make multiple definition of ...??????????????

bendeco13 · 04-20-2006, 03:26 PM

I've been working on this program and it grew very large, so I split it up into individual files. Now I'm trying to set it up with make, but I keep getting this error:

Code:

g++    -c -o test.o test.cpp
g++    -c -o test_config.o test_config.cpp
g++ -o make_test main.o test.o test_config.o
test_config.o:(.bss+0x0): multiple definition of `FVAR'
test.o:(.bss+0x0): first defined here
test_config.o:(.bss+0x4): multiple definition of `SVAR'
test.o:(.bss+0x4): first defined here
collect2: ld returned 1 exit status
make: *** [all] Error 1

These are defined in one header file 'test_options.h' and both test.cpp and test_config.cpp include this file. I used the #ifndef, #define statements, and make 'seems' to ignore this. Here's 'test_options.h':

Code:

#ifndef _TEST_OPTIONS_H
#define _TEST_OPTIONS_H

#include <string>

string FVAR = "FirstVar";
string SVAR = "SecondVar";

#endif

Does anyone know how to fix this?
I tried simply removing '#include "test_options.h"' from the main_config.cpp file, since you would think that it is already included since test.cpp has already included it, but when I do this I get this error:

Code:

g++    -c -o main.o main.cpp
g++    -c -o test.o test.cpp
g++    -c -o test_config.o test_config.cpp
test_config.cpp: In function ‘int Test_Config(std::string)’:
test_config.cpp:9: error: ‘FVAR’ was not declared in this scope
test_config.cpp:10: error: ‘SVAR’ was not declared in this scope
make: *** [test_config.o] Error 1

Any help would be greatly appreciated.
Thanks in advance,
Bendeco

graemef · 04-20-2006, 04:03 PM

Header files should not contain definitions of variables.

A variable can be declared multiple times but must be defined only once. Use the keyword extern to declare the variable and then in the source code that will first use the variables they can be defined.

Code:

#ifndef _TEST_OPTIONS_H
#define _TEST_OPTIONS_H

#include <string>

extern string FVAR;
extern string SVAR;

#endif

Mara · 04-20-2006, 04:05 PM

That's how it works (making things very simple): When the compiler handles main.cpp, it gets test_options.h, finds the definitions and add them to the list of object. That's OK. Then it forgets what it knows and starts with test.cpp. It finds test_options.h and enters it (#ifdef protects from including the same file multiple times in one file, not different ones). It finds the definitions ... Then linking. The linker gets main.o and test.o. They both have the strings. You get an error.

How to fix it...Move the definitions to one file (.c).
In that file you'd have

Code:

string FVAR = "FirstVar";
string SVAR = "SecondVar";

Remove the definitions from .h. Now, in every .c (or .h) that needs it, use

Code:

extern string FVAR;
extern string SVAR;

bendeco13 · 04-20-2006, 04:50 PM

THANKYOU so much,
I got it working now