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1=head1 NAME
2
8e07c86e 3perlxs - XS language reference manual
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4
5=head1 DESCRIPTION
6
7=head2 Introduction
8
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9XS is an interface description file format used to create an extension
10interface between Perl and C code (or a C library) which one wishes
11to use with Perl. The XS interface is combined with the library to
12create a new library which can then be either dynamically loaded
13or statically linked into perl. The XS interface description is
14written in the XS language and is the core component of the Perl
15extension interface.
16
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17Before writing XS, read the L</CAVEATS> section below.
18
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19An B<XSUB> forms the basic unit of the XS interface. After compilation
20by the B<xsubpp> compiler, each XSUB amounts to a C function definition
21which will provide the glue between Perl calling conventions and C
22calling conventions.
23
24The glue code pulls the arguments from the Perl stack, converts these
25Perl values to the formats expected by a C function, call this C function,
26transfers the return values of the C function back to Perl.
27Return values here may be a conventional C return value or any C
28function arguments that may serve as output parameters. These return
29values may be passed back to Perl either by putting them on the
30Perl stack, or by modifying the arguments supplied from the Perl side.
31
32The above is a somewhat simplified view of what really happens. Since
33Perl allows more flexible calling conventions than C, XSUBs may do much
34more in practice, such as checking input parameters for validity,
35throwing exceptions (or returning undef/empty list) if the return value
36from the C function indicates failure, calling different C functions
37based on numbers and types of the arguments, providing an object-oriented
38interface, etc.
39
40Of course, one could write such glue code directly in C. However, this
41would be a tedious task, especially if one needs to write glue for
42multiple C functions, and/or one is not familiar enough with the Perl
43stack discipline and other such arcana. XS comes to the rescue here:
44instead of writing this glue C code in long-hand, one can write
45a more concise short-hand I<description> of what should be done by
46the glue, and let the XS compiler B<xsubpp> handle the rest.
47
48The XS language allows one to describe the mapping between how the C
49routine is used, and how the corresponding Perl routine is used. It
50also allows creation of Perl routines which are directly translated to
51C code and which are not related to a pre-existing C function. In cases
52when the C interface coincides with the Perl interface, the XSUB
53declaration is almost identical to a declaration of a C function (in K&R
54style). In such circumstances, there is another tool called C<h2xs>
55that is able to translate an entire C header file into a corresponding
56XS file that will provide glue to the functions/macros described in
57the header file.
58
59The XS compiler is called B<xsubpp>. This compiler creates
60the constructs necessary to let an XSUB manipulate Perl values, and
61creates the glue necessary to let Perl call the XSUB. The compiler
a0d0e21e 62uses B<typemaps> to determine how to map C function parameters
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63and output values to Perl values and back. The default typemap
64(which comes with Perl) handles many common C types. A supplementary
65typemap may also be needed to handle any special structures and types
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66for the library being linked. For more information on typemaps,
67see L<perlxstypemap>.
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68
69A file in XS format starts with a C language section which goes until the
70first C<MODULE =Z<>> directive. Other XS directives and XSUB definitions
71may follow this line. The "language" used in this part of the file
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72is usually referred to as the XS language. B<xsubpp> recognizes and
73skips POD (see L<perlpod>) in both the C and XS language sections, which
3214bedb 74allows the XS file to contain embedded documentation.
a0d0e21e 75
cb1a09d0 76See L<perlxstut> for a tutorial on the whole extension creation process.
8e07c86e 77
beb31b0b 78Note: For some extensions, Dave Beazley's SWIG system may provide a
b3b6085d 79significantly more convenient mechanism for creating the extension
21b40ab4 80glue code. See L<http://www.swig.org/> for more information.
7b8d334a 81
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82=head2 On The Road
83
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84Many of the examples which follow will concentrate on creating an interface
85between Perl and the ONC+ RPC bind library functions. The rpcb_gettime()
86function is used to demonstrate many features of the XS language. This
87function has two parameters; the first is an input parameter and the second
88is an output parameter. The function also returns a status value.
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89
90 bool_t rpcb_gettime(const char *host, time_t *timep);
91
92From C this function will be called with the following
93statements.
94
95 #include <rpc/rpc.h>
96 bool_t status;
97 time_t timep;
98 status = rpcb_gettime( "localhost", &timep );
99
100If an XSUB is created to offer a direct translation between this function
101and Perl, then this XSUB will be used from Perl with the following code.
102The $status and $timep variables will contain the output of the function.
103
104 use RPC;
105 $status = rpcb_gettime( "localhost", $timep );
106
107The following XS file shows an XS subroutine, or XSUB, which
108demonstrates one possible interface to the rpcb_gettime()
109function. This XSUB represents a direct translation between
110C and Perl and so preserves the interface even from Perl.
111This XSUB will be invoked from Perl with the usage shown
112above. Note that the first three #include statements, for
113C<EXTERN.h>, C<perl.h>, and C<XSUB.h>, will always be present at the
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114beginning of an XS file. This approach and others will be
115expanded later in this document. A #define for C<PERL_NO_GET_CONTEXT>
116should be present to fetch the interpreter context more efficiently,
117see L<perlguts|perlguts/How multiple interpreters and concurrency are
118supported> for details.
a0d0e21e 119
f9d625cd 120 #define PERL_NO_GET_CONTEXT
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121 #include "EXTERN.h"
122 #include "perl.h"
123 #include "XSUB.h"
124 #include <rpc/rpc.h>
125
126 MODULE = RPC PACKAGE = RPC
127
128 bool_t
129 rpcb_gettime(host,timep)
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130 char *host
131 time_t &timep
beb31b0b 132 OUTPUT:
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133 timep
134
135Any extension to Perl, including those containing XSUBs,
136should have a Perl module to serve as the bootstrap which
137pulls the extension into Perl. This module will export the
138extension's functions and variables to the Perl program and
139will cause the extension's XSUBs to be linked into Perl.
140The following module will be used for most of the examples
141in this document and should be used from Perl with the C<use>
142command as shown earlier. Perl modules are explained in
143more detail later in this document.
144
145 package RPC;
146
147 require Exporter;
148 require DynaLoader;
149 @ISA = qw(Exporter DynaLoader);
150 @EXPORT = qw( rpcb_gettime );
151
152 bootstrap RPC;
153 1;
154
155Throughout this document a variety of interfaces to the rpcb_gettime()
156XSUB will be explored. The XSUBs will take their parameters in different
157orders or will take different numbers of parameters. In each case the
158XSUB is an abstraction between Perl and the real C rpcb_gettime()
159function, and the XSUB must always ensure that the real rpcb_gettime()
160function is called with the correct parameters. This abstraction will
161allow the programmer to create a more Perl-like interface to the C
162function.
163
164=head2 The Anatomy of an XSUB
165
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166The simplest XSUBs consist of 3 parts: a description of the return
167value, the name of the XSUB routine and the names of its arguments,
168and a description of types or formats of the arguments.
169
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170The following XSUB allows a Perl program to access a C library function
171called sin(). The XSUB will imitate the C function which takes a single
172argument and returns a single value.
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173
174 double
175 sin(x)
8e07c86e 176 double x
a0d0e21e 177
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178Optionally, one can merge the description of types and the list of
179argument names, rewriting this as
beb31b0b 180
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181 double
182 sin(double x)
183
184This makes this XSUB look similar to an ANSI C declaration. An optional
185semicolon is allowed after the argument list, as in
186
187 double
188 sin(double x);
189
190Parameters with C pointer types can have different semantic: C functions
191with similar declarations
beb31b0b 192
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193 bool string_looks_as_a_number(char *s);
194 bool make_char_uppercase(char *c);
195
196are used in absolutely incompatible manner. Parameters to these functions
197could be described B<xsubpp> like this:
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198
199 char * s
9e24e6f2 200 char &c
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201
202Both these XS declarations correspond to the C<char*> C type, but they have
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203different semantics, see L<"The & Unary Operator">.
204
205It is convenient to think that the indirection operator
beb31b0b 206C<*> should be considered as a part of the type and the address operator C<&>
78a4b226 207should be considered part of the variable. See L<perlxstypemap>
9e24e6f2 208for more info about handling qualifiers and unary operators in C types.
a0d0e21e 209
a0d0e21e 210The function name and the return type must be placed on
beb31b0b 211separate lines and should be flush left-adjusted.
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212
213 INCORRECT CORRECT
214
215 double sin(x) double
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216 double x sin(x)
217 double x
a0d0e21e 218
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219The rest of the function description may be indented or left-adjusted. The
220following example shows a function with its body left-adjusted. Most
221examples in this document will indent the body for better readability.
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222
223 CORRECT
224
225 double
226 sin(x)
227 double x
228
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229More complicated XSUBs may contain many other sections. Each section of
230an XSUB starts with the corresponding keyword, such as INIT: or CLEANUP:.
231However, the first two lines of an XSUB always contain the same data:
232descriptions of the return type and the names of the function and its
233parameters. Whatever immediately follows these is considered to be
234an INPUT: section unless explicitly marked with another keyword.
235(See L<The INPUT: Keyword>.)
236
237An XSUB section continues until another section-start keyword is found.
238
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239=head2 The Argument Stack
240
beb31b0b 241The Perl argument stack is used to store the values which are
a0d0e21e 242sent as parameters to the XSUB and to store the XSUB's
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243return value(s). In reality all Perl functions (including non-XSUB
244ones) keep their values on this stack all the same time, each limited
245to its own range of positions on the stack. In this document the
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246first position on that stack which belongs to the active
247function will be referred to as position 0 for that function.
248
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249XSUBs refer to their stack arguments with the macro B<ST(x)>, where I<x>
250refers to a position in this XSUB's part of the stack. Position 0 for that
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251function would be known to the XSUB as ST(0). The XSUB's incoming
252parameters and outgoing return values always begin at ST(0). For many
253simple cases the B<xsubpp> compiler will generate the code necessary to
254handle the argument stack by embedding code fragments found in the
255typemaps. In more complex cases the programmer must supply the code.
256
257=head2 The RETVAL Variable
258
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259The RETVAL variable is a special C variable that is declared automatically
260for you. The C type of RETVAL matches the return type of the C library
261function. The B<xsubpp> compiler will declare this variable in each XSUB
262with non-C<void> return type. By default the generated C function
263will use RETVAL to hold the return value of the C library function being
264called. In simple cases the value of RETVAL will be placed in ST(0) of
265the argument stack where it can be received by Perl as the return value
266of the XSUB.
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267
268If the XSUB has a return type of C<void> then the compiler will
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269not declare a RETVAL variable for that function. When using
270a PPCODE: section no manipulation of the RETVAL variable is required, the
271section may use direct stack manipulation to place output values on the stack.
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272
273If PPCODE: directive is not used, C<void> return value should be used
274only for subroutines which do not return a value, I<even if> CODE:
54310121 275directive is used which sets ST(0) explicitly.
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276
277Older versions of this document recommended to use C<void> return
278value in such cases. It was discovered that this could lead to
c2611fb3 279segfaults in cases when XSUB was I<truly> C<void>. This practice is
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280now deprecated, and may be not supported at some future version. Use
281the return value C<SV *> in such cases. (Currently C<xsubpp> contains
c2611fb3 282some heuristic code which tries to disambiguate between "truly-void"
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283and "old-practice-declared-as-void" functions. Hence your code is at
284mercy of this heuristics unless you use C<SV *> as return value.)
a0d0e21e 285
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286=head2 Returning SVs, AVs and HVs through RETVAL
287
288When you're using RETVAL to return an C<SV *>, there's some magic
289going on behind the scenes that should be mentioned. When you're
290manipulating the argument stack using the ST(x) macro, for example,
291you usually have to pay special attention to reference counts. (For
292more about reference counts, see L<perlguts>.) To make your life
293easier, the typemap file automatically makes C<RETVAL> mortal when
294you're returning an C<SV *>. Thus, the following two XSUBs are more
295or less equivalent:
296
297 void
298 alpha()
299 PPCODE:
300 ST(0) = newSVpv("Hello World",0);
301 sv_2mortal(ST(0));
302 XSRETURN(1);
6421dfac 303
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304 SV *
305 beta()
306 CODE:
307 RETVAL = newSVpv("Hello World",0);
308 OUTPUT:
309 RETVAL
310
311This is quite useful as it usually improves readability. While
312this works fine for an C<SV *>, it's unfortunately not as easy
313to have C<AV *> or C<HV *> as a return value. You I<should> be
314able to write:
315
316 AV *
317 array()
318 CODE:
319 RETVAL = newAV();
320 /* do something with RETVAL */
321 OUTPUT:
322 RETVAL
323
324But due to an unfixable bug (fixing it would break lots of existing
325CPAN modules) in the typemap file, the reference count of the C<AV *>
326is not properly decremented. Thus, the above XSUB would leak memory
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327whenever it is being called. The same problem exists for C<HV *>,
328C<CV *>, and C<SVREF> (which indicates a scalar reference, not
329a general C<SV *>).
330In XS code on perls starting with perl 5.16, you can override the
331typemaps for any of these types with a version that has proper
332handling of refcounts. In your C<TYPEMAP> section, do
c4e79b56 333
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334 AV* T_AVREF_REFCOUNT_FIXED
335
336to get the repaired variant. For backward compatibility with older
337versions of perl, you can instead decrement the reference count
338manually when you're returning one of the aforementioned
339types using C<sv_2mortal>:
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340
341 AV *
342 array()
343 CODE:
344 RETVAL = newAV();
345 sv_2mortal((SV*)RETVAL);
346 /* do something with RETVAL */
347 OUTPUT:
348 RETVAL
349
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350Remember that you don't have to do this for an C<SV *>. The reference
351documentation for all core typemaps can be found in L<perlxstypemap>.
c4e79b56 352
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353=head2 The MODULE Keyword
354
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355The MODULE keyword is used to start the XS code and to specify the package
356of the functions which are being defined. All text preceding the first
357MODULE keyword is considered C code and is passed through to the output with
358POD stripped, but otherwise untouched. Every XS module will have a
359bootstrap function which is used to hook the XSUBs into Perl. The package
360name of this bootstrap function will match the value of the last MODULE
361statement in the XS source files. The value of MODULE should always remain
362constant within the same XS file, though this is not required.
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363
364The following example will start the XS code and will place
365all functions in a package named RPC.
366
367 MODULE = RPC
368
369=head2 The PACKAGE Keyword
370
371When functions within an XS source file must be separated into packages
372the PACKAGE keyword should be used. This keyword is used with the MODULE
373keyword and must follow immediately after it when used.
374
375 MODULE = RPC PACKAGE = RPC
376
377 [ XS code in package RPC ]
378
379 MODULE = RPC PACKAGE = RPCB
380
381 [ XS code in package RPCB ]
382
383 MODULE = RPC PACKAGE = RPC
384
385 [ XS code in package RPC ]
386
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387The same package name can be used more than once, allowing for
388non-contiguous code. This is useful if you have a stronger ordering
389principle than package names.
390
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391Although this keyword is optional and in some cases provides redundant
392information it should always be used. This keyword will ensure that the
393XSUBs appear in the desired package.
394
395=head2 The PREFIX Keyword
396
397The PREFIX keyword designates prefixes which should be
398removed from the Perl function names. If the C function is
399C<rpcb_gettime()> and the PREFIX value is C<rpcb_> then Perl will
400see this function as C<gettime()>.
401
402This keyword should follow the PACKAGE keyword when used.
403If PACKAGE is not used then PREFIX should follow the MODULE
404keyword.
405
406 MODULE = RPC PREFIX = rpc_
407
408 MODULE = RPC PACKAGE = RPCB PREFIX = rpcb_
409
410=head2 The OUTPUT: Keyword
411
412The OUTPUT: keyword indicates that certain function parameters should be
413updated (new values made visible to Perl) when the XSUB terminates or that
414certain values should be returned to the calling Perl function. For
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415simple functions which have no CODE: or PPCODE: section,
416such as the sin() function above, the RETVAL variable is
417automatically designated as an output value. For more complex functions
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418the B<xsubpp> compiler will need help to determine which variables are output
419variables.
420
7b320f21 421This keyword will normally be used to complement the CODE: keyword.
a0d0e21e 422The RETVAL variable is not recognized as an output variable when the
7b320f21 423CODE: keyword is present. The OUTPUT: keyword is used in this
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424situation to tell the compiler that RETVAL really is an output
425variable.
426
427The OUTPUT: keyword can also be used to indicate that function parameters
428are output variables. This may be necessary when a parameter has been
429modified within the function and the programmer would like the update to
8e07c86e 430be seen by Perl.
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431
432 bool_t
433 rpcb_gettime(host,timep)
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434 char *host
435 time_t &timep
beb31b0b 436 OUTPUT:
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437 timep
438
439The OUTPUT: keyword will also allow an output parameter to
440be mapped to a matching piece of code rather than to a
ef50df4b 441typemap.
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442
443 bool_t
444 rpcb_gettime(host,timep)
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445 char *host
446 time_t &timep
beb31b0b 447 OUTPUT:
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448 timep sv_setnv(ST(1), (double)timep);
449
450B<xsubpp> emits an automatic C<SvSETMAGIC()> for all parameters in the
451OUTPUT section of the XSUB, except RETVAL. This is the usually desired
452behavior, as it takes care of properly invoking 'set' magic on output
453parameters (needed for hash or array element parameters that must be
454created if they didn't exist). If for some reason, this behavior is
455not desired, the OUTPUT section may contain a C<SETMAGIC: DISABLE> line
456to disable it for the remainder of the parameters in the OUTPUT section.
7b320f21 457Likewise, C<SETMAGIC: ENABLE> can be used to reenable it for the
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458remainder of the OUTPUT section. See L<perlguts> for more details
459about 'set' magic.
a0d0e21e 460
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461=head2 The NO_OUTPUT Keyword
462
463The NO_OUTPUT can be placed as the first token of the XSUB. This keyword
464indicates that while the C subroutine we provide an interface to has
465a non-C<void> return type, the return value of this C subroutine should not
466be returned from the generated Perl subroutine.
467
468With this keyword present L<The RETVAL Variable> is created, and in the
469generated call to the subroutine this variable is assigned to, but the value
470of this variable is not going to be used in the auto-generated code.
471
472This keyword makes sense only if C<RETVAL> is going to be accessed by the
473user-supplied code. It is especially useful to make a function interface
474more Perl-like, especially when the C return value is just an error condition
475indicator. For example,
476
477 NO_OUTPUT int
478 delete_file(char *name)
375cc10d 479 POSTCALL:
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480 if (RETVAL != 0)
481 croak("Error %d while deleting file '%s'", RETVAL, name);
482
483Here the generated XS function returns nothing on success, and will die()
484with a meaningful error message on error.
485
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486=head2 The CODE: Keyword
487
488This keyword is used in more complicated XSUBs which require
489special handling for the C function. The RETVAL variable is
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490still declared, but it will not be returned unless it is specified
491in the OUTPUT: section.
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492
493The following XSUB is for a C function which requires special handling of
494its parameters. The Perl usage is given first.
495
496 $status = rpcb_gettime( "localhost", $timep );
497
54310121 498The XSUB follows.
a0d0e21e 499
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500 bool_t
501 rpcb_gettime(host,timep)
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502 char *host
503 time_t timep
beb31b0b 504 CODE:
a0d0e21e 505 RETVAL = rpcb_gettime( host, &timep );
beb31b0b 506 OUTPUT:
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507 timep
508 RETVAL
509
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510=head2 The INIT: Keyword
511
512The INIT: keyword allows initialization to be inserted into the XSUB before
513the compiler generates the call to the C function. Unlike the CODE: keyword
514above, this keyword does not affect the way the compiler handles RETVAL.
515
516 bool_t
517 rpcb_gettime(host,timep)
518 char *host
519 time_t &timep
beb31b0b 520 INIT:
c07a80fd 521 printf("# Host is %s\n", host );
beb31b0b 522 OUTPUT:
c07a80fd 523 timep
a0d0e21e 524
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525Another use for the INIT: section is to check for preconditions before
526making a call to the C function:
527
528 long long
529 lldiv(a,b)
530 long long a
531 long long b
532 INIT:
533 if (a == 0 && b == 0)
534 XSRETURN_UNDEF;
535 if (b == 0)
536 croak("lldiv: cannot divide by 0");
537
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538=head2 The NO_INIT Keyword
539
540The NO_INIT keyword is used to indicate that a function
54310121 541parameter is being used only as an output value. The B<xsubpp>
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542compiler will normally generate code to read the values of
543all function parameters from the argument stack and assign
544them to C variables upon entry to the function. NO_INIT
545will tell the compiler that some parameters will be used for
546output rather than for input and that they will be handled
547before the function terminates.
548
549The following example shows a variation of the rpcb_gettime() function.
54310121 550This function uses the timep variable only as an output variable and does
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551not care about its initial contents.
552
553 bool_t
554 rpcb_gettime(host,timep)
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555 char *host
556 time_t &timep = NO_INIT
beb31b0b 557 OUTPUT:
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558 timep
559
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560=head2 The TYPEMAP: Keyword
561
562Starting with Perl 5.16, you can embed typemaps into your XS code
563instead of or in addition to typemaps in a separate file. Multiple
564such embedded typemaps will be processed in order of appearance in
4c75f49d 565the XS code and like local typemap files take precedence over the
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566default typemap, the embedded typemaps may overwrite previous
567definitions of TYPEMAP, INPUT, and OUTPUT stanzas. The syntax for
568embedded typemaps is
569
570 TYPEMAP: <<HERE
571 ... your typemap code here ...
572 HERE
573
574where the C<TYPEMAP> keyword must appear in the first column of a
575new line.
576
78a4b226 577Refer to L<perlxstypemap> for details on writing typemaps.
00cb3b26 578
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579=head2 Initializing Function Parameters
580
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581C function parameters are normally initialized with their values from
582the argument stack (which in turn contains the parameters that were
583passed to the XSUB from Perl). The typemaps contain the
584code segments which are used to translate the Perl values to
a0d0e21e 585the C parameters. The programmer, however, is allowed to
7ad6fb0b 586override the typemaps and supply alternate (or additional)
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587initialization code. Initialization code starts with the first
588C<=>, C<;> or C<+> on a line in the INPUT: section. The only
589exception happens if this C<;> terminates the line, then this C<;>
590is quietly ignored.
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591
592The following code demonstrates how to supply initialization code for
353c6505 593function parameters. The initialization code is eval'ed within double
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TM
594quotes by the compiler before it is added to the output so anything
595which should be interpreted literally [mainly C<$>, C<@>, or C<\\>]
78a4b226
SM
596must be protected with backslashes. The variables C<$var>, C<$arg>,
597and C<$type> can be used as in typemaps.
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598
599 bool_t
600 rpcb_gettime(host,timep)
bfd025d9 601 char *host = (char *)SvPV_nolen($arg);
8e07c86e 602 time_t &timep = 0;
beb31b0b 603 OUTPUT:
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604 timep
605
606This should not be used to supply default values for parameters. One
607would normally use this when a function parameter must be processed by
608another library function before it can be used. Default parameters are
609covered in the next section.
610
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611If the initialization begins with C<=>, then it is output in
612the declaration for the input variable, replacing the initialization
613supplied by the typemap. If the initialization
614begins with C<;> or C<+>, then it is performed after
615all of the input variables have been declared. In the C<;>
616case the initialization normally supplied by the typemap is not performed.
617For the C<+> case, the declaration for the variable will include the
618initialization from the typemap. A global
c2611fb3 619variable, C<%v>, is available for the truly rare case where
7ad6fb0b
TM
620information from one initialization is needed in another
621initialization.
622
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GS
623Here's a truly obscure example:
624
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TM
625 bool_t
626 rpcb_gettime(host,timep)
4358a253 627 time_t &timep; /* \$v{timep}=@{[$v{timep}=$arg]} */
bfd025d9 628 char *host + SvOK($v{timep}) ? SvPV_nolen($arg) : NULL;
beb31b0b 629 OUTPUT:
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TM
630 timep
631
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632The construct C<\$v{timep}=@{[$v{timep}=$arg]}> used in the above
633example has a two-fold purpose: first, when this line is processed by
634B<xsubpp>, the Perl snippet C<$v{timep}=$arg> is evaluated. Second,
635the text of the evaluated snippet is output into the generated C file
636(inside a C comment)! During the processing of C<char *host> line,
78a4b226 637C<$arg> will evaluate to C<ST(0)>, and C<$v{timep}> will evaluate to
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638C<ST(1)>.
639
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640=head2 Default Parameter Values
641
4628e4f8
GS
642Default values for XSUB arguments can be specified by placing an
643assignment statement in the parameter list. The default value may
a104f515 644be a number, a string or the special string C<NO_INIT>. Defaults should
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645always be used on the right-most parameters only.
646
647To allow the XSUB for rpcb_gettime() to have a default host
648value the parameters to the XSUB could be rearranged. The
649XSUB will then call the real rpcb_gettime() function with
beb31b0b
GS
650the parameters in the correct order. This XSUB can be called
651from Perl with either of the following statements:
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652
653 $status = rpcb_gettime( $timep, $host );
654
655 $status = rpcb_gettime( $timep );
656
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657The XSUB will look like the code which follows. A CODE:
658block is used to call the real rpcb_gettime() function with
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659the parameters in the correct order for that function.
660
661 bool_t
662 rpcb_gettime(timep,host="localhost")
8e07c86e
AD
663 char *host
664 time_t timep = NO_INIT
beb31b0b 665 CODE:
a0d0e21e 666 RETVAL = rpcb_gettime( host, &timep );
beb31b0b 667 OUTPUT:
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668 timep
669 RETVAL
670
c07a80fd
PP
671=head2 The PREINIT: Keyword
672
beb31b0b 673The PREINIT: keyword allows extra variables to be declared immediately
a2293a43 674before or after the declarations of the parameters from the INPUT: section
beb31b0b
GS
675are emitted.
676
677If a variable is declared inside a CODE: section it will follow any typemap
678code that is emitted for the input parameters. This may result in the
679declaration ending up after C code, which is C syntax error. Similar
680errors may happen with an explicit C<;>-type or C<+>-type initialization of
681parameters is used (see L<"Initializing Function Parameters">). Declaring
682these variables in an INIT: section will not help.
683
684In such cases, to force an additional variable to be declared together
685with declarations of other variables, place the declaration into a
686PREINIT: section. The PREINIT: keyword may be used one or more times
687within an XSUB.
c07a80fd
PP
688
689The following examples are equivalent, but if the code is using complex
690typemaps then the first example is safer.
691
692 bool_t
693 rpcb_gettime(timep)
694 time_t timep = NO_INIT
beb31b0b 695 PREINIT:
c07a80fd 696 char *host = "localhost";
beb31b0b 697 CODE:
c07a80fd 698 RETVAL = rpcb_gettime( host, &timep );
beb31b0b 699 OUTPUT:
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PP
700 timep
701 RETVAL
702
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GS
703For this particular case an INIT: keyword would generate the
704same C code as the PREINIT: keyword. Another correct, but error-prone example:
c07a80fd
PP
705
706 bool_t
707 rpcb_gettime(timep)
708 time_t timep = NO_INIT
beb31b0b 709 CODE:
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710 char *host = "localhost";
711 RETVAL = rpcb_gettime( host, &timep );
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712 OUTPUT:
713 timep
714 RETVAL
715
716Another way to declare C<host> is to use a C block in the CODE: section:
717
718 bool_t
719 rpcb_gettime(timep)
720 time_t timep = NO_INIT
721 CODE:
722 {
723 char *host = "localhost";
724 RETVAL = rpcb_gettime( host, &timep );
725 }
726 OUTPUT:
727 timep
728 RETVAL
729
730The ability to put additional declarations before the typemap entries are
731processed is very handy in the cases when typemap conversions manipulate
732some global state:
733
734 MyObject
735 mutate(o)
736 PREINIT:
737 MyState st = global_state;
738 INPUT:
739 MyObject o;
740 CLEANUP:
741 reset_to(global_state, st);
742
743Here we suppose that conversion to C<MyObject> in the INPUT: section and from
744MyObject when processing RETVAL will modify a global variable C<global_state>.
745After these conversions are performed, we restore the old value of
746C<global_state> (to avoid memory leaks, for example).
747
748There is another way to trade clarity for compactness: INPUT sections allow
749declaration of C variables which do not appear in the parameter list of
750a subroutine. Thus the above code for mutate() can be rewritten as
751
752 MyObject
753 mutate(o)
754 MyState st = global_state;
755 MyObject o;
756 CLEANUP:
757 reset_to(global_state, st);
758
759and the code for rpcb_gettime() can be rewritten as
760
761 bool_t
762 rpcb_gettime(timep)
763 time_t timep = NO_INIT
764 char *host = "localhost";
765 C_ARGS:
766 host, &timep
767 OUTPUT:
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PP
768 timep
769 RETVAL
770
84287afe
PP
771=head2 The SCOPE: Keyword
772
773The SCOPE: keyword allows scoping to be enabled for a particular XSUB. If
774enabled, the XSUB will invoke ENTER and LEAVE automatically.
775
776To support potentially complex type mappings, if a typemap entry used
beb31b0b
GS
777by an XSUB contains a comment like C</*scope*/> then scoping will
778be automatically enabled for that XSUB.
84287afe
PP
779
780To enable scoping:
781
782 SCOPE: ENABLE
783
784To disable scoping:
785
786 SCOPE: DISABLE
787
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PP
788=head2 The INPUT: Keyword
789
790The XSUB's parameters are usually evaluated immediately after entering the
791XSUB. The INPUT: keyword can be used to force those parameters to be
792evaluated a little later. The INPUT: keyword can be used multiple times
793within an XSUB and can be used to list one or more input variables. This
794keyword is used with the PREINIT: keyword.
795
796The following example shows how the input parameter C<timep> can be
797evaluated late, after a PREINIT.
798
799 bool_t
800 rpcb_gettime(host,timep)
801 char *host
beb31b0b 802 PREINIT:
c07a80fd 803 time_t tt;
beb31b0b 804 INPUT:
c07a80fd 805 time_t timep
beb31b0b 806 CODE:
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PP
807 RETVAL = rpcb_gettime( host, &tt );
808 timep = tt;
beb31b0b 809 OUTPUT:
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PP
810 timep
811 RETVAL
812
813The next example shows each input parameter evaluated late.
814
815 bool_t
816 rpcb_gettime(host,timep)
beb31b0b 817 PREINIT:
c07a80fd 818 time_t tt;
beb31b0b 819 INPUT:
c07a80fd 820 char *host
beb31b0b 821 PREINIT:
c07a80fd 822 char *h;
beb31b0b 823 INPUT:
c07a80fd 824 time_t timep
beb31b0b 825 CODE:
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PP
826 h = host;
827 RETVAL = rpcb_gettime( h, &tt );
828 timep = tt;
beb31b0b
GS
829 OUTPUT:
830 timep
831 RETVAL
832
833Since INPUT sections allow declaration of C variables which do not appear
834in the parameter list of a subroutine, this may be shortened to:
835
836 bool_t
837 rpcb_gettime(host,timep)
838 time_t tt;
839 char *host;
840 char *h = host;
841 time_t timep;
842 CODE:
843 RETVAL = rpcb_gettime( h, &tt );
844 timep = tt;
845 OUTPUT:
c07a80fd
PP
846 timep
847 RETVAL
848
beb31b0b
GS
849(We used our knowledge that input conversion for C<char *> is a "simple" one,
850thus C<host> is initialized on the declaration line, and our assignment
851C<h = host> is not performed too early. Otherwise one would need to have the
852assignment C<h = host> in a CODE: or INIT: section.)
853
cb79badd 854=head2 The IN/OUTLIST/IN_OUTLIST/OUT/IN_OUT Keywords
9e24e6f2
IZ
855
856In the list of parameters for an XSUB, one can precede parameter names
cb79badd
IZ
857by the C<IN>/C<OUTLIST>/C<IN_OUTLIST>/C<OUT>/C<IN_OUT> keywords.
858C<IN> keyword is the default, the other keywords indicate how the Perl
859interface should differ from the C interface.
860
861Parameters preceded by C<OUTLIST>/C<IN_OUTLIST>/C<OUT>/C<IN_OUT>
862keywords are considered to be used by the C subroutine I<via
863pointers>. C<OUTLIST>/C<OUT> keywords indicate that the C subroutine
864does not inspect the memory pointed by this parameter, but will write
865through this pointer to provide additional return values.
866
867Parameters preceded by C<OUTLIST> keyword do not appear in the usage
868signature of the generated Perl function.
869
870Parameters preceded by C<IN_OUTLIST>/C<IN_OUT>/C<OUT> I<do> appear as
871parameters to the Perl function. With the exception of
872C<OUT>-parameters, these parameters are converted to the corresponding
873C type, then pointers to these data are given as arguments to the C
874function. It is expected that the C function will write through these
875pointers.
9e24e6f2
IZ
876
877The return list of the generated Perl function consists of the C return value
878from the function (unless the XSUB is of C<void> return type or
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IZ
879C<The NO_OUTPUT Keyword> was used) followed by all the C<OUTLIST>
880and C<IN_OUTLIST> parameters (in the order of appearance). On the
881return from the XSUB the C<IN_OUT>/C<OUT> Perl parameter will be
882modified to have the values written by the C function.
883
884For example, an XSUB
9e24e6f2
IZ
885
886 void
887 day_month(OUTLIST day, IN unix_time, OUTLIST month)
888 int day
889 int unix_time
890 int month
891
892should be used from Perl as
893
894 my ($day, $month) = day_month(time);
895
896The C signature of the corresponding function should be
897
898 void day_month(int *day, int unix_time, int *month);
899
cb79badd
IZ
900The C<IN>/C<OUTLIST>/C<IN_OUTLIST>/C<IN_OUT>/C<OUT> keywords can be
901mixed with ANSI-style declarations, as in
9e24e6f2
IZ
902
903 void
904 day_month(OUTLIST int day, int unix_time, OUTLIST int month)
905
906(here the optional C<IN> keyword is omitted).
907
cb79badd 908The C<IN_OUT> parameters are identical with parameters introduced with
cea6626f
MS
909L<The & Unary Operator> and put into the C<OUTPUT:> section (see
910L<The OUTPUT: Keyword>). The C<IN_OUTLIST> parameters are very similar,
911the only difference being that the value C function writes through the
cb79badd
IZ
912pointer would not modify the Perl parameter, but is put in the output
913list.
914
915The C<OUTLIST>/C<OUT> parameter differ from C<IN_OUTLIST>/C<IN_OUT>
d1be9408 916parameters only by the initial value of the Perl parameter not
cb79badd
IZ
917being read (and not being given to the C function - which gets some
918garbage instead). For example, the same C function as above can be
919interfaced with as
920
921 void day_month(OUT int day, int unix_time, OUT int month);
922
923or
9e24e6f2
IZ
924
925 void
926 day_month(day, unix_time, month)
927 int &day = NO_INIT
928 int unix_time
929 int &month = NO_INIT
930 OUTPUT:
931 day
932 month
933
934However, the generated Perl function is called in very C-ish style:
935
936 my ($day, $month);
937 day_month($day, time, $month);
938
08ff138d
IZ
939=head2 The C<length(NAME)> Keyword
940
941If one of the input arguments to the C function is the length of a string
942argument C<NAME>, one can substitute the name of the length-argument by
d7f8936a 943C<length(NAME)> in the XSUB declaration. This argument must be omitted when
08ff138d
IZ
944the generated Perl function is called. E.g.,
945
946 void
947 dump_chars(char *s, short l)
948 {
949 short n = 0;
950 while (n < l) {
951 printf("s[%d] = \"\\%#03o\"\n", n, (int)s[n]);
952 n++;
953 }
954 }
955
956 MODULE = x PACKAGE = x
957
958 void dump_chars(char *s, short length(s))
959
960should be called as C<dump_chars($string)>.
961
962This directive is supported with ANSI-type function declarations only.
963
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964=head2 Variable-length Parameter Lists
965
966XSUBs can have variable-length parameter lists by specifying an ellipsis
967C<(...)> in the parameter list. This use of the ellipsis is similar to that
968found in ANSI C. The programmer is able to determine the number of
969arguments passed to the XSUB by examining the C<items> variable which the
970B<xsubpp> compiler supplies for all XSUBs. By using this mechanism one can
971create an XSUB which accepts a list of parameters of unknown length.
972
973The I<host> parameter for the rpcb_gettime() XSUB can be
974optional so the ellipsis can be used to indicate that the
975XSUB will take a variable number of parameters. Perl should
d1b91892 976be able to call this XSUB with either of the following statements.
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977
978 $status = rpcb_gettime( $timep, $host );
979
980 $status = rpcb_gettime( $timep );
981
982The XS code, with ellipsis, follows.
983
984 bool_t
985 rpcb_gettime(timep, ...)
8e07c86e 986 time_t timep = NO_INIT
beb31b0b 987 PREINIT:
a0d0e21e 988 char *host = "localhost";
beb31b0b
GS
989 CODE:
990 if( items > 1 )
1c5b513e 991 host = (char *)SvPV_nolen(ST(1));
beb31b0b
GS
992 RETVAL = rpcb_gettime( host, &timep );
993 OUTPUT:
a0d0e21e
LW
994 timep
995 RETVAL
996
cfc02341
IZ
997=head2 The C_ARGS: Keyword
998
999The C_ARGS: keyword allows creating of XSUBS which have different
1000calling sequence from Perl than from C, without a need to write
beb31b0b 1001CODE: or PPCODE: section. The contents of the C_ARGS: paragraph is
cfc02341
IZ
1002put as the argument to the called C function without any change.
1003
beb31b0b 1004For example, suppose that a C function is declared as
cfc02341
IZ
1005
1006 symbolic nth_derivative(int n, symbolic function, int flags);
1007
1008and that the default flags are kept in a global C variable
1009C<default_flags>. Suppose that you want to create an interface which
1010is called as
1011
1012 $second_deriv = $function->nth_derivative(2);
1013
1014To do this, declare the XSUB as
1015
1016 symbolic
1017 nth_derivative(function, n)
1018 symbolic function
1019 int n
beb31b0b 1020 C_ARGS:
cfc02341
IZ
1021 n, function, default_flags
1022
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1023=head2 The PPCODE: Keyword
1024
1025The PPCODE: keyword is an alternate form of the CODE: keyword and is used
1026to tell the B<xsubpp> compiler that the programmer is supplying the code to
d1b91892 1027control the argument stack for the XSUBs return values. Occasionally one
a0d0e21e
LW
1028will want an XSUB to return a list of values rather than a single value.
1029In these cases one must use PPCODE: and then explicitly push the list of
7b320f21 1030values on the stack. The PPCODE: and CODE: keywords should not be used
a0d0e21e
LW
1031together within the same XSUB.
1032
beb31b0b
GS
1033The actual difference between PPCODE: and CODE: sections is in the
1034initialization of C<SP> macro (which stands for the I<current> Perl
1035stack pointer), and in the handling of data on the stack when returning
1036from an XSUB. In CODE: sections SP preserves the value which was on
1037entry to the XSUB: SP is on the function pointer (which follows the
1038last parameter). In PPCODE: sections SP is moved backward to the
1039beginning of the parameter list, which allows C<PUSH*()> macros
1040to place output values in the place Perl expects them to be when
1041the XSUB returns back to Perl.
1042
1043The generated trailer for a CODE: section ensures that the number of return
1044values Perl will see is either 0 or 1 (depending on the C<void>ness of the
1045return value of the C function, and heuristics mentioned in
1046L<"The RETVAL Variable">). The trailer generated for a PPCODE: section
1047is based on the number of return values and on the number of times
1048C<SP> was updated by C<[X]PUSH*()> macros.
1049
1050Note that macros C<ST(i)>, C<XST_m*()> and C<XSRETURN*()> work equally
1051well in CODE: sections and PPCODE: sections.
1052
a0d0e21e
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1053The following XSUB will call the C rpcb_gettime() function
1054and will return its two output values, timep and status, to
1055Perl as a single list.
1056
d1b91892
AD
1057 void
1058 rpcb_gettime(host)
8e07c86e 1059 char *host
beb31b0b 1060 PREINIT:
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1061 time_t timep;
1062 bool_t status;
beb31b0b 1063 PPCODE:
a0d0e21e 1064 status = rpcb_gettime( host, &timep );
924508f0 1065 EXTEND(SP, 2);
cb1a09d0
AD
1066 PUSHs(sv_2mortal(newSViv(status)));
1067 PUSHs(sv_2mortal(newSViv(timep)));
a0d0e21e
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1068
1069Notice that the programmer must supply the C code necessary
1070to have the real rpcb_gettime() function called and to have
1071the return values properly placed on the argument stack.
1072
1073The C<void> return type for this function tells the B<xsubpp> compiler that
1074the RETVAL variable is not needed or used and that it should not be created.
1075In most scenarios the void return type should be used with the PPCODE:
1076directive.
1077
1078The EXTEND() macro is used to make room on the argument
1079stack for 2 return values. The PPCODE: directive causes the
924508f0 1080B<xsubpp> compiler to create a stack pointer available as C<SP>, and it
a0d0e21e
LW
1081is this pointer which is being used in the EXTEND() macro.
1082The values are then pushed onto the stack with the PUSHs()
1083macro.
1084
1085Now the rpcb_gettime() function can be used from Perl with
1086the following statement.
1087
1088 ($status, $timep) = rpcb_gettime("localhost");
1089
ef50df4b
GS
1090When handling output parameters with a PPCODE section, be sure to handle
1091'set' magic properly. See L<perlguts> for details about 'set' magic.
1092
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1093=head2 Returning Undef And Empty Lists
1094
5f05dabc 1095Occasionally the programmer will want to return simply
a0d0e21e
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1096C<undef> or an empty list if a function fails rather than a
1097separate status value. The rpcb_gettime() function offers
1098just this situation. If the function succeeds we would like
1099to have it return the time and if it fails we would like to
1100have undef returned. In the following Perl code the value
1101of $timep will either be undef or it will be a valid time.
1102
1103 $timep = rpcb_gettime( "localhost" );
1104
7b8d334a 1105The following XSUB uses the C<SV *> return type as a mnemonic only,
e7ea3e70 1106and uses a CODE: block to indicate to the compiler
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1107that the programmer has supplied all the necessary code. The
1108sv_newmortal() call will initialize the return value to undef, making that
1109the default return value.
1110
e7ea3e70 1111 SV *
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1112 rpcb_gettime(host)
1113 char * host
beb31b0b 1114 PREINIT:
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LW
1115 time_t timep;
1116 bool_t x;
beb31b0b 1117 CODE:
a0d0e21e
LW
1118 ST(0) = sv_newmortal();
1119 if( rpcb_gettime( host, &timep ) )
1120 sv_setnv( ST(0), (double)timep);
a0d0e21e
LW
1121
1122The next example demonstrates how one would place an explicit undef in the
1123return value, should the need arise.
1124
e7ea3e70 1125 SV *
a0d0e21e
LW
1126 rpcb_gettime(host)
1127 char * host
beb31b0b 1128 PREINIT:
a0d0e21e
LW
1129 time_t timep;
1130 bool_t x;
beb31b0b 1131 CODE:
a0d0e21e 1132 if( rpcb_gettime( host, &timep ) ){
7e455f68 1133 ST(0) = sv_newmortal();
a0d0e21e
LW
1134 sv_setnv( ST(0), (double)timep);
1135 }
1136 else{
9cde0e7f 1137 ST(0) = &PL_sv_undef;
a0d0e21e 1138 }
a0d0e21e
LW
1139
1140To return an empty list one must use a PPCODE: block and
1141then not push return values on the stack.
1142
1143 void
1144 rpcb_gettime(host)
8e07c86e 1145 char *host
beb31b0b 1146 PREINIT:
a0d0e21e 1147 time_t timep;
beb31b0b 1148 PPCODE:
a0d0e21e 1149 if( rpcb_gettime( host, &timep ) )
cb1a09d0 1150 PUSHs(sv_2mortal(newSViv(timep)));
a0d0e21e 1151 else{
beb31b0b
GS
1152 /* Nothing pushed on stack, so an empty
1153 * list is implicitly returned. */
a0d0e21e 1154 }
a0d0e21e 1155
f27cfbbe
PP
1156Some people may be inclined to include an explicit C<return> in the above
1157XSUB, rather than letting control fall through to the end. In those
1158situations C<XSRETURN_EMPTY> should be used, instead. This will ensure that
8a2949d9
SB
1159the XSUB stack is properly adjusted. Consult L<perlapi> for other
1160C<XSRETURN> macros.
f27cfbbe 1161
beb31b0b
GS
1162Since C<XSRETURN_*> macros can be used with CODE blocks as well, one can
1163rewrite this example as:
1164
1165 int
1166 rpcb_gettime(host)
1167 char *host
1168 PREINIT:
1169 time_t timep;
1170 CODE:
1171 RETVAL = rpcb_gettime( host, &timep );
1172 if (RETVAL == 0)
1173 XSRETURN_UNDEF;
1174 OUTPUT:
1175 RETVAL
1176
375cc10d 1177In fact, one can put this check into a POSTCALL: section as well. Together
beb31b0b
GS
1178with PREINIT: simplifications, this leads to:
1179
1180 int
1181 rpcb_gettime(host)
1182 char *host
1183 time_t timep;
375cc10d 1184 POSTCALL:
beb31b0b
GS
1185 if (RETVAL == 0)
1186 XSRETURN_UNDEF;
1187
4633a7c4
LW
1188=head2 The REQUIRE: Keyword
1189
1190The REQUIRE: keyword is used to indicate the minimum version of the
1191B<xsubpp> compiler needed to compile the XS module. An XS module which
5f05dabc 1192contains the following statement will compile with only B<xsubpp> version
4633a7c4
LW
11931.922 or greater:
1194
1195 REQUIRE: 1.922
1196
a0d0e21e
LW
1197=head2 The CLEANUP: Keyword
1198
1199This keyword can be used when an XSUB requires special cleanup procedures
7b320f21 1200before it terminates. When the CLEANUP: keyword is used it must follow
818355ac
TC
1201any CODE:, or OUTPUT: blocks which are present in the XSUB. The code
1202specified for the cleanup block will be added as the last statements in
1203the XSUB.
a0d0e21e 1204
375cc10d 1205=head2 The POSTCALL: Keyword
9e24e6f2
IZ
1206
1207This keyword can be used when an XSUB requires special procedures
375cc10d 1208executed after the C subroutine call is performed. When the POSTCALL:
9e24e6f2
IZ
1209keyword is used it must precede OUTPUT: and CLEANUP: blocks which are
1210present in the XSUB.
1211
375cc10d
IZ
1212See examples in L<"The NO_OUTPUT Keyword"> and L<"Returning Undef And Empty Lists">.
1213
1214The POSTCALL: block does not make a lot of sense when the C subroutine
9e24e6f2
IZ
1215call is supplied by user by providing either CODE: or PPCODE: section.
1216
a0d0e21e
LW
1217=head2 The BOOT: Keyword
1218
1219The BOOT: keyword is used to add code to the extension's bootstrap
1220function. The bootstrap function is generated by the B<xsubpp> compiler and
1221normally holds the statements necessary to register any XSUBs with Perl.
1222With the BOOT: keyword the programmer can tell the compiler to add extra
1223statements to the bootstrap function.
1224
1225This keyword may be used any time after the first MODULE keyword and should
1226appear on a line by itself. The first blank line after the keyword will
1227terminate the code block.
1228
1229 BOOT:
1230 # The following message will be printed when the
1231 # bootstrap function executes.
1232 printf("Hello from the bootstrap!\n");
1233
c07a80fd
PP
1234=head2 The VERSIONCHECK: Keyword
1235
1236The VERSIONCHECK: keyword corresponds to B<xsubpp>'s C<-versioncheck> and
5f05dabc 1237C<-noversioncheck> options. This keyword overrides the command line
c07a80fd
PP
1238options. Version checking is enabled by default. When version checking is
1239enabled the XS module will attempt to verify that its version matches the
1240version of the PM module.
1241
1242To enable version checking:
1243
1244 VERSIONCHECK: ENABLE
1245
1246To disable version checking:
1247
1248 VERSIONCHECK: DISABLE
1249
b017ed23
NT
1250Note that if the version of the PM module is an NV (a floating point
1251number), it will be stringified with a possible loss of precision
1252(currently chopping to nine decimal places) so that it may not match
1253the version of the XS module anymore. Quoting the $VERSION declaration
1254to make it a string is recommended if long version numbers are used.
1255
c07a80fd
PP
1256=head2 The PROTOTYPES: Keyword
1257
1258The PROTOTYPES: keyword corresponds to B<xsubpp>'s C<-prototypes> and
54310121 1259C<-noprototypes> options. This keyword overrides the command line options.
19865e6f 1260Prototypes are disabled by default. When prototypes are enabled, XSUBs will
c07a80fd
PP
1261be given Perl prototypes. This keyword may be used multiple times in an XS
1262module to enable and disable prototypes for different parts of the module.
19865e6f
DM
1263Note that B<xsubpp> will nag you if you don't explicitly enable or disable
1264prototypes, with:
1265
1266 Please specify prototyping behavior for Foo.xs (see perlxs manual)
c07a80fd
PP
1267
1268To enable prototypes:
1269
1270 PROTOTYPES: ENABLE
1271
1272To disable prototypes:
1273
1274 PROTOTYPES: DISABLE
1275
1276=head2 The PROTOTYPE: Keyword
1277
1278This keyword is similar to the PROTOTYPES: keyword above but can be used to
1279force B<xsubpp> to use a specific prototype for the XSUB. This keyword
1280overrides all other prototype options and keywords but affects only the
1281current XSUB. Consult L<perlsub/Prototypes> for information about Perl
1282prototypes.
1283
1284 bool_t
1285 rpcb_gettime(timep, ...)
1286 time_t timep = NO_INIT
beb31b0b
GS
1287 PROTOTYPE: $;$
1288 PREINIT:
c07a80fd 1289 char *host = "localhost";
beb31b0b 1290 CODE:
c07a80fd 1291 if( items > 1 )
1c5b513e 1292 host = (char *)SvPV_nolen(ST(1));
c07a80fd 1293 RETVAL = rpcb_gettime( host, &timep );
beb31b0b 1294 OUTPUT:
c07a80fd
PP
1295 timep
1296 RETVAL
1297
dd76e73a
SB
1298If the prototypes are enabled, you can disable it locally for a given
1299XSUB as in the following example:
1300
1301 void
1302 rpcb_gettime_noproto()
1303 PROTOTYPE: DISABLE
1304 ...
1305
c07a80fd
PP
1306=head2 The ALIAS: Keyword
1307
cfc02341 1308The ALIAS: keyword allows an XSUB to have two or more unique Perl names
c07a80fd
PP
1309and to know which of those names was used when it was invoked. The Perl
1310names may be fully-qualified with package names. Each alias is given an
1311index. The compiler will setup a variable called C<ix> which contain the
1312index of the alias which was used. When the XSUB is called with its
1313declared name C<ix> will be 0.
1314
1315The following example will create aliases C<FOO::gettime()> and
1316C<BAR::getit()> for this function.
1317
1318 bool_t
1319 rpcb_gettime(host,timep)
1320 char *host
1321 time_t &timep
beb31b0b 1322 ALIAS:
c07a80fd
PP
1323 FOO::gettime = 1
1324 BAR::getit = 2
beb31b0b 1325 INIT:
c07a80fd 1326 printf("# ix = %d\n", ix );
beb31b0b 1327 OUTPUT:
c07a80fd
PP
1328 timep
1329
54162f5c
JP
1330=head2 The OVERLOAD: Keyword
1331
1332Instead of writing an overloaded interface using pure Perl, you
1333can also use the OVERLOAD keyword to define additional Perl names
1334for your functions (like the ALIAS: keyword above). However, the
daf3bcff
FC
1335overloaded functions must be defined in such a way as to accept the number
1336of parameters supplied by perl's overload system. For most overload
1337methods, it will be three parameters; for the C<nomethod> function it will
1338be four. However, the bitwise operators C<&>, C<|>, C<^>, and C<~> may be
1339called with three I<or> five arguments (see L<overload>).
1340
1341If any
54162f5c 1342function has the OVERLOAD: keyword, several additional lines
3214bedb 1343will be defined in the c file generated by xsubpp in order to
54162f5c
JP
1344register with the overload magic.
1345
1346Since blessed objects are actually stored as RV's, it is useful
1347to use the typemap features to preprocess parameters and extract
78a4b226 1348the actual SV stored within the blessed RV. See the sample for
54162f5c
JP
1349T_PTROBJ_SPECIAL below.
1350
1351To use the OVERLOAD: keyword, create an XS function which takes
daf3bcff 1352three input parameters (or use the C-style '...' definition) like
54162f5c
JP
1353this:
1354
1355 SV *
1356 cmp (lobj, robj, swap)
1357 My_Module_obj lobj
1358 My_Module_obj robj
1359 IV swap
1360 OVERLOAD: cmp <=>
1361 { /* function defined here */}
1362
1363In this case, the function will overload both of the three way
1364comparison operators. For all overload operations using non-alpha
353c6505 1365characters, you must type the parameter without quoting, separating
3214bedb 1366multiple overloads with whitespace. Note that "" (the stringify
54162f5c
JP
1367overload) should be entered as \"\" (i.e. escaped).
1368
daf3bcff
FC
1369Since, as mentioned above, bitwise operators may take extra arguments, you
1370may want to use something like C<(lobj, robj, swap, ...)> (with
1371literal C<...>) as your parameter list.
1372
30d6fba6
JP
1373=head2 The FALLBACK: Keyword
1374
1375In addition to the OVERLOAD keyword, if you need to control how
1376Perl autogenerates missing overloaded operators, you can set the
1377FALLBACK keyword in the module header section, like this:
1378
1379 MODULE = RPC PACKAGE = RPC
1380
1381 FALLBACK: TRUE
1382 ...
1383
1384where FALLBACK can take any of the three values TRUE, FALSE, or
1385UNDEF. If you do not set any FALLBACK value when using OVERLOAD,
3214bedb 1386it defaults to UNDEF. FALLBACK is not used except when one or
30d6fba6 1387more functions using OVERLOAD have been defined. Please see
89da310e 1388L<overload/fallback> for more details.
30d6fba6 1389
cfc02341
IZ
1390=head2 The INTERFACE: Keyword
1391
1392This keyword declares the current XSUB as a keeper of the given
1393calling signature. If some text follows this keyword, it is
1394considered as a list of functions which have this signature, and
beb31b0b 1395should be attached to the current XSUB.
cfc02341 1396
beb31b0b
GS
1397For example, if you have 4 C functions multiply(), divide(), add(),
1398subtract() all having the signature:
cfc02341
IZ
1399
1400 symbolic f(symbolic, symbolic);
1401
beb31b0b 1402you can make them all to use the same XSUB using this:
cfc02341
IZ
1403
1404 symbolic
3214bedb 1405 interface_s_ss(arg1, arg2)
cfc02341
IZ
1406 symbolic arg1
1407 symbolic arg2
1408 INTERFACE:
3214bedb 1409 multiply divide
cfc02341
IZ
1410 add subtract
1411
beb31b0b
GS
1412(This is the complete XSUB code for 4 Perl functions!) Four generated
1413Perl function share names with corresponding C functions.
1414
1415The advantage of this approach comparing to ALIAS: keyword is that there
1416is no need to code a switch statement, each Perl function (which shares
1417the same XSUB) knows which C function it should call. Additionally, one
cfc02341 1418can attach an extra function remainder() at runtime by using
beb31b0b 1419
3214bedb 1420 CV *mycv = newXSproto("Symbolic::remainder",
cfc02341
IZ
1421 XS_Symbolic_interface_s_ss, __FILE__, "$$");
1422 XSINTERFACE_FUNC_SET(mycv, remainder);
1423
beb31b0b
GS
1424say, from another XSUB. (This example supposes that there was no
1425INTERFACE_MACRO: section, otherwise one needs to use something else instead of
1426C<XSINTERFACE_FUNC_SET>, see the next section.)
cfc02341
IZ
1427
1428=head2 The INTERFACE_MACRO: Keyword
1429
1430This keyword allows one to define an INTERFACE using a different way
1431to extract a function pointer from an XSUB. The text which follows
1432this keyword should give the name of macros which would extract/set a
1433function pointer. The extractor macro is given return type, C<CV*>,
1434and C<XSANY.any_dptr> for this C<CV*>. The setter macro is given cv,
1435and the function pointer.
1436
1437The default value is C<XSINTERFACE_FUNC> and C<XSINTERFACE_FUNC_SET>.
1438An INTERFACE keyword with an empty list of functions can be omitted if
1439INTERFACE_MACRO keyword is used.
1440
3214bedb 1441Suppose that in the previous example functions pointers for
cfc02341
IZ
1442multiply(), divide(), add(), subtract() are kept in a global C array
1443C<fp[]> with offsets being C<multiply_off>, C<divide_off>, C<add_off>,
3214bedb 1444C<subtract_off>. Then one can use
cfc02341
IZ
1445
1446 #define XSINTERFACE_FUNC_BYOFFSET(ret,cv,f) \
4ef0c66e 1447 ((XSINTERFACE_CVT_ANON(ret))fp[CvXSUBANY(cv).any_i32])
cfc02341
IZ
1448 #define XSINTERFACE_FUNC_BYOFFSET_set(cv,f) \
1449 CvXSUBANY(cv).any_i32 = CAT2( f, _off )
1450
1451in C section,
1452
1453 symbolic
3214bedb 1454 interface_s_ss(arg1, arg2)
cfc02341
IZ
1455 symbolic arg1
1456 symbolic arg2
3214bedb 1457 INTERFACE_MACRO:
cfc02341
IZ
1458 XSINTERFACE_FUNC_BYOFFSET
1459 XSINTERFACE_FUNC_BYOFFSET_set
beb31b0b 1460 INTERFACE:
3214bedb 1461 multiply divide
cfc02341
IZ
1462 add subtract
1463
1464in XSUB section.
1465
c07a80fd
PP
1466=head2 The INCLUDE: Keyword
1467
1468This keyword can be used to pull other files into the XS module. The other
1469files may have XS code. INCLUDE: can also be used to run a command to
1470generate the XS code to be pulled into the module.
1471
1472The file F<Rpcb1.xsh> contains our C<rpcb_gettime()> function:
1473
1474 bool_t
1475 rpcb_gettime(host,timep)
1476 char *host
1477 time_t &timep
beb31b0b 1478 OUTPUT:
c07a80fd
PP
1479 timep
1480
1481The XS module can use INCLUDE: to pull that file into it.
1482
1483 INCLUDE: Rpcb1.xsh
1484
1485If the parameters to the INCLUDE: keyword are followed by a pipe (C<|>) then
4db98c67
SM
1486the compiler will interpret the parameters as a command. This feature is
1487mildly deprecated in favour of the C<INCLUDE_COMMAND:> directive, as documented
1488below.
c07a80fd
PP
1489
1490 INCLUDE: cat Rpcb1.xsh |
1491
4db98c67
SM
1492Do not use this to run perl: C<INCLUDE: perl |> will run the perl that
1493happens to be the first in your path and not necessarily the same perl that is
1494used to run C<xsubpp>. See L<"The INCLUDE_COMMAND: Keyword">.
1495
1496=head2 The INCLUDE_COMMAND: Keyword
1497
1498Runs the supplied command and includes its output into the current XS
1499document. C<INCLUDE_COMMAND> assigns special meaning to the C<$^X> token
1500in that it runs the same perl interpreter that is running C<xsubpp>:
1501
1502 INCLUDE_COMMAND: cat Rpcb1.xsh
1503
1504 INCLUDE_COMMAND: $^X -e ...
1505
c07a80fd
PP
1506=head2 The CASE: Keyword
1507
1508The CASE: keyword allows an XSUB to have multiple distinct parts with each
1509part acting as a virtual XSUB. CASE: is greedy and if it is used then all
1510other XS keywords must be contained within a CASE:. This means nothing may
1511precede the first CASE: in the XSUB and anything following the last CASE: is
1512included in that case.
1513
1514A CASE: might switch via a parameter of the XSUB, via the C<ix> ALIAS:
1515variable (see L<"The ALIAS: Keyword">), or maybe via the C<items> variable
1516(see L<"Variable-length Parameter Lists">). The last CASE: becomes the
1517B<default> case if it is not associated with a conditional. The following
1518example shows CASE switched via C<ix> with a function C<rpcb_gettime()>
1519having an alias C<x_gettime()>. When the function is called as
b772cb6e
PP
1520C<rpcb_gettime()> its parameters are the usual C<(char *host, time_t *timep)>,
1521but when the function is called as C<x_gettime()> its parameters are
c07a80fd
PP
1522reversed, C<(time_t *timep, char *host)>.
1523
1524 long
1525 rpcb_gettime(a,b)
1526 CASE: ix == 1
beb31b0b 1527 ALIAS:
c07a80fd 1528 x_gettime = 1
beb31b0b 1529 INPUT:
c07a80fd
PP
1530 # 'a' is timep, 'b' is host
1531 char *b
1532 time_t a = NO_INIT
beb31b0b 1533 CODE:
c07a80fd 1534 RETVAL = rpcb_gettime( b, &a );
beb31b0b 1535 OUTPUT:
c07a80fd
PP
1536 a
1537 RETVAL
1538 CASE:
1539 # 'a' is host, 'b' is timep
1540 char *a
1541 time_t &b = NO_INIT
beb31b0b 1542 OUTPUT:
c07a80fd
PP
1543 b
1544 RETVAL
1545
1546That function can be called with either of the following statements. Note
1547the different argument lists.
1548
1549 $status = rpcb_gettime( $host, $timep );
1550
1551 $status = x_gettime( $timep, $host );
1552
948e9987
SM
1553=head2 The EXPORT_XSUB_SYMBOLS: Keyword
1554
1555The EXPORT_XSUB_SYMBOLS: keyword is likely something you will never need.
1556In perl versions earlier than 5.16.0, this keyword does nothing. Starting
1557with 5.16, XSUB symbols are no longer exported by default. That is, they
1558are C<static> functions. If you include
1559
1560 EXPORT_XSUB_SYMBOLS: ENABLE
1561
1562in your XS code, the XSUBs following this line will not be declared C<static>.
1563You can later disable this with
1564
1565 EXPORT_XSUB_SYMBOLS: DISABLE
1566
1567which, again, is the default that you should probably never change.
1568You cannot use this keyword on versions of perl before 5.16 to make
1569XSUBs C<static>.
1570
c07a80fd
PP
1571=head2 The & Unary Operator
1572
beb31b0b
GS
1573The C<&> unary operator in the INPUT: section is used to tell B<xsubpp>
1574that it should convert a Perl value to/from C using the C type to the left
1575of C<&>, but provide a pointer to this value when the C function is called.
1576
1577This is useful to avoid a CODE: block for a C function which takes a parameter
1578by reference. Typically, the parameter should be not a pointer type (an
d1be9408 1579C<int> or C<long> but not an C<int*> or C<long*>).
c07a80fd 1580
beb31b0b 1581The following XSUB will generate incorrect C code. The B<xsubpp> compiler will
c07a80fd
PP
1582turn this into code which calls C<rpcb_gettime()> with parameters C<(char
1583*host, time_t timep)>, but the real C<rpcb_gettime()> wants the C<timep>
1584parameter to be of type C<time_t*> rather than C<time_t>.
1585
1586 bool_t
1587 rpcb_gettime(host,timep)
1588 char *host
1589 time_t timep
beb31b0b 1590 OUTPUT:
c07a80fd
PP
1591 timep
1592
beb31b0b 1593That problem is corrected by using the C<&> operator. The B<xsubpp> compiler
c07a80fd
PP
1594will now turn this into code which calls C<rpcb_gettime()> correctly with
1595parameters C<(char *host, time_t *timep)>. It does this by carrying the
1596C<&> through, so the function call looks like C<rpcb_gettime(host, &timep)>.
1597
1598 bool_t
1599 rpcb_gettime(host,timep)
1600 char *host
1601 time_t &timep
beb31b0b 1602 OUTPUT:
c07a80fd
PP
1603 timep
1604
7817ba4d 1605=head2 Inserting POD, Comments and C Preprocessor Directives
a0d0e21e 1606
7817ba4d 1607C preprocessor directives are allowed within BOOT:, PREINIT: INIT:, CODE:,
375cc10d 1608PPCODE:, POSTCALL:, and CLEANUP: blocks, as well as outside the functions.
7817ba4d
NC
1609Comments are allowed anywhere after the MODULE keyword. The compiler will
1610pass the preprocessor directives through untouched and will remove the
1611commented lines. POD documentation is allowed at any point, both in the
1612C and XS language sections. POD must be terminated with a C<=cut> command;
1613C<xsubpp> will exit with an error if it does not. It is very unlikely that
1614human generated C code will be mistaken for POD, as most indenting styles
1615result in whitespace in front of any line starting with C<=>. Machine
1616generated XS files may fall into this trap unless care is taken to
1617ensure that a space breaks the sequence "\n=".
b772cb6e 1618
f27cfbbe
PP
1619Comments can be added to XSUBs by placing a C<#> as the first
1620non-whitespace of a line. Care should be taken to avoid making the
1621comment look like a C preprocessor directive, lest it be interpreted as
1622such. The simplest way to prevent this is to put whitespace in front of
1623the C<#>.
1624
f27cfbbe
PP
1625If you use preprocessor directives to choose one of two
1626versions of a function, use
1627
1628 #if ... version1
1629 #else /* ... version2 */
1630 #endif
1631
1632and not
1633
1634 #if ... version1
1635 #endif
1636 #if ... version2
1637 #endif
1638
beb31b0b 1639because otherwise B<xsubpp> will believe that you made a duplicate
f27cfbbe
PP
1640definition of the function. Also, put a blank line before the
1641#else/#endif so it will not be seen as part of the function body.
a0d0e21e
LW
1642
1643=head2 Using XS With C++
1644
beb31b0b
GS
1645If an XSUB name contains C<::>, it is considered to be a C++ method.
1646The generated Perl function will assume that
a0d0e21e
LW
1647its first argument is an object pointer. The object pointer
1648will be stored in a variable called THIS. The object should
1649have been created by C++ with the new() function and should
cb1a09d0
AD
1650be blessed by Perl with the sv_setref_pv() macro. The
1651blessing of the object by Perl can be handled by a typemap. An example
1652typemap is shown at the end of this section.
a0d0e21e 1653
beb31b0b
GS
1654If the return type of the XSUB includes C<static>, the method is considered
1655to be a static method. It will call the C++
a0d0e21e 1656function using the class::method() syntax. If the method is not static
f27cfbbe 1657the function will be called using the THIS-E<gt>method() syntax.
a0d0e21e 1658
cb1a09d0 1659The next examples will use the following C++ class.
a0d0e21e 1660
a5f75d66 1661 class color {
cb1a09d0 1662 public:
a5f75d66
AD
1663 color();
1664 ~color();
cb1a09d0
AD
1665 int blue();
1666 void set_blue( int );
1667
1668 private:
1669 int c_blue;
1670 };
1671
1672The XSUBs for the blue() and set_blue() methods are defined with the class
1673name but the parameter for the object (THIS, or "self") is implicit and is
1674not listed.
1675
1676 int
1677 color::blue()
a0d0e21e
LW
1678
1679 void
cb1a09d0
AD
1680 color::set_blue( val )
1681 int val
a0d0e21e 1682
3214bedb 1683Both Perl functions will expect an object as the first parameter. In the
beb31b0b
GS
1684generated C++ code the object is called C<THIS>, and the method call will
1685be performed on this object. So in the C++ code the blue() and set_blue()
1686methods will be called as this:
a0d0e21e 1687
cb1a09d0 1688 RETVAL = THIS->blue();
a0d0e21e 1689
cb1a09d0 1690 THIS->set_blue( val );
a0d0e21e 1691
4628e4f8
GS
1692You could also write a single get/set method using an optional argument:
1693
1694 int
a104f515 1695 color::blue( val = NO_INIT )
4628e4f8
GS
1696 int val
1697 PROTOTYPE $;$
1698 CODE:
1699 if (items > 1)
1700 THIS->set_blue( val );
1701 RETVAL = THIS->blue();
1702 OUTPUT:
1703 RETVAL
1704
cb1a09d0 1705If the function's name is B<DESTROY> then the C++ C<delete> function will be
beb31b0b 1706called and C<THIS> will be given as its parameter. The generated C++ code for
a0d0e21e 1707
d1b91892 1708 void
cb1a09d0
AD
1709 color::DESTROY()
1710
beb31b0b
GS
1711will look like this:
1712
555bd962 1713 color *THIS = ...; // Initialized as in typemap
cb1a09d0
AD
1714
1715 delete THIS;
a0d0e21e 1716
cb1a09d0
AD
1717If the function's name is B<new> then the C++ C<new> function will be called
1718to create a dynamic C++ object. The XSUB will expect the class name, which
1719will be kept in a variable called C<CLASS>, to be given as the first
1720argument.
a0d0e21e 1721
cb1a09d0
AD
1722 color *
1723 color::new()
a0d0e21e 1724
beb31b0b 1725The generated C++ code will call C<new>.
a0d0e21e 1726
beb31b0b 1727 RETVAL = new color();
cb1a09d0
AD
1728
1729The following is an example of a typemap that could be used for this C++
1730example.
1731
1732 TYPEMAP
555bd962 1733 color * O_OBJECT
cb1a09d0
AD
1734
1735 OUTPUT
1736 # The Perl object is blessed into 'CLASS', which should be a
1737 # char* having the name of the package for the blessing.
1738 O_OBJECT
555bd962 1739 sv_setref_pv( $arg, CLASS, (void*)$var );
a6006777 1740
cb1a09d0
AD
1741 INPUT
1742 O_OBJECT
555bd962
BG
1743 if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) )
1744 $var = ($type)SvIV((SV*)SvRV( $arg ));
1745 else{
1746 warn("${Package}::$func_name() -- " .
1747 "$var is not a blessed SV reference");
1748 XSRETURN_UNDEF;
1749 }
a0d0e21e 1750
d1b91892 1751=head2 Interface Strategy
a0d0e21e
LW
1752
1753When designing an interface between Perl and a C library a straight
beb31b0b
GS
1754translation from C to XS (such as created by C<h2xs -x>) is often sufficient.
1755However, sometimes the interface will look
a0d0e21e 1756very C-like and occasionally nonintuitive, especially when the C function
beb31b0b
GS
1757modifies one of its parameters, or returns failure inband (as in "negative
1758return values mean failure"). In cases where the programmer wishes to
a0d0e21e
LW
1759create a more Perl-like interface the following strategy may help to
1760identify the more critical parts of the interface.
1761
beb31b0b
GS
1762Identify the C functions with input/output or output parameters. The XSUBs for
1763these functions may be able to return lists to Perl.
1764
1765Identify the C functions which use some inband info as an indication
1766of failure. They may be
1767candidates to return undef or an empty list in case of failure. If the
1768failure may be detected without a call to the C function, you may want to use
1769an INIT: section to report the failure. For failures detectable after the C
375cc10d 1770function returns one may want to use a POSTCALL: section to process the
beb31b0b
GS
1771failure. In more complicated cases use CODE: or PPCODE: sections.
1772
1773If many functions use the same failure indication based on the return value,
1774you may want to create a special typedef to handle this situation. Put
1775
1776 typedef int negative_is_failure;
1777
1778near the beginning of XS file, and create an OUTPUT typemap entry
1779for C<negative_is_failure> which converts negative values to C<undef>, or
1780maybe croak()s. After this the return value of type C<negative_is_failure>
1781will create more Perl-like interface.
a0d0e21e 1782
d1b91892 1783Identify which values are used by only the C and XSUB functions
beb31b0b
GS
1784themselves, say, when a parameter to a function should be a contents of a
1785global variable. If Perl does not need to access the contents of the value
a0d0e21e
LW
1786then it may not be necessary to provide a translation for that value
1787from C to Perl.
1788
1789Identify the pointers in the C function parameter lists and return
beb31b0b
GS
1790values. Some pointers may be used to implement input/output or
1791output parameters, they can be handled in XS with the C<&> unary operator,
1792and, possibly, using the NO_INIT keyword.
1793Some others will require handling of types like C<int *>, and one needs
1794to decide what a useful Perl translation will do in such a case. When
1795the semantic is clear, it is advisable to put the translation into a typemap
1796file.
a0d0e21e
LW
1797
1798Identify the structures used by the C functions. In many
1799cases it may be helpful to use the T_PTROBJ typemap for
1800these structures so they can be manipulated by Perl as
beb31b0b
GS
1801blessed objects. (This is handled automatically by C<h2xs -x>.)
1802
1803If the same C type is used in several different contexts which require
1804different translations, C<typedef> several new types mapped to this C type,
1805and create separate F<typemap> entries for these new types. Use these
1806types in declarations of return type and parameters to XSUBs.
a0d0e21e 1807
a0d0e21e
LW
1808=head2 Perl Objects And C Structures
1809
1810When dealing with C structures one should select either
1811B<T_PTROBJ> or B<T_PTRREF> for the XS type. Both types are
1812designed to handle pointers to complex objects. The
1813T_PTRREF type will allow the Perl object to be unblessed
1814while the T_PTROBJ type requires that the object be blessed.
1815By using T_PTROBJ one can achieve a form of type-checking
d1b91892 1816because the XSUB will attempt to verify that the Perl object
a0d0e21e
LW
1817is of the expected type.
1818
1819The following XS code shows the getnetconfigent() function which is used
8e07c86e 1820with ONC+ TIRPC. The getnetconfigent() function will return a pointer to a
a0d0e21e
LW
1821C structure and has the C prototype shown below. The example will
1822demonstrate how the C pointer will become a Perl reference. Perl will
1823consider this reference to be a pointer to a blessed object and will
1824attempt to call a destructor for the object. A destructor will be
1825provided in the XS source to free the memory used by getnetconfigent().
1826Destructors in XS can be created by specifying an XSUB function whose name
1827ends with the word B<DESTROY>. XS destructors can be used to free memory
1828which may have been malloc'd by another XSUB.
1829
1830 struct netconfig *getnetconfigent(const char *netid);
1831
1832A C<typedef> will be created for C<struct netconfig>. The Perl
1833object will be blessed in a class matching the name of the C
1834type, with the tag C<Ptr> appended, and the name should not
1835have embedded spaces if it will be a Perl package name. The
1836destructor will be placed in a class corresponding to the
1837class of the object and the PREFIX keyword will be used to
1838trim the name to the word DESTROY as Perl will expect.
1839
1840 typedef struct netconfig Netconfig;
1841
1842 MODULE = RPC PACKAGE = RPC
1843
1844 Netconfig *
1845 getnetconfigent(netid)
8e07c86e 1846 char *netid
a0d0e21e
LW
1847
1848 MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_
1849
1850 void
1851 rpcb_DESTROY(netconf)
8e07c86e 1852 Netconfig *netconf
beb31b0b 1853 CODE:
a0d0e21e
LW
1854 printf("Now in NetconfigPtr::DESTROY\n");
1855 free( netconf );
1856
78a4b226
SM
1857This example requires the following typemap entry. Consult
1858L<perlxstypemap> for more information about adding new typemaps
1859for an extension.
a0d0e21e
LW
1860
1861 TYPEMAP
1862 Netconfig * T_PTROBJ
1863
1864This example will be used with the following Perl statements.
1865
1866 use RPC;
1867 $netconf = getnetconfigent("udp");
1868
1869When Perl destroys the object referenced by $netconf it will send the
1870object to the supplied XSUB DESTROY function. Perl cannot determine, and
1871does not care, that this object is a C struct and not a Perl object. In
1872this sense, there is no difference between the object created by the
1873getnetconfigent() XSUB and an object created by a normal Perl subroutine.
1874
662a0f8c
JH
1875=head2 Safely Storing Static Data in XS
1876
1877Starting with Perl 5.8, a macro framework has been defined to allow
1878static data to be safely stored in XS modules that will be accessed from
1879a multi-threaded Perl.
1880
1881Although primarily designed for use with multi-threaded Perl, the macros
1882have been designed so that they will work with non-threaded Perl as well.
1883
1884It is therefore strongly recommended that these macros be used by all
1885XS modules that make use of static data.
1886
fe854a6f 1887The easiest way to get a template set of macros to use is by specifying
662a0f8c
JH
1888the C<-g> (C<--global>) option with h2xs (see L<h2xs>).
1889
1890Below is an example module that makes use of the macros.
1891
f9d625cd 1892 #define PERL_NO_GET_CONTEXT
662a0f8c
JH
1893 #include "EXTERN.h"
1894 #include "perl.h"
1895 #include "XSUB.h"
7207e29d 1896
662a0f8c 1897 /* Global Data */
7207e29d 1898
662a0f8c 1899 #define MY_CXT_KEY "BlindMice::_guts" XS_VERSION
7207e29d 1900
662a0f8c
JH
1901 typedef struct {
1902 int count;
1903 char name[3][100];
1904 } my_cxt_t;
7207e29d 1905
662a0f8c 1906 START_MY_CXT
7207e29d 1907
662a0f8c 1908 MODULE = BlindMice PACKAGE = BlindMice
7207e29d 1909
662a0f8c
JH
1910 BOOT:
1911 {
1912 MY_CXT_INIT;
1913 MY_CXT.count = 0;
1914 strcpy(MY_CXT.name[0], "None");
1915 strcpy(MY_CXT.name[1], "None");
1916 strcpy(MY_CXT.name[2], "None");
3214bedb 1917 }
662a0f8c
JH
1918
1919 int
1920 newMouse(char * name)
662a0f8c
JH
1921 PREINIT:
1922 dMY_CXT;
1923 CODE:
1924 if (MY_CXT.count >= 3) {
4358a253 1925 warn("Already have 3 blind mice");
662a0f8c
JH
1926 RETVAL = 0;
1927 }
1928 else {
1929 RETVAL = ++ MY_CXT.count;
1930 strcpy(MY_CXT.name[MY_CXT.count - 1], name);
1931 }
81968fbb
TC
1932 OUTPUT:
1933 RETVAL
662a0f8c
JH
1934
1935 char *
1936 get_mouse_name(index)
81968fbb
TC
1937 int index
1938 PREINIT:
1939 dMY_CXT;
1940 CODE:
1941 if (index > MY_CXT.count)
1942 croak("There are only 3 blind mice.");
1943 else
1944 RETVAL = MY_CXT.name[index - 1];
1945 OUTPUT:
1946 RETVAL
662a0f8c 1947
85ce96a1
DM
1948 void
1949 CLONE(...)
1950 CODE:
81968fbb 1951 MY_CXT_CLONE;
85ce96a1 1952
81968fbb 1953=head3 MY_CXT REFERENCE
662a0f8c
JH
1954
1955=over 5
1956
1957=item MY_CXT_KEY
1958
1959This macro is used to define a unique key to refer to the static data
1960for an XS module. The suggested naming scheme, as used by h2xs, is to
1961use a string that consists of the module name, the string "::_guts"
1962and the module version number.
1963
1964 #define MY_CXT_KEY "MyModule::_guts" XS_VERSION
1965
1966=item typedef my_cxt_t
1967
ac036724 1968This struct typedef I<must> always be called C<my_cxt_t>. The other
662a0f8c
JH
1969C<CXT*> macros assume the existence of the C<my_cxt_t> typedef name.
1970
1971Declare a typedef named C<my_cxt_t> that is a structure that contains
1972all the data that needs to be interpreter-local.
1973
1974 typedef struct {
1975 int some_value;
1976 } my_cxt_t;
1977
1978=item START_MY_CXT
1979
1980Always place the START_MY_CXT macro directly after the declaration
1981of C<my_cxt_t>.
1982
1983=item MY_CXT_INIT
1984
4c75f49d 1985The MY_CXT_INIT macro initializes storage for the C<my_cxt_t> struct.
662a0f8c 1986
ac036724 1987It I<must> be called exactly once, typically in a BOOT: section. If you
85ce96a1
DM
1988are maintaining multiple interpreters, it should be called once in each
1989interpreter instance, except for interpreters cloned from existing ones.
f535407b 1990(But see L</MY_CXT_CLONE> below.)
662a0f8c
JH
1991
1992=item dMY_CXT
1993
1994Use the dMY_CXT macro (a declaration) in all the functions that access
1995MY_CXT.
1996
1997=item MY_CXT
1998
1999Use the MY_CXT macro to access members of the C<my_cxt_t> struct. For
3214bedb 2000example, if C<my_cxt_t> is
662a0f8c
JH
2001
2002 typedef struct {
2003 int index;
2004 } my_cxt_t;
2005
2006then use this to access the C<index> member
2007
2008 dMY_CXT;
2009 MY_CXT.index = 2;
2010
85ce96a1
DM
2011=item aMY_CXT/pMY_CXT
2012
2013C<dMY_CXT> may be quite expensive to calculate, and to avoid the overhead
2014of invoking it in each function it is possible to pass the declaration
2015onto other functions using the C<aMY_CXT>/C<pMY_CXT> macros, eg
2016
2017 void sub1() {
2018 dMY_CXT;
2019 MY_CXT.index = 1;
2020 sub2(aMY_CXT);
2021 }
2022
2023 void sub2(pMY_CXT) {
2024 MY_CXT.index = 2;
2025 }
2026
2027Analogously to C<pTHX>, there are equivalent forms for when the macro is the
2028first or last in multiple arguments, where an underscore represents a
2029comma, i.e. C<_aMY_CXT>, C<aMY_CXT_>, C<_pMY_CXT> and C<pMY_CXT_>.
2030
2031=item MY_CXT_CLONE
2032
2033By default, when a new interpreter is created as a copy of an existing one
0a3a8dc0 2034(eg via C<< threads->create() >>), both interpreters share the same physical
85ce96a1
DM
2035my_cxt_t structure. Calling C<MY_CXT_CLONE> (typically via the package's
2036C<CLONE()> function), causes a byte-for-byte copy of the structure to be
2037taken, and any future dMY_CXT will cause the copy to be accessed instead.
2038
f16dd614
DM
2039=item MY_CXT_INIT_INTERP(my_perl)
2040
2041=item dMY_CXT_INTERP(my_perl)
2042
2043These are versions of the macros which take an explicit interpreter as an
2044argument.
2045
662a0f8c
JH
2046=back
2047
f16dd614
DM
2048Note that these macros will only work together within the I<same> source
2049file; that is, a dMY_CTX in one source file will access a different structure
2050than a dMY_CTX in another source file.
2051
832a833b
JH
2052=head2 Thread-aware system interfaces
2053
2054Starting from Perl 5.8, in C/C++ level Perl knows how to wrap
2055system/library interfaces that have thread-aware versions
2056(e.g. getpwent_r()) into frontend macros (e.g. getpwent()) that
2057correctly handle the multithreaded interaction with the Perl
2058interpreter. This will happen transparently, the only thing
2059you need to do is to instantiate a Perl interpreter.
2060
2061This wrapping happens always when compiling Perl core source
2062(PERL_CORE is defined) or the Perl core extensions (PERL_EXT is
59eb8be1
KW
2063defined). When compiling XS code outside of the Perl core, the wrapping
2064does not take place before Perl 5.28. Starting in that release you can
2065
2066 #define PERL_REENTRANT
2067
2068in your code to enable the wrapping. It is advisable to do so if you
2069are using such functions, as intermixing the C<_r>-forms (as Perl compiled
2070for multithreaded operation will do) and the C<_r>-less forms is neither
2071well-defined (inconsistent results, data corruption, or even crashes
2072become more likely), nor is it very portable. Unfortunately, not all
2073systems have all the C<_r> forms, but using this C<#define> gives you
2074whatever protection that Perl is aware is available on each system.
832a833b 2075
a0d0e21e
LW
2076=head1 EXAMPLES
2077
2078File C<RPC.xs>: Interface to some ONC+ RPC bind library functions.
2079
f9d625cd 2080 #define PERL_NO_GET_CONTEXT
a0d0e21e
LW
2081 #include "EXTERN.h"
2082 #include "perl.h"
2083 #include "XSUB.h"
2084
2085 #include <rpc/rpc.h>
2086
2087 typedef struct netconfig Netconfig;
2088
2089 MODULE = RPC PACKAGE = RPC
2090
e7ea3e70 2091 SV *
a0d0e21e 2092 rpcb_gettime(host="localhost")
8e07c86e 2093 char *host
beb31b0b 2094 PREINIT:
a0d0e21e 2095 time_t timep;
beb31b0b 2096 CODE:
a0d0e21e
LW
2097 ST(0) = sv_newmortal();
2098 if( rpcb_gettime( host, &timep ) )
2099 sv_setnv( ST(0), (double)timep );
a0d0e21e
LW
2100
2101 Netconfig *
2102 getnetconfigent(netid="udp")
8e07c86e 2103 char *netid
a0d0e21e
LW
2104
2105 MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_
2106
2107 void
2108 rpcb_DESTROY(netconf)
8e07c86e 2109 Netconfig *netconf
beb31b0b 2110 CODE:
a0d0e21e
LW
2111 printf("NetconfigPtr::DESTROY\n");
2112 free( netconf );
2113
78a4b226 2114File C<typemap>: Custom typemap for RPC.xs. (cf. L<perlxstypemap>)
a0d0e21e
LW
2115
2116 TYPEMAP
2117 Netconfig * T_PTROBJ
2118
2119File C<RPC.pm>: Perl module for the RPC extension.
2120
2121 package RPC;
2122
2123 require Exporter;
2124 require DynaLoader;
2125 @ISA = qw(Exporter DynaLoader);
2126 @EXPORT = qw(rpcb_gettime getnetconfigent);
2127
2128 bootstrap RPC;
2129 1;
2130
2131File C<rpctest.pl>: Perl test program for the RPC extension.
2132
2133 use RPC;
2134
2135 $netconf = getnetconfigent();
2136 $a = rpcb_gettime();
2137 print "time = $a\n";
2138 print "netconf = $netconf\n";
2139
2140 $netconf = getnetconfigent("tcp");
2141 $a = rpcb_gettime("poplar");
2142 print "time = $a\n";
2143 print "netconf = $netconf\n";
2144
8a384d3a
KW
2145=head1 CAVEATS
2146
2147XS code has full access to system calls including C library functions.
2148It thus has the capability of interfering with things that the Perl core
2149or other modules have set up, such as signal handlers or file handles.
2150It could mess with the memory, or any number of harmful things. Don't.
2151
2152Some modules have an event loop, waiting for user-input. It is highly
2153unlikely that two such modules would work adequately together in a
2154single Perl application.
2155
2156In general, the perl interpreter views itself as the center of the
2157universe as far as the Perl program goes. XS code is viewed as a
2158help-mate, to accomplish things that perl doesn't do, or doesn't do fast
2159enough, but always subservient to perl. The closer XS code adheres to
2160this model, the less likely conflicts will occur.
2161
2162One area where there has been conflict is in regards to C locales. (See
2163L<perllocale>.) perl, with one exception and unless told otherwise,
45235d99
KW
2164sets up the underlying locale the program is running in to the locale
2165passed
2166into it from the environment. This is an important difference from a
2167generic C language program, where the underlying locale is the "C"
2168locale unless the program changes it. As of v5.20, this underlying
7b320f21 2169locale is completely hidden from pure Perl code outside the lexical
45235d99
KW
2170scope of C<S<use locale>> except for a couple of function calls in the
2171POSIX module which of necessity use it. But the underlying locale, with
2172that
2173one exception is exposed to XS code, affecting all C library routines
2174whose behavior is locale-dependent. Your XS code better not assume that
2175the underlying locale is "C". The exception is the
8a384d3a
KW
2176L<C<LC_NUMERIC>|perllocale/Category LC_NUMERIC: Numeric Formatting>
2177locale category, and the reason it is an exception is that experience
2178has shown that it can be problematic for XS code, whereas we have not
2179had reports of problems with the
2180L<other locale categories|perllocale/WHAT IS A LOCALE>. And the reason
2181for this one category being problematic is that the character used as a
2182decimal point can vary. Many European languages use a comma, whereas
2183English, and hence Perl are expecting a dot (U+002E: FULL STOP). Many
2184modules can handle only the radix character being a dot, and so perl
2185attempts to make it so. Up through Perl v5.20, the attempt was merely
2186to set C<LC_NUMERIC> upon startup to the C<"C"> locale. Any
2187L<setlocale()|perllocale/The setlocale function> otherwise would change
2188it; this caused some failures. Therefore, starting in v5.22, perl tries
2189to keep C<LC_NUMERIC> always set to C<"C"> for XS code.
2190
2191To summarize, here's what to expect and how to handle locales in XS code:
2192
2193=over
2194
2195=item Non-locale-aware XS code
2196
2197Keep in mind that even if you think your code is not locale-aware, it
e9bc6d6b 2198may call a library function that is. Hopefully the man page for such
8a384d3a
KW
2199a function will indicate that dependency, but the documentation is
2200imperfect.
2201
45235d99
KW
2202The current locale is exposed to XS code except possibly C<LC_NUMERIC>
2203(explained in the next paragraph).
2204There have not been reports of problems with the other categories.
2205Perl initializes things on start-up so that the current locale is the
2206one which is indicated by the user's environment in effect at that time.
2207See L<perllocale/ENVIRONMENT>.
8a384d3a 2208
45235d99
KW
2209However, up through v5.20, Perl initialized things on start-up so that
2210C<LC_NUMERIC> was set to the "C" locale. But if any code anywhere
2211changed it, it would stay changed. This means that your module can't
8a384d3a
KW
2212count on C<LC_NUMERIC> being something in particular, and you can't
2213expect floating point numbers (including version strings) to have dots
2214in them. If you don't allow for a non-dot, your code could break if
45235d99 2215anyone anywhere changed the locale. For this reason, v5.22 changed
8a384d3a
KW
2216the behavior so that Perl tries to keep C<LC_NUMERIC> in the "C" locale
2217except around the operations internally where it should be something
2218else. Misbehaving XS code will always be able to change the locale
2219anyway, but the most common instance of this is checked for and
2220handled.
2221
2222=item Locale-aware XS code
2223
2224If the locale from the user's environment is desired, there should be no
2225need for XS code to set the locale except for C<LC_NUMERIC>, as perl has
49d7d366
KW
2226already set the others up. XS code should avoid changing the locale, as
2227it can adversely affect other, unrelated, code and may not be
2228thread-safe. To minimize problems, the macros
2229L<perlapi/STORE_LC_NUMERIC_SET_TO_NEEDED>,
2230L<perlapi/STORE_LC_NUMERIC_FORCE_TO_UNDERLYING>, and
2231L<perlapi/RESTORE_LC_NUMERIC> should be used to affect any needed
2232change.
2233
e9bc6d6b
KW
2234But, starting with Perl v5.28, locales are thread-safe on platforms that
2235support this functionality. Windows has this starting with Visual
2236Studio 2005. Many other modern platforms support the thread-safe POSIX
22372008 functions. The C C<#define> C<USE_THREAD_SAFE_LOCALE> will be
2238defined iff this build is using these. From Perl-space, the read-only
2239variable C<${SAFE_LOCALES}> is 1 if either the build is not threaded, or
2240if C<USE_THREAD_SAFE_LOCALE> is defined; otherwise it is 0.
2241
2242The way this works under-the-hood is that every thread has a choice of
2243using a locale specific to it (this is the Windows and POSIX 2008
2244functionality), or the global locale that is accessible to all threads
2245(this is the functionality that has always been there). The
2246implementations for Windows and POSIX are completely different. On
2247Windows, the runtime can be set up so that the standard
2248L<C<setlocale(3)>> function either only knows about the global locale or
2249the locale for this thread. On POSIX, C<setlocale> always deals with
2250the global locale, and other functions have been created to handle
2251per-thread locales. Perl makes this transparent to perl-space code. It
2252continues to use C<POSIX::setlocale()>, and the interpreter translates
2253that into the per-thread functions.
2254
2255All other locale-senstive functions automatically use the per-thread
2256locale, if that is turned on, and failing that, the global locale. Thus
2257calls to C<setlocale> are ineffective on POSIX systems for the current
2258thread if that thread is using a per-thread locale. If perl is compiled
2259for single-thread operation, it does not use the per-thread functions,
2260so C<setlocale> does work as expected.
2261
2262If you have loaded the L<C<POSIX>> module you can use the methods given
2263in L<perlcall> to call L<C<POSIX::setlocale>|POSIX/setlocale> to safely
2264change or query the locale (on systems where it is safe to do so), or
2265you can use the new 5.28 function L<perlapi/Perl_setlocale> instead,
2266which is a drop-in replacement for the system L<C<setlocale(3)>>, and
2267handles single-threaded and multi-threaded applications transparently.
2268
2269There are some locale-related library calls that still aren't
2270thread-safe because they return data in a buffer global to all threads.
2271In the past, these didn't matter as locales weren't thread-safe at all.
2272But now you have to be aware of them in case your module is called in a
2273multi-threaded application. The known ones are
2274
2275 asctime()
2276 ctime()
2277 gcvt() [POSIX.1-2001 only (function removed in POSIX.1-2008)]
2278 getdate()
2279 wcrtomb() if its final argument is NULL
2280 wcsrtombs() if its final argument is NULL
2281 wcstombs()
2282 wctomb()
2283
2284Some of these shouldn't really be called in a Perl application, and for
2285others there are thread-safe versions of these already implemented:
2286
2287 asctime_r()
2288 ctime_r()
2289 Perl_langinfo()
2290
2291The C<_r> forms are automatically used, starting in Perl 5.28, if you
2292compile your code, with
2293
2294 #define PERL_REENTRANT
2295
2296See also L<perlapi/Perl_langinfo>.
2297You can use the methods given in L<perlcall>, to get the best available
2298locale-safe versions of these
2299
2300 POSIX::localeconv()
2301 POSIX::wcstombs()
2302 POSIX::wctomb()
2303
2304And note, that some items returned by C<Localeconv> are available
2305through L<perlapi/Perl_langinfo>.
2306
2307The others shouldn't be used in a threaded application.
2308
2309Some modules may call a non-perl library that is locale-aware. This is
2310fine as long as it doesn't try to query or change the locale using the
2311system C<setlocale>. But if these do call the system C<setlocale>,
2312those calls may be ineffective. Instead,
2313L<C<Perl_setlocale>|perlapi/Perl_setlocale> works in all circumstances.
2314Plain setlocale is ineffective on multi-threaded POSIX 2008 systems. It
2315operates only on the global locale, whereas each thread has its own
2316locale, paying no attention to the global one. Since converting
2317these non-Perl libraries to C<Perl_setlocale> is out of the question,
2318there is a new function in v5.28
2319C<switch_to_global_locale> that will
2320switch the thread it is called from so that any system C<setlocale>
2321calls will have their desired effect. The function
2322L<C<sync_locale>|perlapi/sync_locale> must be called before returning to
2323perl.
2324
2325This thread can change the locale all it wants and it won't affect any
2326other thread, except any that also have been switched to the global
2327locale. This means that a multi-threaded application can have a single
2328thread using an alien library without a problem; but no more than a
2329single thread can be so-occupied. Bad results likely will happen.
2330
2331In perls without multi-thread locale support, some alien libraries,
2332such as C<Gtk> change locales. This can cause problems for the Perl
2333core and other modules. For these, before control is returned to
2334perl, starting in v5.20.1, calling the function
8a384d3a
KW
2335L<sync_locale()|perlapi/sync_locale> from XS should be sufficient to
2336avoid most of these problems. Prior to this, you need a pure Perl
45235d99 2337statement that does this:
8a384d3a
KW
2338
2339 POSIX::setlocale(LC_ALL, POSIX::setlocale(LC_ALL));
2340
49d7d366 2341or use the methods given in L<perlcall>.
8a384d3a
KW
2342
2343=back
a0d0e21e 2344
c07a80fd
PP
2345=head1 XS VERSION
2346
78a4b226
SM
2347This document covers features supported by C<ExtUtils::ParseXS>
2348(also known as C<xsubpp>) 3.13_01.
c07a80fd 2349
a0d0e21e
LW
2350=head1 AUTHOR
2351
beb31b0b
GS
2352Originally written by Dean Roehrich <F<roehrich@cray.com>>.
2353
7f2de2d2 2354Maintained since 1996 by The Perl Porters <F<perlbug@perl.org>>.