CODEWITHSUNDEEP
c++objectcompare
wpp
wpp

Reputation: 17

C++ comparing two objects

I got this function:

bool operator==(const foo& foo1, const foo& foo2)

how do I compare the two objects with each other, is there a library function that allows me to doit? or do I have to physically compare each of the variables inside the objects.

EDIT:

foo object holds:

private: 
int *values;
size_t *columns; 
std::map< size_t, std::pair<size_t, unsigned int> > maps;

Upvotes: 0

Views: 5582

Answers (5)

amit kumar
amit kumar

Reputation: 1

bool operator ==(const Student &first, const Student &second)
{
    return (first.rollno == second.rollno && first.str == second.str);
}

class Student
{
public:
    string str;
    int rollno;

    Student(string str1,int rollno1)
    {
        str=str1;
        rollno1=rollno;
    }
};

cout <<"is s1=s2? \n" << boolalpha << operator==(s1,s2) <<endl;

Upvotes: 0

Keith Layne
Keith Layne

Reputation: 3795

The signature of the overloaded operator you have is for a static function defined outside of the foo class. Since you stated that the data members of foo are declared as private, you're going to have a tough time getting your operator to work.

If you are required to use that signature for your homework, you need to research the friend keyword...after all, it is homework, nobody's going to do it for you.

If not, consider making the operator a member of the foo class. This is a great general reference for operator overloading.

Upvotes: 0

steveo225
steveo225

Reputation: 11892

It is dependant on the class foo and what data members it has, and what a vaild equality is. Imagine you foo is the following:

class foo {
private:
    long id;
    ...
};

If you wanted to compare based on the id field:

bool operator==(const foo& foo1, const foo& foo2) { return foo1.id == foo2.id; }

They can be as simple or complicated as your needs require.

Upvotes: 0

AnT stands with Russia
AnT stands with Russia

Reputation: 320747

The semantics of the comparison function depends on your intent and in the nature and semantics of object's internals. In your case only you know what foo is and, therefore, only you know how to properly compare one foo object to another foo object. There's no universal one-fits-all answer to your question.

Upvotes: 5

Seth Carnegie
Seth Carnegie

Reputation: 75150

You have to go through and compare the variables inside yourself.

That way, you define what equality is. If foo represents a person, you can define two foos as equal by just the first name, or by first and last name, or by social security number, or whatever you want. Only you, as the writer of the class, know what it means for two of your objects to be equal.

Upvotes: 2

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