toDouble() is returning wrong numerical value
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I'm storing the value entered by a user inside a lineEdit into a double which I declared in my code... the thing is that the value stored in this double is not always the same one as entered
I entered the number 28.05 and the value stored inside the double is 28.050000000000001 which causes problemsmy code:
num = ui->lineEdit->text().toDouble(); -
This is just how floating point numbers work. It's the same in C++ and other languages, it's one of the fundamental things about how computers store data.
If you want to store exactly what user wrote - store the string. When you need to do maths with the value, convert it to double only for the purpose of the algorithm.
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I'm storing the value entered by a user inside a lineEdit into a double which I declared in my code... the thing is that the value stored in this double is not always the same one as entered
I entered the number 28.05 and the value stored inside the double is 28.050000000000001 which causes problemsmy code:
num = ui->lineEdit->text().toDouble();@Sampi
Exactly as @sierdzio says about how floating point numbers are stored. They are always only approximate values close to your desired value.You could store as strings, as he says, and then convert/to from numbers when needed. Or, some languages (Python. SQL) have a "decimal" type, which have a set number of places after the decimal point so the representation is perfectly accurate to that limit. C++ does not come with that; there are libraries which will provide such with corresponding arithmetic. Or you could roll your own
structwhich hasints for the numbers before & after the decimal place separately, combining them when necessary. Another trick: if, say, all your numbers are money and so have 2 decimal places, then do all your math by multiplying them by up by 100 so that they becomeints and then arithmetic operations won't lose precision: only convert numbers from/to the decimal place representation during input/output.
