Best way to remove the last character from a string built with stringbuilder

Question

I have the following   data AppendFormat   0    dataToAppend     The problem with this is that I am using it in a loop and there will be a trialling comma  What is the best way to remove the trailing comma   Do I have to change data to a string the substring it

User · Answer

Gotcha   Most of the answers on this thread won t work if you use AppendLine like below  var builder   new StringBuilder    builder AppendLine  quot One  quot    builder Length--     Won t work Console Write builder ToString      builder   new StringBuilder    builder AppendLine  quot One  quot    builder Length    -1     Won t work Console Write builder ToString      builder   new StringBuilder    builder AppendLine  quot One  quot    Console Write builder TrimEnd           Won t work  Fiddle Me WHY       amp     amp     The issue is simple but took me a while to figure it out  Because there are 2 more invisible characters at the end CR and LF  Carriage Return and Line Feed   Therefore  you need to take away 3 last characters  var builder   new StringBuilder    builder AppendLine  quot One  quot    builder Length -  3     This will work Console WriteLine builder ToString      In Conclusion Use Length-- or Length -  1 if the last method you called was Append  Use Length  - 3 if you the last method you called AppendLine

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The simplest and most efficient way is to perform this command   data Length--    by doing this you move the pointer  i e  last index  back one character but you don t change the mutability of the object  In fact  clearing a StringBuilder is best done with Length as well  but do actually use the Clear   method for clarity instead because that s what its implementation looks like    data Length   0    again  because it doesn t change the allocation table  Think of it like saying  I don t want to recognize these bytes anymore  Now  even when calling ToString    it won t recognize anything past its Length  well  it can t  It s a mutable object that allocates more space than what you provide it  it s simply built this way

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How About this    string str    The quick brown fox jumps over the lazy dog    StringBuilder sb   new StringBuilder str   sb Remove str Length - 1  1

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The most simple way would be to use the Join   method   public static void Trail         var list   new List lt string gt     lala    lulu    lele         var data   string Join      list       If you really need the StringBuilder  trim the end comma after the loop   data ToString   TrimEnd

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Just use  string Join      yourCollection    This way you don t need the StringBuilder and the loop         Long addition about async case  As of 2019  it s not a rare setup when the data are coming asynchronously    In case your data are in async collection  there is no string Join overload taking IAsyncEnumerable lt T gt   But it s easy to create one manually  hacking the code from string Join   public static class StringEx       public static async Task lt string gt  JoinAsync lt T gt  string separator  IAsyncEnumerable lt T gt  seq                if  seq    null              throw new ArgumentNullException nameof seq             await using  var en   seq GetAsyncEnumerator                          if   await en MoveNextAsync                    return string Empty               string firstString   en Current  ToString                 if   await en MoveNextAsync                    return firstString    string Empty                  Null separator and values are handled by the StringBuilder             var sb   new StringBuilder 256               sb Append firstString                do                               var currentValue   en Current                  sb Append separator                   if  currentValue    null                      sb Append currentValue                             while  await en MoveNextAsync                 return sb ToString                          If the data are coming asynchronously but the interface IAsyncEnumerable lt T gt  is not supported  like the mentioned in comments SqlDataReader   it s relatively easy to wrap the data into an IAsyncEnumerable lt T gt    async IAsyncEnumerable lt  object first  object second  object product  gt  ExtractData          SqlDataReader reader        while  await reader ReadAsync            yield return  reader 0   reader 1   reader 2        and use it   Task lt string gt  Stringify SqlDataReader reader    gt      StringEx JoinAsync                        ExtractData reader  Select x   gt     x first     x second     x product        In order to use Select  you ll need to use nuget package System Interactive Async  Here you can find a compilable example

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Similar SO question here   I liked the using a StringBuilder extension method   RemoveLast Method

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Yes  convert it to a string once the loop is done   String str   data ToString   TrimEnd

User · Answer

You have two options  First one is very easy use Remove method it is quite effective  Second way is to use ToString with start index and end index  MSDN documentation

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Use the following after the loop    TrimEnd        or simply change to  string commaSeparatedList   input Aggregate  a  x    gt  a          x

User · Answer

I recommend  you change your loop algorithm     Add the comma not AFTER the item  but BEFORE Use a boolean variable  that starts with false  do suppress the first comma Set this boolean variable to true after testing it

User · Answer

I prefer manipulating the length of the stringbuilder   data Length   data Length - 1

User · Answer

You should use the string Join method to turn a collection of items into a comma delimited string   It will ensure that there is no leading or trailing comma  as well as ensure the string is constructed efficiently  without unnecessary intermediate strings

[c#] Best way to remove the last character from a string built with stringbuilder

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