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std::cos

Defined in header `<cmath>`
float cos( float arg );	(1)
double cos( double arg );	(2)
long double cos( long double arg );	(3)
double cos( Integral arg );	(4)	(since C++11)

Computes the cosine of arg (measured in radians).

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 representing angle in radians, of a floating-point or Integral type

Return value

If no errors occur, the cosine of arg (cos(arg)) in the range [-1 ; +1], is returned.

The result may have little or no significance if the magnitude of arg is large.

(until C++11)

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.

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

if the argument is ±0, the result is 1.0
if the argument is ±∞, NaN is returned and FE_INVALID is raised
if the argument is NaN, NaN is returned

Notes

The case where the argument is infinite is not specified to be a domain error in C, but it is defined as a domain error in POSIX.

Example

#include <iostream>
#include <cmath>
#include <cerrno>
#include <cfenv>
 
#pragma STDC FENV_ACCESS ON
const double pi = std::acos(-1);
int main()
{
    // typical usage
    std::cout << "cos(pi/3) = " << std::cos(pi/3) << '\n'
              << "cos(pi/2) = " << std::cos(pi/2) << '\n'
              << "cos(-3*pi/4) = " << std::cos(-3*pi/4) << '\n';
    // special values
    std::cout << "cos(+0) = " << std::cos(0.0) << '\n'
              << "cos(-0) = " << std::cos(-0.0) << '\n';
    // error handling 
    std::feclearexcept(FE_ALL_EXCEPT);
    std::cout << "cos(INFINITY) = " << std::cos(INFINITY) << '\n';
    if(std::fetestexcept(FE_INVALID)) std::cout << "    FE_INVALID raised\n";
}

Possible output:

cos(pi/3) = 0.5
cos(pi/2) = 6.12323e-17
cos(-3*pi/4) = -0.707107
cos(+0) = 1
cos(-0) = 1
cos(INFINITY) = -nan
    FE_INVALID raised