How to match all C code comments in a file?

Question

I want to match (search) all C code comments in a file in e.g.

   enum {
       foo,
       /* Foo is so cool, why can't we all be more like foo? */
       bar,
       /* but bar is mysterious and suave, like the James Bond of enum 
          and variable names. */
       etc,

So, I want a regex that will match both the single and multiline C comments delimited by /* and */.

Answer 1

The problem with pure regex based solutions, is that there would be a few false-positives, like in:

/*bar*/

char const* p = "/*";

/* bar */

/// foo

char const* e = "*/";

/* in strings would be matched as well.

I though at first that we could get around it with [* and ]*, but unfortunately, they are also regex based.

Though, we can have the correct behaviour with {skip} parameter in search()

:echo search('/\*\_.\{-}\*/\|//' ,'',0,0, 'synIDattr(synID(line("."), col("."), 0), "name") =~ "\\cstring"')

which is best defined as a mapping

" for a mapping defined this way, we have to double the '\' before the '|' to express the _or_
nnoremap <silent> [< :<c-u>call search('/\*\_.\{-}\*/\\|//' ,'',0,0, 'synIDattr(synID(line("."), col("."), 0), "name") =~ "\\cstring"')<cr>

Answer 2

I already know but I searched the web and couldn't find the definitive answer for VIM (just every other regex language), and I won't remember this again in a week, so I am documenting it here.

And the answer is...

/\/\*\_.\{-}\*\/

Lemme break it down.

To match the first \* you have to escape both the \ and the * so that's \/\*

To match the end you have to do the same for *\ so that's \*\/ at the end.

You want to include everything between those, this is where it gets tricky. You can use \_.* to match everything between (the \_ makes it multiline), but this is too greedy and will match everything between the first \* and the last *\.

To make it non-greedy use \_.\{-} instead of \_.* (\{-} uses a "shortest match first" algorithm) and so we get the above vim search regex.