C++dll的方法为   LPECWATCHDATA  WINAPI  ecwGetExternsionData(WORD widx);
LPECWATCHDATA是这样定义的 
typedef struct {
    WORD     nState;               //状态
    WORD     nIdx;                 //索引
    WORD     wDataCnt;             //数据(lpData)项数
    char     szTime[20];           //时间
    unsigned char* lpIDString;     //设备号码
    unsigned char* lpNameString;   //设备/用户名称
    LPCTSTR  lpData[8];
}ECWATCHDATA,*LPECWATCHDATA;  

我在C#里是这样转的    ECWATCHDATAeds = (ECWATCHDATA)(Marshal.PtrToStructure(ecwGetExternsionData(i), typeof(ExteECWATCHDATA)));     ExternsionDataStruct是我自己定义的一个结构体，结构体为
    [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential, CharSet = System.Runtime.InteropServices.CharSet.Ansi)]
    public struct ECWATCHDATA
    {

        /// WORD->unsigned short
        public ushort nState;

        /// WORD->unsigned short
        public ushort nIdx;

        /// WORD->unsigned short
        public ushort wDataCnt;

        /// char[20]
        [System.Runtime.InteropServices.MarshalAsAttribute(System.Runtime.InteropServices.UnmanagedType.ByValTStr, SizeConst = 20)]
        public string szTime;

        /// char*
        public IntPtr lpIDString;

        /// char*
        public IntPtr lpNameString;

        /// char*[8]
        [System.Runtime.InteropServices.MarshalAsAttribute(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst = 8, ArraySubType = System.Runtime.InteropServices.UnmanagedType.SysUInt)]
        public System.IntPtr[] lpData;
    }
  ECWATCHDATAeds = (ECWATCHDATA)(Marshal.PtrToStructure(ecwGetExternsionData(i), typeof(ECWATCHDATA))); 转化C#的结构体后里面有的值不对。像lpIDString，lpNameString和实际值对不上，这是什么原因？