Solved

curious about multiple defined symbols.

Posted on 2004-09-08
2
207 Views
Last Modified: 2010-04-01
Let's say I have a header file, that is included by two different .cpp files.

//test.h
#ifndef TEST_H
#define TEST_H

int g_int;
#endif

//test1.cpp
#include "test.h"
extern int g_int;
...

//test2.cpp
#include "test.h"
extern int g_int;

I am getting the link error LNK2005: "int g_int" (?g_int@@3HA) already defined in test1.obj

Now I thought that declaring them as extern in the .cpp files would tell the compiler that the g_int variable was already declared externally.  I know that I can move the g_int declaration to the .cpp file and it will work fine.  I was just curious if there was any way at all to have a global variable in a header file.
0
Comment
Question by:lwinkenb
2 Comments
 
LVL 23

Accepted Solution

by:
brettmjohnson earned 125 total points
ID: 12009540
Header files are physically included into the including source in-line,
so your construct is equivalent to:

//test1.cpp
int g_int;
extern int g_int;
...

//test2.cpp
int g_int;
extern int g_int;

You see that g_int is now defined in both test1 and test2.
Generally, the header file contains the declaration ("extern int g_int;")
while the cpp file contains the definition.  You have it backward.

0
 
LVL 5

Author Comment

by:lwinkenb
ID: 12009818
Thanks a lot.
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Article by: SunnyDark
This article's goal is to present you with an easy to use XML wrapper for C++ and also present some interesting techniques that you might use with MS C++. The reason I built this class is to ease the pain of using XML files with C++, since there is…
Introduction This article is the first in a series of articles about the C/C++ Visual Studio Express debugger.  It provides a quick start guide in using the debugger. Part 2 focuses on additional topics in breakpoints.  Lastly, Part 3 focuses on th…
The viewer will learn additional member functions of the vector class. Specifically, the capacity and swap member functions will be introduced.
The viewer will be introduced to the member functions push_back and pop_back of the vector class. The video will teach the difference between the two as well as how to use each one along with its functionality.

895 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

13 Experts available now in Live!

Get 1:1 Help Now