Re: [TUHS] Unix stories

Random832 <random832(a)fastmail.com> wrote: |On Wed, Jan 4, 2017, at 08:04, Steffen Nurpmeso wrote: |> terrible aliasing and "sequence point" rules, where i think it is |> clear what i mean when i write "i = j + ++i" (i believe this is |> undefined behaviour). | |I assume you're imagining it as being equivalent to i = j + i + 1, with |a redundant store operation. | |But why couldn't it equally well mean No i don't, and the thing is that it could definetely not equally mean anything. That is exactly the point. I skip quite a lot here. ... |example is contrived too; why wouldn't you just do i += j + 1? But for a |better example, I was in a discussion a couple weeks ago with someone |who thought it was clear what they meant by an expression like this: | |*a++ = *a | |And not only was I easily able to come up with two reasonable-looking |implementations where it means different things, I guessed wrong on |which one they thought it should mean. My examples were stack-based |architectures with a "store to address" instruction taking operands in So if we agree that a high level language should abstract such problems from the programmer, with a right hand side that is evaluated and stored in the target of the left hand side, then all is fine. |each of the two possible orders, making it natural to evaluate either |the RHS or the address-of-LHS first. A more realistic register-based |architecture with pipelining might make it more efficient to evaluate |one or the other first, or parts of each [assuming more complex |expressions than in the example] mixed together, depending on the exact |data dependencies in both expressions. It is all right by me. "Can't say that on the radio." --steffen