check a string is alphanumeric

Question

i want to validate the text in a textbox as alphanumeric (a-z, A-Z, 0-9) - is there built in method for this or do I have to loop through the string and chaeck each character?

I am placing the code on the textbox changetext event.

jitender · Answer

Its incorrect Try this one: public static Boolean isAlphaNumeric ( string strToCheck ) { Regex rg = new Regex ( @"^[a-zA-Z0-9]*$" ); return rg . IsMatch ( strToCheck ); } or this public static Boolean isAlphaNumeric ( string strToCheck ) { Regex rg = new Regex ( @"^[a-zA-Z0-9]+$" ); return rg . IsMatch ( strToCheck ); } In the example above: ^ - means start of the string []* - could contain any number of characters between brackets a-zA-Z0-9 - any alphanumeric characters $ - end of the string

Vulpes · Answer

The following is a bit cleaner: private void txtChangePasswordUsername_TextChanged(object sender, EventArgs e) { bool isValid = true; foreach(char c in txtChangePasswordUsername.Text) { if(!char.IsLetterOrDigit(c)) { isValid = false; break; } } if(!isValid) { MessageBox.Show("Enter only letters or numbers.", "Alert!"); txtChangePasswordUsername.Text = ""; txtChangePasswordUsername.Focus(); } }

Richard Brennan · Answer

i have used the following code - is there a better way? private void txtChangePasswordUsername_TextChanged( object sender, EventArgs e) { string text = txtChangePasswordUsername.Text; int textLength = text.Length; for ( int i = 0; i { if ( char .IsLetter(text[i]) || char .IsNumber(text[i])) i++; else { MessageBox .Show( "Enter only letters or numbers." , "Alert!" ); txtChangePasswordUsername.Text = "" ; txtChangePasswordUsername.Focus(); i = textLength; ß could i use a break statement here? } } }

Amit Choudhary · Answer

Hi friend, Use below code to validation your input string in textbox using System.Text.RegularExpressions; // Function to Check for AlphaNumeric. public bool IsAlphaNumeric(String strToCheck) { Regex objAlphaNumericPattern= new Regex("[^a-zA-Z0-9]"); return !objAlphaNumericPattern.IsMatch(strToCheck); } Hope this helps you. Thanks.

check a string is alphanumeric

Answers (4)