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    <p><strike><a href="https://stackoverflow.com/questions/3206391/directly-reading-large-binary-file-in-c-w-out-copying/3206424#3206424">dtb's answer</a> is an even better way</strike> (actually, it has to copy the data as well, no gain there), but I just wanted to point out that to extract ushort values from a byte array you should be using <a href="http://msdn.microsoft.com/en-us/library/system.bitconverter.aspx" rel="nofollow noreferrer"><code>BitConverter</code></a> not <code>BinaryReader</code></p> <p>EDIT: example code for p/invoking <a href="http://pinvoke.net/default.aspx/kernel32/ReadFile.html" rel="nofollow noreferrer">ReadFile</a>:</p> <pre><code>[DllImport("kernel32.dll", SetLastError=true)] [return:MarshalAs(UnmanagedType.Bool)] static extern bool ReadFile(IntPtr handle, IntPtr buffer, uint numBytesToRead, out uint numBytesRead, IntPtr overlapped); [DllImport("kernel32.dll", SetLastError=true)] [return:MarshalAs(UnmanagedType.Bool)] static extern bool SetFilePointerEx(IntPtr hFile, long liDistanceToMove, out long lpNewFilePointer, uint dwMoveMethod); unsafe bool read(FileStream fs, ushort[] buffer, int offset, int count) { if (null == fs) throw new ArgumentNullException(); if (null == buffer) throw new ArgumentNullException(); if (offset &lt; 0 || count &lt; 0 || offset + count &gt; buffer.Length) throw new ArgumentException(); uint bytesToRead = 2 * count; if (bytesToRead &lt; count) throw new ArgumentException(); // detect integer overflow long offset = fs.Position; SafeFileHandle nativeHandle = fs.SafeFileHandle; // clears Position property try { long unused; if (!SetFilePositionEx(nativeHandle, offset, out unused, 0); fixed (ushort* pFirst = &amp;buffer[offset]) if (!ReadFile(nativeHandle, new IntPtr(pFirst), bytesToRead, out bytesToRead, IntPtr.Zero) return false; if (bytesToRead &lt; 2 * count) return false; offset += bytesToRead; return true; } finally { fs.Position = offset; // restore Position property } } </code></pre>
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    1. COBen, thanks, I had a look at BitConverter(), but I'm not sure I understand your suggestion. BinaryReader() is for reading from files (which I'm doing), and BitConverter() is for converting existing byte[] arrays to other types. Isn't BinaryReader().ReadUInt16() equivalent to reading in the bytes to an array and calling BitConverter().ToUInt16()? Maybe I'm misunderstanding...
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    2. COBut `ReadUInt16` only reads one element at a time... which is a lousy way to do I/O.
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    3. CONo it isn't. BinaryReader is responsible for converting the bytes of an underlying stream to the requested type, not reading the bytes from IO in the first place.
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