NEXTAFTER(3)               POSIX Programmer's Manual              NEXTAFTER(3)



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

NAME
       nextafter, nextafterf, nextafterl, nexttoward, nexttowardf, nexttowardl
       -- next representable floating-point number

SYNOPSIS
       #include <math.h>

       double nextafter(double _x, double _y);
       float nextafterf(float _x, float _y);
       long double nextafterl(long double _x, long double _y);
       double nexttoward(double _x, long double _y);
       float nexttowardf(float _x, long double _y);
       long double nexttowardl(long double _x, long double _y);

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 nextafter(), nextafterf(), and nextafterl() functions shall compute
       the next representable floating-point value following _x in the
       direction of _y.  Thus, if _y is less than _x, nextafter() shall return
       the largest representable floating-point number less than _x.  The
       nextafter(), nextafterf(), and nextafterl() functions shall return _y if
       _x equals _y.

       The nexttoward(), nexttowardf(), and nexttowardl() functions shall be
       equivalent to the corresponding nextafter() functions, except that the
       second parameter shall have type long double and the functions shall
       return _y converted to the type of the function if _x equals _y.

       An application wishing to check for error situations should set errno
       to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these
       functions. On return, if errno is non-zero or fetestexcept(FE_INVALID |
       FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
       occurred.

RETURN VALUE
       Upon successful completion, these functions shall return the next
       representable floating-point value following _x in the direction of _y.

       If _x==_y, _y (of the type _x) shall be returned.

       If _x is finite and the correct function value would overflow, a range
       error shall occur and +-HUGE_VAL, +-HUGE_VALF, and +-HUGE_VALL (with
       the same sign as _x) shall be returned as appropriate for the return
       type of the function.

       If _x or _y is NaN, a NaN shall be returned.

       If _x!=_y and the correct function value is subnormal, zero, or
       underflows, a range error shall occur, and
       the correct function value (if representable) or
       0.0 shall be returned.

ERRORS
       These functions shall fail if:

       Range Error The correct value overflows.

                   If the integer expression (math__errhandling & MATH_ERRNO)
                   is non-zero, then errno shall be set to [ERANGE].  If the
                   integer expression (math__errhandling & MATH_ERREXCEPT) is
                   non-zero, then the overflow floating-point exception shall
                   be raised.

       Range Error The correct value is subnormal or underflows.

                   If the integer expression (math__errhandling & MATH_ERRNO)
                   is non-zero, then errno shall be set to [ERANGE].  If the
                   integer expression (math__errhandling & MATH_ERREXCEPT) is
                   non-zero, then the underflow floating-point exception shall
                   be raised.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       On error, the expressions (math__errhandling & MATH_ERRNO) and
       (math__errhandling & MATH_ERREXCEPT) are independent of each other, but
       at least one of them must be non-zero.

       When <tgmath.h> is included, note that the return type of nextafter()
       depends on the generic typing deduced from both arguments, while the
       return type of nexttoward() depends only on the generic typing of the
       first argument.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       feclearexcept(), fetestexcept()

       The Base Definitions volume of POSIX.1-2017, Section 4.20, Treatment of
       Error Conditions for Mathematical Functions, <math.h>, <tgmath.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 .



IEEE/The Open Group                  2017                         NEXTAFTER(3)
