CODEWITHSUNDEEP
pythonc
Kostas
Kostas

Reputation: 377

Python, get String from C library

I haven't worked with C for many many years now so I'm stuck on how I can get a string back from a simple library and into Python.

test.c

#include <stdlib.h>
#include <string.h>
#include <stdio.h>

char * get_string() {

        char theString[]= "This is my test string!";

        char *myString = malloc ( sizeof(char) * (strlen(theString)) +1 );

        strcpy(myString, theString);

        return myString;
}

I compile the code using:

gcc -Wall -O3 -shared test.c -o test.so

python.py

#!/usr/bin/env python

import ctypes

def main():
    string_lib = ctypes.cdll.LoadLibrary('test.so')
    myString = string_lib.get_string()
    print ctypes.c_char_p(myString).value

if __name__ == '__main__':
    main()

When I run the Python script I get:

Segmentation fault: 11

if I just print the result I get a numeric value which I assume is the pointer... How can I make it work?

Thanks!

Upvotes: 0

Views: 1082

Answers (1)

deets
deets

Reputation: 6395

The problem is that you are using 64 bit Python. This will truncate the returned pointer.

Declare the restype first:

 import ctypes

 def main():
     string_lib = ctypes.cdll.LoadLibrary('test.so')
     string_lib.get_string.restype = ctypes.c_char_p
     myString = string_lib.get_string()
     print myString

 if __name__ == '__main__':
     main()

Upvotes: 2

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