Member Avatar for jonathan710 
#include <iostream>
using namespace std;

template<class T>
class MyClass {
    private:
        T data;
    public:
        MyClass(T data) { this->data = data; }
};

template<class T>
bool operator< (const MyClass<T> & a, const MyClass<T> & b) {
    return (a.data < b.data);
}

int main() {
    MyClass<int> x(1);
    MyClass<int> y(2);

    if(x < y) cout << "x is less than y!" << endl;
    return 0;
}

when i compile this it says T data is private, i know i needa declare some friend operators but not really sure how to do it :( can anyone help me please??

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  • Latest Post Latest Post by richieking

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Generated

The compiler error happens because the free operator< in Post #1 is trying to access a private member. As shows, a non-member function cannot see data unless the class makes it accessible. was right to suggest an accessor and was pointing toward defining the operator as a class member — both are valid approaches. Below are concise, safe options (with small examples) and the tradeoffs.

Add a public getter (keeps encapsulation; simple):

template<class T>
class MyClass {
    T value;
public:
    explicit MyClass(const T& v) : value(v) {}
    T get() const { return value; }
};

template<class T>
bool operator<(const MyClass<T>& a, const MyClass<T>& b) {
    return a.get() < b.get();
}

Make operator< a member (easy; member can access other instances’ privates, but only allows implicit conversions on the right-hand operand):

template<class T>
class MyClass {
    T value;
public:
    explicit MyClass(const T& v) : value(v) {}
    bool operator<(const MyClass& rhs) const { return value < rhs.value; }
};

Or keep a non-member operator and grant private access with a friend. Two common patterns: define the friend inline inside the class, or declare a friend template and define the operator outside — both let the operator access private members while remaining a non-member (useful for symmetric conversions).

A few practical tips: make the constructor explicit to avoid unwanted implicit conversions; take operands by const&; mark member operators const. For modern codebases consider operator<=> (C++20) to generate all comparison operators automatically.

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Member Avatar for zouhair.kasmi

You don't have a permission to create this line
you should to work with the getter in the class because it is private .

 return (a.data < b.data);

here for example you can type somting like this

Getdata(); // you should to define this method in your class. and to write it as public
Edited by zouhair.kasmi
Member Avatar for richieking

declare the operator inside the class.

Then use bool Myclass::operator<()

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