using System;using System.Diagnostics;using System.Text;using System.Collections;using System.Collections.Generic;class Test{    public class Base    {        public Base()        {            System.Console.WriteLine("Base.Base");            ABitDangerousCall();        }        public virtual void ABitDangerousCall()        {            System.Console.WriteLine("Base.ABitDangerousCall");        }        private class Inner        {            public Inner()            {                System.Console.WriteLine("Base.Inner.Inner");            }        }        private Inner inner = new Inner();    }    class Derived : Base    {        public Derived()        {            System.Console.WriteLine("Derived.Derived");            ctorInitializedMember = 5;        }        // ctorInitializedMember is default initialized to zero before the constructor initializes it.        private int ctorInitializedMember;        private int derivedInt;        public override void ABitDangerousCall()        {            System.Console.WriteLine(String.Format("Derived.ABitDangerousCallctorInitializedMember={0} derivedInt={1}", ctorInitializedMember, derivedInt));        }        private class Inner        {            public Inner()            {                System.Console.WriteLine("Derived.Inner.Inner");            }        }        private Inner inner = new Inner();    }    class Program    {        static void Main(string[] args)        {            Derived d = new Derived();            Console.Read();        }    }}

输出结果：

Derived.Inner.Inner

Base.Inner.Inner

Base.Base

Derived.ABitDangerousCallctorInitializedMember=0 derivedInt=0

Derived.Derived

由于实例构造函数的调用顺序是先基类构造函数再子类构造函数，如上面例子，在基类中调用被子类重写了的虚函数ABitDangerousCall时，实际会调用子类的ABitDangerousCall，

该函数中使用了变量ctorInitializedMember，但此时子类的构造函数还没调用，故ctorInitializedMember未被赋值，这样就出现了不想看到的结果。我们本来是想想看到ctorInitializedMember=5的结果，结果却是0。

因此在基类的构造函数中调用虚函数是很危险的，项目大了代码复杂了就很容易造成极隐蔽的BUG。同时在子类的构造函数中调用虚函数也是要小心的，尽量避免，原因同上。

如果非要调用，那就要细心察看虚函数中的变量是否已经全部在前面处理妥当了