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  • typedef struct, circular dependency, forward definitions

    - by BlueChip
    The problem I have is a circular dependency issue in C header files ...Having looked around I suspect the solution will have something to do with Forward Definitions, but although there are many similar problems listed, none seem to offer the information I require to resolve this one... I have the following 5 source files: // fwd1.h #ifndef __FWD1_H #define __FWD1_H #include "fwd2.h" typedef struct Fwd1 { Fwd2 *f; } Fwd1; void fwd1 (Fwd1 *f1, Fwd2 *f2) ; #endif // __FWD1_H . // fwd1.c #include "fwd1.h" #include "fwd2.h" void fwd1 (Fwd1 *f1, Fwd2 *f2) { return; } . // fwd2.h #ifndef __FWD2_H #define __FWD2_H #include "fwd1.h" typedef struct Fwd2 { Fwd1 *f; } Fwd2; void fwd2 (Fwd1 *f1, Fwd2 *f2) ; #endif // __FWD2_H . // fwd2.c #include "fwd1.h" #include "fwd2.h" void fwd2 (Fwd1 *f1, Fwd2 *f2) { return; } . // fwdMain.c #include "fwd1.h" #include "fwd2.h" int main (int argc, char** argv, char** env) { Fwd1 *f1 = (Fwd1*)0; Fwd2 *f2 = (Fwd2*)0; fwd1(f1, f2); fwd2(f1, f2); return 0; } Which I am compiling with the command: gcc fwdMain.c fwd1.c fwd2.c -o fwd -Wall I have tried several ideas to resolve the compile errors, but have only managed to replace the errors with other errors ...How do I resolve the circular dependency issue with the least changes to my code? ...Ideally, as a matter of coding style, I would like to avoid putting the word "struct" all over my code.

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  • Are .NET's regular expressions Turing complete?

    - by Robert
    Regular expressions are often pointed to as the classical example of a language that is not Turning complete. For example "regular expressions" is given in as the answer to this SO question looking for languages that are not Turing complete. In my, perhaps somewhat basic, understanding of the notion of Turning completeness, this means that regular expressions cannot be used check for patterns that are "balanced". Balanced meaning have an equal number of opening characters as closing characters. This is because to do this would require you to have some kind of state, to allow you to match the opening and closing characters. However the .NET implementation of regular expressions introduces the notion of a balanced group. This construct is designed to let you backtrack and see if a previous group was matched. This means that a .NET regular expressions: ^(?<p>a)*(?<-p>b)*(?(p)(?!))$ Could match a pattern that: ab aabb aaabbb aaaabbbb ... etc. ... Does this means .NET's regular expressions are Turing complete? Or are there other things that are missing that would be required for the language to be Turing complete?

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  • Avoid an "out of memory error" in Java(eclipse), when using large data structure?

    - by gnomed
    OK, so I am writing a program that unfortunately needs to use a huge data structure to complete its work, but it is failing with a "out of memory error" during its initialization. While I understand entirely what that means and why it is a problem, I am having trouble overcoming it, since my program needs to use this large structure and I don't know any other way to store it. The program first indexes a large corpus of text files that I provide. This works fine. Then it uses this index to initialize a large 2D array. This array will have nXn entries, where "n" is the number of unique words in the corpus of text. For the relatively small chunk I am testing it on(about 60 files) it needs to make approximately 30,000x30,000 entries. this will probably be bigger once I run it on my full intended corpus too. It consistently fails every time, after it indexes, while it is initializing the data structure(to be worked on later). Things I have done include: revamp my code to use a primitive "int[]" instead of a "TreeMap" eliminate redundant structures, etc... Also, I have run eclipse with "eclipse -vmargs -Xmx2g" to max out my allocated memory I am fairly confident this is not going to be a simple line of code solution, but is most likely going to require a very new approach. I am looking for what that approach is, any ideas? Thanks, B.

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  • Restoring dev db from production: Running a set of SQL scripts based on a list stored in a table?

    - by mattley
    I need to restore a backup from a production database and then automatically reapply SQL scripts (e.g. ALTER TABLE, INSERT, etc) to bring that db schema back to what was under development. There will be lots of scripts, from a handful of different developers. They won't all be in the same directory. My current plan is to list the scripts with the full filesystem path in table in a psuedo-system database. Then create a stored procedure in this database which will first run RESTORE DATABASE and then run a cursor over the list of scripts, creating a command string for SQLCMD for each script, and then executing that SQLCMD string for each script using xp_cmdshell. The sequence of cursor-sqlstring-xp_cmdshell-sqlcmd feels clumsy to me. Also, it requires turning on xp_cmdshell. I can't be the only one who has done something like this. Is there a cleaner way to run a set of scripts that are scattered around the filesystem on the server? Especially, a way that doesn't require xp_cmdshell?

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  • calculating the index of an array C#

    - by Kerry G
    I want to display a list of the answers a student entered incorrectly. How do I identify the index of these questions? I am hoping to change the contents of a textbox to a list of the questions answered incorrectly, which would require calculating the index of each incorrect question. using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Windows.Forms; namespace WindowsFormsApplication5 { public partial class Form1 : Form { public Form1() { InitializeComponent(); } //return a pass/fail //return number of correct answers //return number of incorrect answers //return index figures of incorrect values public void examResults () { string[] correctAnswers = {B,D,A,A,C,A,B,A,C,D,B,C,D,A,D,C,C,B,D,A}; string[] studentResults = File.ReadAllLines("studentResults.txt"); var c = correctAnswers.Where((x, i) => x.Equals(studentResults[i])).Count(); if ( c <= 14) passFailBox.Text = "Student has failed the exam"; else passFailBox.Text = "Student has passed the exam"; numberCorrectBox.Text = "Student has answered" + c + "answers correctly"; int f; f= 21-c; numberIncorrectBox.Text = "Student has answered" + f + "answers incorrectly"; } } }

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  • Rails : can't write unknown attribute `url'

    - by user2954789
    I am new to ruby on rails,and I am learning by creating a blog. I am not able to save to my blogs table and I get this error "can't write unknown attribute url" Blogs migration :db/migrate/ class CreateBlogs < ActiveRecord::Migration --def change --- create_table :blogs do |t| ---- t.string :title ---- t.text :description ---- t.string :slug ---- t.timestamps --- end --end end Blogs Model :/app/models/blogs.rb class Blogs < ActiveRecord::Base --acts_as_url :title --def to_param ---url --end --validates :title, presence:true end Blogs Controller : /app/controllers/blogs_controller.rb class BlogsController < ApplicationController before_action :require_login --def new --- @blogs = Blogs.new --end --def show ---@blogs = Blogs.find(params[:id]) --end --def create ---@blogs = Blogs.new(blogs_params) --if @blogs.save ---flash[:success] = "Your Blog has been created." ---redirect_to home_path --else ---render 'new' --end -end --def blogs_params ---params.require(:blogs).permit(:title,:description) --end private --def require_login ---unless signed_in? ----flash[:error] = "You must be logged in to create a new Blog" ----redirect_to signin_path ---end --end end Blogs Form:/app/views/blogs/new.html.erb Blockquote <%= form_for @blogs, url: blogs_path do |f| %><br/> <%= render 'shared/error_messages_blogs' %><br/> <%= f.label :title %><br/> <%= f.text_field :title %><br/> <%= f.label :description %><br/> <%= f.text_area :description %><br/> <%= f.submit "Submit Blog", class: "btn btn-large btn-primary" %><br/> <% end %><br/> and I have also added "resources :blogs" to my routes.rb file. I get this error in controller at if @blogs.save

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  • Design pattern to integrate Rails with a Comet server

    - by empire29
    I have a Ruby on Rails (2.3.5) application and an APE (Ajax Push Engine) server. When records are created within the Rails application, i need to push the new record out on applicable channels to the APE server. Records can be created in the rails app by the traditional path through the controller's create action, or it can be created by several event machines that are constantly monitoring various inputstream and creating records when they see data that meets a certain criteria. It seems to me that the best/right place to put the code that pushes the data out to the APE server (which in turn pushes it out to the clients) is in the Model's after_create hook (since not all record creations will flow through the controller's create action). The final caveat is I want to push a piece of formatted HTML out to the APE server (rather than a JSON representation of the data). The reason I want to do this is 1) I already have logic to produce the desired layout in existing partials 2) I don't want to create a javascript implementation of the partials (javascript that takes a JSON object and creates all the HTML around it for presentation). This would quickly become a maintenance nightmare. The problem with this is it would require "rendering" partials from within the Model (which im having trouble doing anyhow because they don't seem to have access to Helpers when they're rendered in this manner). Anyhow - Just wondering what the right way to go about organizing all of this is. Thanks

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  • how to allow unamed user in svn authz file?

    - by dtrosset
    I have a subversion server running with apache. It authenticates users using LDAP in apache configuration and uses SVN authorizations to limit user access to certain repositories. This works perfectly. Apache DAV svn SVNParentPath /srv/svn SVNListParentPath Off SVNPathAuthz Off AuthType Basic AuthName "Subversion Repository" AuthBasicProvider ldap AuthLDAPBindDN # private stuff AuthLDAPBindPassword # private stuff AuthLDAPURL # private stuff Require valid-user AuthzSVNAccessFile /etc/apache2/dav_svn.authz Subversion [groups] soft = me, and, all, other, developpers Adding anonymous access from one machine Now, I have a service I want to setup (rietveld, for code reviews) that needs to have an anonymous access to the repository. As this is a web service, accesses are always done from the same server. Thus I added apache configuration to allow all accesses from this machine. This did not work until I add an additional line in the authorization file to allow read access to user -. Apache <Limit GET PROPFIND OPTIONS REPORT> Order allow,deny Allow from # private IP address Satisfy Any </Limit> Subversion [Software:/] @soft = rw - = r # <-- This is the added line For instance, before I add this, all users were authenticated, and thus had a name. Now, some accesses are done without a user name! I found this - user name in the apache log files. But does this line equals to * = r that I absolutely do not want to enable, or does it only allows the anonymous unnamed user (that is allowed access only from the rietveld server)?

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  • Recommended/Standard image thumbnails sizes

    - by Rakan
    Hello, Based on my experience in web development, HTML page designs for every website may have different < img tags showing the same image in different sizes. i.e: the website's main page might show the image in 500*500, the listing page might show it in 200*150 and other sections of the website will use different sizes. As you can see the ratios of the images to be displayed to the user are different and therefore will cause a problem in having the image stretched, pixelated and/or other quality problems. How i currently handle this issue is by using a jQuery cropping tool to make the user select the area to crop the thumbnail from. the cropped image is then resized using imagick to fit every position in the page design. However, although i can force the user to crop an image based on a pre-defined ratio, the HTML will still contain image placeholders which require a different ratio for its thumbnail. So for every image, i will have to force the user to crop the uploaded image based on every possible ratio my site requires. I don't think this is a friendly solution, how would you do it? is there a standard/recommended ratio for the web? Thanks

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  • what's the performance difference between int and varchar for primary keys

    - by user568576
    I need to create a primary key scheme for a system that will need peer to peer replication. So I'm planning to combine a unique system ID and a sequential number in some way to come up with unique ID's. I want to make sure I'll never run out of ID's, so I'm thinking about using a varchar field, since I could always add another character if I start running out. But I've read that integers are better optimized for this. So I have some questions... 1) Are integers really better optimized? And if they are, how much of a performance difference is there between varchars and integers? I'm going to use firebird for now. But I may switch later. Or possibly support multiple db's. So I'm looking for generalizations, if that's possible. 2) If integers are significantly better optimized, why is that? And is it likely that varchars will catch up in the future, so eventually it won't matter anyway? My varchar keys won't have any meaning, except for the unique system ID part. But I may want to obscure that somehow. Also, I plan to efficiently use all the bits of each character. I don't, for example, plan to code the integer 123 as the character string "123". So I don't think varchars will require more space than integers.

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  • SELECT Statement without duplicate rows on the multiple join tables

    - by theBo
    I have 4 tables built with JOINS and I would like to SELECT DISTINCT rows on the setsTbl.s_id so they always show regardless if there's relational data against them or not!. This is what I have at present which displays the data but doesn't display all of but not the entire distinct row! SELECT setsTbl.s_id, setsTbl.setName, userProfilesTbl.no + ' ' + userProfilesTbl.surname AS Name, trainingTbl.t_date, userAssessmentTbl.o_id FROM userProfilesTbl LEFT OUTER JOIN userAssessmentTbl ON userProfilesTbl.UserId = userAssessmentTbl.UserId FULL OUTER JOIN trainingTbl ON userAssessmentTbl.tt_id = trainingTbl.tt_id RIGHT OUTER JOIN setsTbl ON trainingTbl.s_id = setsTbl.s_id WHERE (userProfilesTbl.st_id=@st_id AND userProfilesTbl.sh_id=@sh_id) AND (DATEPART(yyyy,t_date) = @y_date ) OR (userAssessmentTbl.o_id IS NULL) ORDER BY setName ASC, t_date ASC With this statement I get some of the rows (the ones with data against them) but as stated the s_id field does not return distinct. This following inner select statement works in part when used in SQL Query analyzer and returns pretty much the data i require s_id setName Name o_id ----- ----- ----- ------ 1 100 Barnes 2 2 100 Beardsley 3 3 101 Aldridge 1 4 102 Molby 2 5 102 Whelan 3 but not when used outside of that environment. select * from ( SELECT userProfilesTbl.serviceNo + ' ' + userProfilesTbl.surname AS Name, userProfilesTbl.st_id, userProfilesTbl.sh_id, userAssessmentTbl.o_id, setsTbl.s_id, setsTbl.setName, row_number() over ( partition by setsTbl.s_id order by setsTbl.s_id ) r FROM userProfilesTbl LEFT OUTER JOIN userAssessmentTbl ON userProfilesTbl.UserId = userAssessmentTbl.UserId FULL OUTER JOIN trainingTbl ON userAssessmentTbl.tt_id = trainingTbl.tt_id RIGHT OUTER JOIN setsTbl ON trainingTbl.s_id = setsTbl.s_id ) x where x.r = 1 Not receiving any errors just not displaying the data?

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  • How do I change the viewport of a window in win32?

    - by Colen
    Hi, I have a window with child windows inside in it. The child windows take up about 1000 pixels of vertical space. However, our users don't always have 1000 pixels of vertical space available - they might have as little as 500 or 600 pixels. I want to be able to display this window at a size of 500 pixels high, and have the user "scroll" up and down the window to see the full contents. The window should always be 500 pixels high, but the view within it should change. Assume I can add a scroll bar somewhere so the user can choose which part of the window he wants to see. Windows will normally paint the window contents from height 0 to height 500; how do I tell it instead to "paint from height 250 to height 750", for example? I know that I can set the viewport with functions like SetViewportOrgEx etc, but those functions require a device context - when do I call them if I want them to be "permanent"? Do I call them when I get the WM_PAINT message from windows? Or at some other time? And which functions from that family do I want to use? Thanks.

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  • Where in the standard is forwarding to a base class required in these situations?

    - by pgast
    Maybe even better is: Why does the standard require forwarding to a base class in these situations? (yeah yeah yeah - Why? - Because.) class B1 { public: virtual void f()=0; }; class B2 { public: virtual void f(){} }; class D : public B1,public B2{ }; class D2 : public B1,public B2{ public: using B2::f; }; class D3 : public B1,public B2{ public: void f(){ B2::f(); } }; D d; D2 d2; D3 d3; EDG gives: sourceFile.cpp sourceFile.cpp(24) : error C2259: 'D' : cannot instantiate abstract class due to following members: 'void B1::f(void)' : is abstract sourceFile.cpp(6) : see declaration of 'B1::f' sourceFile.cpp(25) : error C2259: 'D2' : cannot instantiate abstract class due to following members: 'void B1::f(void)' : is abstract sourceFile.cpp(6) : see declaration of 'B and similarly for the MS compiler. I might buy the first case,D. But in D2 - f is unambiguously defined by the using declaration, why is that not enough for the compiler to be required to fill out the vtable? Where in the standard is this situation defined?

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  • Using list() to extract a data.table inside of a function

    - by Nathan VanHoudnos
    I must admit that the data.table J syntax confuses me. I am attempting to use list() to extract a subset of a data.table as a data.table object as described in Section 1.4 of the data.table FAQ, but I can't get this behavior to work inside of a function. An example: require(data.table) ## Setup some test data set.seed(1) test.data <- data.table( X = rnorm(10), Y = rnorm(10), Z = rnorm(10) ) setkey(test.data, X) ## Notice that I can subset the data table easily with literal names test.data[, list(X,Y)] ## X Y ## 1: -0.8356286 -0.62124058 ## 2: -0.8204684 -0.04493361 ## 3: -0.6264538 1.51178117 ## 4: -0.3053884 0.59390132 ## 5: 0.1836433 0.38984324 ## 6: 0.3295078 1.12493092 ## 7: 0.4874291 -0.01619026 ## 8: 0.5757814 0.82122120 ## 9: 0.7383247 0.94383621 ## 10: 1.5952808 -2.21469989 I can even write a function that will return a column of the data.table as a vector when passed the name of a column as a character vector: get.a.vector <- function( my.dt, my.column ) { ## Step 1: Convert my.column to an expression column.exp <- parse(text=my.column) ## Step 2: Return the vector return( my.dt[, eval(column.exp)] ) } get.a.vector( test.data, 'X') ## [1] -0.8356286 -0.8204684 -0.6264538 -0.3053884 0.1836433 0.3295078 ## [7] 0.4874291 0.5757814 0.7383247 1.5952808 But I cannot pull a similar trick for list(). The inline comments are the output from the interactive browser() session. get.a.dt <- function( my.dt, my.column ) { ## Step 1: Convert my.column to an expression column.exp <- parse(text=my.column) ## Step 2: Enter the browser to play around browser() ## Step 3: Verity that a literal X works: my.dt[, list(X)] ## << not shown >> ## Step 4: Attempt to evaluate the parsed experssion my.dt[, list( eval(column.exp)] ## Error in `rownames<-`(`*tmp*`, value = paste(format(rn, right = TRUE), (from data.table.example.R@1032mCJ#7) : ## length of 'dimnames' [1] not equal to array extent return( my.dt[, list(eval(column.exp))] ) } get.a.dt( test.data, "X" ) What am I missing? Update: Due to some confusion as to why I would want to do this I wanted to clarify. My use case is when I need to access a data.table column when when I generate the name. Something like this: set.seed(2) test.data[, X.1 := rnorm(10)] which.column <- 'X' new.column <- paste(which.column, '.1', sep="") get.a.dt( test.data, new.column ) Hopefully that helps.

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  • In Django, how to define a "location path" in order to display it to the users?

    - by naw
    I want to put a "location path" in my pages showing where the user is. Supposing that the user is watching one product, it could be Index > Products > ProductName where each word is also a link to other pages. I was thinking on passing to the template a variable with the path like [(_('Index'), 'index_url_name'), (_('Products'), 'products_list_url_name'), (_('ProductName'), 'product_url_name')] But then I wonder where and how would you define the hierarchy without repeating myself (DRY)? As far I know I have seen two options To define the hierarchy in the urlconf. It could be a good place since the URL hierarchy should be similar to the "location path", but I will end repeating fragments of the paths. To write a context processor that guesses the location path from the url and includes the variable in the context. But this would imply to maintain a independient hierarchy wich will need to be kept in sync with the urls everytime I modify them. Also, I'm not sure about how to handle the urls that require parameters. Do you have any tip or advice about this? Is there any canonical way to do this?

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  • JQuery Delegate and using traveral options in function

    - by Brian
    I am having trouble figuring out how to use the JQuery delegate function to do what I require. Basically, I need to allow users to add Panels (i.e. divs) to a form dynamically by selecting a button. Then when a user clicks a button within a given Panel, I want to be able to to something to that Panel (like change the color in this example). Unfortunately, it seems that references to the JQuery traversing functions don't work in this instance. Can anybody explain how to achieve this effect? Is there anyway to bind a different delegate to the each panel as its added. $('.addPanels').delegate('*', 'click', function() { $(this).parent.css('background-color', 'black'); $('.placeholder').append('Add item'); }); <div class="addPanels"> <div class="panel"> <a href="#" class="addLink">Add item</a> text</div> <div class="placeholder"/> </div> </div>

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  • What's the best way of accessing a DRb object (e.g. Ruby Queue) from Scala (and Java)?

    - by Tom Morris
    I have built a variety of little scripts using Ruby's very simple Queue class, and share the Queue between Ruby and JRuby processes using DRb. It would be nice to be able to access these from Scala (and maybe Java) using JRuby. I've put together something Scala and the JSR-223 interface to access jruby-complete.jar. import javax.script._ class DRbQueue(host: String, port: Int) { private var engine = DRbQueue.factory.getEngineByName("jruby") private var invoker = engine.asInstanceOf[Invocable] engine.eval("require \"drb\" ") private var queue = engine.eval("DRbObject.new(nil, \"druby://" + host + ":" + port.toString + "\")") def isEmpty(): Boolean = invoker.invokeMethod(this.queue, "empty?").asInstanceOf[Boolean] def size(): Long = invoker.invokeMethod(this.queue, "length").asInstanceOf[Long] def threadsWaiting: Long = invoker.invokeMethod(this.queue, "num_waiting").asInstanceOf[Long] def offer(obj: Any) = invoker.invokeMethod(this.queue, "push", obj.asInstanceOf[java.lang.Object]) def poll(): Any = invoker.invokeMethod(this.queue, "pop") def clear(): Unit = { invoker.invokeMethod(this.queue, "clear") } } object DRbQueue { var factory = new ScriptEngineManager() } (It conforms roughly to java.util.Queue interface, but I haven't declared the interface because it doesn't implement the element and peek methods because the Ruby class doesn't offer them.) The problem with this is the type conversion. JRuby is fine with Scala's Strings - because they are Java strings. But if I give it a Scala Int or Long, or one of the other Scala types (List, Set, RichString, Array, Symbol) or some other custom type. This seems unnecessarily hacky: surely there has got to be a better way of doing RMI/DRb interop without having to use JSR-223 API. I could either make it so that the offer method serializes the object to, say, a JSON string and takes a structural type of only objects that have a toJson method. I could then write a Ruby wrapper class (or just monkeypatch Queue) to would parse the JSON. Is there any point in carrying on with trying to access DRb from Java/Scala? Might it just be easier to install a real message queue? (If so, any suggestions for a lightweight JVM-based MQ?)

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  • Creating a 'flexible' XML schema

    - by Fiona Holder
    I need to create a schema for an XML file that is pretty flexible. It has to meet the following requirements: Validate some elements that we require to be present, and know the exact structure of Validate some elements that are optional, and we know the exact structure of Allow any other elements Allow them in any order Quick example: XML <person> <age></age> <lastname></lastname> <height></height> </person> My attempt at an XSD: <xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="person"> <xs:complexType> <xs:sequence> <xs:element name="firstname" minOccurs="0" type="xs:string"/> <xs:element name="lastname" type="xs:string"/> <xs:any processContents="lax" minOccurs="0" maxOccurs="unbounded" /> </xs:sequence> </xs:complexType> </xs:element> </xs:schema> Now my XSD satisfies requirements 1 and 3. It is not a valid schema however, if both firstname and lastname were optional, so it doesn't satisfy requirement 2, and the order is fixed, which fails requirement 4. Now all I need is something to validate my XML. I'm open to suggestions on any way of doing this, either programmatically in .NET 3.5, another type of schema etc. Can anyone think of a solution to satisfy all 4 requirements?

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  • If attacker has original data, and encrypted data, can they determine the passphrase?

    - by Brad Cupit
    If an attacker has several distinct items (for example: e-mail addresses) and knows the encrypted value of each item, can the attacker more easily determine the secret passphrase used to encrypt those items? Meaning, can they determine the passphrase without resorting to brute force? This question may sound strange, so let me provide a use-case: User signs up to a site with their e-mail address Server sends that e-mail address a confirmation URL (for example: https://my.app.com/confirmEmailAddress/bill%40yahoo.com) Attacker can guess the confirmation URL and therefore can sign up with someone else's e-mail address, and 'confirm' it without ever having to sign in to that person's e-mail account and see the confirmation URL. This is a problem. Instead of sending the e-mail address plain text in the URL, we'll send it encrypted by a secret passphrase. (I know the attacker could still intercept the e-mail sent by the server, since e-mail are plain text, but bear with me here.) If an attacker then signs up with multiple free e-mail accounts and sees multiple URLs, each with the corresponding encrypted e-mail address, could the attacker more easily determine the passphrase used for encryption? Alternative Solution I could instead send a random number or one-way hash of their e-mail address (plus random salt). This eliminates storing the secret passphrase, but it means I need to store that random number/hash in the database. The original approach above does not require this extra table. I'm leaning towards the the one-way hash + extra table solution, but I still would like to know the answer: does having multiple unencrypted e-mail addresses and their encrypted counterparts make it easier to determine the passphrase used?

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  • Algorithm for generating an array of non-equal costs for a transport problem optimization

    - by Carlos
    I have an optimizer that solves a transportation problem, using a cost matrix of all the possible paths. The optimiser works fine, but if two of the costs are equal, the solution contains one more path that the minimum number of paths. (Think of it as load balancing routers; if two routes are same cost, you'll use them both.) I would like the minimum number of routes, and to do that I need a cost matrix that doesn't have two costs that are equal within a certain tolerance. At the moment, I'm passing the cost matrix through a baking function which tests every entry for equality to each of the other entries, and moves it a fixed percentage if it matches. However, this approach seems to require N^2 comparisons, and if the starting values are all the same, the last cost will be r^N bigger. (r is the arbitrary fixed percentage). Also there is the problem that by multiplying by the percentage, you end up on top of another value. So the problem seems to have an element of recursion, or at least repeated checking, which bloats the code. The current implementation is basically not very good (I won't paste my GOTO-using code here for you all to mock), and I'd like to improve it. Is there a name for what I'm after, and is there a standard implementation? Example: {1,1,2,3,4,5} (tol = 0.05) becomes {1,1.05,2,3,4,5}

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  • Am I trying to Implement Multiple Inheritance. How can I do this.

    - by Shantanu Gupta
    I have created a class say A which has some functions defined as protected. Now Class B inherits A and class C inherits B. Class A has private default constructor and protected parameterized constructor. I want Class B to be able to access all the protected functions defined in Class A but class C can have access on some of the functions only not all the functions and class C is inheriting class B. How can I restrict access to some of the functions of Class A from Class C ? EDIT: namespace Db { public Class A { private A(){} protected A(string con){assign this value} protected DataTable getTable(){return Table;} protected Sqlparameters setParameters(){return parameter;} } } namespace Data { public Class B:A { protected B():base("constring"){} protected DataTable output(){return getTable();} protected sqlparameter values(param IDataParameter[] parameter){} } } namespace Bsns { public Class C:B { protected C():base(){} protected DataTable show() {return values(setparameter());} } } EDIT I think what I am trying to do here is Multiple inheritance. Please check. Class A { //suppose 10 functions are declared } Class B:A { //5 functions declared which are using A's function in internal body } Class C:B { //using all functions of B but require only 4 functions of A to be accessible by C. }

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  • Forwarding HTTP Request with Direct Server Return

    - by Daniel Crabtree
    I have servers spread across several data centers, each storing different files. I want users to be able to access the files on all servers through a single domain and have the individual servers return the files directly to the users. The following shows a simple example: 1) The user's browser requests http://www.example.com/files/file1.zip 2) Request goes to server A, based on the DNS A record for example.com. 3) Server A analyzes the request and works out that /files/file1.zip is stored on server B. 4) Server A forwards the request to server B. 5) Server B returns file1.zip directly to the user without going through server A. Note: steps 4 and 5 must be transparent to the user and cannot involve sending a redirect to the user as that would violate the requirement of a single domain. From my research, what I want to achieve is called "Direct Server Return" and it is a common setup for load balancing. It is also sometimes called a half reverse proxy. For step 4, it sounds like I need to do MAC Address Translation and then pass the request back onto the network and for servers outside the network of server A tunneling will be required. For step 5, I simply need to configure server B, as per the real servers in a load balancing setup. Namely, server B should have server A's IP address on the loopback interface and it should not answer any ARP requests for that IP address. My problem is how to actually achieve step 4? I have found plenty of hardware and software that can do this for simple load balancing at layer 4, but these solutions fall short and cannot handle the kind of custom routing I require. It seems like I will need to roll my own solution. Ideally, I would like to do the routing / forwarding at the web server level, i.e. in PHP or C# / ASP.net. However, I am open to doing it at a lower level such as Apache or IIS, or at an even lower level, i.e. a custom proxy service in front of everything.

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  • What is Wordpress doing for content encoding in it's mysql database?

    - by qbxk
    For some convoluted reasons best left behind us, I require direct access the contents of a wordpress database. I'm using mysql 5.0.70-r1 on gentoo with wordpress 2.6, and perl 5.8.8 ftr. So, sometimes we get high-order characters in the blog, we have quite a few authors contributing too, for the most part these characters end up in wp's database in wp_posts.post_content or wp_postmeta.meta_value, Wordpress is displaying these correctly on it's site, but the database stores it using single byte encoding that I can't figure out how to convert to the correct string. Today's example: the blog shows this, and doesn't even seem to escape any chars in the html, Hãhãhães but the database, when viewed via the mysql prompt, has, Hãhãhães So clearly this is some kind of double-byte encoding issue, but I don't know how I can correct it. I need to be able to pull that second string from the database (b/c that's what it gives me) and convert it to the first one, and i need to do so using perl. also, just to help unmuddy any waters, I took these strings and printed out the ascii codes for each character using perl's ord() function. Here is the output of the "wrong" string H = 72 à = 195 £ = 163 h = 104 à = 195 £ = 163 h = 104 à = 195 £ = 163 e = 101 s = 115 This is the correct string, that I need to produce in my script H = 72 ã = 227 h = 104 ã = 227 h = 104 ã = 227 e = 101 s = 115

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  • finding N contiguous zero bits in an integer to the left of the MSB from another

    - by James Morris
    First we find the MSB of the first integer, and then try to find a region of N contiguous zero bits within the second number which is to the left of the MSB from the first integer. Here is the C code for my solution: typedef unsigned int t; unsigned const t_bits = sizeof(t) * CHAR_BIT; _Bool test_fit_within_left_of_msb( unsigned width, t val1, t val2, unsigned* offset_result) { unsigned offbit = 0; unsigned msb = 0; t mask; t b; while(val1 >>= 1) ++msb; while(offbit + width < t_bits - msb) { mask = (((t)1 << width) - 1) << (t_bits - width - offbit); b = val2 & mask; if (!b) { *offset_result = offbit; return true; } if (offbit++) /* this conditional bothers me! */ b <<= offbit - 1; while(b <<= 1) offbit++; } return false; } Aside from faster ways of finding the MSB of the first integer, the commented test for a zero offbit seems a bit extraneous, but necessary to skip the highest bit of type t if it is set. I have also implemented similar algorithms but working to the right of the MSB of the first number, so they don't require this seemingly extra condition. How can I get rid of this extra condition, or even, are there far more optimal solutions?

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  • C++ meta-splat function

    - by aaa
    hello. Is there an existing function (in boost mpl or fusion) to splat meta-vector to variadic template arguments? for example: splat<vector<T1, T2, ...>, function>::type same as function<T1, T2, ...> my search have not found one, and I do not want to reinvent one if it already exists. edit: after some tinkering, apparently it's next to impossible to accomplish this in general way, as it would require declaring full template template parameter list for all possible cases. only reasonable solution is to use macro: #define splat(name, function) \ template<class T, ...> struct name; \ template<class T> \ struct name<T,typename boost::enable_if_c< \ result_of::size<T>::value == 1>::type> { \ typedef function< \ typename result_of::value_at_c<T,0>::type \ > type; \ }; Oh well. thank you

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