Returns a reference to the first element in the deque container.
Unlike member deque::begin, which returns an iterator to this same element, this function returns a direct reference.
Calling this function on an empty container causes undefined behavior.
Parameters
none
Return value
A reference to the first element in the deque container.
If the deque object is const-qualified, the function returns a const_reference. Otherwise, it returns a reference.
Member types reference and const_reference are the reference types to the elements of the container (see deque member types).
Example
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
// deque::front
#include <iostream>
#include <deque>
int main ()
{
std::deque<int> mydeque;
mydeque.push_front(77);
mydeque.push_back(20);
mydeque.front() -= mydeque.back();
std::cout << "mydeque.front() is now " << mydeque.front() << '\n';
return 0;
}
Output:
mydeque.front() is now 57
Complexity
Constant.
Iterator validity
No changes.
Data races
The container is accessed (neither the const nor the non-const versions modify the container).
The first element is potentially accessed or modified by the caller. Concurrently accessing or modifying other elements is safe.
Exception safety
If the container is not empty, the function never throws exceptions (no-throw guarantee).
Otherwise, it causes undefined behavior.