stlObjListOpOverloadingAndFiendClass.cpp

// Standard Template Library example using a class.

#include <iostream>
#include <list>
using namespace std;

// The List STL template requires overloading operators =, == and <.

class AAA
{
	friend ostream &operator<<(ostream &, const AAA &);

public:
	int x;
	int y;
	float z;

	AAA();
	AAA(const AAA &);
	~AAA(){};
	AAA &operator=(const AAA &rhs);
	int operator==(const AAA &rhs) const;
	int operator<(const AAA &rhs) const;
};

AAA::AAA()   // Constructor
{
	x = 0;
	y = 0;
	z = 0;
}

AAA::AAA(const AAA &copyin)   // Copy constructor to handle pass by value.
{
	x = copyin.x;
	y = copyin.y;
	z = copyin.z;
}

ostream &operator<<(ostream &output, const AAA &aaa)
{
	output << aaa.x << ' ' << aaa.y << ' ' << aaa.z << endl;
	return output;
}

AAA& AAA::operator=(const AAA &rhs)
{
	this->x = rhs.x;
	this->y = rhs.y;
	this->z = rhs.z;
	return *this;
}

int AAA::operator==(const AAA &rhs) const
{
	if (this->x != rhs.x) return 0;
	if (this->y != rhs.y) return 0;
	if (this->z != rhs.z) return 0;
	return 1;
}

// This function is required for built-in STL list functions like sort
int AAA::operator<(const AAA &rhs) const
{
	if (this->x == rhs.x && this->y == rhs.y && this->z < rhs.z) return 1;
	if (this->x == rhs.x && this->y < rhs.y) return 1;
	if (this->x < rhs.x) return 1;
	return 0;
}

int main()
{
	list<AAA> L;
	AAA Ablob;

	Ablob.x = 7;
	Ablob.y = 2;
	Ablob.z = 4.2355;
	L.push_back(Ablob);  // Insert a new element at the end

	Ablob.x = 5;
	L.push_back(Ablob);  // Object passed by value. Uses default member-wise
	// copy constructor
	Ablob.z = 3.2355;
	L.push_back(Ablob);

	Ablob.x = 3;
	Ablob.y = 7;
	Ablob.z = 7.2355;
	L.push_back(Ablob);

	list<AAA>::iterator i;

	for (i = L.begin(); i != L.end(); ++i) cout << (*i).x << " "; // print member
	cout << endl;

	for (i = L.begin(); i != L.end(); ++i) cout << *i << " "; // print with overloaded operator
	cout << endl;

	cout << "Sorted: " << endl;
	L.sort();
	for (i = L.begin(); i != L.end(); ++i) cout << *i << " "; // print with overloaded operator
	cout << endl;

	return 0;
}