FILE_NOT_FOUND when trying to open COM port C++

Question

I am trying to open a com port for reading and writing using C++ but I can't seem to pass the first stage of actually opening it. I get an INVALID_HANDLE_VALUE on the handle with GetLastError FILE_NOT_FOUND. I have searched around the web for a couple of days I'm fresh out of ideas. I have searched through all the questions regarding COM on this website too.

I have scanned through the existing ports (or so I believe) to get the name of the port right.

I also tried combinations of _T("COM1") with the slashes, without the slashes, with colon, without colon and without the _T

I'm using windows 7 on 64 bit machine.

this is the code i got

I'll be glad for any input on this

void SendToCom(char* data, int len)
{

DWORD cbNeeded = 0;
DWORD dwPorts = 0;
EnumPorts(NULL, 1, NULL, 0, &cbNeeded, &dwPorts);

//What will be the return value
BOOL bSuccess = FALSE;

LPCSTR COM1 ;

BYTE* pPorts = static_cast<BYTE*>(malloc(cbNeeded));
bSuccess = EnumPorts(NULL, 1, pPorts, cbNeeded, &cbNeeded, &dwPorts);
if (bSuccess){
    PORT_INFO_1* pPortInfo = reinterpret_cast<PORT_INFO_1*>(pPorts);
    for (DWORD i=0; i<dwPorts; i++)
    {
        //If it looks like "COMX" then          
        size_t nLen = _tcslen(pPortInfo->pName);
        if (nLen > 3)
        {
            if ((_tcsnicmp(pPortInfo->pName, _T("COM"), 3) == 0) ){
                COM1 =pPortInfo->pName;
                //COM1 ="\\\\.\\COM1";
                HANDLE m_hCommPort = CreateFile( COM1 ,
                    GENERIC_READ|GENERIC_WRITE,  // access ( read and write)
                    0,                           // (share) 0:cannot share the COM port
                    NULL,                           // security  (None)
                    OPEN_EXISTING,               // creation : open_existing
                    FILE_FLAG_OVERLAPPED,        // we want overlapped operation
                    NULL                            // no templates file for COM port...
                    );
                if (m_hCommPort==INVALID_HANDLE_VALUE)
                {
                    DWORD err = GetLastError();
                    if (err == ERROR_FILE_NOT_FOUND) {
                        MessageBox(hWnd,"ERROR_FILE_NOT_FOUND",NULL,MB_ABORTRETRYIGNORE);
                    }
                    else
                        if(err == ERROR_INVALID_NAME) {
                            MessageBox(hWnd,"ERROR_INVALID_NAME",NULL,MB_ABORTRETRYIGNORE);
                        }
                        else
                        {
                            MessageBox(hWnd,"unkown error",NULL,MB_ABORTRETRYIGNORE);
                        }
                }
                else{
                    WriteAndReadPort(m_hCommPort,data);
                }
            }
            pPortInfo++;
        }
    }
 }

}

_T has been redundant for 10 years now. Windows 95 is dead. — Alan Stokes
– Alan Stokes, Commented Nov 1, 2013 at 22:32
Pretty rare to run into COM1 these days, they are reserved for legacy hardware. Don't use EnumPorts(), that's for printers. Use the HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM registry key. — Hans Passant
– Hans Passant, Commented Nov 2, 2013 at 0:54
If CreateFile() fails with error 2 for both \\.\COM1 and COM1, then you really do not have a COM1 port installed. Go into Control Panel > Device Manager > Ports to verify. — Remy Lebeau
– Remy Lebeau, Commented Nov 2, 2013 at 1:08
Thanks for the input guys. 1. I don't have SERIALCOMM 2. I don't have ports entry under device manager — Moutabreath
– Moutabreath, Commented Nov 2, 2013 at 9:50
@RemyLebeau This doesn't appear to be the case. I get that error but the port is definitely listed in the device manager. No idea why. — Timmmm
– Timmmm, Commented Apr 10, 2014 at 10:35

dueck-development.de · Accepted Answer · 2016-06-01 11:27:27Z

4

The Solution is to use

The Problem is, if your port is Bigger then 9 then you have to use the Syntax LPCWSTR szPortName = L"\\\\.\\COM11";.

edited Jun 1, 2016 at 11:27

answered May 20, 2016 at 9:08

dueck-development.de

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2 Comments

Dieter Meemken Over a year ago

Can you explain a bit more?

Morris Bahrami Over a year ago

support.microsoft.com/en-us/topic/…

Adrian · Accepted Answer · 2016-10-19 14:32:50Z

0

If you are on Windows 10 - running all system updates might help !

I had the same issue that opening port "COM4" returned an error ERROR_FILE_NOT_FOUND. When running the program as "Administrator" it worked. Now after a updating to 1511 the program can open "COM4" even not running as "Administrator".

answered Oct 19, 2016 at 14:32

Adrian

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1 Comment

Moutabreath Over a year ago

Well, it can't be windows 10 since this question was asked long before windows 10 came to be :) Thanks anyway

Ray · Accepted Answer · 2017-01-11 06:16:48Z

0

http://www.cplusplus.com/forum/windows/163855/ Use CreateFileA(...) instead of CreateFile(...)

answered Jan 11, 2017 at 6:16

Ray

1

Comments

Mitch · Accepted Answer · 2022-09-21 18:29:02Z

0

ERROR_FILE_NOT_FOUND can be produced from CreateFile(L"\\\\.\\COM1", ...) and CreateFile(L"COM1:", ...) after using the Device Manager to change the assigned COM Port number. Disabling and re-enabling the device, or unplugging and reconnecting the USB adapter resolves the issue.

A useful test to confirm whether it is your program or the system is to send data to the port in command prompt. A successful test will show an empty line. A failed test will show an error message.

C:\drop>echo > \\.\COM1
The system cannot find the file specified.

C:\drop>echo > \\.\COM1

C:\drop>

answered Sep 21, 2022 at 18:29

Mitch

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