But wouldn't that change behavior? An empty, zero initialised array will contain data and a bunch of zeroes after a read, but if the next read only partially fi

But wouldn't that change behavior? An empty, zero initialised array will contain data and a bunch of zeroes after a read, but if the next read only partially fills the buffer you end up with a buffer containing data from two reads. In this specific example there's no issue because the result of read() is being used to only write as much data as was read, but to me this seems like a pretty complicated and unlikely assumption to write optimizations for.