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• Gadget vista error var with flyout

  - by Jiinn

  hello ! i have a problem with a variable for the flyout : var friendsUser = ""; var friendsMdp = ""; System.Gadget.Settings.write("variableName", variableName); System.Gadget.settingsUI = "Settings.html"; System.Gadget.onSettingsClosed = SettingsClosed; System.Gadget.Flyout.visible = SettingsClosed; function SettingsClosed() { variableName = System.Gadget.Settings.read("variableName"); friendsUser = System.Gadget.Settings.read("friendUser"); friendsMdp = System.Gadget.Settings.read("friendMdp"); setContentText(); } function flyFriends() { System.Gadget.Flyout.file = 'friends.htm'; System.Gadget.Flyout.show = true ; var flyoutDiv = System.Gadget.Flyout.document.parentWindow; flyoutDiv.gMyVar = friendsUser; flyoutDiv.gMyVar2 = friendsMdp; } If i use this my flyout var is undefined , and if i write : var friendsUser = "test"; i have Test in var and after use setting i have nothing ... if i write var in flyoutDiv before System.Gadget.Flyout.show = true ; gadget bug . my settings dont have a problem, but the refresh of the var ... have you a idea ? thank you for all !

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• Using pipes in Linux with C

  - by Dave

  Hi, I'm doing a course in Operating Systems and we're supposed to learn how to use pipes to transfer data between processes. We were given this simple piece of code which demonstrates how to use pipes,but I'm having difficulty understanding it. #include <stdio.h> #include <stdlib.h> #include <unistd.h> main() { int pipefd [2], n; char buff[100] ; if( pipe( pipefd) < 0) { printf("can not create pipe \n"); } printf("read fd = %d, write fd = %d \n", pipefd[0], pipefd[1]); if ( write (pipefd[1],"hello world\n", 12)!= 12) { printf("pipe write error \n"); } if( ( n = read ( pipefd[0] , buff, sizeof ( buff) ) ) <= 0 ) { printf("pipe read error \n"); } write ( 1, buff, n ) ; exit (0); } What does the write function do? It seems to send data to the pipe and also print it to the screen (at least it seems like the second time the write function is called it does this). Does anyone have any suggestions of good websites for learning about topics such as this, FIFO, signals, other basic linux commands used in C?

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• Perl, regex, extract data from a line

  - by perlnoob

  Im trying to extract part of a line with perl use strict; use warnings; # Set path for my.txt and extract datadir my @myfile = "C:\backups\MySQL\my.txt"; my @datadir = ""; open READMYFILE, @myfile or die "Error, my.txt not found.\n"; while (<READMYFILE>) { # Read file and extract DataDir path if (/C:\backups/gi) { push @datadir, $_; } } # ensure the path was found print @datadir . " \n"; Basically at first im trying to set the location of the my.txt file. Next im trying to read it and pull part of the line with regex. The error Im getting is: Unrecognized escape \m passed through at 1130.pl line 17. I took a look at http://stackoverflow.com/questions/1040657/how-can-i-grab-multiple-lines-after-a-matching-line-in-perl to get an idea of how to read a file and match a line within it, however im not 100% sure I'm doing this right or in the best way. I also seem to produce the error: Error, my.txt not found. But the file does exist in the folder C:\backups\MySQL\

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• Images from SQL Server JPG/PNG Image Column not being Type Converted to Bitmap in HttpHandlers (cons

  - by kanchirk

  Our Silverlight 3.0 Client consumes Images stored/retrieved on the File System thorough ASP.NET HttpHandlers successfully. We are trying to store and read back Images using a SQL Server 2008 Database. Please find the stripped down code pasted below with the Exception. "Bitmap is not Valid" //Store document to the database private void SaveImageToDatabaseKK(HttpContext context, string pImageFileName) { try { //ADO.NET Entity Framework ImageTable documentDB = new ImageTable(); int intLength = Convert.ToInt32(context.Request.InputStream.Length); //Move the file contents into the Byte array Byte[] arrContent = new Byte[intLength]; context.Request.InputStream.Read(arrContent, 0, intLength); //Insert record into the Document table documentDB.InsertDocument(pImageFileName, arrContent, intLength); } catch { } } =The method to Read Back the Row from the Table and Send it back is below.= private void RetrieveImageFromDatabaseTableKK(HttpContext context, string pImageName) { try { ImageTable documentDB = new ImageTable(); var docRow = documentDB.GetDocument(pImageName); //based on Imagename which is unique //DocData column in table is **Image** if (docRow!=null && docRow.DocData != null && docRow.DocData.Length > 0) { Byte[] bytImage = docRow.DocData; if (bytImage != null && bytImage.Length > 0) { Bitmap newBmp = ConvertToBitmap(context, bytImage ); if (newBmp != null) { newBmp.Save(context.Response.OutputStream, ImageFormat.Jpeg); newBmp.Dispose(); } } } } catch (Exception exRI) { } } // Convert byte array to Bitmap (byte[] to Bitmap) protected Bitmap ConvertToBitmap(byte[] bmp) { if (bmp != null) { try { TypeConverter tc = TypeDescriptor.GetConverter(typeof(Bitmap)); Bitmap b = (Bitmap)tc.ConvertFrom(bmp); **//This is where the Exception Occurs.** return b; } catch (Exception) { } } return null; }

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• Properties vs. Fields: Need help grasping the uses of Properties over Fields.

  - by pghtech

  First off, I have read through a list of postings on this topic and I don't feel I have grasped properties because of what I had come to understand about encapsulation and field modifiers (private, public..ect). One of the main aspects of C# that I have come to learn is the importance of data protection within your code by the use of encapsulation. I 'thought' I understood that to be because of the ability of the use of the modifiers (private, public, internal, protected). However, after learning about properties I am sort of torn in understanding not only properties uses, but the overall importance/ability of data protection (what I understood as encapsulation) within C#. To be more specific, everything I have read when I got to properties in C# is that you should try to use them in place of fields when you can because of: 1) they allow you to change the data type when you can't when directly accessing the field directly. 2) they add a level of protection to data access However, from what I 'thought' I had come to know about the use of field modifiers did #2, it seemed to me that properties just generated additional code unless you had some reason to change the type (#1) - because you are (more or less) creating hidden methods to access fields as opposed to directly. Then there is the whole modifiers being able to be added to Properties which further complicates my understanding for the need of properties to access data. I have read a number of chapters from different writers on "properties" and none have really explained a good understanding of properties vs. fields vs. encapsulation (and good programming methods). Can someone explain: 1) why I would want to use properties instead of fields (especially when it appears I am just adding additional code 2) any tips on recognizing the use of properties and not seeing them as simply methods (with the exception of the get;set being apparent) when tracing other peoples code? 3) Any general rules of thumb when it comes to good programming methods in relation to when to use what? Thanks and sorry for the long post - I didn't want to just ask a question that has been asked 100x without explaining why I am asking it again.

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• XML problem in the basic menu example

  - by arakn0

  Hi there, I am trying to create an app with some menus, an I am following the basic example available in the official android site: http://developer.android.com/guide/topics/ui/menus.html My problems appear when I define the menu in the XML. After creating the folder res/menu and creating the menu_option.xml file from eclipse.... The project (in general) gives an error that can be read from the Problems tab: Unparsed aapt error(s)! Check the console for output Android Packaging Problem So, changing to the Console tab to get more information about the problem, this can be read: [2010-06-02 11:35:54 - TestAudio] Error in an XML file: aborting build. [2010-06-02 11:35:54 - TestAudio] W/ResourceType(11566): Bad XML block: header size 63327 or total size -144759824 is larger than data size 0 [2010-06-02 11:35:54 - TestAudio] /home/User/workspace/TestAudio/res/menu/options_menu.xml:1: error: Error parsing XML: no element found The strange thing is that eclipse recognizes the menu items that I've defined in the XML,I can reference them in the code with no problems and my main activity builds. (and the rest of the files too). Could it be that when eclipse creates a file, for some reason, the Android SDK has problems to read it, or something similar?? The XML code is exactly the same as the one in the example, so I don't really know what is happening. The code in options_menu.xml is this: <menu xmlns:android="http://schemas.android.com/apk/res/android" <item android:id="@+id/new_game" android:title="New Game" / <item android:id="@+id/quit" android:title="Quit" / </menu Thanks in advance for your help!

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• Using sqldatareader in asp.net

  - by Phil

  I have this code to get data; s = "select documents.filename, documents.description, documents.filesize from documents, contentdocuments, content where contentdocuments.contentid = content.id and content.id = @contentid and contentdocuments.documentsid = documents.id ORDER BY documents.description" x = New SqlCommand(s, c) x.Parameters.Add("@contentid", SqlDbType.Int) x.Parameters("@contentid").Value = contentid c.Open() r = x.ExecuteReader If r.Read Then DownloadsRepeater.DataSource = r DownloadsRepeater.DataBind() **imagepath = "<img src='images/'" & getimage(r("filename")) & " border='0'** align='absmiddle'" End If c.Close() r.Close() The problem is on the line; imagepath = "<img src='images/'" & getimage(r("filename")) & " The error is; Invalid attempt to read when no data is present. How can I check to make sure data is present and get rid of this error? I thought the 'if r.read' did this? Thanks :EDIT: Function getimage(ByVal strin As String) As String If strin > "" Then dotpos = InStrRev(strin, ".") ext = Right(strin, Len(strin) - dotpos) getimage = ext & ".gif" End If Return getimage End Function

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• With regards to urllib AttributeError: 'module' object has no attribute 'urlopen'

  - by Matt

  import re import string import shutil import os import os.path import time import datetime import math import urllib from array import array import random filehandle = urllib.urlopen('http://www.google.com/') #open webpage s = filehandle.read() #read print s #display #what i plan to do with it once i get the first part working #results = re.findall('[<td style="font-weight:bold;" nowrap>$][0-9][0-9][0-9][.][0-9][0-9][</td></tr></tfoot></table>]',s) #earnings = '$ ' #for money in results: #earnings = earnings + money[1]+money[2]+money[3]+'.'+money[5]+money[6] #print earnings #raw_input() this is the code that i have so far. now i have looked at all the other forums that give solutions such as the name of the script, which is parse_Money.py, and i have tried doing it with urllib.request.urlopen AND i have tried running it on python 2.5, 2.6, and 2.7. If anybody has any suggestions it would be really welcome, thanks everyone!! --Matt ---EDIT--- I also tried this code and it worked, so im thinking its some kind of syntax error, so if anybody with a sharp eye can point it out, i would be very appreciative. import shutil import os import os.path import time import datetime import math import urllib from array import array import random b = 3 #find URL URL = raw_input('Type the URL you would like to read from[Example: http://www.google.com/] :') while b == 3: #get file name file1 = raw_input('Enter a file name for the downloaded code:') filepath = file1 + '.txt' if os.path.isfile(filepath): print 'File already exists' b = 3 else: print 'Filename accepted' b = 4 file_path = filepath #open file FileWrite = open(file_path, 'a') #acces URL filehandle = urllib.urlopen(URL) #display souce code for lines in filehandle.readlines(): FileWrite.write(lines) print lines print 'The above has been saved in both a text and html file' #close files filehandle.close() FileWrite.close()

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• Zend_Validate_Abstract custom validator not displaying correct error messages.

  - by Jeremy Dowell

  I have two text fields in a form that I need to make sure neither have empty values nor contain the same string. The custom validator that I wrote extends Zend_Validate_Abstract and works correctly in that it passes back the correct error messages. In this case either: isEmpty or isMatch. However, the documentation says to use addErrorMessages to define the correct error messages to be displayed. in this case, i have attached ->addErrorMessages(array("isEmpty"=>"foo", "isMatch"=>"bar")); to the form field. According to everything I've read, if I return "isEmpty" from isValid(), my error message should read "foo" and if i return "isMatch" then it should read "bar". This is not the case I'm running into though. If I return false from is valid, no matter what i set $this-_error() to be, my error message displays "foo", or whatever I have at index[0] of the error messages array. If I don't define errorMessages, then I just get the error code I passed back for the display and I get the proper one, depending on what I passed back. How do I catch the error code and display the correct error message in my form? The fix I have implemented, until I figure it out properly, is to pass back the full message as the errorcode from the custom validator. This will work in this instance, but the error message is specific to this page and doesn't really allow for re-use of code. Things I have already tried: I have already tried validator chaining so that my custom validator only checks for matches: ->setRequired("true") ->addValidator("NotEmpty") ->addErrorMessage("URL May Not Be Empty") ->addValidator([*customValidator]*) ->addErrorMessage("X and Y urls may not be the same") But again, if either throws an error, the last error message to be set displays, regardless of what the error truly is. I'm not entirely sure where to go from here. Any suggestions?

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• What is reading source on an ebook reader like?

  - by Daniel Straight

  There are a few open source projects I would really like to read through the code of to understand better / improve on. The problem is, for me, reading for a long time on the computer screen is tedious. I would love to be able to read code while lounging around and on a screen that was better on my eyes. Has anyone ever tried reading code on an ebook reader? It seems like the e-ink would make it easy on the eyes, plus it would be portable, plus it wouldn't kill any trees. In other words, it sounds perfect, but before I drop a couple benjamins on an ebook reader, I'd like to hear if anyone else has tried this and how it went. It seems Scott Hanselman discussed using the Kindle to read code, but I wouldn't necessarily want a Kindle. Has anyone had a positive experience with some other device? I realize this is not directly about programming, but it relates directly to my ability to improve my skills. I think if a good portable reading device for code exists, it could help a lot of programmers.

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• Threading Practice with Polling.

  - by Stacey

  I have a C# application that has to constantly read from a program; sometimes there is a chance it will not find what it needs, which will throw an exception. This is a limitation of the program it has to read from. This frequently causes the program to lock up as it tries to poll. So I solved it by spawning the 'polling' off into a separate thread. However watching the debugger, the thread is created and destroyed each time. I am uncertain if this is typical or not; but my question is, is this good practice, or am I using the threading for the wrong purpose? ProgramReader { static Thread oThread; public static void Read( Program program ) { // check to see if the program exists if ( false ) oThread = new ThreadStart(program.Poll); if(oThread != null || !oThread.IsAlive ) oThread.Start(); } } This is my general pseudocode. It runs every 10 seconds or so. Is this a huge hit to performance? The operation it performs is relatively small and lightweight; just repetitive.

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• BinaryWriterWith7BitEncoding & BinaryReaderWith7BitEncoding

  - by Tim

  Mr. Ayende wrote in his latest blog post about an implementation of a queue. In the post he's using two magical files: BinaryWriterWith7BitEncoding & BinaryReaderWith7BitEncoding BinaryWriterWith7BitEncoding can write both int and long? using the following method signatures: void WriteBitEncodedNullableInt64(long? value) & void Write7BitEncodedInt(int value) and BinaryReaderWith7BitEncoding can read the values written using the following method signatures: long? ReadBitEncodedNullableInt64() and int Read7BitEncodedInt() So far I've only managed to find a way to read the 7BitEncodedInt: protected int Read7BitEncodedInt() { int value = 0; int byteval; int shift = 0; while(((byteval = ReadByte()) & 0x80) != 0) { value |= ((byteval & 0x7F) << shift); shift += 7; } return (value | (byteval << shift)); } I'm not too good with byte shifting - does anybody know how to read and write the 7BitEncoded long? and write the int ?

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• 1k of Program Space, 64 bytes of RAM. Is assembly an absolute must?

  - by Earlz

  (If your lazy see bottom for TL;DR) Hello, I am planning to build a new (prototype) project dealing with physical computing. Basically, I have wires. These wires all need to have their voltage read at the same time. More than a few hundred microseconds difference between the readings of each wire will completely screw it up. The Arduino takes about 114 microseconds. So the most I could read is 2 or 3 wires before the latency would skew the accuracy of the readings. So my plan is to have an Arduino as the "master" of an array of ATTinys. The arduino is pretty cramped for space, but it's a massive playground compared to the tinys. An ATTiny13A has 1k of flash ROM(program space), 64 bytes of RAM, and 64 bytes of (not-durable and slow) EEPROM. (I'm choosing this for price as well as size) The ATTinys in my system will not do much. Basically, all they will do is wait for a signal from the Master, and then read the voltage of 1 or 2 wires and store it in RAM(or possibly EEPROM if it's that cramped). And then send it to the Master using only 1 wire for data.(no room for more than that!). So far then, all I should have to do is implement trivial voltage reading code (using built in ADC). But this communication bit I'm worried about. Do you think a communication protocol(using just 1 wire!) could even be implemented in such constraints? TL;DR: In less than 1k of program space and 64 bytes of RAM(and 64 bytes of EEPROM) do you think it is possible to implement a 1 wire communication protocol? Would I need to drop to assembly to make it fit? I know that currently my Arduino programs linking to the Wiring library are over 8k, so I'm a bit concerned.

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• Some Async Socket Code - Help with Garbage Collection?

  - by divinci

  Hi all, I think this question is really about my understanding of Garbage collection and variable references. But I will go ahead and throw out some code for you to look at. // Please note do not use this code for async sockets, just to highlight my question // SocketTransport // This is a simple wrapper class that is used as the 'state' object // when performing Async Socket Reads/Writes public class SocketTransport { public Socket Socket; public byte[] Buffer; public SocketTransport(Socket socket, byte[] buffer) { this.Socket = socket; this.Buffer = buffer; } } // Entry point - creates a SocketTransport, then passes it as the state // object when Asyncly reading from the socket. public void ReadOne(Socket socket) { SocketTransport socketTransport_One = new SocketTransport(socket, new byte[10]); socketTransport_One.Socket.BeginRecieve ( socketTransport_One.Buffer, // Buffer to store data 0, // Buffer offset 10, // Read Length SocketFlags.None // SocketFlags new AsyncCallback(OnReadOne), // Callback when BeginRead completes socketTransport_One // 'state' object to pass to Callback. ); } public void OnReadOne(IAsyncResult ar) { SocketTransport socketTransport_One = ar.asyncState as SocketTransport; ProcessReadOneBuffer(socketTransport_One.Buffer); // Do processing // New Read // Create another! SocketTransport (what happens to first one?) SocketTransport socketTransport_Two = new SocketTransport(socket, new byte[10]); socketTransport_Two.Socket.BeginRecieve ( socketTransport_One.Buffer, 0, 10, SocketFlags.None new AsyncCallback(OnReadTwo), socketTransport_Two ); } public void OnReadTwo(IAsyncResult ar) { SocketTransport socketTransport_Two = ar.asyncState as SocketTransport; .............. So my question is: The first SocketTransport to be created (socketTransport_One) has a strong reference to a Socket object (lets call is ~SocketA~). Once the async read is completed, a new SocketTransport object is created (socketTransport_Two) also with a strong reference to ~SocketA~. Q1. Will socketTransport_One be collected by the garbage collector when method OnReadOne exits? Even though it still contains a strong reference to ~SocketA~ Thanks all!

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• Time delay an external RSS feed

  - by x3ja

  I subscribe to a number of RSS feeds, mostly from within my own timezone (UK: currently GMT+1, a.k.a BST). However I'm also interested in news from New Zealand (currently GMT+12). My problem is caused by my addiction to needing to keep my unread count at, or near, zero. When I load up my RSS reader in the mornings it has gathered all the NZ news at once (normally around 100 items) and I feel compelled either to read them all or to mark them all as read to feed my need for zero-unread-count. I figured a good solution to this would be to time delay the RSS feed somehow, so I would be drip-fed the stories at their time +12 hours, so I could read them through the day as they come in. So my question (or, rather, questions): Does such a thing exist currently & what is it? (no point reworking the wheel) If not: What would be the best way to approach doing this myself? I have access to a Linux web server on which I can run scripts, create databases, store files etc, so there should be a way... I'm most conversant in perl and have done a little fiddling with XML within that, so would naturally process ... or is there some simpler way to do it that I'm missing?

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• Interface for reading variable length files with header and footer.

  - by John S

  I could use some hints or tips for a decent interface for reading file of special characteristics. The files in question has a header (~120 bytes), a body (1 byte - 3gb) and a footer (4 bytes). The header contains information about the body and the footer is only a simple CRC32-value of the body. I use Java so my idea was to extend the "InputStream" class and add a constructor such as "public MyInStream( InputStream in)" where I immediately read the header and the direct the overridden read()'s the body. Problem is, I can't give the user of the class the CRC32-value until the whole body has been read. Because the file can be 3gb large, putting it all in memory is a be an idea. Reading it all in to a temporary file is going to be a performance hit if there are many small files. I don't know how large the file is because the InputStream doesn't have to be a file, it could be a socket. Looking at it again, maybe extending InputStream is a bad idea. Thank you for reading the confused thoughts of a tired programmer. :)

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• Which version of Grady Booch's OOA/D book should I buy?

  - by jackj

  Grady Booch's "Object-Oriented Analysis and Design with Applications" is available brand new in both the 2nd edition (1993) and the 3rd edition (2007), while many used copies of both editions are available. Here are my concerns: 1) The 2nd edition uses C++: given that I just finished reading my first two C++ books (Accelerated C++ and C++ Primer) I guess practical tips can only help, so the 2nd edition is probably best (I think the 3rd edition has absolutely no code). On the other hand, the C++ books I read insist on the importance of using standard C++, whereas Booch's 2nd edition was published before the 1998 standard. 2) The 2nd edition is shorter (608 pages vs. 720) so, I guess, it will be slightly easier to get through. 3) The 3rd edition uses UML 2.0, whereas the 2nd edition is pre-UML. Some reviews say that the notation in the 2nd edition is close enough to UML, so it doesn't matter, but I don't know if I should be worrying about this or not. 4) The 2nd edition is available in good-shape used copies for considerably less than what the 3rd one goes for. Given all the above factors, do you think I should buy the 2nd or the 3rd edition? Recommendations on other books are also welcome but I would prefer it if whoever answers has read at least one of the versions of Booch's book (preferably both!). I have already bought but not read GoF and Riel's books. I also know that I should practice a lot with real-life code. Thanks.

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• NSDictionary, NSArray, NSSet and efficiency

  - by ryyst

  Hi, I've got a text file, with about 200,000 lines. Each line represents an object with multiple properties. I only search through one of the properties (the unique ID) of the objects. If the unique ID I'm looking for is the same as the current object's unique ID, I'm gonna read the rest of the object's values. Right now, each time I search for an object, I just read the whole text file line by line, create an object for each line and see if it's the object I'm looking for - which is basically the most inefficient way to do the search. I would like to read all those objects into memory, so I can later search through them more efficiently. The question is, what's the most efficient way to perform such a search? Is a 200,000-entries NSArray a good way to do this (I doubt it)? How about an NSSet? With an NSSet, is it possible to only search for one property of the objects? Thanks for any help! -- Ry

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• how to get the source code as register user.

  - by nir143

  hi. i downloaded a sourcecode of a site,but i downloaded it i saw it identify my program as a guest,i search at google and figure out that i can send a cookie when i "ask" the source code. that what i have managed to do and it still dont identify me as register user: CookieContainer cj = new CookieContainer(); string all = ""; HttpWebRequest req = (HttpWebRequest)WebRequest.Create(Url); req.CookieContainer = cj; HttpWebResponse res = (HttpWebResponse)req.GetResponse(); CookieCollection cs=cj.GetCookies(req.RequestUri); CookieContainer cc = new CookieContainer(); cc.Add(cs); req.CookieContainer = cc; StreamReader read = new StreamReader(res.GetResponseStream()); all = read.ReadToEnd(); read.Close(); return all; what is wrong here? tyvm for help:) (if that help,i can have a simple details of a register user of the site).

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• Rails: Multi-Step New User Signup Form (FSM?)

  - by neezer

  I've read the "Create Multi-Step Wizard" in Advanced Rails Recipes. I've also read and re-read the documentation for the updated FSM I'm using called Workflow, and looked here and here. The Advanced Rails Recipe focuses on records (quizzes) that already exist, and doesn't cover creating new ones. The Workflow docs don't cover any code for controllers or views, so I've no idea what to do with all this model magic, and the last two links barely touch on implementation either. From the aforementioned resources, I have a good understanding of what a FSM in Rails is and how to play with it in the console or IRB, but I've got very little direction or understanding how to implement one into my Rails app. What I would like is this: a simple, multi-step user signup process. Step 1: User enters in their critical details (with validations). Step 2: User enters in their search criteria, for their profile (with validations). Step 3: User agrees to the Terms of Service (with validations). Step 4: User is greeted by a confirmation page, including a link that takes them to their newly created account. I'd also like full navigation between the steps and full capture (saves to the database) with each transition. Can someone please give me a clear implementation of something similar to this? I would LOVE an example app that includes a multi-step signup process where I can look at the code (FULL source code--models AND controllers and views) under the hood, but I've been unable to find anything like that. Any guidance would be appreciated! EDIT: Please help make this a Railscast! Ryan B. (a.k.a. Superman), if you're reading this, we need you! http://feedback.railscasts.com/forums/77-episode-suggestions/suggestions/35553-multi-step-forms-and-wizards

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• Elegant way of parsing Data files for Simulation

  - by sc_ray

  I am working on this project where I need to read in a lot of data from .dat files and use the data to perform simulations. The data in my .dat file looks as follows: DeviceID InteractingDeviceID InteractionStartTime InteractionEndTime 1 2 1101 1105 1,2 1101 and 1105 are tab delimited and it means Device 1 interacted with Device 2 at 1101 ms and ended the interaction at 1105ms. I have a trace data sets that compile thousands of such interactions and my job is to analyze these interactions. The first step is to parse the file. The language of choice is C++. The approach I was thinking of taking was to read the file, for every line that's read create a Device Object. This Device object will contain the property DeviceId and an array/vector of structs, that will contain a list of all the devices the given DeviceId interacted with over the course of the simulation.The struct will contain the Interacting Device Id, Interaction Start Time and Interaction End Time. I have a two fold question here: Is my approach correct? If I am on the right track, how do I rapidly parse these tab delimited data files and create Device objects without excessive memory overhead using C++? A push in the right direction will be much appreciated. Thanks

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• Who architected / designed C++'s IOStreams, and would it still be considered well-designed by today'

  - by stakx

  First off, it may seem that I'm asking for subjective opinions, but that's not what I'm after. I'd love to hear some well-grounded arguments on this topic. In the hope of getting some insight into how a modern streams / serialization framework ought to be designed, I recently got myself a copy of the book Standard C++ IOStreams and Locales by Angelika Langer and Klaus Kreft. I figured that if IOStreams wasn't well-designed, it wouldn't have made it into the C++ standard library in the first place. After having read various parts of this book, I am starting to have doubts if IOStreams can compare to e.g. the STL from an overall architectural point-of-view. Read e.g. this interview with Alexander Stepanov (the STL's "inventor") to learn about some design decisions that went into the STL. What surprises me in particular: It seems to be unknown who was responsible for IOStreams' overall design (I'd love to read some background information about this — does anyone know good resources?); Once you delve beneath the immediate surface of IOStreams, e.g. if you want to extend IOStreams with your own classes, you get to an interface with fairly cryptic and confusing member function names, e.g. getloc/imbue, uflow/underflow, snextc/sbumpc/sgetc/sgetn, pbase/pptr/epptr (and there's probably even worse examples). This makes it so much harder to understand the overall design and how the single parts co-operate. Even the book I mentioned above doesn't help that much (IMHO). Thus my question: If you had to judge by today's software engineering standards (if there actually is any general agreement on these), would C++'s IOStreams still be considered well-designed? (I wouldn't want to improve my software design skills from something that's generally considered outdated.)

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• 1k of Program Space, 64 bytes of RAM. Is 1 wire communication possible?

  - by Earlz

  (If your lazy see bottom for TL;DR) Hello, I am planning to build a new (prototype) project dealing with physical computing. Basically, I have wires. These wires all need to have their voltage read at the same time. More than a few hundred microseconds difference between the readings of each wire will completely screw it up. The Arduino takes about 114 microseconds. So the most I could read is 2 or 3 wires before the latency would skew the accuracy of the readings. So my plan is to have an Arduino as the "master" of an array of ATTinys. The arduino is pretty cramped for space, but it's a massive playground compared to the tinys. An ATTiny13A has 1k of flash ROM(program space), 64 bytes of RAM, and 64 bytes of (not-durable and slow) EEPROM. (I'm choosing this for price as well as size) The ATTinys in my system will not do much. Basically, all they will do is wait for a signal from the Master, and then read the voltage of 1 or 2 wires and store it in RAM(or possibly EEPROM if it's that cramped). And then send it to the Master using only 1 wire for data.(no room for more than that!). So far then, all I should have to do is implement trivial voltage reading code (using built in ADC). But this communication bit I'm worried about. Do you think a communication protocol(using just 1 wire!) could even be implemented in such constraints? TL;DR: In less than 1k of program space and 64 bytes of RAM(and 64 bytes of EEPROM) do you think it is possible to implement a 1 wire communication protocol? Would I need to drop to assembly to make it fit? I know that currently my Arduino programs linking to the Wiring library are over 8k, so I'm a bit concerned.

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• ACL architechture for a Software As a service in Sprgin 3.0

  - by geoaxis

  I am making a software as a service using Spring 3.0 (Spring MVC, Spring Security, Spring Roo, Hibernate) I have to come up with a flexible access control list mechanism.I have three different kinds of users System (who can do any thing to the system, includes admin and internal daemons) Operations (who can add and delete users, organizations, and do maintenance work on behalf of users and organizations) End Users (they belong to one or more organization, for each organization, the user can have one or more roles, like being organization admin, or organization read-only member) (role like orgadmin can also add users for that organization) Now my question is, how should i model the entity of User? If I just take the End User, it can belong to one or more organizations, so each user can contain a set of references to its organizations. But how do we model the users role for each organization, So for example User UX belongs to organizations og1, og2 and og3, and for og1 he is both orgadmin, and org-read-only-user, where as for og2 he is only orgadmin and for og3 he is only org-read-only-user I have the possibility of making each user belong to one organization alone, but that's making the system bounded and I don't like that idea (although i would still satisfy the requirement) If you have a better extensible ACL architecture, please suggest it. Since its a software as a service, one would expect that alot of different organizations would be part if the same system. I had one concern that it is not a good idea to keep og1 and og2 data on the same DB (if og1 decides to spawn a 100 reports on the system, og2 should not suffer) But that is some thing advanced for now and is not directly related to ACL but to the physical distribution of data and setup of services based on those ACLs This is a community Wiki question, please correct any thing which you wish to do so. Thanks

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• Speeding up inner-joins and subqueries while restricting row size and table membership

  - by hiffy

  I'm developing an rss feed reader that uses a bayesian filter to filter out boring blog posts. The Stream table is meant to act as a FIFO buffer from which the webapp will consume 'entries'. I use it to store the temporary relationship between entries, users and bayesian filter classifications. After a user marks an entry as read, it will be added to the metadata table (so that a user isn't presented with material they have already read), and deleted from the stream table. Every three minutes, a background process will repopulate the Stream table with new entries (i.e. whenever the daemon adds new entries after the checks the rss feeds for updates). Problem: The query I came up with is hella slow. More importantly, the Stream table only needs to hold one hundred unread entries at a time; it'll reduce duplication, make processing faster and give me some flexibility with how I display the entries. The query (takes about 9 seconds on 3600 items with no indexes): insert into stream(entry_id, user_id) select entries.id, subscriptions_users.user_id from entries inner join subscriptions_users on subscriptions_users.subscription_id = entries.subscription_id where subscriptions_users.user_id = 1 and entries.id not in (select entry_id from metadata where metadata.user_id = 1) and entries.id not in (select entry_id from stream where user_id = 1); The query explained: insert into stream all of the entries from a user's subscription list (subscriptions_users) that the user has not read (i.e. do not exist in metadata) and which do not already exist in the stream. Attempted solution: adding limit 100 to the end speeds up the query considerably, but upon repeated executions will keep on adding a different set of 100 entries that do not already exist in the table (with each successful query taking longer and longer). This is close but not quite what I wanted to do. Does anyone have any advice (nosql?) or know a more efficient way of composing the query?

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