The usual Emacs comment commands assume that a comment can follow a line
of code. In Fortran, the standard comment syntax requires an entire
line to be just a comment. Therefore, Fortran mode replaces the
standard Emacs comment commands and defines some new variables.
Fortran mode can also handle a non-standard comment syntax where
comments start with `!' and can follow other text. Because only some
Fortran compilers accept this syntax, Fortran mode will not insert such
comments unless you have specified to do so in advance by setting the
variable `comment-start' to `"!"' (Note: Variables).
Align comment or insert new comment (`fortran-comment-indent').
Applies to nonstandard `!' comments only.
Turn all lines of the region into comments, or (with arg) turn
them back into real code (`fortran-comment-region').
`M-;' in Fortran mode is redefined as the command
`fortran-comment-indent'. Like the usual `M-;' command, it recognizes
an existing comment and aligns its text appropriately. If there is no
existing comment, a comment is inserted and aligned.
Inserting and aligning comments is not the same in Fortran mode as in
other modes. When a new comment must be inserted, a full-line comment
is inserted if the current line is blank. On a non-blank line, a
non-standard `!' comment is inserted if you previously specified you
wanted to use them. Otherwise a full-line comment is inserted on a new
line before the current line.
Non-standard `!' comments are aligned like comments in other
languages, but full-line comments are aligned differently. In a
standard full-line comment, the comment delimiter itself must always
appear in column zero. What can be aligned is the text within the
comment. You can choose from three styles of alignment by setting the
variable `fortran-comment-indent-style' to one of these values:
The text is aligned at a fixed column, which is the value of
`fortran-comment-line-column'. This is the default.
The text is aligned as if it were a line of code, but with an
additional `fortran-comment-line-column' columns of indentation.
Text in full-line columns is not moved automatically.
You can also specify the character to be used to indent within
full-line comments by setting the variable `fortran-comment-indent-char'
to the character you want to use.
Fortran mode introduces two variables `comment-line-start' and
`comment-line-start-skip', which do for full-line comments what
`comment-start' and `comment-start-skip' do for ordinary text-following
comments. Normally these are set properly by Fortran mode, so you do
not need to change them.
The normal Emacs comment command `C-x ;' has not been redefined. It
can therefore be used if you use `!' comments, but is useless in
Fortran mode otherwise.
The command `C-c ;' (`fortran-comment-region') turns all the lines
of the region into comments by inserting the string `C$$$' at the front
of each one. With a numeric arg, the region is turned back into live
code by deleting `C$$$' from the front of each line. You can control
the string used for the comments by setting the variable
`fortran-comment-region'. Note that here we have an example of a
command and a variable with the same name; the two uses of the name
never conflict because in Lisp and in Emacs it is always clear from the
context which one is referred to.
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