acosh man page


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

acosh, acoshf, acoshl — inverse hyperbolic cosine functions


#include <math.h>

double acosh(double x);
float acoshf(float x);
long double acoshl(long double x);


The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1‐2008 defers to the ISO C standard.

These functions shall compute the inverse hyperbolic cosine of their argument x.

An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Return Value

Upon successful completion, these functions shall return the inverse hyperbolic cosine of their argument.

For finite values of x < 1, a domain error shall occur, and either a NaN (if supported), or an implementation-defined value shall be returned.

If x is NaN, a NaN shall be returned.

If x is +1, +0 shall be returned.

If x is +Inf, +Inf shall be returned.

If x is -Inf, a domain error shall occur, and a NaN shall be returned.


These functions shall fail if:

Domain Error

The x argument is finite and less than +1.0, or is -Inf.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

The following sections are informative.



Application Usage

On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.



Future Directions


See Also

cosh(), feclearexcept(), fetestexcept()

The Base Definitions volume of POSIX.1‐2008, Section 4.19, Treatment of Error Conditions for Mathematical Functions, <math.h>


2013 IEEE/The Open Group POSIX Programmer's Manual