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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 | |
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 |
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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 |
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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 |
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352 | be seen by Perl. |
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353 | |
354 | bool_t |
355 | rpcb_gettime(host,timep) |
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356 | char *host |
357 | time_t &timep |
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358 | OUTPUT: |
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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 |
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363 | typemap. |
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364 | |
365 | bool_t |
366 | rpcb_gettime(host,timep) |
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367 | char *host |
368 | time_t &timep |
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369 | OUTPUT: |
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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. |
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382 | |
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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 | |
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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 |
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412 | still declared, but it will not be returned unless it is specified |
413 | in the OUTPUT: section. |
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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 | |
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420 | The XSUB follows. |
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421 | |
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422 | bool_t |
423 | rpcb_gettime(host,timep) |
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424 | char *host |
425 | time_t timep |
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426 | CODE: |
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427 | RETVAL = rpcb_gettime( host, &timep ); |
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428 | OUTPUT: |
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429 | timep |
430 | RETVAL |
431 | |
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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 |
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442 | INIT: |
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443 | printf("# Host is %s\n", host ); |
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444 | OUTPUT: |
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445 | timep |
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446 | |
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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 | |
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460 | =head2 The NO_INIT Keyword |
461 | |
462 | The NO_INIT keyword is used to indicate that a function |
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463 | parameter is being used only as an output value. The B<xsubpp> |
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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. |
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472 | This function uses the timep variable only as an output variable and does |
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473 | not care about its initial contents. |
474 | |
475 | bool_t |
476 | rpcb_gettime(host,timep) |
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477 | char *host |
478 | time_t &timep = NO_INIT |
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479 | OUTPUT: |
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480 | timep |
481 | |
482 | =head2 Initializing Function Parameters |
483 | |
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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 |
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488 | the C parameters. The programmer, however, is allowed to |
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489 | override the typemaps and supply alternate (or additional) |
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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. |
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494 | |
495 | The following code demonstrates how to supply initialization code for |
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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 |
499 | must be protected with backslashes. The variables $var, $arg, |
500 | and $type can be used as in typemaps. |
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501 | |
502 | bool_t |
503 | rpcb_gettime(host,timep) |
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504 | char *host = (char *)SvPV($arg,PL_na); |
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505 | time_t &timep = 0; |
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506 | OUTPUT: |
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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 |
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 |
523 | information from one initialization is needed in another |
524 | initialization. |
525 | |
beb31b0b |
526 | Here's a truly obscure example: |
527 | |
7ad6fb0b |
528 | bool_t |
529 | rpcb_gettime(host,timep) |
beb31b0b |
530 | time_t &timep ; /* \$v{timep}=@{[$v{timep}=$arg]} */ |
531 | char *host + SvOK($v{timep}) ? SvPV($arg,PL_na) : NULL; |
532 | OUTPUT: |
7ad6fb0b |
533 | timep |
534 | |
beb31b0b |
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 |
543 | =head2 Default Parameter Values |
544 | |
4628e4f8 |
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 |
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 |
553 | the parameters in the correct order. This XSUB can be called |
554 | from Perl with either of the following statements: |
a0d0e21e |
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 |
566 | char *host |
567 | time_t timep = NO_INIT |
beb31b0b |
568 | CODE: |
a0d0e21e |
569 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b |
570 | OUTPUT: |
a0d0e21e |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
847 | CODE: |
848 | if( items > 1 ) |
849 | host = (char *)SvPV(ST(1), n_a); |
850 | RETVAL = rpcb_gettime( host, &timep ); |
851 | OUTPUT: |
a0d0e21e |
852 | timep |
853 | RETVAL |
854 | |
cfc02341 |
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 |
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 |
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 |
879 | n, function, default_flags |
880 | |
a0d0e21e |
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 |
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 |
889 | together within the same XSUB. |
890 | |
beb31b0b |
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 |
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 |
915 | void |
916 | rpcb_gettime(host) |
8e07c86e |
917 | char *host |
beb31b0b |
918 | PREINIT: |
a0d0e21e |
919 | time_t timep; |
920 | bool_t status; |
beb31b0b |
921 | PPCODE: |
a0d0e21e |
922 | status = rpcb_gettime( host, &timep ); |
924508f0 |
923 | EXTEND(SP, 2); |
cb1a09d0 |
924 | PUSHs(sv_2mortal(newSViv(status))); |
925 | PUSHs(sv_2mortal(newSViv(timep))); |
a0d0e21e |
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 |
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 |
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 |
951 | =head2 Returning Undef And Empty Lists |
952 | |
5f05dabc |
953 | Occasionally the programmer will want to return simply |
a0d0e21e |
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 |
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 |
970 | rpcb_gettime(host) |
971 | char * host |
beb31b0b |
972 | PREINIT: |
a0d0e21e |
973 | time_t timep; |
974 | bool_t x; |
beb31b0b |
975 | CODE: |
a0d0e21e |
976 | ST(0) = sv_newmortal(); |
977 | if( rpcb_gettime( host, &timep ) ) |
978 | sv_setnv( ST(0), (double)timep); |
a0d0e21e |
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 |
984 | rpcb_gettime(host) |
985 | char * host |
beb31b0b |
986 | PREINIT: |
a0d0e21e |
987 | time_t timep; |
988 | bool_t x; |
beb31b0b |
989 | CODE: |
a0d0e21e |
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 |
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 |
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 |
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 |
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 |
1043 | if (RETVAL == 0) |
1044 | XSRETURN_UNDEF; |
1045 | |
4633a7c4 |
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 |
1051 | 1.922 or greater: |
1052 | |
1053 | REQUIRE: 1.922 |
1054 | |
a0d0e21e |
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 |
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 |
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 |
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 |
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 |
1176 | For example, if you have 4 C functions multiply(), divide(), add(), |
1177 | subtract() all having the signature: |
cfc02341 |
1178 | |
1179 | symbolic f(symbolic, symbolic); |
1180 | |
beb31b0b |
1181 | you can make them all to use the same XSUB using this: |
cfc02341 |
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 |
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 |
1199 | CV *mycv = newXSproto("Symbolic::remainder", |
1200 | XS_Symbolic_interface_s_ss, __FILE__, "$$"); |
1201 | XSINTERFACE_FUNC_SET(mycv, remainder); |
1202 | |
beb31b0b |
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 |
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 |
1237 | XSINTERFACE_FUNC_BYOFFSET |
1238 | XSINTERFACE_FUNC_BYOFFSET_set |
beb31b0b |
1239 | INTERFACE: |
cfc02341 |
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 |
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 |
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 |
1387 | |
1388 | =head2 Using XS With C++ |
1389 | |
beb31b0b |
1390 | If an XSUB name contains C<::>, it is considered to be a C++ method. |
1391 | The generated Perl function will assume that |
a0d0e21e |
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 |
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 |
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 |
1408 | color(); |
1409 | ~color(); |
cb1a09d0 |
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 |
1423 | |
1424 | void |
cb1a09d0 |
1425 | color::set_blue( val ) |
1426 | int val |
a0d0e21e |
1427 | |
beb31b0b |
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 |
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 |
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 |
1454 | color::DESTROY() |
1455 | |
beb31b0b |
1456 | will look like this: |
1457 | |
1458 | color *THIS = ...; // Initialized as in typemap |
cb1a09d0 |
1459 | |
1460 | delete THIS; |
a0d0e21e |
1461 | |
cb1a09d0 |
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 |
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 |
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 |
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 |
1496 | |
1497 | When designing an interface between Perl and a C library a straight |
beb31b0b |
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 |
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 |
1503 | create a more Perl-like interface the following strategy may help to |
1504 | identify the more critical parts of the interface. |
1505 | |
beb31b0b |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
1591 | |
1592 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ |
1593 | |
1594 | void |
1595 | rpcb_DESTROY(netconf) |
8e07c86e |
1596 | Netconfig *netconf |
beb31b0b |
1597 | CODE: |
a0d0e21e |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
1648 | TYPEMAP |
1649 | Netconfig *<tab>T_PTROBJ |
a0d0e21e |
1650 | |
1748e8dd |
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 |
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 |
1702 | ST(0) = sv_newmortal(); |
1703 | if( rpcb_gettime( host, &timep ) ) |
1704 | sv_setnv( ST(0), (double)timep ); |
a0d0e21e |
1705 | |
1706 | Netconfig * |
1707 | getnetconfigent(netid="udp") |
8e07c86e |
1708 | char *netid |
a0d0e21e |
1709 | |
1710 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ |
1711 | |
1712 | void |
1713 | rpcb_DESTROY(netconf) |
8e07c86e |
1714 | Netconfig *netconf |
beb31b0b |
1715 | CODE: |
a0d0e21e |
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 |
1755 | =head1 AUTHOR |
1756 | |
beb31b0b |
1757 | Originally written by Dean Roehrich <F<roehrich@cray.com>>. |
1758 | |
7f2de2d2 |
1759 | Maintained since 1996 by The Perl Porters <F<perlbug@perl.org>>. |