QString formatting for rounding a decimal number

[Swati777999]

I've following code for rounding myVal to 6 decimal places i.e 0.314568

 QString myVal ="0.3145678";
  qDebug()<<"Ans=" << QString::asprintf("%10.6f",myVal);

It says no member named 'asprintf' in 'Qstring' . Can someone help me how to do it?

[ChrisW67]

QString::asprintf()

However, the format specifier "%10.6f" requires a numeric value argument (usually a float or double) and you are feeding it a string. Your line compiles with a warning (at least with my compiler) and does something undefined as a result

There is a difference between rounding a numeric value at 6 decimal places, and simply displaying it in human readable form rounded to 6 decimal places. Which do you want?

#include <QCoreApplication>
#include <QDebug>
#include <QString>
#include <cmath>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QString myVal ="0.3145678";

    double value = myVal.toDouble();


    qDebug()<<"Original string =" << myVal;
    qDebug()<<"Original value  =" << QString::asprintf("%10.7f", value);
    qDebug()<<"Rounded display =" << QString::asprintf("%10.6f", value);

    // Round the actual value
    value = std::round(value * 1e6) / 1e6;
    qDebug()<<"Rounded value   =" << QString::asprintf("%10.7f", value);
    qDebug()<<"Rounded display =" << QString::asprintf("%10.6f", value);

    // Your line
    qDebug()<<"Ans=" << QString::asprintf("%10.6f",myVal);

    return 0;
}

The warning

../untitled/main.cpp: In function ‘int main(int, char**)’:
../untitled/main.cpp:25:49: warning: format ‘%f’ expects argument of type ‘double’, but argument 2 has type ‘QString’ [-Wformat=]
     25 |     qDebug()<<"Ans=" << QString::asprintf("%10.6f",myVal);
        |                                            ~~~~~^
        |                                                 |
        |                                                 double

Output

Original string = "0.3145678"
Original value  = " 0.3145678"
Rounded display = "  0.314568"
Rounded value   = " 0.3145680"
Rounded display = "  0.314568"
Ans= "  0.000000"