NAME

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

LIBRARY

       Math library (libm, -lm)

SYNOPSIS

       #include <math.h>

       double nan(const char *tagp);
       float nanf(const char *tagp);
       long double nanl(const char *tagp);

   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 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.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌────────────────────────────────────────────────────────┬───────────────┬────────────────┐
       │Interface                                               │ Attribute     │ Value          │
       ├────────────────────────────────────────────────────────┼───────────────┼────────────────┤
       │nan(), nanf(), nanl()                                   │ Thread safety │ MT-Safe locale │
       └────────────────────────────────────────────────────────┴───────────────┴────────────────┘

STANDARDS

       C11, POSIX.1-2008.

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

HISTORY

       glibc 2.1.  C99, POSIX.1-2001.

SEE ALSO

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