blocks|key|4851309|text|您还没有发布用于BUF_SIZE常量的值，但请确保它是卷扇区大小的整数倍。这是使用无缓冲文件流时的常见陷阱。CreateFile()+documentation中的FILE_FLAG_NO_BUFFERING文档中这样写道：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4851310|4851311|使用FILE_FLAG_NO_BUFFERING标志成功处理使用CreateFile打开的文件有严格的要求，有关详细信息，请参阅File+Buffering。|blockquote|4851312|4851313|4851314|关于文件缓冲注释的页面：|4851315|4851316|如前所述，当使用FILE_FLAG_NO_BUFFERING打开的文件时，应用程序必须满足某些要求。以下详细说明适用：|4851317|4851318|4851319|4851320|文件访问大小(包括重叠结构中的可选文件偏移量)的字节数必须是卷扇区大小的整数倍。例如，如果扇区大小为512字节，则应用程序可以请求512、1,024、1,536或2,048字节的读取和写入，但不能请求335、981或7,171字节的读取和写入。用于读取和写入操作的|unordered-list-item|4851321|文件访问缓冲区地址应与物理扇区对齐，这意味着在内存中的地址是卷物理扇区大小的整数倍。根据磁盘的不同，可能不会强制执行此要求。|4851322|4851323|应用程序开发人员应注意市场上正在推出的物理介质扇区大小为4,096字节的新型存储设备。|BOLD|4851324|在我的系统上，这个值是4K，一次读取任何小于4K的值都会产生错误。在Microsoft的许多代码示例中，1K是默认的缓冲区大小，因此改编示例通常会导致未缓冲的I/O出现错误。|4851325|编辑：还要确保将OVERLAPPED结构的所有成员清零。不要将Internal和InternalHigh成员设置为0。始终按照以下方式清除OVERLAPPED结构：|4851326|OVERLAPPED+overlapped;
ZeroMemory(&overlapped,+sizeof(OVERLAPPED));|code-block|syntax|javascript|4851327|然后，您可以设置文件偏移量和事件句柄。|4851328|编辑：还要考虑以下有关ReadFile()的lpNumberOfBytesRead参数的注意事项|4851329|4851330|如果这是一个异步操作，则对此参数使用NULL，以避免潜在的错误结果。..。有关更多信息，请参阅备注部分。|4851331|4851332|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/windows/desktop/aa363858.aspx|1|http://msdn.microsoft.com/en-us/library/windows/desktop/cc644950.asp|2|http://msdn.microsoft.com/en-us/library/windows/desktop/aa365467.aspx^0|8|8|1I|C|2A|M|1I|Q|0|0|0|1S|E|1|0|0|0|0|0|0|0|0|0|0|0|0|0|17|0|0|0|2|8|A|V|8|14|C|1X|A|0|0|0|0|2|B|A|M|J|B|A|2|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1V|8|@$9|1W|A|1X|B|C]|$9|1Y|A|1Z|B|C]|$9|20|A|21|B|C]]|D|@$9|22|A|23|1|24]]|E|$]]|$1|F|3|-4|5|6|7|25|8|@]|D|@]|E|$]]|$1|G|3|H|5|I|7|26|8|@]|D|@$9|27|A|28|1|29]]|E|$]]|$1|J|3|-4|5|6|7|2A|8|@]|D|@]|E|$]]|$1|K|3|-4|5|6|7|2B|8|@]|D|@]|E|$]]|$1|L|3|M|5|6|7|2C|8|@]|D|@]|E|$]]|$1|N|3|-4|5|6|7|2D|8|@]|D|@]|E|$]]|$1|O|3|P|5|I|7|2E|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|2F|8|@]|D|@]|E|$]]|$1|R|3|-4|5|6|7|2G|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|2H|8|@]|D|@]|E|$]]|$1|T|3|U|5|V|7|2I|8|@]|D|@]|E|$]]|$1|W|3|X|5|V|7|2J|8|@]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|2K|8|@]|D|@]|E|$]]|$1|Z|3|10|5|6|7|2L|8|@$9|2M|A|2N|B|11]]|D|@]|E|$]]|$1|12|3|13|5|6|7|2O|8|@]|D|@]|E|$]]|$1|14|3|15|5|6|7|2P|8|@$9|2Q|A|2R|B|11]|$9|2S|A|2T|B|C]|$9|2U|A|2V|B|C]|$9|2W|A|2X|B|C]|$9|2Y|A|2Z|B|C]]|D|@]|E|$]]|$1|16|3|17|5|18|7|30|8|@]|D|@]|E|$19|1A]]|$1|1B|3|1C|5|6|7|31|8|@]|D|@]|E|$]]|$1|1D|3|1E|5|6|7|32|8|@$9|33|A|34|B|11]|$9|35|A|36|B|C]|$9|37|A|38|B|C]]|D|@$9|39|A|3A|1|3B]]|E|$]]|$1|1F|3|-4|5|6|7|3C|8|@]|D|@]|E|$]]|$1|1G|3|1H|5|I|7|3D|8|@]|D|@]|E|$]]|$1|1I|3|-4|5|6|7|3E|8|@]|D|@]|E|$]]|$1|1J|3|-4|5|6|7|3F|8|@]|D|@]|E|$]]]|1K|$1L|$5|1M|1N|1O|E|$1P|1Q]]|1R|$5|1M|1N|1O|E|$1P|1S]]|1T|$5|1M|1N|1O|E|$1P|1U]]]]

You haven't posted what value you're using for the <code>BUF_SIZE</code> constant, but make sure it's an integer multiple of the volume sector size. This is a common pitfall when using unbuffered file streams. The documentation for <code>FILE_FLAG_NO_BUFFERING</code> in the <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/aa363858.aspx" rel="nofollow"><code>CreateFile()</code> documentation</a> says:

<blockquote>
 There are strict requirements for successfully working with files opened with CreateFile using the FILE_FLAG_NO_BUFFERING flag, for details see <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/cc644950.asp" rel="nofollow">File Buffering</a>.
</blockquote>

The page on file buffering notes:

<blockquote>
 As previously discussed, an application must meet certain requirements when working
 with files opened with FILE_FLAG_NO_BUFFERING. The following specifics apply:
 
 <ul>
 <li>File access sizes, including the optional file offset in the OVERLAPPED structure, if
 specified, must be for a number of bytes that is an integer multiple of the volume sector 
 size. For example, if the sector size is 512 bytes, an application can request reads and
 writes of 512, 1,024, 1,536, or 2,048 bytes, but not of 335, 981, or 7,171 bytes.</li>
 <li>File access buffer addresses for read and write operations should be physical sector 
 aligned, which means aligned on addresses in memory that are integer multiples of the
 volume's physical sector size. Depending on the disk, this requirement may not be
 enforced.</li>
 </ul>
 
 Application developers should take note of new types of storage devices being
 introduced into the market with a physical media sector size of 4,096 bytes.
</blockquote>

On my system, this value is 4K and reading anything smaller than 4K at a time produces errors. In many of Microsoft's code samples, 1K is the default buffer size, so adapting examples often leads to errors with unbuffered I/O.

Edit: also make sure to zero out all members of the <code>OVERLAPPED</code> structure. You don't set the <code>Internal</code> and <code>InternalHigh</code> members to 0. Always clear the <code>OVERLAPPED</code> structure in the following manner:

<pre><code>OVERLAPPED overlapped;
ZeroMemory(&amp;overlapped, sizeof(OVERLAPPED));
</code></pre>

Then, you can set the file offset and event handle.

Edit: also consider the following note about the <code>lpNumberOfBytesRead</code> parameter to <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/aa365467.aspx" rel="nofollow"><code>ReadFile()</code></a>:

<blockquote>
 Use NULL for this parameter if this is an asynchronous operation to avoid potentially erroneous results. [...] For more information, see the Remarks section.
</blockquote>

blocks|key|814482|text|我建议仔细注意重叠的Offset和OffsetHigh字段，特别是在读取一个大小超过32位无符号整数边界的文件时。我相信你面临的问题潜伏在那里。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|814483|entityMap^0|A|6|H|A|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

I would suggest paying careful attention to the overlapped's <code>Offset</code> and <code>OffsetHigh</code> fields, especially when reading a file with the size crossing the boundary of 32-bit unsigned integer. I believe the problem you are facing lurks there.

In my c++ application I'm rying to read iso file asynchronous by <code>createfile</code> - with overlapped flag and after it - <code>readfile</code>.
however when I try this code on a simple file (txt file for example) it works. but when I run this code on iso file - it fails.
I saw in MSDN that compressed file can only read by readfile sync calls. does iso files is in this category?
if yes - do you have other suggestion how to read iso files async?

this is my code:

<pre><code>int _tmain(int argc, _TCHAR* argv[])
{


HANDLE hFile;
 DWORD NumberOfBytesRead = 0, dw;
 BYTE *buf = (BYTE*)malloc(BUF_SIZE*sizeof(BYTE));
 OVERLAPPED overlapped;
 overlapped.Offset = overlapped.OffsetHigh = 0; 
 memset(buf, 0, 1024);

overlapped.hEvent = CreateEvent(NULL, true, false, NULL); 
if(NULL == overlapped.hEvent)
 printf("error");

hFile = CreateFile("xxx.iso",
 GENERIC_READ,
 FILE_SHARE_READ,
 NULL,
 OPEN_EXISTING,
 FILE_FLAG_OVERLAPPED | FILE_ATTRIBUTE_NORMAL | FILE_FLAG_NO_BUFFERING , 
 NULL);



if (hFile == INVALID_HANDLE_VALUE)
 printf("invalid hfile\n");

 int i; 
 i= ReadFile(hFile,
 buf,
 BUF_SIZE,
 &amp;NumberOfBytesRead,
 &amp;overlapped);
 if( GetLastError() == ERROR_IO_PENDING)
 {


 dw = WaitForSingleObject(overlapped.hEvent, INFINITE);
 if(dw == WAIT_OBJECT_0)
 if (GetOverlappedResult(hFile,&amp;overlapped,&amp;NumberOfBytesRead, TRUE) != 0) 
 {
 if (NumberOfBytesRead != 0) 
 {
 printf("!!!\n");
 }

 }

 }
</code></pre>

thanks

Readfile async - iso files c++

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在我的c++应用程序中，我尝试通过createfile异步读取iso文件-带有重叠标志，然后是readfile。但是，当我在一个简单的文件(例如txt文件)上尝试这段代码时，它可以工作。但是当我在iso文件上运行这段代码时-它失败了。我在MSDN中看到压缩文件只能通过readfile sync调用读取。iso文件是否在...

问异步读文件- iso文件c++
EN

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问异步读文件- iso文件c++EN