Is it always the case that sizeof(T) >= alignof(T) for all object types T?

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At least in standard C++, for anything you can make an array of (with length > 1), this will have to be true. If you have

Foo arr[2];

and alignof(Foo) > sizeof(Foo), then arr[0] and arr[1] can’t both be aligned.

As Zalman Stern’s example shows, though, at least some compilers will allow you to declare a type with alignment greater than its size, with the result that the compiler simply won’t let you declare an array of that type. This is not standards-compliant C++ (it uses type attributes, which are a GCC extension), but it means that you can have alignof(T) > sizeof(T) in practice.

The array argument assumes sizeof(Foo) > 0, which is true for any type supported by the standard, but o11c shows an example where compiler extensions break that guarantee: some compilers allow 0-length arrays, with 0 sizeof and positive alignof.

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