atan man page

atan, atanf, atanl — arc tangent function


#include <math.h>

double atan(double x);

float atanf(float x);

long double atanl( long double x);

Link with -lm.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

atanf(), atanl():

|| /* 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 x; that is the value whose tangent is x.

Return Value

On success, these functions return the principal value of the arc tangent of x in radians; the return value is in the range [-pi/2, pi/2].

If x is a NaN, a NaN is returned.

If x is +0 (-0), +0 (-0) is returned.

If x is positive infinity (negative infinity), +pi/2 (-pi/2) is returned.


No errors occur.


For an explanation of the terms used in this section, see attributes(7).

atan(), atanf(), atanl()Thread safetyMT-Safe

Conforming to

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning double also conforms to SVr4, 4.3BSD, C89.

See Also

acos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3)

Referenced By

acos(3), asin(3), atan2(3), cos(3), sin(3), tan(3).

Explore man page connections for atan(3).

atanf(3) and atanl(3) are aliases of atan(3).