//make sure only one instance of the application can be open at a time

#define OBS_WINDOW_CLASS         TEXT("OBSWindowClass")

    HANDLE hOBSMutex = CreateMutex(NULL, TRUE, TEXT("OBSMutex"));

    if(GetLastError() == ERROR_ALREADY_EXISTS)// 如果已有互斥量存在 这里GetLastError则是CreateMutex的Error

    {

        hwndMain = FindWindow(OBS_WINDOW_CLASS, NULL);//获取该窗体句柄

        if(hwndMain)

            SetForegroundWindow(hwndMain);//设置焦点到程序窗口

        CloseHandle(hOBSMutex);//互斥量存在释放句柄并复位互斥量

        return ;

    }