This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       None.

       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 .

IEEE/The Open Group                                   2017                                           NAN(3POSIX)

       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().

       No errors are defined.

       Thefollowingsectionsareinformative.

       None.

       None.

       nan, nanf, nanl — return quiet NaN

       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.

       None.

       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.

strtod()

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

       #include <math.h>

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