Go to the previous, next section.

 what-line

The  what-line command tells you the number of the line in which the cursor is located. The function illustrates the use of the  save-restriction and  save-excursion commands. Here is the text of the function in full:

(defun what-line ()
  "Print the current line number (in the buffer) of point."
  (interactive)
  (save-restriction
    (widen)
    (save-excursion
      (beginning-of-line)
      (message "Line %d"
               (1+ (count-lines 1 (point)))))))

The function has a documentation line and is interactive, as you would expect. The next two lines use the functions  save-restriction and  widen .

The  save-restriction special form notes whatever narrowing is in effect, if any, in the current buffer and restores that narrowing after the code in the body of the  save-restriction has been evaluated.

The  save-restriction special form is followed by  widen . This function undoes any narrowing the current buffer may have had when  what-line was called. (The narrowing that was there is the narrowing that  save-restriction remembers.) This widening makes it possible for the line counting commands to count from the beginning of the buffer. Otherwise, they would have been limited to counting within the accessible region. Any original narrowing is restored just before the completion of the function by the  save-restriction special form.

The call to  widen is followed by  save-excursion , which saves the location of the cursor (i.e., of point) and of the mark, and restores them after the code in the body of the  save-excursion uses the  beginning-of-line function to move point.

(Note that the  (widen) expression comes between  save-restriction and  save-excursion . When you write the two  save- @dots{ } expressions in sequence, write  save-excursion outermost.)

The last two lines of the  what-line function are functions to count the number of lines in the buffer and then print the number in the echo area.

(message "Line %d"
         (1+ (count-lines 1 (point)))))))

The  message function prints a one-line message at the bottom of the Emacs screen. The first argument is inside of quotation marks and is printed as a string of characters. However, it may contain `%d', `%s', or `%c' to print arguments that follow the string. `%d' prints the argument as a decimal, so the message will say something such as `Line 243'.

The number that is printed in place of the `%d' is computed by the last line of the function:

(1+ (count-lines 1 (point)))

What this does is count the lines from the first position of the buffer, indicated by the  1 , up to  (point) , and then add one to that number. (The  1+ function adds one to its argument.) We add one to it because line 2 has only one line before it, and  count-lines counts only the lines before the current line.

After  count-lines has done it job, and the message has been printed in the echo area, the  save-excursion restores point and mark to their original positions; and  save-restriction restores the original narrowing, if any.

Go to the previous, next section.