QString:number with maximum 2 decimal places without trailing zero

Question

I have a division like this:

number / 1000.0

Sometimes it gives answers like 96.0000000001, sometimes the division works as expected.

I want to limit my number to a maximum of two decimal places and without trailing zeros.

If it's 96.5500000001 it should show 96.55.

If it's 96.4000000001 it should show 96.4

It is possible to format a string in this way?

I've checked the documentation and it provides 'f' argument for specifying the number of the decimal places but this way the trailing zeros remain. This is what I have tried:

QString::number(number / 1000.0, 'f', 2)

But this gives me for 96.4000000001 --> 96.40 instead of 96.4

Any solution? How can I format in this way?

Solution 1

The documentation is pretty clear about what you should do:

A precision is also specified with the argument format. For the 'e', 'E', and 'f' formats, the precision represents the number of digits after the decimal point. For the 'g' and 'G' formats, the precision represents the maximum number of significant digits (trailing zeroes are omitted).

Therefore, use either the 'g' or 'G' format.

main.cpp

#include <QString>
#include <QDebug>

int main()
{
    qDebug() << QString::number(96400.0000001 / 1000.0, 'g', 5);
    qDebug() << QString::number(96550.0000001 / 1000.0, 'G', 5);
    return 0;
}

main.pro

TEMPLATE = app
TARGET = main
QT = core
SOURCES += main.cpp

Build and Run

qmake && make && ./main

Output

"96.4"
"96.55"

Solution 2

This returns the formatted number always in fixed (not scientific) notation, and is reasonably efficient:

QString variableFormat(qreal n) { // assumes max precision of 2
    int i = rint(n * 100.0);
    if (i % 100)
        return QString::number(n, 'f', i % 10 ? 2 : 1);
    else
        return QString::number(i / 100);
}

Solution 3

Use QString::number with both 'f' and 'g'. First, use toDouble() on output of 'f'; then use QString::number with default arguments or with 'g' like this.

QString::number(QString::number(number / 1000.0, 'f', 2).toDouble(), 'g', 10);