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  • Getting the median of 3 values using scheme's car & cdr

    - by kristian Roger
    The problem this time is to get the median of three values (easy) I did this: (define (med x y z) (car(cdr(x y z))) and it was accepted but when testing it: (med 3 4 5) I get this error: Error: attempt to call a non-procedure (2 3 4) And when entering letters instead of number i get: (md x y z) Error: undefined varia y (package user) Using something besides x y z I get: (md d l m) Error: undefined variable d (package user) the question was deleted dont know how anyway write a function that return the median of 3 values

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  • c++ class member functions instatiated by traits

    - by Jive Dadson
    I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched stackoverflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instantiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits that are tested at runtime. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state info was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. The compiler (vc++ 2008) always complained that things didn't match. I would yell, "SFINAE, you moron!" but the moron is probably me. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

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  • Approach for authentication and storing user details.

    - by cappuccino
    Hey folks, I am using the Zend Framework but my question is broadly about sessions / databases / auth (PHP MySQL). Currently this is my approach to authentication: 1) User signs in, the details are checked in database. - Standard stuff really. 2) If the details are correct only the user's unique ID is stored in the session and a security token (user unique ID + IP + Browser info + salt). The session in written to the filesystem. I've been reading around and many are saying that storing stuff in sessions is not a good idea, and that you should really only write a unique ID which refers back to the user's details and a security token to prevent session hijacking. So this is the approach i've taken, i use to write the user's details in session, but i've moved that out. Wanted to know your opinions on this. I'm keeping sessions in the filesystem since i don't run on multiple servers, and since i'm only writting a tiny tiny bit of data to sessions, i thought that performance would be greater keeping sessions in the filesystem to reduce load on the database. Once the session is written on authentication, it really is only read-only from then on. 3) The rest of the user's details (like subscription details, permissions, account info etc) are cached in the filesystem (this can always be easily moved to memory if i wanted even more performance). So rather than keeping the user's details in session, the user's details are cached in the file system. I'm using Zend_Cache and the unique cache id is something like md5(/cache/auth/2892), the number is the unique id of the user. I guess the benefit of this method is that once the user is logged in, there is essentially not database queries being run to get the user's details. Just wonder if this approach is better than keeping the whole lot in session... 4) As the user moves throughout the site the only thing that is checked is the ID in the session and the security token. So, overall the first question is 1) is the filesystem more efficient than a database for this purpose 2) have i taken enough security precautions 3) is separating user detail's from the session into a cached file a pointless task? Thanks.

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  • What is the best Linux distribution as a Xen host?

    - by St3fan
    I ordered a server for the home office and I would like to partition it with Xen. I think this will keep things clean and easier to maintain. I will be running things like MySQL, PostgreSQL, Tomcat and my own code on this machine. My question is: what freely available Linux distribution has the best Xen hosting facilities?

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  • Is there a recommended approach to handle saving data in response to within-site navigation without

    - by Carvell Fenton
    Hello all, Preamble to scope my question: I have a web app (or site, this is an internal LAN site) that uses jQuery and AJAX extensively to dynamically load the content section of the UI in the browser. A user navigates the app using a navigation menu. Clicking an item in the navigation menu makes an AJAX call to php, and php then returns the content that is used to populate the central content section. One of the pages served back by php has a table form, set up like a spreadsheet, that the user enters values into. This table is always kept in sync with data in the database. So, when the table is created, is it populated with the relevant database data. Then when the user makes a change in a "cell", that change immediately is written back to the database so the table and database are always in sync. This approach was take to reassure users that the data they entered has been saved (long story...), and to alleviate them from having to click a save button of some kind. So, this always in sync idea is great, except that a user can enter a value in a cell, not take focus out of the cell, and then take any number of actions that would cause that last value to be lost: e.g. navigate to another section of the site via the navigation menu, log out of the app, close the browser, etc. End of preamble, on to the issue: I initially thought that wasn't a problem, because I would just track what data was "dirty" or not saved, and then in the onunload event I would do a final write to the database. Herein lies the rub: because of my clever (or not so clever, not sure) use of AJAX and dynamically loading the content section, the user never actually leaves the original url, or page, when the above actions are taken, with the exception of closing the browser. Therefore, the onunload event does not fire, and I am back to losing the last data again. My question, is there a recommended way to handle figuring out if a person is navigating away from a "section" of your app when content is dynamically loaded this way? I can come up with a solution I think, that involves globals and tracking the currently viewed page, but I thought I would check if there might be a more elegant solution out there, or a change I could make in my design, that would make this work. Thanks in advance as always!

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  • Android/Java Append String + int

    - by xger86x
    Hi, i have a question, what is the best way to append ints and Strings to build a new String? In the allocation debug tool i see too much allocations if i use the operator +. But i have tried also with StringBuffer and there are still too much allocations. Anyone can help me? Thanks

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  • Visualising a 'Smarties' lid using XAML (WPF/Silverlight, Visual Studio/Blend)

    - by Mr. Disappointment
    Hi folks, First off, to clarify something in the title which could well be ambiguous/misleading, I'd like to inform you of my definition of 'Smarties', as I know often products are available all over - only under a different alias. Smarties are a candy product in the UK, little chocolate drops covered in a crispy shell which are distributed in a card tube, this tube used to have a plastic lid/top with an individual letter on the underside (they've taken a more economical approach as of late), the lid/top of the old-style tube is the main element of this question. Familiarisation Link Lid View Link Okay, now with the seller-type pitch out of the way (no, I don't work for Nestlé ;)), hopefully the question is becoming rather clear. Essentially, I'd like to recreate one of these lids using XAML, ultimately to be utilised in a Silverlight web application. That is, I'd like to result in a reusable control, of which the following is true: It looks like a Smarties lid. The colour can be specified. The letter can be specified. The control can be rotated to display either side. The second two seem trivial, but we must bare in mind that the background colour specified will almost, if not always, be the same as the foreground, leaving a visibility issue where the character content is concerned; as for the rotation, I'm hoping this kind of functionality is reasonably available, and acceptable to implement. So, to put this out there, consider a control named SmartiesLid which derives from ToggleButton (appropriate?) and further plotted out using a style in a resource dictionary which applies to it, as follows: <Style TargetType="local:SmartiesLid"> <Setter Property="Background" Value="Red"/> <Setter Property="Foreground" Value="Red"/> <Setter Property="VerticalContentAlignment" Value="Center"/> <Setter Property="HorizontalContentAlignment" Value="Center"/> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="local:SmartiesLid"> <Grid x:Name="LayoutRoot"> <Grid.ColumnDefinitions> <ColumnDefinition Width=".05*"/> <ColumnDefinition/> <ColumnDefinition/> <ColumnDefinition Width=".05*"/> </Grid.ColumnDefinitions> <Grid.RowDefinitions> <RowDefinition Height=".05*"/> <RowDefinition/> <RowDefinition/> <RowDefinition Height=".05*"/> <RowDefinition Height=".1*"/> </Grid.RowDefinitions> <Ellipse Grid.RowSpan="4" Grid.ColumnSpan="4" Fill="{TemplateBinding Background}" Stroke="Transparent"/> <Ellipse Grid.RowSpan="2" Grid.ColumnSpan="2" Grid.Column="1" Grid.Row="1" Fill="{TemplateBinding Background}" Stroke="Transparent"> <Ellipse.Effect> <DropShadowEffect Direction="280" ShadowDepth="6" BlurRadius="6"/> </Ellipse.Effect> </Ellipse> <TextBlock Grid.RowSpan="2" Grid.ColumnSpan="2" Grid.Column="1" Grid.Row="1" Name="LetterTextBlock" Text="{TemplateBinding Content}" Foreground="{TemplateBinding Foreground}" FontSize="190" HorizontalAlignment="Center" VerticalAlignment="Center"> </TextBlock> <!-- <Path Stretch="Fill" Grid.Row="3" Grid.RowSpan="2" Grid.Column="1" Grid.ColumnSpan="2" Fill="Black" Data="..."> How to craw the lid 'tab'? </Path> --> </Grid> <ControlTemplate.Resources> <TranslateTransform x:Key="IndentTransform" X="10" /> <RotateTransform x:Key="RotateTransform" Angle="0" /> <Storyboard x:Key="MouseOver"> </Storyboard> <Storyboard x:Key="MouseLeave"> </Storyboard> </ControlTemplate.Resources> <ControlTemplate.Triggers> <Trigger Property="IsMouseOver" Value="true"> <Trigger.EnterActions> <BeginStoryboard Storyboard="{StaticResource MouseOver}"/> </Trigger.EnterActions> <Trigger.ExitActions> <BeginStoryboard Storyboard="{StaticResource MouseLeave}"/> </Trigger.ExitActions> </Trigger> <Trigger Property="IsPressed" Value="true"> <Setter TargetName="LayoutRoot" Property="RenderTransform" Value="{StaticResource IndentTransform}"/> </Trigger> <Trigger Property="IsChecked" Value="true"> <Setter TargetName="LayoutRoot" Property="RenderTransform" Value="{StaticResource RotateTransform}"/> </Trigger> <Trigger Property="IsEnabled" Value="False"> <Setter Property="Foreground" Value="Gray"/> <Setter Property="Opacity" Value="0.5"/> </Trigger> </ControlTemplate.Triggers> </ControlTemplate> </Setter.Value> </Setter> </Style> With this in mind, can anyone give input on, in decreasing order of my incompetence in an area: Designing the overall look and feel of the damn thing (I'm no designer, and while I could hack away at this single control for days and potentially get something relatively useful, it's always a gamble). The particular barrier for me here is 'pathing' the tab of the lid, as you will see in the XAML as an element commented out. Should Path be used, or would it be more appropriate to transform a rectangle with rounded corners, or any specific suggestions? Bevelling the individually displayed letter; as detailed above, when the colour of both the foreground and background are the same then this will be invisible if no effects are applied, also for a decent level of realism I'd like to be able to apply such an effect/s. So far use of DropShadow and Balder3DEngine have fulfilled my requirements for graphics in XAML, how achievable is a bevel effect? Rotating the control on mouse-click, that is, showing the opposing face. Is this going to be possible using a style and XAML only for the design? Or is it that ugliness may rear it's head in the form of code-behind to show/hide embedded controls? Should the faces be separate controls and later somehow combined? Allowing the control to size dynamically. I'm supposing I will be able to convert a solid, absolute layout to a nice generic one when I actually have the former in place. Obviously this entails sizing the centralised letter and the lid 'tab', but that's it really, other than keeping the aspect ratio equal (since the ellipses grow nicely with the grid). Any suggestions to approaching this would be greatly appreciated, particularly with a dynamically growing font - I've done that before in a web-imaging scenario using code and System.Drawing, and wouldn't like to approach it in even a similar way. By the way, the reason I specify both WPF and Silverlight is that, from my current knowledge, the inputs being written targeting either of these will be fairly transferable for similar output by the other, albeit not without alterations in either scenario. The resulting application is in fact destined to be written in Silverlight, however, so I don't fancy inviting anything from WPF which will guarantee my only being able to convert 90% of it. I'll go give this little project a start, maybe in Blend(?), hopefully can catch up with some advice shortly. Thanks, Mr. D EDIT: Next question, ought this to be broken up into separate questions? :/

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  • How does the proc in the caches_action if clause get execute

    - by Sid
    I have a newbie kind of question which I cant get my head around. How does the Proc in the if condition of the caches_action get executed for the caches_action method. for example caches_action :show, :if=Proc.new{|x| something} what i dont get its how does this get called. I know i can execute a proc defined as proc= Proc.new by proc.call so i dont understand how this gets called. Second how do I pass conditions like if logged_in? I'd appreciate any help on this

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  • Office Web Components compatibility issues

    - by Sebastian
    Hello, I'm doing some research on the convenience of using Office Web Components on a web to show pivot tables and graphics and I have a question regarding this. Does the use of these components will turn my web app (at least for this feature) into a "Internet Explorer only" app Thanks in advance!

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  • Should I be regularly shrinking my DB or at least my log file?

    - by Tom
    My question is, should I be running one or both of the shrink command regularly, DBCC SHRINKDATABASE OR DBCC SHRINKFILE ============================= background Sql Server: Database is 200 gigs, logs are 150 gigs. running this command SELECT name ,size/128.0 - CAST(FILEPROPERTY(name, 'SpaceUsed') AS int) / 128.0 AS AvailableSpaceInMB FROM sys.database_files;` produces this output.. MyDB: 159.812500 MB free MyDB_Log: 149476.390625 MB free So it seems there is some free space. We backup transaction logs every hour, diff backup 5 nights a week, full backup the other 2 nights of the week.

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  • The behavior of send() and recv() in socket communication

    - by gc
    The following is the setup: Server Client | | accept connect | | v | send msg1- | | | v v recv <- send | | v v send msg2- recv | | v v close Here is my question: 1. Client actually receives msg1 before it closes, why is it like this? 2. send msg2 returns normally. Since client closes after receiving msg1, why is send msg2 successful?

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  • Why do so many wpf controls implement CLR properties instead of dependency properties ?

    - by msfanboy
    Hello, is it because the controls programmers are lazy, too hard to implement or not knowledgeable? Wether they are custom controls from 3rd party vendors or Microsoft itself, very much controls have often clr properties instead of DP. Result is I can not bind to them and is wpf not all about binding? :/ My next side question would be, why do so many wpf controls offer visual parts but they are not member of the visual tree ? see wpf datagrid columns, headers... What do you think?

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  • Spring-JSON Used in Spring MVC

    - by Mark Estrada
    Hi, I came across the library Spring-JSON while looking to add Ajax Support in my spring mvc webapp 2.5. My question is, has anybody here have used this library and what are your experiences? Is there any better alternative than this?

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  • Working with utf-8 files in Eclipse.

    - by Pablo Cabrera
    Quite straight forward question. Is there a way to configure Eclipse to work with text files encoded with utf-8 with and without the BOM? So far I've used eclipse with utf-8 encoding and it works, but when I try to edit a file generated by another editor that includes the BOM, Eclipse doesn't handle it properly, it 'shows an invisible character' at the begining of the file (the BOM). Is there a way to make Eclipse understand utf-8 encoded files with BOM?

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  • What's the maximum number of operators you that can be used in an if statement?

    - by DMinGod
    Hi, i'm using jquery and I'm trying to validate a form. My question is - What is the maximum number of tests can you give in a single if statement. function cc_validate () { if ($("#name").val() == "" || $("#ship_name").val() == "" || $("#address").val() == "" || $("#city").val() == "" || $("#ship_city").val() == "" || $("#state").val() == "" || $("#ship_state").val() == "" || $("#postal_code").val() == "" || isNaN($("#postal_code").val()) || $("#phone").val() == "" || $("#ship_phone").val() == "" || isNaN($("#phone").val()) || isNaN($("#ship_phone").val()) || $("#mobile_number").val() == "" || $("#ship_mobile_number").val() == "" || isNaN($("#mobile_number").val()) || isNaN($("#ship_mobile_number").val()) || $("#email").val() == "") { return false; } else { return true; } }

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  • mv() while reading

    - by K'
    on Linux ext3 filesystem, what happens if mv() is called on the same file (file descriptor) while reading the file? It is actually an exam question and I can only say something like: CPU traps OS for interrupt handling etc, etc. I would appreciate if OS guys out there can help me out, please :D

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