# nextafter - Man Page

floating-point number manipulation

## Library

Math library (*libm*, *-lm*)

## Synopsis

#include <math.h> double nextafter(doublex, doubley); float nextafterf(floatx, floaty); long double nextafterl(long doublex, long doubley); double nexttoward(doublex, long doubley); float nexttowardf(floatx, long doubley); long double nexttowardl(long doublex, long doubley);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

**nextafter**():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 500 || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

**nextafterf**(), **nextafterl**():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

**nexttoward**(), **nexttowardf**(), **nexttowardl**():

_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

## Description

The **nextafter**(), **nextafterf**(), and **nextafterl**() functions return the next representable floating-point value following *x* in the direction of *y*. If *y* is less than *x*, these functions will return the largest representable number less than *x*.

If *x* equals *y*, the functions return *y*.

The **nexttoward**(), **nexttowardf**(), and **nexttowardl**() functions do the same as the corresponding **nextafter**() functions, except that they have a *long double* second argument.

## Return Value

On success, these functions return the next representable floating-point value after *x* in the direction of *y*.

If *x* equals *y*, then *y* (cast to the same type as *x*) is returned.

If *x* or *y* is a NaN, a NaN is returned.

If *x* is finite, and the result would overflow, a range error occurs, and the functions return **HUGE_VAL**, **HUGE_VALF**, or **HUGE_VALL**, respectively, with the correct mathematical sign.

If *x* is not equal to *y*, and the correct function result would be subnormal, zero, or underflow, a range error occurs, and either the correct value (if it can be represented), or 0.0, is returned.

## Errors

See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

- Range error: result overflow
*errno*is set to**ERANGE**. An overflow floating-point exception (**FE_OVERFLOW**) is raised.- Range error: result is subnormal or underflows
*errno*is set to**ERANGE**. An underflow floating-point exception (**FE_UNDERFLOW**) is raised.

## Attributes

For an explanation of the terms used in this section, see attributes(7).

Interface | Attribute | Value |
---|---|---|

nextafter(), nextafterf(), nextafterl(), nexttoward(), nexttowardf(), nexttowardl() | Thread safety | MT-Safe |

## Standards

C11, POSIX.1-2008.

This function is defined in IEC 559 (and the appendix with recommended functions in IEEE 754/IEEE 854).

## History

C99, POSIX.1-2001.

## Bugs

In glibc 2.5 and earlier, these functions do not raise an underflow floating-point (**FE_UNDERFLOW**) exception when an underflow occurs.

Before glibc 2.23 these functions did not set *errno*.

## See Also

## Referenced By

The man pages nextafterf(3), nextafterl(3), nexttoward(3), nexttowardf(3) and nexttowardl(3) are aliases of nextafter(3).