Re: Parsing Questions

Stefan Ewing <sewing@uvic.ca> wrote:
>How can the postfix increment/decrement operators in C, C++, and Java
>be represented in a parse tree? For example, if we have the
>epxression
>
>a = b++ + c;
>
>b will be incremented after b + c has been calculated. But the only
>place to put the operator (it seems to me) is between "b" and "+".
>But doesn't this imply we should increment b *before* adding it to c?


You need to distinguish between the *value* of the expression "b++"
and its side effect (the increment). You can do the increment
anywhere you like (modulo a few restrictions), as long as the value
that is added to c is the original value of b. Your parse tree is
attempting to represent the steps required to compute the value of the
expression -- incrementing b doesn't play any part in determining this
value.


So I think your parse tree is probably right; I suspect that you'll
end up worrying about the side effect when you get to code generation.
For instance, you could move the value of b to a temporary, increment
b, and then add the temporary to the value of c.


- Richard

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