std::cos, std::cosf, std::cosl

Defined in header <cmath>
float       cos ( float arg );
float       cosf( float arg );
(since C++11)
double      cos ( double arg );
long double cos ( long double arg );
long double cosl( long double arg );
(since C++11)
double      cos ( IntegralType arg );
(4) (since C++11)
1-3) 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).


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


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.


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

See also

computes sine (\({\small\sin{x} }\)sin(x))
computes tangent (\({\small\tan{x} }\)tan(x))
computes arc cosine (\({\small\arccos{x} }\)arccos(x))
computes cosine of a complex number (\({\small\cos{z} }\)cos(z))
(function template)
applies the function std::cos to each element of valarray
(function template)
C documentation for cos

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