OR'ed together.
+=head2 G_VOID
+
+Calls the Perl subroutine in a void context.
+
+This flag has 2 effects:
+
+=over 5
+
+=item 1.
+
+It indicates to the subroutine being called that it is executing in
+a void context (if it executes I<wantarray> the result will be the
+undefined value).
+
+=item 2.
+
+It ensures that nothing is actually returned from the subroutine.
+
+=back
+
+The value returned by the I<perl_call_*> function indicates how many
+items have been returned by the Perl subroutine - in this case it will
+be 0.
+
+
=head2 G_SCALAR
Calls the Perl subroutine in a scalar context. This is the default
It indicates to the subroutine being called that it is executing in a
scalar context (if it executes I<wantarray> the result will be false).
-
=item 2.
It ensures that only a scalar is actually returned from the subroutine.
returned as being a list with only one element. Any other items that
were returned will not exist by the time control returns from the
I<perl_call_*> function. The section I<Returning a list in a scalar
-context> shows an example of this behaviour.
+context> shows an example of this behavior.
=head2 G_ARRAY
belongs to C<joe>.
-=head2 G_EVAL
+=head2 G_EVAL
It is possible for the Perl subroutine you are calling to terminate
abnormally, e.g., by calling I<die> explicitly or by not actually
=back
-See I<Using G_EVAL> for details of using G_EVAL.
+See I<Using G_EVAL> for details on using G_EVAL.
=head2 G_KEEPERR
See I<Using G_KEEPERR> for an example of a situation that warrants the
use of this flag.
-=head2 Determining the Context
+=head2 Determining the Context
As mentioned above, you can determine the context of the currently
-executing subroutine in Perl with I<wantarray>. The equivalent test can
-be made in C by using the C<GIMME> macro. This will return C<G_SCALAR>
-if you have been called in a scalar context and C<G_ARRAY> if in an
-array context. An example of using the C<GIMME> macro is shown in
-section I<Using GIMME>.
+executing subroutine in Perl with I<wantarray>. The equivalent test
+can be made in C by using the C<GIMME_V> macro, which returns
+C<G_ARRAY> if you have been called in an array context, C<G_SCALAR> if
+in a scalar context, or C<G_VOID> if in a void context (i.e. the
+return value will not be used). An older version of this macro is
+called C<GIMME>; in a void context it returns C<G_SCALAR> instead of
+C<G_VOID>. An example of using the C<GIMME_V> macro is shown in
+section I<Using GIMME_V>.
=head1 KNOWN PROBLEMS
sub fred
{
eval { die "Fatal Error" ; }
- print "Trapped error: $@\n"
+ print "Trapped error: $@\n"
if $@ ;
}
void
Call_fred()
CODE:
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
perl_call_pv("fred", G_DISCARD|G_NOARGS) ;
fprintf(stderr, "back in Call_fred\n") ;
As control never returns to C<Call_fred>, the C<"back in Call_fred">
string will not get printed.
-To work around this problem, you can either upgrade to Perl 5.002 (or
-later), or use the G_EVAL flag with I<perl_call_*> as shown below
+To work around this problem, you can either upgrade to Perl 5.002 or
+higher, or use the G_EVAL flag with I<perl_call_*> as shown below
void
Call_fred()
CODE:
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
perl_call_pv("fred", G_EVAL|G_DISCARD|G_NOARGS) ;
fprintf(stderr, "back in Call_fred\n") ;
{
dSP ;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
perl_call_pv("PrintUID", G_DISCARD|G_NOARGS) ;
}
=item 1.
-Ignore C<dSP> and C<PUSHMARK(sp)> for now. They will be discussed in
+Ignore C<dSP> and C<PUSHMARK(SP)> for now. They will be discussed in
the next example.
=item 2.
{
dSP ;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSVpv(a, 0)));
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
Parameters are passed to the Perl subroutine using the Perl stack.
This is the purpose of the code beginning with the line C<dSP> and
-ending with the line C<PUTBACK>.
-
+ending with the line C<PUTBACK>. The <dSP> declares a local copy
+of the stack pointer. This local copy should B<always> be accessed
+as C<SP>.
=item 2.
pushed onto the stack. In this case we are pushing a string and an
integer.
-See the L<perlguts/"XSUB's and the Argument Stack"> for details
+See L<perlguts/"XSUBs and the Argument Stack"> for details
on how the XPUSH macros work.
=item 6.
ENTER ;
SAVETMPS;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSViv(a)));
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
=over 5
-=item 1.
+=item 1.
The only flag specified this time was G_SCALAR. That means the C<@_>
array will be created and that the value returned by I<Adder> will
will be limited to those which were created after these calls.
The C<FREETMPS>/C<LEAVE> pair will get rid of any values returned by
-the Perl subroutine, plus it will also dump the mortal SV's we have
+the Perl subroutine, plus it will also dump the mortal SVs we have
created. Having C<ENTER>/C<SAVETMPS> at the beginning of the code
makes sure that no other mortals are destroyed.
The purpose of the macro C<SPAGAIN> is to refresh the local copy of the
stack pointer. This is necessary because it is possible that the memory
-allocated to the Perl stack has been re-allocated whilst in the
+allocated to the Perl stack has been reallocated whilst in the
I<perl_call_pv> call.
If you are making use of the Perl stack pointer in your code you must
-always refresh the your local copy using SPAGAIN whenever you make use
+always refresh the local copy using SPAGAIN whenever you make use
of the I<perl_call_*> functions or any other Perl internal function.
=item 4.
ENTER ;
SAVETMPS;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSViv(a)));
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
ENTER ;
SAVETMPS;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSViv(a)));
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
Value 1 = 3
In this case the main point to note is that only the last item in the
-list returned from the subroutine, I<Adder> actually made it back to
+list is returned from the subroutine, I<AddSubtract> actually made it back to
I<call_AddSubScalar>.
sva = sv_2mortal(newSViv(a)) ;
svb = sv_2mortal(newSViv(b)) ;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sva);
XPUSHs(svb);
PUTBACK ;
ENTER ;
SAVETMPS;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSViv(a)));
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
=item 2.
-The code
+The code
if (SvTRUE(GvSV(errgv)))
{
package Foo;
sub new { bless {}, $_[0] }
- sub Subtract {
+ sub Subtract {
my($a,$b) = @_;
die "death can be fatal" if $a < $b ;
$a - $b;
CallSubPV(name)
char * name
CODE:
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
perl_call_pv(name, G_DISCARD|G_NOARGS) ;
-That is fine as far as it goes. The thing is, the Perl subroutine
+That is fine as far as it goes. The thing is, the Perl subroutine
can be specified as only a string. For Perl 4 this was adequate,
but Perl 5 allows references to subroutines and anonymous subroutines.
This is where I<perl_call_sv> is useful.
CallSubSV(name)
SV * name
CODE:
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
perl_call_sv(name, G_DISCARD|G_NOARGS) ;
Because we are using an SV to call I<fred> the following can all be used
void
CallSavedSub1()
CODE:
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
perl_call_sv(rememberSub, G_DISCARD|G_NOARGS) ;
The reason this is wrong is that by the time you come to use the
CallSavedSub1() ;
By the time each of the C<SaveSub1> statements above have been executed,
-the SV*'s which corresponded to the parameters will no longer exist.
+the SV*s which corresponded to the parameters will no longer exist.
Expect an error message from Perl of the form
Can't use an undefined value as a subroutine reference at ...
for each of the C<CallSavedSub1> lines.
-Similarly, with this code
+Similarly, with this code
$ref = \&fred ;
SaveSub1($ref) ;
$ref = 47 ;
CallSavedSub1() ;
-you can expect one of these messages (which you actually get is dependent on
-the version of Perl you are using)
+you can expect one of these messages (which you actually get is dependent on
+the version of Perl you are using)
Not a CODE reference at ...
Undefined subroutine &main::47 called ...
CallSavedSub1() ;
This time whenever C<CallSavedSub1> get called it will execute the Perl
-subroutine C<joe> (assuming it exists) rather than C<fred> as was
+subroutine C<joe> (assuming it exists) rather than C<fred> as was
originally requested in the call to C<SaveSub1>.
To get around these problems it is necessary to take a full copy of the
void
CallSavedSub2()
CODE:
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
perl_call_sv(keepSub, G_DISCARD|G_NOARGS) ;
To avoid creating a new SV every time C<SaveSub2> is called,
will print
1: green
- This is Class Mine version 1.0
+ This is Class Mine version 1.0
Calling a Perl method from C is fairly straightforward. The following
things are required
char * method
int index
CODE:
- PUSHMARK(sp);
+ PUSHMARK(SP);
XPUSHs(ref);
XPUSHs(sv_2mortal(newSViv(index))) ;
PUTBACK;
char * class
char * method
CODE:
- PUSHMARK(sp);
+ PUSHMARK(SP);
XPUSHs(sv_2mortal(newSVpv(class, 0))) ;
PUTBACK;
the method name is not passed via the stack - it is used as the first
parameter to I<perl_call_method>.
-=head2 Using GIMME
+=head2 Using GIMME_V
-Here is a trivial XSUB which prints the context in which it is
+Here is a trivial XSUB which prints the context in which it is
currently executing.
void
PrintContext()
CODE:
- if (GIMME == G_SCALAR)
+ I32 gimme = GIMME_V;
+ if (gimme == G_VOID)
+ printf ("Context is Void\n") ;
+ else if (gimme == G_SCALAR)
printf ("Context is Scalar\n") ;
else
printf ("Context is Array\n") ;
and here is some Perl to test it
+ PrintContext ;
$a = PrintContext ;
@a = PrintContext ;
The output from that will be
+ Context is Void
Context is Scalar
Context is Array
perl --> XSUB --> event handler
...
- event handler --> perl_call --> perl
+ event handler --> perl_call --> perl
|
- event handler <-- perl_call --<--+
+ event handler <-- perl_call <----+
...
- event handler --> perl_call --> perl
+ event handler --> perl_call --> perl
|
- event handler <-- perl_call --<--+
+ event handler <-- perl_call <----+
...
- event handler --> perl_call --> perl
+ event handler --> perl_call --> perl
|
- event handler <-- perl_call --<--+
+ event handler <-- perl_call <----+
In this case the flow of control can consist of only the repeated
sequence
event handler --> perl_call --> perl
-for the practically the complete duration of the program. This means
-that control may I<never> drop back to the surrounding scope in Perl at
-the extreme left.
+for practically the complete duration of the program. This means that
+control may I<never> drop back to the surrounding scope in Perl at the
+extreme left.
So what is the big problem? Well, if you are expecting Perl to tidy up
those temporaries for you, you might be in for a long wait. For Perl
{
dSP ;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
/* Call the Perl sub to process the callback */
perl_call_sv(callback, G_DISCARD) ;
int fh ;
char * buffer ;
{
- ...
+ ...
}
To provide a Perl interface to this library we need to be able to map
if (sv == (SV**)NULL)
croak("Internal error...\n") ;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSViv(fh))) ;
XPUSHs(sv_2mortal(newSVpv(buffer, 0))) ;
PUTBACK ;
Without the file handle there is no straightforward way to map from the
C callback to the Perl subroutine.
-In this case a possible way around this problem is to pre-define a
+In this case a possible way around this problem is to predefine a
series of C functions to act as the interface to Perl, thus
#define MAX_CB 3
{
dSP ;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSVpv(buffer, 0))) ;
PUTBACK ;
Secondly, there is a hard-wired limit (in this case 3) to the number of
callbacks that can exist simultaneously. The only way to increase the
limit is by modifying the code to add more functions and then
-re-compiling. None the less, as long as the number of functions is
+recompiling. None the less, as long as the number of functions is
chosen with some care, it is still a workable solution and in some
cases is the only one available.
ENTER ;
SAVETMPS;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSViv(a)));
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
count = perl_call_pv("AddSubtract", G_ARRAY);
SPAGAIN ;
- sp -= count ;
- ax = (sp - stack_base) + 1 ;
+ SP -= count ;
+ ax = (SP - stack_base) + 1 ;
if (count != 2)
croak("Big trouble\n") ;
The code
SPAGAIN ;
- sp -= count ;
- ax = (sp - stack_base) + 1 ;
+ SP -= count ;
+ ax = (SP - stack_base) + 1 ;
sets the stack up so that we can use the C<ST> macro.
Unlike the original coding of this example, the returned
values are not accessed in reverse order. So C<ST(0)> refers to the
-first value returned by the Perl subroutine and C<ST(count-1)>
+first value returned by the Perl subroutine and C<ST(count-1)>
refers to the last.
=back
+=head2 Creating and calling an anonymous subroutine in C
+
+As we've already shown, L<perl_call_sv> can be used to invoke an
+anonymous subroutine. However, our example showed how Perl script
+invoking an XSUB to preform this operation. Let's see how it can be
+done inside our C code:
+
+ ...
+
+ SV *cvrv = perl_eval_pv("sub { print 'You will not find me cluttering any namespace!' }", TRUE);
+
+ ...
+
+ perl_call_sv(cvrv, G_VOID|G_NOARGS);
+
+L<perlguts/perl_eval_pv> is used to compile the anonymous subroutine, which
+will be the return value as well. Once this code reference is in hand, it
+can be mixed in with all the previous examples we've shown.
+
=head1 SEE ALSO
L<perlxs>, L<perlguts>, L<perlembed>
=head1 DATE
-Version 1.2, 16th Jan 1996
+Version 1.3, 14th Apr 1997
projects / p5sagit/p5-mst-13.2.git / blobdiff