redhat man page for nan

NAN(3)								libc math functions							    NAN(3)

NAME
       nan, nanf, nanl - return 'Not a Number'

SYNOPSIS
       #include <math.h>

       double nan(const char *tagp);

       float nanf(const char *tagp);

       long double nanl(const char *tagp);

DESCRIPTION
       These functions return a representation (determined by tagp) of a quiet NaN. If the implementation does not support quiet NaNs, these func-
       tions return zero.

       The call nan("char-sequence") is equivalent to strtod ("NAN(char-sequence)",NULL) and similarly calls to nanf and nanl  are  equivalent	to
       analogous calls to strtof and strtold.

       The  argument tagp is used in an unspecified manner.  On IEEE 754 systems, there are many representations of NaN, and tagp selects one.	On
       other systems it may do nothing.

CONFORMING TO
       C99. See also IEC 559 and the appendix with recommended functions in IEEE 754/IEEE 854.

SEE ALSO
       isnan(3), strtod(3)

GNU
								    2002-08-10								    NAN(3)