stl中的优先级队列

Question

I followed the article to code a hanffman coding method using stl's priority_queue, however I think there are some bugs in the final code or it's not updated. The main problem is the declaration of the priority_queue, I believe it should take three parameters like: priority_queue< node, vector, greater > q, instead of priority_queue, greater > q. However, even with this changes, the gcc compiler still give the errors like:

  /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_function.h: In member function ‘bool std::greater<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = node]’:
  /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_heap.h:279:   instantiated from ‘void std::__adjust_heap(_RandomAccessIterator, _Distance, _Distance, _Tp, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<node*, std::vector<node, std::allocator<node> > >, _Distance = long int, _Tp = node, _Compare = std::greater<node>]’
  /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_heap.h:404:   instantiated from ‘void std::make_heap(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<node*, std::vector<node, std::allocator<node> > >, _Compare = std::greater<node>]’
  /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_queue.h:367:   instantiated from ‘std::priority_queue<_Tp, _Sequence, _Compare>::priority_queue(const _Compare&, const _Sequence&) [with _Tp = node, _Sequence = std::vector<node, std::allocator<node> >, _Compare = std::greater<node>]’ hanffman.cpp:119:   instantiated from here
  /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_function.h:218: error: no match for ‘operator>’ in ‘__x > __y’

which I don't understand. The full code is available here

Answer 1

You need to define an operator>() for your class because you are using std::greater<> as the comparison in the priority_queue . The only operator I saw in the code was operator<() .

Answer 2

您缺少节点的>运算符的定义（仅定义<运算符）。