Only the top element of the queue has the opportunity to be accessed by the outside world. The queue does not provide traversal functions, nor does it provide iterators.
queue constructor
queue<T> queT; // queue采用模板实现,默认构造
queue(const queue& que); // 拷贝构造函数
Queue access, insert, and delete operations
push(elem); // 往队尾添加元素
pop(); // 从队头移除第一个元素
back(); // 返回最后一个元素
front(); // 返回第一个元素
Queue assignment operation
queue& operator=(const queue & que); // 重载=
Queue size operation
empty(); // 判断队列是否为空
size(); // 返回队列大小