How to convert Win32 HRESULT to int return value?

Question

I'm writing a Windows console application in C++ and would like to return zero on success and a meaningful error code on failure (i.e., S_OK should return 0, and E_OUTOFMEMORY should return a different return value than E_FAIL and so on). Is the following an okay approach?:

int wmain(int argc, wchar_t *argv[])
{
    HRESULT hr = DoSomething();
    return (int) hr;
}

Or is there a better way? Maybe a standard Win32 API function or macro that I'm forgetting or failing to find?

Answer 1

HRESULT is just a 32-bit integer, with each code being a different value, so what you are doing is what you want.

Answer 2

The "better way" is to use a C++ style cast:

HRESULT hr = DoSomething();
return static_cast<int>(hr);

Otherwise, like Steve said, it's just an integer. It is defined as a long, not an int, but instead of casting from HRESULT to long to int, you can obviously just do it in one maneuver.

(That is to say, windows.h makes the assumption that long will be a 32-bit integer, which the C & C++ standard's do not guarantee. But that's just how things go, I suppose.)

---

Even better is that this does not require a cast at all.

Answer 3

There is an implicit conversion, so the cast is unnecessary.

(Rather more unfortunately, there is also an implicit conversion to bool, and to the Win32 BOOL typedef, so S_OK converts to false and all other values (including errors) convert to true - a common source of errors in COM programs.)

Answer 4

The OP wants a return value of zero to indicate success. There are success codes which are non-zero and so...

if ( SUCCEEDED( hr ) )
    return 0;
return hr;