NAME¶

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

Synopsis¶

Defined in header <cmath>
float acos ( float num );

double acos ( double num ); (until C++23)

long double acos ( long double num );
/* floating-point-type */ (since C++23)
acos ( /* floating-point-type */ num ); (constexpr since C++26)
float acosf( float num ); (1) (2) (since C++11)
(constexpr since C++26)
long double acosl( long double num ); (3) (since C++11)
(constexpr since C++26)
Additional overloads (since C++11)
Defined in header <cmath>
template< class Integer > (A) (constexpr since C++26)
double acos ( Integer num );

1-3) Computes the principal value of the arc cosine of num.
The library provides overloads of std::acos for all cv-unqualified floating-point
types as the type of the parameter.
(since C++23)

A) Additional overloads are provided for all integer types, which are (since C++11)
treated as double.

Parameters¶

num - floating-point or integer value

Return value¶

If no errors occur, the arc cosine of num (arccos(num)) 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 num 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 |num| > 1, a domain error occurs and NaN is returned.
* if the argument is NaN, NaN is returned.

Notes¶

The additional overloads are not required to be provided exactly as (A). They only
need to be sufficient to ensure that for their argument num of integer type,
std::acos(num) has the same effect as std::acos(static_cast<double>(num)).

Example¶

// Run this code

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

// #pragma STDC FENV_ACCESS ON

int main()
{
std::cout << "acos(-1) = " << std::acos(-1) << '\n'
<< "acos(0.0) = " << std::acos(0.0) << '\n'
<< "2*acos(0.0) = " << 2 * std::acos(0) << '\n'
<< "acos(0.5) = " << std::acos(0.5) << '\n'
<< "3*acos(0.5) = " << 3 * std::acos(0.5) << '\n'
<< "acos(1) = " << std::acos(1) << '\n';

// error handling
errno = 0;
std::feclearexcept(FE_ALL_EXCEPT);

std::cout << "acos(1.1) = " << std::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
(C++11) (\({\small\arccos{z}}\)arccos(z))
(function template)
acos(std::valarray) applies the function std::acos to each element of valarray
(function template)
C documentation for
acos