Examples of useful C++ snippets

doublequote_op.cc

#include <iostream>
#include <string>

class Yen {
	int _amount;
	
public:
	Yen(size_t amount): _amount(amount) { /* */ }

	friend auto operator<< (std::ostream& os, const Yen& yen) -> std::ostream& {
		os << static_cast<int>(yen.amount()) << " Yen";
		return os;
	}

	virtual auto amount(void) const noexcept -> const int {
		return this->_amount;
	}
	virtual void amount(const int amount) noexcept {
		this->_amount = amount;
	}

};
auto operator"" _Y(unsigned long long yen) -> const Yen {
	return Yen{yen};
}

int main(void) {
	Yen y{134};
	std::cout << y;
	std::cout << 123_Y;
}

shared_ptr.cc

#include <memory>
#include <iostream>
class Widget {
    int _value;
    std::shared_ptr<Widget> _successor;
    
public:
	Widget(void): _value(0) { /* */ };
	Widget(const Widget& rhs): _value(0) { /* */ };
	Widget(Widget&& rhs): _value(0) { /* */ };
    virtual ~Widget(void) { /* */ }
	operator bool(void) const;
    void successor(Widget& successor);
    void pass_value(int a);
    auto pass_value(void) const -> int;
	void value(int a);
    auto value(void) const -> int;
	void swap(Widget& swapper);
	void share(Widget& sharer);
	void reset(void);
};

Widget::operator bool(void) const {
	return !!_successor;
}
void Widget::successor(Widget& successor) {
	this->_successor.reset(&successor);
}
void Widget::pass_value(int a) {
	_successor->_value = a;
}
int Widget::pass_value(void) const {
	return _successor->value();
}
void Widget::value(int a)
{
	this->_value = a;
}
int Widget::value(void) const {
	return this->_value;
}
void Widget::swap(Widget& swapper) {
	this->_successor.swap(swapper._successor);
}
void Widget::share(Widget& sharer) {
	sharer._successor = this->_successor;
}
void Widget::reset(void) {
	this->_successor.reset();
}

void test(Widget& a, Widget& b, Widget& c) {
	a.successor(*new Widget{});
	a.pass_value(111);
	a.share(b);
	b.pass_value(222);
	c.successor(*new Widget{});
	c.pass_value(333);

	std::cout << "Step 1 ------------" << '\n';
	std::cout << "Widget a: " << a.pass_value() << std::endl;
	std::cout << "Widget b: " << b.pass_value() << std::endl;
	std::cout << "Widget c: " << c.pass_value() << std::endl;
	std::cout << '\n';

	b.swap(c);

	std::cout << "Step 2 ------------" << '\n';
	std::cout << "Widget a: " << a.pass_value() << std::endl;
	std::cout << "Widget b: " << b.pass_value() << std::endl;
	std::cout << "Widget c: " << c.pass_value() << std::endl;
	std::cout << '\n';

	c.reset();
}

int main(void) {
	Widget a{}, b{}, c{};

	test(a, b, c);

	std::cout << !!a << '\n';
	std::cout << !!b << '\n';
	std::cout << !!c << '\n';

	std::cout << "Step 1 ------------" << '\n';
	if (a) std::cout << "Widget a: " << a.pass_value() << std::endl;
	if (b) std::cout << "Widget b: " << b.pass_value() << std::endl;
	if (c) std::cout << "Widget c: " << c.pass_value() << std::endl;
}
// Expected output:
// Step 1 ------------
// Widget a: 222
// Widget b: 222
// Widget c: 333
//
// Step 2 ------------
// Widget a: 222
// Widget b: 333
// Widget c: 222
//
// 1
// 1
// 0
// Step 1 ------------
// Widget a: 222
// Widget b: 333

unique_ptr.cc

#include <memory>
#include <iostream>

class Widget {
    int _value;
    std::unique_ptr<Widget> _successor = nullptr;
    
public:
	Widget(void): _value(0) { /* */ };
	Widget(const Widget& rhs): _value(0) { /* */ };
	Widget(Widget&& rhs): _value(0) { /* */ };
	virtual ~Widget(void) { /* */ }
	operator bool(void) const;

	void value(int a);
	auto value(void) const -> int;
	void successor(Widget& successor);
	void swap(Widget& swapper);
	void reset(void);
	void pass_value(int a);
	auto pass_value(void) const -> int;
};

Widget::operator bool(void) const {
	return !!_successor;
}

void Widget::value(int a) {
	this->_value = a;
}
int Widget::value(void) const {
	return this->_value;
}
void Widget::successor(Widget* const& successor) {
	this->_successor.reset(successor);
}
void Widget::swap(Widget& swapper) {
	this->_successor.swap(swapper._successor);
}
void Widget::reset(void) {
	this->_successor.reset(nullptr);
}
void Widget::pass_value(int a) {
	_successor->_value = a;
}
int Widget::pass_value(void) const {
	return _successor->value();
}


void test(Widget& a, Widget& b, Widget& c) {
	Widget* z{ new Widget{}};

	a.successor(z);
	a.pass_value(123);

	b.successor(new Widget{});
	b.pass_value(456);

	// uncomment to see the world burn
	// z will be pointed-to by two object, a and b, this will cause the std::unique_ptr in a to dangle later on
	// b.reset();
	// b.pass_value(z);

	c.successor(new Widget{});
	c.pass_value(789);

	std::cout << "Step 1 ------------" << '\n';
	std::cout << "Widget a: " << a.pass_value() << std::endl;
	std::cout << "Widget b: " << b.pass_value() << std::endl;
	std::cout << "Widget c: " << c.pass_value() << std::endl;
	std::cout << '\n';

	a.swap(b);
	b.swap(c);

	std::cout << "Step 2 ------------" << '\n';
	std::cout << "Widget a: " << a.pass_value() << std::endl;
	std::cout << "Widget b: " << b.pass_value() << std::endl;
	std::cout << "Widget c: " << c.pass_value() << std::endl;
	std::cout << '\n';

	a.pass_value(1111111);
	c.reset();
}

int main(void) {
	Widget a{}, b{}, c{};

	test(a, b, c);

	std::cout << "Step 3 ------------" << '\n';
	if (a) std::cout << "Widget a: " << a.pass_value() << std::endl;
	if (b) std::cout << "Widget b: " << b.pass_value() << std::endl;
	if (c) std::cout << "Widget c: " << c.pass_value() << std::endl;
	std::cout << '\n';
}

// Expected Output:
// Step 1 ------------
// Widget a: 123
// Widget b: 456
// Widget c: 789
//
// Step 2 ------------
// Widget a: 456
// Widget b: 789
// Widget c: 123
//
// Step 3 ------------
// Widget a: 1111111
// Widget b: 789