/C++

# std::arg(std::complex)

Defined in header `<complex>`
```template< class T >
T arg( const complex<T>& z );```
(1)
`long double arg( long double z );`
(2) (since C++11)
```template< class DoubleOrInteger >
double arg( DoubleOrInteger z );```
(3) (since C++11)
`float arg( float z );`
(4) (since C++11)

Calculates the phase angle (in radians) of the complex number `z`.

(since C++11)Additional overloads are provided for `float`, `double`, `long double`, and all integer types, which are treated as complex numbers with zero imaginary component.

### Parameters

 z - complex value

### Return value

If no errors occur, returns the phase angle of `z` in the interval [−π; π].

Errors and special cases are handled as if the function is implemented as `std::atan2(std::imag(z), std::real(z))`.

### Example

```#include <iostream>
#include <complex>

int main()
{
std::complex<double> z1(1, 0);
std::cout << "phase angle of " << z1 << " is " << std::arg(z1) << '\n';

std::complex<double> z2(0, 1);
std::cout << "phase angle of " << z2 << " is " << std::arg(z2) << '\n';

std::complex<double> z3(-1, 0);
std::cout << "phase angle of " << z3 << " is " << std::arg(z3) << '\n';

std::complex<double> z4(-1, -0.0);
std::cout << "phase angle of " << z4 << " (the other side of the cut) is "
<< std::arg(z4) << '\n';
}```

Output:

```phase angle of (1,0) is 0
phase angle of (0,1) is 1.5708
phase angle of (-1,0) is 3.14159
phase angle of (-1,-0) (the other side of the cut) is -3.14159```

 abs(std::complex) returns the magnitude of a complex number (function template) polar constructs a complex number from magnitude and phase angle (function template) atan2atan2fatan2l (C++11)(C++11) arc tangent, using signs to determine quadrants (function) atan2(std::valarray) applies the function `std::atan2` to a valarray and a value (function template)