atan2(3) Library Functions Manual atan2(3) atan2, atan2f, atan2l - (libm -lm) #include double atan2(double y, double x); float atan2f(float y, float x); long double atan2l(long double y, long double x); glibc ( 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 y/x . y/x [-pi, pi]. y +0 (-0) x 0 +pi (-pi). y +0 (-0) x 0 +0 (-0). y 0 x +0 -0 -pi/2. y 0 x +0 -0 pi/2. x y NaN NaN. y +0 (-0) x -0 +pi (-pi). y +0 (-0) x +0 +0 (-0). y () 0 x +pi (-pi). y () 0 x +0 (-0). y ( ) x pi/2 (-pi/2). y ( ) x +3*pi/4 (-3*pi/4). y ( ) x +pi/4 (-pi/4). . attributes(7). +------------+------------------------------------+--------------------+ || | | +------------+------------------------------------+--------------------+ |atan2(), | | MT-Safe | |atan2f(), | | | |atan2l() | | | +------------+------------------------------------+--------------------+ C11, POSIX.1-2008. C99 POSIX.1-2001. double SVr4 4.3BSD C89. acos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3) 3 . . : . 6.18 8 2026 atan2(3)