IEEE Std 1003.1, 2004 Edition

Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

atan, atanf, atanl - arc tangent function

#include <math.h>

double atan(doublex);

float atanf(floatx);

long double atanl(long doublex);

^{[CX]}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 IEEE Std 1003.1-2001 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

errnoto zero and callfeclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, iferrnois non-zero orfetestexcept(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

xin the range [-/2,/2] radians.

^{[MX]}Ifxis NaN, a NaN shall be returned.If

xis ±0,xshall be returned.If

xis ±Inf, ±/2 shall be returned.If

xis subnormal, a range error may occur andxshould be returned.

These functions may fail if:

- Range Error
^{[MX]}The value ofxis subnormal.If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then

errnoshall 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(),feclearexcept(),fetestexcept(),isnan(),tan(), the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions,<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() andatanl() functions are added for alignment with the ISO/IEC 9899:1999 standard.The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.

POSIX ® is a registered Trademark of The IEEE.

[ Main Index | XBD | XCU | XSH | XRAT ]