Where is Round() in C++? [duplicate]

Question

Duplicate of: round() for float in C++

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I'm using VS2008 and I've included math.h but I still can't find a round function. Does it exist?

I'm seeing a bunch of "add 0.5 and cast to int" solutions on google. Is that the best practice?

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.

Answer 2

Using floor(num + 0.5) won't work for negative numbers. In that case you need to use ceil(num - 0.5).

double roundToNearest(double num) {     return (num > 0.0) ? floor(num + 0.5) : ceil(num - 0.5); }