对 vtable 和继承的 C++ 未定义引用
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C++ Undefined Reference to vtable and inheritance
提问by rjmarques
File A.h
档案啊
#ifndef A_H_
#define A_H_
class A {
public:
virtual ~A();
virtual void doWork();
};
#endif
File Child.h
文件 Child.h
#ifndef CHILD_H_
#define CHILD_H_
#include "A.h"
class Child: public A {
private:
int x,y;
public:
Child();
~Child();
void doWork();
};
#endif
And Child.cpp
和Child.cpp
#include "Child.h"
Child::Child(){
x = 5;
}
Child::~Child(){...}
void Child::doWork(){...};
The compiler says that there is a undefined reference to vtable for A.
I have tried lots of different things and yet none have worked.
编译器说有一个对 vtable for 的未定义引用A。我尝试了很多不同的东西，但都没有奏效。
My objective is for class Ato be an Interface, and to seperate implementation code from headers.
我的目标是让类A成为一个接口，并将实现代码与头文件分开。
回答by Alok Save
Why the error & how to resolve it?
为什么会出现错误以及如何解决？
You need to provide definitionsfor all virtual functions in class A. Only pure virtual functions are allowed to have no definitions.
您需要提供的定义为所有虚拟功能class A。只允许纯虚函数没有定义。
i.e: In class Aboth the methods:
即：在class A这两种方法中：
virtual ~A();
virtual void doWork();
should be defined(should have a body)
应该被定义（应该有一个身体）
e.g.:
例如：
A.cpp
A.cpp
void A::doWork()
{
}
A::~A()
{
}
Caveat:
If you want your class Ato act as an interface(a.k.a Abstract classin C++) then you should make the method pure virtual.
警告：
如果您希望自己class A充当接口（又名C++ 中的抽象类），那么您应该使该方法成为纯虚拟的。
virtual void doWork() = 0;
Good Read:
好读：
What does it mean that the "virtual table" is an unresolved external?
When building C++, the linker says my constructors, destructors or virtual tables are undefined.
回答by Mahesh
My objective is for A to be an Interface, and to seperate implementation code from headers.
我的目标是让 A 成为一个接口，并将实现代码与头文件分开。
In that case, make the member function as pure virtual in class A.
在这种情况下，将 A 类中的成员函数设为纯虚函数。
class A {
// ...
virtual void doWork() = 0;
};
回答by ArchZombie0x Ryan P. Nicholl
Make sure to delete any "*.gch" files if none of the other responses help you.
如果其他回复都没有帮助您，请确保删除任何“*.gch”文件。
