c++ float to string non-fixed precision after decimal

Question

Is there an easy way to set a non-fixed precision after decimal in c++ when converting floats to strings?

What std::setprecision( 2 ) does is:

1.00000 -> 1
1.23456 -> 1.2
12.3456 -> 12
12.3000 -> 12.3

What std::fixed adds to it is:

1.00000 -> 1.00
1.23456 -> 1.20
12.3456 -> 12.34
12.3000 -> 12.30

What I want to do is:

1.00000 -> 1
1.23456 -> 1.23
12.3456 -> 12.34
12.3000 -> 12.3

I don't get it. Aren't you asking for a fixed precision in you example (2 in this case)? What do you mean by non fixed precision? — dtell, Sep 20 '17 at 16:34
Please, show the code where you are converting floats to strings. — KelvinS, Sep 20 '17 at 16:35
Please post a [mcve]. It is not clear what you have now vs. what you want. — wally, Sep 20 '17 at 16:39
I've changed the example a little bit, to make it more clear. I want to set the precision only for the digits after the decimal, not for all digits in the number, but don't want trailing zeros. — DrPepperJo, Sep 20 '17 at 16:39
Have a look at [this answer](https://stackoverflow.com/a/17342002/1460794). But honestly, with a short program showing what you are trying to do this would be lot easier to answer. — wally, Sep 20 '17 at 16:48

score 1 · Answer 1 · answered Sep 20 '17 at 17:19

The following rounds to two decimals and then uses the default precision:

#include <iostream>
#include <iomanip>
#include <cmath>

int main()
{
    double vals[]{1.00000, 1.23456, 12.3456, 12.3000};
    for(auto i : vals) {
        i = std::round(i * 100) / 100;
        std::cout << i << '\n';
    }
}

Produces:

c++ float to string non-fixed precision after decimal

1 Answers1