Pinvoke期间第二个值未传递到C ++函数

Question

I have a c++ function which I am calling from c# using pinInvoke. Following is my cpp method-

int test(DWORD verb,DWORD verb2 )
{
    return verb2 *100;
}

My function is exposed as -

extern "C" {
    __declspec(dllexport) int test(DWORD verb, DWORD verb2);
}

Following is my c# code where I am calling the above method:

public class API
{
    [DllImport("mydll.dll", EntryPoint = "test", SetLastError = true, CallingConvention = CallingConvention.Cdecl)]
    [return: MarshalAs(UnmanagedType.U4)]
    public static extern uint test(
        [MarshalAs(UnmanagedType.U8)]ulong verb,
        [MarshalAs(UnmanagedType.U8)]ulong verb2);

    static void Main(string[] args)
    {
        uint x = DPAPI.test(26,10);
        Console.Write("result is-"+x);
    }
}

Here the second value is getting passed as 0,so wrong result is coming. Am I doing something wrong while passing the value?

What I have tried:

I am relatively new to Pinvoke. So I tried debugging to see whether the value is not getting passed to c++ code or whether the c++ code is not returning proper values.I found that the value getting passed itself was wrong.

Answer 1

DWORD is a 32 but unsigned integer. You are mapping that to a 64 bit type. That is the problem. Your p/invoke should be:

[DllImport("mydll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int test(uint verb, uint verb2);

Note that I removed the needless EntryPoint and the erroneous SetLastError from the DllImport attribute.

I also wonder why you have selected DWORD . Unless you are passing those values onto Win32 functions it would likely make more sense to use intrinsic types. Why not use int or unsigned int in your C++ code?