bearophile Wrote:
> Ali:
> > We've been bitten by the following bug recently in C code:
> > uint flag = 0x1;
> > uint flags;
> >
> > if (flags | flag) {
> > dout.writefln("oops");
> > }
> >
> > The programmer intended &.
> > It is (almost?) always an error to use | in a conditional.
>
> Why do you think it's almost always an error?
>
> I have seen more than one time a related bug in C code (once written by me
> and other times written by other people):
> if (foo & bar) {...
>
> instead of:
> if (foo && bar) {...
>
> To avoid this kind of bug you can disallow integers in conditionals
> (requiring something like a ! or == 0 to turn an integral value in a boolean)
> as Java (and partially Pascal), or you can remove the && || from the language
> and replace them with "and" and "or", so it becomes easy to tell them apart
> from bitwise operators. I like the second way.
>
> Bye,
> bearophile
The difference between those two use cases is that (a & b) is commonly used to
check if a bit has been set. (a | b) yields the same result as (a || b) when
used in a conditional.
Is there any valid use for (a | b) as a 'truth' value?
Daniel
