Conversion of HRESULT between C++ and C#

Question

I have C++ code which is called from C# using reflection and etc.

The weird thing I encountered is while on C++ side function declaration looks like this

dppFUNC(HRESULT) dppOnlineGetBalanceInfo(

On C# side it is declared as

[DllImport("dppClientModule.dll", CallingConvention = CallingConvention.StdCall)]
private static extern UInt32 dppOnlineGetBalanceInfo(

Why is the return type on C# code uint? Should not it be int?

What problems can it cause? It has been used like this now, and I would like to know what problems could it cause?

The linked question as duplicate seems different because the result of MAKEHRESULT (C# version) there in accepted answer is int, why?

Answer 1

HRESULT is defined as a long (32-bit signed) in C/C++. So technically, in C#, you would use an int. This is also the type Microsoft itself uses in C# for Exception.HResult.

The downside of using int over uint is that you'll have to explicitly cast, while disabling overflow-checking (unchecked), all the constants listed in the MSDN documentation:

For example:

const int E_FAIL = 0x80004005;

Cannot implicitly convert type 'uint' to 'int'. An explicit conversion exists (are you missing a cast?)

Add an explicit cast:

const int E_FAIL = (int)0x80004005;

Constant value '2147500037' cannot be converted to a 'int' (use 'unchecked' syntax to override)

Now, you have three options:

const int E_FAIL = ‭-2147467259‬;
const int E_FAIL = unchecked((int)0x80004005);
const uint E_FAIL = 0x80004005;

Using the negative values doesn't help to make things more readable. So either define all constants as unchecked((int)...) or treat HRESULT as uint.