# nextafter

## 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



           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.
    


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