atan2, atan2f, atan2l - arc tangent function of two variables

**#include <math.h>**

**double atan2(double ***y***, double ***x***);**
**float atan2f(float ***y***, float ***x***);**
**long double atan2l(long double ***y***, long double ***x***);**

Link with

*-lm*.

Feature Test Macro Requirements for glibc (see

**feature_test_macros**(7)):

**atan2f**(),

**atan2l**():

_ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

These functions calculate the principal value of the arc tangent of

*y/x*,
using the signs of the two arguments to determine the quadrant of the result.

On success, these functions return the principal value of the arc tangent of

*y/x* in radians; the return value is in the range [-pi, pi].

If

*y* is +0 (-0) and

*x* is less than 0, +pi (-pi) is returned.

If

*y* is +0 (-0) and

*x* is greater than 0, +0 (-0) is returned.

If

*y* is less than 0 and

*x* is +0 or -0, -pi/2 is returned.

If

*y* is greater than 0 and

*x* is +0 or -0, pi/2 is returned.

If either

*x* or

*y* is NaN, a NaN is returned.

If

*y* is +0 (-0) and

*x* is -0, +pi (-pi) is returned.

If

*y* is +0 (-0) and

*x* is +0, +0 (-0) is returned.

If

*y* is a finite value greater (less) than 0, and

*x* is negative
infinity, +pi (-pi) is returned.

If

*y* is a finite value greater (less) than 0, and

*x* is positive
infinity, +0 (-0) is returned.

If

*y* is positive infinity (negative infinity), and

*x* is finite,
pi/2 (-pi/2) is returned.

If

*y* is positive infinity (negative infinity) and

*x* is negative
infinity, +3*pi/4 (-3*pi/4) is returned.

If

*y* is positive infinity (negative infinity) and

*x* is positive
infinity, +pi/4 (-pi/4) is returned.

No errors occur.

For an explanation of the terms used in this section, see

**attributes**(7).

Interface |
Attribute |
Value |

atan2 (), atan2f (), atan2l () |
Thread safety |
MT-Safe |

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning

*double* also conforms to SVr4, 4.3BSD, C89.

**acos**(3),

**asin**(3),

**atan**(3),

**carg**(3),

**cos**(3),

**sin**(3),

**tan**(3)