Nominate our 2022 Qt Champions!

[Solved] Print qint as QString without losing bits

  • @
    qint32 my32=1; //dec
    qint16 my16=0x0002; //hex
    qint8 my8=0x03; //hex

    cout << QString::number(my32).toStdString <<"\n";
    cout << QString::number(my16).toStdString <<"\n";
    cout << QString::number(my8).toStdString <<"\n";

    cout will print:

    I would like it to print the complete data type size like:

    The reason is that I have to stick to a protocol that requires that a 32 bit integer shall be represented with a string of 8 chars like "00000000".

    In my code the data is represented with the correct type. however when the data is transformed into a datagram package i have to pad it to fill out the expected data type width.
    for example a datagram message looks like:

    struct datagramHeader
    qint32 segment; //s
    qint16 class; //c
    qint16 length; //l

    when converted to an datagram it needs to look like this:

    I find it convenient to work with the data types as they are like qint for counters etc and cast them to a QString when the datagram message is created. I guess this must be the best way and to solution is to handle the conversion from qint to QString without losing any characters. Or am I wrong?

  • Lifetime Qt Champion


    Unless I've misunderstood you you could use something like:

    datagramHeader header = { 1, 0x02, 0x03 };
    QString datagram("%1%2%3");
    qDebug() << message.arg(header.segment, 8, 10, QChar('0'))
    .arg(header.class, 4, 16, QChar('0'))
    .arg(header.length, 4, 16, QChar('0'));

    Hope it helps

  • You could fix your code like that (fill with leading zeros):
    QString::number(my32).rightJustified(8, '0');

    But I guess your protocol requires hex output? (the value 0xFFFFFFFF represented as decimal would not fit into 8 characters). If so you should also add the formatting base:

    int base = 16;
    int width = sizeof(my32)*2;
    QString::number(my32, base).rightJustified(width, '0');

  • It actually works. I used the .rightJustified method and that in combination with changing all my qint to quint solved all my issues.

    Thanks to SGaist and flandi for your help in this topic!

Log in to reply