Pls hpw does one ensure that only one copy of a file ia # included in the complilation?

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Pls hpw does one ensure that only one copy of a file ia # included in the complilation when several files and base class file require thesame file in an mfc application.
I have been battling this all day.The compliler keep complaining of a redefinition.

Posted 17-May-14 1:30am

Gbenbam

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[no name] 17-May-14 8:40am

http://en.wikipedia.org/wiki/Pragma_once

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leon de boer · Answer 1 · 2014-05-17T02:42:00

In the .H file put protection top and bottom like this

// PROTECTION TO STOP MULTIPLE UNIT LOADING
#ifndef _MYUNIT_									
#define _MYUNIT_

// YOUR NORMAL CURRENT .H DATA HERE

#endif

I always use _UNITNAME_ for each and every unit as a standard and that is the almost standard way to do it. If you had of thought hard you would have simply gone at looked at the ones in the include directory on your compiler system which will usually do the same thing :-)

This is the top of strings.h in Visual Studio 12 & 13

/***
*string.h - declarations for string manipulation functions
*
*       Copyright (c) Microsoft Corporation. All rights reserved.
*
*Purpose:
*       This file contains the function declarations for the string
*       manipulation functions.
*       [ANSI/System V]
*
*       [Public]
*
****/

#pragma once

#ifndef _INC_STRING
#define _INC_STRING

Manikandan10 · Answer 2 · 2014-05-26T17:04:00

Solution 2

Use header guard in the header file:

C++

#ifndef _HEADER_NAME_
#define _HEADER_NAME_
...
...
...
#endif

When the first time this header is loaded, _HEADER_NAME_ is defined. So that prevents redefinition.

Posted 26-May-14 17:04pm

Manikandan10

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Richard MacCutchan 27-May-14 4:18am

This method is deprecated now, see http://msdn.microsoft.com/en-us/library/4141z1cx.aspx.