CODEWITHSUNDEEP
c#.netregexlinq
user3677169
user3677169

Reputation:

Check if a string contains only letters, digits and underscores

I have to check if a string contains only letters, digits and underscores. This is how I tried but it doesn't work:

for(int i = 0; i<=snameA.Length-1; i++)
{
    validA = validA && (char.IsLetterOrDigit(snameA[i])||snameA[i].Equals("_"));
}

Upvotes: 12

Views: 24328

Answers (6)

Dinos
Dinos

Reputation: 411

You could try matching a regular expression. There is a built in type for "letters, digits and underscores", which is "\w".

Regex rgx = new Regex(@"\w*");
rgs.IsMatch(yourString);

If you require 1 or more, then use "\w+".

Further information here: Regex.IsMatch

Upvotes: 3

Dmitrii Bychenko
Dmitrii Bychenko

Reputation: 186668

First, letter is a bit vague term: do you mean a..z and A..Z characters or letter could belong to any alphabet, e.g. а..я and А..Я (Russian, Cyrillic letters). According to your current implementation, you want the second option.

Typical solution with loop is to check until first counter example:

  Boolean validA = true; // true - no counter examples so far

  // Why for? foreach is much readble here
  foreach(Char ch in sname) 
    // "!= '_'" is more readable than "Equals"; and wants no boxing
    if (!char.IsLetterOrDigit(ch) && ! (ch != '_')) { 
      Boolean validA = false; // counter example (i.e. non-letter/digit symbol found)

      break; // <- do not forget this: there's no use to check other characters
    }

However you can simplify the code with either Linq:

  validA = sname.All(ch => Char.IsLetterOrDigit(ch) || ch == '_');

Or regular expression:

  validA = Regex.IsMatch(sname, @"^\w*$");

Upvotes: 1

Sachu
Sachu

Reputation: 7766

you can use regex

Regex regex1 = new Regex(@"^[a-zA-Z0-9_]+$");

if(regex1.IsMatch(snameA))
{

}

Upvotes: 5

Thomas Ayoub
Thomas Ayoub

Reputation: 29431

I love Linq for this kind of question:

bool validA = sname.All(c => Char.IsLetterOrDigit(c) || c.Equals('_'));

Upvotes: 15

Lucas Rodriguez
Lucas Rodriguez

Reputation: 1203

I would use a Regex

string pattern = @"^[a-zA-Z0-9\_]+$";
Regex regex = new Regex(pattern);

// Compare a string against the regular expression
return regex.IsMatch(stringToTest);

Upvotes: 3

Patrick Hofman
Patrick Hofman

Reputation: 156938

You are assigning validA every time again, without checking its previous value. Now you always get the value of the last check executed.

You could 'and' the result:

validA &= (char.IsLetterOrDigit(snameA[i]) || snameA[i] == '_');

This would mean you still run all characters, which might be useless if the first check failed. So it is better to simply step out if it fails:

for(int i = 0; i<=snameA.Length-1; i++)
{
    validA = (char.IsLetterOrDigit(snameA[i]) || snameA[i] == '_');

    if (!validA)
    { break; } // <-- see here
}

Or with LINQ:

validA = snameA.All(c => char.IsLetterOrDigit(c) || c == '_');

Upvotes: 10

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