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copied!<p>I've been bitten by this, too, in the context of crash logging.</p> <p><code>FILE_FLAG_WRITE_THROUGH</code> only guarantees that the data you're sending gets sent to the <em>filesystem</em> before <code>WriteFile</code> returns; it doesn't guarantee that it's actually sent to the physical device. So, for example, if you execute a <code>ReadFile</code> after a <code>WriteFile</code> on a handle with this flag, you're guaranteed that the read will return the bytes you wrote, whether it got the data from the filesystem cache or from the underlying device.</p> <p>If you want to guarantee that the data has been written to the device, then you need <code>FILE_FLAG_NO_BUFFERING</code>, with all the attendant extra work. Those writes have to be aligned, for example, because the buffer is going all the way down to the device driver before returning.</p> <p>The Knowledge Base has a <a href="http://support.microsoft.com/kb/99794" rel="noreferrer">terse but informative article</a> on the difference.</p> <p>In your case, if the parent process is going to outlive the child, then you can:</p> <ol> <li>Use the <code>CreatePipe</code> API to create an inheritable, anonymous pipe.</li> <li>Use <code>CreateFile</code> to create a file with <code>FILE_FLAG_NO_BUFFERING</code> set.</li> <li>Provide the writable handle of the pipe to the child as its STDOUT.</li> <li>In the parent process, read from the readable handle of the pipe into aligned buffers, and write them to the file.</li> </ol>

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