Prevend double launching of app

What is the code to prevend someone from launching more than 1 instance of my programme ? In simpler terms, it means at any time, only 1 abc.exe is running and not 2.
tyfingAsked:
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smurffConnect With a Mentor Commented:
Try this

implementation

var
  mHandle: THandle; // Mutexhandle
  Projekt: string;

initialization
  Project := '';          // define your project-name here

  mHandle := CreateMutex(nil, True, PChar(Projekt));
  if GetLastError = ERROR_ALREADY_EXISTS then begin
    showMessage('Project ' + Project + ' is still running');
    halt;                               // kill the second instance
  end;

finalization                            // alt end free the mHandle
  if mHandle <> 0 then CloseHandle(mHandle)
end.


regards
Smurff
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MadmarlinCommented:
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tyfingAuthor Commented:
sorry, i'm a newbie...can u put the code into a button ?
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tyfingAuthor Commented:
where is the 'Begin'  ?
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smurffCommented:
In the actual project1.dpr copy the code, this is out of one I already have.

program Mdiapp;

uses
  Forms,Windows,Dialogs,
  MAIN in 'MAIN.PAS' {MainForm},
  CHILDWIN in 'CHILDWIN.PAS' {MDIChild},
  about in 'about.pas' {AboutBox};

{$R *.RES}

var
 mHandle: THandle; // Mutexhandle
 Project: string;

begin
  Application.Initialize;
  Application.CreateForm(TMainForm, MainForm);
  Application.CreateForm(TAboutBox, AboutBox);
  Project := 'SmurffsProggy';
  mHandle := CreateMutex(nil, True, PChar(Project));
  if GetLastError = ERROR_ALREADY_EXISTS then begin
   MessageDlg('Application already exists, this instance will now close',mtError,[mbOK],0);
   halt;                               // kill the second instance
  end
  else
  Application.Run;
   if mHandle <> 0 then CloseHandle(mHandle);
end.


To view the project file in the ide goto the delphi menu Project then select view source.

Hope this helps mate,
Regards
Smurff
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smurffCommented:
Also as a newbie you should know about some sites that would have this kind of code on it so you can save your points on EE. Try these first before asking Qs.


www.torry.net and click on tips
www.delphi3000.com
www.delphifaq.com
www.delphipages.com

and theres lots more and these have links to them.
Just a note, if you know them then just ignore me :)
regards
Smurff
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tongaliteCommented:
Hi
here's a routine from another forum
Thanks to RLord:
T.

 
   
 
How to prevent multiple instances  
One of the best way (and the fastest) is with CreateMutex
--------------------------------

Example:
--------------------------------
program project1;

uses....


begin
// make sure this comes before everything else
CreateMutex(nil, false, ’Someproject’);
if GetLastError = ERROR_ALREADY_EXISTS then begin
SendMessage(HWND_BROADCAST,
RegisterWindowMessage(’Someproject’),
0,
0);
Halt(0);
end;
// and other stuff...
end.  
 
 
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smurffCommented:
tongalite,

isnt that what Ive put :)

S.
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tongaliteCommented:
Hi smurff..

errrr...well I guess it is now I come to look at your offering... blame sun glare on my screen :-)
T.
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smurffCommented:
lol the more help the better i suppose :)

Regards
S.
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