Re: 'v' character instead of ACS_DARROW in xterm

[Thomas Dickey]

On Fri, Feb 22, 2008 at 01:54:33PM +0100, Katarina Machalkova wrote:
> Hi, ncurses hackers,
> 
> This is maybe dumb q., but neverethless:  I don't really understand why xterm
> keeps displaying 'v' character instead of down arrow (ACS_DARROW), similarly
> it displays '>' instead of right arrow and so on.  If I set 'TERM=linux', I
> can see ACS_*ARROW characters just fine.

Actually it would be the application using ncurses - I thought at first
that you might be referring to 'dialog', but a quick check shows it
displaying arrows.

That's because the arrow characters aren't in the acsc string for
xterm's terminal description, which is emulating a vt100/vt220.

Those arrow characters happen to be available to an application knowing
that it's running in a Unicode locale in a Unicode terminal (or for some
odd cases such as Linux console which may have provided those
characters).

When ncurses is relying on the terminal description, i.e., the acsc
string, it "knows" that it cannot draw those characters.  There are
wide-character interfaces using line-drawing characters, and for those
ncurses tries to use the known Unicode values if the locale encoding is
UTF-8.  (The ncurses test program demonstrates those - you might build a
copy and compare menus 'f' and 'F')

ncurses uses the terminal description for the narrow interface, arguably
because even if it "knows" what the Unicode values are, the developer
may intend a different mapping than ncurses' built-in table.  (Also note
that the table only defines codes corresponding to the predefined
ACS_xxx symbols).

-- 
Thomas E. Dickey <address@hidden>
http://invisible-island.net
ftp://invisible-island.net

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