What values to return for S_OK or E_FAIL from c# .net code?

E_FAIL is Hex 80004005 in WinError.h

You can see the full Common HRESULT Values. You don't have to install C++ just to see the values.

UPDATE:

The signed and unsigned versions of 0x80004005 are just two representations of the same bit mask. If you're getting a casting error then use the negative signed value. When casted to an UN signed long it will be the "correct" value. Test this yourself in C#, it'll work e.g.

This code

    static void Main(string[] args)
    {
        UInt32 us = 0x80004005;
        Int32 s = (Int32)us;

        Console.WriteLine("Unsigned {0}", us);
        Console.WriteLine("Signed {0}", s);
        Console.WriteLine("Signed as unsigned {0}", (UInt32)s);

        Console.ReadKey();
    }

will produce this output

• Unsigned 2147500037
• Signed -2147467259
• Signed as unsigned 2147500037

So it's safe to use -2147467259 for the value of E_FAIL

From WinError.h for Win32

#define E_FAIL _HRESULT_TYPEDEF_(0x80004005L)

To find answers like this, use visual studio's file search to search the header files in the VC Include directory of your visual studio install directory.

C:\Program Files\Microsoft Visual Studio 9.0\VC\include

Use the "unchecked" keyword to do this.

e.g.

const int E_FAIL = unchecked((int)0x80004005);