How to Call C/C++ Code from Python Using ctypes

When Python performance becomes a bottleneck, you can embed C/C++ code by compiling it into a shared library and loading it with the ctypes module.

The process consists of three steps: write the C/C++ implementation, compile it as a dynamic library, and invoke the library functions from Python.

Calling a C function – compile called_c.c with gcc -o libpycall.so -shared -fPIC called_c.c to produce libpycall.so, then load it in Python and call foo:

import ctypes
dll = ctypes.cdll.LoadLibrary
lib = dll('./libpycall.so')
lib.foo(1, 3)

The program prints a:1, b:3.

Calling a C++ class – wrap the class methods in an extern "C" block, compile with g++ -o libpycallcpp.so -shared -fPIC cpp_called.cpp, and use ctypes to call the exported functions:

import ctypes
dll = ctypes.cdll.LoadLibrary
lib = dll('./libpycallcpp.so')
lib.display()
lib.display_int(0)

The output is:

First display
Second display:0

This tutorial demonstrates the basic workflow; more advanced usage can be added later.