Duplicate Symbol Error - Global Variable

Question

So I have three files:

jarvismarch.c
jarvismarchtools.c
jarvismarchtools.h

After running make, I receive the following error:

Andrew-Carpenters-Laptop:Independent Study ahcarpenter$ make
cc    -c -o jarvismarch.o jarvismarch.c
cc    -c -o jarvismarchtools.o jarvismarchtools.c
cc -o jarvismarch jarvismarch.o jarvismarchtools.o
ld: duplicate symbol _string1 in jarvismarchtools.o and jarvismarch.o for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [all] Error 1

string 1 is declared within jarvismarchtools.c. jarvismarchtools.h is included within jarvismarchtools.c as well as jarvismarch.c.

Any ideas as to how I can resolve this error?

Within jarvismarchtools.h:

/*
    FILENAME: jarvismarchtools.h
    AUTHOR: Andrew H. Carpenter
    DATE: 2 Feb 2013
    DESCRIPTION: This is a header file containing tools for running Jarvis' March.
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>

extern int string1 = 1;

typedef struct Point {
    double x, y;
    char *label;
} point;

/*
    DESCRIPTION: A function that determines the angle (in degrees) between two points.
    INPUT: Requires two points as input.

Within jarvismarchtools.c:

/*
    FILENAME: jarvismarchtools.c
    AUTHOR: Andrew H. Carpenter
    DATE: 2 Feb 2013
    DESCRIPTION: This is an implemenetation file containing tools for running Jarvis' March.
*/
#include "jarvismarchtools.h"

int string1 = 1;

float getAngle(point p1, point p2){

Answer 1

If the variable should be shared:

• Make it extern in the header
• Define it in one of the C files without extern

If the variable shouldn't be shared add a static in front.