atan(), atanf(), atanl()

Synopsis:

#include <math.h>

double atan( double x );

float atanf( float x );

long double atanl( long double x );

Arguments:

x: The tangent for which you want to find the angle.

Library:

libm

Use the -l m option to qcc to link against this library.

Description:

These functions compute the arctangent (in radians) of x.

To check for error situations, use feclearexcept() and fetestexcept(). For example:

Call feclearexcept(FE_ALL_EXCEPT) before calling atan(), atanf(), or atanl().
On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

Returns:

The arctangent, in the range [-π/2, π/2].

If `x` is:	These functions return:	Errors:
±0.0	`x`	—
Inf	`π`/2	—
-Inf	-`π`/2	—
NaN	NaN	—

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

Examples:

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <fenv.h>

int main( void )
{
    int except_flags;

    feclearexcept(FE_ALL_EXCEPT);

    printf( "%f\n", atan(.5) );

    except_flags = fetestexcept(FE_ALL_EXCEPT);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    return EXIT_SUCCESS;
}

produces the output:

0.463648

Classification:

ANSI, POSIX 1003.1

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	No
Thread	Yes