Question

I’m trying to use a regular expression to validate a name entry field. The regular expression is very simple as I only want to allow letters and spaces (for now). Here’s the code that I’m using:

[RegularExpression("[A-Za-z\s]+",ErrorMessage="UserName can only consist of letters or spaces")]
    [Required]
    [DisplayName("User Name")]
    public string UserName { get; set; }

When I try and build this, however, I get an error specifying an “Unrecognised escape sequence”. Playing around with the expression using different characters from this sheet I have noticed that some will build and some will not:

Will build: // /b /n

Will not build: /s /k /B /D /d /? /(escaped space)

Can anyone explain why some of these work and some do not and more to the point how can I get my desired expression to work (spaces and letters)

Answer 1

The compiler is treating the string exactly as it normally would for backslashes. Your backslash is an entry to an escape character. Try this:

[RegularExpression(@"[A-Za-z\s]+",ErrorMessage="UserName can only consist of letters or spaces")]

The @ symbol tells the compiler that you’re handling any escape characters.

Another example is file paths.. backslashes must be escaped with a double backslash:

string fileName = "C:\\my_folder\\my_file.ext";

..otherwise, you can use the @ symbol:

string fileName = @"C:\my_folder\my_file.ext";