View Compilation Error

0_0_15738421_10772.cpp:182:11: error: call of overloaded 'P()' is ambiguous
 P p[_ << 2], on_edge[_ << 2]; int m;
           ^
0_0_15738421_10772.cpp:182:11: note: candidates are:
0_0_15738421_10772.cpp:172:2: note: P::P(int, int)
  P(int _x = 0, int _y = 0) : x(_x), y(_y) {}
  ^
0_0_15738421_10772.cpp:171:9: note: P::P()
         P(){}
         ^
0_0_15738421_10772.cpp:182:28: error: call of overloaded 'P()' is ambiguous
 P p[_ << 2], on_edge[_ << 2]; int m;
                            ^
0_0_15738421_10772.cpp:182:28: note: candidates are:
0_0_15738421_10772.cpp:172:2: note: P::P(int, int)
  P(int _x = 0, int _y = 0) : x(_x), y(_y) {}
  ^
0_0_15738421_10772.cpp:171:9: note: P::P()
         P(){}
         ^