# cos, cosf, cosl

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< c‎ | numeric‎ | math

Defined in header `<math.h>` |  |
float cosf( float arg ); | (1) | (since C99)
double cos( double arg ); | (2) |
long double cosl( long double arg ); | (3) | (since C99)
Defined in header `<tgmath.h>` |  |
#define cos( arg ) | (4) | (since C99)

1-3) Computes the cosine of `arg` (measured in radians).
4) Type-generic macro: If the argument has type long double, `cosl` is called. Otherwise, if the argument has integer type or the type double, `cos` is called. Otherwise, `cosf` is called. If the argument is complex, then the macro invokes the corresponding complex function (ccosf, ccos, ccosl).

### Parameters

arg | - | floating point value representing angle in radians

### 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 <stdio.h>
    #include <math.h>
    #include <errno.h>
    #include <fenv.h>

    #pragma STDC FENV_ACCESS ON
    int main(void)
    {
        double pi = acos(-1);
        // typical usage
        printf("cos(pi/3) = %f\n", cos(pi/3));
        printf("cos(pi/2) = %f\n", cos(pi/2));
        printf("cos(-3*pi/4) = %f\n", cos(-3*pi/4));
        // special values
        printf("cos(+0) = %f\n", cos(0.0));
        printf("cos(-0) = %f\n", cos(-0.0));
        // error handling
        feclearexcept(FE_ALL_EXCEPT);
        printf("cos(INFINITY) = %f\n", cos(INFINITY));
        if(fetestexcept(FE_INVALID)) puts("    FE_INVALID raised");
    }

Possible output:

    cos(pi/3) = 0.500000
    cos(pi/2) = 0.000000
    cos(-3*pi/4) = -0.707107
    cos(+0) = 1.000000
    cos(-0) = 1.000000
    cos(INFINITY) = -nan
        FE_INVALID raised

### References

- C11 standard (ISO/IEC 9899:2011):

  - 7.12.4.5 The cos functions (p: 239)

  - 7.25 Type-generic math <tgmath.h> (p: 373-375)

  - F.10.1.5 The cos functions (p: 519)

- C99 standard (ISO/IEC 9899:1999):

  - 7.12.4.5 The cos functions (p: 220)

  - 7.22 Type-generic math <tgmath.h> (p: 335-337)

  - F.9.1.5 The cos functions (p: 456)

- C89/C90 standard (ISO/IEC 9899:1990):

  - 4.5.2.5 The cos function

### See also

sinsinfsinl (C99)(C99) | computes sine (sin(x)) (function)
tantanftanl (C99)(C99) | computes tangent (tan(x)) (function)
acosacosfacosl (C99)(C99) | computes arc cosine (arccos(x)) (function)
ccosccosfccosl (C99)(C99)(C99) | computes the complex cosine (function)

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