ATAN(3) Library Functions Manual ATAN(3)

atan atanf atanl — arc tangent function

#include <math.h>

double atan(double x);
float atanf(float x);
long double atanl(long double x);

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.

These functions shall compute the principal value of the arc tangent of their argument x.

An application wishing to check for error situations should set errno to zero and call (FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or (FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Upon successful completion, these functions shall return the arc tangent of x in the range [-/2,/2] radians.

[MX] If x is NaN, a NaN shall be returned.

If x is ±0, x shall be returned.

If x is ±Inf, ±/2 shall be returned.

If x is subnormal, a range error may occur and x should be returned.

[MX] If x is not returned, atan (), atanf (), and atanl () shall return an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

These functions may fail if:

[MX] The value of x is subnormal.

If the integer expression ( math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression ( math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised.

None.

On error, the expressions ( math_errhandling & MATH_ERRNO) and ( math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

None.

None.

atan2(3), feclearexcept(3), fetestexcept(3), isnan(3), tan(3)

XBD V1_chap04(7), <math.h>

First released in Issue 1. Derived from Issue 1 of the SVID.

The DESCRIPTION is updated to indicate how an application should check for an error. This text was previously published in the APPLICATION USAGE section.

The atanf () and atanl () functions are added for alignment with the ISO/IEC 9899:1999 (“ISO C99”) standard.

The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 (“ISO C99”) standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 (“ISO C99”) standard are marked.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0037 [68] is applied.

January 1, 2013 posix.fail