# ATAN2(3) - Linux man page online | Library functions

Arc tangent function of two variables.

Chapter

2017-09-15

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

## 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); 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## DESCRIPTION

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

On success, these functions return the principal value of the arc tangent of y/x in radi‐ ans; 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

No errors occur.## ATTRIBUTES

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

C99, POSIX.1-2001, POSIX.1-2008. The variant returning double also conforms to SVr4, 4.3BSD, C89.## SEE ALSO

acos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3)## COLOPHON

This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.**2017-09-15 ATAN2(3)**

This manual | Reference | Other manuals |
---|---|---|

atan2(3) | referred by | acos(3) | asin(3) | atan(3) | cos(3) | grap(1) | perlfunc(1) | sin(3) | tan(3) |

refer to | acos(3) | asin(3) | atan(3) | attributes(7) | carg(3) | cos(3) | feature_test_macros(7) | sin(3) | tan(3) |