NAME

std::acos,std::acosf,std::acosl - std::acos,std::acosf,std::acosl

Synopsis

Defined in header <cmath>
float acos ( float arg );
float acosf( float arg ); (since C++11)
double acos ( double arg ); (1) (2)
long double acos ( long double arg );
long double acosl( long double arg ); (3) (since C++11)
double acos ( IntegralType arg ); (4) (since C++11)

1-3) Computes the principal value of the arc cosine of arg.
4) A set of overloads or a function template accepting an argument of any integral
type. Equivalent to 2) (the argument is cast to double).

Parameters

arg - value of a floating-point or Integral type

Return value

If no errors occur, the arc cosine of arg (arccos(arg)) in the range [0 , π], is
returned.

If a domain error occurs, an implementation-defined value is returned (NaN where
supported)

If a range error occurs due to underflow, the correct result (after rounding) is
returned.

Error handling

Errors are reported as specified in math_errhandling.

Domain error occurs if arg is outside the range [-1.0, 1.0]

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

* If the argument is +1, the value +0 is returned.
* If |arg| > 1, a domain error occurs and NaN is returned.
* if the argument is NaN, NaN is returned

Example

// Run this code

#include <cmath>
#include <iostream>
#include <cerrno>
#include <cfenv>
#include <cstring>

#pragma STDC FENV_ACCESS ON
int main()
{
std::cout << "acos(-1) = " << acos(-1) << '\n'
<< "acos(0.0) = " << acos(0.0) << " 2*acos(0.0) = " << 2*acos(0) << '\n'
<< "acos(0.5) = " << acos(0.5) << " 3*acos(0.5) = " << 3*acos(0.5) << '\n'
<< "acos(1) = " << acos(1) << '\n';
// error handling
errno = 0;
std::feclearexcept(FE_ALL_EXCEPT);
std::cout << "acos(1.1) = " << acos(1.1) << '\n';
if (errno == EDOM)
std::cout << " errno == EDOM: " << std::strerror(errno) << '\n';
if (std::fetestexcept(FE_INVALID))
std::cout << " FE_INVALID raised" << '\n';
}

Output:

acos(-1) = 3.14159
acos(0.0) = 1.5708 2*acos(0.0) = 3.14159
acos(0.5) = 1.0472 3*acos(0.5) = 3.14159
acos(1) = 0
acos(1.1) = nan
errno == EDOM: Numerical argument out of domain
FE_INVALID raised

See also

asin
asinf computes arc sine (\({\small\arcsin{x} }\)arcsin(x))
asinl (function)
(C++11)
(C++11)
atan
atanf computes arc tangent (\({\small\arctan{x} }\)arctan(x))
atanl (function)
(C++11)
(C++11)
atan2
atan2f arc tangent, using signs to determine quadrants
atan2l (function)
(C++11)
(C++11)
cos
cosf computes cosine (\({\small\cos{x} }\)cos(x))
cosl (function)
(C++11)
(C++11)
acos(std::complex) computes arc cosine of a complex number (\({\small\arccos{z}
(C++11) }\)arccos(z))
(function template)
acos(std::valarray) applies the function std::acos to each element of valarray
(function template)