Acos

Defined in header <cmath>.

Description

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 num.  (since C++23)
Additional Overloads are provided for all integer types, which are treated as double.  (since C++11)

Declarations

C++23

// 1)
/* floating-point-type */ acos( /* floating-point-type */ num );
// 2)
float acosf( float num );
// 3)
long double acosl( long double num );

Additional Overloads

// 4)
template< class Integer >
double acos ( Integer num );

C++11

// 1)
float acos ( float num );
// 2)
double acos ( double num );
// 3)
long double acos ( long double num );
// 4)
float acosf( float num );
// 5)
long double acosl( long double num );

Additional Overloads

// 6)
template< class Integer >
double acos ( Integer num );

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 Additional Overloads. 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)).

Examples

#include <cerrno>
#include <cfenv>
#include <cmath>
#include <cstring>
#include <iostream>
 
// #pragma STDC FENV_ACCESS ON
 
int main()
{
    std::cout 
        << "acos(-1) = " 
        << acos(-1) << '\n'
        << "acos(0.0) = " 
        << acos(0.0) << '\n'
        << "2*acos(0.0) = " 
        << 2 * acos(0) << '\n'
        << "acos(0.5) = " 
        << acos(0.5) << '\n'
        << "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';
}

Result

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