重複的符號錯誤 - 全局變量

Question

所以我有三個文件：

jarvismarch.c 
jarvismarchtools.c 
jarvismarchtools.h 

運行make後，我收到以下錯誤：

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是內jarvismarchtools.c聲明。 jarvismarchtools.h包含在jarvismarchtools.c以及jarvismarch.c之內。

任何想法，我怎麼能解決這個問題？

在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. 

在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

如果變量應該共享：

• 使它extern在頭
• 定義它在一個的而不extern

的C文件如果變量不應該被共享在前面加一個static。