table of contents
atan2(3) | Library Functions Manual | atan2(3) |
NAME¶
atan2, atan2f, atan2l - arc tangent function of two variables
LIBRARY¶
Math library (libm, -lm)
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);
atan2f(), atan2l():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 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 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¶
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 |
STANDARDS¶
C11, POSIX.1-2008.
HISTORY¶
C99, POSIX.1-2001.
The variant returning double also conforms to SVr4, 4.3BSD, C89.
SEE ALSO¶
2023-03-30 | Linux man-pages 6.04 |