C#调用DLL结构体,第一次成功,第二次的时候就报错。尝试读取或写入受保护的内存。

C++代码
typedef struct tagIDCardData{
char Name[32]; //姓名

char Sex[6]; //性别
char Nation[20]; //名族
char Born[18]; //出生日期
char Address[72]; //住址
char IDCardNo[38]; //身份证号
char GrantDept[32]; //发证机关
char UserLifeBegin[18]; // 有效开始日期
char UserLifeEnd[18]; // 有效截止日期
char reserved[38]; // 保留
char PhotoFileName[255];// 照片路径
}IDCardData;
int _stdcall Syn_ReadMsg( int iPort,int iIfOpen,IDCardData *pIDCardData );

C#代码
[StructLayoutAttribute(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)]
public struct IDCardData

{

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]

public string Name; //姓名

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 6)]

public string Sex; //性别

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 20)]

public string Nation; //名族

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 18)]

public string Born; //出生日期

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 72)]

public string Address; //住址

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 38)]

public string IDCardNo; //身份证号

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]

public string GrantDept; //发证机关

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 18)]
public string UserLifeBegin; // 有效开始日期

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 18)]
public string UserLifeEnd; // 有效截止日期

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 38)]
public string reserved; // 保留

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 255)]
public string PhotoFileName; // 照片路径

}

[DllImport("SynIDCardAPI.dll", EntryPoint = "Syn_ReadMsg", CharSet = CharSet.Ansi)]

public static extern int Syn_ReadMsg(int iPortID, int iIfOpen, ref IDCardData pIDCardData);
应用代码
public int nRet=0;pulblic int nPort=1001;private void ListenCard()

{

try

{

while (!_bListenCardQuit)

{

IDCardData CardMsg = new IDCardData();
nRet = Syn_ReadMsg(nPort, 0, ref CardMsg);//读取信息
GC.Collect(2, GCCollectionMode.Optimized);

Thread.Sleep(500);
}
_bQuitListenCardDone = true;
#region 异常

catch (Exception eE)

{

}

#endregion

}
运行到这里( nRet = Syn_ReadMsg(nPort, 0, ref CardMsg);//读取信息),第一次成功,运行第二次的时候就报错:出现尝试读取或写入受保护的内存。这通常指示其他内存已损坏!
恳请各位大牛帮忙解决一下问题啊!

尝试一下吧文件设置为可读写状态