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
我有一个包含纯虚函数的基类 MyBase:
I have a base class MyBase that contains a pure virtual function:
void PrintStartMessage() = 0
我希望每个派生类都在它们的构造函数中调用它
I want each derived class to call it in their constructor
然后我把它放在基类(MyBase
)构造函数中
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;
}
但我收到链接器错误.
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:UsersShmuelianDocumentsVisual Studio 2008Projectss1Debugs1.exe : fatal error LNK1120: 1 unresolved externals
1>s1 - 2 error(s), 0 warning(s)
我想强制所有派生类...
I want force to all derived classes to...
A- implement it
B- call it in their constructor
我必须怎么做?
推荐答案
有很多文章解释了为什么在 C++ 中永远不要在构造函数和析构函数中调用虚函数.看看这里和此处 详细了解此类调用期间幕后发生的情况.
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.
简而言之,对象是从基础到派生的.因此,当您尝试从基类构造函数调用虚函数时,尚未发生从派生类的覆盖,因为尚未调用派生构造函数.
In short, objects are constructed from the base up to the derived. So when you try to call a virtual function from the base class constructor, overriding from derived classes hasn't yet happened because the derived constructors haven't been called yet.
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