これは、構造化ファイルで遊んでいるときに作成した小さなクラスです。これは、危険にさらされることを恥ずかしがっていた当時、私が見つけた最速の方法でした（これは、私が交換して同等のパフォーマンスを維持しようとしていたものでした.）
using System;
using System.Collections.Generic;
using System.IO;
using System.Runtime.InteropServices;
namespace PersonalUse.IO {
public sealed class RecordReader<T> : IDisposable, IEnumerable<T> where T : new() {
const int DEFAULT_STREAM_BUFFER_SIZE = 2 << 16; // default stream buffer (64k)
const int DEFAULT_RECORD_BUFFER_SIZE = 100; // default record buffer (100 records)
readonly long _fileSize; // size of the underlying file
readonly int _recordSize; // size of the record structure
byte[] _buffer; // the buffer itself, [record buffer size] * _recordSize
FileStream _fs;
T[] _structBuffer;
GCHandle _h; // handle/pinned pointer to _structBuffer
int _recordsInBuffer; // how many records are in the buffer
int _bufferIndex; // the index of the current record in the buffer
long _recordPosition; // position of the record in the file
/// <overloads>Initializes a new instance of the <see cref="RecordReader{T}"/> class.</overloads>
/// <summary>
/// Initializes a new instance of the <see cref="RecordReader{T}"/> class.
/// </summary>
/// <param name="filename">filename to be read</param>
public RecordReader(string filename) : this(filename, DEFAULT_STREAM_BUFFER_SIZE, DEFAULT_RECORD_BUFFER_SIZE) { }
/// <summary>
/// Initializes a new instance of the <see cref="RecordReader{T}"/> class.
/// </summary>
/// <param name="filename">filename to be read</param>
/// <param name="streamBufferSize">buffer size for the underlying <see cref="FileStream"/>, in bytes.</param>
public RecordReader(string filename, int streamBufferSize) : this(filename, streamBufferSize, DEFAULT_RECORD_BUFFER_SIZE) { }
/// <summary>
/// Initializes a new instance of the <see cref="RecordReader{T}"/> class.
/// </summary>
/// <param name="filename">filename to be read</param>
/// <param name="streamBufferSize">buffer size for the underlying <see cref="FileStream"/>, in bytes.</param>
/// <param name="recordBufferSize">size of record buffer, in records.</param>
public RecordReader(string filename, int streamBufferSize, int recordBufferSize) {
_fileSize = new FileInfo(filename).Length;
_recordSize = Marshal.SizeOf(typeof(T));
_buffer = new byte[recordBufferSize * _recordSize];
_fs = new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.None, streamBufferSize, FileOptions.SequentialScan);
_structBuffer = new T[recordBufferSize];
_h = GCHandle.Alloc(_structBuffer, GCHandleType.Pinned);
FillBuffer();
}
// fill the buffer, reset position
void FillBuffer() {
int bytes = _fs.Read(_buffer, 0, _buffer.Length);
Marshal.Copy(_buffer, 0, _h.AddrOfPinnedObject(), _buffer.Length);
_recordsInBuffer = bytes / _recordSize;
_bufferIndex = 0;
}
/// <summary>
/// Read a record
/// </summary>
/// <returns>a record of type T</returns>
public T Read() {
if(_recordsInBuffer == 0)
return new T(); //EOF
if(_bufferIndex < _recordsInBuffer) {
// update positional info
_recordPosition++;
return _structBuffer[_bufferIndex++];
} else {
// refill the buffer
FillBuffer();
return Read();
}
}
/// <summary>
/// Advances the record position without reading.
/// </summary>
public void Next() {
if(_recordsInBuffer == 0)
return; // EOF
else if(_bufferIndex < _recordsInBuffer) {
_bufferIndex++;
_recordPosition++;
} else {
FillBuffer();
Next();
}
}
public long FileSize {
get { return _fileSize; }
}
public long FilePosition {
get { return _recordSize * _recordPosition; }
}
public long RecordSize {
get { return _recordSize; }
}
public long RecordPosition {
get { return _recordPosition; }
}
public bool EOF {
get { return _recordsInBuffer == 0; }
}
public void Close() {
Dispose(true);
}
void Dispose(bool disposing) {
try {
if(disposing && _fs != null) {
_fs.Close();
}
} finally {
if(_fs != null) {
_fs = null;
_buffer = null;
_recordPosition = 0;
_bufferIndex = 0;
_recordsInBuffer = 0;
}
if(_h.IsAllocated) {
_h.Free();
_structBuffer = null;
}
}
}
#region IDisposable Members
public void Dispose() {
Dispose(true);
}
#endregion
#region IEnumerable<T> Members
public IEnumerator<T> GetEnumerator() {
while(_recordsInBuffer != 0) {
yield return Read();
}
}
#endregion
#region IEnumerable Members
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
return GetEnumerator();
}
#endregion
} // end class
} // end namespace
使用する:
using(RecordReader<CPP_STRUCT_DEF> reader = new RecordReader<CPP_STRUCT_DEF>(path)) {
foreach(CPP_STRUCT_DEF record in reader) {
// do stuff
}
}
（ここではかなり新しいです。投稿するには多すぎないことを願っています...クラスに貼り付けただけで、コメントなどを切り捨てて短くすることはありませんでした。）