Three com ports communication programs in Visual Studio 2019 - winapi

Question

If there are three com ports ex, COM10, COM11, COM12.
I want to connect all NEW three com ports and sequentially transfer data to COM10, COM11, COM12.
Should I use CreateFile three times?
// my source
HANDLE m_hComm;
m_hComm = CreateFile(szPort, // 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
FILE_ATTRIBUTE_NORMAL|FILE_FLAG_OVERLAPPED, // Async I/O
0); // template must be 0 for comm devices
How to set the handle value for each com port when you want to transmit data sequentially to COM10, COM11, COM12?
// my source
n = WriteFile(m_hComm, pBuff, nToWrite, &dwWritten,&m_ovrWrite);

Answer 1

Calling CreateFile three times before using any if the ports is the best way to achieve what you want. Otherwise, you would have to repeatedly 'create' each port, send ('write') the data then close each port's handle (with a call to CloseHandle) - and this will be far less efficient.
(Note: For COM ports with an index greater than 9, you should use the "\\.\COMxx" syntax.)
So, to open the three ports together, you can use an array of handles (and an array of port names); like this:
char szPort[3][10] = { "\\\\.\\COM10", "\\\\.\\COM11", "\\\\.\\COM12" };
HANDLE m_hComm[3];
for (int i = 0; i < 3; ++i) {
m_hComm[i] = CreateFile(szPort[i], // 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
FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED, // Async I/O
0); // template must be 0 for comm devices
}
You can then send data to any one of the open ports using the appropriate value from the m_hComm array. Thus, to send the same data to each of the three ports, you could use a loop like the following:
for (int p = 0; p < 3; ++p) { // Loop to send the same data to all three ports...
//...
BOOL n = WriteFile(m_hComm[p], pBuff, nToWrite, &dwWritten, &m_ovrWrite);
//...
}
Please feel free to ask for further clarification and/or explanation.