# atan2(), atan2f(), atan2l()

Compute the arctangent, determining the quadrant

## Synopsis:

```#include <math.h>

double atan2( double y,
double x );

float atan2f( float y,
float x );

long double atan2l( long double y,
long double x );
```

## Arguments:

y, x
The value (y/x) 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 value of the arctangent (in radians) of y/x, using the signs of both arguments to determine the quadrant of the return value. No errors occur if both arguments are zero, or if y is zero.

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

• Call feclearexcept(FE_ALL_EXCEPT) before calling atan2(), atan2f(), or atan2l().
• On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

## Returns:

The arctangent of y/x, in the range [-π, π].

If y is: And x is: These functions return: Errors:
±0.0 Negative or -0.0 π, with the same sign as y (see below)
±0.0 Positive or +0.0 0.0 (see below)
±Inf Finite π/2, with the same sign as y
±Inf -Inf 3π/4, with the same sign as y
±Inf Inf π/4, with the same sign as y
Negative ±0.0 -π/2
Positive ±0.0 +π/2
Finite and positive -Inf +π
Finite and negative -Inf -π
Finite and positive Inf 0.0
Finite and negative Inf -0.0
Any value NaN x
NaN Any value y
Note: Although the library considers 0.0 to be equal to -0.0, atan2(0.0, 0.0) isn't equal to atan2(0.0, -0.0).

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

int main( void )
{
int except_flags;

feclearexcept(FE_ALL_EXCEPT);

printf( "%f\n", atan2( .5, 1. ) );

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

return EXIT_SUCCESS;
}
```

produces the output:

```0.463648
```

## Classification:

Safety:
Cancellation point No
Interrupt handler No
Signal handler No