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(elisp)Columns

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Counting Columns
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   The column functions convert between a character position (counting
characters from the beginning of the buffer) and a column position
(counting screen characters from the beginning of a line).

   These functions count each character according to the number of
columns it occupies on the screen.  This means control characters count
as occupying 2 or 4 columns, depending upon the value of `ctl-arrow',
and tabs count as occupying a number of columns that depends on the
value of `tab-width' and on the column where the tab begins.  Note:
Usual Display.

   Column number computations ignore the width of the window and the
amount of horizontal scrolling.  Consequently, a column value can be
arbitrarily high.  The first (or leftmost) column is numbered 0.

 - Function: current-column
     This function returns the horizontal position of point, measured in
     columns, counting from 0 at the left margin.  The column position
     is the sum of the widths of all the displayed representations of
     the characters between the start of the current line and point.

     For an example of using `current-column', see the description of
     `count-lines' in Note: Text Lines.

 - Function: move-to-column column &optional force
     This function moves point to COLUMN in the current line.  The
     calculation of COLUMN takes into account the widths of the
     displayed representations of the characters between the start of
     the line and point.

     If column COLUMN is beyond the end of the line, point moves to the
     end of the line.  If COLUMN is negative, point moves to the
     beginning of the line.

     If it is impossible to move to column COLUMN because that is in
     the middle of a multicolumn character such as a tab, point moves
     to the end of that character.  However, if FORCE is non-`nil', and
     COLUMN is in the middle of a tab, then `move-to-column' converts
     the tab into spaces so that it can move precisely to column
     COLUMN.  Other multicolumn characters can cause anomalies despite
     FORCE, since there is no way to split them.

     The argument FORCE also has an effect if the line isn't long
     enough to reach column COLUMN; if it is `t', that means to add
     whitespace at the end of the line to reach that column.

     If COLUMN is not an integer, an error is signaled.

     The return value is the column number actually moved to.