就任何一个程序员来说，对WINDOWS消息机制的认知和对消息的处理，可以说是必修的内容。我们知道，WINDOWS消息的两个参数wParam 、lParam有时是数值类型，有时则是指针类型。特别是指针类型，它指向的是一个内存地址，那么对它们的处理则因开发语言的不同而有所不同。

    都说C#取消了指针（非安全模式例外），可我个人觉得，C#并没有真正取消指针，只是把她装扮得更加迷人罢了！而不需程序员通过 *p 之类去直接处理而已。

    下面我就以一个例程，来看看C#中是如何处理WINDOWS消息中指针类型的参数的。这个例程是AOGO曾经用MASM汇编来实现的，这就是限制一个窗体大小的变化在一个许可的范围内。本例程只限制宽度不超过600。

    这里主要涉及到两个问题：
1. 如何取得指针所指向的内存地址中的内容？
2. 如何将指针指向新的内容？（也可能是将新内容复制到指针所指向的内存地址中）

处理这两个问题的方法哦是知道了，至于它的内部实现机制哦就不明白了 ^_^ ^_^ ^_^
有了这两个方法，我们就可以对WINDOWS的任何消息进行处理了。C#的厉害由此可见！！！

好啦，哦不多说啦。看源码就啥都明白了


===================== Form1.cs =====================

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Runtime.InteropServices;   // 注意这个命名空间

namespace WinMsgApp
{

   public class Form1 : System.Windows.Forms.Form
   {

      // 声明Winodws消息常量
      private const int WM_SIZEING = 0x0214;

      // 声明RECT结构
      public struct RECT
      {
         public int left;
         public int top;
         public int right;
         public int bottom;
      }

      // 以下是C# IDE自动生成的代码
      private System.Windows.Forms.TextBox textBox1;
      private System.Windows.Forms.TextBox textBox2;
      private System.Windows.Forms.TextBox textBox3;
      private System.Windows.Forms.TextBox textBox4;
      private System.Windows.Forms.Label label1;
      private System.Windows.Forms.Label label2;
      private System.Windows.Forms.Label label3;
      private System.Windows.Forms.Label label4;
      
      private System.ComponentModel.Container components = null;

      public Form1()
      {
         InitializeComponent();
      }

      protected override void Dispose( bool disposing )
      {
         if( disposing )
         {
            if (components != null)
            {
               components.Dispose();
            }
         }
         base.Dispose( disposing );
      }

      #region Windows Form Designer generated code

      private void InitializeComponent()
      {
         this.textBox1 = new System.Windows.Forms.TextBox();
         this.textBox2 = new System.Windows.Forms.TextBox();
         this.textBox3 = new System.Windows.Forms.TextBox();
         this.textBox4 = new System.Windows.Forms.TextBox();
         this.label1 = new System.Windows.Forms.Label();
         this.label2 = new System.Windows.Forms.Label();
         this.label3 = new System.Windows.Forms.Label();
         this.label4 = new System.Windows.Forms.Label();
         this.SuspendLayout();
         //
         // textBox1
         //
         this.textBox1.Location = new System.Drawing.Point(80, 8);
         this.textBox1.Name = "textBox1";
         this.textBox1.TabIndex = 0;
         this.textBox1.Text = "";
         //
         // textBox2
         //
         this.textBox2.Location = new System.Drawing.Point(80, 32);
         this.textBox2.Name = "textBox2";
         this.textBox2.TabIndex = 1;
         this.textBox2.Text = "";
         //
         // textBox3
         //
         this.textBox3.Location = new System.Drawing.Point(80, 56);
         this.textBox3.Name = "textBox3";
         this.textBox3.TabIndex = 2;
         this.textBox3.Text = "";
         //
         // textBox4
         //
         this.textBox4.Location = new System.Drawing.Point(80, 80);
         this.textBox4.Name = "textBox4";
         this.textBox4.TabIndex = 3;
         this.textBox4.Text = "";
         //
         // label1
         //
         this.label1.Location = new System.Drawing.Point(0, 8);
         this.label1.Name = "label1";
         this.label1.Size = new System.Drawing.Size(78, 23);
         this.label1.TabIndex = 4;
         this.label1.Text = "Left:";
         this.label1.TextAlign = System.Drawing.ContentAlignment.MiddleRight;
         //
         // label2
         //
         this.label2.Location = new System.Drawing.Point(0, 32);
         this.label2.Name = "label2";
         this.label2.Size = new System.Drawing.Size(78, 23);
         this.label2.TabIndex = 5;
         this.label2.Text = "Top:";
         this.label2.TextAlign = System.Drawing.ContentAlignment.MiddleRight;
         //
         // label3
         //
         this.label3.Location = new System.Drawing.Point(0, 56);
         this.label3.Name = "label3";
         this.label3.Size = new System.Drawing.Size(78, 23);
         this.label3.TabIndex = 6;
         this.label3.Text = "Right:";
         this.label3.TextAlign = System.Drawing.ContentAlignment.MiddleRight;
         //
         // label4
         //
         this.label4.Location = new System.Drawing.Point(0, 80);
         this.label4.Name = "label4";
         this.label4.Size = new System.Drawing.Size(78, 23);
         this.label4.TabIndex = 7;
         this.label4.Text = "Bottom:";
         this.label4.TextAlign = System.Drawing.ContentAlignment.MiddleRight;
         //
         // Form1
         //
         this.AutoScaleBaseSize = new System.Drawing.Size(6, 14);
         this.ClientSize = new System.Drawing.Size(296, 117);
         this.Controls.AddRange(new System.Windows.Forms.Control[] {
                                                        this.label4,
                                                        this.label3,
                                                        this.label2,
                                                        this.label1,
                                                        this.textBox4,
                                                        this.textBox3,
                                                        this.textBox2,
                                                        this.textBox1});
         this.Name = "Form1";
         this.Text = "Form1";
         this.ResumeLayout(false);

      }
      #endregion
      // 自动生成的代码到此结束


      // 以下是处理WINDOWS消息的主要代码
      protected override void WndProc(ref System.Windows.Forms.Message m )
      {
         switch(m.Msg)
         {      
            case WM_SIZEING:
                
               // 第一种方法，简洁明了
               // RECT rc = (RECT)m.GetLParam(typeof(RECT));

               // 第二种方法，易懂稍繁
               RECT rc = new RECT();

               // 将m.LParam指针所指向的RECT结构复制到rc
               rc = (RECT)m.GetLParam(rc.GetType());

               // 将结构rc各字段的值显示出来
               textBox1.Text = rc.left.ToString();
               textBox2.Text = rc.top.ToString();
               textBox3.Text = rc.right.ToString();
               textBox4.Text = rc.bottom.ToString();

               // 限制窗体宽度不超过600
               if (rc.right - rc.left >600)
               {
                  rc.right =rc.left +600;
               }

               // 将结构rc复制到m.LParam指针所指向的RECT结构
               Marshal.StructureToPtr(rc,m.LParam,true);

               break;
            default:
               base.WndProc(ref m);   // 调用基类函数处理其他消息。
               break;
         }
      }
      
  
      [STAThread]
      static void Main()
      {
         Application.Run(new Form1());
      }
   }
}