Re: searching for the highest index within a directory
From: Nick Malik [Microsoft] (nickmalik_at_hotmail.nospam.com)
Date: 03/03/05
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Date: Thu, 3 Mar 2005 07:35:16 -0800
Hi Ada,
(I used to write code in the Ada programming language... ;-)
The reason that I asked about your intent for incrementing file names: if
you just needed a unique file name once, that you were going to delete when
you are done, and you didn't want to overwrite another application using
their own unique file name on the same computer, you could have used
Path.GetTempFileName() which will return a unique name in the users
"Temporary Files" folder. Sounds like that isn't what you are doing.
>
> Nick, to answer your question....
> it's a small exercise for myself. :-)
> an application for this type of naming is a sequential graphic animation
> files.
> i'm doing this to avoid overwriting the existing file and resume sequence
> from the highest index file.
>
> can you elaborate why
> testFile_4
> comes after
> testFile_34?
Because "testFile_34" is a string, not a number. If a string cannot be
converted to a number, there is no way to compare them as numbers. We
compare strings lexically (alphabetical order... kinda... see below). That
means we look at the first character in each string. If one is less than
the other (occurs earlier in the character table), then we stop because we
have found the "earlier" string. If the characters in that position are the
same, we move to the next position and compare.
In this case, the 10th character of testFile_4 is '4' while the 10th
character of testFile_34 is '3'. Since '3' comes before '4' in the
character table, then "testFile_34" comes before "testFile_4". That is why
I suggested that you would want to embed leading zeros in your number
field... In the character table, '0' comes before the rest of the digits, so
your alphabetical sort will be the same as a numeric sort (until you run out
of digits).
Important Note: in the character tables, All of the upper case characters
come before the first lower case character. Therefore, if you use a "case
sensitive sort" (the default), then "ZestFile" will come before "testFile"
even though in a dictionary, it wouldn't work that way. That's because the
capital 'Z' occurs before the lowercase 't'.
If you want to see what the character tables look like, visit
http://www.unicode.org/charts/
Note that we are most familiar with the "Basic Latin" character set.
Another note: read the charts one column at a time (top to bottom, left to
right). I have no idea why they did that :-(.
There is a way around this, of course. You can tell the system to ignore
the case of the letters when sorting your strings.
I've included a snippet of text from an article on DevX.com:
<snippet>
The .NET Framework defines several comparer classes for you to use. One of
them, the CaseInsensitiveComparer class, allows you to sort strings by
ignoring their casing. So in this case, the .NET framework ignores the
String class' CompareTo method, and instead uses the rules defined in the
CaseInsensitiveComparer class. The following code illustrates this feature:
Dim aryLastNames() As String = {"sMiTh, ZULU", "smith, john&", "SMITH,
TerrY"}
Array.Sort(aryLastNames, New CaseInsensitiveComparer)
' aryLastNames order:
'
' smith, john
' SMITH, TerrY
' sMiTh, ZULU
</snippet>You can find the full article at:
http://www.devx.com/dotnet/Article/21089I hope this helps,--
--- Nick Malik [Microsoft]
MCSD, CFPS, Certified Scrummaster
http://blogs.msdn.com/nickmalik
Disclaimer: Opinions expressed in this forum are my own, and not
representative of my employer.
I do not answer questions on behalf of my employer. I'm just a
programmer helping programmers.
-- "Ada" <Ada@discussions.microsoft.com> wrote in message news:F94A4607-88C9-40D6-A17F-746ABB63BE70@microsoft.com... >
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