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

# trunc(3)

round to integer, toward zero

## NAME

trunc, truncf, truncl - round to integer, toward zero

## LIBRARY

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

## SYNOPSIS

```
#include <math.h>
```

**double trunc(double** *x***);** **float truncf(float** *x***);** **long double truncl(long double** *x***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**trunc**(), **truncf**(), **truncl**():

```
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
```

## DESCRIPTION

These functions round *x* to the nearest integer value that is not larger in magnitude than *x*.

## RETURN VALUE

These functions return the rounded integer value, in floating format.

If *x* is integral, infinite, or NaN, *x* itself is returned.

## ERRORS

No errors occur.

## ATTRIBUTES

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

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **trunc**(), **truncf**(), **truncl**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

glibc 2.1. C99, POSIX.1-2001.

## NOTES

The integral value returned by these functions may be too large to store in an integer type (*int*, *long*, etc.). To avoid an overflow, which will produce undefined results, an application should perform a range check on the returned value before assigning it to an integer type.

## SEE ALSO

[**ceil**(3)](/ceil/3.md), [**floor**(3)](/floor/3.md), [**lrint**(3)](/lrint/3.md), [**nearbyint**(3)](/nearbyint/3.md), [**rint**(3)](/rint/3.md), [**round**(3)](/round/3.md)