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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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atan2(3) Library Functions Manual atan2(3)
atan2, atan2f, atan2l - arc tangent function of two variables
Math library (libm, -lm)
#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 <= 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 │
└──────────────────────────────────────┴───────────────┴─────────┘
C11, POSIX.1-2008.
C99, POSIX.1-2001.
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)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 atan2(3)
Pages that refer to this page: acos(3), asin(3), atan(3), cos(3), sin(3), tan(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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