Marshal.SizeOf返回值不正确？

[zhangzhentao]

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;

namespace MarshalTest
{
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct FileInfo_s
{
public Int32 mBlockNum; //4 Bytes

[MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)] //32 Bytes
public char[] mFileName;

[MarshalAs(UnmanagedType.ByValArray, SizeConst = 33)] //33 Bytes
public char[] mMd5;
};

class Program
{
static void Main(string[] args)
{
FileInfo_s fileInfo = new FileInfo_s();
Console.WriteLine(Marshal.SizeOf(fileInfo)); //72 ?
}
}
}

很奇怪为什么输出的是72个字节，而不是4+32+33 = 69个字节？

[gxingmin]

内存对齐 http://bbs.csdn.net/topics/280068138

[骑着蜗牛去爬山]

http://blog.csdn.net/wyqlxy/article/details/6608819

[wetcom]

引用 2 楼 hjywyj 的回复:

http://blog.csdn.net/wyqlxy/article/details/6608819

楼上正解

[Monkey_ye]

第一次知道还有内存对齐的情况

[zhangzhentao]

引用 2 楼 hjywyj 的回复:

http://blog.csdn.net/wyqlxy/article/details/6608819

谢谢hjywyj和gxingmin，基本明白了。 但有一个小疑惑，如果我去掉public Int32 mBlockNum; ，按照引用文章“C#中alignment的字节数为4个字节"所述，推理结果应该依然是4的倍数（即68），然而实际却正常输出了65 ？ using System; using System.Collections.Generic; using System.Text; using System.Runtime.InteropServices; namespace MarshalTest { [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)] public struct FileInfo_s { //public Int32 mBlockNum; //4 Bytes [MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)] //32 Bytes public char[] mFileName; [MarshalAs(UnmanagedType.ByValArray, SizeConst = 33)] //33 Bytes public char[] mMd5; }; class Program { static void Main(string[] args) { FileInfo_s fileInfo = new FileInfo_s(); Console.WriteLine(Marshal.SizeOf(fileInfo)); //65 } } }

[zhangzhentao]

public Int32 mBlockNum正好为4个字节，且位置在该结构中的第一个，按理说不该影响后面的char？

[gxingmin]

一个char只占1个字节

[真相重于对错]

http://baike.baidu.com/view/4786260.htm