I am trying to get up and running with using ctypes to call C++ libraries from Python 2.7 on a Linux machine. For the moment, I'm just trying toy examples. I read and was able to replicate the example given in this thread: Calling C/C++ from python?. Note that the C++ class functions take no inputs.
I'm trying to extend this example as follows.
foo.cpp
#include <iostream>
#include <string>
using namespace std;
class Foo {
public:
Foo(string name);
void bar(void);
private:
string myName;
};
Foo::Foo(string name) {
std::cout << "Entered constructor in C++" << std::endl;
myName = name;
}
void Foo::bar(void) {
std::cout << "Hello, this is " << myName << std::endl;
}
extern "C" {
Foo* Foo_new(string name) {return new Foo(name);}
void Foo_bar(Foo* foo) {foo->bar();}
}
The code compiles cleanly using g++ -c -fPIC foo.cpp -o foo.o and then g++ -shared -Wl,-soname,libfoo.so -o libfoo.so foo.o.
I then use the following wrapper,
fooWrapper.py
from ctypes import cdll, c_char_p
lib = cdll.LoadLibrary('./libfoo.so')
class Foo(object):
def __init__(self,name):
self.name = name
self.obj = lib.Foo_new(c_char_p(name))
def bar(self):
lib.Foo_bar(self.obj)
Because I'm passing a string to the constructor, I'm under the impression that I need to cast it using c_char_p. Maybe this is wrong.
When I execute the code in Python 2.7, I get a segmentation fault,
Python 2.7.2 (default, Feb 27 2012, 18:28:19)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import fooWrapper as f
>>> foo = f.Foo('somename')
Segmentation fault
So I never get into the C++ constructor function. I have the same problem whether or not I include the self.name = name line in the constructor method in the Python code.
What am I doing wrong? Thanks.
