C语言之extern(七十)

1. extern同一个文件：修饰变量声明

#include <stdio.h>int add(){extern int x,y;return x + y;
}int main(){printf("%d\n", add()); 
}int x = 10;
int y = 20;

2. extern文件之间：修饰函数声明

<1>.add.c

int sum(){extern int x ;extern int y ;return x+y;
}

<2>.add.h

extern int sum();

<3>.main.c

#include <stdio.h>
#include "add.h"int x=1;
int y=2;int main(){printf("sum = %d\n",sum());return 0;
}# gcc add.c main.c