从基类构造函数调用纯虚函数 [英] call to pure virtual function from base class constructor

问题描述

我有一个基类MyBase包含一个纯虚函数：

void PrintStartMessage（）= 0

我想让每个派生类在它们的构造函数中调用

code> MyBase ）构造函数

  class MyBase 
 {
 public：
 
 virtual void PrintStartMessage（）= 0; 
 MyBase（）
 {
 PrintStartMessage（）; 
} 
 
}; 
 
 class Derived：public MyBase 
 {
 
 public：
 void PrintStartMessage（）{
 
} 
 }; 
 
 void main（）
 {
派生的派生; 
} 
  

但我得到了一个链接器错误。

 这是错误信息：
 
 1> ------ Build started：项目：s1，配置：Debug Win32 --- --- 
 1>编译... 
 1> s1.cpp 
 1>链接... 
 1> s1.obj：错误LNK2019：未解析的外部符号public ：$ void $ __thiscall MyBase :: MyBase（void）（?? 0MyBase @@ QAE @ XZ）
（@AUEXXZ）引用的函数virtual void __thiscall MyBase :: PrintStartMessage（void）（？PrintStartMessage @ MyBase @ 1> C：\Users\Shmuelian\Documents\Visual Studio 2008\Projects\s1\Debug\s1.exe：fatal error LNK1120：1 unresolved externals 
 1> s1  -  2错误0 b警告b 
  

我想强制所有派生类...

  A-实现它
 
 B-在它们的构造函数中调用
  

我该怎么办呢？

解决方案

有很多文章解释为什么你不应该在C ++中的构造函数和析构函数中调用虚函数。查看此处和这里详细说明在这样的调用期间场景后面发生了什么。

I have a base class MyBase that contains a pure virtual function:

void PrintStartMessage() = 0

I want each derived class to call it in their constructor

then I put it in base class(MyBase) constructor

 class MyBase
 {
 public:

      virtual void PrintStartMessage() =0;
      MyBase()
      {
           PrintStartMessage();
      }

 };

 class Derived:public MyBase
 {     

 public:
      void  PrintStartMessage(){

      }
 };

void main()
 {
      Derived derived;
 }

but I get a linker error.

 this is error message : 

 1>------ Build started: Project: s1, Configuration: Debug Win32 ------
 1>Compiling...
 1>s1.cpp
 1>Linking...
 1>s1.obj : error LNK2019: unresolved external symbol "public: virtual void __thiscall MyBase::PrintStartMessage(void)" (?PrintStartMessage@MyBase@@UAEXXZ) referenced in function "public: __thiscall MyBase::MyBase(void)" (??0MyBase@@QAE@XZ)
 1>C:\Users\Shmuelian\Documents\Visual Studio 2008\Projects\s1\Debug\s1.exe : fatal error LNK1120: 1 unresolved externals
 1>s1 - 2 error(s), 0 warning(s)

I want force to all derived classes to...

A- implement it

B- call it in their constructor 

How I must do it?

解决方案

There are many articles that explain why you should never call virtual functions in constructor and destructor in C++. Take a look here and here for details what happens behind the scene during such calls.

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