Priority_queue element as a pointer, the overloaded operators

When using priority_queue to construct the maximum and minimum heap, when it is found that the element in priority_queue is a pointer, the std::greater/std::less function cannot call the overloaded operator of the custom data, and the sorting result is calculated according to the size of the pointer address, causing the max-min heap to fail.

#include #include #include void log(const char* str){std::cout << str;}void log(const int v){std::cout << "" << +v << " ";}struct Stuent{int score = 0;bool operator >(const Stuent& right) const{return this->score > right.score;}};int main(){//construct min heapstd::priority_queue, std::greater> minHeap;for (auto i : { 1,3,5,9,8,6,2,7,4,0 }){Stuent* stu=new Stuent;stu->score = i * 10;minHeap.push(stu);}log("Minimum heap:\n");while (!minHeap.empty()){auto stu = minHeap.top();log(stu->score);printf("%lld\n", (uint64_t)stu);minHeap.pop();delete stu;stu = nullptr;}getchar();return 0;}

The minimum heap that fails, you can see that it is sorted by pointer address.

How to solve it?

Implement the comparison function:

constexpr bool operator()(const _Ty& _Left, const _Ty& _Right) const {return _Left > _Right;}

The test code is as follows:

#include #include #include void log(const char* str){std::cout << str;}void log(const int v){std::cout << "" << +v << " ";}struct Stuent{int score = 0;bool operator >(const Stuent& right) const{return this->score > right.score;}};struct StuentCmp{bool operator()(const Stuent* left, const Stuent* right) const{return left->score > right->score;}};int main(){//construct min heapstd::priority_queue, StuentCmp> minHeap;for (auto i : { 1,3,5,9,8,6,2,7,4,0 }){Stuent* stu=new Stuent;stu->score = i * 10;minHeap.push(stu);}log("Minimum heap:\n");while (!minHeap.empty()){auto stu = minHeap.top();log(stu->score);minHeap.pop();delete stu;stu = nullptr;}getchar();return 0;}

References: https://en.cppreference.com/w/cpp/utility/functional/greater