How do I check a typed pointer is properly aligned for that type?

Question

Suppose I have a templated function that deals with pointers to yet unknown type T . Now if type T happens to be void* on 64-bit platform then it must be 8-bytes aligned, but if T happens to be char it must be 1-byte aligned and if T happens to be a class then its alignment requirements will depend on its member variables.

This all can be computed on paper, but how do I make the compiler yield the alignment requirements for a given type T ?

Is there a way to find during compile time the alignment requirements for a given type?

Answer 1

In C++11 you can use alignof and alignas to make asserts and provide requirements for alignment. Also look at std::align to control alignment in runtime.

Answer 2

In the absence of C++11, its easiest to use the next power-of-two greater than or equal to sizeof(T) . You might also want to cap it to the alignment of the largest primitive. 8 is a pretty safe bet on a 64-bit architecture (though you might need to keep an eye on things like SSE data types).