请各位帮说说异步串口通讯时WriteFile的工作原理

[fjliningcd]

memset( &m_OverlappedWrite, 0, sizeof(LAPPED ) );
m_OverlappedWrite.hEvent = CreateEvent( NULL, TRUE, FALSE, NULL);
if (!WriteFile (m_hComm,lpBuf,nCount,&writtenCount,&m_OverlappedWrite))
{
if ( GetLastError() == ERROR_IO_PENDING ) {
WaitForSingleObject OverlappedWrite.hEvent, 1000 );

}
}
为什么程序总是进入if中执行

[rwdx]

因为写操作是异步完成的, 所以会立即返回, 当后台写操作完成后会将m_OverlappedWrite.hEvent事件对象设置为激发状态

[sxslyy]

楼上说的对,异步方式会立即返回,其错误提示是ERROR_IO_PENDING,但这已不代表出错了,而是为一个标识信息,WaitForSingleObject OverlappedWrite.hEvent, 1000 );才是等待串口写操作的正真完成时将事件信号设为有效,以便可以进行下一次写操作!

[duyhui]

异步方式不是用返回值来判断的，要用事件机制

[zhangnanonnet]

异步方式是用WaitCommEvent(idComDev,&dwEvtMask,&os);来等待事件的变化
if (WaitForSingleObject(os.hEvent,MAXTIMEOUT)==WAIT_TIMEOUT)
{
CloseHandle(os.hEvent);
return false;
}
超时会退出