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C# › Arrays, Span<T> & Memory<T>

How does 'stackalloc' work together with Span<T> to allocate memory on the stack instead of the heap?

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Answer

'stackalloc' allocates a block of memory directly on the CURRENT STACK FRAME (not the garbage-collected heap), and assigning it to a Span<T> gives you safe, bounds-checked access to that memory — ideal for small, short-lived buffers in performance-critical code, completely avoiding GC pressure, but the memory is only valid for the lifetime of the current method call.
Span<int> buffer = stackalloc int[100]; // allocated on the stack, zero GC pressure
for (int i = 0; i < buffer.Length; i++) {
  buffer[i] = i * i;
}
Real-world example Building a small, fixed-size scratch buffer for a hot-path numeric algorithm, avoiding heap allocation entirely.

Common follow-ups: What happens if you try to stackalloc a very large amount of memory, like 1MB?

Memory & Garbage Collection
All 11 Arrays, Span<T> & Memory<T> questions