Let's say we have a parent class with header parent.h and 2 child classes child1.h and child2.h, since they both inherit from parent, both header files should include parent.h. Including child1.h and child2.h in another file will result of a duplicate definition of the parent class. What is the best way to avoid this? Is using #pragma once a good practice, or are there other ways to fix this?
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Omar Mneimneh
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2 Answers
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This is the exact reason why #ifndef is used as a check in header files.
For example, your `parent.h' may have:
#ifndef PARENT_H
#define PARENT_H
.... //Your header definition
#endif
Then, in child1.h and child2.h
#ifndef PARENT_H
#include "parent.h"
#endif
....//Your source code
Susmit Agrawal
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5You do not need or want that `#ifndef` in the child headers. – Oct 01 '18 at 16:39
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so how do you do it instead? – Omar Mneimneh Oct 01 '18 at 16:43
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1@Omar Simply have each header file have its own include guards. Other files should not know or care what the names of those guards are. – Oct 01 '18 at 16:45
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Yes, you can use pragma or #ifndef
#ifndef _AUTOMOBILE_H
#define _AUTOMOBILE_H
//...
#endif
codeHero
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4Names like `_AUTOMOBILE_H` which begin with an underscore and an uppercase letter are reserved for the C++ implementation - you should not be creating them in your own code. Simply use `AUTOMOBILE_H` – Oct 01 '18 at 16:43