C++ 派生类c+中的向上转换变量+;
如何更改派生类中继承变量的类型? 我有以下课程:C++ 派生类c+中的向上转换变量+;,c++,class,derived-class,upcasting,C++,Class,Derived Class,Upcasting,如何更改派生类中继承变量的类型? 我有以下课程: class Position; class StonePosition; class Position { public: Position() {} }; class StonePosition : public Position { int count; public: StonePosition(const int count) { this->count = count; } int getCou
class Position;
class StonePosition;
class Position {
public:
Position() {}
};
class StonePosition : public Position {
int count;
public:
StonePosition(const int count) { this->count = count; }
int getCount() { return this->count; }
void setCount(int count) { this->count = count; }
friend ostream& operator<<(ostream&, StonePosition);
};
class Board {
protected:
Position* crrPos;
public:
Board() { }
Position* getCrrPos() { return crrPos; }
void setCrrPos(Position* pos) { crrPos=pos; }
};
class StoneBoard : public Board {
public:
StoneBoard(const int &count) { this->crrPos=new StonePosition(count); } //<----------------
StonePosition* getCrrPos() { return (StonePosition*)crrPos; }
void setCrrPos(StonePosition* pos) { crrPos=pos; }
};
类位置;
阶级立场;
阶级地位{
公众:
位置(){}
};
职位类别:公共职位{
整数计数;
公众:
StonePosition(const int count){this->count=count;}
int getCount(){返回此->计数;}
void setCount(int count){this->count=count;}
friend ostream&operator变量“crrPos”不是Position类型,而是指向Position的指针类型,这很重要,因为指向Position的指针可以指向Position或从Position派生的类,而不会丢失任何内容
如果设计好类并使用虚拟函数,通常可以避免完全向上转换
#include <iostream>
class Base {
public:
virtual void foo() { std::cout << "Base::foo()\n"; }
virtual bool isDerived() const { return false; }
};
class Derived : public Base {
public:
void foo() override { std::cout << "Derived::foo()\n"; }
bool isDerived() const { return true; }
};
int main() {
Base* crrPos = new Derived;
crrPos->foo();
bool isDerived = crrPos->isDerived();
std::cout << isDerived << '\n';
delete crrPos;
}
#包括
阶级基础{
公众:
虚拟void foo(){std::cout isDerived();
std::cout问题已经解决,我只使用投影((StonePosition*)Position*):
#包括
使用名称空间std;
阶级地位;
阶级立场;
阶级地位{
公众:
位置(){}
};
职位类别:公共职位{
整数计数;
公众:
StonePosition(const int count){this->count=count;}
int getCount(){返回此->计数;}
void setCount(int count){this->count=count;}
朋友OsFrase& Cuths>代码类模板TB{{}{代码>可能会有帮助。C++不是那么灵活。你不能改变变量的类型。这就是为什么代码>模板/<代码>存在的原因,为什么你需要改变类型?看起来你只要在需要的时候就可以将代码>动态DistaCase< <代码> > <代码> >代码>(正如您对getCrrPos
@lcs所做的那样,因为我需要更改类中StonePosition上变量Position的值StoneBoard@Nawydynamic\u cast
用于将父类型指针安全地强制转换为子类型指针。不要使用C样式强制转换。它们不安全。嗯,指针指向我也是一个问题。例如点er到一个类的位置不知道变量count的存在。
#include <iostream>
using namespace std;
class Position;
class StonePosition;
class Position {
public:
Position() {}
};
class StonePosition : public Position {
int count;
public:
StonePosition(const int count) { this->count = count; }
int getCount() { return this->count; }
void setCount(int count) { this->count = count; }
friend ostream& operator<<(ostream&, StonePosition);
};
template <typename TPos> class TBoard {
protected:
TPos* crrPos;
public:
TBoard() { }
TPos* getCrrPos() { return crrPos; }
void setCrrPos(TPos* pos) { crrPos=pos; }
};
class Board {
protected:
Position* crrPos;
public:
Board() { }
Position* getCrrPos() { return crrPos; }
void setCrrPos(Position* pos) { crrPos=pos; }
};
class StoneBoard : public Board {
public:
StoneBoard(const int &count) { this->crrPos=new StonePosition(count); }
Position* getCrrPos() { return crrPos; }
void setCrrPos(Position* pos) { crrPos=pos; }
};
int main(){
StoneBoard s(7);
cout<<((StonePosition*)s.getCrrPos())->getCount();//<----right here
system("pause");
return 0;
}