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NAN(3P)                    POSIX Programmer's Manual                   NAN(3P)
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.1-2008
       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.1-2008, <math.h>
COPYRIGHT
       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal  and  Electronics  Engineers,  Inc  and  The  Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum  1  applied.)  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.unix.org/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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                              NAN(3P)