File Extensions in C++

Summary

C++ uses multiple file extensions for both header files and implementation files. The choice of extension influences clarity, tooling, and the ability to distinguish C from C++ code. Modern C++ projects commonly use .hpp and .cpp, but other extensions exist based on historical conventions and toolchains.

Header File Extensions

1. .h — legacy and ambiguous

   • Historically from the C language.
   • Does not indicate whether the contents are C or C++.
   • Can conflict with C standard library headers.

2. .hpp — recommended for modern C++

   • Explicitly signals C++ header code.
   • Well supported by IDEs, linters, and C++ parsers.
   • Symmetric counterpart to .cpp.

3. .hh — minimalist C++ style

   • Common in some codebases (often paired with .cc).
   • Short and clean, but less universally recognized.

4. Module-related extensions

   • .ixx, .mxx, .cppm when working with C++20 Modules.
   • Not relevant unless using modular compilation.

Implementation File Extensions

The file extension depends on the implementation and on compiler or project conventions. Common extensions for C++ implementation files include:

• .C
• .cc
• .cxx
• .c (rare for C++ but possible in mixed projects)
• .cpp
• .c++
• .cp

*.cpp is the most widely recognized in modern C++ projects.

Practical Recommendation

For modern, long-term C++ codebases:

• Use .hpp for headers.
• Use .cpp for implementation files.

This yields a clear and idiomatic file structure and reduces ambiguity between C and C++ sources.

Related Notes

• C++ Modules vs Headers
• Header Guards and #pragma once
• C vs C++ Naming Conventions
• C++ File Organization