C++ Header order [closed]

Answer 1

The "how" is not obvious, but the "what" is. Your goal is to make sure that the order in which you include header files never matters (and i mean "NEVER !").

A good help is to test whether header files compile when building cpp files (one for each header file) that only include one of them.

Answer 2

I used to order them in alphabetical order (easier to find)

Answer 3

Good practice: every .h file should have a .cpp that includes that .h first before anything else. This proves that any .h file can be put first.

Even if the header requires no implementation, you make a .cpp that just includes that .h file and nothing else.

This then means that you can answer your question any way you like. It doesn't matter what order you include them in.

For further great tips, try this book: Large-Scale C++ Software Design - it's a shame it's so expensive, but it is practically a survival guide for C++ source code layout.

Answer 4

In a header file you have to include ALL the headers to make it compilable. And don't forget to use forward declarations instead of some headers.

In a source file:

• corresponded header file
• necessary project headers
• 3rd party libraries headers
• standard libraries headers
• system headers

In that order you will not miss any of your header files that forgot to include libraries by their own.

Answer 5

If a header needs other headers then it just includes them in that header.

Try to structure your code so you pass pointers or references and forward declare where you can.

In the implementation then the header that defines it should be listed first (except in Visual Studio if you are using pch then stdafx would go first).

I generally list them as I need.

Answer 6

Google C++ Style Guide, Names and Order of Includes :

In dir/foo.cc, whose main purpose is to implement or test the stuff in dir2/foo2.h, order your includes as follows:

• dir2/foo2.h (preferred location — see details below).
• C system files.
• C++ system files.
• Other libraries' .h files.
• Your project's .h files.