# atanh, atanhf, atanhl

Visual Studio 2013

Calculates the inverse hyperbolic tangent.

```double atanh(
double x
);
float atanh(
float x
);  // C++ only
long double atanh(
long double x
);  // C++ only
float atanhf(
float x
);
long double atanhl(
long double x
);
```

## Parameters

x

Floating-point value.

## Return Value

The atanh functions return the inverse hyberbolic tangent (arc hyperbolic tangent) of x. If x is greater than 1, or less than –1, errno is set to EDOM and the result is a quiet NaN. If x is equal to 1 or -1, a positive or negative infinity is returned, respectively, and errno is set to ERANGE.

Input

SEH Exception

Matherr Exception

± QNAN,IND

none

none

X ≥ 1; x ≤ -1

none

none

## Remarks

Because C++ allows overloading, you can call overloads of atanh that take and return float or long double values. In a C program, atanh always takes and returns double.

## Requirements

Function

atanh, atanhf, atanhl

<math.h>

<cmath>

For additional compatibility information, see Compatibility.

## Example

```// crt_atanh.c
// This program displays the hyperbolic tangent of pi / 4
// and the arc hyperbolic tangent of the result.
//

#include <math.h>
#include <stdio.h>

int main( void )
{
double pi = 3.1415926535;
double x, y;

x = tanh( pi / 4 );
y = atanh( x );
printf( "tanh( %f ) = %f\n", pi/4, x );
printf( "atanh( %f ) = %f\n", x, y );
}
```
```tanh( 0.785398 ) = 0.655794
atanh( 0.655794 ) = 0.785398```

## .NET Framework Equivalent

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.