std::span (C++20)

In a Nutshell

A lightweight, non-owning view that safely references a contiguous block of memory, replacing the traditional approach of passing a pointer paired with a length.

Header

#include <span>

Core API Cheat Sheet

Operation	Signature	Description
Construction	template<class T, size_t E = dynamic_extent> class span	Template class supporting static or dynamic extents
Get pointer	T* data() const	Access the underlying contiguous storage
Element count	size_t size() const	Returns the number of elements
Size in bytes	size_t size_bytes() const	Returns the size of the sequence in bytes
Check if empty	bool empty() const	Checks if the sequence is empty
Subscript access	reference operator[](size_t idx) const	Accesses the specified element (no bounds checking)
First element	reference front() const	Accesses the first element
Last element	reference back() const	Accesses the last element
Take first N	template<size_t C> constexpr span<element_type, C> first() const	Obtains a subview of the first N elements
Take subview	template<size_t O, size_t C> constexpr span<element_type, C> subspan() const	Obtains a subview with the specified offset and length

Minimal Example

// Standard: C++20
#include <iostream>
#include <span>

void print(std::span<const int> s) {
    for (int v : s) std::cout << v << ' ';
    std::cout << '\n';
}

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    std::span<int> s(arr);
    print(s);            // 1 2 3 4 5
    print(s.first(3));   // 1 2 3
    print(s.subspan(2)); // 3 4 5
}

Embedded Applicability: High

• Zero-overhead abstraction: contains only a pointer and a size (or a compile-time constant extent), with no heap allocation
• Perfect replacement for raw pointer parameters: unifies interfaces for arrays, std::array, and std::vector, improving safety
• TriviallyCopyable type (explicitly required since C++23, though mainstream implementations already satisfied this beforehand), safe to use for interrupt and DMA (Direct Memory Access) buffer operations
• size_bytes() and as_bytes() greatly simplify hardware register mapping and low-level byte-level data processing

Compiler Support

GCC	Clang	MSVC
TBA	TBA	TBA

See Also

• Tutorial: span In Depth
• cppreference: std::span

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