nextafter(3) — Linux manual page

```nextafter(3)            Library Functions Manual            nextafter(3)
```

NAME         top

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

LIBRARY         top

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

SYNOPSIS         top

```       #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);

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         top

```       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         top

```       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         top

```       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         top

```       For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────────────────┬───────────────┬─────────┐
│ Interface                           │ Attribute     │ Value   │
├─────────────────────────────────────┼───────────────┼─────────┤
│ nextafter(), nextafterf(),          │ Thread safety │ MT-Safe │
│ nextafterl(), nexttoward(),         │               │         │
│ nexttowardf(), nexttowardl()        │               │         │
└─────────────────────────────────────┴───────────────┴─────────┘
```

STANDARDS         top

```       C11, POSIX.1-2008.

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

HISTORY         top

```       C99, POSIX.1-2001.
```

BUGS         top

```       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.
```

```       nearbyint(3)
```

COLOPHON         top

```       This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project.  Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.