rounding - Where is Round() in C++?

Question

(This question already has answers here): question from:https://stackoverflow.com/questions/554204/where-is-round-in-c

Answer 1

You may use C++11's std::round().

If you are still stuck with older standards, you may use std::floor(), which always rounds to the lower number, and std::ceil(), which always rounds to the higher number.

To get the normal rounding behaviour, you would indeed use floor(i + 0.5).

This way will give you problems with negative numbers, a workaround for that problem is by using ceil() for negative numbers:

double round(double number)
{
    return number < 0.0 ? ceil(number - 0.5) : floor(number + 0.5);
}

Another, cleaner, but more resource-intensive, way is to make use of a stringstream and the input-/output-manipulators:

#include <iostream>
#include <sstream>

double round(double val, int precision)
{
    std::stringstream s;
    s << std::setprecision(precision) << std::setiosflags(std::ios_base::fixed) << val;
    s >> val;
    return val;
}

Only use the second approach if you are not low on resources and/or need to have control over the precision.