如何获得这个 C 程序的输出？

Question

#include <stdio.h>
int main () {
int a[3][5] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15};
int *p[] = {*a, *(a + 1) , *(a + 2) };
int (*ptr)[5];
ptr = a;
printf ("%d\n", *(*(p + 1) + 1));
printf ("%d %d %d\n", ** ptr , *(*( ptr + 1) + 2) , *(*( ptr + 2) + 3));
printf ("%d %d %d\n", ptr [0][0] , ptr [1][2] , ptr [2][3]) ;
return 0;
}

The output is

7
1 8 14
1 8 14

Can someone explain this program step by step? Really confused...

Answer 1

For example for this line:

printf ("%d\n", *(*(p + 1) + 1));

Look at that line:

int *p[] = {*a, *(a + 1) , *(a + 2) };

So p is pointer (array) to integer pointers with some address and value *a at initial index.

Then (p + 1) is next address of p and its value *(p + 1) is pointer *(a + 1)

Next, a is two dimension array and (a + 1) is array of addresses for values 6, 7, 8, 9, 10

Therefore *(p + 1) is address for value 6 and *(p + 1) + 1 is address for value 7.

So we get: *(*(p + 1) + 1) is integer value from address for value 7, ie

printf ("%d\n", *(*(p + 1) + 1));

returns 7

Try to figure out the rest of code. Same method.