//Sequential，按最大成员长度进行对齐，占用内存将是 最大长度成员的整数倍长度
[StructLayout(LayoutKind.Sequential)]
struct Struct1
{
    public short Short1;
    public int Int1;
    public short Short2;
}

//总共占用12字节，每行4字节，两个short各占一半，剩余填充，int占一行
1 Short1  | --------
2        Int1
3 Short2  | --------
//如果 int 改为 long，占用内存将变为 24字节=8*3



[StructLayout(LayoutKind.Sequential)]
struct Struct1
{   
    public int Int1;
    public short Short1;
    public short Short2;
}
//每行4字节，两个short占行，int占一行
1      Int1
2 Short1 | Short2
//如果 int 改为 long，占用内存将变为 16字节=8*2

 //总共8字节  Int1占0-3，Short1占4-5，Short2占6-7，
 [StructLayout(LayoutKind.Explicit)]
 struct Struct1
 {   
     [FieldOffset(0)]
     public int Int1;
     [FieldOffset(4)]
     public short Short1;
     [FieldOffset(6)]
     public short Short2;
 }