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• MYSQL Convert rows to columns performance problem

  - by Tarski

  I am doing a query that converts rows to columns similar to this post but have encountered a performance problem. Here is the query:- SELECT Info.Customer, Answers.Answer, Answers.AnswerDescription, Details.Code1, Details.Code2, Details.Code3 FROM Info LEFT OUTER JOIN Answers ON Info.AnswerID = Answers.AnswerID LEFT OUTER JOIN (SELECT ReferenceNo, MAX(CASE DetailsIndicator WHEN 'cde1' THEN DetailsCode ELSE NULL END ) Code1, MAX(CASE DetailsIndicator WHEN 'cde2' THEN DetailsCode ELSE NULL END ) Code2, MAX(CASE DetailsIndicator WHEN 'cde3' THEN DetailsCode ELSE NULL END ) Code3 FROM DetailsData GROUP BY ReferenceNo) Details ON Info.ReferenceNo = Details.ReferenceNo There are less than 300 rows returned, but the Details table is about 180 thousand rows. The query takes 45 seconds to run and needs to take only a few seconds. When I type show processlist; into MYSQL it is hanging on "Sending Data". Any thoughts as to what the performance problem might be?

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• Can't Use Path in ASP MVC Action

  - by user1477388

  I am trying to use Path() but it has a blue line under it and says, "local variable (path) cannot be referred to until it is declared." How can I use Path()? Imports System.Globalization Imports System.IO Public Class MessageController Inherits System.Web.Mvc.Controller <EmployeeAuthorize()> <HttpPost()> Function SendReply(ByVal id As Integer, ByVal message As String, ByVal files As IEnumerable(Of HttpPostedFileBase)) As JsonResult ' upload files For Each i In files If (i.ContentLength > 0) Then Dim fileName = path.GetFileName(i.FileName) Dim path = path.Combine(Server.MapPath("~/App_Data/uploads"), fileName) i.SaveAs(path) End If Next End Function End Class

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• declarative authorization and has_and_belongs_to_many

  - by Michael Balsiger

  Hi, I have a little problem with declarative-authorization. I have a User and Role Model with a has_and_belongs_to_many association. I've created a Role named :moderator in my authorization_rules.rb Is it possible that a User with the Role Moderator only gets the Users that have the Moderator Role assigned to it?? -- User.with_permissions_to(:index) I thought it would be possible like that: role :moderator do has_permission_on :users, :to => :index do if_attribute :roles => contains { ????? } end end I also created a named_scope in my User Model because I thought it would help... class User has_and_belongs_to_many :roles named_scope :by_role, lambda { |role| { :include => :roles, :conditions => {"roles.name" => role} } } end Does anyone knows if it's possible to do this with declarative_authorization? Thanks for your help!

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• Access/Download server files, not in site root, with PHP

  - by user271619

  Usually I save documents (images, mpegs, excel, word docs, etc...) for my friends or family on my website's root, inside a directory called /files/ or something similar. Nothing too uncommon. But, I have been playing with user session control, and allowing users to upload files to the dedicated /files/ directory. (the file names are saved in a db, with that user's ID) But, that means other people could try to guess and locate other people's files. I do randomize the file names, upon upload. And I stop the apache from displaying the /files/ directory content. However, I'd like to start saving the files outside of the website's root. This way it can't be accessible via the browser. I don't have any code to show, but I didn't want to even start on this endeavor if it's not able to be accomplished. I did find this snippet that shows how to display an image, from outside your website root: $file = $_GET['file']; $fileDir = '/path/to/files/'; if (file_exists($fileDir . $file)) { // Note: You should probably do some more checks // on the filetype, size, etc. $contents = file_get_contents($fileDir . $file); // Note: You should probably implement some kind // of check on filetype header('Content-type: image/jpeg'); echo $contents; } ? Maybe I can use this for any file type, but has anyone heard of a better way to allow users (logged in) to access their files from online, but not letting other users has similar access?

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• VB.NET - ASP.NET - MS-Access - SQL Statement

  - by Brian

  I have a button which when pressed, sets the user's rights in the db. (If Administrator UserTypeID is set to '2' and if Customer it is set to '1'). However when I run the below code, everything remains the same. I think it's from the SQL statement but I;m not sure. Can anyone help please? Protected Sub btnSetUser_Click(sender As Object, e As System.EventArgs) Handles btnSetUser.Click Dim conn As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Users\Brian\Documents\Visual Studio 2010\WebSites\WebSite3\db.mdb;") Dim cmd As OleDbCommand = New OleDbCommand("UPDATE [User] SET [UserTypeID] WHERE Username=?", conn) conn.Open() cmd.Parameters.AddWithValue("@Username", txtUser.Text) If ddUserType.SelectedItem.Text = "Administrator" Then cmd.Parameters.AddWithValue("@UserTypeID", "2") cmd.ExecuteNonQuery() lblSetUser.Text = txtUser.Text + "was set to Administrator." ElseIf ddUserType.SelectedItem.Text = "Customer" Then cmd.Parameters.AddWithValue("@UserTypeID", "1") cmd.ExecuteNonQuery() lblSetUser.Text = txtUser.Text + "was set to Customer." End If conn.Close() End Sub End Class

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• Batch file: Extracting substring from input parameter to use in IF statement

  - by Neomoon

  This is a very basic example of what I am trying to implement in a more complex batch file. I would like to extract a substring from an input parameter (%1) and branch based on if the substring was found or not. @echo off SETLOCAL enableextensions enabledelayedexpansion SET _testvariable=%1 SET _testvariable=%_testvariable:~4,3% ECHO %_testvariable% IF %_testvariable%=act CALL :SOME IF NOT %_testvariable%=act CALL :ACTION :SOME ECHO Substring found GOTO :END :ACTION ECHO Substring not found GOTO :END ENDLOCAL :END This is what my ouput looks like: C:\>test someaction act =act was unexpected at this time. If possible I would like to turn this in to a IF/ELSE statement and evaluate directly from %1. However I have not had success with either.

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• Allow paste in worksheet without overwriting locked cells

  - by jjeaton

  I have a protected worksheet that users would like to copy and paste into. I have no control over the workbook they are copying from. The protected worksheet has some rows that are available for data entry, and other rows that are locked and greyed out to the user. The users would like to be able to paste over the top of the entire worksheet from another random workbook and have all the cells available for data entry filled in, while the locked cells are undisturbed. In the current state, the user gets an error when they try to paste, because it cannot paste over the locked cells. Example: Worksheet 1: Act1 100 100 100 Act2 100 100 100 Act3 100 100 100 Worksheet 2: (The second row is locked) Act1 300 300 300 Act2 200 200 200 Act3 100 100 100 After copying/pasting Worksheet 2 should look like this: Act1 100 100 100 Act2 200 200 200 Act3 100 100 100 The values from worksheet 1 are populated and the locked rows are undisturbed. I've been thinking along the lines of having a hook where on paste, the locked cells are unlocked so that the paste can happen, and then are reverted to their original values and relocked. Is there some way I can loop through the cells in the clipboard and only paste cells where the target isn't locked? It is preferable to not create a separate button for paste, so there is less impact on the users, but if that's the only way, I'm not opposed to it. Currently, I plan on grouping the locked rows together, so that the data entry cells are contiguous, but then the accounts will be out of order, which is not preferred.

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• Find missing birth days in Apple Addressbook

  - by Felix Ogg

  I am trying to clean the holes out of my Mac address book. As a first step I want to ask all my friends for their birth day, to be able to congratulate them with cheesy Hallmark cards. I need a "group" in my address book, to mailmerge personalized messages from. This is the Applescript I came up with: tell application "Address Book" make new group with properties {name:"No Birthday"} set birthdayPeople to (get every person whose birth date is greater than date "Monday, January 1, 1900 12:00:00 AM") repeat with i from 1 to number of items in people set thePerson to item i of people if not (birthdayPeople contains thePerson) then add thePerson to group "No Birthday" end if end repeat save end tell It breaks, but from the error messages I cannot deduce what is wrong: Result: error "Can’t make «class azf4» id \"05F770BA-7492-436B-9B58-E24F494702F8:ABPerson\" of application \"Address Book\" into type vector." number -1700 from «class azf4» id "05F770BA-7492-436B-9B58-E24F494702F8:ABPerson" to vector (BTW: Did I mention this is my first AppleScript code, EVER? So, if this code can be simplified, or made more elegant, that is welcome too.)

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• Spaces in SETX PATH command

  - by Jeremy Stein

  Suppose my PATH is C:\WINDOWS\system32\;C:\Program Files\Important\ SET NEW_PATH=C:\My\Dir\ SETX PATH "%PATH%;%NEW_PATH%" Results in a path of: C:\WINDOWS\system32\;C:\Program Files\Important\;C:\My\Dir" Notice the quotation mark at the end of the path. It's as though the backslash at the end of %NEW_PATH% escaped the final quote mark. I need the quotation marks because I have spaces in my path, but I don't want backslashes to be interpreted as escape characters. What's the right way to include my PATH in the call to SETX?

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• Strategy for locale sensitive sort with pagination

  - by Thom Birkeland

  Hi, I work on an application that is deployed on the web. Part of the app is search functions where the result is presented in a sorted list. The application targets users in several countries using different locales (= sorting rules). I need to find a solution for sorting correctly for all users. I currently sort with ORDER BY in my SQL query, so the sorting is done according to the locale (or LC_LOCATE) set for the database. These rules are incorrect for those users with a locale different than the one set for the database. Also, to further complicate the issue, I use pagination in the application, so when I query the database I ask for rows 1 - 15, 16 - 30, etc. depending on the page I need. However, since the sorting is wrong, each page contains entries that are incorrectly sorted. In a worst case scenario, the entire result set for a given page could be out of order, depending on the locale/sorting rules of the current user. If I were to sort in (server side) code, I need to retrieve all rows from the database and then sort. This results in a tremendous performance hit given the amount of data. Thus I would like to avoid this. Does anyone have a strategy (or even technical solution) for attacking this problem that will result in correctly sorted lists without having to take the performance hit of loading all data? Tech details: The database is PostgreSQL 8.3, the application an EJB3 app using EJB QL for data query, running on JBoss 4.5.

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• Problem with Delete Link?

  - by Kevin

  When I click on the delete link I created, it doesn't do anything (even the flash[:notice] part) in the controller. Am I not calling the .delete? part correctly? The POST part works as I can add tips. Link: <%= link_to "Delete", :controller => "/admin", :action => "tips", :id => t.id, :method => :delete, :confirm => "Are you sure?" %> Admin Controller def tips @tips = Tip.all if request.post? tip = Tip.new(params[:geek_tips]) if tip.save flash[:notice] = "Saved!" redirect_to :action => "tips" else flash[:notice] = "Error!" end elsif request.delete? tip = Tip.find_by_id(params[:id]) tip.delete! flash[:notice] = "Delete Message" redirect_to :action => "tips" end end

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• How to make this code compile?

  - by skydoor

  // File: foo.c static int var; void foo() { var++; } // end of file foo.c // File bar.c: static int var; void bar() { var++; } // end of file bar.c // file main.c static int var; void main() { foo(); bar(); printf("%d", var); } // end of file main.c Question: Will the above program compile ? If so what will be the result ? I tested the code and found it couldn't be compiled. I try to use extern in main.c to use the function foo() and bar() but it still couldn't be compiled.

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• Passing single attributes to associated factories

  - by lambdabutz

  I'm looking for a way to pass fields into the factories of associated models without having to explicitly call the factory itself. For example, lets say I have some factories like so: Factory.define :person do |person| person.name "Default Bob" person.sex "M" person.house {|p| p.association(:house)} end Factory.define :house do |house| house.color "Red" house.has_ac true house.suburb {|h| h.association(:suburb)} end Factory.define :suburb do |suburb| suburb.name "Little boxes" end This is fine and all, but if I want to use factories to create someone in a specific house in a specific suburb I have do this: sub = Factory(:suburb, :name => "Blue town") house = Factory(:house, :color => "Blue", :suburb => sub) person = Factory(:person, :name => "Bill", :house => house) While this isn't bad in this small case, my actual models sometimes have 7 or 8 associations, and when I want to create an object whose associations I only care about a single attribute, the code for this starts to get really heavy. Is there somewhat I can pass attributes to nested Factories without having to recall the Factory itself?

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• Existing Calendar Software for Web Service?

  - by OverClocked

  I'd like to offer users of my web platform calendars, and also offer group calendar and public calendar features. I know of Google Calendar API, of course, but that would require all my users to have Google accounts (although, I guess the question is who does not these days). I am wondering if there are any other alternatives? I can write my own, but this has gotten to have been done thousands of times already! I am looking not so much at the front end; we'd probably going to re-skin the UI anyways. But I want a solution that has good backend support for storing events and recurring events, and maintaining multiple calendars. Ideally, the engine would also support things like shared event between different calendars, syncing with other calendars, etc. Sad thing is that this does seem like Google Calendar would cover it, but asking all the users to have to have google accounts may not be realistic. Especially since we'd also want to create group calendars, and I am not sure under who's google account that'd be, and if that'd even be covered under their terms of use. Your thoughts? Thanks.

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• Looking for a web based, embeddable file manager

  - by Kristi H.

  I'm looking for a web based, embeddable file manager. I haven't found anything suitable through Google or the Stack Overflow archives. Does anyone know of a file manager that meets the following criteria? The file manager must… …be embeddable (e.g. Flash or a Java applet) …run from my server (no storing uploads in a remote location) …be licensed for business use (fees are okay) …let me disable uploads. Users shouldn't be able to upload files, only download them …allow me to tag files and/or place them in folders …let me disable authentication or handle it from the backend. My app already has a login system and I don't want to make users log in twice …allow users to select and download multiple files …have an attractive interface The file manager should… …have an external config file …display thumbnail previews for files …be skinnable …be actively developed or at least actively maintained Thanks for your help. I need a sophisticated file manager and I'd like to avoid writing it from scratch.

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• Why is .NET faster than C++ in this case?

  - by acidzombie24

  -edit- I LOVE SLaks comment. "The amount of misinformation in these answers is staggering." :D Calm down guys. Pretty much all of you were wrong. I DID make optimizations. It turns out whatever optimizations I made wasn't good enough. I ran the code in GCC using gettimeofday (I'll paste code below) and used g++ -O2 file.cpp and got slightly faster results then C#. Maybe MS didn't create the optimizations needed in this specific case but after downloading and installing mingw I was tested and found the speed to be near identical. Justicle Seems to be right. I could have sworn I use clock on my PC and used that to count and found it was slower but problem solved. C++ speed isn't almost twice as slower in the MS compiler. When my friend informed me of this I couldn't believe it. So I took his code and put some timers onto it. Instead of Boo I used C#. I constantly got faster results in C#. Why? The .NET version was nearly half the time no matter what number I used. C++ version: #include <iostream> #include <stdio.h> #include <intrin.h> #include <windows.h> using namespace std; int fib(int n) { if (n < 2) return n; return fib(n - 1) + fib(n - 2); } int main() { __int64 time = 0xFFFFFFFF; while (1) { int n; //cin >> n; n = 41; if (n < 0) break; __int64 start = __rdtsc(); int res = fib(n); __int64 end = __rdtsc(); cout << res << endl; cout << (float)(end-start)/1000000<<endl; break; } return 0; } C# version: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Runtime.InteropServices; using System.ComponentModel; using System.Threading; using System.IO; using System.Diagnostics; namespace fibCSTest { class Program { static int fib(int n) { if (n < 2)return n; return fib(n - 1) + fib(n - 2); } static void Main(string[] args) { //var sw = new Stopwatch(); //var timer = new PAB.HiPerfTimer(); var timer = new Stopwatch(); while (true) { int n; //cin >> n; n = 41; if (n < 0) break; timer.Start(); int res = fib(n); timer.Stop(); Console.WriteLine(res); Console.WriteLine(timer.ElapsedMilliseconds); break; } } } } GCC version: #include <iostream> #include <stdio.h> #include <sys/time.h> using namespace std; int fib(int n) { if (n < 2) return n; return fib(n - 1) + fib(n - 2); } int main() { timeval start, end; while (1) { int n; //cin >> n; n = 41; if (n < 0) break; gettimeofday(&start, 0); int res = fib(n); gettimeofday(&end, 0); int sec = end.tv_sec - start.tv_sec; int usec = end.tv_usec - start.tv_usec; cout << res << endl; cout << sec << " " << usec <<endl; break; } return 0; }

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• Latex multicolumn problems

  - by midtiby

  Hi I am trying to build a table in latex where five columns have a common title centered above the columns. But the generated table does not appear as expected. (the common title is left justified instead of centered above the columns) The code looks like \documentclass{article} \begin{document} \begin{table} \centering \begin{tabular}{|l|c|c|c|r|} \multicolumn{5}{c}{Hydrotalcite} \\ \hline kalhsdfsa & 1 asdf asf asfa &7as dfas fasdf as0 & 003 \\ kalhsdfsa & 1 asdf asf asfa &7as dfas fasdf as0 & 003 \\ kalhsdfsa & 1 asdf asf asfa &7as dfas fasdf as0 & 003 \end{tabular} \caption{lala} \label{tabTableRefereaSDasdnce} \end{table} \end{document} And I'm running miktex 2.8 on Windows XP

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• Is this the right way to organize my database tables?

  - by Moss

  So I'm making a website that allows users to build contact lists. So their are users, the users have lists, and the lists have contacts. It seems to me that I need 3 tables for this but I just want to make sure. There would be a User table of course, and then a "List of Lists" table that has the username, and listname, as primary key along with whatever other info we want to attach to the lists as a whole. Finally, for lack of a better word, the List table which would again have the username/listname p.k., then the contact ID and notes and such that the user attaches to that contact on that specific list. I hope that is a clear explanation. For some reason I feel unsure about this arrangement. For one thing if the website becomes popular the List table could swell to billions of rows. And it also feels a little weird that everybody's list info is all jumbled up in the same table. I suppose I could create separate tables for each user and even for each list but that seems like a bad idea for other reasons. My db explanation assumes I can use foreign keys on my tables which at the moment isn't actually an option. If I can't get InnoDB tables enabled I will probably use ID's for the lists instead of depending on a compound key. Maybe I should do this anyway?

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• How do I copy input from one textbox to another via checkbox using jQuery?

  - by Jesse

  I'm cleaning up a simple form that has a Start Date textbox and an End Date textbox. I want to add a checkbox in between these fields that the user can check if the End Date is the same as the Start Date, so when they check it, the Start Date input value (e.g., 04/01/09) will automagically appear in the End Date textbox, so they don't have to type in the same date twice. Does that make sense? BTW, I'm using the sexy jquery datepicker UI, and it's sweet, but I just can't figure out the above problem. I know there's a simple solution (event handler?) but I'm stumped.

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• Checking for valid email addresses

  - by Roland

  I'm running a website with more than 60 000 registered users. Every week notifications are send to these users via email, now I've noticed some of the mail addresses do not exists anymore eg. the domain address is valid but the email name en asdas@ is not valid anymore since person does not work at a company anymore etc. Now I'm looping through the database and doing some regular expression checks and checking if the MX records exist with the following two functions function verify_email($email){ if(!preg_match('/^[_A-z0-9-]+((\.|\+)[_A-z0-9-]+)*@[A-z0-9-]+(\.[A-z0-9-]+)*(\.[A-z]{2,4})$/',$email)){ return false; } else { return true; } } // Our function to verify the MX records function verify_email_dns($email){ list($name, $domain) = split('@',$email); if(!checkdnsrr($domain,'MX')){ return false; } else { return true; } } If the email address is in an invalid format or the domain does not exists I delete the users account. Are there any methods I could use to check if the email address still exists or not if the domain name is valid and the email address is in the correct format? For example [email protected] does not exist anymore but test.com is a valid domain name.

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• ApplicationPoolIdentity permissions on Temporary Asp.Net files

  - by Anton

  Hi all, at work I am struggling a bit with the following situation: We have a web application that runs on a WIndows Server 2008 64 bits machine. The app's ApplicationPool is running under the ApplicationPoolIdentity and configured for .net 2 and Classic pipeline mode. This works fine up to the moment that XmlSerialization requires creation of Serializer assemblies where MEF is being used to create a collection of knowntypes. To remedy this I was hoping that granting the ApplicationPoolIdentity rights to the ASP.Net Temporary Files directory would be enough, but alas... What I did was the run the following command from a cmd prompt: icacls "c:\windows\microsoft.net\framework64\v2.0.50727\Temporary ASP.NET Files" /grant "IIS AppPool\MyAppPool":(M) Obviously this did not work, otherwise you would not be reading this :) Strange thing is that whenever I grant the Users or even more specific, the Authenticated Users Group those permissions, it works. What's weird as well (in my eyes) is that before I started granting access the ApplicationPoolIdentity was already a member of IIS_IUSRS which does have Modify rights for the temporary asp files directory. And now I'm left wondering why this situation requires Modify rights for the Authenticated Users group. I thought it could be because the apppool account was missing additional rights (googling for this returned some results, so I tried those), but granting the ApplicationPoolIdentity modification rights to the Windows\Temp directory and/or the application directory itself did not fix it. For now we have a workaround, but I hate that I don't know what is exactly going on here, so I was hoping any of you guys could shed some light on this. Thanx in advance!

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• more ruby way of doing project euler #2

  - by aharon

  I'm trying to learn Ruby, and am going through some of the Project Euler problems. I solved two as such: def fib(n) return n if n < 2 vals = [0, 1] n.times do vals.push(vals[-1]+vals[-2]) end return vals.last end i = 1 s = 0 while((v = fib(i)) < 4_000_000) s+=v if v%2==0 i+=1 end puts s While that works, it seems not very ruby-ish—I couldn't come up with any good purely Ruby answer like I could with the first one ( puts ( (0..999).inject{ |sum, n| n%3==0||n%5==0 ? sum : sum+n } )).

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• Does any one knows how to use the WinHttpRequest to login facebook or gmail in VB.NET(2010 Version)?

  - by ???

  Now, I can download the webpage source code to the RichTextBox. But now I want to use the WinHttpRequest to login facebook or gmail,etc. I tried to do, but it didn't work!Any one can help me? Thnak you! This is my code: Public Class Form1 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click RichTextBox1.Text = winhttp("http://www.facebook.com") End Sub Function winhttp(ByVal URL As String) As String Dim pass, email As String pass = "my password" email = "myemail" Dim winHTTPReq : winHTTPReq = CreateObject("WinHttp.WinHttpRequest.5.1") Dim objhttp As Object = CreateObject("WinHttp.WinHttpRequest.5.1") Dim Data As String objhttp.Open("POST", URL, False) ''method objhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded") objhttp.setRequestHeader("Referer", "your refresh url") objhttp.send("email=" & email & "&pass=" & pass & "&perm_login=on") objhttp.WaitForResponse() Data = objhttp.responseText Data = Replace(Data, " ", "") Data = Replace(Data, vbTab, "") Data = Replace(Data, vbCrLf, "") Data = Replace(Data, " ", "") Return Data End Function End Class

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• Trees and macros with tikz

  - by Tsf

  I am trying to build my trees using macros but I don't get the result I want. Here is a minimal example: \documentclass{article} \usepackage{tikz} \usetikzlibrary{trees} \newcommand{\LeafNode}[1]{% child {node {#1}} } \newcommand{\InnerNode}[3]{% child {node {#3} #1 #2 } } \begin{document} \begin{tikzpicture} \node (A) {A} \LeafNode{B} \LeafNode{C} ; \end{tikzpicture}% \hspace{2cm}% \begin{tikzpicture} \node (A) {A} \InnerNode{\LeafNode{D}}{\LeafNode{E}}{B} \LeafNode{C} ; \end{tikzpicture} \end{document} I expected this to produce two trees: A A / \ / \ B C B C / \ D E but I am getting: A | A B | | B D | | C C Am I missing something or there is no way to do it? BTW, if I omit the label on my root node, I get a PGF error: ! Package pgf Error: No shape named is known. -- Tsf

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• Ruby class instance variables and inheritance

  - by rlandster

  I have a Ruby class called LibraryItem. I want to associate with every instance of this class an array of attributes. This array is long and looks something like ['title', 'authors', 'location', ...] Note that these attributes are not really supposed to be methods, just a list of attributes that a LibraryItem has. Next, I want to make a subclass of LibraryItem called LibraryBook that has an array of attributes that includes all the attributes of LibraryItem but will also include many more. Eventually I will want several subclasses of LibraryItem each with their own version of the array @attributes but each adding on to LibraryItem's @attributes (e.g., LibraryBook, LibraryDVD, LibraryMap, etc.). So, here is my attempt: class LibraryItem < Object class << self; attr_accessor :attributes; end @attributes = ['title', 'authors', 'location',] end class LibraryBook < LibraryItem @attributes.push('ISBN', 'pages'] end This does not work. I get the error undefined method `push' for nil:NilClass

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