Line up C block comment continuation lines. Various heuristics are used to handle most of the common comment styles. Some examples:

          /*                 /**               /*
           * text             * text             text
           */                 */               */

          /* text            /*                /**
             text            ** text            ** text
          */                 */                 */

          /**************************************************
           * text
           *************************************************/

          /**************************************************
              Free form text comments:
           In comments with a long delimiter line at the
           start, the indentation is kept unchanged for lines
           that start with an empty comment line prefix.  The
           delimiter line is whatever matches the
           comment-start-skip regexp.
          **************************************************/

The style variable c-comment-prefix-regexp is used to recognize the comment line prefix, e.g. the ‘*’ that usually starts every line inside a comment.

Works with: The c syntactic symbol.

Line up a comment-only line according to the style variable c-comment-only-line-offset. If the comment is lined up with a comment starter on the previous line, that alignment is preserved.

— User Option: c-comment-only-line-offset

This style variable specifies the extra offset for the line. It can contain an integer or a cons cell of the form

               (non-anchored-offset . anchored-offset)

where non-anchored-offset is the amount of offset given to non-column-zero anchored lines, and anchored-offset is the amount of offset to give column-zero anchored lines. Just an integer as value is equivalent to (value . -1000).

Works with: comment-intro.

Line up a comment in the “K&R region” with the declaration. That is the region between the function or class header and the beginning of the block. E.g:

          int main()
          /* Called at startup. */  <- c-lineup-knr-region-comment
          {
            return 0;
          }

Return nil if called in any other situation, to be useful in list expressions.

Works with: comment-intro.