I've heard that MSVC does (did?) that, but if so that's an MSVC problem. gcc and clang don't do that.

https://godbolt.org/z/nasoWeq5M

WDYM? Vector is an abstraction over dynamically sized arrays so sure it does use heap to store its elements.

I think usefulcat interpreted "std::vector<int> allocated and freed on the stack" as creating a default std::vector<int> and then destroying it without pushing elements to it. That's what their godbolt link shows, at least, though to be fair MSVC seems to match the described GCC/Clang behavior these days.

Sure, but my point was that RAII doesn't need to involve the heap. Another example would be acquiring abd releasing a mutex.