std::vector::operator[]

reference operator[]( size_type pos );
const_reference operator[]( size_type pos ) const;

Returns a reference to the element at specified location pos. No bounds checking is performed.

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.

Example

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

Run this code

#include <vector>
#include <iostream>
 
int main()
{
    std::vector<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

Language
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Technical Specifications

array (C++11)
vector
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forward_list (C++11)
list
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map
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unordered_set (C++11)
unordered_multiset (C++11)
unordered_map (C++11)
unordered_multimap (C++11)
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