[cfe-dev] How can I use the result of a void expression? :p
clattner at apple.com
Mon Aug 27 20:38:17 PDT 2007
On Aug 27, 2007, at 1:51 PM, Keith Bauer wrote:
> My point is that in my mind, the warning is there to tell the
> programmer that they've probably done something stupid.
> In the case of an expression without side effects, that's clearly
> the case
> (whether the result is void or not). Even in the situation where the
> expression is nonvoid, if it has side effects, it's probably still
> doing what I want.
Yes. This is why we don't warn for things like:
++x; // returns int
printf("foo"); // returns int
etc. However, we do warn for useless computation like:
We don't warn for operators that have side effects. ?: does not have
a side effect, so we warn for it.
Similar to your use of ?:, we warn for:
foo() || bar();
because || does not have a side effect. Note that C is not perl,
just like C is not ML :). If you want to use conditional code, using
an if statement is a perfectly reasonable thing to do.
> Since the spec allows ?: to work on void, it's obviously intended that
> it can be used as syntactic shorthand for an if statement. Why
> shouldn't it be usable for expressions which happen to be nonvoid, but
> where the side-effect is the more important part - printf/fprintf for
I'm not really sure what to say here. What the spec says is not the
issue. Warnings, again, are for valid code - erroneous code is
rejected by the compiler. Except for a couple of strange things, the
standard has nothing to say about warnings.
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