---
name: "nextupl"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/nextup"
---

# nextupl(3)

return next floating-point number toward positive/negative infinity

Part of [nextup(3)](/nextup/3.md).

## NAME

nextup, nextupf, nextupl, nextdown, nextdownf, nextdownl - return next floating-point number toward positive/negative infinity

## LIBRARY

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

## SYNOPSIS

```
#define _GNU_SOURCE     /* See feature_test_macros(7) */
#include <math.h>
```

**double nextup(double** *x***);** **float nextupf(float** *x***);** **long double nextupl(long double** *x***);**

**double nextdown(double** *x***);** **float nextdownf(float** *x***);** **long double nextdownl(long double** *x***);**

## DESCRIPTION

The **nextup**(), **nextupf**(), and **nextupl**() functions return the next representable floating-point number greater than *x*.

If *x* is the smallest representable negative number in the corresponding type, these functions return -0. If *x* is +0 or -0, the returned value is the smallest representable positive number of the corresponding type.

If *x* is positive infinity, the returned value is positive infinity. If *x* is negative infinity, the returned value is the largest representable finite negative number of the corresponding type.

If *x* is NaN, the returned value is NaN.

The value returned by *nextdown(x)* is *-nextup(-x)*, and similarly for the other types.

## RETURN VALUE

See DESCRIPTION.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **nextup**(), **nextupf**(), **nextupl**(), **nextdown**(), **nextdownf**(), **nextdownl**() | Thread safety | MT-Safe |

## STANDARDS

These functions are described in *IEEE Std 754-2008 - Standard for Floating-Point Arithmetic* and *ISO/IEC TS 18661*.

## HISTORY

glibc 2.24.

## SEE ALSO

[**nearbyint**(3)](/nearbyint/3.md), [**nextafter**(3)](/nextafter/3.md)