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Searching A String For Specific Values

 

Searching A String For Specific Values, Harder than it seems ;)
matto

26 Jun, 2009 - 11:21 AM
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Hi,

I have a program which grabs the source code of a webpage and puts it into a string. I would now like to search the string for two values.

"video_id": "value 1 here"

"t": "value 2 here"

The problem, is that I don't know the position of the values, and I the values change depending on each webpage. All I know, is the text before the value, e.g. "video_id" and "t:"

Here is my code:

CODE
        Dim videoid As String = TextBox1.Text.Trim

        Dim wc As New System.Net.WebClient()
        Dim result As String = wc.DownloadString(videoid)


Any help appreciated, thanks

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jacobjordan

RE: Searching A String For Specific Values

26 Jun, 2009 - 11:40 AM
Post #2

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Well, once you have downloaded the web page as a string, you could use the IndexOf function to find the index of video_id and t, and then use some Substring and IndexOf functions to parse the value out of the quotes. Or, you could use Regular Expressions, but those might be a bit too complicated for the situation, especially if you are not familiar with them. Try to use the IndexOf and Substring approach on your own, and if you need any help with the coding, i (or someone else) will assist.
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matto

RE: Searching A String For Specific Values

26 Jun, 2009 - 12:30 PM
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OK thanks a lot. I will look into what you suggested. BTW, thanks for not giving me some code, I'd rather learn about the functions myself instead of copying and pasting code I don't understand smile.gif
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matto

RE: Searching A String For Specific Values

27 Jun, 2009 - 02:35 AM
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I had a go at it, but I'm finding it hard to understand how to use IndexOf and substring together. Here's what I have so far:

CODE
Dim videoid As String = TextBox1.Text.Trim
        Dim wc As New System.Net.WebClient()
        Dim videosource As String = wc.DownloadString(videoid)

        Dim t As String = videosource.IndexOf("&t=")
        Dim t2 As String = t.Substring(3, 46)
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Pwn

RE: Searching A String For Specific Values

27 Jun, 2009 - 08:13 AM
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indexof returns an integer. you use this integer in your substring to indicate your starting location. You will also need to figure out the length of the string you're looking for, which will be the 2nd parameter to your indexof substring function. Also, unless you know for a fact that your value will be the same length at all times, hard coding values such as length is not recommended. Figuring out how to always have the right number can be tricky.

Edit: wrong function stated

This post has been edited by Pwn: 27 Jun, 2009 - 08:20 AM
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LoveIsNull

RE: Searching A String For Specific Values

27 Jun, 2009 - 08:17 AM
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The IndexOf function returns an integer, which is the location of the first instance of the "value" parameter you specified.
You can then pass the integer value returned by the IndexOf function into the Substring function along with the length of characters you want to retrieve.
Let's say you're looking for "&t=", and that you know you will always want the next 6 characters afterwards.

CODE
        Dim iStart As Integer = theString.IndexOf("&t=")
        Dim strResult As String = theString.Substring(iStart, 10)

strResult will now contain whatever six characters where after the first occurrence of "&t="

Sorry I can't explain much more at the moment, but see if that helps you for now...
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matto

RE: Searching A String For Specific Values

1 Jul, 2009 - 11:25 AM
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Thanks for your code. However, when I used it, strResult still contained "&t=". How can I get only a certain number of characters after "&t="?
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CamoDeveloper

RE: Searching A String For Specific Values

1 Jul, 2009 - 11:31 AM
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Try this:
CODE

Dim iStart As Integer = theString.IndexOf("&t=")
Dim strResult As String = theString.Substring(iStart + 3, 10)


~Camo

This post has been edited by CamoDeveloper: 1 Jul, 2009 - 11:32 AM
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