Look for perl5/typemaps.i in the SWIG Lib directory, you will find there some samples of how to handle output parameters... just grep for OUTPUT.

Thank you very much for your answers.

But in reply to salva, I seems that perl/swig doesn't understand 'unsigned char *' when I pass a string to my function.

In Perl I wrote this:
$message = 'Hello';
&MyCProgram::CopyString($message);

In my C program I wrote that in order to test simpy test the input (I will need to output something later):
void CopyString(unsigned char *string1) {
FILE *pf;
pf = fopen("test.txt","w+");
fputs(string1,pf);
fclose(pf);
}

And finally we can find this in my interface file:
%apply unsigned char *INPUT { unsigned char *string1 };
extern void CopyString(unsigned char *string1);

When I run my Perl program, I get this error message:
Argument "Hello" isn't numeric in subroutine entry at ./index1.pl line 21.

The problem here is that Perl expects a value and not a string. Ideally I would like to pass only the real address of my string.

Have you got any idea how to solve my problem? Any help is welcomed! Merci beaucoup!

Arnaud

Oh, I see, by default SWIG expects unsigned chars to be numbers, not strings...

Try using the typemaps for "signed char" instead:

%apply signed char *INPUT { unsigned char *string1 };
%apply signed char *OUTPUT { unsigned char *string2 };
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