CODEWITHSUNDEEP
c
user3417884
user3417884

Reputation: 1

Getting An Undefined Reference To A Properly Defined Global Variable

So in short, I have two .c files and a shared.h header file in the same directory.

This is shared.h:

    #include <stdio.h>
    #include <stdlib.h>
    #include <unistd.h>
    #include <sys/types.h>
    #include <sys/wait.h>
    #include <string.h>
    #include <fcntl.h>
    #include <signal.h>
    #include <errno.h>


       // declaring the number to factor and the the variable
        factor as shared gloval variables
    extern int n;
    extern int factor;

This is pfact.c:

    #include "shared.h"
    int n;
    int  factor = 0;
    // start main
    int main(int argc, char **argv) {

    // fork
    // if child, exec to child

    return 0;
    }

This is child.c:

   #include "shared.h"

    int main(){

    int m=0, k;
    int status, child_exit_status;
    pid_t pid;
    int fd[2];    //every child will create another pipe to write      to in addition to the pipe it inherits from its parent to read from

    printf("n is %d\n", n);


   // goes more code 

    return 0
    }

What am I doing wrong? the global variable n is declared once in pfact.c, "externed" in the header file shared.h and then the header file is included in child.c

Thanks in advance!

Upvotes: 0

Views: 120

Answers (2)

vonbrand
vonbrand

Reputation: 11791

You need to link your objects together...

gcc -g -Wall -c child.c
gcc -g -Wall -c pfact.c
gcc -g -Wall -o pgm child.o pfact.o

Re: extern lines useless: Yes, they aren't needed in pfact.c; but it is good practice to #include the header with the declaration anyway, so the compiler can cross-check that everything matches.

Upvotes: 0

tcollart
tcollart

Reputation: 1062

Those two lines in child.c are useless, you can remove it

extern int n;
extern int factor;

This could help you understand why:

How do I use extern to share variables between source files?

Child doesn't know n so you can add it in global in child.c but it's certainly not why you are trying to do.

You can't compile two main, you should maybe rethink the way you do your program.

Upvotes: 2

Related Questions