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Compiler Error CS1009

Visual Studio 2010

Unrecognized escape sequence

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

The following sample generates CS1009.

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

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

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

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

C#
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// 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";
   }
}

Reference

string (C# Reference)
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