std::deque<T,Allocator>::at

 

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std::deque

Member types
Member functions
deque::deque deque::~deque deque::operator= deque::assign deque::assign_range (C++23)   deque::get_allocator Element access deque::at deque::operator[] deque::front deque::back Iterators deque::begindeque::cbegin (C++11) deque::enddeque::cend (C++11) deque::rbegindeque::crbegin (C++11) deque::renddeque::crend (C++11)	Capacity deque::empty deque::size deque::max_size deque::shrink_to_fit (DR*) Modifiers deque::clear deque::insert deque::insert_range (C++23) deque::emplace deque::erase deque::push_front deque::emplace_front (C++11) deque::prepend_range (C++23) deque::pop_front deque::push_back deque::emplace_back (C++11) deque::append_range (C++23) deque::pop_back deque::resize deque::swap
Non-member functions
operator==operator<=> (C++20) swap(std::deque) erase(std::deque)erase_if(std::deque) (C++20)(C++20)	operator!=operator<operator>operator<=operator>= (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
Deduction guides(C++17)

 

reference at( size_type pos );	(1)
const_reference at( size_type pos ) const;	(2)

Returns a reference to the element at specified location pos, with bounds checking.

If pos is not within the range of the container, an exception of type std::out_of_range is thrown.

Parameters

pos

-

position of the element to return

Return value

Reference to the requested element, i.e. *(a.begin() + pos).

Exceptions

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

Complexity

Constant.

Example

Run this code

#include <chrono>
#include <cstddef>
#include <iostream>
#include <deque>
#include <stdexcept>
 
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
    {
        // Try to set an element at random position >= size()
        auto moon_phase = []
        {
            return std::chrono::system_clock::now().time_since_epoch().count() % 8;
        };
        data.at(data.size() + moon_phase()) = 13;
    }
    catch(const std::out_of_range& ex)
    {
        std::cout << ex.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 8) >= this->size() (which is 6)
data: 1 88 4 5 5 6

See also

operator[]

access specified element (public member function)