c++ - 模板参数列表中参数 3 的类型/值不匹配

Question

我几乎成功地实现了霍夫曼代码。我遇到错误，错误如下:

>>prog.cpp: In function 'int main()':
>>prog.cpp:49:57: error: type/value mismatch at argument 3 in template parameter list for 'template<class _Tp, class _Sequence, class _Compare> class std::priority_queue'

>>priority_queue<Node*,vector<Node*>,comparitor<Node*>> pq;
                                                         ^
>>prog.cpp:49:57: note: expected a type, got 'comparitor' Node*>

我以前尝试过指针，这是我第一次遇到这样的错误。

谁能解释一下为什么会出现这样的错误？这是我的注释代码:

#include <iostream>
using namespace std;
#include<queue>
class Node{
    public:
    int freq;
};
template<typename T>
bool comparitor(T a, T b)
{
    if(a->freq>b->freq)
    {return true;
    }
    else{
        return false;
    } // this is for the min heap
}

int main() {
        priority_queue<Node*,vector<Node*>,comparitor<Node*>> pq;// min heap please, comparitor is just for node and not a template, though I could have easily created that.
}

Answer 1

std::priority_queue，需要三个参数——全部都是类型。你传递的是一个函数。将 comparator 更改为具有 operator() 函数的类。

// There is no reason to make it a class template. This is specifically
// designed to work only with Node*
struct comparitor
{
    bool operator()(const Node* a, const Node* b) const
    {
       return (a->freq > b->freq);
    }
};

并将其用作:

priority_queue<Node*, vector<Node*>, comparitor> pq;