Is it possible to pass a python string by reference through ctypes?

Question

I\'m sorry, but I generally have a hard time reading the current ctypes docs...

If I have a C function that takes a const char * pointer, and I know

Answer 1

The type ctypes.c_char_p represents a nul-terminated string. If a function takes a const char* you can pass a Python string to it and it will receive a nul-terminated version.

A Windows example DLL:

#include 

__declspec(dllexport) char* func(char* a,size_t len,const char* b)
{
    if(strlen(b) * 2 >= len)
        return NULL;
    strcpy_s(a,len,b);
    strcat_s(a,len,b);
    return a;
}

Python:

Python 2.7.1 (r271:86832, Nov 27 2010, 18:30:46) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from ctypes import *
>>> x=CDLL('x')
>>> x.func.restype=c_char_p
>>> x.func.argtypes=[c_char_p,c_int,c_char_p]
>>> s=create_string_buffer(10)
>>> x.func(s,len(s),'abcd')
'abcdabcd'
>>>