Question

运行程序时，程序崩溃。错误发生在Administrator类的createNewBook（）函数中（bk-＆gt; create_Newbook（）;）。我尝试了很多方法从Administrator类调用Book类的create_Newbook（）函数，但程序总是崩溃。

class Book{
private:
    char bookName[50],bookAuthor[50];
public:
    void create_Newbook()
    {
    cout<<"\nNEW BOOK ENTRY...\n";
    cout<<"\n\nEnter The Name of The Book:";
    cin>>bookName;
    cout<<"\n\nEnter The Author's Name:";
    cin>>bookAuthor;
    cout<<"\n\n\nBook Created..";
    }

};

class Administrator{
private:
    Book *bk;
public:
    void admin_menu();
    void displayStudent(){cout << "Access Student file....." ;}
    void displayStaff() {cout << "Access Staff file....." ;}
    void displayOutsider() {cout << "Access Outsider file....." ;}
    void deleteStudent() {cout << "Access to delete student data.....";}
    void deleteStaff() {cout << "Access to delete staff data.....";}
    void deleteOutsider() {cout << "Access to delete outsider data.....";}
    void createNewBook();
    void displayAllbook() {cout << "Access the file display ALL books.....";}

};

void Administrator::createNewBook() {
char choice;
newBook.open("book.data",ios::out|ios::app);
do
{
    bk->create_Newbook();
    newBook.write((char*)&bk,sizeof(Book));
    cout<<"\n\nDo you want to add more record..(y/n?)";
    cin>>choice;
}while(choice=='y'||choice=='Y');
   newBook.close();

}

Answer 1

这段代码存在很多问题。

首先：

newBook.open("book.data", ios::out | ios::app);

此行使用名为newBook的对象，该对象尚未在任何地方创建或初始化。

第二

bk->create_Newbook();

您尚未在任何地方初始化bk。如果它是一个空指针，那么你的程序将崩溃。你缺少构造函数和析构函数。在代码中的某个时刻，您需要创建对象：例如

bk = new Book()

Answer 2

#include<iostream>
#include<fstream>

using std::cin;
using std::cout;
using std::ios;
using std::fstream;

class Book{
private:
    char bookName[50],bookAuthor[50];
public:
    void create_Newbook()
    {
    cout << "\nNEW BOOK ENTRY...\n";
    cout << "\n\nEnter The Name of The Book:";
    cin >> bookName;
    cout << "\n\nEnter The Author's Name:";
    cin >> bookAuthor;
    cout << "\n\n\nBook Created..";
    }

}; 

class Administrator{
private:
    Book *bk;
public:
    void admin_menu();
    void displayStudent(){cout << "Access Student file....." ;}
    void displayStaff() {cout << "Access Staff file....." ;}
    void displayOutsider() {cout << "Access Outsider file....." ;}
    void deleteStudent() {cout << "Access to delete student data.....";}
    void deleteStaff() {cout << "Access to delete staff data.....";}
    void deleteOutsider() {cout << "Access to delete outsider data.....";}
    void createNewBook();
    void displayAllbook() {cout << "Access the file display ALL books.....";}

};

void Administrator::createNewBook() {
char choice;
fstream newBook; //just create newBook
newBook.open("book.data",ios::out|ios::app);
do
{
    bk->create_Newbook(); //this will work. No need to create a new Book varible to call a public function
    newBook.write((char*)&bk,sizeof(Book));
    cout << "\n\nDo you want to add more record..(y/n?)";
    cin >> choice;
}while(choice=='y'||choice=='Y');
   newBook.close();

}

int main()
{

    Administrator var_a;

    var_a.createNewBook();

    return 0;
}

输出

 NEW BOOK ENTRY...


 Enter The Name of The Book:abcd


 Enter The Author's Name:efgh



 Book Created..

如果你有构造函数

会更好

每次我从另一个C ++类调用类函数时，我的程序都会崩溃

2 个答案: