>you may be surprised to find out that Win32 apps (and by extension all
>programs written with Delphi 2.0) *always* see hPrevInst=0.  This foils
>the traditional test of:

>{ in project source }
>begin
>    if hPrevInst = 0 then begin
>            { this program isn't running elsewhere... but in Win32
>              it may be! }
>    end
>    else
>            messagedlg('I''m already running!', mtinformation, [mbok], 0);
>end;

>This was pretty frustrating in my screen saver, which performs this test
>successfully in Win31, but winds up getting run several time in Win32
>because each instance thinks that it's the only one.
>    If you search the Win32 help files (using the grossly obese Find
>function) for "hprevinstance" you'll find a Knowledge Base article which
>discusses this and provides some suggestions.  Rather than quote the
>article which doesn't give too much guidance, I'll provide my version of
>their Win32 solution:

>program foobar;

>uses
>  windows;  { needed for declarations of ATOM functions }

>{$R *.RES}

>var
>   hMyAtom  :longint;
>begin
>    { look for a unique string ATOM }
>    hMyAtom := GlobalFindAtom('MyUniqueString');

>    if hMyAtom = 0 then begin
>            { the ATOM wasn't found so run the program }

>            { create the ATOM so that other instances won't load }
>            hMyAtom := globaladdatom('MyUniqueString');

>            {
>            do something, such as running the program
>            }

>            { delete the ATOM so that this program can be run again }
>            globaldeleteatom(hMyAtom);
>   end;
>end.

>This works pretty well under all Win32 systems.  Any other suggestions
>along these lines would be welcome.

>                                            Fritz

>"I'll gently raise and softly call,    | Fritz Lowrey
> Goodnight my friends, and joy to all."| Internet: jlow...@ucs.usc.edu
>   "A Parting Glass", Irish Traditional|

> On Tue, 12 Mar 1996 19:29:45 GMT, jlow...@ucs.usc.edu (Fritz Lowrey)
> wrote:

> >       Folks,
> >       For those who write program which only allow themselves to be run once,
> >and use the "hPrevInst" variable from the project source to determine this,

> >you may be surprised to find out that Win32 apps (and by extension all
> >programs written with Delphi 2.0) *always* see hPrevInst=0.  This foils
> >the traditional test of:

> >{ in project source }
> >begin
> >       if hPrevInst = 0 then begin
> >               { this program isn't running elsewhere... but in Win32
> >                 it may be! }
> >       end
> >       else
> >               messagedlg('I''m already running!', mtinformation, [mbok], 0);
> >end;

> >This was pretty frustrating in my screen saver, which performs this test
> >successfully in Win31, but winds up getting run several time in Win32
> >because each instance thinks that it's the only one.
> >       If you search the Win32 help files (using the grossly obese Find
> >function) for "hprevinstance" you'll find a Knowledge Base article which
> >discusses this and provides some suggestions.  Rather than quote the
> >article which doesn't give too much guidance, I'll provide my version of
> >their Win32 solution:

> >program foobar;

> >uses
> >  windows;     { needed for declarations of ATOM functions }

> >{$R *.RES}

> >var
> >   hMyAtom  :longint;
> >begin
> >       { look for a unique string ATOM }
> >       hMyAtom := GlobalFindAtom('MyUniqueString');

> >       if hMyAtom = 0 then begin
> >               { the ATOM wasn't found so run the program }

> >               { create the ATOM so that other instances won't load }
> >               hMyAtom := globaladdatom('MyUniqueString');

> >               {
> >               do something, such as running the program
> >               }

> >               { delete the ATOM so that this program can be run again }
> >               globaldeleteatom(hMyAtom);
> >   end;
> >end.

> >This works pretty well under all Win32 systems.  Any other suggestions
> >along these lines would be welcome.

> >                                               Fritz

> >"I'll gently raise and softly call,    | Fritz Lowrey
> > Goodnight my friends, and joy to all."| Internet: jlow...@ucs.usc.edu
> >   "A Parting Glass", Irish Traditional|

> This is how I've been doing it...

> procedure tmyclass.create(sender:tobject);
> var
>         tempcaption:string;
> begin
>         tempcaption:=caption;
>         caption:=''; {do this to keep from finding yourself}
>         if findwindow(myclass,tempcaption) then halt;
>         caption:=tempcaption;
> end;

> Zane Rathwick
> Indigo Software
> Za...@aol.com