Program.cs

using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Text;

namespace InspectClipboard;

internal class Program
{
    [STAThread]
    static void Main(string[] args)
    {
        if (!OpenClipboard(IntPtr.Zero))
        {
            Console.WriteLine("Failed to open clipboard");
            return;
        }

        try
        {
            uint fmt = 0;

            while ((fmt = EnumClipboardFormats(fmt)) != 0)
            {
                string name = GetFormatName(fmt);
                IntPtr h = GetClipboardData(fmt);
                if (h == IntPtr.Zero)
                {
                    Console.WriteLine($"Format: {name} ({fmt}), GetClipboardData returned NULL");
                    continue;
                }

                var sz = GlobalSize(h);
                var size = (int)sz;

                IntPtr p = GlobalLock(h);
                if (p == IntPtr.Zero)
                {
                    Console.WriteLine($"Format: {name} ({fmt}), GlobalLock returned NULL");
                    continue;
                }

                try
                {
                    byte[] data = new byte[size];
                    Marshal.Copy(p, data, 0, size);
                    Console.WriteLine($"Format: {name} ({fmt}), Size: {size}");

                    if (data[^1] != 0)
                    {
                        Console.WriteLine($"**** Data does not end with null terminator ****");
                    }
                }
                finally
                {
                    GlobalUnlock(h);
                }
            }

            var errror = Marshal.GetLastWin32Error();
            if (errror != 0)
            {
                Debug.WriteLine($"EnumClipboardFormats error: {errror}");
            }


        }
        finally
        {
            CloseClipboard();
        }
    }

    private static string GetFormatName(uint fmt)
    {
        StringBuilder sb = new(128);
        if (fmt >= 0xC000 && GetClipboardFormatName(fmt, sb, sb.Capacity) > 0)
        {
            return sb.ToString();
        }

        return fmt.ToString();
    }

    [DllImport("user32.dll", SetLastError = true)]
    static extern bool OpenClipboard(IntPtr hWndNewOwner);
    [DllImport("user32.dll", SetLastError = true)]
    static extern bool CloseClipboard();
    [DllImport("user32.dll", SetLastError = true)]
    static extern uint EnumClipboardFormats(uint format);
    [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
    static extern uint GetClipboardFormatName(uint format, StringBuilder lpszFormatName, int cchMaxCount);
    [DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr GetClipboardData(uint uFormat);

    [DllImport("kernel32.dll", SetLastError = true)]
    static extern IntPtr GlobalLock(IntPtr hMem);
    [DllImport("kernel32.dll", SetLastError = true)]
    static extern bool GlobalUnlock(IntPtr hMem);
    [DllImport("kernel32.dll", SetLastError = true)]
    static extern uint GlobalSize(IntPtr hMem);
}