使用ReadFile()时如何更改ReadFile的timeout

使用ReadFile()函数时，当在N秒内没有收到自己定义的数据包，则会timeout。那么N秒的具体时间如何定义？

用异步方式（OVERLAPPED）打开，即ReadFile()最后一个参数关联一个OVERLAPPED指针，然后用WaitForSingleObject去等待这个异步的句柄,即可实现。

WaitForSingleObject()函数的第二个参数，即可简单理解为timeout时间。

 

WaitForSingleObject的用法

DWORDWaitForSingleObject  (  HANDLEhHandle,   DWORDdwMilliseconds );

参数 hHandle是一个事件的句柄，第二个参数dwMilliseconds是时间间隔。如果时间是有信号状态返回 WAIT_OBJECT_0，如果时间超过 dwMilliseconds值但时间事件还是无信号状态则返回 WAIT_TIMEOUT 。

WaitForSingleObject函数用来检测hHandle事件的信号状态，当函数的执行时间超过dwMilliseconds就返回，但如果参数dwMilliseconds为INFINITE时函数将直到相应时间事件变成有信号状态才返回，否则就一直等待下去，直到WaitForSingleObject有返回直才执行后面的代码。

http://www.cnblogs.com/andyhere/archive/2008/10/20/1314803.html

 

程序实例：

<span style="font-size:14px;">/*API call:ReadFile
	"Returns: the report in InputReport.
	"Requires: a device handle returned by CreateFile
	"(for overlapped I/O, CreateFile must be called with FILE_FLAG_OVERLAPPED),
	"the Input report length in bytes returned by HidP_GetCaps,
	"and an overlapped structure whose hEvent member is set to an event object.
	*/

	if (ReadHandle != INVALID_HANDLE_VALUE)
		{
		Result = ReadFile 
		(ReadHandle, 
		InputReport, 
		Capabilities.InputReportByteLength, 
		&NumberOfBytesRead,
		(LPOVERLAPPED) &HIDOverlapped
		); 
		}
 
//	DisplayLastError("ReadFile: ") ;

	/*API call:WaitForSingleObject
	"Used with overlapped ReadFile.
	"Returns when ReadFile has received the requested amount of data or on timeout.
	"Requires an event object created with CreateEvent
	"and a timeout value in milliseconds.
	*/

	Result = WaitForSingleObject 
		(hEventObject, 
		20000);		// 这个时间就可以理解为timeout时间
		
	switch (Result)
	{
		case WAIT_OBJECT_0:
		{
			// 接收到自定义数据包处理程序
			break;
		}
		case WAIT_TIMEOUT:
		{
			// timeout处理程序
			break;
		}
	}	</span>

reference:http://bbs.eeworld.com.cn/thread-150077-1-1.html