/C

# cos, cosf, cosl

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

```#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

 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) C++ documentation for `cos`