一个关于串口通信的问题，在线等待

我得串口通信采用轮询的方法取数据
串口初始化：

if(m_ctrlComm.GetPortOpen())
m_ctrlComm.SetPortOpen(FALSE);

m_ctrlComm.SetCommPort(1); //选择com1
if( !m_ctrlComm.GetPortOpen())
m_ctrlComm.SetPortOpen(TRUE);//打开串口
else
AfxMessageBox("cannot open serial port");

m_ctrlComm.SetSettings("1200,n,7,2"); //波特率1200，无校验，7个数据位，2个停止位
m_ctrlComm.SetRThreshold(0);
m_ctrlComm.SetInputMode(1); //1 通过 Input 属性以二进制方式检取回数据。
m_ctrlComm.SetInputLen(0); //设置当前接收区数据长度为0
m_ctrlComm.GetInput();//先预读缓冲区以清除残留数据


采用定时器采数据：

void CData_RevDlg::OnTimer(UINT nIDEvent)
{
// TODO: Add your message handler code here and/or call default
CString sDate; //日期
CString sTime;//时间
switch(nIDEvent)
{
case 1:
........
/* case 2:
{
VARIANT variant_inp;
COleSafeArray safearray_inp;
LONG len,k;
BYTE rxdata[2048]; //设置BYTE数组 An 8-bit integerthat is not signed.
CString strtemp;
CString temp;
int Rxcount=0;
variant_inp=m_ctrlComm.GetInput(); //读缓冲区 safearray_inp=variant_inp; //VARIANT型变量转换为ColeSafeArray型变量
len=safearray_inp.GetOneDimSize(); //得到有效数据长度
for(k=0;k<len;k++)
...............

当运行到
safearray_inp=variant_inp;

时，就出错
提示：
Debug Assertion Failed!
Program:e:\mytest.exe
File:olevar.cpp
Line:2553

For information on how your program can cause an assertion failure,see....