C++ <deque> - at() Function

The C++ deque::at function returns a reference to the element of the deque at the specified position. If the specified position is not within the bounds of valid elements in the deque, the function throws an out_of_range exception.

Note: The deque::at function produces the same result as deque::operator[] function, except deque::operator[] does not check the specified position against bounds of valid elements in the deque.

Syntax

• C++98
• C++11

reference at (size_type n);
const_reference at (size_type n) const;

reference at (size_type n);
const_reference at (size_type n) const;

Parameters

Return Value

The element at the specified position in the deque.

Time Complexity

Constant i.e, Θ(1).

Example:

In the example below, the deque::at function returns a reference to the element of the deque called MyDeque at the specified positions.

#include <iostream>
#include <deque>
using namespace std;
 
int main (){
  deque<int> MyDeque{10, 20, 30};
  MyDeque.push_back(40);
  MyDeque.push_back(50);

  cout<<"The deque contains:";
  for(int i = 0; i < MyDeque.size(); i++)
    cout<<" "<<MyDeque.at(i);

  return 0;
}

The output of the above code will be:

The deque contains: 10 20 30 40 50