Pointer to pointer dereference with pre-increment operator

Question

The following program gives output as 17,29,45; I can't understand what does **++pp; mean. Can anyone explain the program in detail.

    #include <stdio.h>

    int main() {
        static int a[] = {10, 22, 17, 29, 45};
        static int *p[] = {a, a + 2, a + 1, a + 4, a + 3};
        int **pp = p;
        **++pp;
        printf("%d %d %d", **pp, *pp[3], pp[0][2]);
    }

Sourav Ghosh · Accepted Answer · 2016-07-27T14:27:22.850

3

In your code, **++pp; is the same as * (* ( ++pp));. It first increments the pointer, then deferences twice (the first dereference result is of pointer type, to be elaborate).

However, the value obtained by dereferencing is not used. If you have compiler warnings enabled, you'll get to see something like

warning: value computed is not used

You can remove the dereferencing, it's no use.

edited Jul 27 '16 at 14:27

answered Jul 27 '16 at 14:13

Sourav Ghosh

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output is affected when i comment out this statement – Nikhil Verma Jul 27 '16 at 14:17
1

@NikhilVerma I'm not asking to comment out the statement, remove the dereferences, use `++pp;` and you'll get the same result. – Sourav Ghosh Jul 27 '16 at 14:18
1

Of course it is affected, as `pp` is not incremented, if you comment it out. – Eugene Sh. Jul 27 '16 at 14:26

Pointer to pointer dereference with pre-increment operator

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