qt怎么设置一个对象只实例化一次

1. 共享内存的方法
Unix: QSharedMemory "owns" the shared memory segment. When the last thread or process that has an instance of QSharedMemory attached to a particular shared memory segment detaches from the segment by destroying its instance of QSharedMemory, the Unix kernel release the shared memory segment. But if that last thread or process crashes without running the QSharedMemory destructor, the shared memory segment survives the crash.
（据说这种方法在Linux系统下会有一个内存释放的问题，在某种情况下会引起程序的异常或崩溃）

[cpp] view plain copy

// 确保只运行一次

QSystemSemaphore sema("JAMKey",1,QSystemSemaphore::Open);
sema.acquire();// 在临界区操作共享内存 SharedMemory

QSharedMemory mem("SystemObject");// 全局对象名
if (!mem.create(1))// 如果全局对象以存在则退出
{
QMessageBox::information(0, MESSAGEB