---
name: "tanh"
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/tanh"
---

# tanh(3)

hyperbolic tangent function

## NAME

tanh, tanhf, tanhl - hyperbolic tangent function

## LIBRARY

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

## SYNOPSIS

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

**double tanh(double** *x***);** **float tanhf(float** *x***);** **long double tanhl(long double** *x***);**

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

**tanhf**(), **tanhl**():

```
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

## DESCRIPTION

These functions return the hyperbolic tangent of *x*, which is defined mathematically as:

```
    tanh(x) = sinh(x) / cosh(x)
```

## RETURN VALUE

On success, these functions return the hyperbolic tangent of *x*.

If *x* is a NaN, a NaN is returned.

If *x* is +0 (-0), +0 (-0) is returned.

If *x* is positive infinity (negative infinity), +1 (-1) 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** |
| **tanh**(), **tanhf**(), **tanhl**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

C99, POSIX.1-2001.

The variant returning *double* also conforms to SVr4, 4.3BSD, C89.

## SEE ALSO

[**acosh**(3)](/acosh/3.md), [**asinh**(3)](/asinh/3.md), [**atanh**(3)](/atanh/3.md), [**cosh**(3)](/cosh/3.md), [**ctanh**(3)](/ctanh/3.md), [**sinh**(3)](/sinh/3.md)