In C++, a queue is a data structure that follows the FIFO (First-In-First-Out) principle. It allows elements to be inserted at the back and removed from the front. To work effectively with a queue, it is essential to understand its size and capacity.

Size of a Queue

The size of a queue represents the number of elements it currently contains. You can use the size() function to retrieve the size of a queue in C++. Let’s see an example:

#include <iostream>
#include <queue>

int main() {
    std::queue<int> myQueue;
    
    myQueue.push(10);
    myQueue.push(20);
    myQueue.push(30);
    
    std::cout << "Size of the queue: " << myQueue.size() << std::endl;
    
    return 0;
}

Output:

Size of the queue: 3

In the above example, we create a queue myQueue and insert three elements. The size() function is then used to retrieve the size of the queue, which is printed as output.

Capacity of a Queue

In C++, the std::queue is an implementation of a queue using a deque (double-ended queue) as its underlying container. A deque dynamically allocates memory for its elements, allowing it to grow as needed. Therefore, there is no explicit capacity for a queue. It can theoretically hold as many elements as the available memory allows.

However, when working with limited resources, it’s crucial to ensure that memory allocation for the queue doesn’t result in an out-of-memory error. One way to handle this is by checking the available memory before performing any operations.

Conclusion

In C++, the size of a queue represents the number of elements it currently contains, which can be retrieved using the size() function. On the other hand, the capacity of a queue dynamically grows as needed due to the underlying deque container’s memory allocation capabilities.

Remember to consider the available memory of the system when working with queues or any other data structure to avoid potential resource exhaustion issues.

#tech #C++