man3/round.3

   1 .\" Copyright 2001 Andries Brouwer <aeb@cwi.nl>.
   2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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  27 .TH ROUND 3  2017-09-15 "" "Linux Programmer's Manual"
  28 .SH NAME
  29 round, roundf, roundl \- round to nearest integer, away from zero
  30 .SH SYNOPSIS
  31 .nf
  32 .B #include <math.h>
  33 .PP
  34 .BI "double round(double " x );
  35 .BI "float roundf(float " x );
  36 .BI "long double roundl(long double " x );
  37 .fi
  38 .PP
  39 Link with \fI\-lm\fP.
  40 .PP
  41 .in -4n
  42 Feature Test Macro Requirements for glibc (see
  43 .BR feature_test_macros (7)):
  44 .in
  45 .PP
  46 .ad l
  47 .BR round (),
  48 .BR roundf (),
  49 .BR roundl ():
  50 .RS 4
  51 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  52 .RE
  53 .ad
  54 .SH DESCRIPTION
  55 These functions round
  56 .I x
  57 to the nearest integer, but
  58 round halfway cases away from zero (regardless of the current rounding
  59 direction, see
  60 .BR fenv (3)),
  61 instead of to the nearest even integer like
  62 .BR rint (3).
  63 .PP
  64 For example,
  65 .IR round(0.5)
  66 is 1.0, and
  67 .IR round(\-0.5)
  68 is \-1.0.
  69 .SH RETURN VALUE
  70 These functions return the rounded integer value.
  71 .PP
  72 If
  73 .I x
  74 is integral, +0, \-0, NaN,  or infinite,
  75 .I x
  76 itself is returned.
  77 .SH ERRORS
  78 No errors occur.
  79 POSIX.1-2001 documents a range error for overflows, but see NOTES.
  80 .SH VERSIONS
  81 These functions first appeared in glibc in version 2.1.
  82 .SH ATTRIBUTES
  83 For an explanation of the terms used in this section, see
  84 .BR attributes (7).
  85 .TS
  86 allbox;
  87 lbw27 lb lb
  88 l l l.
  89 Interface       Attribute       Value
  90 T{
  91 .BR round (),
  92 .BR roundf (),
  93 .BR roundl ()
  94 T}      Thread safety   MT-Safe
  95 .TE
  96 .SH CONFORMING TO
  97 C99, POSIX.1-2001, POSIX.1-2008.
  98 .SH NOTES
  99 POSIX.1-2001 contains text about overflow (which might set
 100 .I errno
 101 to
 102 .BR ERANGE ,
 103 or raise an
 104 .B FE_OVERFLOW
 105 exception).
 106 In practice, the result cannot overflow on any current machine,
 107 so this error-handling stuff is just nonsense.
 108 .\" The POSIX.1-2001 APPLICATION USAGE SECTION discusses this point.
 109 (More precisely, overflow can happen only when the maximum value
 110 of the exponent is smaller than the number of mantissa bits.
 111 For the IEEE-754 standard 32-bit and 64-bit floating-point numbers
 112 the maximum value of the exponent is 128 (respectively, 1024),
 113 and the number of mantissa bits is 24 (respectively, 53).)
 114 .PP
 115 If you want to store the rounded value in an integer type,
 116 you probably want to use one of the functions described in
 117 .BR lround (3)
 118 instead.
 119 .SH SEE ALSO
 120 .BR ceil (3),
 121 .BR floor (3),
 122 .BR lround (3),
 123 .BR nearbyint (3),
 124 .BR rint (3),
 125 .BR trunc (3)