It is impossible to overload the comparison operator "<". I use Qt.
point.h
class Point { private: double x; double y; double z; ... public: double getX(); double getY(); double getZ(); ... friend bool operator<(Point &first, Point &sec); } point.cpp
... bool Point::operator<(Point &first, Point &sec) { return sqrt(first.getX()*first.getX() + first.getY()*first.getY() + first.getZ()*first.getZ()) < sqrt(sec.getX()*sec.getX() + sec.getY()*sec.getY() + sec.getZ()*sec.getZ()); } main.cpp
... QList<Point> list; ... qSort(list.begin(), list.end()); ... With this implementation, it gives an error:
...\point.cpp:23: ошибка: 'bool Point::operator<(Point&, Point&)' must take exactly one argument bool Point::operator<(Point &first, Point &sec) ^ If I remove the second argument: point.h
... friend bool operator<(Point &first); ... point.cpp
... bool Point::operator<(Point &first) { return sqrt(first.getX()*first.getX() + first.getY()*first.getY() + first.getZ()*first.getZ()) < sqrt(x*x+y*y+z*z); } ... That gives out:
...\point.h:46: ошибка: 'bool operator<(Point&)' must take exactly two arguments friend bool operator<(Point &first); ^ Tell me what the problem is and how to make it work.
Writing to .h inside the class
friend bool operator<(const Point &first, const Point &sec); in .cpp
bool operator<(Point const &first, Point const &sec){ return sqrt(first.getX()*first.getX() + first.getY()*first.getY() + first.getZ()*first.getZ()) < sqrt(sec.getX()*sec.getX() + sec.getY()*sec.getY() + sec.getZ()*sec.getZ()); } It gives a number of similar errors (for each get)
...\point.cpp:24: ошибка: passing 'const Point' as 'this' argument of 'double Point::getX()' discards qualifiers [-fpermissive] return sqrt(first.getX()*first.getX() + first.getY()*first.getY() + first.getZ()*first.getZ()) < ^ 
operator<for points does not look very natural, because the set of points does not form an order. - Fat-Zer