string reference type? - C# Discussion Boards

Regular expressions in C#

13-Mar-09 0:14

~~I know nothing about this - but google turned up this example[^]... maybe it will help?~~

Scrub that, a bit more research reveals there are many ways of doing this, and even different RFCs, so it seems it depends on which one you're using, and how you've created that implementation in your code.

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)

modified on Friday, March 13, 2009 6:21 AM

KeithF12-Mar-09 23:28

KeithF

12-Mar-09 23:28

Hi All,

I need to compare a string to a regular expression to determine if the string is in this format. I am setting the string equal to a line read from a file.

Once i have read the line i want to compare it to a regx to determine if the string is formatted as follows:

Date Time (5-10 spaces) 123-12-123456

An example line:

09-02-2009 10:33 001-01-218913

The code i have currently is:

strFile = "C:\\test.txt";
using (StreamReader srTlog = new StreamReader(new FileStream(strFile, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)))    
{        
  while ((strLine = srTlog.ReadLine()) != null)        
  {            
    Regex pattern=new Regex("NOT SURE WHAT GOES HERE");            
    if(pattern.IsMatch(strToCheck))            
    {                
      //DO WHATEVER NOW            
    }
  }
}

I would appreciate any help.

Thanks

Re: Regular expressions in C#

whaka12-Mar-09 23:48

whaka

12-Mar-09 23:48

string patternStr = @"^\d{2}-\d{2}-\d{4} \d{2}:\d{2} \d{3}-\d{2}-\d{6}$";

^ is beginning of line
$ is end of line
\d is any digit

It should match the given string, although it will also match strings with invalid dates such as 99-99-2009 34:10 123-45-123456
But if you know that the datestring will always be correct and the important thing is the last bit, the pattern above should work fine (didnt test it though).

Re: Regular expressions in C#

psi_u13-Mar-09 1:05

psi_u

13-Mar-09 1:05

// Find formats: dd/mm/yy or dd/mm/yyy, seperators: -/. (i.e. 31.01.08 31-01-08 etc.)
Regex rx = new Regex(@"([1-9]|0[1-9]|[12][0-9]|3[01])[- /.]([1-9]|0[1-9]|1[012])[- /.]((19|20)\d\d|\d\d)");

// Define a test string.        
string text = fileName;


// Find matches.
MatchCollection matches = rx.Matches(text);

// Report the number of matches found.
if (matches.Count > 1)
     DoST();

// Report on each match.
foreach (Match match in matches)
{
	textBoxDocumentDate.Text = match.Value;
}

Re: Regular expressions in C#

#realJSOP13-Mar-09 2:26

#realJSOP

13-Mar-09 2:26

Why go through the hassle of using regex? Just use DateTime.ParseExact, and handle the bool return value.

"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

string reference type?

__DukeNukem__12-Mar-09 23:25

__DukeNukem__

12-Mar-09 23:25

Hi you all,

I am currently teaching myself C# and .Net. This works fine so long but now I have a question:

I experimented a bit with the hash codes of objects and when I ran my example app I had to notice that string does not behave like I expected. But first the example:

string s1 = "teststring";
string s2 = s1;
Console.WriteLine(s1 + " " + s1.GetHashCode());
Console.WriteLine(s2 + " " + s2.GetHashCode());

s2 = "changed";
Console.WriteLine(s1 + " " + s1.GetHashCode());
Console.WriteLine(s2 + " " + s2.GetHashCode());

The result I expected was that s2 will point to the same string object as s1. Therefore changing s2 would result in changing the same object that both string references point to, i.e. that both strings have the same values. But the output of the code is the following:

teststring -1549391391
teststring -1549391391
teststring -1549391391
changed 114681301

So I just have a simple question: Why?

Would be happy to get some help on this.

Thank you in advance!

DaveyM6912-Mar-09 23:37

12-Mar-09 23:37

The confusion comes from the fact that the string is immutable. When you change the value of s2, it's actually a whole new string object that is created. If it had changed the contents of the memory that s2 was pointing to, it would have changed s1 too.

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)

__DukeNukem__12-Mar-09 23:45

__DukeNukem__

12-Mar-09 23:45

Thank you! It's getting clearer Smile | :)

DaveyM6912-Mar-09 23:59

12-Mar-09 23:59

No problem Big Grin | :-D

We've all been there at some point on this one!

There are reasons why the string class is like this - a reference type that behaves like a value type. Research it if you're interested, but it's down to the fact that a string isn't really a string, it's a null terminated char array - i.e. each character is stored in ajacent memory locations with a null character at the end to dertermine where the string finishes.

It is possible to create a mutable string by using 'unsafe', 'fixed' and pointers to manipulte the contents of the array in memory but it's not advised.

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)

Luc Pattyn13-Mar-09 3:10

Luc Pattyn

13-Mar-09 3:10

Hi Dave,

DaveyM69 wrote:
a string ... is a null terminated char array - i.e. each character is stored in ajacent memory locations with a null character at the end to dertermine where the string finishes

Not so. That is true for C/C++ but not Java/C#.
How else would this snippet output "len=2":

char c='\0';  // or (char)0
string s="";
s=s+c;
s=s+c;
log("len="+s.Length);

I don't think we are supposed to even know *how* strings get stored, it suffices to know strings are collections of characters and there aren't any special characters, so NULL is handled like everything else.

The good thing is string.Length seems to be an O(1) operation. So it suggests a length+content implementation, as was used in Pascal.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

DaveyM6913-Mar-09 4:25

13-Mar-09 4:25

Interesting. I never thought to look it up.

This page[^] has some stuff on it, and the Memory Usage secions has some more details specific to this.

Thanks for the correction - learned something new today Big Grin | :-D

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)

vehicle tracking

R.Krishnakumar12-Mar-09 23:14

R.Krishnakumar

12-Mar-09 23:14

Hi,
can anyone suggest me some idea about "vehicle tracking using sensor network"....
can this can be implemented in c#

Eddy Vluggen12-Mar-09 23:23

Eddy Vluggen

12-Mar-09 23:23

R.Krishnakumar wrote:
can anyone suggest me some idea about "vehicle tracking using sensor network"....

Get a GPS-tracker (cheap), use it to find out where you are, use some map-api to draw that (Microsoft has maps, Google has maps, Yahoo does maps)

R.Krishnakumar wrote:
can this can be implemented in c#

Yes.

I are troll Smile | :)

R.Krishnakumar12-Mar-09 23:39

R.Krishnakumar

12-Mar-09 23:39

its possible to bring google earth map on to my application

Pete O'Hanlon12-Mar-09 23:49

Pete O'Hanlon

12-Mar-09 23:49

Was that a question or a statement? Either way, this is a big task - are you really sure you're up to doing this. I ask this because my company specialises in doing this type of work, and it's not a trivial undertaking. You need some form of transponder in the vehicle to update you with the position in real time. Companies can end up paying hundreds of thousands (sometimes even millions) for reliable solutions to this problem.

"WPF has many lovers. It's a veritable porn star!" - Josh Smith

As Braveheart once said, "You can take our freedom but you'll never take our Hobnobs!" - Martin Hughes.

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stancrm13-Mar-09 0:05

stancrm

13-Mar-09 0:05

google earth map is online. you can use it, if you have an internet connection.
try to search it in google for "google maps api".
It is only javascript code.

Eddy Vluggen13-Mar-09 1:33

Eddy Vluggen

13-Mar-09 1:33

Yeah, but you can only use the free version if the service you base on the maps is publicly available. For internal use/behind a firewall/anything company, you'll need to register for the Enterprise version of Maps Smile | :)

I are troll Smile | :)

Michael Bookatz13-Mar-09 0:30

Michael Bookatz

13-Mar-09 0:30

Cross post!!!!!!!