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

Since C++26

Header: <cmath>

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)

# Declarations

float acos ( float num );
double acos ( double num );
long double acos ( long double num );

(until C++23)

/*floating-point-type*/
acos ( /*floating-point-type*/ num );

(since C++23) (constexpr since C++26)

float acosf( float num );

(since C++11) (constexpr since C++26)

long double acosl( long double num );

(since C++11) (constexpr since C++26)

SIMD overload (since C++26)

template< /*math-floating-point*/ V >
constexpr /*deduced-simd-t*/<V>
acos ( const V& v_num );

(since C++26)

Additional overloads (since C++11)

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

(constexpr since C++26)

# Parameters

# Return value

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

# Example

#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';
}

# See also