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)