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

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

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)

Contents

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)