how to realize serial writing is ended in windows - c++

Question

I everyone,
I'm trying to write on serial and also the serial should wait until all bytes are sent.
how can the serial wait to send all bytes?
I was surfing on the internet that I saw this.then, I tried to use the samples. unluckily, they didn't work well.
For example, I tried for use the following code:
BOOL WriteABuffer(char * lpBuf, DWORD dwToWrite)
{
OVERLAPPED osWrite = {0};
DWORD dwWritten;
DWORD dwRes;
BOOL fRes;
// Create this write operation's OVERLAPPED structure's hEvent.
osWrite.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (osWrite.hEvent == NULL)
// error creating overlapped event handle
return FALSE;
// Issue write.
if (!WriteFile(hComm, lpBuf, dwToWrite, &dwWritten, &osWrite)) {
if (GetLastError() != ERROR_IO_PENDING) {
// WriteFile failed, but isn't delayed. Report error and abort.
fRes = FALSE;
}
else
// Write is pending.
dwRes = WaitForSingleObject(osWrite.hEvent, INFINITE);
switch(dwRes)
{
// OVERLAPPED structure's event has been signaled.
case WAIT_OBJECT_0:
if (!GetOverlappedResult(hComm, &osWrite, &dwWritten, FALSE))
fRes = FALSE;
else
// Write operation completed successfully.
fRes = TRUE;
break;
default:
// An error has occurred in WaitForSingleObject.
// This usually indicates a problem with the
// OVERLAPPED structure's event handle.
fRes = FALSE;
break;
}
}
}
else
// WriteFile completed immediately.
fRes = TRUE;
CloseHandle(osWrite.hEvent);
return fRes;
}
But, it doesn't wait to send all bytes. after WriteFile(..) I expect to wait. But, it'll reach to this line.
else
// WriteFile completed immediately.
fRes = TRUE; <--------------------------- this line
And then it returns true.
why doesn't it wait ?
==========Edit========
It's my current function for writing to serial but still it doesn't wait.
int RS232_SendBuf(int comport_number, unsigned char *buf, int size)
{
int n;
DWORD dwCommEvent;
DWORD dwStoredFlags;
dwStoredFlags = EV_BREAK | EV_CTS | EV_DSR | EV_ERR | EV_RING | \
EV_RLSD | EV_RXCHAR | EV_RXFLAG | EV_TXEMPTY;
if (!SetCommMask(Cport[comport_number], dwStoredFlags)) {
// Error setting communications mask
return FALSE;
}
if(WriteFile(Cport[comport_number], buf, size, (LPDWORD)((void *)&n), NULL))
{
if (WaitCommEvent(Cport[comport_number], &dwCommEvent, NULL)) {
// An error occurred waiting for the event.
return FALSE;
}
else {
return(n);
}
}
//while (!PurgeComm(Cport[comport_number], PURGE_TXABORT));
return(-1);
}