it would be a good idea to have read the following two documents -
L<perlxs> and L<perlguts>.
-=head1 THE PERL_CALL FUNCTIONS
+=head1 THE CALL_ FUNCTIONS
Although this stuff is easier to explain using examples, you first need
be aware of a few important definitions.
Perl has a number of C functions that allow you to call Perl
subroutines. They are
- I32 perl_call_sv(SV* sv, I32 flags) ;
- I32 perl_call_pv(char *subname, I32 flags) ;
- I32 perl_call_method(char *methname, I32 flags) ;
- I32 perl_call_argv(char *subname, I32 flags, register char **argv) ;
+ I32 call_sv(SV* sv, I32 flags) ;
+ I32 call_pv(char *subname, I32 flags) ;
+ I32 call_method(char *methname, I32 flags) ;
+ I32 call_argv(char *subname, I32 flags, register char **argv) ;
-The key function is I<perl_call_sv>. All the other functions are
+The key function is I<call_sv>. All the other functions are
fairly simple wrappers which make it easier to call Perl subroutines in
-special cases. At the end of the day they will all call I<perl_call_sv>
+special cases. At the end of the day they will all call I<call_sv>
to invoke the Perl subroutine.
-All the I<perl_call_*> functions have a C<flags> parameter which is
+All the I<call_*> functions have a C<flags> parameter which is
used to pass a bit mask of options to Perl. This bit mask operates
identically for each of the functions. The settings available in the
bit mask are discussed in L<FLAG VALUES>.
=over 5
-=item perl_call_sv
+=item call_sv
-I<perl_call_sv> takes two parameters, the first, C<sv>, is an SV*.
+I<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
C string (which has first been converted to an SV) or a reference to a
-subroutine. The section, I<Using perl_call_sv>, shows how you can make
-use of I<perl_call_sv>.
+subroutine. The section, I<Using call_sv>, shows how you can make
+use of I<call_sv>.
-=item perl_call_pv
+=item call_pv
-The function, I<perl_call_pv>, is similar to I<perl_call_sv> except it
+The function, I<call_pv>, is similar to I<call_sv> except it
expects its first parameter to be a C char* which identifies the Perl
-subroutine you want to call, e.g., C<perl_call_pv("fred", 0)>. If the
+subroutine you want to call, e.g., C<call_pv("fred", 0)>. If the
subroutine you want to call is in another package, just include the
package name in the string, e.g., C<"pkg::fred">.
-=item perl_call_method
+=item call_method
-The function I<perl_call_method> is used to call a method from a Perl
+The function I<call_method> is used to call a method from a Perl
class. The parameter C<methname> corresponds to the name of the method
to be called. Note that the class that the method belongs to is passed
on the Perl stack rather than in the parameter list. This class can be
either the name of the class (for a static method) or a reference to an
object (for a virtual method). See L<perlobj> for more information on
-static and virtual methods and L<Using perl_call_method> for an example
-of using I<perl_call_method>.
+static and virtual methods and L<Using call_method> for an example
+of using I<call_method>.
-=item perl_call_argv
+=item call_argv
-I<perl_call_argv> calls the Perl subroutine specified by the C string
+I<call_argv> calls the Perl subroutine specified by the C string
stored in the C<subname> parameter. It also takes the usual C<flags>
parameter. The final parameter, C<argv>, consists of a NULL terminated
list of C strings to be passed as parameters to the Perl subroutine.
-See I<Using perl_call_argv>.
+See I<Using call_argv>.
=back
=head1 FLAG VALUES
-The C<flags> parameter in all the I<perl_call_*> functions is a bit mask
+The C<flags> parameter in all the I<call_*> functions is a bit mask
which can consist of any combination of the symbols defined below,
OR'ed together.
=back
-The value returned by the I<perl_call_*> function indicates how many
+The value returned by the I<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
-context flag setting for all the I<perl_call_*> functions.
+context flag setting for all the I<call_*> functions.
This flag has 2 effects:
=back
-The value returned by the I<perl_call_*> function indicates how many
+The value returned by the I<call_*> function indicates how many
items have been returned by the Perl subroutine - in this case it will
be either 0 or 1.
accessible from the stack - think of the case where only one value is
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
+I<call_*> function. The section I<Returning a list in a scalar
context> shows an example of this behavior.
=item 1.
-It indicates to the subroutine being called that it is executing in an
-array context (if it executes I<wantarray> the result will be true).
+It indicates to the subroutine being called that it is executing in a
+list context (if it executes I<wantarray> the result will be true).
=item 2.
It ensures that all items returned from the subroutine will be
-accessible when control returns from the I<perl_call_*> function.
+accessible when control returns from the I<call_*> function.
=back
-The value returned by the I<perl_call_*> function indicates how many
+The value returned by the I<call_*> function indicates how many
items have been returned by the Perl subroutine.
If 0, then you have specified the G_DISCARD flag.
=head2 G_DISCARD
-By default, the I<perl_call_*> functions place the items returned from
+By default, the I<call_*> functions place the items returned from
by the Perl subroutine on the stack. If you are not interested in
these items, then setting this flag will make Perl get rid of them
automatically for you. Note that it is still possible to indicate a
=head2 G_NOARGS
-Whenever a Perl subroutine is called using one of the I<perl_call_*>
+Whenever a Perl subroutine is called using one of the I<call_*>
functions, it is assumed by default that parameters are to be passed to
the subroutine. If you are not passing any parameters to the Perl
subroutine, you can save a bit of time by setting this flag. It has
In fact, what can happen is that the Perl subroutine you have called
can access the C<@_> array from a previous Perl subroutine. This will
-occur when the code that is executing the I<perl_call_*> function has
+occur when the code that is executing the I<call_*> function has
itself been called from another Perl subroutine. The code below
illustrates this
type of event, specify the G_EVAL flag. It will put an I<eval { }>
around the subroutine call.
-Whenever control returns from the I<perl_call_*> function you need to
+Whenever control returns from the I<call_*> function you need to
check the C<$@> variable as you would in a normal Perl script.
-The value returned from the I<perl_call_*> function is dependent on
+The value returned from the I<call_*> function is dependent on
what other flags have been specified and whether an error has
occurred. Here are all the different cases that can occur:
=item *
-If the I<perl_call_*> function returns normally, then the value
+If the I<call_*> function returns normally, then the value
returned is as specified in the previous sections.
=item *
append any new errors to any existing value of C<$@>.
The G_KEEPERR flag is meant to be used in conjunction with G_EVAL in
-I<perl_call_*> functions that are used to implement such code. This flag
+I<call_*> functions that are used to implement such code. This flag
has no effect when G_EVAL is not used.
When G_KEEPERR is used, any errors in the called code will be prefixed
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_V> macro, which returns
-C<G_ARRAY> if you have been called in an array context, C<G_SCALAR> if
+C<G_ARRAY> if you have been called in a list 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
=head1 KNOWN PROBLEMS
This section outlines all known problems that exist in the
-I<perl_call_*> functions.
+I<call_*> functions.
=over 5
Specifically, if the two flags are used when calling a subroutine and
that subroutine does not call I<die>, the value returned by
-I<perl_call_*> will be wrong.
+I<call_*> will be wrong.
=item 2.
-In Perl 5.000 and 5.001 there is a problem with using I<perl_call_*> if
+In Perl 5.000 and 5.001 there is a problem with using I<call_*> if
the Perl sub you are calling attempts to trap a I<die>.
The symptom of this problem is that the called Perl sub will continue
Call_fred()
CODE:
PUSHMARK(SP) ;
- perl_call_pv("fred", G_DISCARD|G_NOARGS) ;
+ call_pv("fred", G_DISCARD|G_NOARGS) ;
fprintf(stderr, "back in Call_fred\n") ;
When C<Call_fred> is executed it will print
string will not get printed.
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
+higher, or use the G_EVAL flag with I<call_*> as shown below
void
Call_fred()
CODE:
PUSHMARK(SP) ;
- perl_call_pv("fred", G_EVAL|G_DISCARD|G_NOARGS) ;
+ call_pv("fred", G_EVAL|G_DISCARD|G_NOARGS) ;
fprintf(stderr, "back in Call_fred\n") ;
=back
to any changes made to Perl in the future.
Another point worth noting is that in the first series of examples I
-have made use of only the I<perl_call_pv> function. This has been done
+have made use of only the I<call_pv> function. This has been done
to keep the code simpler and ease you into the topic. Wherever
-possible, if the choice is between using I<perl_call_pv> and
-I<perl_call_sv>, you should always try to use I<perl_call_sv>. See
-I<Using perl_call_sv> for details.
+possible, if the choice is between using I<call_pv> and
+I<call_sv>, you should always try to use I<call_sv>. See
+I<Using call_sv> for details.
=head2 No Parameters, Nothing returned
dSP ;
PUSHMARK(SP) ;
- perl_call_pv("PrintUID", G_DISCARD|G_NOARGS) ;
+ call_pv("PrintUID", G_DISCARD|G_NOARGS) ;
}
Simple, eh.
We aren't interested in anything returned from I<PrintUID>, so
G_DISCARD is specified. Even if I<PrintUID> was changed to
return some value(s), having specified G_DISCARD will mean that they
-will be wiped by the time control returns from I<perl_call_pv>.
+will be wiped by the time control returns from I<call_pv>.
=item 4.
-As I<perl_call_pv> is being used, the Perl subroutine is specified as a
+As I<call_pv> is being used, the Perl subroutine is specified as a
C string. In this case the subroutine name has been 'hard-wired' into the
code.
=item 5.
Because we specified G_DISCARD, it is not necessary to check the value
-returned from I<perl_call_pv>. It will always be 0.
+returned from I<call_pv>. It will always be 0.
=back
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
- perl_call_pv("LeftString", G_DISCARD);
+ call_pv("LeftString", G_DISCARD);
FREETMPS ;
LEAVE ;
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<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>
+the same as our local copy. If we didn't do this I<call_pv>
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 4.
-The only flag specified this time is G_DISCARD. Because we are passing 2
-parameters to the Perl subroutine this time, we have not specified
-G_NOARGS.
-
-=item 5.
-
Next, we come to XPUSHs. This is where the parameters actually get
pushed onto the stack. In this case we are pushing a string and an
integer.
See L<perlguts/"XSUBs and the Argument Stack"> for details
on how the XPUSH macros work.
-=item 6.
+=item 5.
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.
See the section I<Using Perl to dispose of temporaries> for details of
an alternative to using these macros.
-=item 7.
+=item 6.
-Finally, I<LeftString> can now be called via the I<perl_call_pv>
-function.
+Finally, I<LeftString> can now be called via the I<call_pv> function.
+The only flag specified this time is G_DISCARD. Because we are passing
+2 parameters to the Perl subroutine this time, we have not specified
+G_NOARGS.
=back
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
- count = perl_call_pv("Adder", G_SCALAR);
+ count = call_pv("Adder", G_SCALAR);
SPAGAIN ;
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
-still exist after the call to I<perl_call_pv>.
+still exist after the call to I<call_pv>.
=item 2.
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
-I<perl_call_pv> call.
+I<call_pv> call.
If you are making use of the Perl stack pointer in your code you must
always refresh the local copy using SPAGAIN whenever you make use
-of the I<perl_call_*> functions or any other Perl internal function.
+of the I<call_*> functions or any other Perl internal function.
=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>
+it is still good practice to check the return code from I<call_pv>
anyway.
Expecting a single value is not quite the same as knowing that there
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
- count = perl_call_pv("AddSubtract", G_ARRAY);
+ count = call_pv("AddSubtract", G_ARRAY);
SPAGAIN ;
=item 1.
-We wanted array context, so G_ARRAY was used.
+We wanted list context, so G_ARRAY was used.
=item 2.
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
- count = perl_call_pv("AddSubtract", G_SCALAR);
+ count = call_pv("AddSubtract", G_SCALAR);
SPAGAIN ;
XPUSHs(svb);
PUTBACK ;
- count = perl_call_pv("Inc", G_DISCARD);
+ count = call_pv("Inc", G_DISCARD);
if (count != 0)
croak ("call_Inc: expected 0 values from 'Inc', got %d\n",
}
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
+after they return from I<call_pv> it is necessary to make a note
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
-the time control returns from I<perl_call_pv>.
+the time control returns from I<call_pv>.
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
- count = perl_call_pv("Subtract", G_EVAL|G_SCALAR);
+ count = call_pv("Subtract", G_EVAL|G_SCALAR);
SPAGAIN ;
Note that the stack is popped using C<POPs> in the block where
C<SvTRUE(ERRSV)> is true. This is necessary because whenever a
-I<perl_call_*> function invoked with G_EVAL|G_SCALAR returns an error,
+I<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
the stack is tidied up by removing the I<undef>.
This example will fail to recognize that an error occurred inside the
C<eval {}>. Here's why: the call_Subtract code got executed while perl
was cleaning up temporaries when exiting the eval block, and because
-call_Subtract is implemented with I<perl_call_pv> using the G_EVAL
+call_Subtract is implemented with I<call_pv> using the G_EVAL
flag, it promptly reset C<$@>. This results in the failure of the
outermost test for C<$@>, and thereby the failure of the error trap.
-Appending the G_KEEPERR flag, so that the I<perl_call_pv> call in
+Appending the G_KEEPERR flag, so that the I<call_pv> call in
call_Subtract reads:
- count = perl_call_pv("Subtract", G_EVAL|G_SCALAR|G_KEEPERR);
+ count = call_pv("Subtract", G_EVAL|G_SCALAR|G_KEEPERR);
will preserve the error and restore reliable error handling.
-=head2 Using perl_call_sv
+=head2 Using call_sv
In all the previous examples I have 'hard-wired' the name of the Perl
subroutine to be called from C. Most of the time though, it is more
char * name
CODE:
PUSHMARK(SP) ;
- perl_call_pv(name, G_DISCARD|G_NOARGS) ;
+ call_pv(name, G_DISCARD|G_NOARGS) ;
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.
+This is where I<call_sv> is useful.
The code below for I<CallSubSV> is identical to I<CallSubPV> except
that the C<name> parameter is now defined as an SV* and we use
-I<perl_call_sv> instead of I<perl_call_pv>.
+I<call_sv> instead of I<call_pv>.
void
CallSubSV(name)
SV * name
CODE:
PUSHMARK(SP) ;
- perl_call_sv(name, G_DISCARD|G_NOARGS) ;
+ call_sv(name, G_DISCARD|G_NOARGS) ;
Because we are using an SV to call I<fred> the following can all be used
CallSubSV($ref) ;
CallSubSV( sub { print "Hello there\n" } ) ;
-As you can see, I<perl_call_sv> gives you much greater flexibility in
+As you can see, I<call_sv> gives you much greater flexibility in
how you can specify the Perl subroutine.
You should note that if it is necessary to store the SV (C<name> in the
CallSavedSub1()
CODE:
PUSHMARK(SP) ;
- perl_call_sv(rememberSub, G_DISCARD|G_NOARGS) ;
+ call_sv(rememberSub, G_DISCARD|G_NOARGS) ;
The reason this is wrong is that by the time you come to use the
pointer C<rememberSub> in C<CallSavedSub1>, it may or may not still refer
CallSavedSub2()
CODE:
PUSHMARK(SP) ;
- perl_call_sv(keepSub, G_DISCARD|G_NOARGS) ;
+ call_sv(keepSub, G_DISCARD|G_NOARGS) ;
To avoid creating a new SV every time C<SaveSub2> is called,
the function first checks to see if it has been called before. If not,
the existing SV, C<keepSub>, is overwritten with the new value using
C<SvSetSV>.
-=head2 Using perl_call_argv
+=head2 Using call_argv
Here is a Perl subroutine which prints whatever parameters are passed
to it.
foreach (@list) { print "$_\n" }
}
-and here is an example of I<perl_call_argv> which will call
+and here is an example of I<call_argv> which will call
I<PrintList>.
static char * words[] = {"alpha", "beta", "gamma", "delta", NULL} ;
{
dSP ;
- perl_call_argv("PrintList", G_DISCARD, words) ;
+ call_argv("PrintList", G_DISCARD, words) ;
}
Note that it is not necessary to call C<PUSHMARK> in this instance.
-This is because I<perl_call_argv> will do it for you.
+This is because I<call_argv> will do it for you.
-=head2 Using perl_call_method
+=head2 Using call_method
Consider the following Perl code
XPUSHs(sv_2mortal(newSViv(index))) ;
PUTBACK;
- perl_call_method(method, G_DISCARD) ;
+ call_method(method, G_DISCARD) ;
void
call_PrintID(class, method)
XPUSHs(sv_2mortal(newSVpv(class, 0))) ;
PUTBACK;
- perl_call_method(method, G_DISCARD) ;
+ call_method(method, G_DISCARD) ;
So the methods C<PrintID> and C<Display> can be invoked like this
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
-parameter to I<perl_call_method>.
+parameter to I<call_method>.
=head2 Using GIMME_V
=head2 Using Perl to dispose of temporaries
In the examples given to date, any temporaries created in the callback
-(i.e., parameters passed on the stack to the I<perl_call_*> function or
+(i.e., parameters passed on the stack to the I<call_*> function or
values returned via the stack) have been freed by one of these methods
=over 5
=item *
-specifying the G_DISCARD flag with I<perl_call_*>.
+specifying the G_DISCARD flag with I<call_*>.
=item *
...
error occurs
...
- external library --> perl_call --> perl
+ external library --> call_* --> perl
|
- perl <-- XSUB <-- external library <-- perl_call <----+
+ perl <-- XSUB <-- external library <-- call_* <----+
-After processing of the error using I<perl_call_*> is completed,
+After processing of the error using I<call_*> is completed,
control reverts back to Perl more or less immediately.
In the diagram, the further right you go the more deeply nested the
perl --> XSUB --> event handler
...
- event handler --> perl_call --> perl
+ event handler --> call_* --> perl
|
- event handler <-- perl_call <----+
+ event handler <-- call_* <----+
...
- event handler --> perl_call --> perl
+ event handler --> call_* --> perl
|
- event handler <-- perl_call <----+
+ event handler <-- call_* <----+
...
- event handler --> perl_call --> perl
+ event handler --> call_* --> perl
|
- event handler <-- perl_call <----+
+ event handler <-- call_* <----+
In this case the flow of control can consist of only the repeated
sequence
- event handler --> perl_call --> perl
+ event handler --> call_* --> perl
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
PUSHMARK(SP) ;
/* Call the Perl sub to process the callback */
- perl_call_sv(callback, G_DISCARD) ;
+ call_sv(callback, G_DISCARD) ;
}
PUTBACK ;
/* Call the Perl sub */
- perl_call_sv(*sv, G_DISCARD) ;
+ call_sv(*sv, G_DISCARD) ;
}
For completeness, here is C<asynch_close>. This shows how to remove
PUTBACK ;
/* Call the Perl sub */
- perl_call_sv(Map[index].PerlSub, G_DISCARD) ;
+ call_sv(Map[index].PerlSub, G_DISCARD) ;
}
static void
XPUSHs(sv_2mortal(newSViv(b)));
PUTBACK ;
- count = perl_call_pv("AddSubtract", G_ARRAY);
+ count = call_pv("AddSubtract", G_ARRAY);
SPAGAIN ;
SP -= count ;
=head2 Creating and calling an anonymous subroutine in C
-As we've already shown, C<perl_call_sv> can be used to invoke an
+As we've already shown, C<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);
+ SV *cvrv = eval_pv("sub { print 'You will not find me cluttering any namespace!' }", TRUE);
...
- perl_call_sv(cvrv, G_VOID|G_NOARGS);
+ 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
+C<eval_pv> is used to compile the anonymous subroutine, which
+will be the return value as well (read more about C<eval_pv> in
+L<perlapi/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
https://perl5.git.perl.org / perl5.git / blobdiff