格式化输出width，fill

#include <iostream>using namespace std;class Wf{int w;char f;public:Wf(int w, char f):w(w), f(f){}friend ostream& operator<<(ostream& os, const Wf& o){os.width(o.w);os.fill(o.f);return os;}};int main(){cout << Wf(8,'$') << 123 << endl;return 0;}