Parsing CSV files in C with header

Question

Is there a default official recommended way to parse CSV files in C   I don t want to roll my own parser   Also  I ve seen instances of people using ODBC OLE DB to read CSV via the Text driver  and a lot of people discourage this due to its  drawbacks   What are these drawbacks   Ideally  I m looking for a way through which I can read the CSV by column name  using the first record as the header   field names  Some of the answers given are correct but work to basically deserialize the file into classes

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A CSV parser is now a part of  NET Framework   Add a reference to Microsoft VisualBasic dll  works fine in C   don t mind the name   using  TextFieldParser parser   new TextFieldParser   c  temp test csv          parser TextFieldType   FieldType Delimited      parser SetDelimiters           while   parser EndOfData                  Process row         string   fields   parser ReadFields            foreach  string field in fields                          TODO  Process field                     The docs are here - TextFieldParser Class  P S  If you need a CSV exporter  try CsvExport  discl  I m one of the contributors

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Let a library handle all the nitty-gritty details for you   -   Check out FileHelpers and stay DRY - Don t Repeat Yourself - no need to re-invent the wheel a gazillionth time      You basically just need to define that shape of your data - the fields in your individual line in the CSV - by means of a public class  and so well-thought out attributes like default values  replacements for NULL values and so forth   point the FileHelpers engine at a file  and bingo - you get back all the entries from that file  One simple operation - great performance

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I know its a bit late but just found a library Microsoft VisualBasic FileIO which has TextFieldParser class to process csv files

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CsvHelper  a library I maintain  will read a CSV file into custom objects   var csv   new CsvReader  File OpenText   file csv       var myCustomObjects   csv GetRecords lt MyCustomObject gt       Sometimes you don t own the objects you re trying to read into  In this case  you can use fluent mapping because you can t put attributes on the class   public sealed class MyCustomObjectMap   CsvClassMap lt MyCustomObject gt        public MyCustomObjectMap                 Map  m   gt  m Property1   Name   Column Name             Map  m   gt  m Property2   Index  4            Map  m   gt  m Property3   Ignore            Map  m   gt  m Property4   TypeConverter lt MySpecialTypeConverter gt                 EDIT   CsvReader now requires CultureInfo to be passed into the constuctor  https   github com JoshClose CsvHelper issues 1441    Example   var csv   new CsvReader File OpenText  file csv    System Globalization CultureInfo CurrentCulture

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I have written TinyCsvParser for  NET  which is one of the fastest  NET parsers around and highly configurable to parse almost any CSV format   It is released under MIT License    https   github com bytefish TinyCsvParser   You can use NuGet to install it  Run the following command in the Package Manager Console   PM gt  Install-Package TinyCsvParser   Usage  Imagine we have list of Persons in a CSV file persons csv with their first name  last name and birthdate   FirstName LastName BirthDate Philipp Wagner 1986 05 12 Max Musterman 2014 01 02   The corresponding domain model in our system might look like this   private class Person       public string FirstName   get  set        public string LastName   get  set        public DateTime BirthDate   get  set        When using TinyCsvParser you have to define the mapping between the columns in the CSV data and the property in you domain model   private class CsvPersonMapping   CsvMapping lt Person gt         public CsvPersonMapping             base                 MapProperty 0  x   gt  x FirstName           MapProperty 1  x   gt  x LastName           MapProperty 2  x   gt  x BirthDate             And then we can use the mapping to parse the CSV data with a CsvParser   namespace TinyCsvParser Test        TestFixture      public class TinyCsvParserTest                Test          public void TinyCsvTest                         CsvParserOptions csvParserOptions   new CsvParserOptions true  new                         CsvPersonMapping csvMapper   new CsvPersonMapping                CsvParser lt Person gt  csvParser   new CsvParser lt Person gt  csvParserOptions  csvMapper                var result   csvParser                  ReadFromFile   persons csv   Encoding ASCII                   ToList                 Assert AreEqual 2  result Count                Assert IsTrue result All x   gt  x IsValid                 Assert AreEqual  Philipp   result 0  Result FirstName               Assert AreEqual  Wagner   result 0  Result LastName                Assert AreEqual 1986  result 0  Result BirthDate Year               Assert AreEqual 5  result 0  Result BirthDate Month               Assert AreEqual 12  result 0  Result BirthDate Day                Assert AreEqual  Max   result 1  Result FirstName               Assert AreEqual  Mustermann   result 1  Result LastName                Assert AreEqual 2014  result 1  Result BirthDate Year               Assert AreEqual 1  result 1  Result BirthDate Month               Assert AreEqual 1  result 1  Result BirthDate Day                       User Guide  A full User Guide is available at    http   bytefish github io TinyCsvParser

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In a business application  i use the Open Source project on codeproject com  CSVReader   It works well  and has good performance  There is some benchmarking on the link i provided   A simple example  copied from the project page   using  CsvReader csv   new CsvReader new StreamReader  data csv    true         int fieldCount   csv FieldCount      string   headers   csv GetFieldHeaders         while  csv ReadNextRecord                  for  int i   0  i  lt  fieldCount  i                Console Write string Format   0     1     headers i   csv i              Console WriteLine              As you can see  it s very easy to work with

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Here is a helper class I use often  in case any one ever comes back to this thread  I wanted to share it    I use this for the simplicity of porting it into projects ready to use   public class CSVHelper   List lt string   gt      protected string csv   string Empty    protected string separator           public CSVHelper string csv  string separator                    this csv   csv      this separator   separator       foreach  string line in Regex Split csv  System Environment NewLine  ToList   Where s   gt   string IsNullOrEmpty s                string   values   Regex Split line  separator          for  int i   0  i  lt  values Length  i                      Trim values         values i    values i  Trim                       this Add values                 And use it like   public List lt Person gt  GetPeople string csvContent      List lt Person gt  people   new List lt Person gt       CSVHelper csv   new CSVHelper csvContent     foreach string   line in csv          Person person   new Person        person Name   line 0       person TelephoneNo   line 1       people Add person         return people       Updated csv helper  bug fixed where the last new line character created a new line

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This solution is using the official Microsoft VisualBasic assembly to parse CSV   Advantages    delimiter escaping ignores Header  trim spaces ignore comments   Code       using Microsoft VisualBasic FileIO       public static List lt List lt string gt  gt  ParseCSV  string csv                List lt List lt string gt  gt  result   new List lt List lt string gt  gt                  To use the TextFieldParser a reference to the Microsoft VisualBasic assembly has to be added to the project           using  TextFieldParser parser   new TextFieldParser new StringReader csv                           parser CommentTokens   new string                        parser SetDelimiters new string                         parser HasFieldsEnclosedInQuotes   true                  Skip over header line                parser ReadLine                 while   parser EndOfData                                var values   new List lt string gt                      var readFields   parser ReadFields                    if  readFields    null                      values AddRange readFields                   result Add values                                    return result

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Single source file solution for straightforward parsing needs  useful  Deals with all the nasty edge cases  Such as new line normalization and handling new lines in quoted string literals  Your welcome   If you CSV file has a header you just read out the column names  and compute column indexes  from the first row  Simple as that   Note that Dump is a LINQPad method  you might want to remove that if you are not using LINQPad   void Main         var file1    a b c r nx y z       CSV ParseText file1  Dump         var file2    a   b   c r nx   y z         CSV ParseText file2  Dump         var file3    a   b   c r nx   y r nz         CSV ParseText file3  Dump         var file4                   CSV ParseText file4  Dump       static class CSV       public struct Record               public readonly string   Row           public string this int index    gt  Row index            public Record string   row                        Row   row                       public static List lt Record gt  ParseText string text                return Parse new StringReader text               public static List lt Record gt  ParseFile string fn                using  var reader   File OpenText fn                         return Parse reader                        public static List lt Record gt  Parse TextReader reader                var data   new List lt Record gt              var col   new StringBuilder            var row   new List lt string gt             for                              var ln   reader ReadLine                if  ln    null  break              if  Tokenize ln  col  row                                 data Add new Record row ToArray                      row Clear                                     return data             public static bool Tokenize string s  StringBuilder col  List lt string gt  row                int i   0           if  col Length  gt  0                        col AppendLine       continuation              if   TokenizeQuote s  ref i  col  row                                 return false                                   while  i  lt  s Length                        var ch   s i               if  ch                                       row Add col ToString   Trim                     col Length   0                  i                              else if  ch                                       i                    if   TokenizeQuote s  ref i  col  row                                         return false                                              else                               col Append ch                   i                                     if  col Length  gt  0                        row Add col ToString   Trim                 col Length   0                     return true             public static bool TokenizeQuote string s  ref int i  StringBuilder col  List lt string gt  row                while  i  lt  s Length                        var ch   s i               if  ch                                          escape sequence                 if  i   1  lt  s Length  amp  amp  s i   1                                                col Append                           i                        i                        continue                                    i                    return true                            else                               col Append ch                   i                                    return false

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Here is my KISS implementation     using System  using System Collections Generic  using System Text   class CsvParser       public static List lt string gt  Parse string line                const char escapeChar                const char splitChar                bool inEscape   false          bool priorEscape   false           List lt string gt  result   new List lt string gt             StringBuilder sb   new StringBuilder            for  int i   0  i  lt  line Length  i                          char c   line i               switch  c                                case escapeChar                      if   inEscape                          inEscape   true                      else                                               if   priorEscape                                                        if  i   1  lt  line Length  amp  amp  line i   1     escapeChar                                  priorEscape   true                              else                                 inEscape   false                                                    else                                                       sb Append c                               priorEscape   false                                                                      break                  case splitChar                      if  inEscape    if in escape                         sb Append c                       else                                               result Add sb ToString                             sb Length   0                                            break                  default                      sb Append c                       break                                   if  sb Length  gt  0              result Add sb ToString              return result

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Here is a short and simple solution                   using  TextFieldParser parser   new TextFieldParser outputLocation                                              parser TextFieldType   FieldType Delimited                          parser SetDelimiters                               string   headers   parser ReadLine   Split                               foreach  string header in headers                                                        dataTable Columns Add header                                                     while   parser EndOfData                                                        string   fields   parser ReadFields                                dataTable Rows Add fields

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This code reads csv to DataTable   public static DataTable ReadCsv string path        DataTable result   new DataTable  SomeData        using  TextFieldParser parser   new TextFieldParser path                 parser TextFieldType   FieldType Delimited          parser SetDelimiters               bool isFirstRow   true            IList lt string gt  headers   new List lt string gt              while   parser EndOfData                        string   fields   parser ReadFields                if  isFirstRow                                foreach  string field in fields                                        result Columns Add new DataColumn field  typeof string                                       isFirstRow   false                            else                               int i   0                  DataRow row   result NewRow                    foreach  string field in fields                                        row i      field                                    result Rows Add row                                     return result

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Another one to this list  Cinchoo ETL - an open source library to read and write multiple file formats  CSV  flat file  Xml  JSON etc   Sample below shows how to read CSV file quickly  No POCO object required   string csv     Id  Name 1  Carl 2  Tom 3  Mark    using  var p   ChoCSVReader LoadText csv       WithFirstLineHeader               foreach  var rec in p                Console WriteLine   Id   rec Id             Console WriteLine   Name   rec Name               Sample below shows how to read CSV file using POCO object  public partial class EmployeeRec       public int Id   get  set        public string Name   get  set       static void CSVTest         string csv     Id  Name 1  Carl 2  Tom 3  Mark        using  var p   ChoCSVReader lt EmployeeRec gt  LoadText csv           WithFirstLineHeader                           foreach  var rec in p                        Console WriteLine   Id   rec Id                 Console WriteLine   Name   rec Name                         Please check out articles at CodeProject on how to use it

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Some time ago I had wrote simple class for CSV read write based on Microsoft VisualBasic 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 usage   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      For reading header only you need is to read csv Rows 0  cells

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If you need only reading csv files then I recommend this library  A Fast CSV Reader If you also need to generate csv files then use this one  FileHelpers  Both of them are free and opensource

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If anyone wants a snippet they can plop into their code without having to bind a library or download a package  Here is a version I wrote       public static string FormatCSV List lt string gt  parts                string result                foreach  string s in parts                        if  result Length  gt  0                                result                          if  s Length    0                      continue                             if  s Length  gt  0                                result           s Replace                                                 else                                  cannot output double quotes since its considered an escape for a quote                 result                                          return result             enum CSVMode               CLOSED   0          OPENED RAW   1          OPENED QUOTE   2            public static List lt string gt  ParseCSV string input                List lt string gt  results           CSVMode mode           char   letters           string content            mode   CSVMode CLOSED           content               results   new List lt string gt             letters   input ToCharArray             for  int i   0  i  lt  letters Length  i                          char letter   letters i               char nextLetter     0                if  i  lt  letters Length - 1                  nextLetter   letters i   1                   If its a quote character             if  letter                                          If that next letter is a quote                 if  nextLetter         amp  amp  mode    CSVMode OPENED QUOTE                                           Then this quote is escaped and should be added to the content                      content    letter                          Skip the escape character                     i                        continue                                    else                                          otherwise its not an escaped quote and is an opening or closing one                        Character is skipped                         If it was open  then close it                     if  mode    CSVMode OPENED QUOTE                                                results Add content                               reset the content                         content                                mode   CSVMode CLOSED                              If there is a next letter available                         if  nextLetter      0                                                            If it is a comma                             if  nextLetter                                                                       i                                    continue                                                            else                                                               throw new Exception  Expected comma  Found      nextLetter                                                                                                     else if  mode    CSVMode OPENED RAW                                                   If it was opened raw  then just add the quote                          content    letter                                            else if  mode    CSVMode CLOSED                                                   Otherwise open it as a quote                           mode   CSVMode OPENED QUOTE                                                                       If its a comma seperator             else if  letter                                          If in quote mode                 if  mode    CSVMode OPENED QUOTE                                           Just read it                     content    letter                                       If raw  then close the content                 else if  mode    CSVMode OPENED RAW                                        results Add content                        content                            mode   CSVMode CLOSED                                       If it was closed  then open it raw                 else if  mode    CSVMode CLOSED                                        mode   CSVMode OPENED RAW                       results Add content                        content                                                   else                                  If opened quote  just read it                 if  mode    CSVMode OPENED QUOTE                                        content    letter                                       If opened raw  then read it                 else if  mode    CSVMode OPENED RAW                                        content    letter                                       It closed  then open raw                 else if  mode    CSVMode CLOSED                                        mode   CSVMode OPENED RAW                       content    letter                                                        If it was still reading when the buffer finished         if  mode    CSVMode CLOSED                        results Add content                      return results

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Based on unlimit s post on How to properly split a CSV using C  split   function     string   tokens   System Text RegularExpressions Regex Split paramString          NOTE  this doesn t handle escaped   nested commas  etc   and therefore is only suitable for certain simple CSV lists

[c#] Parsing CSV files in C#, with header

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