To check if a priority queue is empty in C++, you can use the empty() method. It returns true if the priority queue is empty, and false otherwise. Here's an example:

#include <iostream>
#include <queue>

int main() {
    std::priority_queue<int> pq;
    
    if (pq.empty()) {
        std::cout << "The priority queue is empty." << std::endl;
    } else {
        std::cout << "The priority queue is not empty." << std::endl;
    }
    
    return 0;
}

Output:

The priority queue is empty.