不同 类 面向对象编程 C++ 的不可访问基础

Question

我一直在尝试编译这段代码。它有一个名为 books 的 class，其他类型的书籍都继承自它。但是，当我编译程序时，它一直说 Book is an an accessible base of Police。然后它在前两个 add_book 呼叫下方显示红线，主要是他们添加新警察的地方。 我没有看到我的代码中哪里缺少访问权限？

#include <iostream>
#include <vector>
#include <string>
using namespace std; 

class Book{
public: 
virtual double calc_price()const;
Book(string t, string a, int pg, bool bs)
: title(t), author(a), pages(pg), bestseller(bs){}
virtual ~Book(){}; 
virtual void display() const; 

protected: 
string title; 
string author; 
int pages; 
bool bestseller;      
}; 

void Book::display() const {
cout << "Title: " << title << endl;
cout << "Author: " << author << endl; 
cout << "Number of pages: " << pages << endl; 
cout << "Bestseller: "; if(bestseller==true){ cout << "Yep" 
<< endl; } else      {cout << "Nope" << endl; 
cout << "Price: " << calc_price() << endl; }
}

double Book::calc_price() const {    
if(bestseller==true){ return (pages*0.3 + 50); }
else { return (pages*0.3); }}



class Roman : public Book {
public: 
Roman(string t, string a, int pg, bool bs, bool bio)
: Book(t,a,pg,bs), biography(bio){}
virtual ~Roman(); 
virtual void display()const override; 
protected:
bool biography; 
}; 

void Roman::display() const{
Book::display(); 
cout << "Ce roman ";
if(biography==true){ cout << "is a biography. " << endl;
} else { cout << "isn't a biography. " << endl; }
}
class Police : Roman {
public: 
Police(string t, string a, int pg, bool bs, bool bio)
: Roman(t,a,pg,bs,bio){}
virtual double calc_price() const {
double price; 
price = Book::calc_price() - 10; 
if(price < 0) { return 1; } else { return price; }}
virtual~Police();
}; 

class Fantasy : public Livre {
public: 
Fantasy(string t, string a, int pg, bool bs)
: Book(t,a,pg,bs){}
virtual ~Fantasy();     
virtual double calc_price() const { 
return (Book::calc_price() + 30); }

}; 
class Library{
public: 
void display() const; 
void add_book(Book* l); 
void empty_stock(); 
private: 
vector<Book*> books; 
}; 

void Library::add_book(Book* b){
books.push_back(b);     
}
void Library::display() const {
 for(size_t i(0); i < books.size(); ++i){
    books[i]->display();     
} }

void Library::empty_stock(){
for(size_t i(0); i < books.size(); ++i){
    delete books[i]; } books.clear(); 
 }




int main()
{
 Library l;

l.add_book(new Police("Dogs of Baskerville", "A.C.Doyle", 221, false,false));
l.add_book(new Police("Le Parrain ", "A.Cuso", 367, true, false));
l.add_book(new Roman("Book3", "I. Calvino", 283, false, false));
l.add_book(new Roman ("Geronimoe memories", "S.M. Barrett", 173, false,  true));
l.add_book(new Fantasy ("European rivers", "C. Osborne", 150, false));

l.display();
l.empty_stock();

return 0;
}

Answer 1

在 class Police : public Roman 中更改 class Police : Roman。

如果未指定 public，则 Roman 将为 Police 的 private 基础 class。

Answer 2

更改此行

class Police : Roman {

至

class Police : public Roman {