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dta1

Simple problem

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I have 3 files. header.h
    
int x = 2;
  
main.cpp
        
#include <iostream.h>
#include "header.h"

int main()
{
   cout << x;
   return 0;
}
  
main2.cpp
      
#include <iostream.h>
#include "header.h"

int func()
{
   x = 4;
   cout << x;
   return 0;
}
  
And of course I get this error: Linking... main2.obj : error LNK2005: "int x" (?x@@3HA) already defined in main.obj Debug/TestProg.exe : fatal error LNK1169: one or more multiply defined symbols found Error executing link.exe. I know it must be very easy to fix, but how? [edited by - dta1 on November 9, 2002 7:57:55 AM] [edited by - dta1 on November 9, 2002 8:39:37 AM]

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header.h:
 extern int x; 

main.cpp:
#include "header.h"
int x = 2;
...

main2.cpp:
#include "header.h"
...

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None of that works (and I want x to be 2 in header.h).

But it works if I declare it as static (static int x = 2). But that doesn''t seem to be a good the way.

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quote:
Original post by Pipo DeClown
header.h:

extern int x = 2;

main.cpp:

int x;
// x should be 2?


Sorry, can''t get that to work.
And yes, x should be two in main.cpp.

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Guest Anonymous Poster
header.h

#ifndef HEADER_H
#define HEADER_H
int x=5;
#endif

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quote:
None of that works (and I want x to be 2 in header.h)


which begs the questions: why do you want x to be 2 in header.h? what does it mean? why do you want a new variable x made in every file that header.h is included?

the explanation of oluseyi''s answer is this:

you want one copy of the variable x to be available to your program. by declaring x in a header you can include that header in places that need to know about x. the statement x = 2 is not a declaration though. it is a definition. whats that? there''s a difference?

the difference:
the declaration will tell your program that somewhere there exists a variable x. it will be able to find it when the program finally links.

the definition will actually declare and define the variable. that variable is the object. you can only have one of them. that''s why it''s a problem to put the definition in the header file.

the solution:
put a definition of the variable in one cpp file.
put a declaration of the variable as ''extern''. this means it will look for it elsewhere at link time (and hopefully find it defined in your cpp file)

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