Question: Export function with out parameter

Hi, I’m trying to migrate code that previously used DllExport so it could be used by InnoSetup.

Previously I had

[MarshalAs(UnmanagedType.LPWStr)] string input, [MarshalAs(UnmanagedType.BStr)] out string output

I can’t make an out IntPtr though

  [UnmanagedCallersOnly(CallConvs = new[] { typeof(System.Runtime.CompilerServices.CallConvStdcall) })]
        public static void ReturnString(IntPtr value, out IntPtr result)
        {
            var message = Marshal.PtrToStringUni(value);
            _ = NativeMethods.MsgBox(IntPtr.Zero, message, ":)", 0);

            result = Marshal.StringToBSTR("???"); 
        }

This required for interaction with Pascal/Delphi, where the return value is passed as parameter by reference when using stdcall: https://stackoverflow.com/a/9353800/4503491

[AaronRobinsonMSFT]

public static unsafe void ReturnString(IntPtr value, int* result)

@CoenraadS This is a bit questionable if your previous API was using out IntPtr. Instead this should be:

public static unsafe void ReturnString(IntPtr value, IntPtr* result)
{
    var message = Marshal.PtrToStringUni(value);
    _ = NativeMethods.MsgBox(IntPtr.Zero, message, ":)", 0);
    *result = Marshal.StringToBSTR("???");
}

[AaronRobinsonMSFT]

The default for x86 on Windows is stdcall but on non-Windows it is cdecl.

I think I will probably build a small code generation layer ontop of DNNE so I abstract away these pointers and put out & marshal types in the signature, but thought first I would ask if something perhaps already exists?

When you say “on top of”, I assume you mean to say that the method UnmanagedCallersOnly calls a method that uses the C# keyword - this is fine. If this isn’t the case, please elaborate.