Why use #if 0 for block commenting out?

Question

Reverse engineering code and I'm kind of appalled at the style, but I wanted to make sure there's no good reason for doing these things....

Is it just me or is this a horrible coding style

if ( pwbuf ) sprintf(username,"%s",pwbuf->pw_name);
else sprintf(username,"%d",user_id);

And why wrap code not intended for compilation in an

#if 0
....
#endif

Instead of comments?

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EDIT: So as some explained below, this is due to the possibility to flummox /* */ which I didn't realize.

But I still don't understand, why not just use your programming environment tools or favorite text editor's macro's to block comment it out using "//"

wouldn't this be MUCH more straightforward and easy to know to visually skip?

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Am I just inexperienced in C and missing why these things might be a good idea -- or is there no excuse, and I'm justified in feeling irritated at how ugly this code is?

Answer 1

if ( pwbuf ) sprintf(username,"%s",pwbuf->pw_name);
else sprintf(username,"%d",user_id);

Idiomatic and concise. If it got touched more than 2 or 3 times, I would bracket and next-line it. It's not very maintainable if you add logging information or other conditions.

#if 0
....
#endif

Good to turn on blocks of debug code or not. Also, would avoid compilation errors related to trying to block comment this sort of thing out:

/* line comment */
...
/* line comment again */

Since C block comments don't nest.

Answer 2

As far as block commenting using // is concerned, one reason that I can think of is that, should you check that code into your source control system, the blame log will show you as the last editor for those lines of code. While you probably want the commenting to be attributed to you, at the same time the code itself is also being attributed to you. Sure, you can go back and look at previous revisions if you need to check the blame log for the "real" author of the code, but it would save time if one preserved that information in the current revision.

Answer 3

points above noted. But monitors being widescreen and all, these days, I sort of don't mind

if (pwbuf) sprintf(username,"%s",pwbuf->pw_name);
else       sprintf(username,"%d",user_id);

Always seem to have too much horizontal space, and not enough vertical space on my screen!

Also, if the code block already has preprocessor directives, don't use #if 0; if the code already has block comments, don't use /* */. If it already has both, either resort to an editor that has a ctrl+/, to comment out lots of lines. If not, you're stuffed, delete the code outright!

Answer 4

Comments are comments. They describe the code.

Code that's being excluded from compilation is code, not comments. It will often include comments, that describe the code that isn't being compiled, for the moment/

They are two distinct concepts, and forcing the same syntax strikes me as being a mistake.

Answer 5

Obviously, everyone has their own opinions on this sort of thing. So here's mine:

I would never write code like the above, and would think less of anyone who did. I can't count the number of times people think it's ok to get away without scope braces, and then been bitten by it.

Putting the control statement on the same line as the code block is even worse; the lack of indenting makes it harder to see the flow control whilst reading. Once you've been coding for a few years, you get used to being able to read and interpret code quickly and accurately, so long as you can rely on certain visual cues. Circumventing these cues for "special cases" means that the reader has to stop and do a double-take, for no good reason.

#if (0), on the other hand, is ok during development, but should be removed once code is "stable" (or at least replace 0 with some meaningful preprocessor symbol name).