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Header Files

Posted on 1998-12-22
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Last Modified: 2010-04-02
I'm in Dialog mode. I have a main Dialog and several Dialogs that come off of the Main Dialog. I created a Header file and in the CMyProgram1Dlg (which is the Main Dialog) I used

#include "header.h"

Everything works fine.

The problem is when I want to #include the same Header file in one of the Sub Dialogs I get this error:

pddlg.obj : error LNK2005: "unsigned int  port" (?port@@3IA) already defined in Program1.obj

pddlg.obj : error LNK2005: "int __cdecl trans(unsigned int,unsigned int,int)" (?trans@@YAHIIH@Z) already defined in Program1.obj

If I don't #include the Header file I get errors that the variables are undefined.

What am I doing wrong and what do I have to do to correct it?

Thanks
Randy
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Question by:randyg
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6 Comments
 
LVL 23

Accepted Solution

by:
chensu earned 100 total points
ID: 1180868
In the header.h, you should only declare the variables and functions like the following.

extern unsigned int port;

int __cdecl trans(unsigned int,unsigned int,int);

Put the definitions in a source file, for example common.c like the following.

unsigned int port;

int __cdecl trans(unsigned int,unsigned int,int)
{
//...
}

Insert the source file into your project. Include the header file wherever you use the variables and functions.
0
 

Expert Comment

by:Gawande
ID: 1180869
Always put *.h code in # directive as follows

#ifndef _HEADER_FILE_NAME           // If this variable is not defined then only header file
#define _HEADER_FILE_NAME         // will get included. Header file should be loaded                                                             // only once.  So when you include this header file
// next time, the variable is already declared and hence, it will not give you any error

.



//// Header file contents

#endif // _HEADER_FILE_NAME
0
 

Expert Comment

by:Gawande
ID: 1180870
It seems that my commnets are destorted, please put your code in following way

#ifndef _FILE_NAME
#define _FILE_NAME

// Header file contents

#endif
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LVL 23

Expert Comment

by:chensu
ID: 1180871
Yes, you should do what Gawande suggests. However, it does not solve the problem randyg is facing.

It does solve the problem in the following example.

Header files: a.h, b.h, c.h
Source files: a.cpp

In the a.cpp,
#include "a.h"
#include "c.h"

In the a.h,
#include "b.h"
#include "c.h"

In this case, c.h is included twice.

It does not solve the problem in the following example.

Header files: a.h
Source files: a.cpp, b.cpp

In the a.h,
unsigned int port;

In the a.cpp,
#include "a.h"

In the b.cpp,
#include "a.h"

In this case, there are two global variables port with the same name.

To solve this problem,

In the a.h,
extern unsigned int port;

Add another source file c.cpp,
unsigned int port;
0
 

Expert Comment

by:talb
ID: 1180872
hi
try to save your header file in two diffrent names
then use it.
0
 
LVL 23

Expert Comment

by:chensu
ID: 1180873
talb,

But the variables and the functions are the same. It will still cause the linking error.
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