//queue STL//queue is just a container adaptor, which is a class that use other container.//just like stackq1.push(x)     //push x into the queueq1.pop()        //pop the first element in the queueq1.front()       //return the first element in the queueq1.back()        //return the last element in the queueq1.empty()      q1.size()//C++11q1.emplace(x)    //add a new element at the end of the queue, after its current last element //the differences between emplace and push//though they are both the functions to add elements in the queue//if you use emplace ,you will not make a new class.//Let's see a examplestruct node{	int x, y;	node(int a, int b) :x(a), y(b){}};int main(){	queue
     
      q1,q2;	q1.emplace(1, 2);	q2.push(node(1, 2));	cout << q1.front().x << endl;	return 0;}