Johnny Johnny - 3 months ago 19
C# Question

Replace single backslash with double backslash

It seems simple enough, right? Well, I don't know.

Here's the code I'm trying:

input = Regex.Replace(input, "\\", "\\\\\\");


However, I'm receiving an error,


ArgumentException was unhandled - parsing "\" - Illegal \ at end of pattern.


How do I do this?

Answer

The first one should be "\\\\", not "\\". It works like this:

  • You have written "\\".
  • This translates to the sequence \ in a string.
  • The regex engine then reads this, which translates as backslash which isn't escaping anything, so it throws an error.

With regex, it's much easier to use a "verbatim string". In this case the verbatim string would be @"\\". When using verbatim strings you only have to consider escaping for the regex engine, as backslashes are treated literally. The second string will also be @"\\", as it will not be interpreted by the regex engine.