C++ Coding Standards: 101 Rules, Guidelines, and Best Practices

24. SummaryDiscussionExceptionsReferences...

Wear head(er) protection: Prevent unintended multiple inclusions by using #include guards with unique names for all of your header files....

Each header file should be guarded by an internal #include guard to avoid redefinitions in case it is included multiple times. For example, a header...

In very rare cases, a header file may be intended to be included multiple times....

[C++03, §2.1] • [Stroustrup00] §9.3.3...