bytes or integer address expected instead of str instance Python 3 [duplicate]

Question

fib.cpp

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <iostream>
using namespace std;

extern "C" const char *hello (char* b){
static string s = "hello ";
s = s + b;
return s.c_str();
}

wrap.py

import ctypes
_libfib = ctypes.CDLL('./fib.so');

def ctypes_hello(a):
    _libfib.hello.restype = ctypes.c_char_p;
    return _libfib.hello(ctypes.c_char_p(a));

Generate .so files

g++ -std=c++11 -shared -c -fPIC fib.cpp -o fib.o
g++ -std=c++11 -shared -Wl,-soname,fib.so -o fib.so fib.o

Run wrap.py from command line

from wrap import *
ctypes_hello("world")

Its working perfectly with python 2. I am getting Error bytes or integer address expected instead of str instance when I switch to Python 3

mshildt · Accepted Answer · 2017-11-30 14:14:20Z

2

Python 3 differentiates between byte strings and unicode strings. So in Python 3 your "world" string is a sequence of Unicode code points, not a simple byte string. So in Python 3 try:

ctypes_hello(b"world")

To pass a byte string to the function.

answered Nov 30, 2017 at 14:14

mshildt

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