Can't load QtBluetooth 5.12.0 under Windows 7

Question

I migrated some code from Qt 5.6.0 to Qt 5.12.0 both compiled with Visual Studio 2015. It has some code using QtBluetooth for regular (no "low energy") bluetooth. With 5.6.0, this used to work perfectly.

With Qt 5.12.0, my app won't load. It reports missing API-MS-WIN-CORE-WINRT-L1-1-0.DLL and API-MS-WIN-CORE-WINRT-STRING-L1-1-0.DLL. I don't understand why those WinRT files are required. Dependency Walker for QtBluetooth.dll reports those libraries as missing.

I tried both with Qt 5.12.0 compiled my selft and downloaded as part of a QtCreator install. I tried both Windows 7 and 10, Windows 10 works smartly. Always getting this error and I found no information about where to find those libraries or how to have QtBluetooth not use them.

What should I do to be simply able to run a QtBluetooth based app under Windows?

Edit: Submitted Qt bug: https://bugreports.qt.io/browse/QTBUG-73272

Answer 1

If you have no requirement for low-energy and can bother your users to pair the device using the windows system settings dialog, then I'd recommend to write wrapper code for windows which does not use QtBluetooth. I.e.

#include <Windows.h>

class win_con {
    ....

    HANDLE hcon;
    COMMTIMEOUTS *timeouts;

    // i.e. com_port = L"\\\\.\\COM1"; 
    void open_com(std::wstring com_port, int read_timeout, int write_timeout)
    {

        hcom = CreateFile(com_port.c_str(), GENERIC_READ | GENERIC_WRITE, 0, nullptr, 
            OPEN_EXISTING, 0, nullptr);
        if (hcom == INVALID_HANDLE_VALUE) ...

        timeouts = new COMMTIMEOUTS();
        memset(timeouts, 0, sizeof(COMMTIMEOUTS));
        timeouts->ReadTotalTimeoutConstant = read_timeout;
        timeouts->WriteTotalTimeoutConstant = write_timeout;
        if (!SetCommTimeouts(hcom, timeouts)) ...

    }

    void write_data(QString data)
    {
        std::string stddata = data.toStdString();
        DWORD numwritten = 0;
        if (!WriteFile(hcom, stddata.c_str(),
                static_cast<DWORD>(stddata.length()), &numwritten, nullptr)) {
            ...
        }
    }

    QString read_data(int len)
    {
        #define BUFFER_SIZE 256
        char buffer[BUFFER_SIZE];
        DWORD data_read = 0;
        if (BUFFER_SIZE < len) ....
        for (int i = 0; i < BUFFER_SIZE; i++)
            buffer[i] = 0;

        ReadFile(hcom, &buffer, len, &data_read, nullptr);

        if (read == 0) ...
        if (read < len) ...

        return QString(buffer);
    }
}