DllImport Attempted to read or write protected memory

[lixinwin2003]

int ReadCard(char *room, char *gate,char *stime, char *guestname, char *guestid, char *track1, char *track2, long *cardno, int *st);
这是dll里的原函数
其中：room、gate、stime、guestname、guestid、track1、track2、cardno、st为输出参数
gate、Guestname 、Guestid 、track1 、track2 可以为null
翻译成C#的代码：
int ReadCard(ref string room, string gate, ref string stime,
ref string guestname, ref string guestid, string track1, string track2,
ref int cardno, ref int st);


这样写报错哟，你帮我看看！！
Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
试图读取或写入受保护的内存。这往往是一个迹象表明其他内存已损坏。

[lixinwin2003]

调用代码： string room = ""; //String gate = null; string stime = ""; //string guestname = null; string guestid = ""; //String track1 = null; //String track2 = null; int cardno = 0; int st = 1; int restul = adelMain.ReadCard(ref room, null, ref stime, null, ref guestid, null, null, ref cardno, ref st); if (restul == 0) { MessageBox.Show("成功！"); } else { MessageBox.Show("失败！" + restul); } 原型： [DllImport("MainDll.dll")] public static extern int ReadCard(ref string room, string gate, ref string stime, string guestname, ref string guestid, string track1, string track2, ref int cardno, ref int st);

[lixinwin2003]

问题已经自己解决，这里数据类型错误，用StringBuilder，去ref，就可以！！都没有人回我！