Constants and pointers

  One 、  Constant pointer

#include<stdio.h>
int main()

{
	int num = 520;
	const int cnum = 880;
	const int* pc = &cnum;     //pc Deposited cnum The address of 
                               //*pc Deposited cnum Value 
	printf("cnum:%d,&cnum:%p\n", cnum, &cnum);
	printf("*pc:%d,pc:%p\n", *pc, pc);

	pc = &num;           // change pc The storage address is num;*pc Deposited num Value 

	printf("num:%d,&num:%p\n", num, &num);
	printf("*pc:%d,pc:%p\n", *pc, pc);

}

  Two 、 pointer to const ：（const keyword ）
1、 Pointers can be modified to point to different constants
2、 Pointers can be modified to point to different variables
3、 You can use dereference to read the data pointed to by the pointer
4、 You cannot modify the data pointed to by dereference

#include <stdio.h>
int main()

{
	int num = 520;
	const int cnum = 880;
	int* const p = &num;

	*p = 1024;            // The value pointed to by the pointer can be changed 
	printf("*p:%d\n", *p);

	//p = &cnum;
	//printf("*p:%d\n", *p);      // Will report a mistake , The pointer itself cannot be modified 

	return 0;
}

3、 ... and 、 Constant pointer ：（const keyword ）
  A constant pointer to a non constant quantity
   ---- The pointer itself cannot be modified
   ---- The value pointed to by the pointer can be modified
  Constant pointer to constant
   ---- The pointer itself cannot be modified
   ---- The value pointed to by the pointer cannot be modified

Four 、 Point to “ Constant pointer to constant ” The pointer to

#include<stdio.h>
int main()

{
	int num = 520;
	const int cnum = 880;
	const int* const p = &num;
	const int* const* pp = &p;

	printf("pp:%p, &p:%p\n", pp, &p);  //pp Deposited p The address of 
	printf("*pp:%p, p:%p, &num:%p\n", *pp, p, &num);// Yes pp Make a layer of dereference , That is to say num The address of 
	printf("**pp:%d, *p:%d, num:%d\n", **pp, *p, num);//  Yes pp Two levels of dereference , Deposit is num Value 

	return 0;
}