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Reading and Writing CSV Files in C#

, 4 Jul 2012 CPOL 573.7K 69
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Here's some lightweight C# code for reading and writing CSV files.

Introduction

A common requirement is to have applications share data with other programs. Although there are interfaces available to work with, for example, Microsoft Excel data files, this approach is generally complex, involves a fair amount of overhead, and requires that support libraries accompany your application.

Comma-Separated Values (CSV) Files

A much simpler way to have your application share data is by reading and writing Comma-Separated Values (CSV) files. CSV files can easily be read and written by many programs, including Microsoft Excel.

For the most part, reading and writing CSV files is trivial. As the name suggestions, a CSV file is simply a plain text file that contains one or more values per line, separated by commas. Each value is a field (or column in a spreadsheet), and each line is a record (or row in a spreadsheet).

However, there is slightly more work involved. Double quotes are used to wrap values that contain commas so that the commas are not interpreted as a value separator. The same is also done for values that contain double quotes. In addition, two double quotes together signify a double quote in the value and not a value separator.

So this seems like a perfect task for a handy little C# class. Listing 1 shows my CsvFileWriter and CsvFileReader classes. 

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

namespace ReadWriteCsv
{
    /// <summary>
    /// Class to store one CSV row
    /// </summary>
    public class CsvRow : List<string>
    {
        public string LineText { get; set; }
    }

    /// <summary>
    /// Class to write data to a CSV file
    /// </summary>
    public class CsvFileWriter : StreamWriter
    {
        public CsvFileWriter(Stream stream)
            : base(stream)
        {
        }

        public CsvFileWriter(string filename)
            : base(filename)
        {
        }

        /// <summary>
        /// Writes a single row to a CSV file.
        /// </summary>
        /// <param name="row">The row to be written</param>
        public void WriteRow(CsvRow row)
        {
            StringBuilder builder = new StringBuilder();
            bool firstColumn = true;
            foreach (string value in row)
            {
                // Add separator if this isn't the first value
                if (!firstColumn)
                    builder.Append(',');
                // Implement special handling for values that contain comma or quote
                // Enclose in quotes and double up any double quotes
                if (value.IndexOfAny(new char[] { '"', ',' }) != -1)
                    builder.AppendFormat("\"{0}\"", value.Replace("\"", "\"\""));
                else
                    builder.Append(value);
                firstColumn = false;
            }
            row.LineText = builder.ToString();
            WriteLine(row.LineText);
        }
    }

    /// <summary>
    /// Class to read data from a CSV file
    /// </summary>
    public class CsvFileReader : StreamReader
    {
        public CsvFileReader(Stream stream)
            : base(stream)
        {
        }

        public CsvFileReader(string filename)
            : base(filename)
        {
        }

        /// <summary>
        /// Reads a row of data from a CSV file
        /// </summary>
        /// <param name="row"></param>
        /// <returns></returns>
        public bool ReadRow(CsvRow row)
        {
            row.LineText = ReadLine();
            if (String.IsNullOrEmpty(row.LineText))
                return false;

            int pos = 0;
            int rows = 0;

            while (pos < row.LineText.Length)
            {
                string value;

                // Special handling for quoted field
                if (row.LineText[pos] == '"')
                {
                    // Skip initial quote
                    pos++;

                    // Parse quoted value
                    int start = pos;
                    while (pos < row.LineText.Length)
                    {
                        // Test for quote character
                        if (row.LineText[pos] == '"')
                        {
                            // Found one
                            pos++;

                            // If two quotes together, keep one
                            // Otherwise, indicates end of value
                            if (pos >= row.LineText.Length || row.LineText[pos] != '"')
                            {
                                pos--;
                                break;
                            }
                        }
                        pos++;
                    }
                    value = row.LineText.Substring(start, pos - start);
                    value = value.Replace("\"\"", "\"");
                }
                else
                {
                    // Parse unquoted value
                    int start = pos;
                    while (pos < row.LineText.Length && row.LineText[pos] != ',')
                        pos++;
                    value = row.LineText.Substring(start, pos - start);
                }

                // Add field to list
                if (rows < row.Count)
                    row[rows] = value;
                else
                    row.Add(value);
                rows++;

                // Eat up to and including next comma
                while (pos < row.LineText.Length && row.LineText[pos] != ',')
                    pos++;
                if (pos < row.LineText.Length)
                    pos++;
            }
            // Delete any unused items
            while (row.Count > rows)
                row.RemoveAt(rows);

            // Return true if any columns read
            return (row.Count > 0);
        }
    }
}
Listing 1: CsvFileWriter and CsvFileReader Classes

Because the .NET stream classes generally seem to be split into reading and writing, I decided to follow that pattern with my CSV class and split it into CsvFileWriter and CsvFileReader. This also simplifies the code because neither class needs to worry about which mode the file is in or protect against the user switching modes.

The writer class performs any encoding necessary, as I described above, and the reader class performs any necessary decoding. 

Using the code

Both classes take a CsvRow argument. The CsvRow class derives from List<string>, so it's basically just a list of strings.

When you call CsvFileWriter.WriteRow(), the row argument specifies the string values to write out. And when you call CsvFileReader.ReadRow(), the row argument returns the values that were read in.

CsvFileReader.ReadRow() also places the entire line into the CsvRow.LineText member, just in case the caller wants to inspect that. Finally, CsvFileReader.ReadRow() returns a Boolean value that is false when no values could be read at the current line. Under normal circumstances, this would indicate the end of the file.

Listing 2 demonstrates using the classes. 

void WriteTest()
{
    // Write sample data to CSV file
    using (CsvFileWriter writer = new CsvFileWriter("WriteTest.csv"))
    {
        for (int i = 0; i < 100; i++)
        {
            CsvRow row = new CsvRow();
            for (int j = 0; j < 5; j++)
                row.Add(String.Format("Column{0}", j));
            writer.WriteRow(row);
        }
    }
}

void ReadTest()
{
    // Read sample data from CSV file
    using (CsvFileReader reader = new CsvFileReader("ReadTest.csv"))
    {
        CsvRow row = new CsvRow();
        while (reader.ReadRow(row))
        {
            foreach (string s in row)
            {
                Console.Write(s);
                Console.Write(" ");
            }
            Console.WriteLine();
        }
    }
}
Listing 2: Sample Code to Write and Read CSV files

Conclusion 

That's about all there is to it. The classes are fairly simple so I didn't include a sample project. All the code for the classes is shown in Listing 1. Note that this code, as presented, does not handle quoted values that span multiple lines. 

This code should be helpful for anyone wanting an easy way to share data with Microsoft Excel or any other program that can read or write CSV files. 

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Jonathan Wood
Black Belt Coder
United States United States
Jonathan Wood has been a software developer for more years than he cares to admit. His current focus is on using C# and ASP.NET MVC to develop website applications, and C++ and MFC to develop desktop applications. His consulting company, SoftCircuits, is known for producing various commercial and shareware products.

Having an entrepreneurial spirit, Jonathan also has a number of other online businesses that he built from scratch such as Black Belt Coder, Trail Calendar and others. He also has expertise in designing brands (including graphics and logos) and search-engine optimization (SEO).

Jonathan is always willing to discuss consulting work or joint ventures with people looking to develop software or online businesses.

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Comments and Discussions

 
Questiona double quote found in a quoted field issue Pin
brian lam29-Jun-15 22:40
memberbrian lam29-Jun-15 22:40 
QuestionNice, concise explanation and code Pin
MitchellBaldwin6-May-15 2:25
memberMitchellBaldwin6-May-15 2:25 
Questionvery helpful Pin
pravin.ovhal30-Mar-15 3:28
memberpravin.ovhal30-Mar-15 3:28 
QuestionRead choosed line from CSV Pin
Member 1051353727-Oct-14 23:27
memberMember 1051353727-Oct-14 23:27 
QuestionThank You Pin
younismo28-Aug-14 2:12
memberyounismo28-Aug-14 2:12 
QuestionThis versus TextFieldParser Pin
Saw Naw25-Jun-14 0:44
memberSaw Naw25-Jun-14 0:44 
GeneralMy vote of 3 Pin
Will_保哥31-May-14 6:08
memberWill_保哥31-May-14 6:08 
GeneralRe: My vote of 3 Pin
Jonathan Wood31-May-14 6:35
memberJonathan Wood31-May-14 6:35 
QuestionUTF-8 Encoding Problem Pin
Member 1050541421-May-14 4:16
memberMember 1050541421-May-14 4:16 
AnswerRe: UTF-8 Encoding Problem Pin
Jonathan Wood21-May-14 4:58
memberJonathan Wood21-May-14 4:58 
GeneralRe: UTF-8 Encoding Problem Pin
Member 1148172910-Mar-15 22:48
memberMember 1148172910-Mar-15 22:48 
QuestionWorks Great! Pin
Roy Parker1-Apr-14 8:28
memberRoy Parker1-Apr-14 8:28 
QuestionReading and writing csv files Pin
srvishnukumar17-Mar-14 17:46
membersrvishnukumar17-Mar-14 17:46 
AnswerRe: Reading and writing csv files Pin
Jonathan Wood17-Mar-14 18:28
memberJonathan Wood17-Mar-14 18:28 
GeneralRe: Reading and writing csv files Pin
srvishnukumar17-Mar-14 22:22
membersrvishnukumar17-Mar-14 22:22 
GeneralRe: Reading and writing csv files Pin
Jonathan Wood18-Mar-14 5:56
memberJonathan Wood18-Mar-14 5:56 
QuestionAdd rows to existing csv file Pin
Member 994058312-Dec-13 21:10
memberMember 994058312-Dec-13 21:10 
AnswerRe: Add rows to existing csv file Pin
Jonathan Wood17-Mar-14 18:29
memberJonathan Wood17-Mar-14 18:29 
QuestionMessage Automatically Removed Pin
9-Jul-13 20:47
groupjason6639-Jul-13 20:47 
QuestionMessage Automatically Removed Pin
8-Jul-13 7:39
groupjason6638-Jul-13 7:39 
Question.net CSV Reader Pin
jason6635-Jul-13 5:06
groupjason6635-Jul-13 5:06 
GeneralQuick & Simple Pin
ItalloSan30-Apr-13 3:23
memberItalloSan30-Apr-13 3:23 
QuestionAlternative library Pin
Matt Perdeck5-Mar-13 2:29
memberMatt Perdeck5-Mar-13 2:29 
QuestionQuestion Pin
Member 136816224-Aug-12 12:21
memberMember 136816224-Aug-12 12:21 
GeneralMissing new line handling... Pin
Andreas Gieriet6-Jul-12 3:45
memberAndreas Gieriet6-Jul-12 3:45 
GeneralRe: Missing new line handling... Pin
Jonathan Wood6-Jul-12 4:10
memberJonathan Wood6-Jul-12 4:10 
GeneralRe: Missing new line handling... Pin
Andreas Gieriet6-Jul-12 5:23
memberAndreas Gieriet6-Jul-12 5:23 
GeneralRe: Missing new line handling... Pin
Jonathan Wood6-Jul-12 8:12
memberJonathan Wood6-Jul-12 8:12 
GeneralRe: Missing new line handling... Pin
Andreas Gieriet6-Jul-12 17:10
memberAndreas Gieriet6-Jul-12 17:10 
GeneralRe: Missing new line handling... Pin
Titip3-Oct-12 10:34
memberTitip3-Oct-12 10:34 
QuestionRe: Missing new line handling... Pin
Jonathan Wood3-Oct-12 11:47
memberJonathan Wood3-Oct-12 11:47 
AnswerRe: Missing new line handling... Pin
Titip3-Oct-12 23:13
memberTitip3-Oct-12 23:13 
GeneralRe: Missing new line handling... Pin
Jonathan Wood7-Oct-12 12:42
memberJonathan Wood7-Oct-12 12:42 
GeneralTried looking at your new code... Pin
trehug26-Oct-12 5:29
membertrehug26-Oct-12 5:29 
GeneralRe: Tried looking at your new code... Pin
trehug26-Oct-12 5:43
membertrehug26-Oct-12 5:43 
GeneralRe: Tried looking at your new code... Pin
trehug26-Oct-12 6:12
membertrehug26-Oct-12 6:12 
GeneralRe: Tried looking at your new code... Pin
Jonathan Wood26-Oct-12 5:49
memberJonathan Wood26-Oct-12 5:49 
GeneralRe: Tried looking at your new code... Pin
trehug26-Oct-12 6:16
membertrehug26-Oct-12 6:16 
GeneralRe: Tried looking at your new code... Pin
Jonathan Wood26-Oct-12 6:23
memberJonathan Wood26-Oct-12 6:23 

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