对象数组打印空白字符串

Question

（问题已解决，解决方案已作为注释行添加到 main.cpp）

main.cpp 文件中描述了我遇到的问题。我已经检查了有关此的其他问题，但没有一个真正有帮助。

我正在尝试使用 C++ 创建一个控制台应用程序，您可以在其中将 BOOKS 添加到 LIBRARY。在 library 类中，有一个 displayInfo() 函数可以显示特定书籍的信息。它可以显示整数或双值信息而不会出现问题，但是当我尝试显示字符串类型的信息时它会出现问题。它只是打印空白。让我给你一些我的代码示例。

这是 Book.h

#ifndef BOOK_H
#define BOOK_H
#include <string>

class Book
{
    friend class Library;
public:
    void setName();
    std::string getName();
private:
    std::string nameOfBook;
};

#endif

Book.cpp

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

using namespace std;

void Book::setName()
{
    string nameOfBook;
    cout << "Please enter the name of the book: ";
    cin >> nameOfBook;
    this->nameOfBook = nameOfBook;
}

string Book::getName()
{
    return nameOfBook;
}

Library.h

#ifndef LIBRARY_H
#define LIBRARY_H

#include "Book.h"
#include <array>

class Library
{
private:
    std::array <Book , 10> bookArray; // I have to use this

public:
    void addBook();
    void displayInfo();
};

#endif

Library.cpp

#include "Library.h"
#include "Book.h"

#include <iostream>
#include <string>
#include <array>

using namespace std;

void Library::addBook()
{
    bookArray[0].setName();
}

void Library::displayInfo() 
{
    cout << "The book: " << bookArray[0].getName() << endl;
}

还有 main.cpp

#include <iostream>
#include "Book.h"
#include "Library.h"
#include <string>
#include <array>

using namespace std;

int main()
{
    // The problem is solved
    // Create the objects out of the loop
    // Library obj1 <---- this solved it
    while (true)
    {

        int number; // Ask user what to do
        cout << "Press 1 to add a book\n"
             << "Press 2 to display info\n"
             << "Press 0 to quit\n";
        cin >> number;
        if (number == 1) // Add a book
        {
            Library obj1; // <------ THIS IS WRONG
            obj1.addBook(); // Consider we named the book as 'Fly'
        }
        else if (number == 2)   
        {
            Library obj1; // <------ THIS IS WRONG
            obj1.displayInfo(); // ******* The output I'm expecting is The Book: Fly
                                // But instead, it only gives me The Book:
            // I have 4 more strings like this in the main project and all of them have the same problem
        }
        else if (number == 0) // Everything else
        {
            break;
        }
        else
        {
            cout << "Wrong input\n";
            continue;
        }
    }
}

编辑： 我用 VS Code 对此进行了编码，并在必要时用 MinGW (8.2.0) 对其进行了编译。

Answer 1

您的代码中的一个问题是您有许多库类的实例，因此 addBook 登陆一个对象，而 displayInfo 登陆一个新对象（空的）

你必须：

int main()
{
    Library obj1; // declare the lib in scope for all the cases
    while (true)
    {
        int number; // Ask user what to do
        cout << "Press 1 to add a book\n"
             << "Press 2 to display info\n"
             << "Press 0 to quit\n";
        cin >> number;
        if (number == 1) // Add a book
        {

            obj1.addBook(); // Consider we named the book as 'Fly'
        }
        else if (number == 2)   
        {
            //Library obj1;
            obj1.displayInfo(); // ******* The output I'm expecting is The Book: Fly
                                // But instead, it only gives me The Book:
            // I have 4 more strings like this in the main project and all of them have the same problem
        }
        else if (number == 0) // Everything else
        {
            break;
        }
        else
        {
            cout << "Wrong input\n";
            continue;
        }
    }
}

Answer 2

你在循环的每次迭代中再次创建对象。因此覆盖已命名的旧对象。