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Old 01-14-2001, 03:31 AM
whatever_ whatever_ is offline
Join Date: Jan 2001
Posts: 36
Default Command Line Arguments?

I am limiting the instances of my program to one.. When a 2nd instance is being executed it is terminated and the first instance is being focused.

But how do I pass the command line arguments from the 2nd instance to the 1st?
ATM I am copying the arguments from 2nd instance to clipboard and pasting back in 1st...
But this solution isn't very good because clipbrd is bein overwritten

so any1 knows a better solution?
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Old 01-14-2001, 10:07 PM
medialight medialight is offline
Junior Member
Join Date: Nov 2000
Posts: 4
Default RE: Command Line Arguments?

I have some suggestions for you:

1). Try to do the same, but with files
2). Try to move all lines from the ClipBoard to TStrinList and then add it back
3). or

Kind Regards,
Serge M.
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Old 01-15-2001, 02:04 AM
Lapince Lapince is offline
Senior Member
Join Date: Jan 2001
Posts: 163
Default RE: Command Line Arguments?

Here's the best way for me to do so... It's an article published in UNDU April 1998... If you don't want to read the article, just copy the unit included in it... I used it many times, and it's perfect, and you don't have to overwrite data in clipboard...
If you want more details, mail me (
The article :

For many programs, having more than one instance running at the same time isn't a problem. It may even be a desirable feature, in SDI applications like Notepad, for instance. Often, though, the program will read and write data files (or registry keys) in a way which will cause corruption if another copy is launched, or it may simply not make any sense to have multiple instances running. In these cases it is valuable to have a simple mechanism to detect and control instance launches, especially with Windows 98 and its single-click launch interface.

Under 16 bit Windows, the solution was simple; Just examine the previous instance global variable to see if a copy is already running, and do the right thing. Under Win32, things are a bit more complicated. Several solutions are available on the Web, including one on the Borland Tips page, but I still felt compelled to write my own for several reasons. First, I needed to transmit the command line parameters of a second launch attempt to the primary instance in one program I wrote (it processes BMP files dragged onto its Explorer icon). Second, I wanted a plug-in unit which required minimal alteration from one program to the next, and little or no foolery in my DPR file. Third, I wanted it to be secure, reliable, and fast; In particular, it should run before any other VCL code initializes or allocates anything.

To meet the first requirement, I used WM_COPYDATA on the command line string. This in turn required me to get a window handle from the primary instance to use as a target for the message. FindWindow handles this nicely, but I couldn't use the automatic application window or any other standard window of the application, because of the third requirement.

The second requirement led me to place all of the code into a unit which is simply placed in the DPR "uses" clause. The actual instance management code runs in the unit's initialization. Global variables in the interface part provide the event hook and passed data storage.

Due to the third requirement, the unit must be the very first unit used by the DPR, and could not use any other application unit. In particular, almost every unit is likely to use Forms, and Forms is normally the first unit used by a DPR, but Forms sets up and initializes the whole Application framework.

The result of all this is the InstanceManager unit below. Simply make it the first unit in your program's DPR's uses list, and edit the constant declarations to fit your needs. Note that by using the same string constant for two or more different programs, you can create a "family" of executables which share instance management - I use this ability in a timeclock program, which not only should not run more than once, but cannot run at the same time as its administative utility. Also, this unit doesn't just prevent a second instance from running. It can call a notification event, which can decide on a case-by-case basis whether to allow the other instance to run, perhaps by examining the command line.

unit InstanceManager;

{Notes: make InstanceManager the *very first* unit in your program's USES
clause. To take advantage of the notification and launch-string, put a
method with no parameters in one of your forms and assign it to triggerProc.
Once triggerProc is called, rcvStr contains the command line of the launch

If the only reaction you want is to bring the first instance to the front,
just put a method like the following in your main form, and in the form's
OnCreate set InstanceManager.triggerProc:=ToFront;

procedure TForm1.ToFront;

If you don't have a dependable main form, make ToFront a class procedure of
any old class.}

{ Customize these constants before using }
const UniqueAppName = 'Unique application name';
AppNotifyValue: integer = 0;

var rcvStr: string;
rcvValue: integer;
ForbidOtherInstance: boolean = True;
triggerProc: procedure of object;


uses Windows, SysUtils, Messages;

var mutex, thisWnd: HWND;
IMWndClass: TWndClassA;
mustHalt: boolean;

function IMWndProc(HWindow: HWnd; Message, WParam: Longint; LParam: Longint): Longint; stdcall;
if Message=WM_COPYDATA then
rcvStr := StrPas(PCOPYDATASTRUCT(lParam).lpData);
rcvValue := PCOPYDATASTRUCT(lParam).dwData;
if Assigned(triggerProc) then triggerProc;
Result := Ord(ForbidOtherInstance);
Result := DefWindowProc(hWindow, Message, WParam, LParam);


FillChar(IMWndClass, SizeOf(IMWndClass), 0);
IMWndClass.lpfnWndProc := @IMWndProc;
IMWndClass.hInstance := HINSTANCE;
IMwndClass.lpszClassName := 'TInstanceManager';
if Windows.RegisterClass(IMWndClass) = 0 then RaiseLastWin32Error;
mutex := CreateMutex(nil, True, UniqueAppName);
if GetLastError = ERROR_ALREADY_EXISTS then
mustHalt := True;
if WaitForSingleObject(mutex, 5000)=WAIT_OBJECT_0 then
thisWnd := FindWindow(IMwndClass.lpszClassName, UniqueAppName);
if thisWnd = 0 then RaiseLastWin32Error;
CopyData.dwData := AppNotifyValue;
CopyData.lpData := CmdLine;
CopyData.cbData := StrLen(CmdLine);
mustHalt := (SendMessage(thisWnd,WM_COPYDATA,0,Integer(@CopyDa ta))>0);
thisWnd := 0;
if mustHalt then Halt;
thisWnd := CreateWindow(IMwndClass.lpszClassName,UniqueAppNam e,0,0,0,0,0,0,0,hInstance, nil);
if thisWnd = 0 then RaiseLastWin32Error;

if thisWnd>0 then DestroyWindow(thisWnd);

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