CODEWITHSUNDEEP
c++headerinclude-guards
Simplicity
Simplicity

Reputation: 48916

C++ - How can I avoid this header from appearing twice?

At: http://www.learncpp.com/cpp-tutorial/110-a-first-look-at-the-preprocessor/

Under Header guards, there are those code snippets:

add.h:

#include "mymath.h"
int add(int x, int y);

subtract.h:

#include "mymath.h"
int subtract(int x, int y);

main.cpp:

#include "add.h"
#include "subtract.h"

How can I avoid #include "mymath.h" from appearing twice in main.cpp?

Thanks.

Upvotes: 1

Views: 4074

Answers (4)

JaredC
JaredC

Reputation: 5300

The lines right below that example explain it. Your mymath.h file should look like this:

#ifndef MYMATH_H
#define MYMATH_H

// your declarations here

#endif

Every header file should follow this basic format. This allows a header file to be included by any file that needs it (both header and source files), but the actual declarations will only be included at most once in each source file.

Upvotes: 6

detunized
detunized

Reputation: 15289

That's ok if they included twice if all the headers files have header guards. The second and all subsequent inclusions would just add empty lines and there won't be any code duplication. Just make sure that mymath.h has header guards as well.

Upvotes: 2

Andrew T Finnell
Andrew T Finnell

Reputation: 13628

use #pragma once if you using MS VC++ or the standard way

inside mymath.h

#ifndef MYMATH_H
#define MYMATH_H

[code here]

#endif // MYMATH_H

Upvotes: 4

peoro
peoro

Reputation: 26060

You should put your header guards in any header, also in mymath.h.

Upvotes: 1

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