Parsing in between strings using Regex

  • Thread starter Thread starter CJ
  • Start date Start date
C

CJ

Is this the format to parse a string and return the value between the item?

Regex pRE = new Regex("<File_Name>.*>(?<insideText>.*)</File_Name>");

I am trying to parse this string.

<File_Name>Services</File_Name>


Thanks
 
CJ said:
Is this the format to parse a string and return the value between the item?

Regex pRE = new Regex("<File_Name>.*>(?<insideText>.*)</File_Name>");

I am trying to parse this string.

<File_Name>Services</File_Name>
Click to expand...

Regex re = new Regex("<File_Name>(?<insideText>.*)</File_Name>");
string fn = re.Match(s).Groups["insideText"].Value;

seems to work.

Arne
 
Thanks Arne,

Seems like the ".*" was messing me up.

This regular expression is so hard at times, I don't know how
you guys have this thing figured out.

CJ


Arne Vajhøj said:
CJ said:
Is this the format to parse a string and return the value between the
item?

Regex pRE = new Regex("<File_Name>.*>(?<insideText>.*)</File_Name>");

I am trying to parse this string.

<File_Name>Services</File_Name>
Click to expand...

Regex re = new Regex("<File_Name>(?<insideText>.*)</File_Name>");
string fn = re.Match(s).Groups["insideText"].Value;

seems to work.

Arne
Click to expand...
 
Hello cj,
Thanks Arne,

Seems like the ".*" was messing me up.

This regular expression is so hard at times, I don't know how you guys
have this thing figured out.
Click to expand...

This looks a lot like XML data. If it is, you really should try to avoid
regex and use XPath to fetch the data you need.

If it isn't wellformed Regex can help you, but the regex you have still has
a few issues in it.

dor one, if your input would contain "<file_name>bbbbbbbbb</file_name><file_name>aaaaaaaaaaaa</file_name>"
you would get this as your whole value:
"bbbbbbbbb</file_name><file_name>aaaaaaaaaaaa". Obviously not what's required.

You can adjust your regex to prevent this from happening in two ways:

1) Use Reluctant Matching
Regex re = new Regex("<File_Name>(?<insideText>.*?)</File_Name>");
string fn = re.Match(s).Groups["insideText"].Value;

2) Use a negative Look Ahead
Regex re = new Regex("<File_Name>(?<insideText>((?!</File_Name>).)*)</File_Name>");
string fn = re.Match(s).Groups["insideText"].Value;

One thing that migth also catch up with you is afile that is formatted like
this (let's hope the newsreader will leave this in tact):
<file_name>
bbbbbbbbb
</file_name>

This is probably syntactically correct, but as . normally doesn't match over
the end of a line, it will require you to use an extra switch in your regex
constructor (either case) which will allow . to match newline.
Regex re = new Regex("your regex here", RegexOptions.Singleline);

Alternatively you could 'eat up' all whitespace around the File_Name. But
only if you're very sure the filename itself will never contain a newline
or have whitespace in it at the strat or end of the filename.

1)
Regex re = new Regex("<File_Name>\s*(?<insideText>.*?)\s*</File_Name>");
2)
Regex re = new Regex("<File_Name>\s*(?<insideText>((?!</File_Name>).)*?)\s*</File_Name>");

Kind Regards,

Jesse Houwing
CJ

CJ said:
Is this the format to parse a string and return the value between
the item?

Regex pRE = new
Regex("<File_Name>.*>(?<insideText>.*)</File_Name>");

I am trying to parse this string.

<File_Name>Services</File_Name>
Click to expand...
Regex re = new Regex("<File_Name>(?<insideText>.*)</File_Name>");
string fn = re.Match(s).Groups["insideText"].Value;

seems to work.

Arne
Click to expand...
Click to expand...
 
Hi,

CJ said:
Thanks Arne,

Seems like the ".*" was messing me up.

This regular expression is so hard at times, I don't know how
you guys have this thing figured out.
Click to expand...

Practice, you should try it a couple of times until you find the correct way

Also a book would help you ;)
 
Hello Ignacio Machin ( .NET/ C# MVP )" machin TA laceupsolutions.com,
Hi,


Practice, you should try it a couple of times until you find the
correct way

Also a book would help you ;)
Click to expand...

Dan Appleman has a very affordable ebook available on Amazon which is made
specifically for the .NET syntax. It is from the 1.1 timeframe, so there
are a few features that aren't described, but you probably won't miss them.

A great resource on Regular expressions at a whole (once a free ebook) is
Mastering regular expressions (probably 4th edition by now, last time I checked
they released the 3rd) from O'Reilly.
 
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