在 C 编程语言中，指向指针的指针或双指针是一个保存另一个指针地址的变量。
声明
下面给出的是指向指针的指针的声明 -
datatype ** pointer_name;
例如int **p；
这里，p是一个指向指针的指针。
初始化
'&'用于初始化。
例如，
int a = 10; int *p; int **q; p = &a;
访问
间接运算符(*)用于访问
示例程序
以下是双指针的C程序 -
现场演示#include<stdio.h>
main ( ){
int a = 10;
int *p;
int **q;
p = &a;
q = &p;
printf("a =%d ",a);
printf(" a value through pointer = %d", *p);
printf(" a value through pointer to pointer = %d", **q);
}输出
当执行上述程序时，会产生以下结果 -
a=10 a value through pointer = 10 a value through pointer to pointer = 10
示例
现在，考虑另一个 C 程序，它显示了指针到指针之间的关系。
实时演示
#include<stdio.h>
void main(){
//Declaring variables and pointers//
int a=10;
int *p;
p=&a;
int **q;
q=&p;
//Printing required O/p//
printf("Value of a is %d</p><p>",a);//10//
printf("Address location of a is %d</p><p>",p);//address of a//
printf("Value of p which is address location of a is %d</p><p>",*p);//10//
printf("Address location of p is %d</p><p>",q);//address of p//
printf("Value at address location q(which is address location of p) is %d</p><p>",*q);//address of a//
printf("Value at address location p(which is address location of a) is %d</p><p>",**q);//10//
}输出
当执行上述程序时，会产生以下结果 -
Value of a is 10 Address location of a is 6422036 Value of p which is address location of a is 10 Address location of p is 6422024 Value at address location q(which is address location of p) is 6422036 Value at address location p(which is address location of a) is 10
