BEtter solution to retrieve serial COM ports and fill a ComboBox (with MFC)

Question

BEtter solution to retrieve serial COM ports and fill a ComboBox (with MFC)

SG 35

Hi,
Despite the lack of any function to retrieve a list of serial COM ports in MFC, I wrote my own. It's working but I'm a bit confuse with all those Windows data types and I had to do some tricks to convert strings.
I use CreatefileW() to iterate over COM ports and I store the file name in a ComboBox if the port's handle is valid.

Both elements use a LPCTSTR , but I did not find any way to concatenate this data type.

To stay in adequation with MFC, I tried to use CFile instead of CreateFileW but it's more "file" oriented.

I found GetCommPorts(), a Win32 function (winbase.h) but I haven't found any sample code.

Is my code on the right way or I need to take another approach ?

int CMFCArduinoDlg::ListComPorts() 
{ 	
	HANDLE hComm;	// Handle for COM port 	
	CString tempFileName;	// Temporary filename	  	

	// Iterate 20 times to find any existing COM port 	
	for (int i = 1; i < 20; i++) 	
		{		 		
			std::string commonBaseName = "\\\\.\\COM";	// Common base for the filename
			commonBaseName += std::to_string(i); // Add port number at the end
			// Store the full filename into a CString
			tempFileName = commonBaseName.c_str();	
			// Cstring to LPCTSTR conversion	 		
			LPCTSTR lpFileName = tempFileName;			  		

			// Scan current port (COM+i) 		
			hComm = CreateFileW(lpFileName, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL); 		
			if (hComm != INVALID_HANDLE_VALUE) 		
				{
					// If hComm exists, add the COM port to ComboBox 
					comboBoxControl.AddString(lpFileName); 	
					CloseHandle(hComm);		 			
				} 	
		} 	
		return 0; 
}

Thanks and sorry for the headache.

3 answers

Your answer

Answer 1

David Lowndes 2,640 MVP

Using GetCommPorts should mean you don't have to try each one - it should give you the available port numbers.
Other than that, since you're using MFC, your code could be a little simpler if you just stick to using CString. Use its Format method to create the port number string, and there's no need to have lpFileName - it already has a cast method, so your code looks cleaner.

Example of GetCommPorts.

Answer 2

SG 35

OK found it in Naughter's code:
I replaced

CString portList[20];

by

	std::vector<CString> portList{ puPortNumbersFound, std::allocator<CString>{} };

Now the function returns a std::vector<CString>

I never used this before, it makes the code cleaner and can save lot of memory.

Thanks very much for your help

Answer 3

SG 35

OK, this GetCommPort function is a bit hard to tame.
I found a piece of code I re-adapted:

CString* CMFCArduinoDlg::ListCommPorts() 
{	 	
	std::vector<ULONG> lpPortNumbers;	// Array to store port numbers 	
	lpPortNumbers.resize(255);
	ULONG puPortNumbersFound = 0; 	
	ULONG nReturn = GetCommPorts(&(lpPortNumbers[0]), static_cast<ULONG>(lpPortNumbers.size()), &puPortNumbersFound); 	
	if (nReturn != ERROR_SUCCESS) 	
	{ 		
		SetLastError(nReturn); 		
		return false; 	
	}  	
	CString portList[20];	// Pre-allocated CString array 	 	
	for (int i = 0; i < puPortNumbersFound; i++) 	
	{ 		
		portList[i].Format(L"\\\\.\\COM%d", lpPortNumbers[i]);	// Port number full string (COMx) 	
	} 	
	return portList; 
}

This code is working but my problem is I don't know (anymore) how to pre-allocate the CString array to store the formatted strings.

I left C++ for almost 25 years, things come back little by little. (With my old book: Ivor Horton Visual C++ 6.0 of 1999).

David Lowndes 2,640 Reputation points MVP

2023-10-21T12:39:47.42+00:00

If you want to eliminate the fixed size array of CString that you have, use a vector of them.
The general usage pattern of functions that you don't know how much data they'll need is to pass none initially and have the function tell you how much you'll need, then allocate the storage and call it again. See what the code here does. http://www.naughter.com/enumser.html
Xiaopo Yang - MSFT 12,731 Reputation points Microsoft External Staff

2023-10-24T02:10:31.9933333+00:00

@SG, could you please complete the question?

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BEtter solution to retrieve serial COM ports and fill a ComboBox (with MFC)

3 answers

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