c语言：如何编写函数，改变传入的指针参数的值

#include<stdio.h>
 int source =1;
 int* cope_adress(int *a)
 {
    a=&source;
 }
 int main()
 {
     int b=2;
     int *purposes;
     printf("source  address  is  %p\n",&source);
     purposes=&b;
     cope_adress(purposes);
     printf("cope_adress  is  %p\n",purposes);
 
 }
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book@xxx:~/work$ g++ myname.c 
book@xxx:~/work$ ./a.out
source  address  is  0x601040
cope_adress  is  0x7ffdad9a7b7c

#include<stdio.h>
 int source =1; 
 int* cope_adress(int **a)
 {
    *a=&source;
 }
 int main()
 {
     int b=2;
     int **purposes;
     printf("source  address  is  %p\n",&source);
     int *myb=&b;
     purposes=&myb;
     cope_adress(purposes);
     printf("cope_adress  is  %p\n",*purposes);
 
 }
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*************************************
book@xxx:~/work$ gcc 1.c
book@xxx:~/work$ ./a.out
source  address  is  0x601040
cope_adress  is  0x601040

看上去，只有 函数形参 是函数体内的使用的变量的地址才可以赋值成功。