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    std::span<T,Extent>::front

    From cppreference.com
     
    C++
     
    Containers library
     
    std::span
     
    constexpr reference front() const;
    		 (since C++20)
    See More

    Returns a reference to the first element in the span.

    If empty() is true, the behavior is undefined.

    		(until C++26)

    If empty() is true:

    • 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)

    Return value

    A reference to the first element.

    Complexity

    Constant.

    Notes

    For a span c, the expression c.front() is equivalent to *c.begin().

    Example

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

void print(std::span<const int> const data)
{
    for (auto offset{0U}; offset != data.size(); ++offset)
        std::cout << data.subspan(offset).front() << ' ';
    std::cout << '\n';
}

int main()
{
    constexpr int data[]{0, 1, 2, 3, 4, 5, 6};
    print({data, 4});
}

    Output: 

    0 1 2 3

    See also

    		 access the last element
    (public member function) [edit]