man3/nan.3

   1 .\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
   2 .\"
   3 .\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
   4 .\" Distributed under GPL
   5 .\" %%%LICENSE_END
   6 .\"
   7 .\" Based on glibc infopages
   8 .\"
   9 .\" Corrections by aeb
  10 .\"
  11 .TH NAN 3 2015-04-19 "GNU" "Linux Programmer's Manual"
  12 .SH NAME
  13 nan, nanf, nanl \- return 'Not a Number'
  14 .SH SYNOPSIS
  15 .B #include <math.h>
  16 .sp
  17 .BI "double nan(const char *" tagp );
  18 .br
  19 .BI "float nanf(const char *" tagp );
  20 .br
  21 .BI "long double nanl(const char *" tagp );
  22 .sp
  23 Link with \fI\-lm\fP.
  24 .sp
  25 .in -4n
  26 Feature Test Macro Requirements for glibc (see
  27 .BR feature_test_macros (7)):
  28 .in
  29 .sp
  30 .ad l
  31 .BR nan (),
  32 .BR nanf (),
  33 .BR nanl ():
  34 .RS 4
  35 _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
  36 _POSIX_C_SOURCE\ >=\ 200112L;
  37 .br
  38 or
  39 .I cc\ -std=c99
  40 .RE
  41 .ad
  42 .SH DESCRIPTION
  43 These functions return a representation (determined by
  44 .IR tagp )
  45 of a quiet NaN.
  46 If the implementation does not support
  47 quiet NaNs, these functions return zero.
  48 .LP
  49 The call
  50 .I nan("char-sequence")
  51 is equivalent to:
  52 .nf
  53
  54     strtod("NAN(char-sequence)", NULL);
  55 .fi
  56 .PP
  57 Similarly, calls to
  58 .BR nanf ()
  59 and
  60 .BR nanl ()
  61 are equivalent to analogous calls to
  62 .BR strtof (3)
  63 and
  64 .BR strtold (3).
  65 .PP
  66 The argument
  67 .I tagp
  68 is used in an unspecified manner.
  69 On IEEE 754 systems, there are many representations of NaN, and
  70 .I tagp
  71 selects one.
  72 On other systems it may do nothing.
  73 .SH VERSIONS
  74 These functions first appeared in glibc in version 2.1.
  75 .SH ATTRIBUTES
  76 For an explanation of the terms used in this section, see
  77 .BR attributes (7).
  78 .TS
  79 allbox;
  80 lbw21 lb lb
  81 l l l.
  82 Interface       Attribute       Value
  83 T{
  84 .BR nan (),
  85 .BR nanf (),
  86 .BR nanl ()
  87 T}      Thread safety   MT-Safe locale
  88 .TE
  89 .SH CONFORMING TO
  90 C99, POSIX.1-2001, POSIX.1-2008.
  91 See also IEC 559 and the appendix with
  92 recommended functions in IEEE 754/IEEE 854.
  93 .SH SEE ALSO
  94 .BR isnan (3),
  95 .BR strtod (3),
  96 .BR math_error (7)