The comment column is stored in the variable comment-column. You
can set it to a number explicitly. Alternatively, the command C-x ;
(set-comment-column) sets the comment column to the column point is
at. C-u C-x ; sets the comment column to match the last comment
before point in the buffer, and then does a M-; to align the
current line's comment under the previous one. Note that C-u - C-x ;
runs the function kill-comment as described above.
The variable comment-column is per-buffer: setting the variable
in the normal fashion affects only the current buffer, but there is a
default value which you can change with setq-default.
See section Local Variables. Many major modes initialize this variable for the
current buffer.
The comment commands recognize comments based on the regular
expression that is the value of the variable comment-start-skip.
Make sure this regexp does not match the null string. It may match more
than the comment starting delimiter in the strictest sense of the word;
for example, in C mode the value of the variable is "/\\*+
*", which matches extra stars and spaces after the `/*' itself.
(Note that `\\' is needed in Lisp syntax to include a `\' in
the string, which is needed to deny the first star its special meaning
in regexp syntax. See section Syntax of Regular Expressions.)
When a comment command makes a new comment, it inserts the value of
comment-start to begin it. The value of comment-end is
inserted after point, so that it will follow the text that you will insert
into the comment. In C mode, comment-start has the value
"/* " and comment-end has the value " */".
The variable comment-multi-line controls how C-M-j
(indent-new-comment-line) behaves when used inside a comment. If
comment-multi-line is nil, as it normally is, then the
comment on the starting line is terminated and a new comment is started
on the new following line. If comment-multi-line is not
nil, then the new following line is set up as part of the same
comment that was found on the starting line. This is done by not
inserting a terminator on the old line, and not inserting a starter on
the new line. In languages where multi-line comments work, the choice
of value for this variable is a matter of taste.
The variable comment-indent-function should contain a function
that will be called to compute the indentation for a newly inserted
comment or for aligning an existing comment. It is set differently by
various major modes. The function is called with no arguments, but with
point at the beginning of the comment, or at the end of a line if a new
comment is to be inserted. It should return the column in which the
comment ought to start. For example, in Lisp mode, the indent hook
function bases its decision on how many semicolons begin an existing
comment, and on the code in the preceding lines.
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