<![CDATA[[solved] Addition of Float does not give precise result]]>Hi,

I am doing addition of prices in my application. I have values as QStrings and I convert to float and add. When it reaches high value, result is not precise. I read like float or double should not be used for currency addition and use separate variable for integer part and fractional part. My code and log is below:

@ qDebug ("m_totalPrice: %f + %f =", m_totalPrice, item.price.toFloat());
m_totalPrice += item.price.toFloat();
qDebug ("m_totalPrice: %f", m_totalPrice);
ui->totalLabel->setText(QString::number(m_totalPrice, 'f', 2));
@

m_totalPrice is float and item.price is QString

logs:

m_totalPrice: 424659.500000 + 22350.500000 =

m_totalPrice: 447010.000000

m_totalPrice: 447010.000000 + 18.900000 =

m_totalPrice: 447028.906250

m_totalPrice: 447028.906250 + 125.900002 =

m_totalPrice: 447154.812500

m_totalPrice: 447154.812500 + 125.900002 =

m_totalPrice: 447280.718750

m_totalPrice: 447280.718750 + 11.500000 =

m_totalPrice: 447292.218750

m_totalPrice: 447292.218750 + 22.500000 =

m_totalPrice: 447314.718750

Error is from line 2. Can someone tell how to resolve this?

]]>https://forum.qt.io/topic/42943/solved-addition-of-float-does-not-give-precise-resultRSS for NodeSat, 02 May 2026 05:52:15 GMTWed, 25 Jun 2014 08:43:25 GMT60<![CDATA[Reply to [solved] Addition of Float does not give precise result on Sat, 28 Jun 2014 09:48:30 GMT]]>[quote author="Abin" date="1403934198"]Thanks all,

using double solved the issue[/quote]

Not quite. The issue is still there, hiding from you. As your numbers cannot be represented exactly as base-2 floating point numbers, you will always have rounding errors, and eventually that may still affect your computation. The correct solution is to use integer arithmetic on cents.

]]>https://forum.qt.io/post/233804https://forum.qt.io/post/233804Sat, 28 Jun 2014 09:48:30 GMT<![CDATA[Reply to [solved] Addition of Float does not give precise result on Sat, 28 Jun 2014 05:43:18 GMT]]>Thanks all,

using double solved the issue

]]>https://forum.qt.io/post/233793https://forum.qt.io/post/233793Sat, 28 Jun 2014 05:43:18 GMT<![CDATA[Reply to [solved] Addition of Float does not give precise result on Thu, 26 Jun 2014 22:30:16 GMT]]>http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html

]]>https://forum.qt.io/post/233636https://forum.qt.io/post/233636Thu, 26 Jun 2014 22:30:16 GMT<![CDATA[Reply to [solved] Addition of Float does not give precise result on Thu, 26 Jun 2014 21:20:57 GMT]]>Hi,

float is a 32bit data type with 8 precision digits; you need more precision so you must use double (16 precision digits) or long double (24 precision digits).

PS: long double precision depends on the platform

]]>https://forum.qt.io/post/233617https://forum.qt.io/post/233617Thu, 26 Jun 2014 21:20:57 GMT