# nextafter man page

nextafter, nextafterf, nextafterl, nexttoward, nexttowardf, nexttowardl — floating-point number manipulation

## 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***);**

`Link with `

*-lm*.

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 versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

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

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* Glibc versions <= 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
An overflow floating-point exception (

**FE_OVERFLOW**) is raised.- Range error: result is subnormal or underflows
An underflow floating-point exception (

**FE_UNDERFLOW**) is raised.

These functions do not set *errno*.

## 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 |

## Conforming to

C99, POSIX.1-2001, POSIX.1-2008. This function is defined in IEC 559 (and the appendix with recommended functions in IEEE 754/IEEE 854).

## Bugs

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

## See Also

## Colophon

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## Referenced By

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