Proplem toDouble QString?

[A Former User]

I have code:

QString number = "1.001";
double value = number.toDouble();
double value1 = 1;
if(value - value1 < 0.001)
{
    qDebug()<<"True";
}else
{
  qDebug()<<"False";
}

I run and show log "True". I do not understand why this is so. Please help me!

[A Former User]

Hi. double is a floating point number. It can not represent 0.001 exactly. It's more like 0.000999999999999889865875...

[A Former User]

@HAHAHAHAHA
This is not a problem with Qt. Using double always leads to precision errors.

double value = 1.001;
double value1 = 1.000;
if (value - value1 < 0.001)
{
  qDebug()<<"True";
}

This will print True

[raven-worx]

just in case you are wondering why this is like it is, here is a detailed explaination.

[kshegunov]

@raven-worx
Superb resource. You'd probably be surprised how many non-computer scientists and regular programmers haven't the slightest idea of those issues.

@HAHAHAHAHA
If you wish to compare two floating points you could use Qt's qFuzzyCompare function or qFuzzyIsNull to check if a floating point number is zero.

[A Former User]

I understand. Thank all =))