With the following mappings, you can press \c to change all C++ comments to C comments, or press \C to change all C comments to C++ comments (assuming you are using backslash for your <Leader> key).

Note: The mappings only handle single-line C comments.

For example, if you press \c then the following C++ code:

int i = 12;    // this is a comment
char c = 'A';  // and here is another comment

changes to use C comments:

int i = 12;    /* this is a comment */
char c = 'A';  /* and here is another comment */

Here are the mappings. You could put these in your vimrc:

" C++ //-comment to C /*-comment-*/
:noremap <Leader>c :%s://\(.*\):/*\1 */:<CR>

" C /*-single-line-*/ to C++ //-comment
:noremap <Leader>C :%s:/\*\(.\{-\}\)\s*\*/://\1:<CR>

CommentsEdit

I tested, and even though the "dodgy" comment said it didn't work, it did work on my setup with no modifications. If you have any problems using this tip, please leave a comment below with exactly what it did wrong so we can fix the tip! --Fritzophrenic 04:14, 13 July 2009 (UTC)

I just tried it and it failed because of something I don't understand about the "... Vim comment. When I removed the Vim comments, it worked fine. In more detail: Copy the four lines in the pre block to Vim and set up a test case. In Vim: use V movement to select the four lines, then y to copy, then @" to execute the copied commands. Bug: It doesn't work! Perhaps the comment on the first line masks out the remaining three lines??

Copying just the two :noremap lines and executing them caused it to work.

Note that an inline C comment with code following will cause trouble. Say:

    i = myfunc(a, /* b, */ c);

Converting the above to a C++ comment will eliminate the c);. JohnBeckett 07:47, 13 July 2009 (UTC)

You can't use @" to execute with the comments, or it will use the " like it was a register specification, since @" executes normal mode, not ex, commands. Using :@" (which you probably intended) works fine AFAICT.

Saving the commands (with the comments) to a file and then :source-ing it also works fine.

Good point about the inline C comments, maybe that was the original issue noted. Perhaps the mapping should replace the */ with a newline instead of simply removing it?

The second mapping would become:

:noremap <Leader>C :%s:/\*\(.\{-\}\)\s*\*/://\1\r:<CR>

--Fritzophrenic 14:56, 13 July 2009 (UTC)

Ah, yes. My brain said "the commands start with colon, therefore I can use @" rather than :@", but as you say the comment lines will be interpreted as normal mode commands. JohnBeckett 22:46, 13 July 2009 (UTC)