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Top Forums Programming C program multiple definition error during linking time Post 302785717 by royalibrahim on Tuesday 26th of March 2013 08:38:20 AM
Old 03-26-2013
C program multiple definition error during linking time

Hi,

I have the following files:

// file.h
HTML Code:
void foo();
int i = 5; // should be just declared as extern int i;
// file1.c
Code:
#include <stdio.h>
#include "file.h"

void foo() {
    i = 10;
    printf("%d\n", i);
}

// file2.c
Code:
#include <stdio.h>
#include "file.h"

int main() {
    foo();
    printf("%d\n", i);
}

When I compiled the above files using gcc compiler, I got the following linker error

gcc -c file1.c
gcc -c file2.c
gcc -o a.out file*.o // linker error: file2.o: multiple definition of 'i'

After searching in the google, I got below links where I found the solution
Solving multiple definition - C++ Forum
multiple definition of 'variable_name'
"multiple definition" error - C++ Forum

Now, I have changed the code in the file.h as:
Code:
extern int i;

Now, my question is, if I want to print the value of i before calling the foo() function in the file2.c, what should I do in order to not to end up in the linker error?

// file2.c
Code:
#include <stdio.h>
#include "file.h"

i = 20; // treats as an altogether a new definition of i, implicitly adds int keyword before i
int main() {
        i = 20; // multiple definition error
        printf("%d\n", i);
        foo();
        printf("%d\n", i);
}


Last edited by royalibrahim; 03-27-2013 at 02:54 AM..
 

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DIFF(1) 						      General Commands Manual							   DIFF(1)

NAME
diff - print differences between two files SYNOPSIS
diff [-c | -e | -C n] [-br]file1 file2 OPTIONS
-C n Produce output that contains n lines of context -b Ignore white space when comparing -c Produce output that contains three lines of context -e Produce an ed-script to convert file1 into file2 -r Apply diff recursively to files and directories of EXAMPLES
diff file1 file2 # Print differences between 2 files diff -C 0 file1 file2 # Same as above diff -C 3 file1 file2 # Output three lines of context with every diff -c file1 file2 # Same diff /etc /dev # Compares recursively the directories /etc and /dev diff passwd /etc # Compares ./passwd to /etc/passwd DESCRIPTION
the same name, when file1 and file2 are both directories" difference encountered" Diff compares two files and generates a list of lines telling how the two files differ. Lines may not be longer than 128 characters. If the two arguments on the command line are both directories, diff recursively steps through all subdirectories comparing files of the same name. If a file name is found only in one directory, a diagnostic message is written to stdout. A file that is of either block special, character special or FIFO special type, cannot be compared to any other file. On the other hand, if there is one directory and one file given on the command line, diff tries to compare the file with the same name as file in the directory directory. SEE ALSO
cdiff(1), cmp(1), comm(1), patch(1). DIFF(1)
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