atan(3) Library Functions Manual atan(3) atan, atanf, atanl - (libm -lm) #include double atan(double x); float atanf(float x); long double atanl(long double x); glibc ( feature_test_macros(7)): atanf(), atanl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE x x. x [-pi/2, pi/2]. x (NaN) NaN. x +0 (-0) +0 (-0). x ( ) +pi/2 (-pi/2). . attributes(7). +------------+------------------------------------+--------------------+ || | | +------------+------------------------------------+--------------------+ |atan(), | | MT-Safe | |atanf(), | | | |atanl() | | | +------------+------------------------------------+--------------------+ C11, POSIX.1-2008. C99 POSIX.1-2001. double SVr4 4.3BSD C89. acos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3) 3 . . : . 6.18 8 2026 atan(3)