std::span (C++20)

In a nutshell

A lightweight non-owning view that safely refers to a stretch of contiguous memory, replacing the traditional way of passing a pointer plus a length around.

Header file

#include <span>

Core API Cheat Sheet

Operation	Signature	Description
Construction	template<class T, size_t E = dynamic_extent> class span	Class template supporting a static or dynamic length
Get pointer	T* data() const	Accesses the underlying contiguous storage
Element count	size_t size() const	Returns the number of elements
Byte size	size_t size_bytes() const	Returns the number of bytes the sequence occupies
Is empty	bool empty() const	Checks whether the sequence is empty
Subscript access	reference operator[](size_t idx) const	Accesses the element at the given index (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	Gets a subview of the first N elements
Take subview	template<size_t O, size_t C> constexpr span<element_type, C> subspan() const	Gets a subview at 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 Suitability: High

• Zero-overhead abstraction: holds nothing but a pointer and a length (or a compile-time constant length), with no heap allocation
• A perfect replacement for passing raw pointers around: unifies the interface of arrays, std::array, and std::vector, improving safety
• A TriviallyCopyable type (explicitly required since C++23; mainstream implementations already satisfied this before that), safe to use in interrupt and DMA buffer operations
• size_bytes() and as_bytes() greatly simplify mapping hardware registers and doing low-level byte-wise data processing

Compiler Support

GCC	Clang	MSVC
To be added	To be added	To be added

See Also

• Tutorial: Deep Dive into span
• cppreference: std::span

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