# std::arg(std::complex)

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< cpp‎ | numeric‎ | 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

Run this code

    #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

### See also

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)

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