replacing all regEx matches in large string

Question

0.00/5 (No votes)

See more:

Ok i have the following code, but when it runs it doesn't return the replaced string;

C#

private string ReplaceDescription(string description)
       {
           var newDescription = description.Replace("/en/products/purpose/", "/en/");
           return newDescription;
       }

       private string ReplaceProductDescription(string description)
       {
           string pattern = @"/en/products/\d{4}/\d{4}\.aspx";
           Regex regEx = new Regex(pattern);
           foreach (Match match in regEx.Matches(description))
           {
               string matchedValue = match.Value;
               string productNumber = System.IO.Path.GetFileNameWithoutExtension(matchedValue);
               description.Replace(matchedValue, "newString");
           }
           return description;

       }

The first method works fine, but the second one wont return the description with replacements, any help would be great many thanks.

Posted 21-Nov-14 6:29am

Grant Weatherston

Add a Solution

2 solutions

Solution 1

The Replace method does not change the original string. This means that the Replace method has no effect in your second method.

Try this instead:

C#

private string ReplaceProductDescription(string description)
{
    string pattern = @"/en/products/\d{4}/\d{4}\.aspx";
    Regex regEx = new Regex(pattern);
    string updatedDescription = description;
    foreach (Match match in regEx.Matches(description))
    {
        string matchedValue = match.Value;
        string productNumber = System.IO.Path.GetFileNameWithoutExtension(matchedValue);
        updatedDescription = updatedDescription.Replace(matchedValue, "newString");
    }
    return updatedDescription;
}

Posted 21-Nov-14 6:54am

Thomas Daniels

Updated 21-Nov-14 7:23am

v2

Comments

Grant Weatherston 21-Nov-14 13:05pm

Would that work though as updated would get overwritten each loop when a new match is iterated, as updated = current description. Replace it would t have all replacements done.

Thomas Daniels 21-Nov-14 13:21pm

You're right. I will edit my answer.

Thomas Daniels 21-Nov-14 13:24pm

I edited my answer. Now the value of updatedDescription is the same as description before the loop starts, and the value of updatedDescription gets always changed inside the loop.

Maciej Los 21-Nov-14 14:51pm

As many matches as many times updatedDescription is created. String is immutable!
http://www.codeproject.com/Articles/406046/Why-strings-are-immutable-and-what-are-the-implica

Thomas Daniels 22-Nov-14 8:53am

I know. It's true that the string gets recreated many times, but it does what the OP wants.

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Matt T Heffron · Accepted Answer · 2014-11-21T07:13:00

Solution 2

Why not just have the Regex do the replacement?

C#

private string ReplaceProductDescription(string description)
{
    string pattern = @"/en/products/(?<pn1>\d{4})/(?<pn2>\d{4})\.aspx";
    Regex regEx = new Regex(pattern);
    return regEx.Replace(description, "newString pn1 here:${pn1} pn2 here:${pn2}");
}

And you probably want to pre-construct the Regex once, instead of on each call.

Posted 21-Nov-14 7:13am

Matt T Heffron

Updated 21-Nov-14 8:12am

v3

Comments

Grant Weatherston 21-Nov-14 13:19pm

I would but I need to access the match in order to retrieve the product number as the product number is in the new string .

Matt T Heffron 21-Nov-14 14:13pm

Well you didn't say that in the first place...
So you can use captured patterns in the substitution string.
I've updated my solution.
You should read up on all of the capabilities of the Regex.Replace() !
Of course, you can arrange the capture(s) of the pattern however you need. You don't need to split it into two parts.

Matt T Heffron 21-Nov-14 21:33pm

How's this working for you?
Please "Accept" this Solution (if appropriate).

Maciej Los 21-Nov-14 14:53pm

+5!

Matt T Heffron 21-Nov-14 16:36pm

Thanks