correct input value with toFloat() in Qt

Question

I want to change text into float number for calculation in Qt

float test = ui.tableWidget->item(0, 1)->text().replace(",", ".", Qt::CaseSensitive).toFloat();

when I type 2.86, actually I see test = 2.85999990 in debug. How can I receive correctly what i typed ?

I can use this for showing

qDebug() << QString::number( test, 'f', 2 );

But I want a value for calculation, not for showing.

Unfortunately floating point numbers won't give you much more precise results. This is the way they are - you usually get the closest number that can be expressed in *some size* floating point number. I'd recommend reading some wikipedia on the reasons why (take a look at the equations there). Note: `double` could give you slightly better results. — hauron, Jul 25 '16 at 13:53
@hauron: thank you. Yes, I have checked with `double`, but the result is just slightly better as you said. Do we have any way to receive exactly what we want ? — songvan, Jul 25 '16 at 14:23

score 1 · Answer 1 · edited May 23 '17 at 12:08

1

As @hauron already said this is format specific but normal behaviour. You might want to take a read on this.

Additionally you might also take a look at another answer here. Using some additional library may work for you, if applicable.

edited May 23 '17 at 12:08

Community

answered Jul 25 '16 at 22:46

maxik

thank you, i decided to use `double`, the result after that will be rounded, looks also ok. – songvan Jul 26 '16 at 11:54

1 Answers1