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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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Ns_Url(3aolserver)					   AOLserver Library Procedures 					Ns_Url(3aolserver)

__________________________________________________________________________________________________________________________________________________

NAME
Ns_AbsoluteUrl, Ns_ParseUrl, Ns_RelativeUrl, Ns_SkipUrl - URL manipulation routines SYNOPSIS
#include "ns.h" int Ns_AbsoluteUrl(Ns_DString *pds, char *url, char *baseurl) int Ns_ParseUrl(char *url, char **pprotocol, char **phost, char **pport, char **ppath, char **ptail) char * Ns_RelativeUrl(char *url, char *location) char * Ns_SkipUrl(Ns_Request *request, int n) _________________________________________________________________ DESCRIPTION
Ns_AbsoluteUrl(pds, url, baseurl) Construct an URL based on baseurl but with as many parts of the incomplete url as possible. Return NS_OK or NS_ERROR. Ns_ParseUrl(url, pprotocol, phost, pport, ppath, ptail) Parse a URL into its component parts. Pointers to the protocol, host, port, path, and "tail" (last path element) will be set by ref- erence in the passed-in pointers. The passed-in url will be modified. Ns_RelativeUrl(url, location) If the url passed in is for this server, then the initial part of the URL is stripped off. e.g., on a server whose location is http://www.foo.com, Ns_RelativeUrl of "http://www.foo.com/hello" will return "/hello". Returns a pointer to the beginning of the relative url in the passed-in url, or NULL if error. Will set errno on error. Ns_SkipUrl(request, n) Return a pointer n elements into the request's url. SEE ALSO
nsd(1), info(n) KEYWORDS
AOLserver 4.0 Ns_Url(3aolserver)
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