std::deque at() method

od C++98

// Non const version
reference at( size_type pos );

// Const version
const_reference at( size_type pos ) const;

Returns a reference

to the element at specified index pos.

Bounds checking is performed and exception of type std::out_of_range will be thrown on invalid access, see Exceptions.

Parameters

• pos - position of the element to return

Return value

Reference to the requested element.

Exceptions

Throws std::out_of_range if pos >= size().

Complexity

Constant - O(1).

Example

Main.cpp

#include <iostream>
#include <deque>
 
int main()
{
    std::deque<int> data = { 1, 2, 4, 5, 5, 6 };
 
    // Set element 1
    data.at(1) = 88;
 
    // Read element 2
    std::cout << "Element at index 2 has value " << data.at(2) << '\n';
 
    std::cout << "data size = " << data.size() << '\n';
 
    try {
        // Set element 6
        data.at(6) = 666;
    } catch (std::out_of_range const& exc) {
        std::cout << exc.what() << '\n';
    }
 
    // Print final values
    std::cout << "data:";
    for (int elem : data)
        std::cout << " " << elem;
    std::cout << '\n';
}

Possible output

Element at index 2 has value 4
data size = 6
deque::_M_range_check: __n (which is 6) >= this->size() (which is 6)
data: 1 88 4 5 5 6