# std::cos

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< cpp‎ | numeric‎ | math

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

Run this code

    #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

### See also

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

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