How to check if an application is already running - cppbuilder

A great little function that is used to check if an application is already running. Change the mutex string to an unique value for each application that requires it.

C++ Code:
//---------------------------------------------------------------------------
//  Function: CheckDuplicate
//  Reason: To check if an application is already running.
//  Usage: 
//  bool running = CheckDuplicate();
//  if (running)
//  {
//      ShowMessage("You cannot run two instances of this application");
//      this->Close();
//  }
//---------------------------------------------------------------------------
bool CheckDuplicate()
{
    /* Change the ABCDEF-0123456789 value to a random string */
    HANDLE hMutex = ::CreateMutex(NULL, FALSE, "ABCDEF-0123456789");
    bool isRunning = (GetLastError() == ERROR_ALREADY_EXISTS);
    if (hMutex) ::ReleaseMutex(hMutex);
    return isRunning;
}
//---------------------------------------------------------------------------

Example of usage (cppbuilder project):
//---------------------------------------------------------------------------
#include <vcl.h>
#pragma hdrstop
//---------------------------------------------------------------------------
bool CheckDuplicate();
//---------------------------------------------------------------------------
USEFORM("Unit1.cpp", Form1);
//---------------------------------------------------------------------------
WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
{
    try
    {
         // Don't run if we're already running
         if (CheckDuplicate()) return -1;
         Application->Initialize();
         Application->Title = "My App";
         Application->CreateForm(__classid(TForm1), &Form1);
         Application->Run();
    }
    catch (Exception &exception)
    {
         Application->ShowException(&exception);
    }
    catch (...)
    {
         try
         {
             throw Exception("");
         }
         catch (Exception &exception)
         {
             Application->ShowException(&exception);
         }
    }
    return 0;
}
//---------------------------------------------------------------------------
bool CheckDuplicate()
{
    HANDLE hMutex = ::CreateMutex(NULL, FALSE, "MY-APPLICATION-1234");
    bool isRunning = (GetLastError() == ERROR_ALREADY_EXISTS);
    if (hMutex) ::ReleaseMutex(hMutex);
    return isRunning;
}
//---------------------------------------------------------------------------

You can download a complete project example (built with Borland C++ Builder 6) here.