类或结构体的静态变量

#include <iostream>
struct Node {
	int a, b, c;
	static int k;
	Node() { ++k; }
};
int Node::k = 0;
int main() {
	for (int i = 0; i < 10; ++i) {
		Node x;
		x.a = i, x.b = i+1, x.c = i+2;
		printf("%d: %d %d %d\n", x.k, x.a, x.b, x.c);
	}
}