所以我有三个文件：
jarvismarch.c
jarvismarchtools.c
jarvismarchtools.h
运行后make，我收到以下错误：
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内声明jarvismarchtools.c。jarvismarchtools.h包含在jarvismarchtools.c以及 中jarvismarch.c。
关于如何解决此错误的任何想法？
内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.
内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){