/C

# tan, tanf, tanl

Defined in header `<math.h>`
`float       tanf( float arg );`
(1) (since C99)
`double      tan( double arg );`
(2)
`long double tanl( long double arg );`
(3) (since C99)
Defined in header `<tgmath.h>`
`#define tan( arg )`
(4) (since C99)
1-3) Computes the tangent of `arg` (measured in radians).
4) Type-generic macro: If the argument has type `long double`, `tanl` is called. Otherwise, if the argument has integer type or the type `double`, `tan` is called. Otherwise, `tanf` is called. If the argument is complex, then the macro invokes the corresponding complex function (`ctanf`, `ctan`, `ctanl`).

### Parameters

 arg - floating point value representing angle in radians

### Return value

If no errors occur, the tangent of `arg` (tan(arg)) is returned.

 The result may have little or no significance if the magnitude of `arg` is large. (until C99)

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, it is returned unmodified
• 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.

The function has mathematical poles at π(1/2 + n); however no common floating-point representation is able to represent π/2 exactly, thus there is no value of the argument for which a pole error occurs.

### 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("tan  (pi/4) = %+f\n", tan(  pi/4)); //   45 deg
printf("tan(3*pi/4) = %+f\n", tan(3*pi/4)); //  135 deg
printf("tan(5*pi/4) = %+f\n", tan(5*pi/4)); // -135 deg
printf("tan(7*pi/4) = %+f\n", tan(7*pi/4)); //  -45 deg
// special values
printf("tan(+0) = %f\n", tan(0.0));
printf("tan(-0) = %f\n", tan(-0.0));
// error handling
feclearexcept(FE_ALL_EXCEPT);
printf("tan(INFINITY) = %f\n", tan(INFINITY));
if(fetestexcept(FE_INVALID)) puts("    FE_INVALID raised");
}```

Possible output:

```tan  (pi/4) = +1.000000
tan(3*pi/4) = -1.000000
tan(5*pi/4) = +1.000000
tan(7*pi/4) = -1.000000
tan(+0) = 0.000000
tan(-0) = -0.000000
tan(INFINITY) = -nan
FE_INVALID raised```
• C11 standard (ISO/IEC 9899:2011):
• 7.12.4.7 The tan functions (p: 240)
• 7.25 Type-generic math <tgmath.h> (p: 373-375)
• F.10.1.7 The tan functions (p: 519)
• C99 standard (ISO/IEC 9899:1999):
• 7.12.4.7 The tan functions (p: 220)
• 7.22 Type-generic math <tgmath.h> (p: 335-337)
• F.9.1.7 The tan functions (p: 457)
• C89/C90 standard (ISO/IEC 9899:1990):
• 4.5.2.7 The tan function