Regular expressions in C# to detect more than one space between words

I need to use regular expressions in C# to validate a TextBox. I need to add this role in ValidationExpress for a Validation Control 开发者_StackOverflowin ASP.NET. Regular expressions should not allow this:

• more that ONE space between words
• considering also beginning and end of the string

Any ideas?

No need for regexps.

if (string.StartsWith(" ") || string.EndsWith(" ") || string.Contains("  ")) throw...

If you are limited to validating a string, try the following pattern (example):

^[ ]?([^ ]+[ ])*[^ ]*$

It doesn't allow strings with two spaces anywhere in the string. This pattern ignores tabs and newlines, by the way. I've picked [ ] so you can see the spaces, but a simple space is the same. \s may not be right for you. For one, it might match a windows new line, \r\n.

Similarly, you can use a negative lookahead (example):

^(?!.*[ ]{2})

If you're using a client side validator you need to match from start to end, so use the pattern (?!.*[ ]{2}).*. It implicitly adds ^...$ around your pattern.
Either way, consider using a custom validator and writing a simple line of code to negate searching for two spaces. Here's how it's done. First, look at the documentation add a JavaScript function to your page:

function noTwoSpaces(source, arguments) {
    arguments.IsValid = (arguments.Value.indexOf('  ') == -1);
}

Next, add the CustomValidator control to use it:

<asp:CustomValidator ID="CustomValidator1" runat="server" 
    ControlToValidate="TextBox1" Display="Dynamic" ErrorMessage=":-(" 
    ClientValidationFunction="noTwoSpaces"></asp:CustomValidator>

And that's it. Much easier than an elusive regex.

I believe you want:

 if (myText.Split(" ", StringSplitOptions.RemoveEmptyEntries).Length != 
     myText.Split(" ").Length)
 {
    //String contains multiple spaces
 }

As you've now said you DO want regexes I'd use

 @"\s\s+"

to match two or more whitespaces or:

 @"\ \ +"

to match two or more spaces.

var rex = new Regex(@"\s{2,}");

Edit: Didn't see the start/end of the string.

        string poo = "a b";
        string poo1 = "a  b";
        string poo2 = "a   b";
        string poo3 = "a    b";
        string poo4 = " a  b";
        string poo5 = "a   b ";
        string poo6 = " a    b ";
        string poo7 = " a b ";
        var rex = new Regex(@"^\s{0}.\s{0,1}.\s{0}$");

        Console.WriteLine(rex.IsMatch(poo));
        Console.WriteLine(rex.IsMatch(poo1));
        Console.WriteLine(rex.IsMatch(poo2));
        Console.WriteLine(rex.IsMatch(poo3));
        Console.WriteLine(rex.IsMatch(poo4));
        Console.WriteLine(rex.IsMatch(poo5));
        Console.WriteLine(rex.IsMatch(poo6));
        Console.WriteLine(rex.IsMatch(poo7));

This returns:

True
False
False
False
False
False
False
False

Since the only valid string is the first one.

If you want to use regex, use this:

 {2,}

(NB: There is a space before the brackets).

How about something like

string s = " tada  bling zap  ";
Regex reg = new Regex(@"\s\s+");
MatchCollection m = reg.Matches(s);

Can be done without regex, but imho it's less obvious to not use regex:

\s{2,} or \s\s+ if .NET doesn't support the match-min-max syntax (I don't recall).

For beginning and ending no white spaces ^[^\s](.*\s.*)+[^\s]$

Mary bought a shoe match

MarySqeezeIntoAshoe no match