c++ - May I clear a priority_queue by clearing its underlying container? -

the following code inherits std::priority_queue , provides clear() calls internal std::vector's clear()

#include<iostream> #include<queue> using namespace std; template<class type> struct mypq :public priority_queue<type> {     void clear(){         this->c.clear();     } }; mypq<int>pq; int main() {     for(int i=0;i<10;++i)         pq.push(i);     pq.clear();     for(int j=-5;j<0;++j)         pq.push(j);     while (!pq.empty()){         cerr<<pq.top()<<endl;         pq.pop();     } } 

when tested g++, msvc++ , clang, produces expected output:

-1 -2 -3 -4 -5 

but haven't seen guarantee this, i.e. clearing internal vector same calling pop() when priority_queue isn't empty. although know other ways clear such swap or assign using empty priority_queue, think if code can work well, more efficient since allocated memory in vector reusable. wonder if code portable or won't work?

a question. while can't seem find strict guarantee correct method, there reasons think is.

for example, consider docs operator=:

copy assignment operator. replaces contents copy of contents of other. calls c = other.c;. (implicitly declared)

since other queue may of different size, means there no internal state dependent on size. moreover, implies assigning empty queue replaces container empty 1 , nothing else.

with in mind, , fact reasonable implementation of priority queue hardly need maintain state except size of queue, believe can safely assumed clearing underlying container valid way empty queue.