c++ - 错误 c2678 : binary '=='

Question

完整错误:

错误 2 error C2678: binary '==' : no operator found which takes a left-hand operand of type 'Item' (or there is no acceptable conversion) c:\program files (x86)\microsoft visual studio 12.0\vc\include\algorithm 1734 1 GameStore

---

库存类(cpp 文件)

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <Windows.h>
#include "item.h"

class Inventory
{


public:

void Inventory::viewInventory()
{
    for (int i = 0; i < inventory.size(); i++)
    {
        Inventory::inventory[i].getItemName();
    }
}

void Inventory::addItem(Item& item)
{
    inventory.push_back(item);
}


void Inventory::removeItem(Item& item)
{
    if (std::find(inventory.begin(), inventory.end(), item) != inventory.end())
    {
        inventory.erase(std::remove(inventory.begin(), inventory.end(), item), inventory.end());
    }

    else
    {
        std::cout << "Item does not exist" << std::endl;
    }
}

//Player Gold methods
int Inventory::getGold()
{
    return playerGold;
}

void Inventory::setGold(int newGold)
{
    playerGold = newGold;
}


int Inventory::addGold(int newGold)
{
    playerGold += newGold;
    return playerGold;
}

int Inventory::removeGold(int newGold)
{
    playerGold -= newGold;
    return playerGold;
}
//Player Gold methods




private:
std::vector<Item> inventory = {};
int playerGold;

};

---

基本上我想做的是制作一个库存系统，用于保存“Item”类中的对象。我花了很长时间让我的 for 循环和我所有的工作方法，然后由于天空从未如此清晰，我得到了一个错误，这是我无法解决的问题。

---

元素等级 (CPP)

#include "item.h"
#include <iostream>
#include <string>


Item::Item(int id, std::string name, std::string description, std::string examime)
{
    itemName = name;
    itemID = id;
    itemDescription = description;
    itemExamine = examime;

}

void Item::setItemName(std::string newName)
{
    itemName = newName;
}

void Item::setItemDescription(std::string newDescription)
{
    itemDescription = newDescription;

}

void Item::setItemExamine(std::string newExamine)
{
    itemExamine = newExamine;
}

void Item::setItemID(int newID)
{
    itemID = newID;
}

std::string Item::getItemName()
{
    return itemName;
}

std::string Item::getItemDescription()
{
    return itemDescription;
}

std::string Item::getItemExamine()
{
    return itemExamine;
}

int Item::getItemID()
{
    return itemID;
}

项目类(标题)

#include <iostream>
#include <string>

class Item
{
public:
    //constructor
    Item::Item(int id, std::string name, std::string description, std::string examime);

    //setters
    void setItemName(std::string newName);
    void Item::setItemDescription(std::string newDescription);
    void Item::setItemExamine(std::string newExamine);
    void Item::setItemID(int newID);

    //getters
    std::string Item::getItemName();
    std::string Item::getItemDescription();
    std::string Item::getItemExamine();
    int Item::getItemID();

private:
    std::string itemName;
    int itemID;
    std::string itemDescription;
    std::string itemExamine;

};

---

如果您有任何建议，即使是重做我的整个系统，那就太好了。这些类(class)显然非常简单，我将添加更多内容。意思是我不是在寻找像“你甚至不需要 Item 类”这样的答案

感谢您的帮助!

Answer 1

您的代码的“核心”问题似乎是缺少 operator==为您的 Item 实现类，正如编译器错误告诉您的那样。

作为 C++ 初学者(不用担心:我们每个人都是初学者)，您可能会问为什么是这个 op==必需，因为您没有在代码中显式 调用它。好吧，您确实没有显式调用它，但标准库实现 中的代码会调用它。特别是，您调用 std::find (在您的错误消息中引用的 <algorithm> header 中实现):

void Inventory::removeItem(...)
{
    if (std::find(inventory.begin(), inventory.end(), item) != inventory.end())
    {
        ...

std::find需要比较Item带有 op== 的实例.因此，要尝试修复您的代码，请定义一个 operator==用于比较 Item s，像这样:

// In the Item class header:

class Item 
{
   ...
};

inline bool operator==(const Item& a, const Item& b) 
{
    // Implement your comparison logic for Items a and b.
    // ...
    // Return true if "a == b".
}

---

作为附加说明，当您在类中声明成员函数时，您不需要使用 Item::成员函数前的前缀:

class Item
{
public:
    //constructor
    Item::Item(int id, std::string name, std::string description, std::string examime);

    //setters
    void setItemName(std::string newName);
    void Item::setItemDescription(std::string newDescription);
    void Item::setItemExamine(std::string newExamine);
    void Item::setItemID(int newID);
    ...

只是做:

class Item
{
public:
    //constructor
    Item(int id, std::string name, std::string description, std::string examime);

    //setters
    void setItemName(std::string newName);
    void setItemDescription(std::string newDescription);
    void setItemExamine(std::string newExamine);
    void setItemID(int newID);

    ...

此外，考虑让你的 getters const , 使你的类常量正确，例如:

   class Item 
   {
     public:
       ... 
       std::string getItemName() const;
       std::string getItemDescription() const;
       std::string getItemExamine() const;
       int getItemID() const;

       ...
   };