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how to convert text (real number) in LineEdit to an array of bytes in Hexadecimal

  • Hello Qt, How I can convert a real number entered by user in Line-edit to 4-bytes array represented in Hexadecimal, lets say the user enters the speed of DC motor =3564 (RPM), I want to save it as an array of hex this array looks like {(DE C0 00 00)} , where (3564)DC=(DE C0 00 00)HEX.
    I tried in this code but it not work correctly.

        void MainWindow::on_speed_ref2_lineEdit_returnPressed()
           float fdata2 = 0.0f;
           fdata2 = ui->speed_ref2_lineEdit->text().toFloat();
          uint8_t *data2 = new uint8_t();
          data2 = (uint8_t*)&fdata2;
          frame2[3] =data2[0];
          frame2[4] = data2[1];
          frame2[5] = data2[2];
          frame2[6] = data2[3];
        serial->write((char*)frame2, 4);

  • @hussam.Yones Hi, and welcome to the Qt forum!

    const int input = 3564;
    const QByteArray ba = QString::number(input, 16).toLatin1();
    const char * result = ba.constData(); // pointer remains valid as long as 'ba' is alive

  • @Wieland , Thank you very much it works for input of type integer, but in fact I need more precision I mean I consider the entered value is of type float, (ie float a=3564.0).

  • I'm not sure if what you're doing there makes any sense: In the resulting hex string, how do you know where the decimal point is? Anyways:

        const double input = 23.42f;
        const QStringList list = QString::number(input).split('.');
        const int ia =;
        const int ib =;
        const QByteArray a = QString::number(ia, 16).toLatin1();
        const QByteArray b = QString::number(ib, 16).toLatin1();
        const QByteArray ba = a + b;
        const char * result = ba.constData();

  • @Wieland, this float number is represent the speed Value of DC motor in RPM, may you mean I it should be in double type or something else!!.
    in fact I don't know obviously whit's the type I should use this is the GUI I built
    link text
    you can see in Stack-overflow here:
    link text
    may you get what I need, I'am sory to be annoying but I spent alot of time in this problem :(