C#中怎样定义API中因平台而异的结构体？解决方案

C#中怎样定义API中因平台而异的结构体？
例如，TBBUTTON的定义为

C/C++ code

typedef struct {  int       iBitmap;  int       idCommand;  BYTE      fsState;  BYTE      fsStyle;#ifdef _WIN64  BYTE      bReserved[6];#else #if defined(_WIN32)  BYTE      bReserved[2];#endif #endif   DWORD_PTR dwData;  INT_PTR   iString;} TBBUTTON, *PTBBUTTON, *LPTBBUTTON;

C# code

[MarshalAsAttribute(UnmanagedType.ByValArray, SizeConst = 6)]public byte[] bReserved;

C# code

[MarshalAsAttribute(UnmanagedType.ByValArray, SizeConst = 2)]public byte[] bReserved;