c++11，std::vector::size() 返回值是unsigned，下面这段代码输出   3   wtf!  int in[] = {1,2,3}; vector<int> input(in, in+sizeof(in)/sizeof(int)); cout<<input.size()<<endl; if(-3>input.size()) cout<<"wtf!"<<endl; //-3被当做是unsigned值了 if(-3>(int)input.size()) cout<<&q...