How Python can get binary data(char*) from C++ by SWIG?

Question

I am using C++ functions in Python by SWIG,and I met a problem now. When I pass a char * from C++ to Python, the char * is truncted by Python.

For example:

e

Answer 1

First of all, you should not use char * if you are dealing with binary data (swig thinks that they are normal strings). Instead you should use void *. swig provides a module named 'cdata.i' - you should include this in the interface definition file.

Once you include this, it gives two functions - cdata() and memmove().

• Given a void * and the length of the binary data, cdata() converts it into a string type of the target language.
• memmove() does the reverse - given a string type, it will copy the contents of the string(including embedded null bytes) into the C void* type.

Handling binary data becomes much simpler with this module. I hope this is what you need.

example.i
%module example
%include "cdata.i"
%{
void *fun()
{
        return "abc\0de";
}
%}

test.py
import example
print example.cdata(example.fun(), 6)