std:: span

The class template span describes an object that can refer to a contiguous sequence of objects with the first element of the sequence at position zero. A span can either have a static extent, in which case the number of elements in the sequence is known at compile-time and encoded in the type, or a dynamic extent.

For a span s , pointers, iterators, and references to elements of s are invalidated when an operation invalidates a pointer in the range [ s. data ( ) , s. data ( ) + s. size ( ) ) .

A typical implementation holds a pointer to T , if the extent is dynamic, the implementation also holds a size.

Template parameters

Member types

Note: iterator is a mutable iterator if T is not const-qualified.

All requirements on the iterator types of a Container apply to the iterator type of span as well.

Member constant

Member functions

Non-member functions

Non-member constant

Helper templates

This specialization of ranges::enable_borrowed_range makes span satisfy borrowed_range .

This specialization of ranges::enable_view makes span satisfy view .

Deduction guides

Notes

Specializations of std::span are already trivially copyable types in all existing implementations, even before the formal requirement introduced in C++23.

Example

#include <algorithm>
#include <cstddef>
#include <iostream>
#include <span>
 
template<class T, std::size_t N>
[[nodiscard]]
constexpr auto slide(std::span<T, N> s, std::size_t offset, std::size_t width)
{
    return s.subspan(offset, offset + width <= s.size() ? width : 0U);
}
 
template<class T, std::size_t N, std::size_t M>
constexpr bool starts_with(std::span<T, N> data, std::span<T, M> prefix)
{
    return data.size() >= prefix.size()
        && std::equal(prefix.begin(), prefix.end(), data.begin());
}
 
template<class T, std::size_t N, std::size_t M>
constexpr bool ends_with(std::span<T, N> data, std::span<T, M> suffix)
{
    return data.size() >= suffix.size()
        && std::equal(data.end() - suffix.size(), data.end(),
                      suffix.end() - suffix.size());
}
 
template<class T, std::size_t N, std::size_t M>
constexpr bool contains(std::span<T, N> span, std::span<T, M> sub)
{
    return std::ranges::search(span, sub).begin() != span.end();
}
 
void println(const auto& seq)
{
    for (const auto& elem : seq)
        std::cout << elem << ' ';
    std::cout << '\n';
}
 
int main()
{
    constexpr int a[]{0, 1, 2, 3, 4, 5, 6, 7, 8};
    constexpr int b[]{8, 7, 6};
    constexpr static std::size_t width{6};
 
    for (std::size_t offset{}; ; ++offset)
        if (auto s = slide(std::span{a}, offset, width); !s.empty())
            println(s);
        else
            break;
 
    static_assert(""
        && starts_with(std::span{a}, std::span{a, 4})
        && starts_with(std::span{a + 1, 4}, std::span{a + 1, 3})
        && !starts_with(std::span{a}, std::span{b})
        && !starts_with(std::span{a, 8}, std::span{a + 1, 3})
        && ends_with(std::span{a}, std::span{a + 6, 3})
        && !ends_with(std::span{a}, std::span{a + 6, 2})
        && contains(std::span{a}, std::span{a + 1, 4})
        && !contains(std::span{a, 8}, std::span{a, 9})
    );
}

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Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also