=head2 On The Road
-Many of the examples which follow will concentrate on creating an
-interface between Perl and the ONC+ RPC bind library functions.
-Specifically, the rpcb_gettime() function will be used to demonstrate many
-features of the XS language. This function has two parameters; the first
-is an input parameter and the second is an output parameter. The function
-also returns a status value.
+Many of the examples which follow will concentrate on creating an interface
+between Perl and the ONC+ RPC bind library functions. The rpcb_gettime()
+function is used to demonstrate many features of the XS language. This
+function has two parameters; the first is an input parameter and the second
+is an output parameter. The function also returns a status value.
bool_t rpcb_gettime(const char *host, time_t *timep);
double x sin(x)
double x
+The function body may be indented or left-adjusted. The following example
+shows a function with its body left-adjusted. Most examples in this
+document will indent the body.
+
+ CORRECT
+
+ double
+ sin(x)
+ double x
+
=head2 The Argument Stack
The argument stack is used to store the values which are
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
timep
RETVAL
-In many of the examples shown here the CODE: block (and
-other blocks) will often be contained within braces ( C<{> and
-C<}> ). This protects the CODE: block from complex INPUT
-typemaps and ensures the resulting C code is legal.
+=head2 The INIT: Keyword
+
+The INIT: keyword allows initialization to be inserted into the XSUB before
+the compiler generates the call to the C function. Unlike the CODE: keyword
+above, this keyword does not affect the way the compiler handles RETVAL.
+
+ bool_t
+ rpcb_gettime(host,timep)
+ char *host
+ time_t &timep
+ INIT:
+ printf("# Host is %s\n", host );
+ OUTPUT:
+ timep
=head2 The NO_INIT Keyword
timep
RETVAL
+=head2 The PREINIT: Keyword
+
+The PREINIT: keyword allows extra variables to be declared before the
+typemaps are expanded. If a variable is declared in a CODE: block then that
+variable will follow any typemap code. This may result in a C syntax
+error. To force the variable to be declared before the typemap code, place
+it into a PREINIT: block. The PREINIT: keyword may be used one or more
+times within an XSUB.
+
+The following examples are equivalent, but if the code is using complex
+typemaps then the first example is safer.
+
+ bool_t
+ rpcb_gettime(timep)
+ time_t timep = NO_INIT
+ PREINIT:
+ char *host = "localhost";
+ CODE:
+ RETVAL = rpcb_gettime( host, &timep );
+ OUTPUT:
+ timep
+ RETVAL
+
+A correct, but error-prone example.
+
+ bool_t
+ rpcb_gettime(timep)
+ time_t timep = NO_INIT
+ CODE:
+ char *host = "localhost";
+ RETVAL = rpcb_gettime( host, &timep );
+ OUTPUT:
+ timep
+ RETVAL
+
+=head2 The SCOPE: Keyword
+
+The SCOPE: keyword allows scoping to be enabled for a particular XSUB. If
+enabled, the XSUB will invoke ENTER and LEAVE automatically.
+
+To support potentially complex type mappings, if a typemap entry used
+by this XSUB contains a comment like C</*scope*/> then scoping will
+automatically be enabled for that XSUB.
+
+To enable scoping:
+
+ SCOPE: ENABLE
+
+To disable scoping:
+
+ SCOPE: DISABLE
+
+=head2 The INPUT: Keyword
+
+The XSUB's parameters are usually evaluated immediately after entering the
+XSUB. The INPUT: keyword can be used to force those parameters to be
+evaluated a little later. The INPUT: keyword can be used multiple times
+within an XSUB and can be used to list one or more input variables. This
+keyword is used with the PREINIT: keyword.
+
+The following example shows how the input parameter C<timep> can be
+evaluated late, after a PREINIT.
+
+ bool_t
+ rpcb_gettime(host,timep)
+ char *host
+ PREINIT:
+ time_t tt;
+ INPUT:
+ time_t timep
+ CODE:
+ RETVAL = rpcb_gettime( host, &tt );
+ timep = tt;
+ OUTPUT:
+ timep
+ RETVAL
+
+The next example shows each input parameter evaluated late.
+
+ bool_t
+ rpcb_gettime(host,timep)
+ PREINIT:
+ time_t tt;
+ INPUT:
+ char *host
+ PREINIT:
+ char *h;
+ INPUT:
+ time_t timep
+ CODE:
+ h = host;
+ RETVAL = rpcb_gettime( h, &tt );
+ timep = tt;
+ OUTPUT:
+ timep
+ RETVAL
+
=head2 Variable-length Parameter Lists
XSUBs can have variable-length parameter lists by specifying an ellipsis
bool_t
rpcb_gettime(timep, ...)
time_t timep = NO_INIT
- CODE:
- {
+ PREINIT:
char *host = "localhost";
-
- if( items > 1 )
- host = (char *)SvPV(ST(1), na);
- RETVAL = rpcb_gettime( host, &timep );
- }
+ CODE:
+ if( items > 1 )
+ host = (char *)SvPV(ST(1), na);
+ RETVAL = rpcb_gettime( host, &timep );
OUTPUT:
timep
RETVAL
void
rpcb_gettime(host)
char *host
- PPCODE:
- {
+ PREINIT:
time_t timep;
bool_t status;
+ PPCODE:
status = rpcb_gettime( host, &timep );
EXTEND(sp, 2);
PUSHs(sv_2mortal(newSViv(status)));
PUSHs(sv_2mortal(newSViv(timep)));
- }
Notice that the programmer must supply the C code necessary
to have the real rpcb_gettime() function called and to have
=head2 Returning Undef And Empty Lists
-Occasionally the programmer will want to simply return
+Occasionally the programmer will want to return simply
C<undef> or an empty list if a function fails rather than a
separate status value. The rpcb_gettime() function offers
just this situation. If the function succeeds we would like
$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
- CODE:
- {
+ PREINIT:
time_t timep;
bool_t x;
+ CODE:
ST(0) = sv_newmortal();
if( rpcb_gettime( host, &timep ) )
sv_setnv( ST(0), (double)timep);
- }
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
- CODE:
- {
+ PREINIT:
time_t timep;
bool_t x;
+ CODE:
ST(0) = sv_newmortal();
if( rpcb_gettime( host, &timep ) ){
sv_setnv( ST(0), (double)timep);
else{
ST(0) = &sv_undef;
}
- }
To return an empty list one must use a PPCODE: block and
then not push return values on the stack.
void
rpcb_gettime(host)
char *host
- PPCODE:
- {
+ PREINIT:
time_t timep;
+ PPCODE:
if( rpcb_gettime( host, &timep ) )
PUSHs(sv_2mortal(newSViv(timep)));
else{
/* Nothing pushed on stack, so an empty */
/* list is implicitly returned. */
}
- }
+
+Some people may be inclined to include an explicit C<return> in the above
+XSUB, rather than letting control fall through to the end. In those
+situations C<XSRETURN_EMPTY> should be used, instead. This will ensure that
+the XSUB stack is properly adjusted. Consult L<perlguts/"API LISTING"> for
+other C<XSRETURN> macros.
=head2 The REQUIRE: Keyword
The REQUIRE: keyword is used to indicate the minimum version of the
B<xsubpp> compiler needed to compile the XS module. An XS module which
-contains the following statement will only compile with B<xsubpp> version
+contains the following statement will compile with only B<xsubpp> version
1.922 or greater:
REQUIRE: 1.922
# bootstrap function executes.
printf("Hello from the bootstrap!\n");
+=head2 The VERSIONCHECK: Keyword
+
+The VERSIONCHECK: keyword corresponds to B<xsubpp>'s C<-versioncheck> and
+C<-noversioncheck> options. This keyword overrides the command line
+options. Version checking is enabled by default. When version checking is
+enabled the XS module will attempt to verify that its version matches the
+version of the PM module.
+
+To enable version checking:
+
+ VERSIONCHECK: ENABLE
+
+To disable version checking:
+
+ VERSIONCHECK: DISABLE
+
+=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.
+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.
+
+To enable prototypes:
+
+ PROTOTYPES: ENABLE
+
+To disable prototypes:
+
+ PROTOTYPES: DISABLE
+
+=head2 The PROTOTYPE: Keyword
+
+This keyword is similar to the PROTOTYPES: keyword above but can be used to
+force B<xsubpp> to use a specific prototype for the XSUB. This keyword
+overrides all other prototype options and keywords but affects only the
+current XSUB. Consult L<perlsub/Prototypes> for information about Perl
+prototypes.
+
+ bool_t
+ rpcb_gettime(timep, ...)
+ time_t timep = NO_INIT
+ PROTOTYPE: $;$
+ PREINIT:
+ char *host = "localhost";
+ CODE:
+ if( items > 1 )
+ host = (char *)SvPV(ST(1), na);
+ RETVAL = rpcb_gettime( host, &timep );
+ OUTPUT:
+ timep
+ RETVAL
+
+=head2 The ALIAS: Keyword
+
+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
+index of the alias which was used. When the XSUB is called with its
+declared name C<ix> will be 0.
+
+The following example will create aliases C<FOO::gettime()> and
+C<BAR::getit()> for this function.
+
+ bool_t
+ rpcb_gettime(host,timep)
+ char *host
+ time_t &timep
+ ALIAS:
+ FOO::gettime = 1
+ BAR::getit = 2
+ INIT:
+ printf("# ix = %d\n", ix );
+ OUTPUT:
+ timep
+
+=head2 The INCLUDE: Keyword
+
+This keyword can be used to pull other files into the XS module. The other
+files may have XS code. INCLUDE: can also be used to run a command to
+generate the XS code to be pulled into the module.
+
+The file F<Rpcb1.xsh> contains our C<rpcb_gettime()> function:
+
+ bool_t
+ rpcb_gettime(host,timep)
+ char *host
+ time_t &timep
+ OUTPUT:
+ timep
+
+The XS module can use INCLUDE: to pull that file into it.
+
+ INCLUDE: Rpcb1.xsh
+
+If the parameters to the INCLUDE: keyword are followed by a pipe (C<|>) then
+the compiler will interpret the parameters as a command.
+
+ INCLUDE: cat Rpcb1.xsh |
+
+=head2 The CASE: Keyword
+
+The CASE: keyword allows an XSUB to have multiple distinct parts with each
+part acting as a virtual XSUB. CASE: is greedy and if it is used then all
+other XS keywords must be contained within a CASE:. This means nothing may
+precede the first CASE: in the XSUB and anything following the last CASE: is
+included in that case.
+
+A CASE: might switch via a parameter of the XSUB, via the C<ix> ALIAS:
+variable (see L<"The ALIAS: Keyword">), or maybe via the C<items> variable
+(see L<"Variable-length Parameter Lists">). The last CASE: becomes the
+B<default> case if it is not associated with a conditional. The following
+example shows CASE switched via C<ix> with a function C<rpcb_gettime()>
+having an alias C<x_gettime()>. When the function is called as
+C<rpcb_gettime()> its parameters are the usual C<(char *host, time_t *timep)>,
+but when the function is called as C<x_gettime()> its parameters are
+reversed, C<(time_t *timep, char *host)>.
+
+ long
+ rpcb_gettime(a,b)
+ CASE: ix == 1
+ ALIAS:
+ x_gettime = 1
+ INPUT:
+ # 'a' is timep, 'b' is host
+ char *b
+ time_t a = NO_INIT
+ CODE:
+ RETVAL = rpcb_gettime( b, &a );
+ OUTPUT:
+ a
+ RETVAL
+ CASE:
+ # 'a' is host, 'b' is timep
+ char *a
+ time_t &b = NO_INIT
+ OUTPUT:
+ b
+ RETVAL
+
+That function can be called with either of the following statements. Note
+the different argument lists.
+
+ $status = rpcb_gettime( $host, $timep );
+
+ $status = x_gettime( $timep, $host );
+
+=head2 The & Unary Operator
+
+The & unary operator is used to tell the compiler that it should dereference
+the object when it calls the C function. This is used when a CODE: block is
+not used and the object is a not a pointer type (the object is an C<int> or
+C<long> but not a C<int*> or C<long*>).
+
+The following XSUB will generate incorrect C code. The xsubpp compiler will
+turn this into code which calls C<rpcb_gettime()> with parameters C<(char
+*host, time_t timep)>, but the real C<rpcb_gettime()> wants the C<timep>
+parameter to be of type C<time_t*> rather than C<time_t>.
+
+ bool_t
+ rpcb_gettime(host,timep)
+ char *host
+ time_t timep
+ OUTPUT:
+ timep
+
+That problem is corrected by using the C<&> operator. The xsubpp compiler
+will now turn this into code which calls C<rpcb_gettime()> correctly with
+parameters C<(char *host, time_t *timep)>. It does this by carrying the
+C<&> through, so the function call looks like C<rpcb_gettime(host, &timep)>.
+
+ bool_t
+ rpcb_gettime(host,timep)
+ char *host
+ time_t &timep
+ OUTPUT:
+ timep
+
=head2 Inserting Comments and C Preprocessor Directives
-Comments and C preprocessor directives are allowed within
-CODE:, PPCODE:, BOOT:, and CLEANUP: blocks. The compiler
-will pass the preprocessor directives through untouched and
-will remove the commented lines. Comments can be added to
-XSUBs by placing a C<#> at the beginning of the line. Care
-should be taken to avoid making the comment look like a C
-preprocessor directive, lest it be interpreted as such.
+C preprocessor directives are allowed within BOOT:, PREINIT: INIT:,
+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.
+
+Comments can be added to XSUBs by placing a C<#> as the first
+non-whitespace of a line. Care should be taken to avoid making the
+comment look like a C preprocessor directive, lest it be interpreted as
+such. The simplest way to prevent this is to put whitespace in front of
+the C<#>.
+
+If you use preprocessor directives to choose one of two
+versions of a function, use
+
+ #if ... version1
+ #else /* ... version2 */
+ #endif
+
+and not
+
+ #if ... version1
+ #endif
+ #if ... version2
+ #endif
+
+because otherwise xsubpp will believe that you made a duplicate
+definition of the function. Also, put a blank line before the
+#else/#endif so it will not be seen as part of the function body.
=head2 Using XS With C++
If the method is defined as static it will call the C++
function using the class::method() syntax. If the method is not static
-the function will be called using the THIS->method() syntax.
+the function will be called using the THIS-E<gt>method() syntax.
The next examples will use the following C++ class.
- class colors {
+ class color {
public:
- colors();
- ~colors();
+ color();
+ ~color();
int blue();
void set_blue( int );
MODULE = RPC PACKAGE = RPC
- void
+ SV *
rpcb_gettime(host="localhost")
char *host
- CODE:
- {
+ PREINIT:
time_t timep;
+ CODE:
ST(0) = sv_newmortal();
if( rpcb_gettime( host, &timep ) )
sv_setnv( ST(0), (double)timep );
- }
Netconfig *
getnetconfigent(netid="udp")
print "netconf = $netconf\n";
+=head1 XS VERSION
+
+This document covers features supported by C<xsubpp> 1.935.
+
=head1 AUTHOR
-Dean Roehrich F<E<lt>roehrich@cray.comE<gt>>
-Dec 10, 1995
+Dean Roehrich <F<roehrich@cray.com>>
+Jul 8, 1996
projects / p5sagit/p5-mst-13.2.git / blobdiff