I’m creating a new framework which uses a mix of C and C++, and recently I stopped to consider my choice of header file extension.
I have spent my career as a C programmer, so many of my habits are simply ossified from my C days. One such habit is using .h for all header file extensions.
To make matters worse, it seems there is still not a fixed approach to C/C++ header file differentiation. While surveying comments around the internet, I see many developers only use .hpp for C++ headers which also include implementations. Other C++-only headers are left with the .h extension. Unhelpfully, many IDEs still seem to recommend .h as the default header extension, even if you are using C++.
The problem with allowing .h to represent both C and C++ code without differentiation is that you increase friction for developers:
- How can you know that you can’t include a specific library
.hfile in your C program because it’s really C++? - What if you are trying to adjust your build system and want to exclude all C++ files from a specific project?
I think it is important to make conventions and language type apparent to developers without requiring manual inspection. In my new framework, I have decided to use .hpp for all headers that are C++-only. .h will be reserved for headers which can be included by either C or C++ sources. I’m not alone in this convention – at the very least, Boost uses the same approach. To quote from the Boost FAQ:
Why do Boost headers have a .hpp suffix rather than .h or none at all?
File extensions communicate the “type” of the file, both to humans and to computer programs. The ‘.h’ extension is used for C header files, and therefore communicates the wrong thing about C++ header files. Using no extension communicates nothing and forces inspection of file contents to determine type. Using ‘.hpp’ unambiguously identifies it as C++ header file, and works well in actual practice. (Rainer Deyke)
As an aside, it is helpful to make your C-style headers compatible with C++. Here are some simple strategies to keep in mind:
- protect C-only code with the
__cplusplusmacro, which is only defined by the C++ compiler - Mark C functions code as
extern "C"when compiling C++ code
I hope that you take some time to think about header extensions in your own projects!
it’s so much painful stuff.
Why cannot we make it simple?
.c for implmetation
.h for head file?
and try to make it consistent in a sense of human being?
well, that simply isn’t going to work because what about .cpp?