as question says, i want to write custom data type data of a class maybe to a file using ifstream in c++. Need help.
+4
A:
For an arbitrary class, say, Point, here's a fairly clean way to write it out to an ostream.
#include <iostream>
class Point
{
public:
Point(int x, int y) : x_(x), y_(y) { }
std::ostream& write(std::ostream& os)
{
return os << "[" << x_ << ", " << y << "]";
}
private:
int x_, y_;
};
std::ostream& operator<<(std::ostream& os, const Point& point)
{
return point.write(os);
}
int main() {
Point point(20, 30);
std::cout << "point = " << point << "\n";
}
Marcelo Cantos
2010-05-02 09:11:36
+1. The only thing I'd like to add is that if one doesn't want a public `write` method in the class itself, one could declare the global overloaded `operator <<` (the _inserter_) as `friend` inside the class and then either make `write` private, or move its code directly into the inserter.
stakx
2010-05-02 09:24:07
Thank you for suggestion, @stakx. I used to code it up as a `friend` without a `write`, but found that it was tedious to write `point.`. I must admit that I never considered the private `write` option. I guess once you decide to use a `friend`, the repeated prefix is less effort than a private `write`.
Marcelo Cantos
2010-05-02 09:49:32
@Marcelo Cantos: In fact, I find your solution very clean and a public `write` certainly doesn't hurt, esp. as it communicates to another developer that a `<<` inserter is probably available for that class, too. I am personally no big friend of `friend` but thought it needed to be mentioned for completeness' sake. ;)
stakx
2010-05-02 10:03:02