std::deque<T,Allocator>::operator[]

 

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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 operator[]( size_type pos );	(1)	(constexpr since C++26)
const_reference operator[]( size_type pos )const;	(2)	(constexpr since C++26)

Returns a reference to the element at specified location pos.

If pos < size() is false, the behavior is undefined.	(until C++26)
If pos < size() is false: If the implementation is hardened, a contract violation occurs. Moreover, if the contract-violation handler returns under “observe” evaluation semantic, the behavior is undefined. If the implementation is not hardened, the behavior is undefined.	(since C++26)

Parameters

pos

-

position of the element to return

Return value

Reference to the requested element.

Complexity

Constant.

Notes

Unlike std::map::operator[], this operator never inserts a new element into the container. Accessing a nonexistent element through this operator is undefined behavior, unless the implementation is hardened(since C++26).

Example

The following code uses operator[] to read from and write to a std::deque<int>:

Run this code

#include <deque>#include <iostream>   int main(){std::deque<int> numbers{2, 4, 6, 8};   std::cout<<"Second element: "<< numbers[1]<<'\n';   numbers[0]=5;   std::cout<<"All numbers:";for(auto i : numbers)std::cout<<' '<< i;std::cout<<'\n';}

Output:

Second element: 4 All numbers: 5 4 6 8

See also

at	access specified element with bounds checking (public member function)