你能创建一个继承类的std :: map吗？ [英] Can you create a std::map of inherited classes?

问题描述

我想知道是否可以创建一个继承类指针的映射。以下是我正在尝试做的一个示例：

I'm wondering if it's possible to create a map of pointers of inherited classes. Here's an example of what I'm trying to do:

#include <string>
#include <map>

using namespace std;

class BaseClass
{
    string s;
};

class Derived1 : public BaseClass
{
    int i;
};

class Derived2 : public Derived1
{
    float f;
};

// Here's what I was trying, but isn't working
template<class myClass>
map<string, myClass>m;

int main()
{
    // Add BaseClasses, Derived1's, and/or Derived2's to m here
    return 0;
}

我得到的错误是：

main.cpp(23): error C2133: 'm' : unknown size
main.cpp(23): error C2998: 'std::map<std::string,myClass>m' : cannot be a template definition

我明白为什么我会收到此错误，但我想知道是否可以创建一个地图可以持有不同级别的继承类吗？如果没有，是否有可能创建一种可以容纳各种类型的管理系统？或者我必须制作不同的地图/矢量/数组/等。对于每种类型的类？

I get why I'm getting this error, but I'm wondering if it's possible to create a map that can hold different levels of inherited classes? If not, is it possible to create some sort of management system that can hold various class types? Or would I have to make different maps/vectors/arrays/etc. for each type of class?

推荐答案

是的，您可以在地图中存储继承的类，但指向它们，而不是对象本身。这是一个简短的例子（它缺少对指针的内存管理）

Yes you can store inherited classes in map, but pointers to them, not objects themselves. Here's a short example (it lacks memory management on pointers)

#include <iostream>
#include <string>
#include <map>
#include <utility>

using namespace std;

class BaseClass
{
    string s;
public: 
    BaseClass() { s = "BaseClass";} 
    virtual void print() 
    {
        cout << s << std::endl;
    }
};

class Derived1 : public BaseClass
{
    int i;
public:
    Derived1() { i = 10; }
    void print() 
    {
        cout << i << std::endl;
    }

};

class Derived2 : public Derived1
{
    float f;
public:
    Derived2() { f = 4.3;}
    void print() 
    {
        cout << f << std::endl;
    }
};

int main()
{
    map<string, BaseClass*>m;
    m.insert(make_pair("base", new BaseClass()));
    m.insert(make_pair("d1", new Derived1()));
    m.insert(make_pair("d2", new Derived2()));
    m["base"]->print();
    m["d1"]->print();
    m["d2"]->print();

    return 0;
}

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