man3/nan.3

   1 .\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
   2 .\" Distributed under GPL
   3 .\" Based on glibc infopages
   4 .\"
   5 .\" Corrections by aeb
   6 .TH NAN 3 2010-09-20 "GNU" "Linux Programmer's Manual"
   7 .SH NAME
   8 nan, nanf, nanl \- return 'Not a Number'
   9 .SH SYNOPSIS
  10 .B #include <math.h>
  11 .sp
  12 .BI "double nan(const char *" tagp );
  13 .br
  14 .BI "float nanf(const char *" tagp );
  15 .br
  16 .BI "long double nanl(const char *" tagp );
  17 .sp
  18 Link with \fI\-lm\fP.
  19 .sp
  20 .in -4n
  21 Feature Test Macro Requirements for glibc (see
  22 .BR feature_test_macros (7)):
  23 .in
  24 .sp
  25 .ad l
  26 .BR nan (),
  27 .BR nanf (),
  28 .BR nanl ():
  29 .RS 4
  30 _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
  31 _POSIX_C_SOURCE\ >=\ 200112L;
  32 .br
  33 or
  34 .I cc\ -std=c99
  35 .RE
  36 .ad
  37 .SH DESCRIPTION
  38 These functions return a representation (determined by
  39 .IR tagp )
  40 of a quiet NaN.
  41 If the implementation does not support
  42 quiet NaNs, these functions return zero.
  43 .LP
  44 The call
  45 .I nan("char-sequence")
  46 is equivalent to:
  47 .nf
  48
  49     strtod("NAN(char-sequence)", NULL);
  50 .fi
  51 .PP
  52 Similarly, calls to
  53 .BR nanf ()
  54 and
  55 .BR nanl ()
  56 are equivalent to analogous calls to
  57 .BR strtof (3)
  58 and
  59 .BR strtold (3).
  60 .PP
  61 The argument
  62 .I tagp
  63 is used in an unspecified manner.
  64 On IEEE 754 systems, there are many representations of NaN, and
  65 .I tagp
  66 selects one.
  67 On other systems it may do nothing.
  68 .SH VERSIONS
  69 These functions first appeared in glibc in version 2.1.
  70 .SH CONFORMING TO
  71 C99, POSIX.1-2001.
  72 See also IEC 559 and the appendix with
  73 recommended functions in IEEE 754/IEEE 854.
  74 .SH SEE ALSO
  75 .BR isnan (3),
  76 .BR strtod (3),
  77 .BR math_error (7)