How can I override operator== to compare two objects?-CodePudding

#include <iostream>
using namespace

class Book{
    string title;
    int price, pages;
public:
    Book(string title = "", int price = 0, int pages = 0){
        this->title = title;
        this->price = price;
        this->pages = pages;
    }
    bool operator==(Book);
};
bool Book::operator==(Book op1){
    if(*(this) == op1)
        return true;
    else
        return false;
}

int main()
    Book a("Good C  ", 30000, 500), b("Bad C  ", 30000, 500);
    if (a == b)
        cout << "Same books" << endl;
}

When run the code. I get the following error

zsh: segmentation fault ./main

How can I compare two objects?

this == op1

I tried this, but an error occurred because the data format is different

CodePudding user response：

You need to actually perform the comparison within the operator. The way you had it, the == operator calls itself, which would end up causing a crash.

class Book{
    string title;
    int price, pages;
public:
    Book(string title = "", int price = 0, int pages = 0){
        this->title = title;
        this->price = price;
        this->pages = pages;
    }
    bool operator==(const Book&) const;
};
bool Book::operator==(const Book& op1) const{
    return title == op1.title && 
           price == op1.price && 
           pages == op1.pages;
}

CodePudding user response：

bool Book::operator==(Book &op1){
    if(*(this) == op1) // this lines calls the operator== function again.
        return true;
    else
        return false;
}

The mentioned code is the wrong way of comparing objects. The above code keeps on calling the operator == again and again which result in segmentation fault

You have to compare each attributes(or any number of attribute as per requirement). The above code can be rewritten as:

bool Book::operator==(const Book& op1) const{
    return (title == op1.title && price == op1.price && pages == op1.pages);
}

CodePudding user response：

Since C 20 you can put:

bool operator== (const Book&) const = default;

which does the same comparison you were trying to code.

You can write auto operator<=> instead of bool operator== to get all the relational comparison operators as well.

Prior to C 20 you can still keep your code tidy using tie to combine all the members into one expression:

bool Book::operator==(const Book& op1) const
{
    return std::tie(title, price, pages) == std::tie(op1.title, op1.price, op1.pages);
}