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

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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:

  • 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

idx - the index of the element to access

Return value

data()[idx]

Exceptions

Throws nothing.

Example

#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:

See also

access specified element with bounds checking
(public member function) [edit]
direct access to the underlying contiguous storage
(public member function) [edit]
returns the number of elements
(public member function) [edit]
converts a span into a view of its underlying bytes
(function template) [edit]