C语言extern调用外部函数

> ls

xuanzeSort.c
common.c

---

> cat common.c

#include<stdio.h>
//公共函数文件

//打印long型数组的内容
void print_array_long(long arr[],long length)
{
long i;
for(i = 0;i<length;i++){
printf("%ld ",arr[i]);
    }
printf("\n");
}

---

> cat xuanzeSort.c

#include<stdio.h>
//选择排序
void selectSort(long *arr,long length){
int i,j,temp;
for(i = 0;i<length;i++){
for(j = i+1;j<length;j++){
if(arr[i]>arr[j]){
                temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }
    }
}

//外部声明common.c中的print_array_long函数 打印long型数组
extern void print_array_long(long arr[],long length);

int main()
{
long a[5] = {1,5,88,-1,0};
    print_array_long(a,5);
    selectSort(a,5);
    print_array_long(a,5);
}

---

> gcc xuanzeSort.c common.c