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Editorial Team
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Asked: 2026-05-20T04:53:53+00:00

Just noticed something that looks strange to me. Visual C++ doesn’t align object in

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Just noticed something that looks strange to me. Visual C++ doesn’t align object in their required boundary by default. For example long long is aligned to 4 bytes boundary, while __alignof(T) returns 8 (as far as I see it always returns size of the type). So it looks like it is not properly aligned. For example

long long a1;
char g;
long long a2;
// alignment check for &a2 fails
if (((uintptr_t)&a2 & (__alignof(long long) - 1)) != 0) // failed

I also tried just to print the pointer, the value of &a2 is 0x0035F8FC(3537148 in dec).

Is there something I get wrong? I need properly aligned object of type long long. What can I do about that?
I could use __declspec(align()) Microsoft extension, but it requires literal number, so I can’t write anything like that.

__declspec(align(__alignof(long long))) long long object;
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1 Answer

  1. Editorial Team

    VC doesn’t guarantee automatic stack alignment of variables, at most the variable will be aligned to the stacks alignment(generally 4 bytes on 32 bit systems). If you need special alignment, you need to use __declspec(align(x)), just like MSVC’s SSE types(like __m128), else you’ll need to use _aligned_malloc instead

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