#include <math.h> double atanh(double x);Link with -lm.
float atanhf(float x);
long double atanhl(long double x);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
If x is a NaN, a NaN is returned.
If x is +0 (-0), +0 (-0) is returned.
If x is +1 or -1, a pole error occurs, and the functions return HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the mathematically correct sign.
The following errors can occur:
|atanh(), atanhf(), atanhl()||Thread safety||MT-Safe|