c ++重载操作符<<和运算符>> [英] c++ overloading operator<< and operator>>
问题描述
class Book
{
string title;
int category;
public：
Book（const string& abook，int num）;
string getTitle（）const;
int getCategory（）const;
friend ostream&运算符<<（ostream& os，const Book& abook）;
friend istream& operator>>（istream& is，Book& abook）;
};
class Reader //基类
{
private：
string reader_name;
vector< Book>书列表;
public：
string showname（）const;
void add（const Book& abook）; //组织书目列表
friend ostream& operator<<（ostream& os，const Reader& read_name）;
friend istream& operator>>（istream& is，Reader& read_name）;
};
class fantasyReader：public Reader {};
class horrorReader：public Reader {};
class scienceReader：public Reader {};
class mysteryReader：public Reader {};
我有两个给定的文本文件。
1）Reader.txt< ---包含读者姓名和类别
例如
David< - 读者姓名
0 < - david is幻想阅读器
2）Book.txt< ----包含图书的标题和类别
对于ex
Riddick< - 书名
0< - 书的类别是幻想
在主函数中，读者对象的指针数组指向每个派生类;
ex
Reader * obj [10];
int pos = 0;
obj [pos ++] = new fantasyReader（）;
主要目标是整理书本列表并放入适当的类别和适当的读者
将它们写入新的文本文件。
ex。
-David-
Riddick
-John-
乌鸦
我的问题
我不确定应该在运营商内部<<和运算符>>
类和类读者
>你应该把什么放在重载的<<和>>运算符？
实际上，您可以在重载的<< c $ c>>> 运算符。
例如：
Book obj;
cout<< obj; // Calls your overloaded<< operator
作为一般原则，当重载运算符时，您应该遵循 ，这意味着您的代码应该进行类似于操作符对内在数据类型的操作。在上面的例子中，我希望我的<< 操作符显示我的 Book 类的内容， case我将重载它如下：
//显示标题和类别
ostream& operator<<（ostream& os，const Book& abook）;
{
os<< abook.title<< \\\
;
os<< abook.category< \\\
;
return os; //必须返回ostream对象
}
我需要返回一个流对象， 链接例如：
Book obj1，obj2，obj3;
cout<<< obj1<< obj2<< obj3;
同样，>> 运算符我希望运算符从用户获取数据。
例如：
Book obj;
cin>> obj; // Calls your overloaded>> operator
我会重载>> 运算符如下：
//获取书名来自用户的类别
istream& operator>>（istream& is，Book& abook）
{
cout< Enter Book Title：;
是>> abook.title;
cout<< 输入书类别：;
是>> abook.category;
return is; //必须返回流对象
}
是您可以在>> 和<< 操作符中放置任何功能，但不要忘记原则的最低惊讶！
class Book
{
string title;
int category;
public:
Book(const string& abook, int num);
string getTitle() const;
int getCategory() const;
friend ostream& operator<<(ostream& os, const Book& abook);
friend istream& operator>>(istream& is, Book& abook);
};
class Reader // base class
{
private:
string reader_name;
vector<Book> bookLists;
public:
string showname() const;
void add(const Book& abook); // organize book list
friend ostream& operator<<(ostream& os, const Reader& read_name);
friend istream& operator>>(istream& is, Reader& read_name);
};
class fantasyReader : public Reader { };
class horrorReader : public Reader { };
class scienceReader : public Reader { } ;
class mysteryReader : public Reader { };
I have two given text files.
1) Reader.txt <--- contains reader's name and category
For ex.
David <- reader's name
0 <- david is Fantasy reader
2) Book.txt <---- contains Book's title and category
For ex
Riddick <- Book's title
0 <- Book's category is fantasy
In the main function, array of pointers to Reader's obj are pointing each dervied class;
ex
Reader *obj[10];
int pos =0;
obj[pos++] = new fantasyReader();
The main goal is to organize book's list and put into a appropriate category and appropriate reader
and write them into a new text file.
ex.
-David-
Riddick
-John-
The Crow
MY QUESTION
I'm not sure what should be inside of operator<< and operator>>
for class Book and class Reader
What should you put inside the overloaded << and >> operators?
Well, You can actually put anything inside the overloaded << and >> operator. They will just be simple function calls whenever a appropriate opportunity presents.
For eg:
Book obj;
cout<< obj; //Calls your overloaded << operator
As a general principle while overloading operators you should follow Principle of Least Astonishment, which means your code should be doing something similar what the operator does for a intrinsic data type. In the above example I would expect my << operator to display the contents of my Book class, in that case I would overload it as follows:
// Display title and category
ostream& operator<<(ostream& os, const Book& abook);
{
os << abook.title << "\n";
os << abook.category<< "\n";
return os; // must return ostream object
}
I need to return a stream object since it allows for the chaining ex:
Book obj1,obj2,obj3;
cout<<obj1<<obj2<<obj3;
Similarly, for >> Extraction operator I would expect the operator to get the data from user.
For ex:
Book obj;
cin>>obj; //Calls your overloaded >> operator
I would overload the >> operator as follows:
//Get the Book Title & Category from User
istream& operator>>(istream& is, Book& abook)
{
cout << "Enter Book Title: ";
is >> abook.title ;
cout << "Enter Book Category: ";
is >> abook.category;
return is; //Must return stream object
}
So, the bottomline is You can put any functionality inside >> and << operators but don't forget the Principle of Least Astonishment!
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