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1 | =head1 NAME |
2 | |
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3 | perlxs - XS language reference manual |
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4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | =head2 Introduction |
8 | |
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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 |
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60 | uses B<typemaps> to determine how to map C function parameters |
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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 |
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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. |
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72 | |
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73 | See L<perlxstut> for a tutorial on the whole extension creation process. |
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74 | |
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75 | Note: For some extensions, Dave Beazley's SWIG system may provide a |
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76 | significantly more convenient mechanism for creating the extension |
77 | glue code. See http://www.swig.org/ for more information. |
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78 | |
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79 | =head2 On The Road |
80 | |
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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. |
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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) |
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123 | char *host |
124 | time_t &timep |
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125 | OUTPUT: |
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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 | |
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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 | |
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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. |
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166 | |
167 | double |
168 | sin(x) |
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169 | double x |
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170 | |
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171 | Optionally, one can merge the description of types and the list of |
172 | argument names, rewriting this as |
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173 | |
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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 |
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185 | |
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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: |
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191 | |
192 | char * s |
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193 | char &c |
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194 | |
195 | Both these XS declarations correspond to the C<char*> C type, but they have |
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196 | different semantics, see L<"The & Unary Operator">. |
197 | |
198 | It is convenient to think that the indirection operator |
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199 | C<*> should be considered as a part of the type and the address operator C<&> |
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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. |
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202 | |
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203 | The function name and the return type must be placed on |
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204 | separate lines and should be flush left-adjusted. |
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205 | |
206 | INCORRECT CORRECT |
207 | |
208 | double sin(x) double |
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209 | double x sin(x) |
210 | double x |
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211 | |
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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. |
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215 | |
216 | CORRECT |
217 | |
218 | double |
219 | sin(x) |
220 | double x |
221 | |
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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 | |
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232 | =head2 The Argument Stack |
233 | |
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234 | The Perl argument stack is used to store the values which are |
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235 | sent as parameters to the XSUB and to store the XSUB's |
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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 |
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239 | first position on that stack which belongs to the active |
240 | function will be referred to as position 0 for that function. |
241 | |
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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 |
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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 | |
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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. |
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260 | |
261 | If the XSUB has a return type of C<void> then the compiler will |
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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. |
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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: |
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268 | directive is used which sets ST(0) explicitly. |
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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 |
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272 | segfaults in cases when XSUB was I<truly> C<void>. This practice is |
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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 |
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275 | some heuristic code which tries to disambiguate between "truly-void" |
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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.) |
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278 | |
279 | =head2 The MODULE Keyword |
280 | |
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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. |
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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 | |
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313 | The same package name can be used more than once, allowing for |
314 | non-contiguous code. This is useful if you have a stronger ordering |
315 | principle than package names. |
316 | |
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317 | Although this keyword is optional and in some cases provides redundant |
318 | information it should always be used. This keyword will ensure that the |
319 | XSUBs appear in the desired package. |
320 | |
321 | =head2 The PREFIX Keyword |
322 | |
323 | The PREFIX keyword designates prefixes which should be |
324 | removed from the Perl function names. If the C function is |
325 | C<rpcb_gettime()> and the PREFIX value is C<rpcb_> then Perl will |
326 | see this function as C<gettime()>. |
327 | |
328 | This keyword should follow the PACKAGE keyword when used. |
329 | If PACKAGE is not used then PREFIX should follow the MODULE |
330 | keyword. |
331 | |
332 | MODULE = RPC PREFIX = rpc_ |
333 | |
334 | MODULE = RPC PACKAGE = RPCB PREFIX = rpcb_ |
335 | |
336 | =head2 The OUTPUT: Keyword |
337 | |
338 | The OUTPUT: keyword indicates that certain function parameters should be |
339 | updated (new values made visible to Perl) when the XSUB terminates or that |
340 | certain values should be returned to the calling Perl function. For |
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341 | simple functions which have no CODE: or PPCODE: section, |
342 | such as the sin() function above, the RETVAL variable is |
343 | automatically designated as an output value. For more complex functions |
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344 | the B<xsubpp> compiler will need help to determine which variables are output |
345 | variables. |
346 | |
347 | This keyword will normally be used to complement the CODE: keyword. |
348 | The RETVAL variable is not recognized as an output variable when the |
349 | CODE: keyword is present. The OUTPUT: keyword is used in this |
350 | situation to tell the compiler that RETVAL really is an output |
351 | variable. |
352 | |
353 | The OUTPUT: keyword can also be used to indicate that function parameters |
354 | are output variables. This may be necessary when a parameter has been |
355 | modified within the function and the programmer would like the update to |
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356 | be seen by Perl. |
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357 | |
358 | bool_t |
359 | rpcb_gettime(host,timep) |
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360 | char *host |
361 | time_t &timep |
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362 | OUTPUT: |
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363 | timep |
364 | |
365 | The OUTPUT: keyword will also allow an output parameter to |
366 | be mapped to a matching piece of code rather than to a |
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367 | typemap. |
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368 | |
369 | bool_t |
370 | rpcb_gettime(host,timep) |
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371 | char *host |
372 | time_t &timep |
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373 | OUTPUT: |
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374 | timep sv_setnv(ST(1), (double)timep); |
375 | |
376 | B<xsubpp> emits an automatic C<SvSETMAGIC()> for all parameters in the |
377 | OUTPUT section of the XSUB, except RETVAL. This is the usually desired |
378 | behavior, as it takes care of properly invoking 'set' magic on output |
379 | parameters (needed for hash or array element parameters that must be |
380 | created if they didn't exist). If for some reason, this behavior is |
381 | not desired, the OUTPUT section may contain a C<SETMAGIC: DISABLE> line |
382 | to disable it for the remainder of the parameters in the OUTPUT section. |
383 | Likewise, C<SETMAGIC: ENABLE> can be used to reenable it for the |
384 | remainder of the OUTPUT section. See L<perlguts> for more details |
385 | about 'set' magic. |
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386 | |
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387 | =head2 The NO_OUTPUT Keyword |
388 | |
389 | The NO_OUTPUT can be placed as the first token of the XSUB. This keyword |
390 | indicates that while the C subroutine we provide an interface to has |
391 | a non-C<void> return type, the return value of this C subroutine should not |
392 | be returned from the generated Perl subroutine. |
393 | |
394 | With this keyword present L<The RETVAL Variable> is created, and in the |
395 | generated call to the subroutine this variable is assigned to, but the value |
396 | of this variable is not going to be used in the auto-generated code. |
397 | |
398 | This keyword makes sense only if C<RETVAL> is going to be accessed by the |
399 | user-supplied code. It is especially useful to make a function interface |
400 | more Perl-like, especially when the C return value is just an error condition |
401 | indicator. For example, |
402 | |
403 | NO_OUTPUT int |
404 | delete_file(char *name) |
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405 | POSTCALL: |
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406 | if (RETVAL != 0) |
407 | croak("Error %d while deleting file '%s'", RETVAL, name); |
408 | |
409 | Here the generated XS function returns nothing on success, and will die() |
410 | with a meaningful error message on error. |
411 | |
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412 | =head2 The CODE: Keyword |
413 | |
414 | This keyword is used in more complicated XSUBs which require |
415 | special handling for the C function. The RETVAL variable is |
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416 | still declared, but it will not be returned unless it is specified |
417 | in the OUTPUT: section. |
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418 | |
419 | The following XSUB is for a C function which requires special handling of |
420 | its parameters. The Perl usage is given first. |
421 | |
422 | $status = rpcb_gettime( "localhost", $timep ); |
423 | |
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424 | The XSUB follows. |
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425 | |
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426 | bool_t |
427 | rpcb_gettime(host,timep) |
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428 | char *host |
429 | time_t timep |
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430 | CODE: |
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431 | RETVAL = rpcb_gettime( host, &timep ); |
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432 | OUTPUT: |
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433 | timep |
434 | RETVAL |
435 | |
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436 | =head2 The INIT: Keyword |
437 | |
438 | The INIT: keyword allows initialization to be inserted into the XSUB before |
439 | the compiler generates the call to the C function. Unlike the CODE: keyword |
440 | above, this keyword does not affect the way the compiler handles RETVAL. |
441 | |
442 | bool_t |
443 | rpcb_gettime(host,timep) |
444 | char *host |
445 | time_t &timep |
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446 | INIT: |
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447 | printf("# Host is %s\n", host ); |
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448 | OUTPUT: |
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449 | timep |
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450 | |
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451 | Another use for the INIT: section is to check for preconditions before |
452 | making a call to the C function: |
453 | |
454 | long long |
455 | lldiv(a,b) |
456 | long long a |
457 | long long b |
458 | INIT: |
459 | if (a == 0 && b == 0) |
460 | XSRETURN_UNDEF; |
461 | if (b == 0) |
462 | croak("lldiv: cannot divide by 0"); |
463 | |
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464 | =head2 The NO_INIT Keyword |
465 | |
466 | The NO_INIT keyword is used to indicate that a function |
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467 | parameter is being used only as an output value. The B<xsubpp> |
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468 | compiler will normally generate code to read the values of |
469 | all function parameters from the argument stack and assign |
470 | them to C variables upon entry to the function. NO_INIT |
471 | will tell the compiler that some parameters will be used for |
472 | output rather than for input and that they will be handled |
473 | before the function terminates. |
474 | |
475 | The following example shows a variation of the rpcb_gettime() function. |
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476 | This function uses the timep variable only as an output variable and does |
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477 | not care about its initial contents. |
478 | |
479 | bool_t |
480 | rpcb_gettime(host,timep) |
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481 | char *host |
482 | time_t &timep = NO_INIT |
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483 | OUTPUT: |
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484 | timep |
485 | |
486 | =head2 Initializing Function Parameters |
487 | |
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488 | C function parameters are normally initialized with their values from |
489 | the argument stack (which in turn contains the parameters that were |
490 | passed to the XSUB from Perl). The typemaps contain the |
491 | code segments which are used to translate the Perl values to |
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492 | the C parameters. The programmer, however, is allowed to |
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493 | override the typemaps and supply alternate (or additional) |
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494 | initialization code. Initialization code starts with the first |
495 | C<=>, C<;> or C<+> on a line in the INPUT: section. The only |
496 | exception happens if this C<;> terminates the line, then this C<;> |
497 | is quietly ignored. |
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498 | |
499 | The following code demonstrates how to supply initialization code for |
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500 | function parameters. The initialization code is eval'd within double |
501 | quotes by the compiler before it is added to the output so anything |
502 | which should be interpreted literally [mainly C<$>, C<@>, or C<\\>] |
19799a22 |
503 | must be protected with backslashes. The variables $var, $arg, |
504 | and $type can be used as in typemaps. |
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505 | |
506 | bool_t |
507 | rpcb_gettime(host,timep) |
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508 | char *host = (char *)SvPV($arg,PL_na); |
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509 | time_t &timep = 0; |
beb31b0b |
510 | OUTPUT: |
a0d0e21e |
511 | timep |
512 | |
513 | This should not be used to supply default values for parameters. One |
514 | would normally use this when a function parameter must be processed by |
515 | another library function before it can be used. Default parameters are |
516 | covered in the next section. |
517 | |
beb31b0b |
518 | If the initialization begins with C<=>, then it is output in |
519 | the declaration for the input variable, replacing the initialization |
520 | supplied by the typemap. If the initialization |
521 | begins with C<;> or C<+>, then it is performed after |
522 | all of the input variables have been declared. In the C<;> |
523 | case the initialization normally supplied by the typemap is not performed. |
524 | For the C<+> case, the declaration for the variable will include the |
525 | initialization from the typemap. A global |
c2611fb3 |
526 | variable, C<%v>, is available for the truly rare case where |
7ad6fb0b |
527 | information from one initialization is needed in another |
528 | initialization. |
529 | |
beb31b0b |
530 | Here's a truly obscure example: |
531 | |
7ad6fb0b |
532 | bool_t |
533 | rpcb_gettime(host,timep) |
beb31b0b |
534 | time_t &timep ; /* \$v{timep}=@{[$v{timep}=$arg]} */ |
535 | char *host + SvOK($v{timep}) ? SvPV($arg,PL_na) : NULL; |
536 | OUTPUT: |
7ad6fb0b |
537 | timep |
538 | |
beb31b0b |
539 | The construct C<\$v{timep}=@{[$v{timep}=$arg]}> used in the above |
540 | example has a two-fold purpose: first, when this line is processed by |
541 | B<xsubpp>, the Perl snippet C<$v{timep}=$arg> is evaluated. Second, |
542 | the text of the evaluated snippet is output into the generated C file |
543 | (inside a C comment)! During the processing of C<char *host> line, |
544 | $arg will evaluate to C<ST(0)>, and C<$v{timep}> will evaluate to |
545 | C<ST(1)>. |
546 | |
a0d0e21e |
547 | =head2 Default Parameter Values |
548 | |
4628e4f8 |
549 | Default values for XSUB arguments can be specified by placing an |
550 | assignment statement in the parameter list. The default value may |
a104f515 |
551 | be a number, a string or the special string C<NO_INIT>. Defaults should |
a0d0e21e |
552 | always be used on the right-most parameters only. |
553 | |
554 | To allow the XSUB for rpcb_gettime() to have a default host |
555 | value the parameters to the XSUB could be rearranged. The |
556 | XSUB will then call the real rpcb_gettime() function with |
beb31b0b |
557 | the parameters in the correct order. This XSUB can be called |
558 | from Perl with either of the following statements: |
a0d0e21e |
559 | |
560 | $status = rpcb_gettime( $timep, $host ); |
561 | |
562 | $status = rpcb_gettime( $timep ); |
563 | |
564 | The XSUB will look like the code which follows. A CODE: |
565 | block is used to call the real rpcb_gettime() function with |
566 | the parameters in the correct order for that function. |
567 | |
568 | bool_t |
569 | rpcb_gettime(timep,host="localhost") |
8e07c86e |
570 | char *host |
571 | time_t timep = NO_INIT |
beb31b0b |
572 | CODE: |
a0d0e21e |
573 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b |
574 | OUTPUT: |
a0d0e21e |
575 | timep |
576 | RETVAL |
577 | |
c07a80fd |
578 | =head2 The PREINIT: Keyword |
579 | |
beb31b0b |
580 | The PREINIT: keyword allows extra variables to be declared immediately |
a2293a43 |
581 | before or after the declarations of the parameters from the INPUT: section |
beb31b0b |
582 | are emitted. |
583 | |
584 | If a variable is declared inside a CODE: section it will follow any typemap |
585 | code that is emitted for the input parameters. This may result in the |
586 | declaration ending up after C code, which is C syntax error. Similar |
587 | errors may happen with an explicit C<;>-type or C<+>-type initialization of |
588 | parameters is used (see L<"Initializing Function Parameters">). Declaring |
589 | these variables in an INIT: section will not help. |
590 | |
591 | In such cases, to force an additional variable to be declared together |
592 | with declarations of other variables, place the declaration into a |
593 | PREINIT: section. The PREINIT: keyword may be used one or more times |
594 | within an XSUB. |
c07a80fd |
595 | |
596 | The following examples are equivalent, but if the code is using complex |
597 | typemaps then the first example is safer. |
598 | |
599 | bool_t |
600 | rpcb_gettime(timep) |
601 | time_t timep = NO_INIT |
beb31b0b |
602 | PREINIT: |
c07a80fd |
603 | char *host = "localhost"; |
beb31b0b |
604 | CODE: |
c07a80fd |
605 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b |
606 | OUTPUT: |
c07a80fd |
607 | timep |
608 | RETVAL |
609 | |
beb31b0b |
610 | For this particular case an INIT: keyword would generate the |
611 | same C code as the PREINIT: keyword. Another correct, but error-prone example: |
c07a80fd |
612 | |
613 | bool_t |
614 | rpcb_gettime(timep) |
615 | time_t timep = NO_INIT |
beb31b0b |
616 | CODE: |
c07a80fd |
617 | char *host = "localhost"; |
618 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b |
619 | OUTPUT: |
620 | timep |
621 | RETVAL |
622 | |
623 | Another way to declare C<host> is to use a C block in the CODE: section: |
624 | |
625 | bool_t |
626 | rpcb_gettime(timep) |
627 | time_t timep = NO_INIT |
628 | CODE: |
629 | { |
630 | char *host = "localhost"; |
631 | RETVAL = rpcb_gettime( host, &timep ); |
632 | } |
633 | OUTPUT: |
634 | timep |
635 | RETVAL |
636 | |
637 | The ability to put additional declarations before the typemap entries are |
638 | processed is very handy in the cases when typemap conversions manipulate |
639 | some global state: |
640 | |
641 | MyObject |
642 | mutate(o) |
643 | PREINIT: |
644 | MyState st = global_state; |
645 | INPUT: |
646 | MyObject o; |
647 | CLEANUP: |
648 | reset_to(global_state, st); |
649 | |
650 | Here we suppose that conversion to C<MyObject> in the INPUT: section and from |
651 | MyObject when processing RETVAL will modify a global variable C<global_state>. |
652 | After these conversions are performed, we restore the old value of |
653 | C<global_state> (to avoid memory leaks, for example). |
654 | |
655 | There is another way to trade clarity for compactness: INPUT sections allow |
656 | declaration of C variables which do not appear in the parameter list of |
657 | a subroutine. Thus the above code for mutate() can be rewritten as |
658 | |
659 | MyObject |
660 | mutate(o) |
661 | MyState st = global_state; |
662 | MyObject o; |
663 | CLEANUP: |
664 | reset_to(global_state, st); |
665 | |
666 | and the code for rpcb_gettime() can be rewritten as |
667 | |
668 | bool_t |
669 | rpcb_gettime(timep) |
670 | time_t timep = NO_INIT |
671 | char *host = "localhost"; |
672 | C_ARGS: |
673 | host, &timep |
674 | OUTPUT: |
c07a80fd |
675 | timep |
676 | RETVAL |
677 | |
84287afe |
678 | =head2 The SCOPE: Keyword |
679 | |
680 | The SCOPE: keyword allows scoping to be enabled for a particular XSUB. If |
681 | enabled, the XSUB will invoke ENTER and LEAVE automatically. |
682 | |
683 | To support potentially complex type mappings, if a typemap entry used |
beb31b0b |
684 | by an XSUB contains a comment like C</*scope*/> then scoping will |
685 | be automatically enabled for that XSUB. |
84287afe |
686 | |
687 | To enable scoping: |
688 | |
689 | SCOPE: ENABLE |
690 | |
691 | To disable scoping: |
692 | |
693 | SCOPE: DISABLE |
694 | |
c07a80fd |
695 | =head2 The INPUT: Keyword |
696 | |
697 | The XSUB's parameters are usually evaluated immediately after entering the |
698 | XSUB. The INPUT: keyword can be used to force those parameters to be |
699 | evaluated a little later. The INPUT: keyword can be used multiple times |
700 | within an XSUB and can be used to list one or more input variables. This |
701 | keyword is used with the PREINIT: keyword. |
702 | |
703 | The following example shows how the input parameter C<timep> can be |
704 | evaluated late, after a PREINIT. |
705 | |
706 | bool_t |
707 | rpcb_gettime(host,timep) |
708 | char *host |
beb31b0b |
709 | PREINIT: |
c07a80fd |
710 | time_t tt; |
beb31b0b |
711 | INPUT: |
c07a80fd |
712 | time_t timep |
beb31b0b |
713 | CODE: |
c07a80fd |
714 | RETVAL = rpcb_gettime( host, &tt ); |
715 | timep = tt; |
beb31b0b |
716 | OUTPUT: |
c07a80fd |
717 | timep |
718 | RETVAL |
719 | |
720 | The next example shows each input parameter evaluated late. |
721 | |
722 | bool_t |
723 | rpcb_gettime(host,timep) |
beb31b0b |
724 | PREINIT: |
c07a80fd |
725 | time_t tt; |
beb31b0b |
726 | INPUT: |
c07a80fd |
727 | char *host |
beb31b0b |
728 | PREINIT: |
c07a80fd |
729 | char *h; |
beb31b0b |
730 | INPUT: |
c07a80fd |
731 | time_t timep |
beb31b0b |
732 | CODE: |
c07a80fd |
733 | h = host; |
734 | RETVAL = rpcb_gettime( h, &tt ); |
735 | timep = tt; |
beb31b0b |
736 | OUTPUT: |
737 | timep |
738 | RETVAL |
739 | |
740 | Since INPUT sections allow declaration of C variables which do not appear |
741 | in the parameter list of a subroutine, this may be shortened to: |
742 | |
743 | bool_t |
744 | rpcb_gettime(host,timep) |
745 | time_t tt; |
746 | char *host; |
747 | char *h = host; |
748 | time_t timep; |
749 | CODE: |
750 | RETVAL = rpcb_gettime( h, &tt ); |
751 | timep = tt; |
752 | OUTPUT: |
c07a80fd |
753 | timep |
754 | RETVAL |
755 | |
beb31b0b |
756 | (We used our knowledge that input conversion for C<char *> is a "simple" one, |
757 | thus C<host> is initialized on the declaration line, and our assignment |
758 | C<h = host> is not performed too early. Otherwise one would need to have the |
759 | assignment C<h = host> in a CODE: or INIT: section.) |
760 | |
cb79badd |
761 | =head2 The IN/OUTLIST/IN_OUTLIST/OUT/IN_OUT Keywords |
9e24e6f2 |
762 | |
763 | In the list of parameters for an XSUB, one can precede parameter names |
cb79badd |
764 | by the C<IN>/C<OUTLIST>/C<IN_OUTLIST>/C<OUT>/C<IN_OUT> keywords. |
765 | C<IN> keyword is the default, the other keywords indicate how the Perl |
766 | interface should differ from the C interface. |
767 | |
768 | Parameters preceded by C<OUTLIST>/C<IN_OUTLIST>/C<OUT>/C<IN_OUT> |
769 | keywords are considered to be used by the C subroutine I<via |
770 | pointers>. C<OUTLIST>/C<OUT> keywords indicate that the C subroutine |
771 | does not inspect the memory pointed by this parameter, but will write |
772 | through this pointer to provide additional return values. |
773 | |
774 | Parameters preceded by C<OUTLIST> keyword do not appear in the usage |
775 | signature of the generated Perl function. |
776 | |
777 | Parameters preceded by C<IN_OUTLIST>/C<IN_OUT>/C<OUT> I<do> appear as |
778 | parameters to the Perl function. With the exception of |
779 | C<OUT>-parameters, these parameters are converted to the corresponding |
780 | C type, then pointers to these data are given as arguments to the C |
781 | function. It is expected that the C function will write through these |
782 | pointers. |
9e24e6f2 |
783 | |
784 | The return list of the generated Perl function consists of the C return value |
785 | from the function (unless the XSUB is of C<void> return type or |
cb79badd |
786 | C<The NO_OUTPUT Keyword> was used) followed by all the C<OUTLIST> |
787 | and C<IN_OUTLIST> parameters (in the order of appearance). On the |
788 | return from the XSUB the C<IN_OUT>/C<OUT> Perl parameter will be |
789 | modified to have the values written by the C function. |
790 | |
791 | For example, an XSUB |
9e24e6f2 |
792 | |
793 | void |
794 | day_month(OUTLIST day, IN unix_time, OUTLIST month) |
795 | int day |
796 | int unix_time |
797 | int month |
798 | |
799 | should be used from Perl as |
800 | |
801 | my ($day, $month) = day_month(time); |
802 | |
803 | The C signature of the corresponding function should be |
804 | |
805 | void day_month(int *day, int unix_time, int *month); |
806 | |
cb79badd |
807 | The C<IN>/C<OUTLIST>/C<IN_OUTLIST>/C<IN_OUT>/C<OUT> keywords can be |
808 | mixed with ANSI-style declarations, as in |
9e24e6f2 |
809 | |
810 | void |
811 | day_month(OUTLIST int day, int unix_time, OUTLIST int month) |
812 | |
813 | (here the optional C<IN> keyword is omitted). |
814 | |
cb79badd |
815 | The C<IN_OUT> parameters are identical with parameters introduced with |
cea6626f |
816 | L<The & Unary Operator> and put into the C<OUTPUT:> section (see |
817 | L<The OUTPUT: Keyword>). The C<IN_OUTLIST> parameters are very similar, |
818 | the only difference being that the value C function writes through the |
cb79badd |
819 | pointer would not modify the Perl parameter, but is put in the output |
820 | list. |
821 | |
822 | The C<OUTLIST>/C<OUT> parameter differ from C<IN_OUTLIST>/C<IN_OUT> |
d1be9408 |
823 | parameters only by the initial value of the Perl parameter not |
cb79badd |
824 | being read (and not being given to the C function - which gets some |
825 | garbage instead). For example, the same C function as above can be |
826 | interfaced with as |
827 | |
828 | void day_month(OUT int day, int unix_time, OUT int month); |
829 | |
830 | or |
9e24e6f2 |
831 | |
832 | void |
833 | day_month(day, unix_time, month) |
834 | int &day = NO_INIT |
835 | int unix_time |
836 | int &month = NO_INIT |
837 | OUTPUT: |
838 | day |
839 | month |
840 | |
841 | However, the generated Perl function is called in very C-ish style: |
842 | |
843 | my ($day, $month); |
844 | day_month($day, time, $month); |
845 | |
08ff138d |
846 | =head2 The C<length(NAME)> Keyword |
847 | |
848 | If one of the input arguments to the C function is the length of a string |
849 | argument C<NAME>, one can substitute the name of the length-argument by |
850 | C<length(NAME)> in the XSUB declaration. This argument must be omited when |
851 | the generated Perl function is called. E.g., |
852 | |
853 | void |
854 | dump_chars(char *s, short l) |
855 | { |
856 | short n = 0; |
857 | while (n < l) { |
858 | printf("s[%d] = \"\\%#03o\"\n", n, (int)s[n]); |
859 | n++; |
860 | } |
861 | } |
862 | |
863 | MODULE = x PACKAGE = x |
864 | |
865 | void dump_chars(char *s, short length(s)) |
866 | |
867 | should be called as C<dump_chars($string)>. |
868 | |
869 | This directive is supported with ANSI-type function declarations only. |
870 | |
a0d0e21e |
871 | =head2 Variable-length Parameter Lists |
872 | |
873 | XSUBs can have variable-length parameter lists by specifying an ellipsis |
874 | C<(...)> in the parameter list. This use of the ellipsis is similar to that |
875 | found in ANSI C. The programmer is able to determine the number of |
876 | arguments passed to the XSUB by examining the C<items> variable which the |
877 | B<xsubpp> compiler supplies for all XSUBs. By using this mechanism one can |
878 | create an XSUB which accepts a list of parameters of unknown length. |
879 | |
880 | The I<host> parameter for the rpcb_gettime() XSUB can be |
881 | optional so the ellipsis can be used to indicate that the |
882 | XSUB will take a variable number of parameters. Perl should |
d1b91892 |
883 | be able to call this XSUB with either of the following statements. |
a0d0e21e |
884 | |
885 | $status = rpcb_gettime( $timep, $host ); |
886 | |
887 | $status = rpcb_gettime( $timep ); |
888 | |
889 | The XS code, with ellipsis, follows. |
890 | |
891 | bool_t |
892 | rpcb_gettime(timep, ...) |
8e07c86e |
893 | time_t timep = NO_INIT |
beb31b0b |
894 | PREINIT: |
a0d0e21e |
895 | char *host = "localhost"; |
2d8e6c8d |
896 | STRLEN n_a; |
beb31b0b |
897 | CODE: |
898 | if( items > 1 ) |
899 | host = (char *)SvPV(ST(1), n_a); |
900 | RETVAL = rpcb_gettime( host, &timep ); |
901 | OUTPUT: |
a0d0e21e |
902 | timep |
903 | RETVAL |
904 | |
cfc02341 |
905 | =head2 The C_ARGS: Keyword |
906 | |
907 | The C_ARGS: keyword allows creating of XSUBS which have different |
908 | calling sequence from Perl than from C, without a need to write |
beb31b0b |
909 | CODE: or PPCODE: section. The contents of the C_ARGS: paragraph is |
cfc02341 |
910 | put as the argument to the called C function without any change. |
911 | |
beb31b0b |
912 | For example, suppose that a C function is declared as |
cfc02341 |
913 | |
914 | symbolic nth_derivative(int n, symbolic function, int flags); |
915 | |
916 | and that the default flags are kept in a global C variable |
917 | C<default_flags>. Suppose that you want to create an interface which |
918 | is called as |
919 | |
920 | $second_deriv = $function->nth_derivative(2); |
921 | |
922 | To do this, declare the XSUB as |
923 | |
924 | symbolic |
925 | nth_derivative(function, n) |
926 | symbolic function |
927 | int n |
beb31b0b |
928 | C_ARGS: |
cfc02341 |
929 | n, function, default_flags |
930 | |
a0d0e21e |
931 | =head2 The PPCODE: Keyword |
932 | |
933 | The PPCODE: keyword is an alternate form of the CODE: keyword and is used |
934 | to tell the B<xsubpp> compiler that the programmer is supplying the code to |
d1b91892 |
935 | control the argument stack for the XSUBs return values. Occasionally one |
a0d0e21e |
936 | will want an XSUB to return a list of values rather than a single value. |
937 | In these cases one must use PPCODE: and then explicitly push the list of |
beb31b0b |
938 | values on the stack. The PPCODE: and CODE: keywords should not be used |
a0d0e21e |
939 | together within the same XSUB. |
940 | |
beb31b0b |
941 | The actual difference between PPCODE: and CODE: sections is in the |
942 | initialization of C<SP> macro (which stands for the I<current> Perl |
943 | stack pointer), and in the handling of data on the stack when returning |
944 | from an XSUB. In CODE: sections SP preserves the value which was on |
945 | entry to the XSUB: SP is on the function pointer (which follows the |
946 | last parameter). In PPCODE: sections SP is moved backward to the |
947 | beginning of the parameter list, which allows C<PUSH*()> macros |
948 | to place output values in the place Perl expects them to be when |
949 | the XSUB returns back to Perl. |
950 | |
951 | The generated trailer for a CODE: section ensures that the number of return |
952 | values Perl will see is either 0 or 1 (depending on the C<void>ness of the |
953 | return value of the C function, and heuristics mentioned in |
954 | L<"The RETVAL Variable">). The trailer generated for a PPCODE: section |
955 | is based on the number of return values and on the number of times |
956 | C<SP> was updated by C<[X]PUSH*()> macros. |
957 | |
958 | Note that macros C<ST(i)>, C<XST_m*()> and C<XSRETURN*()> work equally |
959 | well in CODE: sections and PPCODE: sections. |
960 | |
a0d0e21e |
961 | The following XSUB will call the C rpcb_gettime() function |
962 | and will return its two output values, timep and status, to |
963 | Perl as a single list. |
964 | |
d1b91892 |
965 | void |
966 | rpcb_gettime(host) |
8e07c86e |
967 | char *host |
beb31b0b |
968 | PREINIT: |
a0d0e21e |
969 | time_t timep; |
970 | bool_t status; |
beb31b0b |
971 | PPCODE: |
a0d0e21e |
972 | status = rpcb_gettime( host, &timep ); |
924508f0 |
973 | EXTEND(SP, 2); |
cb1a09d0 |
974 | PUSHs(sv_2mortal(newSViv(status))); |
975 | PUSHs(sv_2mortal(newSViv(timep))); |
a0d0e21e |
976 | |
977 | Notice that the programmer must supply the C code necessary |
978 | to have the real rpcb_gettime() function called and to have |
979 | the return values properly placed on the argument stack. |
980 | |
981 | The C<void> return type for this function tells the B<xsubpp> compiler that |
982 | the RETVAL variable is not needed or used and that it should not be created. |
983 | In most scenarios the void return type should be used with the PPCODE: |
984 | directive. |
985 | |
986 | The EXTEND() macro is used to make room on the argument |
987 | stack for 2 return values. The PPCODE: directive causes the |
924508f0 |
988 | B<xsubpp> compiler to create a stack pointer available as C<SP>, and it |
a0d0e21e |
989 | is this pointer which is being used in the EXTEND() macro. |
990 | The values are then pushed onto the stack with the PUSHs() |
991 | macro. |
992 | |
993 | Now the rpcb_gettime() function can be used from Perl with |
994 | the following statement. |
995 | |
996 | ($status, $timep) = rpcb_gettime("localhost"); |
997 | |
ef50df4b |
998 | When handling output parameters with a PPCODE section, be sure to handle |
999 | 'set' magic properly. See L<perlguts> for details about 'set' magic. |
1000 | |
a0d0e21e |
1001 | =head2 Returning Undef And Empty Lists |
1002 | |
5f05dabc |
1003 | Occasionally the programmer will want to return simply |
a0d0e21e |
1004 | C<undef> or an empty list if a function fails rather than a |
1005 | separate status value. The rpcb_gettime() function offers |
1006 | just this situation. If the function succeeds we would like |
1007 | to have it return the time and if it fails we would like to |
1008 | have undef returned. In the following Perl code the value |
1009 | of $timep will either be undef or it will be a valid time. |
1010 | |
1011 | $timep = rpcb_gettime( "localhost" ); |
1012 | |
7b8d334a |
1013 | The following XSUB uses the C<SV *> return type as a mnemonic only, |
e7ea3e70 |
1014 | and uses a CODE: block to indicate to the compiler |
a0d0e21e |
1015 | that the programmer has supplied all the necessary code. The |
1016 | sv_newmortal() call will initialize the return value to undef, making that |
1017 | the default return value. |
1018 | |
e7ea3e70 |
1019 | SV * |
a0d0e21e |
1020 | rpcb_gettime(host) |
1021 | char * host |
beb31b0b |
1022 | PREINIT: |
a0d0e21e |
1023 | time_t timep; |
1024 | bool_t x; |
beb31b0b |
1025 | CODE: |
a0d0e21e |
1026 | ST(0) = sv_newmortal(); |
1027 | if( rpcb_gettime( host, &timep ) ) |
1028 | sv_setnv( ST(0), (double)timep); |
a0d0e21e |
1029 | |
1030 | The next example demonstrates how one would place an explicit undef in the |
1031 | return value, should the need arise. |
1032 | |
e7ea3e70 |
1033 | SV * |
a0d0e21e |
1034 | rpcb_gettime(host) |
1035 | char * host |
beb31b0b |
1036 | PREINIT: |
a0d0e21e |
1037 | time_t timep; |
1038 | bool_t x; |
beb31b0b |
1039 | CODE: |
a0d0e21e |
1040 | ST(0) = sv_newmortal(); |
1041 | if( rpcb_gettime( host, &timep ) ){ |
1042 | sv_setnv( ST(0), (double)timep); |
1043 | } |
1044 | else{ |
9cde0e7f |
1045 | ST(0) = &PL_sv_undef; |
a0d0e21e |
1046 | } |
a0d0e21e |
1047 | |
1048 | To return an empty list one must use a PPCODE: block and |
1049 | then not push return values on the stack. |
1050 | |
1051 | void |
1052 | rpcb_gettime(host) |
8e07c86e |
1053 | char *host |
beb31b0b |
1054 | PREINIT: |
a0d0e21e |
1055 | time_t timep; |
beb31b0b |
1056 | PPCODE: |
a0d0e21e |
1057 | if( rpcb_gettime( host, &timep ) ) |
cb1a09d0 |
1058 | PUSHs(sv_2mortal(newSViv(timep))); |
a0d0e21e |
1059 | else{ |
beb31b0b |
1060 | /* Nothing pushed on stack, so an empty |
1061 | * list is implicitly returned. */ |
a0d0e21e |
1062 | } |
a0d0e21e |
1063 | |
f27cfbbe |
1064 | Some people may be inclined to include an explicit C<return> in the above |
1065 | XSUB, rather than letting control fall through to the end. In those |
1066 | situations C<XSRETURN_EMPTY> should be used, instead. This will ensure that |
8a2949d9 |
1067 | the XSUB stack is properly adjusted. Consult L<perlapi> for other |
1068 | C<XSRETURN> macros. |
f27cfbbe |
1069 | |
beb31b0b |
1070 | Since C<XSRETURN_*> macros can be used with CODE blocks as well, one can |
1071 | rewrite this example as: |
1072 | |
1073 | int |
1074 | rpcb_gettime(host) |
1075 | char *host |
1076 | PREINIT: |
1077 | time_t timep; |
1078 | CODE: |
1079 | RETVAL = rpcb_gettime( host, &timep ); |
1080 | if (RETVAL == 0) |
1081 | XSRETURN_UNDEF; |
1082 | OUTPUT: |
1083 | RETVAL |
1084 | |
375cc10d |
1085 | In fact, one can put this check into a POSTCALL: section as well. Together |
beb31b0b |
1086 | with PREINIT: simplifications, this leads to: |
1087 | |
1088 | int |
1089 | rpcb_gettime(host) |
1090 | char *host |
1091 | time_t timep; |
375cc10d |
1092 | POSTCALL: |
beb31b0b |
1093 | if (RETVAL == 0) |
1094 | XSRETURN_UNDEF; |
1095 | |
4633a7c4 |
1096 | =head2 The REQUIRE: Keyword |
1097 | |
1098 | The REQUIRE: keyword is used to indicate the minimum version of the |
1099 | B<xsubpp> compiler needed to compile the XS module. An XS module which |
5f05dabc |
1100 | contains the following statement will compile with only B<xsubpp> version |
4633a7c4 |
1101 | 1.922 or greater: |
1102 | |
1103 | REQUIRE: 1.922 |
1104 | |
a0d0e21e |
1105 | =head2 The CLEANUP: Keyword |
1106 | |
1107 | This keyword can be used when an XSUB requires special cleanup procedures |
1108 | before it terminates. When the CLEANUP: keyword is used it must follow |
1109 | any CODE:, PPCODE:, or OUTPUT: blocks which are present in the XSUB. The |
1110 | code specified for the cleanup block will be added as the last statements |
1111 | in the XSUB. |
1112 | |
375cc10d |
1113 | =head2 The POSTCALL: Keyword |
9e24e6f2 |
1114 | |
1115 | This keyword can be used when an XSUB requires special procedures |
375cc10d |
1116 | executed after the C subroutine call is performed. When the POSTCALL: |
9e24e6f2 |
1117 | keyword is used it must precede OUTPUT: and CLEANUP: blocks which are |
1118 | present in the XSUB. |
1119 | |
375cc10d |
1120 | See examples in L<"The NO_OUTPUT Keyword"> and L<"Returning Undef And Empty Lists">. |
1121 | |
1122 | The POSTCALL: block does not make a lot of sense when the C subroutine |
9e24e6f2 |
1123 | call is supplied by user by providing either CODE: or PPCODE: section. |
1124 | |
a0d0e21e |
1125 | =head2 The BOOT: Keyword |
1126 | |
1127 | The BOOT: keyword is used to add code to the extension's bootstrap |
1128 | function. The bootstrap function is generated by the B<xsubpp> compiler and |
1129 | normally holds the statements necessary to register any XSUBs with Perl. |
1130 | With the BOOT: keyword the programmer can tell the compiler to add extra |
1131 | statements to the bootstrap function. |
1132 | |
1133 | This keyword may be used any time after the first MODULE keyword and should |
1134 | appear on a line by itself. The first blank line after the keyword will |
1135 | terminate the code block. |
1136 | |
1137 | BOOT: |
1138 | # The following message will be printed when the |
1139 | # bootstrap function executes. |
1140 | printf("Hello from the bootstrap!\n"); |
1141 | |
c07a80fd |
1142 | =head2 The VERSIONCHECK: Keyword |
1143 | |
1144 | The VERSIONCHECK: keyword corresponds to B<xsubpp>'s C<-versioncheck> and |
5f05dabc |
1145 | C<-noversioncheck> options. This keyword overrides the command line |
c07a80fd |
1146 | options. Version checking is enabled by default. When version checking is |
1147 | enabled the XS module will attempt to verify that its version matches the |
1148 | version of the PM module. |
1149 | |
1150 | To enable version checking: |
1151 | |
1152 | VERSIONCHECK: ENABLE |
1153 | |
1154 | To disable version checking: |
1155 | |
1156 | VERSIONCHECK: DISABLE |
1157 | |
1158 | =head2 The PROTOTYPES: Keyword |
1159 | |
1160 | The PROTOTYPES: keyword corresponds to B<xsubpp>'s C<-prototypes> and |
54310121 |
1161 | C<-noprototypes> options. This keyword overrides the command line options. |
c07a80fd |
1162 | Prototypes are enabled by default. When prototypes are enabled XSUBs will |
1163 | be given Perl prototypes. This keyword may be used multiple times in an XS |
1164 | module to enable and disable prototypes for different parts of the module. |
1165 | |
1166 | To enable prototypes: |
1167 | |
1168 | PROTOTYPES: ENABLE |
1169 | |
1170 | To disable prototypes: |
1171 | |
1172 | PROTOTYPES: DISABLE |
1173 | |
1174 | =head2 The PROTOTYPE: Keyword |
1175 | |
1176 | This keyword is similar to the PROTOTYPES: keyword above but can be used to |
1177 | force B<xsubpp> to use a specific prototype for the XSUB. This keyword |
1178 | overrides all other prototype options and keywords but affects only the |
1179 | current XSUB. Consult L<perlsub/Prototypes> for information about Perl |
1180 | prototypes. |
1181 | |
1182 | bool_t |
1183 | rpcb_gettime(timep, ...) |
1184 | time_t timep = NO_INIT |
beb31b0b |
1185 | PROTOTYPE: $;$ |
1186 | PREINIT: |
c07a80fd |
1187 | char *host = "localhost"; |
2d8e6c8d |
1188 | STRLEN n_a; |
beb31b0b |
1189 | CODE: |
c07a80fd |
1190 | if( items > 1 ) |
2d8e6c8d |
1191 | host = (char *)SvPV(ST(1), n_a); |
c07a80fd |
1192 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b |
1193 | OUTPUT: |
c07a80fd |
1194 | timep |
1195 | RETVAL |
1196 | |
dd76e73a |
1197 | If the prototypes are enabled, you can disable it locally for a given |
1198 | XSUB as in the following example: |
1199 | |
1200 | void |
1201 | rpcb_gettime_noproto() |
1202 | PROTOTYPE: DISABLE |
1203 | ... |
1204 | |
c07a80fd |
1205 | =head2 The ALIAS: Keyword |
1206 | |
cfc02341 |
1207 | The ALIAS: keyword allows an XSUB to have two or more unique Perl names |
c07a80fd |
1208 | and to know which of those names was used when it was invoked. The Perl |
1209 | names may be fully-qualified with package names. Each alias is given an |
1210 | index. The compiler will setup a variable called C<ix> which contain the |
1211 | index of the alias which was used. When the XSUB is called with its |
1212 | declared name C<ix> will be 0. |
1213 | |
1214 | The following example will create aliases C<FOO::gettime()> and |
1215 | C<BAR::getit()> for this function. |
1216 | |
1217 | bool_t |
1218 | rpcb_gettime(host,timep) |
1219 | char *host |
1220 | time_t &timep |
beb31b0b |
1221 | ALIAS: |
c07a80fd |
1222 | FOO::gettime = 1 |
1223 | BAR::getit = 2 |
beb31b0b |
1224 | INIT: |
c07a80fd |
1225 | printf("# ix = %d\n", ix ); |
beb31b0b |
1226 | OUTPUT: |
c07a80fd |
1227 | timep |
1228 | |
54162f5c |
1229 | =head2 The OVERLOAD: Keyword |
1230 | |
1231 | Instead of writing an overloaded interface using pure Perl, you |
1232 | can also use the OVERLOAD keyword to define additional Perl names |
1233 | for your functions (like the ALIAS: keyword above). However, the |
1234 | overloaded functions must be defined with three parameters (except |
1235 | for the nomethod() function which needs four parameters). If any |
1236 | function has the OVERLOAD: keyword, several additional lines |
1237 | will be defined in the c file generated by xsubpp in order to |
1238 | register with the overload magic. |
1239 | |
1240 | Since blessed objects are actually stored as RV's, it is useful |
1241 | to use the typemap features to preprocess parameters and extract |
1242 | the actual SV stored within the blessed RV. See the sample for |
1243 | T_PTROBJ_SPECIAL below. |
1244 | |
1245 | To use the OVERLOAD: keyword, create an XS function which takes |
1246 | three input parameters ( or use the c style '...' definition) like |
1247 | this: |
1248 | |
1249 | SV * |
1250 | cmp (lobj, robj, swap) |
1251 | My_Module_obj lobj |
1252 | My_Module_obj robj |
1253 | IV swap |
1254 | OVERLOAD: cmp <=> |
1255 | { /* function defined here */} |
1256 | |
1257 | In this case, the function will overload both of the three way |
1258 | comparison operators. For all overload operations using non-alpha |
1259 | characters, you must type the parameter without quoting, seperating |
1260 | multiple overloads with whitespace. Note that "" (the stringify |
1261 | overload) should be entered as \"\" (i.e. escaped). |
1262 | |
30d6fba6 |
1263 | =head2 The FALLBACK: Keyword |
1264 | |
1265 | In addition to the OVERLOAD keyword, if you need to control how |
1266 | Perl autogenerates missing overloaded operators, you can set the |
1267 | FALLBACK keyword in the module header section, like this: |
1268 | |
1269 | MODULE = RPC PACKAGE = RPC |
1270 | |
1271 | FALLBACK: TRUE |
1272 | ... |
1273 | |
1274 | where FALLBACK can take any of the three values TRUE, FALSE, or |
1275 | UNDEF. If you do not set any FALLBACK value when using OVERLOAD, |
1276 | it defaults to UNDEF. FALLBACK is not used except when one or |
1277 | more functions using OVERLOAD have been defined. Please see |
1278 | L<overload/Fallback> for more details. |
1279 | |
cfc02341 |
1280 | =head2 The INTERFACE: Keyword |
1281 | |
1282 | This keyword declares the current XSUB as a keeper of the given |
1283 | calling signature. If some text follows this keyword, it is |
1284 | considered as a list of functions which have this signature, and |
beb31b0b |
1285 | should be attached to the current XSUB. |
cfc02341 |
1286 | |
beb31b0b |
1287 | For example, if you have 4 C functions multiply(), divide(), add(), |
1288 | subtract() all having the signature: |
cfc02341 |
1289 | |
1290 | symbolic f(symbolic, symbolic); |
1291 | |
beb31b0b |
1292 | you can make them all to use the same XSUB using this: |
cfc02341 |
1293 | |
1294 | symbolic |
1295 | interface_s_ss(arg1, arg2) |
1296 | symbolic arg1 |
1297 | symbolic arg2 |
1298 | INTERFACE: |
1299 | multiply divide |
1300 | add subtract |
1301 | |
beb31b0b |
1302 | (This is the complete XSUB code for 4 Perl functions!) Four generated |
1303 | Perl function share names with corresponding C functions. |
1304 | |
1305 | The advantage of this approach comparing to ALIAS: keyword is that there |
1306 | is no need to code a switch statement, each Perl function (which shares |
1307 | the same XSUB) knows which C function it should call. Additionally, one |
cfc02341 |
1308 | can attach an extra function remainder() at runtime by using |
beb31b0b |
1309 | |
cfc02341 |
1310 | CV *mycv = newXSproto("Symbolic::remainder", |
1311 | XS_Symbolic_interface_s_ss, __FILE__, "$$"); |
1312 | XSINTERFACE_FUNC_SET(mycv, remainder); |
1313 | |
beb31b0b |
1314 | say, from another XSUB. (This example supposes that there was no |
1315 | INTERFACE_MACRO: section, otherwise one needs to use something else instead of |
1316 | C<XSINTERFACE_FUNC_SET>, see the next section.) |
cfc02341 |
1317 | |
1318 | =head2 The INTERFACE_MACRO: Keyword |
1319 | |
1320 | This keyword allows one to define an INTERFACE using a different way |
1321 | to extract a function pointer from an XSUB. The text which follows |
1322 | this keyword should give the name of macros which would extract/set a |
1323 | function pointer. The extractor macro is given return type, C<CV*>, |
1324 | and C<XSANY.any_dptr> for this C<CV*>. The setter macro is given cv, |
1325 | and the function pointer. |
1326 | |
1327 | The default value is C<XSINTERFACE_FUNC> and C<XSINTERFACE_FUNC_SET>. |
1328 | An INTERFACE keyword with an empty list of functions can be omitted if |
1329 | INTERFACE_MACRO keyword is used. |
1330 | |
1331 | Suppose that in the previous example functions pointers for |
1332 | multiply(), divide(), add(), subtract() are kept in a global C array |
1333 | C<fp[]> with offsets being C<multiply_off>, C<divide_off>, C<add_off>, |
1334 | C<subtract_off>. Then one can use |
1335 | |
1336 | #define XSINTERFACE_FUNC_BYOFFSET(ret,cv,f) \ |
1337 | ((XSINTERFACE_CVT(ret,))fp[CvXSUBANY(cv).any_i32]) |
1338 | #define XSINTERFACE_FUNC_BYOFFSET_set(cv,f) \ |
1339 | CvXSUBANY(cv).any_i32 = CAT2( f, _off ) |
1340 | |
1341 | in C section, |
1342 | |
1343 | symbolic |
1344 | interface_s_ss(arg1, arg2) |
1345 | symbolic arg1 |
1346 | symbolic arg2 |
beb31b0b |
1347 | INTERFACE_MACRO: |
cfc02341 |
1348 | XSINTERFACE_FUNC_BYOFFSET |
1349 | XSINTERFACE_FUNC_BYOFFSET_set |
beb31b0b |
1350 | INTERFACE: |
cfc02341 |
1351 | multiply divide |
1352 | add subtract |
1353 | |
1354 | in XSUB section. |
1355 | |
c07a80fd |
1356 | =head2 The INCLUDE: Keyword |
1357 | |
1358 | This keyword can be used to pull other files into the XS module. The other |
1359 | files may have XS code. INCLUDE: can also be used to run a command to |
1360 | generate the XS code to be pulled into the module. |
1361 | |
1362 | The file F<Rpcb1.xsh> contains our C<rpcb_gettime()> function: |
1363 | |
1364 | bool_t |
1365 | rpcb_gettime(host,timep) |
1366 | char *host |
1367 | time_t &timep |
beb31b0b |
1368 | OUTPUT: |
c07a80fd |
1369 | timep |
1370 | |
1371 | The XS module can use INCLUDE: to pull that file into it. |
1372 | |
1373 | INCLUDE: Rpcb1.xsh |
1374 | |
1375 | If the parameters to the INCLUDE: keyword are followed by a pipe (C<|>) then |
1376 | the compiler will interpret the parameters as a command. |
1377 | |
1378 | INCLUDE: cat Rpcb1.xsh | |
1379 | |
1380 | =head2 The CASE: Keyword |
1381 | |
1382 | The CASE: keyword allows an XSUB to have multiple distinct parts with each |
1383 | part acting as a virtual XSUB. CASE: is greedy and if it is used then all |
1384 | other XS keywords must be contained within a CASE:. This means nothing may |
1385 | precede the first CASE: in the XSUB and anything following the last CASE: is |
1386 | included in that case. |
1387 | |
1388 | A CASE: might switch via a parameter of the XSUB, via the C<ix> ALIAS: |
1389 | variable (see L<"The ALIAS: Keyword">), or maybe via the C<items> variable |
1390 | (see L<"Variable-length Parameter Lists">). The last CASE: becomes the |
1391 | B<default> case if it is not associated with a conditional. The following |
1392 | example shows CASE switched via C<ix> with a function C<rpcb_gettime()> |
1393 | having an alias C<x_gettime()>. When the function is called as |
b772cb6e |
1394 | C<rpcb_gettime()> its parameters are the usual C<(char *host, time_t *timep)>, |
1395 | but when the function is called as C<x_gettime()> its parameters are |
c07a80fd |
1396 | reversed, C<(time_t *timep, char *host)>. |
1397 | |
1398 | long |
1399 | rpcb_gettime(a,b) |
1400 | CASE: ix == 1 |
beb31b0b |
1401 | ALIAS: |
c07a80fd |
1402 | x_gettime = 1 |
beb31b0b |
1403 | INPUT: |
c07a80fd |
1404 | # 'a' is timep, 'b' is host |
1405 | char *b |
1406 | time_t a = NO_INIT |
beb31b0b |
1407 | CODE: |
c07a80fd |
1408 | RETVAL = rpcb_gettime( b, &a ); |
beb31b0b |
1409 | OUTPUT: |
c07a80fd |
1410 | a |
1411 | RETVAL |
1412 | CASE: |
1413 | # 'a' is host, 'b' is timep |
1414 | char *a |
1415 | time_t &b = NO_INIT |
beb31b0b |
1416 | OUTPUT: |
c07a80fd |
1417 | b |
1418 | RETVAL |
1419 | |
1420 | That function can be called with either of the following statements. Note |
1421 | the different argument lists. |
1422 | |
1423 | $status = rpcb_gettime( $host, $timep ); |
1424 | |
1425 | $status = x_gettime( $timep, $host ); |
1426 | |
1427 | =head2 The & Unary Operator |
1428 | |
beb31b0b |
1429 | The C<&> unary operator in the INPUT: section is used to tell B<xsubpp> |
1430 | that it should convert a Perl value to/from C using the C type to the left |
1431 | of C<&>, but provide a pointer to this value when the C function is called. |
1432 | |
1433 | This is useful to avoid a CODE: block for a C function which takes a parameter |
1434 | by reference. Typically, the parameter should be not a pointer type (an |
d1be9408 |
1435 | C<int> or C<long> but not an C<int*> or C<long*>). |
c07a80fd |
1436 | |
beb31b0b |
1437 | The following XSUB will generate incorrect C code. The B<xsubpp> compiler will |
c07a80fd |
1438 | turn this into code which calls C<rpcb_gettime()> with parameters C<(char |
1439 | *host, time_t timep)>, but the real C<rpcb_gettime()> wants the C<timep> |
1440 | parameter to be of type C<time_t*> rather than C<time_t>. |
1441 | |
1442 | bool_t |
1443 | rpcb_gettime(host,timep) |
1444 | char *host |
1445 | time_t timep |
beb31b0b |
1446 | OUTPUT: |
c07a80fd |
1447 | timep |
1448 | |
beb31b0b |
1449 | That problem is corrected by using the C<&> operator. The B<xsubpp> compiler |
c07a80fd |
1450 | will now turn this into code which calls C<rpcb_gettime()> correctly with |
1451 | parameters C<(char *host, time_t *timep)>. It does this by carrying the |
1452 | C<&> through, so the function call looks like C<rpcb_gettime(host, &timep)>. |
1453 | |
1454 | bool_t |
1455 | rpcb_gettime(host,timep) |
1456 | char *host |
1457 | time_t &timep |
beb31b0b |
1458 | OUTPUT: |
c07a80fd |
1459 | timep |
1460 | |
7817ba4d |
1461 | =head2 Inserting POD, Comments and C Preprocessor Directives |
a0d0e21e |
1462 | |
7817ba4d |
1463 | C preprocessor directives are allowed within BOOT:, PREINIT: INIT:, CODE:, |
375cc10d |
1464 | PPCODE:, POSTCALL:, and CLEANUP: blocks, as well as outside the functions. |
7817ba4d |
1465 | Comments are allowed anywhere after the MODULE keyword. The compiler will |
1466 | pass the preprocessor directives through untouched and will remove the |
1467 | commented lines. POD documentation is allowed at any point, both in the |
1468 | C and XS language sections. POD must be terminated with a C<=cut> command; |
1469 | C<xsubpp> will exit with an error if it does not. It is very unlikely that |
1470 | human generated C code will be mistaken for POD, as most indenting styles |
1471 | result in whitespace in front of any line starting with C<=>. Machine |
1472 | generated XS files may fall into this trap unless care is taken to |
1473 | ensure that a space breaks the sequence "\n=". |
b772cb6e |
1474 | |
f27cfbbe |
1475 | Comments can be added to XSUBs by placing a C<#> as the first |
1476 | non-whitespace of a line. Care should be taken to avoid making the |
1477 | comment look like a C preprocessor directive, lest it be interpreted as |
1478 | such. The simplest way to prevent this is to put whitespace in front of |
1479 | the C<#>. |
1480 | |
f27cfbbe |
1481 | If you use preprocessor directives to choose one of two |
1482 | versions of a function, use |
1483 | |
1484 | #if ... version1 |
1485 | #else /* ... version2 */ |
1486 | #endif |
1487 | |
1488 | and not |
1489 | |
1490 | #if ... version1 |
1491 | #endif |
1492 | #if ... version2 |
1493 | #endif |
1494 | |
beb31b0b |
1495 | because otherwise B<xsubpp> will believe that you made a duplicate |
f27cfbbe |
1496 | definition of the function. Also, put a blank line before the |
1497 | #else/#endif so it will not be seen as part of the function body. |
a0d0e21e |
1498 | |
1499 | =head2 Using XS With C++ |
1500 | |
beb31b0b |
1501 | If an XSUB name contains C<::>, it is considered to be a C++ method. |
1502 | The generated Perl function will assume that |
a0d0e21e |
1503 | its first argument is an object pointer. The object pointer |
1504 | will be stored in a variable called THIS. The object should |
1505 | have been created by C++ with the new() function and should |
cb1a09d0 |
1506 | be blessed by Perl with the sv_setref_pv() macro. The |
1507 | blessing of the object by Perl can be handled by a typemap. An example |
1508 | typemap is shown at the end of this section. |
a0d0e21e |
1509 | |
beb31b0b |
1510 | If the return type of the XSUB includes C<static>, the method is considered |
1511 | to be a static method. It will call the C++ |
a0d0e21e |
1512 | function using the class::method() syntax. If the method is not static |
f27cfbbe |
1513 | the function will be called using the THIS-E<gt>method() syntax. |
a0d0e21e |
1514 | |
cb1a09d0 |
1515 | The next examples will use the following C++ class. |
a0d0e21e |
1516 | |
a5f75d66 |
1517 | class color { |
cb1a09d0 |
1518 | public: |
a5f75d66 |
1519 | color(); |
1520 | ~color(); |
cb1a09d0 |
1521 | int blue(); |
1522 | void set_blue( int ); |
1523 | |
1524 | private: |
1525 | int c_blue; |
1526 | }; |
1527 | |
1528 | The XSUBs for the blue() and set_blue() methods are defined with the class |
1529 | name but the parameter for the object (THIS, or "self") is implicit and is |
1530 | not listed. |
1531 | |
1532 | int |
1533 | color::blue() |
a0d0e21e |
1534 | |
1535 | void |
cb1a09d0 |
1536 | color::set_blue( val ) |
1537 | int val |
a0d0e21e |
1538 | |
beb31b0b |
1539 | Both Perl functions will expect an object as the first parameter. In the |
1540 | generated C++ code the object is called C<THIS>, and the method call will |
1541 | be performed on this object. So in the C++ code the blue() and set_blue() |
1542 | methods will be called as this: |
a0d0e21e |
1543 | |
cb1a09d0 |
1544 | RETVAL = THIS->blue(); |
a0d0e21e |
1545 | |
cb1a09d0 |
1546 | THIS->set_blue( val ); |
a0d0e21e |
1547 | |
4628e4f8 |
1548 | You could also write a single get/set method using an optional argument: |
1549 | |
1550 | int |
a104f515 |
1551 | color::blue( val = NO_INIT ) |
4628e4f8 |
1552 | int val |
1553 | PROTOTYPE $;$ |
1554 | CODE: |
1555 | if (items > 1) |
1556 | THIS->set_blue( val ); |
1557 | RETVAL = THIS->blue(); |
1558 | OUTPUT: |
1559 | RETVAL |
1560 | |
cb1a09d0 |
1561 | If the function's name is B<DESTROY> then the C++ C<delete> function will be |
beb31b0b |
1562 | called and C<THIS> will be given as its parameter. The generated C++ code for |
a0d0e21e |
1563 | |
d1b91892 |
1564 | void |
cb1a09d0 |
1565 | color::DESTROY() |
1566 | |
beb31b0b |
1567 | will look like this: |
1568 | |
1569 | color *THIS = ...; // Initialized as in typemap |
cb1a09d0 |
1570 | |
1571 | delete THIS; |
a0d0e21e |
1572 | |
cb1a09d0 |
1573 | If the function's name is B<new> then the C++ C<new> function will be called |
1574 | to create a dynamic C++ object. The XSUB will expect the class name, which |
1575 | will be kept in a variable called C<CLASS>, to be given as the first |
1576 | argument. |
a0d0e21e |
1577 | |
cb1a09d0 |
1578 | color * |
1579 | color::new() |
a0d0e21e |
1580 | |
beb31b0b |
1581 | The generated C++ code will call C<new>. |
a0d0e21e |
1582 | |
beb31b0b |
1583 | RETVAL = new color(); |
cb1a09d0 |
1584 | |
1585 | The following is an example of a typemap that could be used for this C++ |
1586 | example. |
1587 | |
1588 | TYPEMAP |
1589 | color * O_OBJECT |
1590 | |
1591 | OUTPUT |
1592 | # The Perl object is blessed into 'CLASS', which should be a |
1593 | # char* having the name of the package for the blessing. |
1594 | O_OBJECT |
1595 | sv_setref_pv( $arg, CLASS, (void*)$var ); |
a6006777 |
1596 | |
cb1a09d0 |
1597 | INPUT |
1598 | O_OBJECT |
1599 | if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) ) |
1600 | $var = ($type)SvIV((SV*)SvRV( $arg )); |
1601 | else{ |
1602 | warn( \"${Package}::$func_name() -- $var is not a blessed SV reference\" ); |
1603 | XSRETURN_UNDEF; |
1604 | } |
a0d0e21e |
1605 | |
d1b91892 |
1606 | =head2 Interface Strategy |
a0d0e21e |
1607 | |
1608 | When designing an interface between Perl and a C library a straight |
beb31b0b |
1609 | translation from C to XS (such as created by C<h2xs -x>) is often sufficient. |
1610 | However, sometimes the interface will look |
a0d0e21e |
1611 | very C-like and occasionally nonintuitive, especially when the C function |
beb31b0b |
1612 | modifies one of its parameters, or returns failure inband (as in "negative |
1613 | return values mean failure"). In cases where the programmer wishes to |
a0d0e21e |
1614 | create a more Perl-like interface the following strategy may help to |
1615 | identify the more critical parts of the interface. |
1616 | |
beb31b0b |
1617 | Identify the C functions with input/output or output parameters. The XSUBs for |
1618 | these functions may be able to return lists to Perl. |
1619 | |
1620 | Identify the C functions which use some inband info as an indication |
1621 | of failure. They may be |
1622 | candidates to return undef or an empty list in case of failure. If the |
1623 | failure may be detected without a call to the C function, you may want to use |
1624 | an INIT: section to report the failure. For failures detectable after the C |
375cc10d |
1625 | function returns one may want to use a POSTCALL: section to process the |
beb31b0b |
1626 | failure. In more complicated cases use CODE: or PPCODE: sections. |
1627 | |
1628 | If many functions use the same failure indication based on the return value, |
1629 | you may want to create a special typedef to handle this situation. Put |
1630 | |
1631 | typedef int negative_is_failure; |
1632 | |
1633 | near the beginning of XS file, and create an OUTPUT typemap entry |
1634 | for C<negative_is_failure> which converts negative values to C<undef>, or |
1635 | maybe croak()s. After this the return value of type C<negative_is_failure> |
1636 | will create more Perl-like interface. |
a0d0e21e |
1637 | |
d1b91892 |
1638 | Identify which values are used by only the C and XSUB functions |
beb31b0b |
1639 | themselves, say, when a parameter to a function should be a contents of a |
1640 | global variable. If Perl does not need to access the contents of the value |
a0d0e21e |
1641 | then it may not be necessary to provide a translation for that value |
1642 | from C to Perl. |
1643 | |
1644 | Identify the pointers in the C function parameter lists and return |
beb31b0b |
1645 | values. Some pointers may be used to implement input/output or |
1646 | output parameters, they can be handled in XS with the C<&> unary operator, |
1647 | and, possibly, using the NO_INIT keyword. |
1648 | Some others will require handling of types like C<int *>, and one needs |
1649 | to decide what a useful Perl translation will do in such a case. When |
1650 | the semantic is clear, it is advisable to put the translation into a typemap |
1651 | file. |
a0d0e21e |
1652 | |
1653 | Identify the structures used by the C functions. In many |
1654 | cases it may be helpful to use the T_PTROBJ typemap for |
1655 | these structures so they can be manipulated by Perl as |
beb31b0b |
1656 | blessed objects. (This is handled automatically by C<h2xs -x>.) |
1657 | |
1658 | If the same C type is used in several different contexts which require |
1659 | different translations, C<typedef> several new types mapped to this C type, |
1660 | and create separate F<typemap> entries for these new types. Use these |
1661 | types in declarations of return type and parameters to XSUBs. |
a0d0e21e |
1662 | |
a0d0e21e |
1663 | =head2 Perl Objects And C Structures |
1664 | |
1665 | When dealing with C structures one should select either |
1666 | B<T_PTROBJ> or B<T_PTRREF> for the XS type. Both types are |
1667 | designed to handle pointers to complex objects. The |
1668 | T_PTRREF type will allow the Perl object to be unblessed |
1669 | while the T_PTROBJ type requires that the object be blessed. |
1670 | By using T_PTROBJ one can achieve a form of type-checking |
d1b91892 |
1671 | because the XSUB will attempt to verify that the Perl object |
a0d0e21e |
1672 | is of the expected type. |
1673 | |
1674 | The following XS code shows the getnetconfigent() function which is used |
8e07c86e |
1675 | with ONC+ TIRPC. The getnetconfigent() function will return a pointer to a |
a0d0e21e |
1676 | C structure and has the C prototype shown below. The example will |
1677 | demonstrate how the C pointer will become a Perl reference. Perl will |
1678 | consider this reference to be a pointer to a blessed object and will |
1679 | attempt to call a destructor for the object. A destructor will be |
1680 | provided in the XS source to free the memory used by getnetconfigent(). |
1681 | Destructors in XS can be created by specifying an XSUB function whose name |
1682 | ends with the word B<DESTROY>. XS destructors can be used to free memory |
1683 | which may have been malloc'd by another XSUB. |
1684 | |
1685 | struct netconfig *getnetconfigent(const char *netid); |
1686 | |
1687 | A C<typedef> will be created for C<struct netconfig>. The Perl |
1688 | object will be blessed in a class matching the name of the C |
1689 | type, with the tag C<Ptr> appended, and the name should not |
1690 | have embedded spaces if it will be a Perl package name. The |
1691 | destructor will be placed in a class corresponding to the |
1692 | class of the object and the PREFIX keyword will be used to |
1693 | trim the name to the word DESTROY as Perl will expect. |
1694 | |
1695 | typedef struct netconfig Netconfig; |
1696 | |
1697 | MODULE = RPC PACKAGE = RPC |
1698 | |
1699 | Netconfig * |
1700 | getnetconfigent(netid) |
8e07c86e |
1701 | char *netid |
a0d0e21e |
1702 | |
1703 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ |
1704 | |
1705 | void |
1706 | rpcb_DESTROY(netconf) |
8e07c86e |
1707 | Netconfig *netconf |
beb31b0b |
1708 | CODE: |
a0d0e21e |
1709 | printf("Now in NetconfigPtr::DESTROY\n"); |
1710 | free( netconf ); |
1711 | |
1712 | This example requires the following typemap entry. Consult the typemap |
1713 | section for more information about adding new typemaps for an extension. |
1714 | |
1715 | TYPEMAP |
1716 | Netconfig * T_PTROBJ |
1717 | |
1718 | This example will be used with the following Perl statements. |
1719 | |
1720 | use RPC; |
1721 | $netconf = getnetconfigent("udp"); |
1722 | |
1723 | When Perl destroys the object referenced by $netconf it will send the |
1724 | object to the supplied XSUB DESTROY function. Perl cannot determine, and |
1725 | does not care, that this object is a C struct and not a Perl object. In |
1726 | this sense, there is no difference between the object created by the |
1727 | getnetconfigent() XSUB and an object created by a normal Perl subroutine. |
1728 | |
a0d0e21e |
1729 | =head2 The Typemap |
1730 | |
1731 | The typemap is a collection of code fragments which are used by the B<xsubpp> |
1732 | compiler to map C function parameters and values to Perl values. The |
7817ba4d |
1733 | typemap file may consist of three sections labelled C<TYPEMAP>, C<INPUT>, and |
beb31b0b |
1734 | C<OUTPUT>. An unlabelled initial section is assumed to be a C<TYPEMAP> |
1735 | section. The INPUT section tells |
7e9d670d |
1736 | the compiler how to translate Perl values |
a0d0e21e |
1737 | into variables of certain C types. The OUTPUT section tells the compiler |
1738 | how to translate the values from certain C types into values Perl can |
1739 | understand. The TYPEMAP section tells the compiler which of the INPUT and |
1740 | OUTPUT code fragments should be used to map a given C type to a Perl value. |
7e9d670d |
1741 | The section labels C<TYPEMAP>, C<INPUT>, or C<OUTPUT> must begin |
1742 | in the first column on a line by themselves, and must be in uppercase. |
a0d0e21e |
1743 | |
dcd2ee75 |
1744 | The default typemap in the C<lib/ExtUtils> directory of the Perl source |
1745 | contains many useful types which can be used by Perl extensions. Some |
1746 | extensions define additional typemaps which they keep in their own directory. |
1747 | These additional typemaps may reference INPUT and OUTPUT maps in the main |
a0d0e21e |
1748 | typemap. The B<xsubpp> compiler will allow the extension's own typemap to |
1749 | override any mappings which are in the default typemap. |
1750 | |
1751 | Most extensions which require a custom typemap will need only the TYPEMAP |
1752 | section of the typemap file. The custom typemap used in the |
1753 | getnetconfigent() example shown earlier demonstrates what may be the typical |
1754 | use of extension typemaps. That typemap is used to equate a C structure |
1755 | with the T_PTROBJ typemap. The typemap used by getnetconfigent() is shown |
1756 | here. Note that the C type is separated from the XS type with a tab and |
1757 | that the C unary operator C<*> is considered to be a part of the C type name. |
1758 | |
beb31b0b |
1759 | TYPEMAP |
1760 | Netconfig *<tab>T_PTROBJ |
a0d0e21e |
1761 | |
1748e8dd |
1762 | Here's a more complicated example: suppose that you wanted C<struct |
1763 | netconfig> to be blessed into the class C<Net::Config>. One way to do |
1764 | this is to use underscores (_) to separate package names, as follows: |
1765 | |
1766 | typedef struct netconfig * Net_Config; |
1767 | |
1768 | And then provide a typemap entry C<T_PTROBJ_SPECIAL> that maps underscores to |
1769 | double-colons (::), and declare C<Net_Config> to be of that type: |
1770 | |
1771 | |
1772 | TYPEMAP |
1773 | Net_Config T_PTROBJ_SPECIAL |
1774 | |
1775 | INPUT |
1776 | T_PTROBJ_SPECIAL |
1777 | if (sv_derived_from($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")) { |
1778 | IV tmp = SvIV((SV*)SvRV($arg)); |
1779 | $var = ($type) tmp; |
1780 | } |
1781 | else |
1782 | croak(\"$var is not of type ${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\") |
1783 | |
1784 | OUTPUT |
1785 | T_PTROBJ_SPECIAL |
1786 | sv_setref_pv($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\", |
1787 | (void*)$var); |
1788 | |
1789 | The INPUT and OUTPUT sections substitute underscores for double-colons |
1790 | on the fly, giving the desired effect. This example demonstrates some |
1791 | of the power and versatility of the typemap facility. |
1792 | |
662a0f8c |
1793 | =head2 Safely Storing Static Data in XS |
1794 | |
1795 | Starting with Perl 5.8, a macro framework has been defined to allow |
1796 | static data to be safely stored in XS modules that will be accessed from |
1797 | a multi-threaded Perl. |
1798 | |
1799 | Although primarily designed for use with multi-threaded Perl, the macros |
1800 | have been designed so that they will work with non-threaded Perl as well. |
1801 | |
1802 | It is therefore strongly recommended that these macros be used by all |
1803 | XS modules that make use of static data. |
1804 | |
fe854a6f |
1805 | The easiest way to get a template set of macros to use is by specifying |
662a0f8c |
1806 | the C<-g> (C<--global>) option with h2xs (see L<h2xs>). |
1807 | |
1808 | Below is an example module that makes use of the macros. |
1809 | |
1810 | #include "EXTERN.h" |
1811 | #include "perl.h" |
1812 | #include "XSUB.h" |
7207e29d |
1813 | |
662a0f8c |
1814 | /* Global Data */ |
7207e29d |
1815 | |
662a0f8c |
1816 | #define MY_CXT_KEY "BlindMice::_guts" XS_VERSION |
7207e29d |
1817 | |
662a0f8c |
1818 | typedef struct { |
1819 | int count; |
1820 | char name[3][100]; |
1821 | } my_cxt_t; |
7207e29d |
1822 | |
662a0f8c |
1823 | START_MY_CXT |
7207e29d |
1824 | |
662a0f8c |
1825 | MODULE = BlindMice PACKAGE = BlindMice |
7207e29d |
1826 | |
662a0f8c |
1827 | BOOT: |
1828 | { |
1829 | MY_CXT_INIT; |
1830 | MY_CXT.count = 0; |
1831 | strcpy(MY_CXT.name[0], "None"); |
1832 | strcpy(MY_CXT.name[1], "None"); |
1833 | strcpy(MY_CXT.name[2], "None"); |
1834 | } |
1835 | |
1836 | int |
1837 | newMouse(char * name) |
1838 | char * name; |
1839 | PREINIT: |
1840 | dMY_CXT; |
1841 | CODE: |
1842 | if (MY_CXT.count >= 3) { |
1843 | warn("Already have 3 blind mice") ; |
1844 | RETVAL = 0; |
1845 | } |
1846 | else { |
1847 | RETVAL = ++ MY_CXT.count; |
1848 | strcpy(MY_CXT.name[MY_CXT.count - 1], name); |
1849 | } |
1850 | |
1851 | char * |
1852 | get_mouse_name(index) |
1853 | int index |
1854 | CODE: |
1855 | dMY_CXT; |
1856 | RETVAL = MY_CXT.lives ++; |
1857 | if (index > MY_CXT.count) |
1858 | croak("There are only 3 blind mice."); |
1859 | else |
1860 | RETVAL = newSVpv(MY_CXT.name[index - 1]); |
1861 | |
1862 | |
1863 | B<REFERENCE> |
1864 | |
1865 | =over 5 |
1866 | |
1867 | =item MY_CXT_KEY |
1868 | |
1869 | This macro is used to define a unique key to refer to the static data |
1870 | for an XS module. The suggested naming scheme, as used by h2xs, is to |
1871 | use a string that consists of the module name, the string "::_guts" |
1872 | and the module version number. |
1873 | |
1874 | #define MY_CXT_KEY "MyModule::_guts" XS_VERSION |
1875 | |
1876 | =item typedef my_cxt_t |
1877 | |
1878 | This struct typedef I<must> always be called C<my_cxt_t> -- the other |
1879 | C<CXT*> macros assume the existence of the C<my_cxt_t> typedef name. |
1880 | |
1881 | Declare a typedef named C<my_cxt_t> that is a structure that contains |
1882 | all the data that needs to be interpreter-local. |
1883 | |
1884 | typedef struct { |
1885 | int some_value; |
1886 | } my_cxt_t; |
1887 | |
1888 | =item START_MY_CXT |
1889 | |
1890 | Always place the START_MY_CXT macro directly after the declaration |
1891 | of C<my_cxt_t>. |
1892 | |
1893 | =item MY_CXT_INIT |
1894 | |
1895 | The MY_CXT_INIT macro initialises storage for the C<my_cxt_t> struct. |
1896 | |
1897 | It I<must> be called exactly once -- typically in a BOOT: section. |
1898 | |
1899 | =item dMY_CXT |
1900 | |
1901 | Use the dMY_CXT macro (a declaration) in all the functions that access |
1902 | MY_CXT. |
1903 | |
1904 | =item MY_CXT |
1905 | |
1906 | Use the MY_CXT macro to access members of the C<my_cxt_t> struct. For |
1907 | example, if C<my_cxt_t> is |
1908 | |
1909 | typedef struct { |
1910 | int index; |
1911 | } my_cxt_t; |
1912 | |
1913 | then use this to access the C<index> member |
1914 | |
1915 | dMY_CXT; |
1916 | MY_CXT.index = 2; |
1917 | |
1918 | =back |
1919 | |
a0d0e21e |
1920 | =head1 EXAMPLES |
1921 | |
1922 | File C<RPC.xs>: Interface to some ONC+ RPC bind library functions. |
1923 | |
1924 | #include "EXTERN.h" |
1925 | #include "perl.h" |
1926 | #include "XSUB.h" |
1927 | |
1928 | #include <rpc/rpc.h> |
1929 | |
1930 | typedef struct netconfig Netconfig; |
1931 | |
1932 | MODULE = RPC PACKAGE = RPC |
1933 | |
e7ea3e70 |
1934 | SV * |
a0d0e21e |
1935 | rpcb_gettime(host="localhost") |
8e07c86e |
1936 | char *host |
beb31b0b |
1937 | PREINIT: |
a0d0e21e |
1938 | time_t timep; |
beb31b0b |
1939 | CODE: |
a0d0e21e |
1940 | ST(0) = sv_newmortal(); |
1941 | if( rpcb_gettime( host, &timep ) ) |
1942 | sv_setnv( ST(0), (double)timep ); |
a0d0e21e |
1943 | |
1944 | Netconfig * |
1945 | getnetconfigent(netid="udp") |
8e07c86e |
1946 | char *netid |
a0d0e21e |
1947 | |
1948 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ |
1949 | |
1950 | void |
1951 | rpcb_DESTROY(netconf) |
8e07c86e |
1952 | Netconfig *netconf |
beb31b0b |
1953 | CODE: |
a0d0e21e |
1954 | printf("NetconfigPtr::DESTROY\n"); |
1955 | free( netconf ); |
1956 | |
1957 | File C<typemap>: Custom typemap for RPC.xs. |
1958 | |
1959 | TYPEMAP |
1960 | Netconfig * T_PTROBJ |
1961 | |
1962 | File C<RPC.pm>: Perl module for the RPC extension. |
1963 | |
1964 | package RPC; |
1965 | |
1966 | require Exporter; |
1967 | require DynaLoader; |
1968 | @ISA = qw(Exporter DynaLoader); |
1969 | @EXPORT = qw(rpcb_gettime getnetconfigent); |
1970 | |
1971 | bootstrap RPC; |
1972 | 1; |
1973 | |
1974 | File C<rpctest.pl>: Perl test program for the RPC extension. |
1975 | |
1976 | use RPC; |
1977 | |
1978 | $netconf = getnetconfigent(); |
1979 | $a = rpcb_gettime(); |
1980 | print "time = $a\n"; |
1981 | print "netconf = $netconf\n"; |
1982 | |
1983 | $netconf = getnetconfigent("tcp"); |
1984 | $a = rpcb_gettime("poplar"); |
1985 | print "time = $a\n"; |
1986 | print "netconf = $netconf\n"; |
1987 | |
1988 | |
c07a80fd |
1989 | =head1 XS VERSION |
1990 | |
f27cfbbe |
1991 | This document covers features supported by C<xsubpp> 1.935. |
c07a80fd |
1992 | |
a0d0e21e |
1993 | =head1 AUTHOR |
1994 | |
beb31b0b |
1995 | Originally written by Dean Roehrich <F<roehrich@cray.com>>. |
1996 | |
7f2de2d2 |
1997 | Maintained since 1996 by The Perl Porters <F<perlbug@perl.org>>. |