Question

I want to map \c to comment the current line in vim (add ‘// ‘ to before the first non-blank to the line) and \d to delete the ‘// ‘ at the beginning of line(uncomment).

I’ve added these two lines in my vimrc:

imap \c <Esc>:s/^/\/\/ <CR>j$a

imap \d <Esc>:s/^\/\/ /<CR>j$a

but when I call this in this line:

    for (int i = 0; i < n; i++)

then it is converted to:

//    for (int i = 0; i < n; i++)

but I want to convert it to:

    // for (int i = 0; i < n; i++)

one of the reasons I want this is that when I want vim to indent this line, it will add an extra tab at the beginning of the line and convert it to:

    //    for (int i = 0; i < n; i++)

what should I do? I thought that ^ refers to first non-blank character of line but it wasn’t true.

P.S: I’ve found these two commands, but I don’t know what are they doing. could you please explain them to me (because I need to remember them and they’re easier to remember when I know what are they). if any part of them is unnecessary please tell me:

imap \c <ESC>:s,^\(\s*\)[^/ \t]\@=,\1// ,e<CR>j$a

imap \d <ESC>:s,^\(\s*\)// \s\@!,\1,e<CR>j$a

Answer 1

About those commands you found:

imap \c :s,^(\s*)[^# \t]\@=,\1// ,ej$a

Let’s start with the pattern match, comparing it with your :s/^/\/\/ <CR>j$a.

• :s, is exactly equivalent to :s/ – you can choose a nonstandard seperator where it makes the expression more readable, so here using , instead of / means less escaping, and no confusion between the comment // and the seperator
• ^(\s*) matches the beginning of the line (same as yours) and any leading whitespace, capturing the whitespace so we can reuse it later
• [^# \t]\@= just requires some character other than space, tab or # before the line end, but doesn’t capture it (ie, that character won’t be replaced)
• ,\1// , replaces the matched string with the leading whitespace (\1 is whatever was captured by the (\s*) group) followed by //

---

For example:

^    void foo();

should match like so: ^(\s*)[^# \t]\@= -> ^( )(v@=)void foo();, ie, the first group matches the leading whitespace, and the next expression matches but doesn’t consume the v from void.
Then, \1// expands to:

^    // 

and the final substitution result is:

^    // void foo();`

(I’ve marked the start of line with ^ since the indentation is ambiguous otherwise)