Qt - custom decimal point and thousand separator

Question

How can I convert a number (double) to string, with custom decimal point and thousand separator chars?

I've seen QLocale, but I don't want to choose the localization country, but rather specify my own decimal point and thousand separator chars.

Thanks

Teresiateresina

I can't help but ask - why is it necessary to use custom separators? Are you parsing a list and forced to use decimals (or periods) for delimiters? – Daysidayspring

Since it's math app client wants options to specify custom decimal point and thousand separator chars. Why these irrelevant questions... – Teresiateresina

Answer 1

Qt doesn't support custom locale. But to deal with just group and decimal point characters is trivial:

const QLocale & cLocale = QLocale::c();
QString ss = cLocale.toString(yourDoubleNumber, 'f');
ss.replace(cLocale.groupSeparator(), yourGroupChar);
ss.replace(cLocale.decimalPoint(), yourDecimalPointChar);

BTW, spbots' question is not irrelevant. More detail about the goal always helps and it could lead to different approach that may serve you better.

Mcmullin

This code fails if, for example, one wants to use German notation (using . as group separator and , as a decimal point). – Olympia

Answer 2

Here is how you do it just using the std::lib (no QT). Define your own numpunct-derived class which can specify decimal point, grouping character, and even the spacing between groupings. Imbue an ostringstream with a locale containing your facet. Set the flags on that ostringstream as desired. Output to it and get the string from it.

#include <locale>
#include <sstream>
#include <iostream>

class my_punct
    : public std::numpunct<char>
{
protected:
    virtual char do_decimal_point() const {return ',';}
    virtual char do_thousands_sep() const {return '.';}
    virtual std::string do_grouping() const  {return std::string("\2\3");}
};

int main()
{
    std::ostringstream os;
    os.imbue(std::locale(os.getloc(), new my_punct));
    os.precision(2);
    fixed(os);
    double x = 123456789.12;
    os << x;
    std::string s = os.str();
    std::cout << s << '\n';
}

1.234.567.89,12

Payday

And for a Unicode-based thousands separator, e.g. Narrow No-Break Space U+202F, you can use std::basic_stringstream<wchar_t>, std::numpunct<wchar_t> and std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>, wchar_t>. Live example here. – Holmquist

Answer 3

The easiest way is to use arg of QString.

QString str = QString("%L1").arg(yourDouble);

Torchbearer

Answer 4

for qml users:

function thousandSeparator(input){
    return input.toString().replace(/(\d)(?=(\d{3})+(?!\d))/g, "$1,");
}

Hild

Although this code may be help to solve the problem, providing additional context regarding why and/or how it answers the question would significantly improve its long-term value. Please edit your answer to add some explanation. – Standing

The answer is perfectly appropriate for me the way it is. Thank you! – Deangelis

Answer 5

Since you don't want QLocale perhaps you could do a simple conversion (with QString::number, for example) and then replace the desired characters afterwards.

Devon

Answer 6

pretty horrible, but got the job done

double doubleNumber = 5234556.3545;
int precision = 2;

QString stringNumber = QString::number(doubleNumber, 'f', precision);

for(int point = 0, i = (stringNumber.lastIndexOf('.') == -1 ? stringNumber.length() : stringNumber.lastIndexOf('.')); i > 0; --i, ++point)
{
    if(point != 0 && point % 3 == 0)
    {
        stringNumber.insert(i, ',');
    }
}

Harassed