Should every C or C++ file have an associated header file?

Question

Should every .C or .cpp file should have a header (.h) file for it?

Suppose there are following C files :

1. Main.C

2. Func1.C

3. Func2.C

4. Func3.C

where main() is in Main.C file. Should there be four header files

1. Main.h

2. Func1.h

3. Func2.h

4. Func3.h

Or there should be only one header file for all .C files?

What is a better approach?

Answer 1

For a start, it would be unusual to have a main.h since there's usually nothing that needs to be exposed to the other compilation units at compile time. The main() function itself needs to be exposed for the linker or start-up code but they don't use header files.

You can have either one header file per C file or, more likely in my opinion, a header file for a related group of C files.

One example of that is if you have a BTree implementation and you've put add, delete, search and so on in their own C files to minimise recompilation when the code changes.

It doesn't really make sense in that case to have separate header files for each C file, as the header is the API. In other words, it's the view of the library as seen by the user. People who use your code generally care very little about how you've structured your source code, they just want to be able to write as little code as possible to use it.

Forcing them to include multiple distinct header files just so they can create, insert into, delete from, and search, a tree, is likely to have them questioning your sanity :-)

You would be better off with one btree.h file and a single btree.lib file containing all of the BTree object files that were built from the individual C files.

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Another example can be found in the standard C headers.

We don't know for certain whether there are multiple C files for all the stdio.h functions (that's how I'd do it but it's not the only way) but, even if there were, they're treated as a unit in terms of the API.

You don't have to include stdio_printf.h, stdio_fgets.h and so on - there's a single stdio.h for the standard I/O part of the C runtime library.

Answer 2

1. Header files are not mandatory.

2. #include simply copy/paste whatever file included (including .c source files)

3. Commonly used in real life projects are global header files like config.h and constants.h that contains commonly used information such as compile-time flags and project wide constants.

4. A good design of a library API would be to expose an official interface with one set of header files and use an internal set of header files for implementation with all the details. This adds a nice extra layer of abstraction to a C library without adding unnecessary bloat.

5. Use common sense. C/C++ is not really for the ones without it.