The precision of std::to_string(double)

Question

Is there any way to set the precision of the result when converting a double to string using std::to_string()?

Answer 1

I believe that using std::stringstream with setprecision would be the most flexible/portable choice, but if you know your data, as an workaround, you could try to substring the to_string result. For example:

std::string seriesSum(int n)
{
    double sum = 0, div = 1;
    for(int i = 0; i < n; i++) {
      sum += 1.0 / div;
      div += 3;
    }

    return std::to_string(round(sum * 100)/100).substr(0,4);
}

In the code above I'm printing with two decimal places 0.00 by taking the first 4 digits of the string, but it only works because I know the integer part is never going above one digit. You could also use string.find() to search for the decimal separator and use it's position to calculate the size of the substring, making it a bit more dynamic.