=over 5
-=item B<perl_call_sv>
+=item perl_call_sv
I<perl_call_sv> takes two parameters, the first, C<sv>, is an SV*.
This allows you to specify the Perl subroutine to be called either as a
subroutine. The section, I<Using perl_call_sv>, shows how you can make
use of I<perl_call_sv>.
-=item B<perl_call_pv>
+=item perl_call_pv
The function, I<perl_call_pv>, is similar to I<perl_call_sv> except it
expects its first parameter to be a C char* which identifies the Perl
subroutine you want to call is in another package, just include the
package name in the string, e.g., C<"pkg::fred">.
-=item B<perl_call_method>
+=item perl_call_method
The function I<perl_call_method> is used to call a method from a Perl
class. The parameter C<methname> corresponds to the name of the method
static and virtual methods and L<Using perl_call_method> for an example
of using I<perl_call_method>.
-=item B<perl_call_argv>
+=item perl_call_argv
I<perl_call_argv> calls the Perl subroutine specified by the C string
stored in the C<subname> parameter. It also takes the usual C<flags>
As a general rule you should I<always> check the return value from
these functions. Even if you are expecting only a particular number of
values to be returned from the Perl subroutine, there is nothing to
-stop someone from doing something unexpected - don't say you haven't
+stop someone from doing something unexpected--don't say you haven't
been warned.
=head1 FLAG VALUES
It is possible for the Perl subroutine you are calling to terminate
abnormally, e.g., by calling I<die> explicitly or by not actually
-existing. By default, when either of these of events occurs, the
-process will terminate immediately. If though, you want to trap this
+existing. By default, when either of these events occurs, the
+process will terminate immediately. If you want to trap this
type of event, specify the G_EVAL flag. It will put an I<eval { }>
around the subroutine call.
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 a scalar context, or C<G_VOID> if in a void context (i.e. the
+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
void
Call_fred()
CODE:
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
perl_call_pv("fred", G_DISCARD|G_NOARGS) ;
fprintf(stderr, "back in Call_fred\n") ;
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.
=head2 Passing Parameters
Now let's make a slightly more complex example. This time we want to
-call a Perl subroutine, C<LeftString>, which will take 2 parameters - a
-string (C<$s>) and an integer (C<$n>). The subroutine will simply
-print the first C<$n> characters of the string.
+call a Perl subroutine, C<LeftString>, which will take 2 parameters--a
+string ($s) and an integer ($n). The subroutine will simply
+print the first $n characters of the string.
So the Perl subroutine would look like this
{
dSP ;
- PUSHMARK(sp) ;
+ ENTER ;
+ SAVETMPS ;
+
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSVpv(a, 0)));
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
perl_call_pv("LeftString", G_DISCARD);
+
+ FREETMPS ;
+ LEAVE ;
}
Here are a few notes on the C function I<call_LeftString>.
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 C<dSP> declares a local copy
+of the stack pointer. This local copy should B<always> be accessed
+as C<SP>.
=item 2.
If you are going to put something onto the Perl stack, you need to know
-where to put it. This is the purpose of the macro C<dSP> - it declares
+where to put it. This is the purpose of the macro C<dSP>--it declares
and initializes a I<local> copy of the Perl stack pointer.
All the other macros which will be used in this example require you to
The exception to this rule is if you are calling a Perl subroutine
directly from an XSUB function. In this case it is not necessary to
-use the C<dSP> macro explicitly - it will be declared for you
+use the C<dSP> macro explicitly--it will be declared for you
automatically.
=item 3.
stack pointer. Even if you aren't passing any parameters (like the
example shown in the section I<No Parameters, Nothing returned>) you
must still call the C<PUSHMARK> macro before you can call any of the
-I<perl_call_*> functions - Perl still needs to know that there are no
+I<perl_call_*> functions--Perl still needs to know that there are no
parameters.
The C<PUTBACK> macro sets the global copy of the stack pointer to be
the same as our local copy. If we didn't do this I<perl_call_pv>
-wouldn't know where the two parameters we pushed were - remember that
+wouldn't know where the two parameters we pushed were--remember that
up to now all the stack pointer manipulation we have done is with our
local copy, I<not> the global copy.
=item 6.
+Because we created temporary values (by means of sv_2mortal() calls)
+we will have to tidy up the Perl stack and dispose of mortal SVs.
+
+This is the purpose of
+
+ ENTER ;
+ SAVETMPS ;
+
+at the start of the function, and
+
+ FREETMPS ;
+ LEAVE ;
+
+at the end. The C<ENTER>/C<SAVETMPS> pair creates a boundary for any
+temporaries we create. This means that the temporaries we get rid of
+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 (see next example), 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.
+
+Think of these macros as working a bit like using C<{> and C<}> in Perl
+to limit the scope of local variables.
+
+See the section I<Using Perl to dispose of temporaries> for details of
+an alternative to using these macros.
+
+=item 7.
+
Finally, I<LeftString> can now be called via the I<perl_call_pv>
function.
ENTER ;
SAVETMPS;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSViv(a)));
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
array will be created and that the value returned by I<Adder> will
still exist after the call to I<perl_call_pv>.
-
-
=item 2.
-Because we are interested in what is returned from I<Adder> we cannot
-specify G_DISCARD. This means that we will have to tidy up the Perl
-stack and dispose of any temporary values ourselves. This is the
-purpose of
-
- ENTER ;
- SAVETMPS ;
-
-at the start of the function, and
-
- FREETMPS ;
- LEAVE ;
-
-at the end. The C<ENTER>/C<SAVETMPS> pair creates a boundary for any
-temporaries we create. This means that the temporaries we get rid of
-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 SVs we have
-created. Having C<ENTER>/C<SAVETMPS> at the beginning of the code
-makes sure that no other mortals are destroyed.
-
-Think of these macros as working a bit like using C<{> and C<}> in Perl
-to limit the scope of local variables.
-
-See the section I<Using Perl to dispose of temporaries> for details of
-an alternative to using these macros.
-
-=item 3.
-
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 reallocated whilst in the
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.
+=item 3.
Although only a single value was expected to be returned from I<Adder>,
it is still good practice to check the return code from I<perl_call_pv>
stack would end up in an inconsistent state. That is something you
I<really> don't want to happen ever.
-=item 5.
+=item 4.
The C<POPi> macro is used here to pop the return value from the stack.
In this case we wanted an integer, so C<POPi> was used.
POPi integer
POPl long
-=item 6.
+=item 5.
The final C<PUTBACK> is used to leave the Perl stack in a consistent
state before exiting the function. This is necessary because when we
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 ;
sva = sv_2mortal(newSViv(a)) ;
svb = sv_2mortal(newSViv(b)) ;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sva);
XPUSHs(svb);
PUTBACK ;
To be able to access the two parameters that were pushed onto the stack
after they return from I<perl_call_pv> it is necessary to make a note
-of their addresses - thus the two variables C<sva> and C<svb>.
+of their addresses--thus the two variables C<sva> and C<svb>.
The reason this is necessary is that the area of the Perl stack which
held them will very likely have been overwritten by something else by
ENTER ;
SAVETMPS;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSViv(a)));
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
SPAGAIN ;
/* Check the eval first */
- if (SvTRUE(GvSV(errgv)))
+ if (SvTRUE(ERRSV))
{
- printf ("Uh oh - %s\n", SvPV(GvSV(errgv), na)) ;
+ STRLEN n_a;
+ printf ("Uh oh - %s\n", SvPV(ERRSV, n_a)) ;
POPs ;
}
else
The code
- if (SvTRUE(GvSV(errgv)))
+ if (SvTRUE(ERRSV))
{
- printf ("Uh oh - %s\n", SvPV(GvSV(errgv), na)) ;
+ STRLEN n_a;
+ printf ("Uh oh - %s\n", SvPV(ERRSV, n_a)) ;
POPs ;
}
print "Uh oh - $@\n" if $@ ;
-C<errgv> is a perl global of type C<GV *> that points to the
-symbol table entry containing the error. C<GvSV(errgv)> therefore
+C<PL_errgv> is a perl global of type C<GV *> that points to the
+symbol table entry containing the error. C<ERRSV> therefore
refers to the C equivalent of C<$@>.
=item 3.
Note that the stack is popped using C<POPs> in the block where
-C<SvTRUE(GvSV(errgv))> is true. This is necessary because whenever a
+C<SvTRUE(ERRSV)> is true. This is necessary because whenever a
I<perl_call_*> function invoked with G_EVAL|G_SCALAR returns an error,
the top of the stack holds the value I<undef>. Because we want the
program to continue after detecting this error, it is essential that
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
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
Not a CODE reference at ...
Undefined subroutine &main::47 called ...
-The variable C<$ref> may have referred to the subroutine C<fred>
+The variable $ref may have referred to the subroutine C<fred>
whenever the call to C<SaveSub1> was made but by the time
C<CallSavedSub1> gets called it now holds the number C<47>. Because we
saved only a pointer to the original SV in C<SaveSub1>, any changes to
-C<$ref> will be tracked by the pointer C<rememberSub>. This means that
+$ref will be tracked by the pointer C<rememberSub>. This means that
whenever C<CallSavedSub1> gets called, it will attempt to execute the
code which is referenced by the SV* C<rememberSub>. In this case
though, it now refers to the integer C<47>, so expect Perl to complain
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,
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;
call_PrintID('Mine', 'PrintID') ;
The only thing to note is that in both the static and virtual methods,
-the method name is not passed via the stack - it is used as the first
+the method name is not passed via the stack--it is used as the first
parameter to I<perl_call_method>.
=head2 Using GIMME_V
never happen. This means that as time goes on, your program will
create more and more temporaries, none of which will ever be freed. As
each of these temporaries consumes some memory your program will
-eventually consume all the available memory in your system - kapow!
+eventually consume all the available memory in your system--kapow!
-So here is the bottom line - if you are sure that control will revert
+So here is the bottom line--if you are sure that control will revert
back to the enclosing Perl scope fairly quickly after the end of your
callback, then it isn't absolutely necessary to dispose explicitly of
any temporaries you may have created. Mind you, if you are at all
{
dSP ;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
/* Call the Perl sub to process the callback */
perl_call_sv(callback, G_DISCARD) ;
the Perl subroutine we want to be called for that file.
Say the i/o library has a function C<asynch_read> which associates a C
-function C<ProcessRead> with a file handle C<fh> - this assumes that it
+function C<ProcessRead> with a file handle C<fh>--this assumes that it
has also provided some routine to open the file and so obtain the file
handle.
if (sv == (SV**)NULL)
croak("Internal error...\n") ;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSViv(fh))) ;
XPUSHs(sv_2mortal(newSVpv(buffer, 0))) ;
PUTBACK ;
{
dSP ;
- PUSHMARK(sp) ;
+ PUSHMARK(SP) ;
XPUSHs(sv_2mortal(newSVpv(buffer, 0))) ;
PUTBACK ;
In this case the functions C<fn1>, C<fn2>, and C<fn3> are used to
remember the Perl subroutine to be called. Each of the functions holds
-a separate hardwired index which is used in the function C<Pcb> to
+a separate hard
-wired index which is used in the function C<Pcb> to
access the C<Map> array and actually call the Perl subroutine.
There are some obvious disadvantages with this technique.
Firstly, the code is considerably more complex than with the previous
example.
-Secondly, there is a hardwired limit (in this case 3) to the number of
+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
recompiling. None the less, as long as the number of functions is
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 - PL_stack_base) + 1 ;
if (count != 2)
croak("Big trouble\n") ;
The code
SPAGAIN ;
- sp -= count ;
- ax = (sp - stack_base) + 1 ;
+ SP -= count ;
+ ax = (SP - PL_stack_base) + 1 ;
sets the stack up so that we can use the C<ST> macro.
=back
+=head2 Creating and calling an anonymous subroutine in C
+
+As we've already shown, C<perl_call_sv> can be used to invoke an
+anonymous subroutine. However, our example showed a Perl script
+invoking an XSUB to perform 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);
+
+C<perl_eval_pv> is used to compile the anonymous subroutine, which
+will be the return value as well (read more about C<perl_eval_pv> in
+L<perlguts/perl_eval_pv>). 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
https://perl5.git.perl.org / perl5.git / blobdiff