Class equality check

[jmrag]

Is there any way to check if A==B within a function??

Class A{
public: int id;
        string description}

Main()
{
Class A a;
a.id=5;
a.string="hello";
a=b;
Class a B;
}

I'm looking for a code to check if a=b smthing like

if(a==b)
//i know it doesnt works...
cout<<"the same"

[Wazzak]

Yes, it's called the copy-constructor^[1].

References:
^[1] http://www.learncpp.com/cpp-tutorial/911-the-copy-constructor-and-overloading-the-assignment-operator/

_Wazzak

[jmrag]

Sry for editing the post this is what i meant..

[Wazzak]

You'll need to overload the equality operator, either globally, or internally to the class.

// Internally:
class A
{
    public:
        bool operator == (const A &Ref) const 
        {
            return(this->Member == Ref.GetMember());
        }

        const int GetMember() const
        {
            return(this->Member);
        }

    private:
        int Member;
};

// Globally:
bool operator == (const A &L, const A &R)
{
    return(L.GetMember() == R.GetMember());
}

Note: If you overload an operator globally, be careful.

_Wazzak

[jmrag]

Good idea! thx.. Will this work and for any derived class?

[Wazzak]

Yeah.

_Wazzak

[LB]

@OFramew: Why did you call the getter function instead of accessing the member directly?

        bool operator == (const A &Ref) const 
        {
            return(this->Member == Ref.GetMember()); //why not Ref.Member?
        }

[Gaminic]

To minimize the difference between the internal and global, I suppose.

[Wazzak]

@LB: No idea. I'm just a simple pencil sharpener. No, seriously, I admit that I didn't know you could do that. How is it possible? Aren't private members, well... private?

_Wazzak

[Gaminic]

Any member function of a class can access all members of that class, regardless of 'privateness'.
Alternatively, your global version would not work that way (unless you make it a 'friend' of the class), because it has no access to private members.

[Wazzak]

OK, so if I understand this correctly, if an internal function, such as the overloaded equality operator above, references any instance of the same class, I can access the private members of the referenced instance?

I wish I knew this before. Thanks, Gaminic.

_Wazzak

[Gaminic]

#include <iostream>

class myClass {
public:
	bool operator==(const myClass& rhs) { return anInt == rhs.anInt; }
	myClass(int A) : anInt(A) {}
private: 
	int anInt;

};

int main() {
	myClass a(6), b(6), c(10);
	if (a == b) std::cout << "a equals b!" << std::endl;
	if (a == c) std::cout << "a equals c!" << std::endl;
	if (b == c) std::cout << "b equals c!" << std::endl;
	return 0;
}

a equals b!

[Wazzak]

I understand now, Gaminic. Thanks again :)

_Wazzak