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 2002-08-10 "GNU" "libc math functions"
   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 Compile with \-std=c99; link with \-lm.
  19 .SH DESCRIPTION
  20 These functions return a representation (determined by
  21 .IR tagp )
  22 of a quiet NaN.
  23 If the implementation does not support
  24 quiet NaNs, these functions return zero.
  25 .LP
  26 The call
  27 .I nan("char-sequence")
  28 is equivalent to
  29 .I strtod ("NAN(char-sequence)",NULL)
  30 and similarly calls to
  31 .BR nanf ()
  32 and
  33 .BR nanl ()
  34 are equivalent to analogous calls to
  35 .BR strtof ()
  36 and
  37 .BR strtold ().
  38 .PP
  39 The argument
  40 .I tagp
  41 is used in an unspecified manner.
  42 On IEEE 754 systems, there are many representations of NaN, and
  43 .I tagp
  44 selects one.
  45 On other systems it may do nothing.
  46 .SH "CONFORMING TO"
  47 C99.
  48 See also IEC 559 and the appendix with
  49 recommended functions in IEEE 754/IEEE 854.
  50 .SH "SEE ALSO"
  51 .BR isnan (3),
  52 .BR strtod (3)