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 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.

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 │
       └──────────────────────┴───────────────┴────────────────┘

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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