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

Question

#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

Answer 1

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;
}

Answer 2

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);
}

Answer 3

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);
}