將函數轉換爲成員函數？

Question

我是新來的，我在用C++編寫的程序尋求幫助。

我想轉換下列功能不在一個班，也沒有在main（）爲一類庫存的公共職能的成員有沒有參數和返回任何結果我的程序

void PrintInventory(vector<Item*> inventory); 
vector<Item*> AddItemToInventory(vector<Item*> inventory); 
vector<Item*> UpdateItemQtyInInventory(vector<Item*> inventory); 
vector<Item*> RemoveItemFromInventory(vector<Item*> inventory); 

的。

我一直對4天了，只是想不通，我應該如何改變這些功能是無效的，並具有不破壞整個程序沒有參數...

如果我去完全按指令說什麼這是使空/無參數出的四大功能，我會得到這樣的：

class Inventory 
{ 
public: 
    void PrintInventory() {} 
    void AddItemToInventory() {} 
    void UpdateItemQtyInInventory() {} 
    void RemoveItemFromInventory() {} 

private: 
    vector<Item*> inventory; 
}; 

請給我一個提示。我覺得解決方案必須簡單，但我已經完全陷入了數天。

感謝您的幫助。

編輯： 我仍然收到一堆錯誤，並認爲我需要多說一點我的代碼： 我有一個基類Item和兩個派生類Produce和Book。然後，我有四個功能調用：

// Print all items in the inventory 
void PrintInventory(vector<Item*> inventory); 

// Dialogue to create a new item, then add that item to the inventory 
vector<Item*> AddItemToInventory(vector<Item*> inventory); 

// Dialogue to update the quantity of an item, then update that item in the inventory 
vector<Item*> UpdateItemQtyInInventory(vector<Item*> inventory); 

// Dialogue to remove a specific item, then remove that specific item from the inventory 
vector<Item*> RemoveItemFromInventory(vector<Item*> inventory); 

接下來是，現在有沒有回報4個轉換功能和無參數原本未類庫存裏面，面前放參數/返回主，我班庫存。

這裏是整個代碼，我認爲這是更好地理解是這樣的：

#include <iostream> 
#include <string> 
#include <vector> 
#include <sstream> 
#include <cstring> 
using namespace std; 

class Item { 
public: 
    void SetName(string nm) 
    { 
     name = nm; 
    }; 
    void SetQuantity(int qnty) 
    { 
     quantity = qnty; 
    }; 
    void SetPrice(int prcInDllrs) //step1 
    { 
     priceInDollars = prcInDllrs; //step1 
    }; 
    virtual void Print() 
    { 
     cout << name << " " << quantity << endl; 
    }; 
    virtual ~Item() 
    { 
     return; 
    }; 
protected: 
    string name; 
    int quantity; 
    int priceInDollars; //step1 
}; 

class Produce : public Item { // Derived from Item class 
public: 
    void SetExpiration(string expir) 
    { 
     expiration = expir; 
    }; 
    void Print() 
    { 
     cout << name << " x" << quantity 
      << " for $" << priceInDollars //step1 
      << " (Expires: " << expiration << ")" 
      << endl; 
    }; 
private: 
    string expiration; 
}; 

//step 2 add derived class Book 
class Book : public Item { // Derived from Item class 
public: 
    void SetAuthor(string authr) //create author function with parameter 
    { 
     author = authr; 
    }; 
    void Print() 
    { 
     cout << name << " x" << quantity 
      << " for $" << priceInDollars //step1 
      << " (Author: " << author << ")" 
      << endl; 
    }; 
private: 
    string author; 
}; 

// Print all items in the inventory 
void PrintInventory(vector<Item*> inventory); 

// Dialogue to create a new item, then add that item to the inventory 
vector<Item*> AddItemToInventory(vector<Item*> inventory); 

// Dialogue to update the quantity of an item, then update that item in the inventory 
vector<Item*> UpdateItemQtyInInventory(vector<Item*> inventory); 

// Dialogue to remove a specific item, then remove that specific item from the inventory 
vector<Item*> RemoveItemFromInventory(vector<Item*> inventory); 

int main() { 
    vector<Item*> inventory; 
    string usrInptOptn = "default"; 

    while (true) { 
     // Get user choice 
     cout << "\nEnter (p)rint, (a)dd, (u)pdate, (r)emove, or (q)uit: "; 
     getline(cin, usrInptOptn); 

     // Process user choice 
     if (usrInptOptn.size() == 0) { 
      continue; 
     } 
     else if (usrInptOptn.at(0) == 'p') { 
      PrintInventory(inventory); 
     } 
     else if (usrInptOptn.at(0) == 'a') { 
      inventory = AddItemToInventory(inventory); 
     } 
     else if (usrInptOptn.at(0) == 'u') { 
      inventory = UpdateItemQtyInInventory(inventory); 
     } 
     else if (usrInptOptn.at(0) == 'r') { 
      inventory = RemoveItemFromInventory(inventory); 
     } 
     else if (usrInptOptn.at(0) == 'q') { 
      cout << "\nGood bye." << endl; 
      break; 
     } 
    } 

    return 0; 
} 

class Inventory { 
public: 

    void PrintInventory() { 
     unsigned int i = 0; 
     if (inventory.size() == 0) { 
      cout << "No items to print." << endl; 
     } 
     else { 
      for (i = 0; i<inventory.size(); ++i) { 
       cout << i << " - "; 
       inventory.at(i)->Print(); 
      } 
     }; 
    } 
    void AddItemToInventory() { 


     Produce* prdc; 
     Book* book; //create new pointer object of class book 
     string usrInptName = ""; 
     string usrInptQntyStr = ""; 
     istringstream inSS; 
     int usrInptQnty = 0; 
     string usrInptExpr = ""; 
     int usrInptPrc = 0; //step1 
     string usrInptAuthr = ""; //declare variable 
     string usrInptBookName = ""; 
     int usrInptQntyBook = 0; 
     string usrInptQntyBookStr = ""; 
     string usrInptChoice = " "; 


     //loop user choice and ask again if choice is not valid 
     do { 
      cout << "Enter choice of adding (b)ook or (p)roduce: "; 
      getline(cin, usrInptChoice); 
      if (usrInptChoice != "b" && usrInptChoice != "p") { 
       cout << "Invalid Choice" << endl; 
      } 
     } while (usrInptChoice != "b" && usrInptChoice != "p"); 

     //only ask for inventory type accoring to user input p or b 
     if (usrInptChoice == "p") { 

      cout << "Enter name of new produce: "; 
      getline(cin, usrInptName); 

      cout << "Enter quantity: "; 
      getline(cin, usrInptQntyStr); 
      inSS.str(usrInptQntyStr); 
      inSS >> usrInptQnty; 
      inSS.clear(); 

      cout << "Enter expiration date: "; 
      getline(cin, usrInptExpr); 

      cout << "Enter the price per item : $"; //step1 
      cin >> usrInptPrc; //step1 

      prdc = new Produce; 
      prdc->SetName(usrInptName); 
      prdc->SetQuantity(usrInptQnty); 
      prdc->SetExpiration(usrInptExpr); 
      prdc->SetPrice(usrInptPrc); 

      inventory.push_back(prdc); 
     } 

     if (usrInptChoice == "b") { 
      cout << "Enter name of new book: "; 
      getline(cin, usrInptBookName); 

      cout << "Enter quantity: "; 
      getline(cin, usrInptQntyBookStr); 
      inSS.str(usrInptQntyBookStr); 
      inSS >> usrInptQntyBook; 
      inSS.clear(); 

      cout << "Enter author: "; 
      getline(cin, usrInptAuthr); 

      cout << "Enter the price per item : $"; //step1 
      cin >> usrInptPrc; //step1 

      book = new Book; 
      book->SetName(usrInptBookName); 
      book->SetQuantity(usrInptQntyBook); 
      book->SetAuthor(usrInptAuthr); 
      book->SetPrice(usrInptPrc); 

      inventory.push_back(book); 
     }; 
    } 

    void UpdateItemQtyInInventory() { 
     string usrIndexChoiceStr = ""; 
     unsigned int usrIndexChoice = 0; 
     istringstream inSS; 
     string usrInptQntyStr = ""; 
     int usrInptQnty = 0; 

     if (inventory.size() == 0) { 
      cout << "No items to update." << endl; 
     } 
     else { 
      PrintInventory(); 

      do { 
       cout << "Update which item #: "; 
       getline(cin, usrIndexChoiceStr); 
       inSS.str(usrIndexChoiceStr); 
       inSS >> usrIndexChoice; 
       inSS.clear(); 
      } while (!(usrIndexChoice < inventory.size())); 

      cout << "Enter new quantity: "; 
      getline(cin, usrInptQntyStr); 
      inSS.str(usrInptQntyStr); 
      inSS >> usrInptQnty; 
      inSS.clear(); 

      inventory.at(usrIndexChoice)->SetQuantity(usrInptQnty); 
     }; 
    } 

    void RemoveItemFromInventory() { 
     istringstream inSS; 
     string usrIndexChoiceStr = ""; 
     unsigned int usrIndexChoice = 0; 
     string usrInptQntyStr = ""; 

     if (inventory.size() == 0) { 
      cout << "No items to remove." << endl; 
     } 
     else { 
      PrintInventory(); 

      do { 
       cout << "Remove which item #: "; 
       getline(cin, usrIndexChoiceStr); 
       inSS.str(usrIndexChoiceStr); 
       inSS >> usrIndexChoice; 
       inSS.clear(); 
      } while (!(usrIndexChoice < inventory.size())); 

      inventory.erase(inventory.begin() + usrIndexChoice); 
     }; 
    } 

    private: 
     vector<Item*> inventory; 
}; 

我沒有在Visual Studio中得到任何編譯錯誤，但是當我嘗試建立，有5個錯誤。編譯在Geany程序沒有給我任何的錯誤，但是當我建立了，它說：

undefined reference to `PrintInventory(std::vector<Item*, std::allocator<Item*> >)' 
    undefined reference to `AddItemToInventory(std::vector<Item*, std::allocator<Item*> >)' 
    undefined reference to `UpdateItemQtyInInventory(std::vector<Item*, std::allocator<Item*> >)' 
    undefined reference to `RemoveItemFromInventory(std::vector<Item*, std::allocator<Item*> >)' 
    collect2.exe: error: ld returned 1 exit status 
    Compilation failed. 

我覺得我缺少一些基本的，簡單的事情，但我無法弄清楚。當我說要將函數PrintInventory，AddItemToInventory，UpdateItemQtyInInventory， 和RemoveItemFromInventory轉換爲void/no參數，但是它涉及到哪些函數時，該指令讓我感到困惑。四條定義線？實際功能？都？那麼主要和其他課程呢？我不需要改變那裏的事嗎？

Answer 1

基本測試：

注意，也有在這裏

void test() 
{ 
    class T_item 
    { 
    public: 
     string name; 
     int quantity; 
     int priceInDollars; 
    }; 

    vector<T_item> inventory; 

    T_item temp; 

    //add item: 
    temp.name = "name1"; 
    temp.quantity = 1; 
    temp.priceInDollars = 1; 
    inventory.push_back(temp); 

    temp.name = "name2"; 
    temp.quantity = 2; 
    temp.priceInDollars = 2; 
    inventory.push_back(temp); 

    cout << "print:\n"; 
    for each(T_item item in inventory) 
    { 
     cout << item.name << endl; 
     cout << item.quantity << endl; 
     cout << item.priceInDollars << endl << endl; 
    } 

    //modify item at index 1: 
    inventory[1].name = "modified"; 

    //delete item at index 0: 
    inventory.erase(inventory.begin() + 0); 

    cout << "print again:\n"; 
    for each(T_item item in inventory) 
    { 
     cout << item.name << endl; 
     cout << item.quantity << endl; 
     cout << item.priceInDollars << endl << endl; 
    } 
} 

int main() 
{ 
    test(); 
    return 0; 
} 

Answer 2

沒有指針，我相信你的代碼的轉換是否正確。由於「庫存向量」是一個成員變量，因此它可以被所有其他成員函數訪問，也可以被操縱。這消除了將向量作爲參數傳遞的要求。 現在爲了返回矢量，我建議添加一個新的「GetInventory（）」方法，該方法返回矢量或採用引用來傳遞矢量。

希望它有幫助。

Answer 3

感謝WhozCraig，我的問題已經解決：

「庫存的類定義必須來之前的主（）以某種方式將它上面的main（），它應該工作。」