访问头文件 C++ 中声明的向量（非全局）

Question

我提交了一个满足所有条件的作业，除了我不允许使用全局变量，除非它们是常量，并且我将我的向量设置为全局变量。

我现在发现在我的头文件以及我的类函数文件和我的主类文件中使用我的向量是不可能的。

我有一个主类和一个派生类，向量项属于派生类。现在，我已将矢量定义放在主要类的标题中：

vector<Stock> arrStock;

但是当尝试将对象从输入文件添加到向量中并随后对其执行操作时，我可以在 classes 函数类中设置函数，或者调用我在 main 中设置的函数类（如果我将函数设置为静态）。

我做错了什么？目前，按照代码的设置方式，我在主类中调用的所有函数都出现错误 E0245“非静态成员引用必须相对于特定对象”。可能值得注意的是，当我将向量设置为全局变量时，这些函数被定义为静态并且它们工作得很好，所以我对它们需要是静态的并且我的问题在于应用程序的事实持开放态度代替 Assignment2_classes.cpp 文件中的数组。

请看下面我的代码sn-ps：

作业2.h：

class Product 
{

private:
    string  title, surname;
    long long int isbn;
    double  wholesalePrice;

public:
    string getTitle();
    string getSurname();
    long long int getIsbn();
    double getWholesalePrice();

    void setTitle(string);
    void setSurname(string);
    void setIsbn(long long int);
    void setWholesalePrice(double);
    
    Product();
    ~Product();
    Product(string, string, long long int, double);

    void importProducts();
    void newProduct();
    void delProduct();
    void runReport();
    void checkStock();
    void clrStock();

    vector<Stock> arrStock;
};

// creating the derived class Stock
class Stock :public Product 
{

public:
    double retailPrice;
    char bookFormat;
    int stockLevel;

    double getRetailPrice();
    char getBookFormat();
    int getStockLevel();
    
    void setRetailPrice(double);
    void setBookFormat(char);
    void setStockLevel(int);

    Stock();
    ~Stock();
    Stock(string, int, char, string, double, long long int, double);
    
    void setStockInfo(long long int, string, string, double, int, double, char);
    
};

Assignment2_classes.cpp：

void Product::importProducts()
{
    // code adapted from: https://stackoverflow.com/questions/16878259/how-to-read-in-a-set-of-values-from-a-text-file-then-go-to-the-next-line-and-do
    // telling the function which input file it is reading from
    ifstream productsFile("products_v5.txt");
    
    // creating local variables
    Stock aStock;
    double tempRetailPrice = 0;
    string undsc = "_";
    string space = " ";
    size_t position;


    std::cout << "Importing books...\n";
    
    // reading the books into an array
    while (productsFile >> aStock.title >> aStock.stockLevel >> aStock.bookFormat >> aStock.surname >> aStock.wholesalePrice >> aStock.isbn)
    {
        // replacing the underscores in the title names with spaces so the output looks better
        // code adapted from https://www.educba.com/c-plus-plus-replace/
        while ((position = aStock.title.find(undsc)) != string::npos)
        {
            aStock.title.replace(position, 1, space);
        }
        
        // calculating the retail prices of the books depending on their format
        switch (aStock.bookFormat)
        {
        case 'a': tempRetailPrice = aStock.wholesalePrice * 1.43;
            break;
        case 'e': tempRetailPrice = aStock.wholesalePrice * 1.08;
            break;
        case 'h': tempRetailPrice = aStock.wholesalePrice * 1.45;
            break;
        case 's': tempRetailPrice = aStock.wholesalePrice * 1.27;
            break;
        }
        aStock.setRetailPrice(tempRetailPrice);
        arrStock.push_back(aStock);
    }

    // letting the user know how many books have been added and how many books are currently in the array
    std::cout << "\n" << to_string(arrStock.size()) << " books have been added.\n";
    std::cout << "\nBiblioden Books currently has " << to_string(arrStock.size()) << " different books.\n";
}

Assignment2_main.cpp：

int main()
{

    char createBook;
    char deleteBook;
    char viewReport;
    char checkOrders;

    // creating the heading of the output
    cout << "-----------------------------------------------------------------------------------------\n" << "  Biblioden Systems\n" << "-----------------------------------------------------------------------------------------\n";
    
    ifstream productsFile("products_v5.txt");
    
    // checking whether the file is open and gracefully exiting if it can't be opened
    if (!productsFile.is_open())
    {
        cout << "\nCannot open file.\n";
        return 1;
    }
    Product::importProducts();
    
    //closing the file
    productsFile.close();
    
    cout << "\nWould you like to enter a new book? (Y/N): ";
    cin >> createBook;
    if (createBook == 'Y' || createBook == 'y')
    {
        Product::newProduct();
    }

    cout << "\nWould you like to delete a book? (Y/N) ";
    cin >> deleteBook;

    if (deleteBook == 'Y' || deleteBook == 'y')
    {
        Product::delProduct();
    }

    cout << "\nWould you like to view a report? (Y/N) ";
    cin >> viewReport;
    if (viewReport == 'Y' || viewReport == 'y')
    {
        ofstream report("report.txt");

        // checking whether the file is open and gracefully exiting if it can't be opened
        if (!report.is_open())
        {
            cout << "\nCannot open file.\n";
            return 1;
        }
        else
        {
            Product::runReport();
            
            // closing the file
            report.close();
        }
    }

    cout << "\nWould you like to check the order list against the stock list? (Y/N) ";
    cin >> checkOrders;
    if (checkOrders == 'Y' || checkOrders == 'y')
    {
        ifstream ordersFile("orders_v5.txt");

        // checking whether the file is open and gracefully exiting if it can't be opened
        if (!ordersFile.is_open())
        {
            cout << "\nCannot open file.\n";
            return 1;
        }
        else
        {
            Product::checkStock();
            // closing the file
            ordersFile.close();
        }
    }

    // clearing out the array once the user is finished with it
    Product::clrStock();
    return 0;
}

Answer 1

如 cmets 中所述，调用 Product::importProducts(); 要求 importProducts() 是 Product 的 static 成员函数。

在您的情况下，您不能将其声明为 static（这样做没有意义），因为您在函数内部使用（非静态）类成员。

您需要一个Product 的实例来调用成员函数。
例如：

Product p;          // Create an instance of Product
p.importProducts(); // Call importProducts() from (and for) the previously created instance

---

另一方面，如果您不想创建Product 的任何实例，因此您想要整个程序的唯一向量，您可以标记您的成员（和成员函数）static 来解决您的问题问题。

Answer 2

成员变量arrStock 的声明在Stock 类声明之前。您不能引用尚未声明的类。您必须将向量设为指针向量（或 shared_ptr），然后您可以在声明 Product 之前转发声明该类：

class Stock;