C程序中的指针

Question

I have a question about pointers in C. For example:

int data[SIZE] = {2,4,5,1,0};
int *p = &data[2];
int **s=&p;
p++;
printf("%p  ", *s);

Is here the pointer *s equal to *p, ie is the adress of *s equal to *p?

*It may be an easy question, but we didnt spend enough time learning C

Answer 1

After the declarations, you have the following:

  s == &p                   // int ** == int **
 *s ==  p == &data[2]       // int *  == int *  == int *
**s == *p ==  data[2] == 5  // int    == int    == int    == int

After p++ :

 *s ==  p == &data[3]
**s == *p ==  data[3] == 1

Answer 2

If you run

    int data[5] = {2,4,5,1,0};
    int *p = &data[2];
    int **s=&p;
    p++;
    int data[5] = {2,4,5,1,0};
    int *p = &data[2];
    int **s=&p;
    p++;
    printf("*p: %d  \n", *p);
    printf("&p: %p  \n", &p);
    
    printf("s: %p  \n", s);
    printf("*s: %p  \n", *s);
    printf("**s: %d  \n", **s);

you'll get:

*p: 1  
&p: 0x7ffc69a74650  
s: 0x7ffc69a74650  
*s: 0x7ffc69a7466c  
**s: 1  

Which shows that the value pointed by both *p and **s is the same (1), also &p == s but &p and *s are not the same, as there's an extra "step".

Answer 3

Here's a possible execution of your program:

int data[SIZE] = {2,4,5,1,0};
// your memory looks like this:
// Address (name) -> Value
// 0x80 (data[0]) -> 2
// 0x84 (data[1]) -> 4
// 0x88 (data[2]) -> 5
// 0x8C (data[3]) -> 1
// 0x90 (data[4]) -> 0
int *p = &data[2];
// 0x80 (data[0]) -> 2
// 0x84 (data[1]) -> 4
// 0x88 (data[2]) -> 5
// 0x8C (data[3]) -> 1
// 0x90 (data[4]) -> 0
// 0xC0 (p)       -> 0x88
int **s=&p;
// 0x80 (data[0]) -> 2
// 0x84 (data[1]) -> 4
// 0x88 (data[2]) -> 5
// 0x8C (data[3]) -> 1
// 0x90 (data[4]) -> 0
// 0xC0 (p)       -> 0x88
// 0xD8 (s)       -> 0xC0
p++;
// 0x80 (data[0]) -> 2
// 0x84 (data[1]) -> 4
// 0x88 (data[2]) -> 5
// 0x8C (data[3]) -> 1
// 0x90 (data[4]) -> 0
// 0xC0 (p)       -> 0x8C
// 0xD8 (s)       -> 0xC0
printf("%p  ", *s); //Will print 0x8C

So no, *s (the value pointed by s) won't be equal to *p (the value pointed by p) but to p (the address of the p pointer)