Nugetを見ればCSVHelperとか便利なものがありますが、ちょと自前でやらなくてはいけなかったので作りました。
処理内容は「Perl正規表現雑技」というサイトからいただきました。
感謝 
2018/2/1 追記
いくらか手直しして、こちらにソースを置きました。
https://github.com/sengokyu/csvreader-csvwriter-for-dot-net
概要
Streamオブジェクトを受け取り、CSVを1レコードずつ読み込んで返します。
特長
- 値中にあるカンマに対応しています。 "a,a" ===> a,a
- 値中にあるエスケープされたダブルクォートに対応しています。 "a,"",a" ===> a,",a
- 値中にある改行に対応しています。
使い方
// どこかにStreamオブジェクトがあったとしまして
using (var reader = new CSVReader(stream)) {
while (!reader.EndOfStream) {
var record = reader.ReadLine();
// ここで色々楽しいことをする
}
}
ソース
CSVReader.cs
/// <summary>
/// generic CSV reader
/// </summary>
public class CSVReader : IDisposable
{
private static readonly string END_OF_FILE = "\x1a";
private static readonly string DELIMITER = "\"";
private readonly StreamReader _reader;
public CSVReader(Stream inputStream, Encoding encoding)
{
_reader = new StreamReader(inputStream, encoding);
}
public IEnumerable<string> ReadLine()
{
var line = ReadSemanticLine();
if (line == null)
{
return null;
}
line = TrimRight(line);
line += ",";
var matches = Regex.Matches(line, "(\"[^\"]*(?:\"\"[^\"]*)*\"|[^,]*),");
return matches.Cast<Match>().Select(x => Dequote(x));
}
public bool EndOfStream
{
get
{
return _reader.EndOfStream;
}
}
private String TrimRight(string src)
{
return Regex.Replace(src, "(?:\x0D\x0A|[\x0D\x0A])?$", "", RegexOptions.Singleline);
}
private string Dequote(Match match)
{
var s = match.Groups[1].Value;
var quoted = Regex.Match(s, "^\"(.*)\"$", RegexOptions.Singleline);
if (quoted.Success)
{
return quoted.Groups[1].Value.Replace("\"\"", "\"");
}
else
{
return s;
}
}
private string ReadSemanticLine()
{
if (_reader.EndOfStream)
{
return null;
}
var line = _reader.ReadLine();
if (line == null | line == END_OF_FILE || line.Length == 0)
{
return null;
}
while (!HasEnoughQuote(line) && !_reader.EndOfStream)
{
// Complete missing line break.
line += "\n" + _reader.ReadLine();
}
return line;
}
private bool HasEnoughQuote(string line)
{
return (Regex.Matches(line, DELIMITER).Count % 2) == 0;
}
#region IDisposable Support
private bool disposedValue = false; // To detect redundant calls
protected virtual void Dispose(bool disposing)
{
if (!disposedValue)
{
if (disposing)
{
if (_reader != null)
{
_reader.Dispose();
}
}
// TODO: free unmanaged resources (unmanaged objects) and override a finalizer below.
// TODO: set large fields to null.
disposedValue = true;
}
}
// TODO: override a finalizer only if Dispose(bool disposing) above has code to free unmanaged resources.
// ~CSVReader() {
// // Do not change this code. Put cleanup code in Dispose(bool disposing) above.
// Dispose(false);
// }
// This code added to correctly implement the disposable pattern.
public void Dispose()
{
// Do not change this code. Put cleanup code in Dispose(bool disposing) above.
Dispose(true);
// TODO: uncomment the following line if the finalizer is overridden above.
// GC.SuppressFinalize(this);
}
#endregion
}
テスト
CSVReaderTests.cs
[TestClass]
public class CSVReaderTests
{
[TestMethod]
public void TestReadLineReturnsSimpleResult()
{
var csvsample = "a,\"b\",c\r\nd,e,\r\n";
using (var instance = CreateInstance(csvsample))
{
var result = instance.ReadLine();
Check.That(result).HasSize(3);
Check.That(result).ContainsExactly("a", "b", "c");
result = instance.ReadLine();
Check.That(result).HasSize(3);
Check.That(result).ContainsExactly("d", "e", "");
}
}
[TestMethod]
public void TestReadLineTreatMultilieCsv()
{
var csvsample = "a,b,\"c\n\nc\"\r\n";
using (var instance = CreateInstance(csvsample))
{
var result = instance.ReadLine();
Check.That(result).HasSize(3);
Check.That(result).ContainsExactly("a", "b", "c\n\nc");
}
}
[TestMethod]
public void TestReadLineUnescapeQuote()
{
var csvsample = "\"a,a\",\"b,\"\"c\"\r\n";
using (var instance = CreateInstance(csvsample))
{
var result = instance.ReadLine();
Check.That(result).HasSize(2);
Check.That(result).ContainsExactly("a,a", "b,\"c");
}
}
[TestMethod]
public void TestEndOfStream()
{
var csvsample = "a,b,c\r\na,b,c\r\n";
using (var instance = CreateInstance(csvsample))
{
Check.That(instance.EndOfStream).IsFalse();
instance.ReadLine();
Check.That(instance.EndOfStream).IsFalse();
instance.ReadLine();
Check.That(instance.EndOfStream).IsTrue();
}
}
private CSVReader CreateInstance(string src)
{
return new CSVReader(CreateStream(src), Encoding.UTF8);
}
private Stream CreateStream(string src)
{
return new MemoryStream(Encoding.UTF8.GetBytes(src));
}
}