Include guards for modules

Question

This may be a ridiculous question and I'm 99% sure of the answer but I wanted to be sure.

C++20 modules do not require any type of include guards for module interface files.

Is my statement correct? Everything I've read about modules thus far leads me to believe that guards are not required as modules are only ever compiled once and then reused for each translation unit that imports that module.

user_5699329 · Answer

Include guards are not needed. Modules are only imported once.

Preprocessor defines do not escape from modules, so include guards would not work anyway.

Macros, preprocessor directives, and non-exported names declared in a module are not visible and therefore have no effect on the compilation of the translation unit that imports the module.

Include guards for modules

1 Answers