Using sizeof a Managed Structure in C#

Question

I am trying to port C++ code to C#. The code is meant to register a window class using RegisterClassEx.

The C++ code has an object WNDCLASSEX wcex. Object wcex has a property

wcex.cbSize = sizeof(WNDCLASSEX);

In C#, I have defined the structure as

    [StructLayout(LayoutKind.Sequential)]
    public struct WNDCLASSEX
    {
        public uint cbSize;
        public uint style;
        [MarshalAs(UnmanagedType.FunctionPtr)]
        public PlatformInvokeGDI32.WNDPROC lpfnWndProc;
        public int cbClsExtra;
        public int cbWndExtra;
        public IntPtr hInstance;
        public IntPtr hIcon;
        public IntPtr hCursor;
        public IntPtr hbrBackground;
        public string lpszMenuName;
        public string lpszClassName;
        public IntPtr hIconSm;
    }

I have tried to get the size using

wcex.cbSize = (uint)sizeof(WNDCLASSEX);

The function containing this stament is declared as

unsafe private void

I hoped the unsafe would make the statment work. However, I get this error in the IDE:

Cannot take the address of, get the size of, or declare a pointer to a managed type ('CaptureScreen.PlatformInvokeGDI32.WNDCLASSEX')

Can I make the structure into an unmanaged structure? If so, how? Is there a way to use sizeof without making the structure unmanaged? Is there a .NET version of sizeof that would work?

Just to be sure.. you know that using Win32 API to create windows can be done a million times more easily with Windows Forms, the C#/.NET equivalent? — Kieren Johnstone, Oct 25 '11 at 20:37
I do. My project is just supposed to help me learn about the Win32 API. — Jacob Quisenberry, Oct 25 '11 at 22:05

score 10 · Accepted Answer · answered Oct 25 '11 at 20:35

10

Use Marshal.SizeOf instead.

answered Oct 25 '11 at 20:35

Gabe

84,912
12
139
238

Thank you. I ended up using `wcex.cbSize = (uint)Marshal.SizeOf(typeof(PlatformInvokeUSER32.WNDCLASSEX));` – Jacob Quisenberry Oct 25 '11 at 22:05
Things change over time, and now MS recommends the generic form of this method, e.g. `(uint)Marshal.SizeOf();` https://learn.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.marshal.sizeof?view=netcore-3.1 – Paul Williams May 14 '20 at 17:22

Using sizeof a Managed Structure in C#

1 Answers1