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    <p>Unfortunately, <code>HANDLE</code>s are completely different beasts from <code>FILE*</code>s and file descriptors. The CRT ultimately handles files in terms of <code>HANDLE</code>s and associates those <code>HANDLE</code>s to a file descriptor. Those file descriptors in turn backs the structure pointer by <code>FILE*</code>.</p> <p>Fortunately, there is a section on <a href="http://msdn.microsoft.com/en-US/library/kdfaxaay.aspx" rel="noreferrer">this MSDN page</a> that describes functions that "provide a way to change the representation of the file between a <strong>FILE</strong> structure, a file descriptor, and a Win32 file handle":</p> <blockquote> <ul> <li><code>_fdopen</code>, <code>_wfdopen</code>: Associates a stream with a file that was previously opened for low-level I/O and returns a pointer to the open stream.</li> <li><code>_fileno</code>: Gets the file descriptor associated with a stream.</li> <li><code>_get_osfhandle</code>: Return operating-system file handle associated with existing C run-time file descriptor</li> <li><code>_open_osfhandle</code>: Associates C run-time file descriptor with an existing operating-system file handle.</li> </ul> </blockquote> <p>Looks like what you need is <a href="http://msdn.microsoft.com/en-US/library/bdts1c9x.aspx" rel="noreferrer"><code>_open_osfhandle</code></a> followed by <a href="http://msdn.microsoft.com/en-US/library/dye30d82.aspx" rel="noreferrer"><code>_fdopen</code></a> to obtain a <code>FILE*</code> from a <code>HANDLE</code>.</p> <p>Here's an example involving <code>HANDLE</code>s obtained from <code>CreateFile()</code>. When I tested it, it shows the first 255 characters of the file "test.txt" and appends " --- Hello World! --- " at the end of the file:</p> <pre><code>#include &lt;windows.h&gt; #include &lt;io.h&gt; #include &lt;fcntl.h&gt; #include &lt;cstdio&gt; int main() { HANDLE h = CreateFile("test.txt", GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0); if(h != INVALID_HANDLE_VALUE) { int fd = _open_osfhandle((intptr_t)h, _O_APPEND | _O_RDONLY); if(fd != -1) { FILE* f = _fdopen(fd, "a+"); if(f != 0) { char rbuffer[256]; memset(rbuffer, 0, 256); fread(rbuffer, 1, 255, f); printf("read: %s\n", rbuffer); fseek(f, 0, SEEK_CUR); // Switch from read to write const char* wbuffer = " --- Hello World! --- \n"; fwrite(wbuffer, 1, strlen(wbuffer), f); fclose(f); // Also calls _close() } else { _close(fd); // Also calls CloseHandle() } } else { CloseHandle(h); } } } </code></pre> <p>This should work for pipes as well.</p>
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    1. POIs there a Windows equivalent to fdopen for HANDLEs?
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