Attribute error while using methods from linked libraries in python - c++

Question

I'm trying to use some C++ method in my python code and I'm using ctypes library. I have wrote a simple C++ code using a simple main with no arguments and another simple method named printArgs which takes an argument of type char *. I also have wrote a simple python code to import these two methods. I made two linked libraries(one .so and one .a because I'm using Debian) with this command:
g++ -o hello.so -shared -fPIC hello.cpp
And then used export LD_LIBRARY_PATH=/the/path/to/the/linked/libraries/directory.
There is no problem in getting the main method, bu when I'm trying to get printArgs I get AttributeError. Here's the C++ code:
#include <iostream>
using namespace std;
int printArgs(char * args_array){
for (int i = 0; i < 5; i++){
cout<<i<<"- "<<args_array[i]<<"\n";
}
return 0;
}
int main(){
cout<<"Hello\n";
return 0;
}
Here's the Python code:
from ctypes import *
helloInCPP_lib = cdll.LoadLibrary("hello.a")
print helloInCPP_lib
helloInCPPMain = helloInCPP_lib.main
print helloInCPPMain
helloInCPPPrint = helloInCPP_lib.printArgs
print helloInCPPPrint
I get this output:
<CDLL 'hello.a', handle 9c45488 at b73d1e6c>
<_FuncPtr object at 0xb73e67e4>
Traceback (most recent call last):
File "testHelloInCPP.py", line 9, in <module>
helloInCPPPrint = helloInCPP_lib.printArgs(None)
File "/usr/lib/python2.6/ctypes/__init__.py", line 366, in __getattr__
func = self.__getitem__(name)
File "/usr/lib/python2.6/ctypes/__init__.py", line 371, in __getitem__
func = self._FuncPtr((name_or_ordinal, self))
AttributeError: /etc/linked_libraries/hello.a: undefined symbol: printArgs
I also tried cdll.LoadLibrary("hello.so") and/or helloInCPPPrint = helloInCPP_lib.printArgs(None); got the same error in both conditions. Any idea?
I'm using Debian 32 bit on a VMWare Workstation and Python 2.6.

Answer 1

Declare the printArgs using extern "C":
#include <iostream>
using namespace std;
extern "C" {
int printArgs(char * args_array);
}
int printArgs(char * args_array){
for (int i = 0; i < 5; i++){
cout<<i<<"- "<<args_array[i]<<"\n";
}
}
int main(){
cout<<"Hello\n";
}
BTW, you should pass a string (c_char_p), not None:
...
helloInCPPPrint = helloInCPP_lib.printArgs
helloInCPPPrint.argtypes = [c_char_p]
print helloInCPPPrint("ABCDE")
About argtypes, see Specifying the required argument types (function prototypes).

Answer 2

I tired compiling the solution by #falsetru using
g++ -O3 -shared -std=c++11 -fPIC code.cpp -o lib.so
but could not without this small modification to code.c, according to the link provided in their answer extern "C":
#include <iostream>
using namespace std;
extern "C" int printArgs(char * args_array){
for (int i = 0; i < 5; i++){
cout<<i<<"- "<<args_array[i]<<"\n";
}
}