How do I use a pointer to char from SWIG, in Perl? - c++

Question

I used SWIG to generate a Perl module for a C++ program. I have one function in the C++ code which returns a "char pointer". Now I dont know how to print or get the returned char pointer in Perl.
Sample C code:
char* result() {
return "i want to get this in perl";
}
I want to invoke this function "result" in Perl and print the string.
How to do that?
Regards,
Anandan

Answer 1

Depending on the complexity of the C++ interface, it may be easier, faster, and more maintainable to skip SWIG and write the XS code yourself. XS&C++ is a bit of an arcane art. That's why there is Mattia Barbon's excellent ExtUtils::XSpp module on CPAN. It make wrapping C++ easy (and almost fun).
The ExtUtils::XSpp distribution includes a very simple (and contrived) example of a class that has a string (char*) and an integer member. Here's what the cut-down interface file could look like:
// This will be used to generate the XS MODULE line
%module{Object::WithIntAndString};
// Associate a perl class with a C++ class
%name{Object::WithIntAndString} class IntAndString
{
// can be called in Perl as Object::WithIntAndString->new( ... );
IntAndString();
// Object::WithIntAndString->newIntAndString( ... );
// %name can be used to assign methods a different name in Perl
%name{newIntAndString} IntAndString( const char* str, int arg );
// standard DESTROY method
~IntAndString();
// Will be available from Perl given that the types appear in the typemap
int GetInt();
const char* GetString ();
// SetValue is polymorphic. We want separate methods in Perl
%name{SetString} void SetValue( const char* arg = NULL );
%name{SetInt} void SetValue( int arg );
};
Note that this still requires a valid XS typemap. It's really simple, so I won't add it here, but you can find it in the example distribution linked above.

Answer 2

You must have referred to the SWIG tutorial at www.swig.org/tutorial.html
Anyways, since you just want to invoke the function the C function from perl,
1. Type your interface file(having all the function declarations in the wrapper and the module sections).
2. Compile with swig and options.
3. Compile with gcc to create the objects.
4. Compile with gcc options to create the shared object.
5. run the program as follows:
perl
use moduleName;
$a = moduleName::result();
[NOTE: Look into the generated module file(.pm) for the correct funvtion prototype which points to the correct function in the wrapper file.]