Copyright 1993 David Metcalfe (firstname.lastname@example.org) and Copyright 2008, Linux Foundation, written by Michael Kerrisk <email@example.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting ...
NAMEatan, atanf, atanl - arc tangent function
#include <math.h> double atan(double x);Link with -lm.
float atanf(float x);
long double atanl( long double x);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
DESCRIPTIONThese functions calculate the principal value of the arc tangent of x; that is the value whose tangent is x.
RETURN VALUEOn 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.
ERRORSNo errors occur.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
|atan(), atanf(), atanl()||Thread safety||MT-Safe|
CONFORMING TOC99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD, C89.