Use this:
QString number = QStringLiteral("%1").arg(yourNumber, 5, 10, QLatin1Char('0'));
5 here corresponds to 5 in printf("%05d"). 10 is the radix, you can put 16 to print the number in hex.
Use this:
QString number = QStringLiteral("%1").arg(yourNumber, 5, 10, QLatin1Char('0'));
5 here corresponds to 5 in printf("%05d"). 10 is the radix, you can put 16 to print the number in hex.