Question

Check for Special Characters in String

Asked by: msyed1

Hello,

I have a textbox on my web page that is basically meant for comments/notes, but it gets updated to a DB2 database table/column defined as CHAR.  If the user happens to enter a ' " or & (special characters) in the comments textbox, my update process crashes.  

What I want to do is put in validation for the textbox so that if the user enters any special characters, they get an error message displayed to them that special characters are not allowed.

Can someone please send me the code in VB.Net/ASP.Net that checks a string value for special characters anywhere in the string....and displays an error message, if found...thanks...

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Asked On
2005-10-04 at 06:53:58ID21583186
Tags

special

,

characters

,

string

,

check

Topic

Microsoft Visual Basic.Net

Participating Experts
5
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Comments
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Answers

 

by: TimCotteePosted on 2005-10-04 at 06:58:44ID: 15013914

Hi msyed1,

For the first two situation, you should be able to double the ' and " characters and they will be inserted into the record and stored with a single ' or ".

Otherwise you can do this any number of ways, using regular expressions or something like this:

Dim Specials() As string = {"'","""","&"}
If MySourceString.IndexOfAny(Specials) > 0 Then
    Msgbox "Ooops, entered a special character"
End If

Tim Cottee

 

by: jake072Posted on 2005-10-04 at 07:03:13ID: 15013970

Try this:

        Dim delimStr As String = "'""&"
        Dim delimiter As Char() = delimStr.ToCharArray()
        If TextBox1.Text.IndexOfAny(delimiter) > -1 Then
            MessageBox.Show("Cannot contain Special Characters ', "", or & ", "Update Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        End If

However, you might be better off to simply parse the string to insert escape characters that will not blow the update.  Then, you just parse out the escape characters when you want to show the text again.

Let me know if you want some help parsing the Text to allow special characters.

Jake

 

by: StylezHousePosted on 2005-10-04 at 07:09:35ID: 15014035

I would just use a regular expression validator and save the postback.  

ie.  If you want only alpha characters you can use
^[a-zA-Z]$

www.regexlib.com has a boatload of regular expressions

 

by: msyed1Posted on 2005-10-04 at 07:12:52ID: 15014078

Jake/Tim,
I just found that in fact I need to allow special characters in the comment field, but like you said, it needs to be parsed to insert escape characters, so the database update won't blow up.

Yes, please let me know how to insert the escape characters for database update and also how to parse out the escape characters in order to display the comments back on the page.
E.g. Comments = "Inserted System number '030' - 10/04/2005"

Thanks a bunch. msyed1.

 

by: DimandjaPosted on 2005-10-04 at 07:14:36ID: 15014104

There are many options.

1.  To prevent crashes, you can double your quotes like this:
newValue = Replace(oldValue, "'", "''")

2.  This is my favorite.  You can translate the special characters into escape sequences.  And reverse the process when retrieving data.  The most popular escape sequences are constructed as %HH, where "H" is a hex digit.    "Nick" would result in %22Nick%22 being stored.

 

by: gangwischPosted on 2005-10-04 at 07:14:48ID: 15014105

the best way i use is this:
replace(myvalue,"'","\'")
and do that for every reserved character

 

by: jake072Posted on 2005-10-04 at 07:25:42ID: 15014227

msyed1,

As Dimandja and gangwisch have pointed out (And not to be repetitive, but the question was addressed to Jake/Tim :)): Generally, when updating, you can be safe in the fact that if you have a special character that is killing your update, simply double the character in the update, and then replace it back when you want to show it so:

            Dim strUpdate As String = Replace(TextBox1.Text, "'", "''")
            ...
            strUpdate = Replace(strUpdate, """", """""")

You can keep doing Replace for any characters that are killing your update (might be different, depending on the DB you use).

Then, when you want to display the text again, just reverse the Replace, like:

            Dim strShow As String = Replace(strUpdate, "''", "'")
            ...
            strShow = Replace(strShow, """""", """")

Let me know if you need more help,

Jake

 

by: DimandjaPosted on 2005-10-04 at 09:01:47ID: 15015139

I should also mention that constructing your SQL query strings with verbatim user input is extremely unsafe.   A wicked user could invade your database by embedding a malicious query within the data input.

It is best to carefully build a user interface where input is limited to the choices your application makes available.  Free input should always be handled as hazmat.

 

by: jake072Posted on 2005-10-04 at 09:06:18ID: 15015195

msyed1,

Dimandja raises a very interesting point...  How are you using the query to update to the DataBase, could you post your code?  If a user was really smart and devious, he could theoretically write his own SQL in this field, and then destroy/damage your data, depending on how you interact with the DataBase...

Jake

 

by: msyed1Posted on 2005-10-04 at 10:54:47ID: 15016155

Jake/Dimandja,

Thanks for all the very useful suggestions.  At this time, I am only writing a quick and dirty prototype.  When I do it for real, I will be using stored procedures.  

For now, Jake's solution to double-up the characters with a 'replace' looks easy to me.  Thanks for the help. msyed1.
 

20120131-EE-VQP-002

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