用OnSerialMsg进行串口通信

串口通信程序，利用OnSerialMsg消息响应函数
LRESULT CProjectViewDlg::OnSerialMsg (WPARAM wParam, LPARAM /*lParam*/)
{
CSerial::EEvent eEvent = CSerial::EEvent(LOWORD(wParam));
CSerial::EError eError = CSerial::EError(HIWORD(wParam));

char sinkcom[101]; //接收的数据先放在sinkcom中
memset(sinkcom,0,sizeof(sinkcom));
if (eEvent & CSerial::EEventRecv)
{
// Obtain the data from the serial port
do
{
// Read data from the COM-port
lreadError = g_SerialComm.Read(sinkcom,sizeof(sinkcom)-1,&dwReadcom); //将数据读到sinkcom中

if (dwReadcom > 0)
{
if ((m_nCountcom+dwReadcom)<sizeof(m_Bufcom))
{
memcpy(m_Bufcom+m_nCountcom,sinkcom,dwReadcom);

m_nCountcom += dwReadcom;
m_Bufcom[m_nCountcom] = /*_T*/('\0');

}

}

}while (dwReadcom > 0);
}

return 0;
}

单步执行的时候，为什么在这个地方执行三次？dwReadcom 是用来干嘛的？

帮帮忙啊