ACOS(3M) | Mathematical Library Functions | ACOS(3M) |

acos, acosf, acosl - arc cosine functions

c99 [flag... ]file...-lm[library... ] #include <math.h>doubleacos(doublex);

floatacosf(floatx);

long doubleacosl(long doublex);

These functions compute the principal value of the arc cosine of
*x*. The value of *x* should be in the range [−1,1].

Upon successful completion, these functions return the arc cosine
of *x* in the range [0, pi] radians.

For finite values of *x* not in the range [−1,1], a
domain error occurs and NaN is returned.

If *x* is NaN, NaN is returned.

If *x* is +1, +0 is returned.

If *x* is ±Inf, a domain error occurs and NaN is
returned.

For exceptional cases, matherr(3M) tabulates the values to
be returned by **acos()** as specified by SVID3 and XPG3.

These functions will fail if:

**Domain Error**

The *x* argument is finite and not in the range
[-1,1], or is ±Inf.

If the integer expression (**math_errhandling** &
**MATH_ERREXCEPT**) is non-zero, the invalid floating-point exception is
raised.

The **acos()** function sets **errno** to **EDOM** if
*x* is not ±Inf or NaN and is not in the range
[−1,1].

An application wanting to check for exceptions should call
**feclearexcept**(**FE_ALL_EXCEPT**) before calling these functions.
On return, if **fetestexcept**(**FE_INVALID** | **FE_DIVBYZERO** |
**FE_OVERFLOW** | **FE_UNDERFLOW**) is non-zero, an exception has been
raised. An application should either examine the return value or check the
floating point exception flags to detect exceptions.

An application can also set **errno** to 0 before calling
**acos()**. On return, if **errno** is non-zero, an error has
occurred. The **acosf()** and **acosl()** functions do not set
**errno**.

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE | ATTRIBUTE VALUE |

Interface Stability | Standard |

MT-Level | MT-Safe |

math.h(3HEAD), cos(3M), feclearexcept(3M), fetestexcept(3M), isnan(3M), matherr(3M), attributes(7), standards(7)

July 12, 2006 | SunOS 5.11 |