Why am i getting missing template arguments before ‘(’ token while using priority queue?

Question

I was implementing an algorithm using priority queue. Here is my code

#include <iostream>
#include<bits/stdc++.h>
using namespace std;
int first[2]={2,-2};
int second[2]={1,-1};
vector<pair<pair<int,int>,int>>vec;
class compare{
    public:
    bool operator()(pair<pair<int,int>,int>a,pair<pair<int,int>,int>b)
    {
        return a.second>b.second;
    }
};
int main() {
    long long int a,b,c,d;
    while(cin>>a>>b>>c>>d)
    {
        priority_queue(pair<pair<int,int>,int>,vector<pair<pair<int,int>,int>>,compare) q;
        map<pair<int,int>,bool>visited;
        map<pair<int,int>,int>dist;
        map<pair<int,int>,pair<int,int>> parent;
        for(int i=1;i<=9;i++)
        for(int j=1;j<=9;j++)
        {
            dist[make_pair(i,j)]=INT_MAX;
            visited[make_pair(i,j)]=false;
        }
        dist[make_pair(a,b)] = 0;
        visited[make_pair(a,b)] = true;
        q.push(make_pair(make_pair(a,b),0));
        while(!q.empty())
        {
            pair<int,int> node = q.top().first;
            int distance = q.top().second;
            q.pop();
            //followed by relaxation step 
        }
    }
    // your code goes here
    return 0;
}

The problem is I am getting the following errors:

rog.cpp: In function ‘int main()’:
prog.cpp:39:17: error: missing template arguments before ‘(’ token
   priority_queue(pair<pair<int,int>,int>,vector<pair<pair<int,int>,int>>,compare) q;
                 ^
prog.cpp:39:41: error: expected primary-expression before ‘,’ token
   priority_queue(pair<pair<int,int>,int>,vector<pair<pair<int,int>,int>>,compare) q;
                                         ^
prog.cpp:39:73: error: expected primary-expression before ‘,’ token
   priority_queue(pair<pair<int,int>,int>,vector<pair<pair<int,int>,int>>,compare) q;
                                                                         ^
prog.cpp:39:73: error: expected primary-expression before ‘)’ token
   priority_queue(pair<pair<int,int>,int>,vector<pair<pair<int,int>,int>>,compare) q;

I am not able to understand what exactly is the meaning of the error.It wold be of great help if someone could clarify it for me.

You should not [include bits/stdc++.h](https://stackoverflow.com/q/31816095/1782465) in your code. — Angew is no longer proud of SO, Dec 27 '17 at 12:58

score 2 · Accepted Answer · answered Dec 27 '17 at 12:10

You are not using proper syntax. Instead of writing

priority_queue(pair<pair<int,int>,int>,vector<pair<pair<int,int>,int>>,compare) q;

You should write

priority_queue<pair<pair<int,int>,int>,vector<pair<pair<int,int>,int>>,compare> q;

For more information, refer to this link: http://en.cppreference.com/w/cpp/container/priority_queue

score 1 · Answer 2 · answered Dec 27 '17 at 12:11

Change this:

priority_queue(pair<pair<int,int>,int>,vector<pair<pair<int,int>,int>>,compare) q;

to this:

priority_queue<pair<pair<int,int>,int>,vector<pair<pair<int,int>,int>>,compare> q;

and you will get this code compiled.

However, this code is unreadable. Consider using a typedef.

Why am i getting missing template arguments before ‘(’ token while using priority queue?

2 Answers2