QString : conversion number from double

[Wotan]

I am making a function to display the value of a double value. So for example :

• if my variable is 2000000000 I want to display 2000000000
• if my variable is 2000000010.893 I want to display 2000000010.893
• if my variable is 1.43 I want to display 1.43

But whatever was my try I never succeed here is the code I made

#include <QtGlobal>
#include <QString>
#include <QDebug>

void AfficherQString_01(const double& rVal)
{
   QString qstrTest("%1");
   qDebug() << qstrTest.arg(rVal, 0, 'g');
}

void AfficherQString_02(const double& rVal)
{
   QString qstrTest("%1");
   qDebug() << qstrTest.arg(rVal, 0, 'f');
}

void AfficherQString_03(const double& rVal)
{
   QString qstrTest("%1");
   qDebug() << qstrTest.arg(rVal, 0, 'f', 0);
}

int main(int argc, char *argv[])
{
   Q_UNUSED(argc)
   Q_UNUSED(argv)

   AfficherQString_01(2000000000);     // Affiche : 2e+9 => KO
   AfficherQString_01(2000000010.893); // Affiche : 2e+9 => KO
   AfficherQString_01(1.43);           // Affiche : 1.43 => OK

   AfficherQString_02(2000000000);     // Affiche : 2000000000.000000 => KO
   AfficherQString_02(2000000010.893); // Affiche : 2000000010.893000 => KO
   AfficherQString_02(1.43);           // Affiche : 1.430000          => KO

   AfficherQString_03(2000000000);     // Affiche : 2000000000 => OK
   AfficherQString_03(2000000010.893); // Affiche : 2000000011 => KO
   AfficherQString_03(1.43);           // Affiche : 1          => KO

   return 0;
}

I have the feeling that it is not possible with a direct conversion (double -> QString) and I will first have to test the value of my double to choose the format of arg(...). Am I right ?

Thanks for your help ...

[J.Hilk]

@Wotan It seems like I have seen this question before.

Anyway. With the standard double QString convertion it'snot possible to do.

You''ll have to do some magic yourself. e.g:

Untested code, no guarantee of working

QString doubleToString(double value){
    QString s = QString::number(value, 'f', 12);

   while(s.at(s.size()-1) == '0'){
       s = s.remove(s.size()-1,1);
       if(s.at(s.size()-1) == '.'){
       s = s.remove(s.size()-1,1);
       break;
      }
   }
   return s;
}

[VRonin]

// needs #include <cmath>
int guessPrecision(double val){
int precision=0;
for(double junk=0.0;!qFuzzyIsNull(std::modf(val,&junk));++precision) val*=10.0;
return precision;
}

double d = 12000000.0;
QString s = QString::number(d,'f',guessPrecision(d)); //or use locale().toString() for localised version
qDebug() << s;

source: https://forum.qt.io/topic/75939/how-to-search-for-a-specific-character-in-a-qstring/17

Example (my system locale is en-uk):

int main(int argc, char *argv[])
    {
        QApplication app(argc,argv);
        double d = 2000000000.0;
        qDebug() << d << QString::number(d,'f',guessPrecision(d)) << QLocale().toString(d,'f',guessPrecision(d)) << QLocale(QLocale::French).toString(d,'f',guessPrecision(d));
        d=2000000010.893;
        qDebug() << d << QString::number(d,'f',guessPrecision(d)) << QLocale().toString(d,'f',guessPrecision(d)) << QLocale(QLocale::French).toString(d,'f',guessPrecision(d));
        d=1.43;
        qDebug() << d << QString::number(d,'f',guessPrecision(d)) << QLocale().toString(d,'f',guessPrecision(d)) << QLocale(QLocale::French).toString(d,'f',guessPrecision(d));
        return 0;
    }

2e+09 "2000000000" "2,000,000,000" "2 000 000 000"
2e+09 "2000000010.893" "2,000,000,010.893" "2 000 000 010,893"
1.43 "1.43" "1.43" "1,43"

[Wotan]

Thanks to you all ! You have been very helpful !