C#,正则表达式:如何解析逗号分隔值,其中某些值可能引用包含逗号的字符串本身

Question

在C#中,使用Regex该类,如何解析以逗号分隔的值,其中某些值可能引用包含逗号的字符串？

using System ;
using System.Text.RegularExpressions ;

class  Example
    {
    public static void Main ( )
        {
        string  myString  =  "cat,dog,\"0 = OFF, 1 = ON\",lion,tiger,'R = red, G = green, B = blue',bear" ;
        Console.WriteLine ( "\nmyString is ...\n\t" + myString + "\n" ) ;
        Regex   regex  =  new Regex  (  "(?<=,(\"|\')).*?(?=(\"|\'),)|(^.*?(?=,))|((?<=,).*?(?=,))|((?<=,).*?$)"  )  ;
        Match   match  =  regex.Match ( myString ) ;
        int j = 0 ;
        while ( match.Success )
            {
            Console.WriteLine ( j++ + " \t" + match ) ;
            match  =  match.NextMatch() ;
            }
        }
    }

输出(部分)如下所示:

0       cat
1       dog
2       "0 = OFF
3        1 = ON"
4       lion
5       tiger
6       'R = red
7        G = green
8        B = blue'
9       bear

但是,所需的输出是:

0       cat
1       dog
2       0 = OFF, 1 = ON
3       lion
4       tiger
5       R = red, G = green, B = blue
6       bear

Answer 1

试试这个正则表达式:

"[^"\r\n]*"|'[^'\r\n]*'|[^,\r\n]*

    Regex regexObj = new Regex(@"""[^""\r\n]*""|'[^'\r\n]*'|[^,\r\n]*");
    Match matchResults = regexObj.Match(input);
    while (matchResults.Success) 
    {
        Console.WriteLine(matchResults.Value);
        matchResults = matchResults.NextMatch();
    }

.OUPUTS:

• 猫
• 狗
• "0 = OFF,1 = ON"
• 狮子
• 虎
• 'R =红色,G =绿色,B =蓝色'
• 熊

注意:此正则表达式解决方案适用于您的情况,但我建议您使用像FileHelpers这样的专用库.

Answer 2

为什么不听从专家的意见,不要推出自己的CSV解析器.

你的第一个想法是,"我需要在引号内处理逗号."

你的下一个想法是,"哦,废话,我需要在引号内处理引号.转义引号.双引号.单引号......"

这是一条通向疯狂的道路.不要自己写.找到一个具有广泛的单元测试覆盖率的图书馆,该图书馆覆盖了所有的硬件,并为您经历了地狱.对于.NET,请使用免费和开源的FileHelpers库.

Answer 3

它不是正则表达式,但我使用Microsoft.VisualBasic.FileIO.TextFieldParser来完成csv文件.是的,在C#应用程序中添加对Microsoft.VisualBasic的引用可能会有点奇怪,甚至可能有点脏,但是嘿它有效.

Answer 4

啊,RegEx.现在你有两个问题.;)

我使用了一个标记器/解析器,因为它非常简单,更重要的是,它更易于阅读以便以后进行维护.

这有效,例如:

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Text;

class Program
{
    static void Main(string[] args)
    {
        string myString = "cat,dog,\"0 = OFF, 1 = ON\",lion,tiger,'R = red, G = green,     B = blue',bear"; 
        Console.WriteLine("\nmyString is ...\n\t" + myString + "\n");
        CsvParser parser = new CsvParser(myString);

        Int32 lineNumber = 0;
        foreach (string s in parser)
        {
            Console.WriteLine(lineNumber + ": " + s);
        }

        Console.ReadKey();
    }
}

internal enum TokenType
{
    Comma,
    Quote,
    Value
}

internal class Token
{
    public Token(TokenType type, string value)
    {
        Value = value;
        Type = type;
    }

    public String Value { get; private set; }
    public TokenType Type { get; private set; }
}

internal class StreamTokenizer : IEnumerable<Token>
{
    private TextReader _reader;

    public StreamTokenizer(TextReader reader)
    {
        _reader = reader;    
    }

    public IEnumerator<Token> GetEnumerator()
    {
        String line;
        StringBuilder value = new StringBuilder();

        while ((line = _reader.ReadLine()) != null)
        {
            foreach (Char c in line)
            {
                switch (c)
                {
                    case '\'':
                    case '"':
                        if (value.Length > 0)
                        {
                            yield return new Token(TokenType.Value, value.ToString());
                            value.Length = 0;
                        }
                        yield return new Token(TokenType.Quote, c.ToString());
                        break;
                    case ',':
                       if (value.Length > 0)
                        {
                            yield return new Token(TokenType.Value, value.ToString());
                            value.Length = 0;
                        }
                        yield return new Token(TokenType.Comma, c.ToString());
                        break;
                    default:
                        value.Append(c);
                        break;
                }
            }

            // Thanks, dpan
            if (value.Length > 0) 
            {
                yield return new Token(TokenType.Value, value.ToString()); 
            }
        }
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

internal class CsvParser : IEnumerable<String>
{
    private StreamTokenizer _tokenizer;

    public CsvParser(Stream data)
    {
        _tokenizer = new StreamTokenizer(new StreamReader(data));
    }

    public CsvParser(String data)
    {
        _tokenizer = new StreamTokenizer(new StringReader(data));
    }

    public IEnumerator<string> GetEnumerator()
    {
        Boolean inQuote = false;
        StringBuilder result = new StringBuilder();

        foreach (Token token in _tokenizer)
        {
            switch (token.Type)
            {
                case TokenType.Comma:
                    if (inQuote)
                    {
                        result.Append(token.Value);
                    }
                    else
                    {
                        yield return result.ToString();
                        result.Length = 0;
                    }
                    break;
                case TokenType.Quote:
                    // Toggle quote state
                    inQuote = !inQuote;
                    break;
                case TokenType.Value:
                    result.Append(token.Value);
                    break;
                default:
                    throw new InvalidOperationException("Unknown token type: " +    token.Type);
            }
        }

        if (result.Length > 0)
        {
            yield return result.ToString();
        }
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

Answer 5

只需添加我今天早上工作的解决方案.

var regex = new Regex("(?<=^|,)(\"(?:[^\"]|\"\")*\"|[^,]*)");

foreach (Match m in regex.Matches("<-- input line -->"))
{
    var s = m.Value; 
}

如您所见,您需要每行调用regex.Matches().然后它将返回一个MatchCollection,其具有与列相同数量的项目.显然,每个匹配的Value属性是已解析的值.

这仍然是一项正在进行中的工作,但它很乐意解析CSV字符串,如:

2,3.03,"Hello, my name is ""Joshua""",A,B,C,,,D