使用DllImport时，在C＃中包装C ++参考参数

[DllImport(TestCppDLL.dll)]
public static extern void foo(out int a, out int b, out double c);

public void main()
{
    int a;
    int b;
    double c;

    this.foo(out a, out b, out c);
    Console.WriteLine(a + b + c);
}

extern void foo(int &a, int &b, double &c)
{
     a = 1;
     b = 2;
     c = 3;
}