C#中结构和类成员指针的内存分配

作者:Magci 日期:2009-01-08 02:29

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通过结构和类成员指针的操作，观察内存分配情况：
1.结构、类成员是按顺序排列在内存中的；
2.通过指针操作可以方便的指向任意变量。

TestPointerExampleTwo.cs:
using System; 
  
namespace Magci.Test.Pointers 
{ 
    //结构 
    internal struct CurrencyStruct 
    { 
        public long Dollars; 
        public byte Cents; 
  
        public override string ToString() 
        { 
            return "$" + Dollars + "." + Cents; 
        } 
    } 
  
    //类 
    internal class CurrencyClass 
    { 
        public long Dollars; 
        public byte Cents; 
  
        public override string ToString() 
        { 
            return "$" + Dollars + "." + Cents; 
        } 
    } 
  
    public class TestPointerExampleTwo 
    { 
        public static unsafe void Main() 
        { 
            Console.WriteLine("Size of CurrencyStruct struct is " + sizeof(CurrencyStruct)); 
            CurrencyStruct amount1, amount2; 
            CurrencyStruct* pAmount = &amount1; 
            long* pDollars = & (pAmount->Dollars); 
            byte* pCents = & (pAmount->Cents); 
  
            Console.WriteLine("Address of amount1 is [0x{0:X}]", (uint)&amount1); 
            Console.WriteLine("Address of amount2 is [0x{0:X}]", (uint)&amount2); 
            Console.WriteLine("Address of pAmount is [0x{0:X}]", (uint)&pAmount); 
            Console.WriteLine("Address of pDollars is [0x{0:X}]", (uint)&pDollars); 
            Console.WriteLine("Address of pCents is [0x{0:X}]", (uint)&pCents); 
  
            pAmount->Dollars = 20; 
            *pCents = 50; 
              
            Console.WriteLine("amount1 contains [{0}]", amount1); 
            //amount2存储在amount1后面的地址上，pAmount开始指向amount1，递减后就指向了amount2 
            --pAmount; 
            //amount2没有进行初始化，值是随机的；使用指针时会绕过很多通常的编译检查，因此指针算法是不安全的 
            Console.WriteLine("amount2 has address [0x{0:X}] and contains [{1}]", (uint)pAmount, *pAmount); 
  
            //将pCents指向amount2.Cents 
            CurrencyStruct* pTempCurrency = (CurrencyStruct*)pCents; 
            pCents = (byte*)(--pTempCurrency); 
            Console.WriteLine("Address of pCents is now [0x{0:X}]", (uint)&pCents); 
              
            Console.WriteLine("\nNow with classes"); 
            CurrencyClass amount3 = new CurrencyClass(); 
  
            fixed (long* pDollars2 = &(amount3.Dollars)) 
            fixed (byte* pCents2 = &(amount3.Cents)) 
            { 
                Console.WriteLine("amount3.Dollars has address [0x{0:X}]", (uint)pDollars2); 
                Console.WriteLine("amount3.Cents has address [0x{0:X}]", (uint)pCents2); 
                *pDollars2 = -100; 
                Console.WriteLine("amount3 contains [{0}]", amount3); 
            } 
        } 
    } 
}