Round a positive or negative number

Question

I need to do rounding on a number, but I don't know if the number is negative or positive.

Is there a better way to round up foo

to do this:

static_cast<int>(foo > 0 ? foo + 0.5 : foo - 0.5)

Basically, I want this behavior:

3.4 => 3
3.5 => 4
-3.4 => -3
-3.5 => -4

+3

Jonathan Mee 01 jul. 15 at 13:36

3 answers

Going back to the old school tricks that count on bool

converting to 1 if true

and 0 if false

:

 static_cast <int>(foo + 0.5 - (foo < 0.0))

You should normally use library functions, but you can perform a performance test against this if this is a critical section

+2

Glenn teitelbaum 01 jul. 15 at 14:19

The C-math library has,

double round  (double x);

or exists,

double nearbyint  (double x);

+1

HarryQuake 01 jul. 15 at 13:43

marom · Accepted Answer · 2015-07-01T13:39:53+0000

For C ++ there is one: std::lround