nan

NAN(3)                     Linux Programmer's Manual                    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);

       Link with -lm.

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

       nan(), nanf(), nanl():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

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);

       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  sys-
       tems,  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.

ATTRIBUTES
       For an  explanation  of  the  terms  used  in  this  section,  see  at-
       tributes(7).

       +----------------------+---------------+----------------+
       |Interface             | Attribute     | Value          |
       +----------------------+---------------+----------------+
       |nan(), nanf(), nanl() | Thread safety | MT-Safe locale |
       +----------------------+---------------+----------------+
CONFORMING TO
       C99,  POSIX.1-2001,  POSIX.1-2008.   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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       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

GNU                               2016-03-15                            NAN(3)