Standard Template Library Programmer's Guide

[3] One might wonder why pop() returns void , instead of value_type . That is, why must one use top() and pop() to examine and remove the top element, instead of combining the two in a single member function? In fact, there is a good reason for this design. If pop() returned the top element, it would have to return by value rather than by reference: return by reference would create a dangling pointer. Return by value, however, is inefficient: it involves at least one redundant copy constructor call. Since it is impossible for pop() to return a value in such a way as to be both efficient and correct, it is more sensible for it to return no value at all and to require clients to use top() to inspect the value at the top of the stack.

queue , priority_queue , Container, Sequence

Categories: containers, adaptors

Component type: type

A queue is an adaptor that provides a restricted subset of Container functionality A queue is a "first in first out" (FIFO) data structure. [1] That is, elements are added to the back of the queue and may be removed from the front; Q.front() is the element that was added to the queue least recently. Queue does not allow iteration through its elements. [2]

Queue is a container adaptor, meaning that it is implemented on top of some underlying container type. By default that underlying type is deque , but a different type may be selected explicitly.

int main() {

queue Q;

Q.push(8);

Q.push(7);

Q.push(6);

Q.push(2);

assert(Q.size() == 4);

assert(Q.back() == 2);

assert(Q.front() == 8);

Q.pop();

assert(Q.front() == 7);

Q.pop();

assert(Q.front() == 6);

Q.pop();

assert(Q.front() == 2);

Q.pop();

assert(Q.empty());

}

Defined in the standard header queue, and in the nonstandard backward-compatibility header stack.h.

Assignable, Default Constructible

• T is a model of Assignable.

• Sequence is a model of Front Insertion Sequence.

• Sequence is a model of Back Insertion Sequence.

• Sequence::value_type is the same type as T .

• If operator== is used, then T is a model of Equality Comparable

• If operator< is used, then T is a model of LessThan Comparable.

None.

These members are not defined in the Assignable and Default Constructible requirements, but are specific to queue .

[1] Queues are a standard data structure, and are discussed in all algorithm books. See, for example, section 2.2.1 of Knuth. (D. E. Knuth, The Art of Computer Programming. Volume 1: Fundamental Algorithms , second edition. Addison-Wesley, 1973.)