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std::span<T,Extent>::begin, std::span<T,Extent>::cbegin - cppreference.com

From cppreference.com

constexpr iterator begin() const noexcept;

 (1) (since C++20)

constexpr const_iterator cbegin() const noexcept;

 (2) (since C++23)

Returns an iterator to the first element of the span.

If the span is empty, the returned iterator will be equal to end().

Return value

Iterator to the first element.

Complexity

Constant.

Example

#include <iostream>
#include <span>

void print(std::span<const int> array)
{
    std::cout << "array = ";
    for (auto it = array.begin(); it != array.end(); ++it)
        std::cout << *it << ' ';
    std::cout << '\n';
}

void set_first_element(std::span<int> sp, int new_value)
{
    if (!sp.empty())
    {
        std::cout << "old *begin = " << *sp.begin() << '\n';
        *sp.begin() = new_value;
        std::cout << "new *begin = " << *sp.begin() << '\n';
    }
}

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

Output: 

array = 1 3 4 5
old *begin = 1
new *begin = 2
array = 2 3 4 5

See also

returns an iterator to the end
(public member function) [edit]
returns an iterator to the beginning of a container or array
(function template) [edit]