acos, acosf, acosl − arc cosine function
float acosf(float x);
long double acosl(long double x);
Link with −lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
These functions calculate the arc cosine of x; that is the value whose cosine is x.
On success, these functions return the arc cosine of x in radians; the return value is in the range [0, pi].
If x is a NaN, a NaN is returned.
If x is +1, +0 is returned.
If x is positive infinity or negative infinity, a domain error occurs, and a NaN is returned.
If x is outside the range [−1, 1], a domain error occurs, and a NaN is returned.
See math_error(7) for information on how to determine whether an error has occurred when calling these functions.
errors can occur:
Domain error: x is outside the range [−1, 1]
errno is set to EDOM. An invalid floating-point exception (FE_INVALID) is raised.
For an explanation of the terms used in this section, see attributes(7).
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD, C89.
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