Why does my regular expression pattern in C# return an empty string?

Question

I have a a string that's formatted such \\\State\city".

I want to return only the State portion and then only the city portion into respective variables.

I tried using a pattern of ^\\\\[a-zA-Z]\ to return the state portion and then a pattern of ^\\[a-zA-Z] for the city portion. The results are always an empty string.

state = Regex.Match("\\\Washington\\Seattle","^\\\\[a-zA-Z]\"].ToString();

Answer 1

Consider the following code to match State and City...

var state = Regex.Match(@"\\Washington\Seattle", @"(?<=\\\\).*(?=\\)");
var city = Regex.Match(@"\\Washington\Seattle", @"(?<=\\\\.*?\\).*");

Answer 2

Backslash serves as an escape character. For every single (\) backslash you need two backslashes (\\).

Also you do not need the beginning of line anchor ^ on your second regular expression example because that part is obviously not at the beginning of the string. Below is an example of how you could do this.

String s = @"\\Washington\Seattle";
Match m  = Regex.Match(s, @"(?i)^\\\\([a-z]+)\\([a-z]+)");

if (m.Success) {
   String state = m.Groups[1].Value;
   String city  = m.Groups[2].Value;

   Console.WriteLine("{0}, {1}", city, state); // => "Seattle, Washington"
} 

Answer 3

Try this non-RegEx answer:

string data = @"\\Washington\Seattle";
string state = data.Trim('\\').Split('\\')[0];
string city = data.Trim('\\').Split('\\')[1];

Console.WriteLine("{0}, {1}", city, state);

This is trimming the double backslashes, then splitting at the first backslash.

Answer 4

You need to escape backslashes in regex. So anywhere that you would have a single \, instead have \\

Also [a-zA-Z] will only match once. Use a + to match once or more

So that would make your state regex:

^\\\\[a-zA-Z]+\\

Additionally, backslashes in strings in C# also need to be escaped. So either double up again, or use the @ character:

state = Regex.Match(@"\\Washington\Seattle",@"^\\\\[a-zA-Z]+\\").ToString();

Answer 5

You only allow one character to stand between your backslashes. what you actually want is [a-zA-Z]* with the asterisk.