将32位值转换为HANDLE

Question

I am dealing with a component that provides a 32-bit custom handle, and I'd like to wrap that using the standard windows HANDLE type. In a legacy component, I've seen use of the following two conversion methods:

// value is 32-bits
auto value = GetCustomHandle();

HANDLE hA = HANDLE(value);
HANDLE hB = (void*)(SIZE_T)value;

Are hA and hB always equivalent? If not, under what circumstances are they not?

In this instance, I think they are always equivalent because:

1. There's no difference between functional and c-like casts.
2. HANDLE is equivalent to void*.
3. The size of void* and SIZE_T is 32-bits on 32-bit systems, and 64-bits on 64-bit systems.

Thanks.

Answer 1

Personally, I would go with the C++ style cast:

 HANDLE hCPP = reinterpret_cast<HANDLE>(value);

You may get a warning for "casting narrow type to wider type" (or whatever the terminology the compiler uses for that), in which case the expression should be:

 HANDLE hCPP = reinterpret_cast<HANDLE>(static_cast<uintptr_t>(value));

The type uintptr_t is guaranteed to be unsigned and match the size of a pointer. Using MS-defined types will just make it less portable - not generally a big problem in Windows software, but it's certainly no benefit to make code LESS portable.