Compilation error if field class does not have default constructor and the field was not initialized during pre-constructor initialization.

test_1.cpp

#include <iostream>


class Point {
public:
	int x;
	int y;

	Point() {
		std::cout << "A point has been initialized by default constructor" << std::endl;
	}

	Point(int _x, int _y) {
		std::cout << "A point has been initialized by Point(int, int) constructor" << std::endl;
		x = _x;
		y = _y;
	}
};

class City {
public:
	Point position;
	int population;

	City(Point const & _position, int _population): position(_position), population(_population) {
		std::cout << "A city has been initialized" << std::endl;
	}

	City() {
		position = Point(10, 20);
	}
};

int main () {
	Point p1 = Point(1, 2);
	int population = 1000;
	City c1 = City(p1, population);
	City c2 = City();
}

Output is:

A point has been initialized
A city has been initialized

rev2:

g++ ./default_constructor_2.cpp
./default_constructor_2.cpp: In constructor ‘City::City()’:
./default_constructor_2.cpp:24:9: error: no matching function for call to ‘Point::Point()’
  City() {}
         ^
./default_constructor_2.cpp:24:9: note: candidates are:
./default_constructor_2.cpp:8:2: note: Point::Point(int, int)
  Point(int _x, int _y) {
  ^
./default_constructor_2.cpp:8:2: note:   candidate expects 2 arguments, 0 provided
./default_constructor_2.cpp:4:7: note: Point::Point(const Point&)
 class Point {
       ^
./default_constructor_2.cpp:4:7: note:   candidate expects 1 argument, 0 provided

rev3:

A point has been initialized by Point(int, int) constructor
A city has been initialized
A point has been initialized by default constructor
A point has been initialized by Point(int, int) constructor

There are 2 calls of Point constructors for the second city!! Omg =(