understand. The TYPEMAP section tells the compiler which of the INPUT and | |
1629 | OUTPUT code fragments should be used to map a given C type to a Perl value. | |
7e9d670d GS |
1630 | The section labels C<TYPEMAP>, C<INPUT>, or C<OUTPUT> must begin |
1631 | in the first column on a line by themselves, and must be in uppercase. | |
a0d0e21e | 1632 | |
dcd2ee75 YST |
1633 | The default typemap in the C<lib/ExtUtils> directory of the Perl source |
1634 | contains many useful types which can be used by Perl extensions. Some | |
1635 | extensions define additional typemaps which they keep in their own directory. | |
1636 | These additional typemaps may reference INPUT and OUTPUT maps in the main | |
a0d0e21e LW |
1637 | typemap. The B<xsubpp> compiler will allow the extension's own typemap to |
1638 | override any mappings which are in the default typemap. | |
1639 | ||
1640 | Most extensions which require a custom typemap will need only the TYPEMAP | |
1641 | section of the typemap file. The custom typemap used in the | |
1642 | getnetconfigent() example shown earlier demonstrates what may be the typical | |
1643 | use of extension typemaps. That typemap is used to equate a C structure | |
1644 | with the T_PTROBJ typemap. The typemap used by getnetconfigent() is shown | |
1645 | here. Note that the C type is separated from the XS type with a tab and | |
1646 | that the C unary operator C<*> is considered to be a part of the C type name. | |
1647 | ||
beb31b0b GS |
1648 | TYPEMAP |
1649 | Netconfig *<tab>T_PTROBJ | |
a0d0e21e | 1650 | |
1748e8dd RS |
1651 | Here's a more complicated example: suppose that you wanted C<struct |
1652 | netconfig> to be blessed into the class C<Net::Config>. One way to do | |
1653 | this is to use underscores (_) to separate package names, as follows: | |
1654 | ||
1655 | typedef struct netconfig * Net_Config; | |
1656 | ||
1657 | And then provide a typemap entry C<T_PTROBJ_SPECIAL> that maps underscores to | |
1658 | double-colons (::), and declare C<Net_Config> to be of that type: | |
1659 | ||
1660 | ||
1661 | TYPEMAP | |
1662 | Net_Config T_PTROBJ_SPECIAL | |
1663 | ||
1664 | INPUT | |
1665 | T_PTROBJ_SPECIAL | |
1666 | if (sv_derived_from($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")) { | |
1667 | IV tmp = SvIV((SV*)SvRV($arg)); | |
1668 | $var = ($type) tmp; | |
1669 | } | |
1670 | else | |
1671 | croak(\"$var is not of type ${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\") | |
1672 | ||
1673 | OUTPUT | |
1674 | T_PTROBJ_SPECIAL | |
1675 | sv_setref_pv($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\", | |
1676 | (void*)$var); | |
1677 | ||
1678 | The INPUT and OUTPUT sections substitute underscores for double-colons | |
1679 | on the fly, giving the desired effect. This example demonstrates some | |
1680 | of the power and versatility of the typemap facility. | |
1681 | ||
a0d0e21e LW |
1682 | =head1 EXAMPLES |
1683 | ||
1684 | File C<RPC.xs>: Interface to some ONC+ RPC bind library functions. | |
1685 | ||
1686 | #include "EXTERN.h" | |
1687 | #include "perl.h" | |
1688 | #include "XSUB.h" | |
1689 | ||
1690 | #include <rpc/rpc.h> | |
1691 | ||
1692 | typedef struct netconfig Netconfig; | |
1693 | ||
1694 | MODULE = RPC PACKAGE = RPC | |
1695 | ||
e7ea3e70 | 1696 | SV * |
a0d0e21e | 1697 | rpcb_gettime(host="localhost") |
8e07c86e | 1698 | char *host |
beb31b0b | 1699 | PREINIT: |
a0d0e21e | 1700 | time_t timep; |
beb31b0b | 1701 | CODE: |
a0d0e21e LW |
1702 | ST(0) = sv_newmortal(); |
1703 | if( rpcb_gettime( host, &timep ) ) | |
1704 | sv_setnv( ST(0), (double)timep ); | |
a0d0e21e LW |
1705 | |
1706 | Netconfig * | |
1707 | getnetconfigent(netid="udp") | |
8e07c86e | 1708 | char *netid |
a0d0e21e LW |
1709 | |
1710 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ | |
1711 | ||
1712 | void | |
1713 | rpcb_DESTROY(netconf) | |
8e07c86e | 1714 | Netconfig *netconf |
beb31b0b | 1715 | CODE: |
a0d0e21e LW |
1716 | printf("NetconfigPtr::DESTROY\n"); |
1717 | free( netconf ); | |
1718 | ||
1719 | File C<typemap>: Custom typemap for RPC.xs. | |
1720 | ||
1721 | TYPEMAP | |
1722 | Netconfig * T_PTROBJ | |
1723 | ||
1724 | File C<RPC.pm>: Perl module for the RPC extension. | |
1725 | ||
1726 | package RPC; | |
1727 | ||
1728 | require Exporter; | |
1729 | require DynaLoader; | |
1730 | @ISA = qw(Exporter DynaLoader); | |
1731 | @EXPORT = qw(rpcb_gettime getnetconfigent); | |
1732 | ||
1733 | bootstrap RPC; | |
1734 | 1; | |
1735 | ||
1736 | File C<rpctest.pl>: Perl test program for the RPC extension. | |
1737 | ||
1738 | use RPC; | |
1739 | ||
1740 | $netconf = getnetconfigent(); | |
1741 | $a = rpcb_gettime(); | |
1742 | print "time = $a\n"; | |
1743 | print "netconf = $netconf\n"; | |
1744 | ||
1745 | $netconf = getnetconfigent("tcp"); | |
1746 | $a = rpcb_gettime("poplar"); | |
1747 | print "time = $a\n"; | |
1748 | print "netconf = $netconf\n"; | |
1749 | ||
1750 | ||
c07a80fd | 1751 | =head1 XS VERSION |
1752 | ||
f27cfbbe | 1753 | This document covers features supported by C<xsubpp> 1.935. |
c07a80fd | 1754 | |
a0d0e21e LW |
1755 | =head1 AUTHOR |
1756 | ||
beb31b0b GS |
1757 | Originally written by Dean Roehrich <F<roehrich@cray.com>>. |
1758 | ||
7f2de2d2 | 1759 | Maintained since 1996 by The Perl Porters <F<perlbug@perl.org>>. |