Hi Bernhard,

> Starting Guide centered on our desired coordinates works already fine.
> Is there a possiblity that Guide opens only just once? (only one instance).
>
> That means if an instance of Guide is already opened and we send a
> command line then the already existing Guide window should be centered on
> our desired object and no second Guide window should be opened.
>
> Is this possible?

Hmmm... for this, you'd really want something a little different. If
you simply invoked Guide again, it'll just generate another instance of
the program; it won't simply affect the existing instance, which is what
you really want.

For that, what you'd really want would be some sort of interprocess
communication, i.e., "find thus-and-such window and send it thus-and-such
message." For simple situations, the following code will suffice. Save
it as, say, 'xtrol_g.c' and compile it, start up Guide, and run the
program you've just compiled as

xtrol_g 2204

If you look in the 'toolbar.dat' file, you will see that action 2204
corresponds to 'center on Mars'. When you run the above, Guide should,
in fact, recenter on Mars.

The program works by using the EnumWindows function from the Windows
API. This examines each window; if the window title starts with 'Guide
9.0', we assume we have the right one, and send it the command.

You can do a lot with this little code snippet. As you'll see,
'toolbar.dat' has a long list of possible commands. But you can run
into trouble if what you want to do is, say, tell Guide to center
on NGC 3141, or set the date/time to 2017 Jul 13 02:14:50. Still
looking into that one... Microsoft suggests nine different methods
for interprocess communication :

http://msdn.microsoft.com/en-us/library/windows/desktop/aa365574%28v=vs.85%29.aspx

The 'data copy' method looks somewhat promising for this situation,
though I've hit a rough spot or two in it thus far.

-- Bill

#include <windows.h>

BOOL CALLBACK enum_func( HWND hwnd, LPARAM lparam)
{
char title[80];

GetWindowText( hwnd, title, sizeof( title));
if( !memicmp( title, "Guide 9.0", 9))
PostMessage( hwnd, WM_COMMAND, lparam, 0);
return( TRUE);
}

int main( const int argc, const char **argv)
{
EnumWindows( enum_func, (LPARAM)atoi( argv[1]));
return( 0);
}