Compiler Error CS1009

Unrecognized escape sequence

An unexpected character follows a backslash (\) in a string of an escape sequence or character literal. The compiler expects one of the valid escape characters. For more information, see Character Escapes.

The following sample generates CS1009.

// CS1009-a.cs  
class MyClass  
{  
   static void Main()  
   {  
      // The following escape sequence causes CS1009:  
      string a = "\m";
      // Try the following line instead.  
      // string a = "\t";  

      // The following character literals causes CS1009:
      // CS1009; a lowercase \u-style Unicode escape sequence must have exactly 4 hex digits
      string unicodeEscapeSequence = '\u061';
      // CS1009; a hex escape sequence must start with lowercase \x
      string hexEscapeSequence = '\X061';
      // CS1009; an uppercase \U-style Unicode escape sequence must have exactly 8 hex digits
      string uppercaseUnicodeEscape = '\U0061';
   }  
}  

A common cause of this error is using the backslash character in a file name, as the following example shows.

string filename = "c:\myFolder\myFile.txt";  

To resolve this error, use "\" or the @-quoted string literal, as the following example shows.

// CS1009-b.cs  
class MyClass  
{  
   static void Main()  
   {  
      // The following line causes CS1009.  
      string filename = "c:\myFolder\myFile.txt";
      // Try one of the following lines instead.  
      // string filename = "c:\\myFolder\\myFile.txt";  
      // string filename = @"c:\myFolder\myFile.txt";  
   }  
}  

See also

• string