Read error in Serial port communication

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MFC

I was trying to implement a serial port communication, the SetCommState function returns error(0).
I have tried with the following code.

COMMPROP commprop = {0};
COMMTIMEOUTS timeouts = {0};
    m_hComm = CreateFile(_T("COM1"),						// communication port string (COMX)
    GENERIC_READ | GENERIC_WRITE,	// read/write types
    0,								// comm devices must be opened with exclusive access
    NULL,							// no security attributes
    OPEN_EXISTING,					// comm devices must use OPEN_EXISTING
    0,			// Async I/O
    NULL);

if (0 == GetCommProperties(m_hComm,&commprop)) {

    MessageBox(_T("Error in setting params"), _T("Error"), 
    MB_ICONERROR | MB_OK);
}
if (m_hComm == INVALID_HANDLE_VALUE)
{
    // port not found
    MessageBox(_T("Cannot open port"), _T("Error"), 
    MB_ICONERROR | MB_OK);
}
else
{
    MessageBox(_T("Port open"), _T("Info"), 
    MB_ICONINFORMATION | MB_OK);
}

DWORD size =1;
char readBuf[5];
char sendBuf[10];
DCB dcb;

memset(readBuf,0,5);
memset(sendBuf,0,10);
memset(&dcb,0,sizeof(dcb));
dcb.DCBlength=sizeof(dcb);
GetCommState(m_hComm,&dcb);		
dcb.BaudRate=5;
dcb.ByteSize = 8;
dcb.StopBits = ONESTOPBIT;
dcb.Parity = NOPARITY;

if (0 == SetCommState(m_hComm,&dcb))
{
    AfxMessageBox(_T("error on setting baud rate"));
}
while(size ==0)
{
    if(!ReadFile(m_hComm, &readBuf[0], 1, &size, NULL))
    {
        MessageBox(_T("Read Error"), _T("Error"), 
        MB_ICONERROR | MB_OK);
    }
}

Is it valid to use FILE_FLAG_OVERLAPPED when calling the CreateFile method? I cannot identify why this issue happens, Please help me to find the trouble with this code.