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++; } } } }