---
name: "casinh"
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/casinh"
---

# casinh(3)

complex arc sine hyperbolic

## NAME

casinh, casinhf, casinhl - complex arc sine hyperbolic

## LIBRARY

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

## SYNOPSIS

```
#include <complex.h>
```

**double complex casinh(double complex** *z***);** **float complex casinhf(float complex** *z***);** **long double complex casinhl(long double complex** *z***);**

## DESCRIPTION

These functions calculate the complex arc hyperbolic sine of *z*. If *y = casinh(z)*, then *z = csinh(y)*. The imaginary part of *y* is chosen in the interval \[-pi/2,pi/2\].

One has:

```
casinh(z) = clog(z + csqrt(z * z + 1))
```

## ATTRIBUTES

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

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **casinh**(), **casinhf**(), **casinhl**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

glibc 2.1. C99, POSIX.1-2001.

## SEE ALSO

[**asinh**(3)](/asinh/3.md), [**cabs**(3)](/cabs/3.md), [**cimag**(3)](/cimag/3.md), [**csinh**(3)](/csinh/3.md), [**complex**(7)](/complex/7.md)