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Include guards

Include guards are used to avoid the problem of double/circular inclusion: every time you #include, the pre-processor copy-pastes the whole content of the included file into the includer, which can lead to errors.

Include guards help avoid this by ensuring a file is included only once.

For example, in file myfile.h, you would put:

// !! NO CODE HERE
#ifndef PROJECT_NAME_MYFILE_H
#define PROJECT_NAME_MYFILE_H

// Your code goes here...

#endif
// !! NO CODE HERE
  • #ifndef checks if the identifier (PROJECT_NAME_SCANNER_H) is not yet defined
  • #define defines the identifier, marking the file as included
  • #endif ends the guard

You can use whatever name you want for the PROJECT_NAME_MYFILE_H identifier, but it's common practice to use the project name and the filename to avoid potential naming conflicts