如何在C++中調用全局函數中的類對象？

Question

我有一個全局函數void start_menu()，我用它作爲接口。

void start_menu() 
{ 
    int x; 

    cout << " ------------------------------------" << endl; 
    cout << " WELCOME TO LIBRARY MANAGEMENT SYSTEM" << endl; 
    cout << "------------------------------------" << endl; 
    cout << "     1. ABOUT Books " << endl; 
    cout << "     2. ABOUT Members " << endl; 
    cout << "   CHOOSE:"; 
    cin >> x; 

    Books MyBooks; //object of books class 

    do 
    { 
     if (x==1) 
     { 
      system("cls"); 

      MyBooks.INTR_Books(); //calling function of Books Class  
     } 
    }; 
} 

然後，我有class Books{}，我想在全局函數void start_menu()被調用，但是當我做Books類，它被定義爲Books MyBooks;的對象，上面的代碼給了我這個錯誤：

error: 'Books' was not declared in this scope.

這是後Books類全局函數void start_menu()：

class Books 
{ 
public: 
    string BookName; //name of the Book 
    string Auth; //Author of the book 
    string Trans; // translator of the book 
    string myArray[20]; 
    int BookCode; // code of the book 
    int BookNum; // number of copies exist 

    void INTR_Books(); //show interface related to books 
    void ADD_BOOK(); 
    void DELETE_BOOK(); 
    void SEARCH(); 
    void SHOW_ALL(); 
    void BR_BOOK(); 
}; 

Answer 1

基於在評論中，我曾經在void start_menu()全局函數之後調用Books類。