check a string is alphanumeric

Richard Brennan

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.

4 Replies

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jitender13y ago

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

Vulpes15y ago
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();
}
}
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Richard Brennan15y ago
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 < textLength; )
            {
                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?
                }
            }
        }
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Amit Choudhary15y ago
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.
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