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

**#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

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.

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.

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*.

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 |

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).

In glibc version 2.5 and earlier, these functions do not raise an underflow
floating-point (

**FE_UNDERFLOW**) exception when an underflow occurs.

**nearbyint**(3)