std::span<T,Extent>::operator[] - cppreference.com
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    std::span<T,Extent>::operator[]

    From cppreference.com
     
    C++
     
    Containers library
     
    std::span
     
    constexpr reference operator[]( size_type idx ) const;
    		(since C++20)

    Returns a reference to the idxth element of the sequence.

    If idx < size() is false, the behavior is undefined.

    		(until C++26)

    If idx < size() is false:

    		(since C++26)

    Parameters

    idx - the index of the element to access

    Return value

    data()[idx]

    Exceptions

    Throws nothing.

    Example

    Run this code
    #include <cstddef>
#include <iostream>
#include <span>
#include <utility>

void reverse(std::span<int> span)
{
    for (std::size_t i = 0, j = std::size(span); i < j; ++i)
    {
        --j;
        std::swap(span[i], span[j]);
    }
}

void print(const std::span<const int> span)
{
    for (int element : span)
        std::cout << element << ' ';
    std::cout << '\n';
}

int main()
{
    int data[]{1, 2, 3, 4, 5};
    print(data);
    reverse(data);
    print(data);
}

    Output: 

    1 2 3 4 5
5 4 3 2 1

    See also