atanh, atanhf, atanhl

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


Floating-point 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.


SEH Exception

Matherr Exception




X ≥ 1; x ≤ -1



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.


C header

C++ header

atanh, atanhf, atanhl



For additional compatibility information, see Compatibility.

// 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

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