• Daniel Murphy <yebbliesnospam gmail.com> Jan 22 2010

Daniel Murphy <yebbliesnospam gmail.com> writes:

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