GNU Info

(emacs-lisp-intro.info)Body of mark-whole-buffer

---

Prev: mark-whole-buffer overview Up: mark-whole-buffer

---

Enter node , (file) or (file)node

Body of `mark-whole-buffer'
---------------------------

   The body of the `mark-whole-buffer' function consists of three lines
of code:

     (push-mark (point))
     (push-mark (point-max))
     (goto-char (point-min))

   The first of these lines is the expression, `(push-mark (point))'.

   This line does exactly the same job as the first line of the body of
the `simplified-beginning-of-buffer' function, which is written
`(push-mark)'.  In both cases, the Lisp interpreter sets a mark at the
current position of the cursor.

   I don't know why the expression in `mark-whole-buffer' is written
`(push-mark (point))' and the expression in `beginning-of-buffer' is
written `(push-mark)'.  Perhaps whoever wrote the code did not know
that the arguments for `push-mark' are optional and that if `push-mark'
is not passed an argument, the function automatically sets mark at the
location of point by default.  Or perhaps the expression was written so
as to parallel the structure of the next line.  In any case, the line
causes Emacs to determine the position of point and set a mark there.

   The next line of `mark-whole-buffer' is `(push-mark (point-max)'.
This expression sets a mark at the point in the buffer that has the
highest number.  This will be the end of the buffer (or, if the buffer
is narrowed, the end of the accessible portion of the buffer.  Note:
Narrowing and Widening, for more about
narrowing.)  After this mark has been set, the previous mark, the one
set at point, is no longer set, but Emacs remembers its position, just
as all other recent marks are always remembered.  This means that you
can, if you wish, go back to that position by typing `C-u C-<SPC>'
twice.

   (In GNU Emacs 21, the `(push-mark (point-max)' is slightly more
complicated than shown here.  The line reads

     (push-mark (point-max) nil t)

(The expression works nearly the same as before.  It sets a mark at the
highest numbered place in the buffer that it can.  However, in this
version, `push-mark' has two additional arguments.  The second argument
to `push-mark' is `nil'.  This tells the function it _should_ display a
message that says `Mark set' when it pushes the mark.  The third
argument is `t'.  This tells `push-mark' to activate the mark when
Transient Mark mode is turned on.  Transient Mark mode highlights the
currently active region.  It is usually turned off.)

   Finally, the last line of the function is `(goto-char
(point-min)))'.  This is written exactly the same way as it is written
in `beginning-of-buffer'.  The expression moves the cursor to the
minimum point in the buffer, that is, to the beginning of the buffer
(or to the beginning of the accessible portion of the buffer).  As a
result of this, point is placed at the beginning of the buffer and mark
is set at the end of the buffer.  The whole buffer is, therefore, the
region.