Question

Possible Duplicate:
Pointer arithmetics in C++ uses sizeof(type) incremention instead of byte incremention?

Tried to find the answer but could not.
I have the following c++ code:

struct A {
    uint16_t a;
    uint16_t b;
    uint16_t c;
}

int main() {
    uint16_t * B = new uint16_t[5000];
    for (int i=0;i<5000;i++)
        B[i] = i;

    uint16_t * D = &B[500]+sizeof(A);
}

Question is: why *D=512 after this? When I debug sizeof(A) = 6 as it should be. Yet I add to memory address of B[500] the size of A it adds 12 instead of 6.
I am working with memory address still there is a multiplication and I cannot figure out why it is so.

Please advise.

Thank you!

Answer 1

It’s a compiler bug if sizeof(A) is indeed 6.

&B[500] + 6 == &B[506]

and thus *D ought to be 506 then. And it is when I compile

#include <iostream>
#include <cstdint>

struct A {
    uint16_t a;
    uint16_t b;
    uint16_t c;
};

int main() {
    uint16_t * B = new uint16_t[5000];
    for (int i=0;i<5000;i++)
        B[i] = i;

    uint16_t * D = &B[500]+sizeof(A);
    std::cout << (*D) << std::endl;
    return 0;
}

with g++-4.7.1 or clang++-3.1.