可能的循環引用？

Question

也許是因爲我一直盯着這個5個小時，我只是讀了一個明顯的解決方案，但Xcode聲明我的矢量對象（在頭文件中聲明）未聲明在一個.cpp文件;但是，我的其他.cpp文件可以訪問矢量，所以我不確定問題是什麼。也許我的頭文件不合適，或者我無意中「循環引用」？請提出建議？

publications.h

#ifndef PUBLICATIONS_H 
#define PUBLICATIONS_H 

#include "std_lib_facilities.h" 

class Publication { 
    private: 
     string 
      publication_title, 
      publication_author, 
      publication_year, 
      publication_genre, 
      publication_media, 
      publication_target_age, 
      publication_ISBN; 

     bool currently_checked_out; 

    public: 
     Publication(string title, string author, string year, string genre, string media, string target_age, string ISBN, bool checked_out) { 
      publication_title = title; 
      publication_author = author; 
      publication_year = year; 
      publication_genre = genre; 
      publication_media = media; 
      publication_target_age = target_age; 
      publication_ISBN = ISBN; 
      currently_checked_out = checked_out; 
     } 

     Publication(){}; 

}; 
#endif /* PUBLICATIONS_H */ 

library.h

#ifndef LIBRARY_H 
#define LIBRARY_H 

#include "std_lib_facilities.h" 

class Publication; 

class Library { 
    private: 
     vector<Publication> lb; 

    public: 
     Library(){}; 

     void documentation(); 
     void list_all_publications(); 
     void new_publication(string title, string author, string year, string genre, string media, string target_age, string ISBN, bool currently_checked_out); 
}; 
#endif /* LIBRARY_H */ 

patron.h

#ifndef PATRON_H 
#define PATRON_H 

#include "std_lib_facilities.h" 

class Publication; 

class Patron { 
    private: 
     string 
      customer_name, 
      customer_telephone; 

    public: 

     void check_out_publication(string publication_requested); 
     void return_publication(string check_in_publication_name); 
     void check_out(); 
     bool is_checked_out(); 

     Patron(){}; 


}; 
#endif /* PATRON_H */ 

library.cpp （工作完全正常，可以訪問向量在library.h）

#include "library.h" 
#include "patron.h" 
#include "publications.h" 
#include "std_lib_facilities.h" 

Patron p; 

void Library::documentation() { 
    cout << "\n-----Create a new publication----\n"; 
    cout << "You will enter all the necessary info for a new publication (title, author, year, genre, media, target age, and ISBN).\n"; 

    cout << "\n----List all Publications-----\n"; 
    cout << "List all publications that have been entered (in this current session).\n"; 

    cout << "\n---Check out Publication----\n"; 
    cout << "You will enter your name and telephone number and the publication will be checked out.\n"; 

    cout << "\n-----Return Publication------\n"; 
    cout << "A previously checked out publication will be marked as returned.\n"; 
} 

void Library::new_publication(string title, string author, string year, string genre, string media, string target_age, string ISBN, bool checked_out) { 

    lb.push_back(Publication(title, author, year, genre, media, target_age, ISBN, checked_out)); 
} 

void Library::list_all_publications() { 
    for (int i = 0; i < lb.size(); i++) { 
     cout << "Title: " << "\tChecked Out: " << p.is_checked_out() << endl; 
    } 

} 

patron.cpp（有問題的文件，可以在library.h不訪問向量）

#include "publications.h" 
#include "library.h" 
#include "patron.h" 
#include "std_lib_facilities.h" 

void Patron::check_out_publication(string publication_requested) { 
    // check to make sure publication isn't already checked out. 

    for (int i = 0; i < lb.size(); i++) { 

     if ((publication_requested == lb[i].publication_title) && lb[i].currently_checked_out) { 
      cout << "Sorry, this publication is currently checked out." << endl; 

     } else if ((publication_requested == lb[i].publication_title) && !(lb[i].currently_checked_out)) { 
      cout << "Enter your name: "; 
      getline(cin, customer_name); 

      cout << "Enter your telephone number (no dashes/no spaces): "; 
      cin >> customer_telephone; 
     } else { 
      continue; 

     } 
    } 

} 

void Patron::return_publication(string check_in) { 
    for (int i = 0; i < lb.size(); i++) { 
     if ((check_in == lb[i].publication_title) && lb[i].currently_checked_out) { 
      // marked as no longer checked out. 
      lb[i].currently_checked_out = false; 
     } 
    } 
} 

bool Patron::is_checked_out() { 
    return currently_checked_out; 
} 

void Patron::check_out() { 
    currently_checked_out = true; 
} 

在patron.cpp中出錯

USE OF UNDECLARED IDENTIFIER "lb" 

Answer 1

lb是Library類的私人成員。您可以在您的library.cpp文件中訪問它，因爲您在Library成員函數中使用它。而在Patron類中，您直接訪問它。但編譯器將其視爲另一個變量，您尚未聲明。可能你需要添加一個訪問器到Library。