C# Marshal類基本概念和入門示例程式

marshal:直譯為“編排”， 在計算機中特 指将資料按某種描述格式編排出來，通常來說一般是從非文本格式到文本格式的資料轉化。

unmarshal是指marshal的逆過程。比如在WebService中，我們需要把java對象以xml方式表示并在網絡間傳輸，把java對象轉化成xml片段的過程就是marshal.

微軟對C#中Marshal類描述的連結在此；

https://docs.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.marshal?view=net-5.0

Provides a collection of methods for allocating unmanaged memory, copying unmanaged memory blocks, and converting managed to unmanaged types, as well as other miscellaneous methods used when interacting with unmanaged code.

提供一個方法集合，配置設定非托管記憶體，拷貝非托管記憶體塊，轉換托管和非托管類型，以及一些和非托管代碼互動的雜類方法；

    這是Marshal類的基本功能；.net一共包含四個Marshal類，每個都有一些方法；

下面來看一個Marshal類基本程式；程式運作結果如下；

代碼如下；

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace marshalDemo1
{
    public struct Point
    {
        public Int32 x, y;
    }

    public partial class Form1 : Form
    {

        [DllImport("Kernel32", ExactSpelling = true, SetLastError = true)]
        static extern Boolean CloseHandle(IntPtr h);

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            textBox1.Text = Marshal.SystemDefaultCharSize.ToString();
            textBox2.Text = Marshal.SystemMaxDBCSCharSize.ToString();
            textBox3.Text = Marshal.SizeOf(typeof(Point)).ToString();
            Point p = new Point(); 
            textBox4.Text = Marshal.SizeOf(p).ToString();
            IntPtr hglobal = Marshal.AllocHGlobal(100);
            textBox5.Text = hglobal.ToString();
            Marshal.FreeHGlobal(hglobal);

            Boolean f = CloseHandle(new IntPtr(-1));
            if (!f)
            {
                Console.WriteLine("CloseHandle call failed with an error code of: {0}",
                    Marshal.GetLastWin32Error());
            }
        }
    }
}