# nextafterf (3)

# NAME

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

|| _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

|| /* 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.

*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

**nearbyint**(3)