# tan, tanf, tanl

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< c‎ | numeric‎ | math

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

### 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.

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

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("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

### References

- 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

### See also

sin sinf sinl (C99)(C99) | computes sine (sin(x)) (function)
cos cosf cosl (C99)(C99) | computes cosine (cos(x)) (function)
atan atanf atanl (C99)(C99) | computes arc tangent (arctan(x)) (function)
ctan ctanf ctanl (C99)(C99)(C99) | computes the complex tangent (function)

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