Why doesn't std::queue support a clear() function?
Solution 1
According to http://www.cplusplus.com/reference/stl/queue/,
queues are implemented as containers adaptors, which are classes that use an encapsulated object of a specific container class as its underlying container, providing a specific set of member functions to access it elements.
which means that the queue uses an already existing container, and is just really is an interface to this container as a FIFO queue.
This means queues are not meant to be cleared. If you need to clear a queue, this means you actually need to use an object that is not a queue, and therefore you should instead use the actual underlying container type, being a deque by default.
Solution 2
Apart from what has been said already, you can clear a queue very easily:
queue<int> q;
...
q = queue<int>(); // Assign an empty queue
or in C++11
q = {};
Solution 3
queue
is just an adapter for some underlying container, by default a deque
, with restricted function (as you noted here). If you want the full blown function use the underlying deque
instead of queue
.
Solution 4
Added this to my growing list of 'make STL readable' functions:
template <typename T>
void Clear(std::queue<T>& Queue)
{
Queue = std::queue<T>(); // Assign to empty queue
}
It's just a wrapper around sellibitze's excellent answer, but means I don't have to also add a comment every time I use the technique.
Comments
-
bjskishore123 about 4 years
I have requirement: for a function, I get the input as a stream of numbers. I mean, the function keeps on getting called with single number in each call. I am using
std::queue
for storing the stream of numbers. I need to process a collected set of numbers only when some condition is satisfied. If the condition is not satisfied I need to put all the elements into the queue and then start storing new numbers in there. For emptying the queue, I couldn't find aclear()
method. So I am looping like this:while(!q.empty()) q.pop();
I got an efficient algorithm for clearing a
std::queue
atHow do I clear the std::queue efficiently?
My question is: Why doesn't
std::queue
support aclear()
function?Since
std::deque
andstd::vector
both support aclear()
method, what is the technical difficulty in supporting it forstd::queue
?Or is my above use case very rare and hence not supported?