PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.

NAME

       nan, nanf, nanl — return quiet NaN

SYNOPSIS

       #include <math.h>

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

DESCRIPTION

       The functionality described on this reference page is aligned with the ISO C standard. Any
       conflict between the requirements described here and the ISO C standard is  unintentional.
       This volume of POSIX.1‐2017 defers to the ISO C standard.

       The function call nan("n-char-sequence") shall be equivalent to:

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

       The function call nan("") shall be equivalent to:

           strtod("NAN()", (char **) NULL)

       If  tagp  does not point to an n-char sequence or an empty string, the function call shall
       be equivalent to:

           strtod("NAN", (char **) NULL)

       Function calls to nanf() and nanl() are equivalent to the corresponding function calls  to
       strtof() and strtold().

RETURN VALUE

       These  functions  shall  return  a quiet NaN, if available, with content indicated through
       tagp.

       If the implementation does not support quiet NaNs, these functions shall return zero.

ERRORS

       No errors are defined.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       strtod()

       The Base Definitions volume of POSIX.1‐2017, <math.h>

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1-2017,  Standard  for  Information Technology -- Portable Operating System Interface
       (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C)  2018  by
       the  Institute  of  Electrical  and Electronics Engineers, Inc and The Open Group.  In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most  likely  to  have
       been  introduced  during  the conversion of the source files to man page format. To report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .