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How to check if title has already been included before

I am doing a project and I am stunned by the problem.

I have 3 library.h, which includes another special library, .h definitions, but in my main module I want to include all libraries only once, I mean, I want to check if there is a definitions.h library already included and include it or not depending on the result.

Sort of

 If !(#include"definitions.h") (#include"definitions.h")
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3 answers

You are looking to include guards.

Example

 #ifndef DEFINITIONS_H #define DEFINITIONS_H ... ... #endif
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 #ifndef DEFINITIONS_H #define DEFINITIONS_H //lots of code // // // // #endif

There is also a non-standard #pragma once , see. Is #pragma after secure enable protection?

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If your header syntax is correct, this should not be a problem. In fact, it is for this reason that you write

 #ifndef _DEFINITIONS_H #define _DEFINITIONS_H [header content] #endif

So, if your title complies with C conventions, you should be fine.

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Source: https://habr.com/ru/post/1485185/

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