When Should You Use `std::span` in C ?

Understanding "span" in C

The "span" type is a lightweight abstraction that represents a contiguous sequence of values in memory. It can be seen as a cross between a raw pointer and a container, but without the overhead or ownership semantics of the latter.

When to Use span

Consider using span over raw pointers when the allocated length or size matters. For instance, instead of functions like:

void read_into(int* buffer, size_t buffer_size);

You can use:

void read_into(span<int> buffer);

Don't use span if you have an existing container that suits your needs. Spans are not intended to replace standard library containers.

Benefits of Using span

• Enhanced syntax: Spans can be used like standard library containers with features like iteration and predicate-based search.
• Compiler assistance: Spans allow the compiler to perform additional optimizations, such as detecting buffer overruns.
• Clear Ownership Semantics: Spans indicate that your code does not own the referenced memory.

Additionally, spans facilitate code readability and static analysis, helping to identify potential errors.

Availability

C 20: Span was officially adopted into the standard library in C 20 as std::span.

C 17 or Earlier:

If you're using C 17 or earlier, you can access span through third-party libraries like Microsoft's GSL or GSL-Lite, which provide implementations based on the Core Guidelines's Support Library (GSL).

Further Resources:

• Official C 20 Proposal: [P0122R7]( https://wg21.link/p0122r7 )
• C 20 Comparison Semantics: [Tony van Eerd Paper]( https://leanpub.com/unifiedfundamentals )
• Multi-dimensional Span Implementation: [mdspans]( https://stackoverflow.com/questions/40084847/alternative-to-c-style-2d-arrays-in-c )

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