QString::toDouble() giving me double with wrong precision

Question

I have a QString myNumber containing "09338.712001". When I do:

myNumber.toDouble();, it returns 9338.71, but I want the double to be the original value, which is 09338.712001. Does anyone know how to get the double returned by toDouble to have the same precision as the QString? Thanks.

Answer 1

Your problem probably is in how you output these values.

 QString s("9338.712001");
 bool ok = false;

 double a = 9338.712001;
 double b = s.toDouble(&ok);
 double c = 1/3.0;

 qDebug() << "a: " << a;
 qdebug() << "b: " << b;

 qDebug() << "a: " << QString("%1").arg(a, 0, 'g', 13) 
 qDebug() << "b: " << QString("%1").arg(b, 0, 'e', 13);

 qDebug() << "c: " << QString("%1").arg(c, 0, 'g', 30);

result:

 a:  9338.71  
 b:  9338.71  
 a:  "9338.712001"
 b:  "9.3387120010000e+03"
 c:  "0.333333333333333314829616256247"

But anyways, maybe now it's a good moment to read this: What Every Computer Scientist Should Know About Floating-Point Arithmetic