std::acos,std::acosf,std::acosl(3)

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