#include <math.h>

       double round(double x);
       float roundf(float x);
       long double roundl(long double x);

       Link with -lm.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       round(), roundf(), roundl():
           _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
           _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99

       These functions round x to the nearest integer, but round halfway cases
       away  from  zero  (regardless  of  the  current rounding direction, see
       fenv(3)), instead of to the nearest even integer like rint(3).

       For example, round(0.5) is 1.0, and round(-0.5) is -1.0.

       These functions return the rounded integer value.

       If x is integral, +0, -0, NaN,  or infinite, x itself is returned.

       No errors occur.  POSIX.1-2001 documents a range error  for  overflows,
       but see NOTES.

       These functions first appeared in glibc in version 2.1.

   Multithreading (see pthreads(7))
       The round(), roundf(), and roundl() functions are thread-safe.

       C99, POSIX.1-2001.

       POSIX.1-2001  contains  text  about  overflow (which might set errno to
       ERANGE, or raise an FE_OVERFLOW exception).  In  practice,  the  result
       cannot overflow on any current machine, so this error-handling stuff is
       just nonsense.  (More precisely, overflow can happen only when the max-
       imum value of the exponent is smaller than the number of mantissa bits.
       For the IEEE-754 standard 32-bit and 64-bit floating-point numbers  the
       maximum value of the exponent is 128 (respectively, 1024), and the num-
       ber of mantissa bits is 24 (respectively, 53).)

       If you want to store the rounded value in an integer type, you probably
                                  2013-06-21                          ROUND(3)
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