Question

也许是因为我已经连续5个小时盯着这个，我只是阅读了明显的解决方案，但是Xcode声明我的对象向量（在头文件中声明）是未声明的。 cpp文件;但是，我的另一个.cpp文件可以访问该向量，所以我不确定是什么问题。也许我的头文件不合适，或者我无意中“循环引用”？建议好吗？

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（完全没问题，可以 在library.h中访问向量）

#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（有问题的文件，不能 访问库中的 ）

#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;
}

patron.cpp中的错误

USE OF UNDECLARED IDENTIFIER "lb"

Answer 1

lb是Library类的私人成员。您可以在library.cpp文件中访问它，因为您在Library成员函数中使用它。而Patron课程中您直接访问它。但编译器认为它只是另一个变量，你还没有声明。可能你需要为Library添加一个访问者。

可能的循环引用？

1 个答案: