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[QUOTE="Arthur J. O'Dwyer, post: 1699259"]
[re: introducing a logical XOR operator]

Possibly dumb, and possibly OT, question: What if 'a' and/or 'b' are
doubles with the IEEE value NaN, that screws up comparisons?  Does

Well, a logical xor operator wouldn't add anything to the capabilities
of the language, but then neither does having a special operator for
subtraction.  I have, on occasion, run across situations where an XOR
operator would have been useful.  Christopher mentioned command-line
argument parsing, such as:

[...]
    switch (argv[i][j]) {
      case 'K': KNRStyle = 1; break;
      case 'A': AnsiStyle = 1; break;
    }
  [...]
  if (KNRStyle ^^ AnsiStyle)
    process(infp, outfp);
  else
    do_error("You must specify exactly one of -K, -A!\n");

Here the ^^ operator would capture the spirit of the condition better
than the != alternative, as well as being slightly more robust.  The
suggested alternative,

if (!KNRStyle != !AnsiStyle)

is IMO so obfuscated as to be actually worse than simply enumerating
the cases:

if (KNRStyle && !AnsiStyle || AnsiStyle && !KNRStyle)

I also submit for consideration, as I've done before, the usefulness
of logical operators when dealing with pointers:

struct btnode {
     int value;
     struct btnode *left;
     struct btnode *right;
  };

int bt_IsUselessBranch(struct btnode *p)
  {
      return (p->value == 0) && (p->left ^^ p->right);
  }

versus

return (p->value == 0) && (!(p->left) != !(p->right));

Of course, both cases are pretty ugly, here.  But I haven't yet
come up with a good example. ;-)
  And while I think it would have been cool if C had been designed
with a ^^ operator from the start, IMHO it's much too late now to
try adding it to the standard language.  C doesn't need any more
syntax, and even if it did, I don't think the new syntax would find
many willing users.  A new version of C would IMHO suffer the same
problems as C99 still suffers w.r.t. market share, only worse.
  Now, a *new* language... :-)

-Arthur[/i]
[/QUOTE]

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