[ C++ ]Include guard

 In the C and C++ programming languages, an #include guard, sometimes called a macro guard, is a particular construct used to avoid the problem of double inclusion when dealing with the include directive. The addition of #include guards to a header file is one way to make that file idempotent.

#ifndef GRANDFATHER_H
#define GRANDFATHER_H
 
struct foo {
    int member;
};
 
#endif /* GRANDFATHER_H */