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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);

       Link with -lm.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       nan(), nanf(), nanl():
           _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99

DESCRIPTION

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

       The call nan("char-sequence") is equivalent to:

           strtod("NAN(char-sequence)", NULL);

       Similarly, calls to nanf() and nanl() are equivalent to analogous calls to  strtof(3)  and
       strtold(3).

       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.

VERSIONS

       These functions first appeared in glibc in version 2.1.

CONFORMING TO

       C99, POSIX.1-2001.  See also IEC 559 and the appendix with recommended functions  in  IEEE
       754/IEEE 854.

SEE ALSO

       isnan(3), strtod(3), math_error(7)

COLOPHON

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