If the XSUB has a return type of C<void> then the compiler will
not supply a RETVAL variable for that function. When using
-the PPCODE: directive the RETVAL variable may not be needed.
+the PPCODE: directive the RETVAL variable is not needed, unless used
+explicitly.
+
+If PPCODE: directive is not used, C<void> return value should be used
+only for subroutines which do not return a value, I<even if> CODE:
+directive is used which sets ST(0) explicitly.
+
+Older versions of this document recommended to use C<void> return
+value in such cases. It was discovered that this could lead to
+segfaults in cases when XSUB was I<truely> C<void>. This practice is
+now deprecated, and may be not supported at some future version. Use
+the return value C<SV *> in such cases. (Currently C<xsubpp> contains
+some heuristic code which tries to disambiguate between "truely-void"
+and "old-practice-declared-as-void" functions. Hence your code is at
+mercy of this heuristics unless you use C<SV *> as return value.)
=head2 The MODULE Keyword
OUTPUT:
timep sv_setnv(ST(1), (double)timep);
+B<xsubpp> emits an automatic C<SvSETMAGIC()> for all parameters in the
+OUTPUT section of the XSUB, except RETVAL. This is the usually desired
+behavior, as it takes care of properly invoking 'set' magic on output
+parameters (needed for hash or array element parameters that must be
+created if they didn't exist). If for some reason, this behavior is
+not desired, the OUTPUT section may contain a C<SETMAGIC: DISABLE> line
+to disable it for the remainder of the parameters in the OUTPUT section.
+Likewise, C<SETMAGIC: ENABLE> can be used to reenable it for the
+remainder of the OUTPUT section. See L<perlguts> for more details
+about 'set' magic.
+
=head2 The CODE: Keyword
This keyword is used in more complicated XSUBs which require
$status = rpcb_gettime( "localhost", $timep );
-The XSUB follows.
+The XSUB follows.
bool_t
rpcb_gettime(host,timep)
=head2 The NO_INIT Keyword
The NO_INIT keyword is used to indicate that a function
-parameter is being used as only an output value. The B<xsubpp>
+parameter is being used only as an output value. The B<xsubpp>
compiler will normally generate code to read the values of
all function parameters from the argument stack and assign
them to C variables upon entry to the function. NO_INIT
before the function terminates.
The following example shows a variation of the rpcb_gettime() function.
-This function uses the timep variable as only an output variable and does
+This function uses the timep variable only as an output variable and does
not care about its initial contents.
bool_t
bool_t status;
PPCODE:
status = rpcb_gettime( host, &timep );
- EXTEND(sp, 2);
+ EXTEND(SP, 2);
PUSHs(sv_2mortal(newSViv(status)));
PUSHs(sv_2mortal(newSViv(timep)));
The EXTEND() macro is used to make room on the argument
stack for 2 return values. The PPCODE: directive causes the
-B<xsubpp> compiler to create a stack pointer called C<sp>, and it
+B<xsubpp> compiler to create a stack pointer available as C<SP>, and it
is this pointer which is being used in the EXTEND() macro.
The values are then pushed onto the stack with the PUSHs()
macro.
($status, $timep) = rpcb_gettime("localhost");
+When handling output parameters with a PPCODE section, be sure to handle
+'set' magic properly. See L<perlguts> for details about 'set' magic.
+
=head2 Returning Undef And Empty Lists
Occasionally the programmer will want to return simply
$timep = rpcb_gettime( "localhost" );
-The following XSUB uses the C<void> return type to disable the generation of
-the RETVAL variable and uses a CODE: block to indicate to the compiler
+The following XSUB uses the C<SV *> return type as a mneumonic only,
+and uses a CODE: block to indicate to the compiler
that the programmer has supplied all the necessary code. The
sv_newmortal() call will initialize the return value to undef, making that
the default return value.
- void
+ SV *
rpcb_gettime(host)
char * host
PREINIT:
The next example demonstrates how one would place an explicit undef in the
return value, should the need arise.
- void
+ SV *
rpcb_gettime(host)
char * host
PREINIT:
=head2 The PROTOTYPES: Keyword
The PROTOTYPES: keyword corresponds to B<xsubpp>'s C<-prototypes> and
-C<-noprototypes> options. This keyword overrides the command-line options.
+C<-noprototypes> options. This keyword overrides the command line options.
Prototypes are enabled by default. When prototypes are enabled XSUBs will
be given Perl prototypes. This keyword may be used multiple times in an XS
module to enable and disable prototypes for different parts of the module.
=head2 The ALIAS: Keyword
-The ALIAS: keyword allows an XSUB to have two more more unique Perl names
+The ALIAS: keyword allows an XSUB to have two more unique Perl names
and to know which of those names was used when it was invoked. The Perl
names may be fully-qualified with package names. Each alias is given an
index. The compiler will setup a variable called C<ix> which contain the
=head2 Inserting Comments and C Preprocessor Directives
C preprocessor directives are allowed within BOOT:, PREINIT: INIT:,
-CODE:, PPCODE: and CLEANUP: blocks, as well as outside the functions.
+CODE:, PPCODE:, and CLEANUP: blocks, as well as outside the functions.
Comments are allowed anywhere after the MODULE keyword. The compiler
will pass the preprocessor directives through untouched and will remove
the commented lines.
# char* having the name of the package for the blessing.
O_OBJECT
sv_setref_pv( $arg, CLASS, (void*)$var );
-
+
INPUT
O_OBJECT
if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) )
TYPEMAP
Netconfig *<tab>T_PTROBJ
+Here's a more complicated example: suppose that you wanted C<struct
+netconfig> to be blessed into the class C<Net::Config>. One way to do
+this is to use underscores (_) to separate package names, as follows:
+
+ typedef struct netconfig * Net_Config;
+
+And then provide a typemap entry C<T_PTROBJ_SPECIAL> that maps underscores to
+double-colons (::), and declare C<Net_Config> to be of that type:
+
+
+ TYPEMAP
+ Net_Config T_PTROBJ_SPECIAL
+
+ INPUT
+ T_PTROBJ_SPECIAL
+ if (sv_derived_from($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")) {
+ IV tmp = SvIV((SV*)SvRV($arg));
+ $var = ($type) tmp;
+ }
+ else
+ croak(\"$var is not of type ${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")
+
+ OUTPUT
+ T_PTROBJ_SPECIAL
+ sv_setref_pv($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\",
+ (void*)$var);
+
+The INPUT and OUTPUT sections substitute underscores for double-colons
+on the fly, giving the desired effect. This example demonstrates some
+of the power and versatility of the typemap facility.
+
=head1 EXAMPLES
File C<RPC.xs>: Interface to some ONC+ RPC bind library functions.
MODULE = RPC PACKAGE = RPC
- void
+ SV *
rpcb_gettime(host="localhost")
char *host
PREINIT:
=head1 AUTHOR
-Dean Roehrich F<E<lt>roehrich@cray.comE<gt>>
+Dean Roehrich <F<roehrich@cray.com>>
Jul 8, 1996
projects / p5sagit/p5-mst-13.2.git / blobdiff