How to pass a string to a C library function that accepts char** as an argument?

Table of Contants

Introduction

When working with C libraries in Python using the ctypes module, you may encounter functions that accept a char** argument. This typically represents a pointer to a pointer to a character, which can be used to pass strings or arrays of strings to C functions. This guide will show you how to pass a string from Python to such a function.

Passing a String to a C Library Function Accepting char**

1. Import the ctypes Module

First, make sure to import the ctypes module.

2. Define the C Function

For demonstration purposes, let’s assume you have a simple C function that takes a char** argument. Below is a simple example of such a function:

Compile this C code into a shared library (e.g., example.so on Linux or example.dll on Windows).

3. Load the Shared Library

In your Python code, load the shared library using ctypes:

4. Define the Argument Types

Next, define the argument types for the C function. In this case, the function accepts a char** and an int:

To pass a string (or an array of strings) to the C function, you need to create an array of c_char_p. Here's how you can do that:

6. Call the C Function

Now you can call the C function, passing the array of strings and the count:

7. Full Example

Here’s the complete code to illustrate the entire process:

Conclusion

Passing a string (or an array of strings) to a C library function that accepts char** can be easily accomplished in Python using the ctypes module. By defining the function's argument types, preparing your string data, and calling the function with the correct arguments, you can seamlessly interface with C libraries from Python. This capability allows for powerful integrations and can help leverage existing C code within Python applications.