Creating a basic C++ .dll for p/invoke in C#

Question

I am a C# programmer, and unfortunately due to both age and experience, I did not have the luxury of getting the chance to go through the C++ era of programming in my learni

Answer 1

The third parameter needs to be a byte[], marshalled as a char*, of size 16.

If you check the documentation for ReadProcessMemory, it takes a buffer and a size, and this function passes the size as 16 bytes. This means that you will need a 16-byte array. The runtime should be perfectly happy to marshal a byte[] of size 16. Be careful not to mix C++ char with C# char- the C# char is actually a C++ wchar_t on Windows. The C++ char is C#'s byte.

Not that I have any actual idea about how that functions works- I just traced the usage of the third parameter and it only actually gets passed to ReadProcessMemory, the parameters for which are quite clearly documented.

To package into a .dll (assuming you have nothing else to go into that .dll), you want to add a couple things on to the beginning to ask the C++ compiler not to mangle the name and to export it for you, producing this as the first line

extern "C" __declspec(dllexport) void GetListItemData( HWND hListWnd, long index, char *outputResult )

You'll only need one C++ source file, no headers, and compile as DLL (it's in the project settings). You won't need any code except the function and any includes that you need.

In C#

[System.Runtime.InteropServices.DllImport(
    DLLPath,
    CallingConvention = CallingConvention.Cdecl
)]
private static extern void GetListItemData(
    System.IntPtr hWnd,
    System.Int32 index,
    [MarshalAs(UnmanagedType.LPArray)]byte[] buffer
);

Unfortunately, it's up to you to make sure that buffer is of sufficient size.