CODEWITHSUNDEEP
qtdoubleprecisionqstring
user446836
user446836

Reputation: 733

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

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.

Upvotes: 9

Views: 35679

Answers (1)

dschulz
dschulz

Reputation: 4806

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

Upvotes: 21

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