# ATAN2

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
COLOPHON

## NAME

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

## SYNOPSIS

#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():

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99

## DESCRIPTION

The atan2() function calculates 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

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.

## ATTRIBUTES

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

C99, POSIX.1-2001. The variant returning double also conforms to SVr4, 4.3BSD, C89.