IEEE Std 1003.1-2001

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

atan2, atan2f, atan2l - arc tangent functions

#include <math.h>

double atan2(doubley, doublex);

float atan2f(floaty, floatx);

long double atan2l(long doubley, 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

y/x, using the signs of both arguments to determine the quadrant of the return value.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

y/xin the range [-,] radians.If

yis ±0 andxis < 0, ± shall be returned.If

yis ±0 andxis > 0, ±0 shall be returned.If

yis < 0 andxis ±0, -/2 shall be returned.If

yis > 0 andxis ±0, /2 shall be returned.If

xis 0, a pole error shall not occur.

^{[MX]}If eitherxoryis NaN, a NaN shall be returned.If the result underflows, a range error may occur and

y/xshould be returned.If

yis ±0 andxis -0, ± shall be returned.If

yis ±0 andxis +0, ±0 shall be returned.For finite values of ±

y> 0, ifxis -Inf, ± shall be returned.For finite values of ±

y> 0, ifxis +Inf, ±0 shall be returned.For finite values of

x, ifyis ±Inf, ±/2 shall be returned.If

yis ±Inf andxis -Inf, ±3/4 shall be returned.If

yis ±Inf andxis +Inf, ±/4 shall be returned.If both arguments are 0, a domain error shall not occur.

These functions may fail if:

- Range Error
^{[MX]}The result underflows.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.

atan() ,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

atan2f() andatan2l() 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 ]