nan, nanf, nanl − return ’Not a Number’


     );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

     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

These functions return a representation (determined by 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 and are equivalent to analogous
calls to and

     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.

These functions first appeared in glibc in version 2.1.

For an explanation of the terms used in this section, see

│Interface             Attribute     Value          │
│                      │ Thread safety MT‐Safe locale │

C99, POSIX.1‐2001, POSIX.1‐2008.  See also IEC 559 and the
appendix with recommended functions in IEEE 754/IEEE 854.

This page is part of release 5.07 of the Linux man‐pages
project.  A description of the project, information about
reporting bugs, and the latest version of this page, can be
found at−pages/.