C＃string.IsNullOrWhiteSpace（“\\ t”）== true

Question

I have a line of code

var delimiter = string.IsNullOrWhiteSpace(foundDelimiter) ? "," : foundDelimiter;

when foundDelimiter is "\\t" , string.IsNullOrWhiteSpace returns true.

Why? And what is the approriate way to work around this?

Answer 1

\\t is the tab character, which is whitespace. In C# can do either of these to get a tab:

var tab1 = "\t";
var tab2 = "    ";

var areEqual = tab1 == tab2; //returns true

Edit: As noted by Magus, SO is converting my tab character into spaces when the answer gets rendered. If you're in your IDE you'd just hit quote, tab, quote.

As far as a workaround goes, I'd suggest you just add a check for tabs in your conditional.

var delimiter = string.IsNullOrWhiteSpace(foundDelimiter) && foundDelimiter != "\t" ? "," : foundDelimiter;

Answer 2

Welcome to Unicode.

What did you expect would happen? HT (horizontal tab) has been a whitespace character for decades. The "classic" C-language definition of white-space characters consists of the US-ASCII characters:

• SP : space (0x20, ' ' )
• HT : horizontal tab (0x09, '\\t' )
• LF : line feed (0x0A, '\\n' )
• VT : vertical tab (0x0B, '\\v' )
• FF : vertical tab (0x0C, '\\f' )
• CR : carriage return (0x0C, '\\r' )

Unicode is a little more...ecumenical in its approach: its definition of white-space characters is this set:

• Members of the Unicode category SpaceSeparator :

  • SPACE (U+0020)
  • OGHAM SPACE MARK (U+1680)
  • MONGOLIAN VOWEL SEPARATOR (U+180E)
  • EN QUAD (U+2000)
  • EM QUAD (U+2001)
  • EN SPACE (U+2002)
  • EM SPACE (U+2003)
  • THREE-PER-EM SPACE (U+2004)
  • FOUR-PER-EM SPACE (U+2005)
  • SIX-PER-EM SPACE (U+2006)
  • FIGURE SPACE (U+2007)
  • PUNCTUATION SPACE (U+2008)
  • THIN SPACE (U+2009)
  • HAIR SPACE (U+200A)
  • NARROW NO-BREAK SPACE (U+202F)
  • MEDIUM MATHEMATICAL SPACE (U+205F)
  • IDEOGRAPHIC SPACE (U+3000)

• Members of the Unicode category LineSeparator , which consists solely of

  • LINE SEPARATOR (U+2028)

• Member of the Unicode category ParagraphSeparator , which consists solely of

  • PARAGRAPH SEPARATOR (U+2029)

• These Basic Latin/C0 Controls/US-ASCII characters:

  • CHARACTER TABULATION (U+0009)
  • LINE FEED (U+000A)
  • LINE TABULATION (U+000B)
  • FORM FEED (U+000C)
  • CARRIAGE RETURN (U+000D)

• These C1 Controls and Latin-1 Supplement characters

  • NEXT LINE (U+0085)
  • NO-BREAK SPACE (U+00A0)

If you don't like the definition, roll your own along these lines (plug in your own character set):

public static bool IsNullOrCLanguageWhitespace( this string s )
{
  bool value = ( s == null || rxWS.IsMatch(s) ) ;
  return value ;
}
private static Regex rxWS = new Regex( @"^[ \t\n\v\f\r]*$") ;

You might want to add a char analog as well:

public static bool IsCLanguageWhitespace( this char c )
{
  bool value ;
  switch ( c )
  {
  case ' '  : value = true  ; break ;
  case '\t' : value = true  ; break ;
  case '\n' : value = true  ; break ;
  case '\v' : value = true  ; break ;
  case '\f' : value = true  ; break ;
  case '\r' : value = true  ; break ;
  default   : value = false ; break ;
  }
  return  value ;
}