Reading CSV files using C#

Question

I\'m writing a simple import application and need to read a CSV file, show result in a DataGrid and show corrupted lines of the CSV file in another grid. For ex

Answer 1

CSV can get complicated real fast.

Use something robust and well-tested:
FileHelpers: www.filehelpers.net

The FileHelpers are a free and easy to use .NET library to import/export data from fixed length or delimited records in files, strings or streams.

Answer 2

Another one to this list, Cinchoo ETL - an open source library to read and write CSV files

For a sample CSV file below

Id, Name
1, Tom
2, Mark

Quickly you can load them using library as below

using (var reader = new ChoCSVReader("test.csv").WithFirstLineHeader())
{
   foreach (dynamic item in reader)
   {
      Console.WriteLine(item.Id);
      Console.WriteLine(item.Name);
   }
}

If you have POCO class matching the CSV file

public class Employee
{
   public int Id { get; set; }
   public string Name { get; set; }
}

You can use it to load the CSV file as below

using (var reader = new ChoCSVReader<Employee>("test.csv").WithFirstLineHeader())
{
   foreach (var item in reader)
   {
      Console.WriteLine(item.Id);
      Console.WriteLine(item.Name);
   }
}

Please check out articles at CodeProject on how to use it.

Disclaimer: I'm the author of this library

Answer 3

I'd highly suggest using CsvHelper.

Here's a quick example:

public class csvExampleClass
{
    public string Id { get; set; }
    public string Firstname { get; set; }
    public string Lastname { get; set; }
}

var items = DeserializeCsvFile<List<csvExampleClass>>( csvText );

public static List<T> DeserializeCsvFile<T>(string text)
{
    CsvReader csv = new CsvReader( new StringReader( text ) );
    csv.Configuration.Delimiter = ",";
    csv.Configuration.HeaderValidated = null;
    csv.Configuration.MissingFieldFound = null;
    return (List<T>)csv.GetRecords<T>();
}

Full documentation can be found at: https://joshclose.github.io/CsvHelper

Answer 4

Here's a solution I coded up today for a situation where I needed to parse a CSV without relying on external libraries. I haven't tested performance for large files since it wasn't relevant to my particular use case but I'd expect it to perform reasonably well for most situations.

        static List<List<string>> ParseCsv(string csv) {
            var parsedCsv = new List<List<string>>();
            var row = new List<string>();
            string field = "";
            bool inQuotedField = false;

            for (int i = 0; i < csv.Length; i++) {
                char current = csv[i];
                char next = i == csv.Length - 1 ? ' ' : csv[i + 1];

                // if current character is not a quote or comma or carriage return or newline (or not a quote and currently in an a quoted field), just add the character to the current field text
                if ((current != '"' && current != ',' && current != '\r' && current != '\n') || (current != '"' && inQuotedField)) {
                    field += current;
                } else if (current == ' ' || current == '\t') {
                    continue; // ignore whitespace outside a quoted field
                } else if (current == '"') {
                    if (inQuotedField && next == '"') { // quote is escaping a quote within a quoted field
                        i++; // skip escaping quote
                        field += current;
                    } else if (inQuotedField) { // quote signifies the end of a quoted field
                        row.Add(field);
                        if (next == ',') {
                            i++; // skip the comma separator since we've already found the end of the field
                        }
                        field = "";
                        inQuotedField = false;
                    } else { // quote signifies the beginning of a quoted field
                        inQuotedField = true; 
                    }
                } else if (current == ',') { //
                    row.Add(field);
                    field = "";
                } else if (current == '\n') {
                    row.Add(field);
                    parsedCsv.Add(new List<string>(row));
                    field = "";
                    row.Clear();
                }
            }

            return parsedCsv;
        }

Answer 5

Don't reinvent the wheel. Take advantage of what's already in .NET BCL.

• add a reference to the Microsoft.VisualBasic (yes, it says VisualBasic but it works in C# just as well - remember that at the end it is all just IL)
• use the Microsoft.VisualBasic.FileIO.TextFieldParser class to parse CSV file

Here is the sample code:

using (TextFieldParser parser = new TextFieldParser(@"c:\temp\test.csv"))
{
    parser.TextFieldType = FieldType.Delimited;
    parser.SetDelimiters(",");
    while (!parser.EndOfData) 
    {
        //Processing row
        string[] fields = parser.ReadFields();
        foreach (string field in fields) 
        {
            //TODO: Process field
        }
    }
}

It works great for me in my C# projects.

Here are some more links/informations:

• MSDN: Read From Comma-Delimited Text Files in Visual Basic
• MSDN: TextFieldParser Class

Answer 6

First of all need to understand what is CSV and how to write it.

1. Every next string ( /r/n ) is next "table" row.
2. "Table" cells is separated by some delimiter symbol. Most often used symbols is \t or ,
3. Every cell possibly can contain this delimiter symbol (cell must to start with quotes symbol and ends with this symbol in this case)
4. Every cell possibly can contains /r/n sybols (cell must to start with quotes symbol and ends with this symbol in this case)

The easiest way for C#/Visual Basic to work with CSV files is to use standard Microsoft.VisualBasic library. You just need to add needed reference, and the following string to your class:

using Microsoft.VisualBasic.FileIO;

Yes, you can use it in C#, don't worry. This library can read relatively big files and supports all of needed rules, so you will be able to work with all of CSV files.

Some time ago I had wrote simple class for CSV read/write based on this library. Using this simple class you will be able to work with CSV like with 2 dimensions array. You can find my class by the following link: https://github.com/ukushu/DataExporter

Simple example of using:

Csv csv = new Csv("\t");//delimiter symbol

csv.FileOpen("c:\\file1.csv");

var row1Cell6Value = csv.Rows[0][5];

csv.AddRow("asdf","asdffffff","5")

csv.FileSave("c:\\file2.csv");