Cextension

A C extension is a component written in the C programming language that extends the capabilities of a host programming language by exposing additional functions, types, or modules to its runtime. It is typically compiled into a shared library and loaded by the interpreter when the module is imported or required.

C extensions interact with the host language through its C API. Each host language provides initialization and API hooks to create objects, manage memory, and convert values between C and language-native representations. For example, Python extensions use a module initialization function to register functions and types with the interpreter and to define the module’s interface.

Advantages of C extensions include improved performance for critical code paths, direct access to low-level system interfaces and libraries, and the ability to reuse existing C libraries. They are commonly used to speed up computation, perform memory-intensive tasks, or enable features not readily available in the high-level language.

Common hosts for C extensions include Python (CPython), Ruby, PHP, Lua, and Node.js, each using its own mechanism for loading and binding C code (for Node.js, native addons using N-API or NAN are typical). Development typically involves a dedicated build process and tooling to compile the C code into a platform-specific shared library.

Development considerations include ABI compatibility across language versions, portability across operating systems, and the complexity of debugging native code. Safety and stability are important, as crashes or memory errors in C can impact the host process, and some languages have global state or threading models that complicate concurrency.