Pointers (2)-(const) pointers and constants

const use

Declare a constant

The keyword const is used to tell the compiler that a variable once initialized cannot be modified

int a;
const int n;

A constant pointer

Pointer to a constant

Modified pointer points to

#include<stdio.h>

int main() {
    
    
	//常量指针

	const int num = 10;
	// num = 100;
	int* p1 = &num;
	*p1 = 100;
	printf("%d\n", num); // 可以通过p1修改num (c语言可以c++不可以)

	// 不可以通过p2,p3修改num
	const int* p2 = &num;
	//*p2 = 100;
	printf("%d\n", num);
	int const* p3 = &num;
	//*p3 = 100;
	printf("%d\n", num);

	return 0;
}

// 不能通过指针修改指向的内容(必须初始化变量)
// 可以改变指针指向

Two pointer constant

The pointer itself is a constant

Decorate the pointer itself

// 指针常量：
int a = 0;
int* const pa = &a;
// pa = NULL;
*pa = 100;

// 可以通过指针修改指向的内容
// 不能改变指针指向(必须初始化指针)

Three constant pointer constants

The pointer itself is a constant and points to a constant

Simultaneous modification

// 常量指针常量
const int b = 0;
const int * const pb = &b;
// pb = NULL;
// *pb = 0;

// 不能通过指针修改指向的内容(必须初始化变量)
// 不能改变指针指向(必须初始化指针)