# std::arg(std::complex)

< cpp‎ | numeric‎ | complex

定义于头文件 `<complex>` |  |
template< class T > T arg( const complex<T>& z ); | (1) |
long double arg( long double z ); | (2) | (C++11 起)
template< class DoubleOrInteger > double arg( DoubleOrInteger z ); | (3) | (C++11 起)
float arg( float z ); | (4) | (C++11 起)

计算复数 `z` 的辐角（以弧度表示）

(C++11 起)为 float 、 double 、 long double 及所有整数类型提供重载，它们被当做有零虚部的复数

### 参数

z | - | 复数值

### 返回值

若无错误发生，则返回 `z` 在区间 (−π; π) 内的辐角。

错误和特殊情况按照函数宛如以 std::atan2(std::imag(z), std::real(z)) 实现来处理。

### 示例

    #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';
    }

输出：

    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

### 参阅

abs(std::complex) | 返回复数的模 (函数模板)
polar | 从模和辐角构造复数 (函数模板)
atan2 atan2f atan2l (C++11)(C++11) | 反正切，用符号确定象限 (函数)
atan2(std::valarray) | 应用函数 std::atan2 到一个 valarray 和一个值 (函数模板)