Inconsistency in using pointer to an array and address of an array directly

Question

This code sample prints the array correctly.

int b[2] = {1, 2};
int *c = &b;
int  i, j,k = 0;
for (i = 0;i < 2; i++) {
    printf(\"%d \", *(c+i));
}
         


        

Answer 1

This is because of the pointer type to which the pointer arithmetic operation ptr+i is applied:

• In the first case, you add i to a pointer to int, which is the same as indexing an array. Since the pointer to an array is the same as the pointer to its first element, the code works.
• In the second case, you add i to a pointer to an array of two ints. Therefore, the addition puts you beyond the allocated memory, causing undefined behavior.

Here is a quick illustration of this point:

int b[2] = {1,2};
printf("%p\n%p\n%p\n", (void*)&b, (void*)(&b+1), (void*)(&b+2));

On a system with 32-bit ints this prints addresses separated by eight bytes - the size of int[2]:

0xbfbd2e58
0xbfbd2e60
0xbfbd2e68