[GRASS5] 5.7: d.colors - problem with control sequence in tcltk version

Glynn Clements glynn.clements at virgin.net
Wed Sep 22 17:36:51 EDT 2004

Moritz Lennert wrote:

> Similarly to the problem with d.measure, I get the following output in the
> tcltk version of d.colors:
> - Unknown Command
> Seems that there is also a terminal command that doesn't work in tcltk.

The specific problem there is that d.colors tries to read from stdin:

        cur_char = getchar() & 0177 ;

[d.colors/interact.c, line 62.]

But stdin is closed (stdin is actually the pipe through which G_gui()
feeds the Tcl code to wish), so getchar() returns -1, so cur_char gets
set to 127 (0177, 0x7f). This isn't a valid "command" (i.e. key) for
d.colors, so it ends up in the default case of the switch statement:


                sprintf(buffer,"  %c - Unknown Command",cur_char) ;
                Write_message(2, buffer) ;
                break ;

Of course, the general problem is that d.colors is an interactive
program which requires a terminal (if it wasn't for the stdin issue,
you would still end up with curses dumping garbage into the text box),
but G_gui, d.m, tcltkgrass etc don't have any way of knowing that.

We could fix d.m and tcltkgrass by having separate "execute" and
"execute_term" commands (and changing the menu entries to use the
latter where necessary). The latter would record the fact that the
program requires a terminal so that, when you press the Run button, it
would would be started via xterm.

However, this won't work for the G_gui() case, as there isn't any way
for G_gui() to discover that the program requires a terminal. The only
thing which will fix that case is for the programs themselves to
indicate that they require a terminal before they call G_parser(). 
That would also eliminate the need for a separate execute_term

Glynn Clements <glynn.clements at virgin.net>

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