CODEWITHSUNDEEP
c#stringreplace
Idan Tabachnik
Idan Tabachnik

Reputation: 81

Using Replace() to remove quotation marks from the start removes them all

I am trying to filter a csv file from quotation marks. This line strangely deletes all the quotation marks in the line:

before : "NewClient"Name" 

foo = foo.Replace(foo.Substring(0, 1), "");

after : NewClientName

Why is this happening? Shouldn't the Replace() method just delete the first occurence?

Upvotes: 1

Views: 499

Answers (4)

Dmitrii Bychenko
Dmitrii Bychenko

Reputation: 186678

Usually when working with CSV we double quotations:

a                 -> "a"
a"b               -> "a""b"
NewClient"Name    -> "NewClient""Name"

To cut such a quotation, i.e. 

"NewClient""Name" -> NewClient"Name

when "NewClient"Name" being a syntax error you can try

private static string CutQuotation(string value) {
  if (string.IsNullOrEmpty(value))
    return value;
  else if (!value.Contains('"'))
    return value;

  if (value.Length == 1)
    throw new FormatException("Incorrect quotation format: string can't be of length 1.");
  else if (value[0] != '"')
    throw new FormatException("Incorrect quotation format: string must start with \".");
  else if (value[value.Length - 1] != '"')
    throw new FormatException("Incorrect quotation format: string must end with \".");

  StringBuilder builder = new StringBuilder(value.Length);

  for (int i = 1; i < value.Length - 1; ++i) 
    if (value[i] == '"') 
      if (i == value.Length - 2)
        throw new FormatException("Incorrect quotation format. Dangling \".");
      else if (value[++i] == '"') 
        builder.Append(value[i]);
      else
        throw new FormatException("Incorrect quotation format. Dangling \".");
    else
      builder.Append(value[i]);

  return builder.ToString();
}

As you can see, it's not just single Replace() routine.

Tests:

 // abc - no quotation
 Console.WriteLine(CutQuotation("abc")); 
 // abc - simple quotation cut
 Console.WriteLine(CutQuotation("\"abc\"")); 
 // "abc" - double quotation
 Console.WriteLine(CutQuotation("\"\"abc\"\"")); 
 // a"bc - quotation in the middle
 Console.WriteLine(CutQuotation("\"a\"\"bc\""));

Upvotes: 2

jvigneshprabhu
jvigneshprabhu

Reputation: 26

Your requirement works with this.

string strTest = "\"NewClient\"Name\"";
strTest = strTest.TrimStart('"');

which in your case it is

result[i, 0] = result[i, 0].TrimStart('"');

*Replace will remove and replace all matching char/string in the given instance.

Upvotes: 0

CodeCaster
CodeCaster

Reputation: 151594

Shouldn't the replace method just delete the first occurence?

You would think so, because you're using Substring(0, 1):

string foo = "\"NewClient\"Name\"";
foo = foo.Replace(foo.Substring(0, 1), "");

But the substring is obtained before the call to Replace(). In other words, your Substring() and Replace() have no relation to each other whatsoever, so the code is equivalent to:

string foo = "\"NewClient\"Name\"";
foo  = foo.Replace("\"", "");

And String.Replace() replaces all occurrences.

If you only want to replace the first instance, see How do I replace the *first instance* of a string in .NET?. If instead you only and always want to remove the first character, see Fastest way to remove first char in a string. If you want to remove specific characters from the start of the string, see C# TrimStart with string parameter.

Upvotes: 1

Sierrodc
Sierrodc

Reputation: 887

No, Replace method replace all occurrencies of a char in the string (see https://msdn.microsoft.com/en-us/library/fk49wtc1(v=vs.110).aspx).

If you need to remove just fist/last char (if any) you can use Trim function: https://msdn.microsoft.com/en-us/library/d4tt83f9(v=vs.110).aspx

in your case:

 result[i, 0] = result[i, 0].Trim('"')

Upvotes: 0

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