I use the code from the following article to allow only a single instance of my programs (mostly written using Qt Framework) to run on Windows. Some programs (specially the ones which connect to a specific type of hardware or resource) need this limitation to avoid conflicts.
Please also note that this code is specific to Windows.
http://support.microsoft.com/en-us/kb/243953
#ifndef LimitSingleInstance_H
#define LimitSingleInstance_H
#include <windows.h>
//This code is from Q243953 in case you lose the article and wonder
//where this code came from.
class CLimitSingleInstance
{
protected:
DWORD m_dwLastError;
HANDLE m_hMutex;
public:
CLimitSingleInstance(TCHAR *strMutexName)
{
//Make sure that you use a name that is unique for this application otherwise
//two apps may think they are the same if they are using same name for
//3rd parm to CreateMutex
m_hMutex = CreateMutex(NULL, FALSE, strMutexName); //do early
m_dwLastError = GetLastError(); //save for use later...
}
~CLimitSingleInstance()
{
if (m_hMutex) //Do not forget to close handles.
{
CloseHandle(m_hMutex); //Do as late as possible.
m_hMutex = NULL; //Good habit to be in.
}
}
BOOL IsAnotherInstanceRunning()
{
return (ERROR_ALREADY_EXISTS == m_dwLastError);
}
};
#endif