Re: Order of argument evaluation in C++, etc.

Paul Eggert <eggert@twinsun.com> wrote:
>In my opinion, order-of-evaluation is the most important problem
>area in the C Standard proper. Other language standards since Algol 68
>(e.g. Ada, Fortran, PL/I, Scheme) have addressed this issue more clearly.
>Future C and C++ standards should do so as well.


I don't know about the others, but the Scheme standard (The Revised ^
4 Report on the Algorithmic Language Scheme) states very clearly in
section 4.1.3 (Procedure Calls) that, as in C, evaluation order is
undefined.


I think undefined order of evaluation makes all the sense in the
world. Clearly no one order of evaluation is best; as someone's
mentioned here, some optimizers will even change the order of
evaluation within a program. I don't think it's worth constraining
optimization for dubious gain.


Also, backward compatibility is a serious problem. If anyone starts
writing code that depends on order of evaluation, then it will not be
portable to any existing compiler.


I do very much like the idea of a compiler flag to specify evaluation
order for debugging purposes. Any gcc implementors out there?


Seth
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