## SYNOPSIS

**#include <math.h>
**

double nextafter(double *x***, double** *y***);
float nextafterf(float**

*x*

**, float**

*y*

**);**

long double nextafterl(long double

long double nextafterl(long double

*x*

**, long double**

*y*

**);**

double nexttoward(double

double nexttoward(double

*x*

**, long double**

*y*

**);**

float nexttowardf(float

float nexttowardf(float

*x*

**, long double**

*y*

**);**

long double nexttowardl(long double

long double nexttowardl(long double

*x*

**, long double**

*y*

**);**

## DESCRIPTION

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 either
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.

## RATIONALE

None.

## FUTURE DIRECTIONS

None.

## COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .