从地图复制到指针列表

问题描述

我有一个有趣的作业，其中我有一个std::map的CTurist(上一个类)和unsigned变量.这是代码:

I have this interesting assignment where I have a std::map of CTurist (previous class) and unsigned variable. Here's the code:

class CTurist
{
protected:
    string tName;
    int age;

public:
    CTurist() {};

    CTurist(string name, int age2)
    {
        tName = name;
        age = age2;
    }


    bool operator<(const CTurist& e) const
    {
        return age < e.age;
    }

    friend ostream& operator<<(ostream& os, const CTurist&& e);
    friend ifstream& operator>>(ifstream& is, CTurist&& e);
};

class CHotel:public CTurist
{
protected:

    string hName;
    int stars;
    int beds;
    map<CTurist, unsigned> Turisti;

public:
    unsigned Sum = 0;

    CHotel(){};

    CHotel(string hName2, int zvezdi, int legla)
    {
        hName = hName;
        stars = zvezdi;
        beds = legla;
    }



    int Compare()
    {
        list<CTurist*> list;

        int br=0;
        CTurist vyzrast;
        map<CTurist, unsigned>::iterator it = Turisti.begin();
        while (it != Turisti.end())
        {
            if (it->first < vyzrast)
            {
                br++;
            }
            else
            {
                list.push_back(std::move(&it->first));
            }
        }
    }
};

我知道这很长，但是我认为最好向您提供所有信息.

I know it's quite a long one, but I thought it's best to give you all the information.

现在，底部的int Compare()功能是导致我遇到问题的功能.

Now, the int Compare() function AT THE BOTTOM is the one causing me problems.

我必须检查游客的年龄是否高于或低于我在这里称为vyzrast的参数.我们正在比较age.如果在下方，则非常简单.

I have to check if the age of the tourists is above or below a parameter which I've called vyzrast here. We're comparing the age. If it's below, it's quite straight forward.

如果在上面，我必须将那些游客添加到list<CTurist*>中.指向指针列表.如果我从对象而不是指针创建列表.对此不走运，因此，为什么我要在此处寻求解决方法的建议.

If it's above though, I have to add those Tourists to a list<CTurist*>, aka. to a list of pointers. If I make the list from objects, not pointers. No luck with this, hence why I'm looking for suggestions how to fix it here.

推荐答案

为什么在operator重载中使用右值引用?您应该将const CTurist &用于operator<<，将CTurist&用于operator>>.而且您应该对operator>>使用std::istream:

Why are you using rvalue references for your operator overloads? You should be using const CTurist & for operator<< and CTurist& for operator>>. And you should be using std::istream for operator>>:

friend ostream& operator<<(ostream& os, const CTurist &e);
friend istream& operator>>(istream& is, CTurist &e);

除此之外，Compare()根本没有理由在填充std::list时使用std::move()，因为它添加了指针，而不移动实际对象.

Aside from that, there is no reason for Compare() to use std::move() at all when populating the std::list, as it is adding pointers, not moving actual objects.

Compare()由于以下几个原因而无法正确显示:

Compare() doesn't won't correctly for several reasons:

1. it->first是实际的const CTurist对象，但是您的std::list期望使用CTurist*指针. std::map键是const，因此&it->first是CTurist const *指针(指向const对象的非const指针)，而不是您期望的CTurist*指针(指向非const对象的非const指针) .

1. it->first is an actual const CTurist object, but your std::list is expecting CTurist* pointers. std::map keys are const, so &it->first is a CTurist const * pointer (non-const pointer to const object), not a CTurist* pointer (non-const pointer to non-const object) like you are expecting.

您的vyzrast对象未初始化.您根本没有为其age(和tName)成员分配任何值，因此比较的结果不确定.

Your vyzrast object is uninitialized. You are not assigning any value to its age (and tName) member at all, so the result of your comparisons is indeterminate.

您不会在每次循环迭代时增加您的it迭代器，因此如果std::map不为空，则会陷入无限循环.

You are not incrementing your it iterator on each loop iteration, so you are stuck in an infinite loop if the std::map is not empty.

请尝试以下类似操作:

int Compare()
{
    std::list<const CTurist *> clist;

    int br = 0;
    CTurist vyzrast("", SomeAgeValueHere);

    std::map<CTurist, unsigned>::iterator it = Turisti.begin();
    while (it != Turisti.end())
    {
        if (it->first < vyzrast)
        {
            br++;
        }
        else
        {
            clist.push_back(&it->first);
        }
        ++it;
    }

    // use clist as needed...

    return SomeValueHere;
}

实时演示

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