I once found this in a c++ long method while searching for optimizable loops and unnecessary processes, it was a rendering update for a skeletal animated actor, the method itself was a good 150 lines long total and in the midst of its implementation there was this while loop:

//The following block of code should not be executed anymore, keeping it around for fallback reasons
while(0)
{
    ... do about 20 lines of stuff...
}

Seeing this actually hung my brain for about a minute before I yelled "Who the F* doesn't know how to comment a block of code on C++?" to the whole office.

The perpetrator was no longer working for the company and was responsible for many ridiculous pieces of code of which this was one of the last that didn't get deleted and fell through the cracks.

Granted, the code didn't actually get executed and the compiler likely did away with the whole loop, but it was still blasphemous.

Was the code originally a while loop?

Granted, the code didn't actually get executed and the compiler likely did away with the whole loop, but it was still blasphemous.

Yep, it probably isn't even present in the executable. The main advantage of removing code this way is that the compiler still has to check its syntax is valid which can help keeping it usable if you ever need it back. Of course, chances are by the time you go back to the code the program behavior changed so much that the old code isn't useful anymore anyway =P

Was the code originally a while loop?

No, the while was added as a sort of /**/ block comment.
Personally I believe dead code like this should be outright deleted, especially if you have some subversion system in place, having to browse through dead code and in this case even maintain it is a huge waste of time in production.

some of this is an area where nestable block-comments would be useful sometimes.

granted, there is always #if 0 ... #endif, but still...

things get ugly with nested dead code

Yea, I wish C++ allowed: /*** /** /* */ **/ ***/, and so on. Sometimes I use /* */ for multiline comments (that's what it's for, after all) and trying to comment out several functions means I need to go and add a space after the stars: /* / * * / */

or, possibly alternate syntax:

/[[ ... ]]/

which could be nestable, and shouldn't likely interfere with any other valid constructions (and wouldn't break on documentation-comments for Doxygen or similar).

if I could have a wish-list, I might also add:

endianess specifiers for struct members;

triple-quoted strings or similar;

...

granted, there is always #if 0 ... #endif, but still...

I like #if 0. I have my editor setup to identify such "frozen code" blocks and highlight them in a different color (generally light gray or light blue, different from comments). I find it handy to temporarily remove large blocks of code for debugging or prototyping. I never leave this stuff after, though, it just looks ugly and confusing.

Sure, it could probably be argued that it's not using the preprocessor for its intended usage, but what the hell, it's an idiom now so who cares

I wouldn't mind a clean nested comment feature for C++, though. It should probably nest by default, anyway. What was the reason for not allowing /* /* */ */? Harder/impossible to parse or something? I doubt it so there must be some other explanation.