🚀 go-pugleaf

Slawomir Marczynski wrote:
> 
> Richard Baldwin (richard@ormesci.demon.co.uk) wrote:
> : >I've been striving for so long now to find a SAVE way to start only one
> : >instance of my C++ program under Windows NT and 95. As you might recall, this
> 
> : In CMainFrame
> : =============
> : BOOL CMainFrame::PreCreateWindow(CREATESTRUCT& cs)
> 
> There is also an example (I've forgotten this name) on BC5.01 CDROM
> with OWL instead MFC.
> 
> --
> Slawomir Marczynski (Mr)
> Institute of Physics, Technical University of Szczecin
> Al. Piastow 48/49, 70-310 Szczecin, Poland
> slawek@arcadia.inter.tuniv.szczecin.pl, tel:+(048-91)-494056

For Delphi programmers I have a solution that ask user in case of starting the 2nd time to switch 
to the first or to cancel:

Horst Schmid, http://ourworld.compuserve.com/homepages/Horst_Schmid


unit once; {Ask User to switch to the first Instance instead of starting a second}
{Simply add this Unit to your uses-Statement of your Delphi2.0-Project.dpr
 to prevent starting Your App. more than once!}

interface
const Titel:pchar='Warning'; {You can change this to whatever you want}
      Msg:String='App. %s is already running, switch to it?';
implementation
uses windows,sysutils,tlhelp32;

procedure SwitchToThisWindow(h1:hWnd; x:bool);stdCall; external user32 name 'SwitchToThisWindow';
{x=false: Size unchanged, x=true: normal size}

function EnumThreadWndProc(h1:hWnd;LPARAM:lParam):bool;stdCall;  {Callback}
var hp:word;
begin
  if IsWindowVisible(h1) then begin
    hp:=GetLastActivePopup(h1);
    if IsWindow(hp) then begin
      SwitchToThisWindow(hp,true);
      end end;
  EnumThreadWndProc:=true;
end;

var mHandle: THandle;    // Mutexhandle
    s:string;
    i:integer;
    b:bool;
    h,h2:tHandle;
    lppe: TProcessEntry32;
    lpte: TThreadEntry32;
    pid0,tid:dWord;
    x:array[0..255]of char;

Initialization     {called when App is started}
  s:=ParamStr(0);   {Progname as MutexName}
  i:=length(s);
  while (i>0) and (s[i]<>'\') do dec(i); {without Path}
  mHandle := CreateMutex(nil,True,pchar(copy(s,i+1,255)));
  if GetLastError = ERROR_ALREADY_EXISTS then begin   // App is running
    i:=MessageBox(0,pchar(Format(Msg,[copy(s,i+1,255)]))
     ,Titel,MB_ICONQUESTION+MB_OKCANCEL);
    if i=IDOK then begin   {find the other Task and bring to top}
      tid:=0;
      h:=CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS,0);
      lppe.dwSize:=SizeOf(lppe);
      b:=Process32First(h,lppe);
      pid0:=GetCurrentProcess;
      s:=s+#0; {make String to ASCIIZ}
      while b do begin {Proccess-Loop}
        if (StrComp(@s[1],lppe.szExeFile)=0)and(lppe.th32ProcessID<>pid0) then begin
          h2:=CreateToolhelp32Snapshot(TH32CS_SNAPTHREAD,0);
          lpte.dwSize:=SizeOf(lpte);
          b:=Thread32First(h2,lpte);
          tid:=0;
          while b do begin {Thread-Loop}
            if lpte.th32OwnerProcessID=lppe.th32ProcessID then begin
              tid:=lpte.th32ThreadID;
              EnumThreadWindows(tid,@EnumThreadWndProc,0) end;
            b:=Thread32Next(h2,lpte) end;
          end
        else b:=Process32Next(h,lppe) end;
      CloseHandle(h2);
      CloseHandle(h);
      end;
    halt;{Cancel second start. Delete this line if the the second Choice
     should be to start a second App.}
  end;

finalization {End of App:Delete Mutex}
  if mHandle <> 0 then CloseHandle(mHandle)
end.