[英]Classes, Inheritence and virtual functions
class Musician {
public: virtual void play() { std::cout << "Play an instrument"; }
};
class Guitarist : public Musician {
public: void play() { std::cout << "Play a guitar"<<endl; }
};
int main(){
Musician armstrong;
Guitarist steve;
Musician* m = &armstrong;
m->play();
m = &steve; //type of (m)=Musician type of (*m) = Guitarist???
}
为什么 (*m) 的类型 = Guitarist? 为什么如果我删除音乐家 class 的 function 中的虚拟关键字,那么 (*m) 的类型 = 音乐家?
class Musician {
public: void play() { std::cout << "Play an instrument"; } //this makes type of(*m) = Musician
};
如果我添加armstrong = static_cast<Musician>(steve);
最后它不会给出错误,但不会导致 armstrong (地址和类型)发生任何变化。 那条线是什么意思? 而steve = static_cast<Guitarist>(armstrong);
给出错误:
error: no matching function for call to 'Guitarist::Guitarist(Musician&)'
27 | steve=static_cast<Guitarist>(armstrong);
| ^
在我在这里学习之前尝试过这样做,我提供了一个解决方案,您可以用 Musician 替换 A,用 Guitarist 替换 B。
#include <iostream>
class A {
public:
void Same(){
std::cout << "From A" << std::endl;
}
virtual A& operator= (const A& a) {
assign(a);
return *this;
}
protected:
void assign(const A& a) {
}
};
class B : public A {
public:
void Same(){
std::cout << "From B" << std::endl;
}
virtual B& operator= (const A& a) {
if (const B* b = dynamic_cast<const B*>(&a))
assign(*b);
return *this;
}
protected:
void assign(const B& b) {
A::assign(b);
}
};
int main(){
A a;
B b;
a.Same();
a = b;
a.Same();
return 0;
}
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