```ATAN2(3)                  Linux Programmer's Manual                 ATAN2(3)
```

## NAME         top

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

## SYNOPSIS         top

```       #include <math.h>

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

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
```

## DESCRIPTION         top

```       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.
```

## RETURN VALUE         top

```       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.
```

## ERRORS         top

```       No errors occur.
```

## ATTRIBUTES         top

```       For an explanation of the terms used in this section, see
attributes(7).

┌─────────────────────────────┬───────────────┬─────────┐
│Interface                    │ Attribute     │ Value   │
├─────────────────────────────┼───────────────┼─────────┤
│atan2(), atan2f(), atan2l()  │ Thread safety │ MT-Safe │
└─────────────────────────────┴───────────────┴─────────┘
```

## CONFORMING TO         top

```       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)
```

## COLOPHON         top

```       This page is part of release 5.00 of the Linux man-pages project.  A
description of the project, information about reporting bugs, and the