Struct alignment is always 4

Question

Why pragma pack does not work in here? sizeof() returning the size aligned to 4. I use compiler which comes with Microsoft Visual Studio 2015

#pragma pack(push,1)

struct Header {
    uint16_t zero = 0;
    uint32_t id{};
};

struct ImageBlock : Header {
    uint32_t currentValidLength{};
};

#pragma pack(pop)
constexpr int sz = sizeof(ImageBlock);  // returns 12 but should be 10

Tried to also set Struct member alignment (/Zp1) compiler option with no luck

Answer 1

Looks like it's an IntelliSense bug. At runtime, the size is correct, but Visual Studio shows me an incorrect value of sz while editing. I've also tried static_assert on the size: VS shows that it will fail at compile time, but in fact, everything is ok.