stof() and stod() precision

Question

I'm parsing a file with some numbers. I'm trying to change the numbers from string to float or double, but I found out a precision problem with stof and stod, they are off by slight amount in VS C++. For example

string str1="3.14", str2="45.106";
double number1, number2;
number1=stod(str1);
number2=stof(str2);

When I test (number1==3.14), it returns "false". When I look in debugger, number1 is actually 3.139999999 or something like that! number2 may be 45.1060000002 or something like that. Any explanation or solution?

Explanation: http://en.wikipedia.org/wiki/Floating_point#Accuracy_problems. One need to take care when using equality comparisons with floating point types. — Zeta, Mar 05 '13 at 20:33

score 0 · Answer 1 · edited May 23 '17 at 11:57

You may wish to take a look at this example:

How is floating point stored? When does it matter?

The thing to learn from this, is that it is almost never the solution to do a direct compare between two floating point numbers. You only have a certain amount of precision in floating point numbers, thus there is a limit to the precision you can expect, this is well put in the link in the comments by Zeta.

stof() and stod() precision

1 Answers1