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

	(1)
reference at( size_type pos );		(until C++20)
constexpr reference at( size_type pos );		(since C++20)
	(2)
const_reference at( size_type pos ) const;		(until C++20)
constexpr const_reference at( size_type pos ) const;		(since C++20)

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.

Exceptions

std::out_of_range if !(pos < size()).

Complexity

Constant.

Example

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