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• Which book should I pick to improve my program designs/design patterns?

  - by zxcvbnm

  I want to learn about design patterns and from what I've seen the most recommended ones are the Gang of Four's Design Patterns and Head First Design Patterns. There are also language specific books, but I never see them recommended. I suppose it ties you to whatever strengths/weaknesses are inherent to each language, so not a good idea to learn design patterns in general. The Gang of Four's book is kinda old, so I'm wondering if there isn't a better alternative out today? I've heard the Heard First one isn't quite as good. But I'm not sure why, so it's really hard to pick either one. I've see some answers on this very site recommending both, but if I can only read one, which should I pick? I've been coding for 3+ years, though I've never had a good class on this subject. Also, would a book like Code Complete help me with this? One more thing: how often are these techniques supposed to be useful? For example, this question has me wondering if this stuff is worth the trouble. And please, tell me more than just "read x". I'd like to know why you're suggesting x.

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• What OOP pattern to use when only adding new methods, not data?

  - by Jonathon Reinhart

  Hello eveyone... In my app, I have deal with several different "parameters", which derive from IParameter interface, and also ParamBase abstract base class. I currently have two different parameter types, call them FooParameter and BarParameter, which both derive from ParamBase. Obviously, I can treat them both as IParameters when I need to deal with them generically, or detect their specific type when I need to handle their specific functionality. My question lies in specific FooParameters. I currently have a few specific ones with their own classes which derive from FooParameter, we'll call them FP12, FP13, FP14, etc. These all have certain characteristics, which make me treat them differently in the UI. (Most have names associated with the individual bits, or ranges of bits). Note that these specific, derived FP's have no additional data associated with them, only properties (which refer to the same data in different ways) or methods. Now, I'd like to keep all of these parameters in a Dictionary<String, IParameter> for easy generic access. The problem is, if I want to refer to a specific one with the special GUI functions, I can't write: FP12 fp12 = (FP12)paramList["FP12"] because you can't downcast to a derived type (rightfully so). But in my case, I didn't add any data, so the cast would theoretically work. What type of programming model should I be using instead? Thanks!

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• Paperclip failing to upload on specific scaffold, yet works on others

  - by Saifis

  I know there are tons of questions about paperclip, but I failed to find the answer to my problem. I know its prob just something simple, but I I'm running out of hair to pull out. I have paperclip working on other parts of my project, they work with no problem, however, a certain scaffold fails to upload, all the attributes to the uploaded file are nil. Here are the relevant information. Model: has_attached_file :foo, :styles => { :thumb => "140x140>" }, :url => "/data/:id/:style/:basename.:extension", :path => ":rails_root/public/data/:id/:style/:basename.:extension" View: <% form_for(@bar, :html => { :multipart => true }) do |f| %> <%= f.error_messages %> ---------- <li><%= f.label :top %> <%= f.file_field :foo %></li> ---------- <ul><%= f.submit "Save" %></ul> <% end %> Also, comparing the logs to the parts that work, the :foo attribute seems to be passing different values than in the ones that work. In the logs, when the paperclip function works, it looks like this "image"=>#<File:/var/folders/M5/M5HEb+WhFxmqNDGH5s-pNE+++TI/-Tmp-/RackMultipart20100512-1302-5e2e6e-0> when it does not, it seems to pass the file name directly "foo"=>"foo_image.png" I am developing locally on MacOSX using local rails and ruby libs.

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• jQuery AJAX Redirection problem

  - by meosoft

  Hello please consider this: On page A I have a link that takes you to page B when JS is off, but when JS is on, I want to replace content on current page with content from the page B. Pages A and B are in fact the same script that is able to tell AJAX calls from regular ones and serve the content appropriately. Everything works fine, as long as there are no redirects involved. But, sometimes there is a 301 redirect and what seems to be happening is that client browser then makes a second request, which will return with a 200 OK. Only the second request is sent without a X-Requested-With header, therefore I cannot tell within my script wether it came from AJAX or not, and will send a complete page instead of just the content. I have tried checking for 301 status code in my error, success, and complete handlers but none of them worked. It seems to be handling the 301 behind the scenes. Could anyone help me with this? jQuery 1.4, PHP 5 Edit: People requested the code to this, which I didn't think was necessary but here goes: // hook up menu ajax loading $('#menu a').live("click", function(){ // update menu highlight if($(this).parents('#menu').size() > 0){ $("#menu>li").removeClass("current_page_item"); $(this).parent().addClass("current_page_item"); } // get the URL where we will be retrieving content from var url = $(this).attr('href'); window.location.hash = hash = url; $.ajax({ type: "GET", url: url, success: function(data){ // search for an ID that is only present if page is requested directly if($(data).find('#maincontent').size() > 0){ data = $(data).find('#maincontent .content-slide *').get(); } // the rest is just animating the content into view $("#scroller").html(data); $('.content-slide').each(setHeight); $('.content-slide').animate({ left: "0px" }, 1000, 'easeOutQuart', function(){ $('#home').css("left", "-760px").html(data); $('#scroller').css("left", "-760px"); $('.content-slide').each(setHeight); } ); } }); return false; });

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• Flex : providing data with a PHP Class

  - by Tristan

  Hello, i'm a very new user to flex (never use flex, nor flashbuilder, nor action script before), but i want to learn this langage because of the beautiful RIA and chart it can do. I watched the video on adobe : 1 hour to build your first program but i'm stuck : On the video it says that we have to provide a PHP class for accessing data and i used the example that flash builder gave (with zend framework and mysqli). I never used those ones and it makes a lot to learn if i count zen + mysqli. My question is : can i use a PHP class like this one ? What does flash builder except in return ? i hear that was automatic. example it may be wrong, i'm not very familiar with classes when acessing to database : <?php class DBConnection { protected $server = "localhost"; protected $username = "root"; protected $password = "root"; protected $dbname = "something"; protected $connection; function __construct() { $this->connection = mysql_connect($this->server, $this->username, $this->password); mysql_select_db($this->dbname,$this->connection); mysql_query("SET NAMES 'utf8'", $this->connection); } function query($query) { $result = mysql_query($query, $this->connection); if (!$result) { echo 'request error ' . mysql_error($this->connection); exit; } return $result; } function getAll() { $req = "select * from servers"; $result = query($req) return $result } function num_rows() { return mysql_num_rows($result); } function end() { mysql_close($this->connection); } } ?> Thank you,

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• Reload images in a UIWebView after they have been downloaded by a background thread

  - by dantastic

  I have an application that frequently checks in with a server and downloads a batch of articles to the iphone. The articles are in html and just stored using core data. An article has 0-n images on the page. Downloading all associated images at the same time as the text will be too slow and take too much bandwidth. Users are not likely to open every article. If they open an article once it is likely they will open it several times. So I want to download and store the images locally when they are needed. These articles are listed in a UITableView. When you tap an article you pop open a UIWebView that displays the article. I have a function that checks if I have downloaded the images associated with the article already. If I have I just pop open the the UIWebView - everything works fine. If I don't have the images downloaded I go off and download them and store them to my Documents directory. Although this i working, the app is hanging while the images are downloading. Not very tidy. I want the article to open in a snap and download the images with the article open. So what I've done is I check if the images are downloaded, if they aren't I go ahead and just "touch" the files I need and load the webview. The UIWebView opens up but the images referenced contain no data. Then in a background thread I download the images and overwrite the "dummy" ones. This will save the images and everything but it won't reload the images in my current UIWebView. I have to go back out of the article back back in again to see the images. Are there any ways around this? reloading just an image in a UIWebView?

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• JSP: Refresh ComboBox options

  - by framara

  Hi, There's a class 'Car' with brand and model as properties. I have a list of items of this class List<Car> myCars. I need to represent in a JSP website 2 ComboBox, one for brand and another for model, that when you select the brand, in the model list only appear the ones from that brand. I don't know how to do this in a dynamic way. Any suggestion where to start? Thanks Update Ok, what I do now is send in the request a list with all the brand names, and a list of the items. The JSP code is like: <select name="manufacturer" id="id_manufacturer" onchange="return getManufacturer();"> <option value=""></option> <c:forEach items="${manufacturers}" var="man"> <option value="${man}" >${man}</option> </c:forEach> </select> <select name="model" id="id_model"> <c:forEach items="${mycars}" var="car"> <c:if test="${car.manufacturer eq man_selected}"> <option value="${car.id}">${car.model}</option> </c:if> </c:forEach> </select> <script> function getManufacturer() { man_selected = document.getElementById('id_manufacturer').value; } </script> How do I do to refresh the 'model' select options according to the selected 'man_selected' ?

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• Career day in kindergarten

  - by Péter Török

  I was invited to the kindergarten group of my elder daughter to talk and answer the kids' questions about my profession. There are 26 kids of age 4-6 in the group, plus 3 teachers who are fairly scared of anything related to programming and IT themselves, but bold enough to learn new tricks. I would have about 20-30 minutes, without projector or anything. They have an old computer though, which by its look may be a 486, and I am not even sure if it's functioning. My research turned up excellent earlier threads, with lots of good tips: How would you explain your job to a 5-year old? Career Day: how do I make “computer programmer” sound cool to 8 year olds? What things can I teach a group of children about programming in one day? My situation is different from each of the above though: the latter ones are concerned with older children, while the first one is about talking to a single kid (or elder person)—a group of 20 is a whole different challenge. How can I teach the kids and their teachers about programming in a fun way?

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• Problems solving oddly acting labels in ie7.

  - by Qwibble

  Okay so this is sort of a double question so I'll split it into two. First part In modern browsers the main bold labels sit above their corresponding form elements, and align to the left as is expected. However in ie7, they randomly site 10-15px inset. I went through the developer tools and could find nothing to fix it. I've made sure all my margins and padding is reset so I don't really understand =S Here's the page demo - link Maybe some of you ie bug fixing genius's know what the problem is? =D Second part Again with labels, this time the in-line ones resident next to the check boxes and radio buttons. In modern browsers again, the side beside the form elements as expected, but not so in ie7 where they take a new line. I've tried floating, changing margins and everything but to no effect in sitting it in-line with the div.checker or div.radio that is created by the uniform Jquery plugin. Here's the page demo - link Sorry for troubling you with my ie7 problems, I know they arent the most fun to solve. Hopefully someone has the patience to help. Matt

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• (nested) user controls within a mvp pattern causing sporadic problems

  - by LLEA

  hi everyone, I have a serious problem with nested user controls (UCs) in WinForms while trying to implement the mvp pattern (passive view). The project consists of one model (designed as a singleton) and a set of different presenters with corresponding view interfaces. To avoid one huge view interface and therefore an overloaded main UI, I decided to make use of a set of different UCs. Each UC has one view interface and one presenter that can access the model. But there are nested UCs: meaning that one specialised UC implements sort of a basic UC. The main UI just represents a container for all those UCs. So far, so good (if not, please ask)?! There are two problems that I am facing now (but I guess both are of the same origin): From time to time it is not possible anymore to load the UCs and test them within the Visual Studio 2008 User Control Test Container. The error message just says that a project with an output type of class library cannot be started directly etc. I can "handle" that by unloading all UC projects and reloading them afterwards. (I guess the references to all mvp components and other UCs are then updated). Assuming that the implementation of my mvp pattern is okay and all those UCs are testable within the VS Test Container at a certain time - there is the biggest problem still left: I am not able to add any UC (even the basic and unnested ones) to a simple Form (UI). The error message: error message.jpg Could it be that my basic UC causes all these Problems?! It consists of two simple ComboBoxes and implements a basic presenter and basic view interface. Whenever I add this UC to a different UC the VS designer adds two references to the public getter methods of the UC as resources. I then manually remove those resources from the resx-file and commend the corresponding lines in the designer file. thx in advance

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• Do you have health checks in your web app or web site?

  - by Pekka

  I have built PHP based "health check" scripts for several projects, but they were always custom-made for the occasion and not written for abstraction as an independent product. I would like to know whether such a solution exists. What I meam by "health check" is a protected web page that functions much like a suite of unit tests, but on a more operational level, showing red/yellow/green statuses for things like Are the cache directories writable? Is the PHP version correct, are required extensions installed? Is the configuration file protected from writing? Is the database server reachable? Do the key tables exist in the database? Is there enough disk space available? Is the site's front page reachable and renders fully ( = no PHP errors)? Do the project's libraries' MD5 checksums match the original ones? Do you do this - or parts of it - in your applications and web sites? Are there any standardized tools for this that bring along all the functionality to perform the tests (ideally as plugins), and just need to be configured accordingly? Is there a way to set this up using one of the Unit Testing frameworks available for PHP (preferably PHPUnit)? If so, do you know any resources / tutorials outlining how?

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• Developing Job References

  - by Joe Smith

  How do you develop references for jobs? I have 6 years of programming experience spanning two jobs, but sadly I don't have a lot of people I can draw on as references. It's been several years since I left my last job, which was at a small company, and I've lost touch with the few people I knew there. I now work at another small company. I think I've gone as far as I can in my current position, and would like to look for greener pastures, but I can't exactly use my current boss as a reference, even though I have a very good repore with him. I'm sure he'd make a great reference down the road, but I'm afraid I'd insult him or jeopardize my current job by mentioning that I'm thinking of leaving and would like him to help me. I've applied to some jobs, and I have gotten several replies like, "Oh, you're exactly what we're looking for. Send us a couple references and we'll schedule an interview. Oh, no references? You must be a psychopath, nevermind." I've tried doing some small freelance work on the side, just so I can have a contact who can vouch for my work, but the competition for even small projects is pretty fierce and I can rarely devote adequate time to freelancing while holding a full time job. In addition, I often encounter a Catch-22 where a lot of freelancing jobs also require references. So how do programmers maintain existing references and develop new ones, especially while holding a full time job?

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• What happens to existing workspaces after upgrading to TFS 2010

  - by e-mre

  Hi, I was looking for some insight about what happens to existing workspaces and files that are already checked-out on people, after an upgrade to TFS2010. Surprisingly enough I can not find any satisfactory information on this. (I am talking about upgrading on new hardware by the way. Fresh TFS instance, upgraded databases) I've checked TFS Installation guide, I searched through the web, all I could find is upgrade scenarios for the server side. Nobody even mentions what happens to source control clients. I've created a virtual machine to test the upgrade process, The upgrade was successful and all my files and workspaces exist in the new server too. The problem is: The new TFS installation has a new instanceID. When I redirected on the clients to the new server, the client seemed unable to match files and file states in the workspace with the ones on the new server. This makes me wonder if it will be possible to keep working after the production upgrade. As I mentioned above I can not find anything on this, it would be great if anyone could point me to some paper or blog post about this. Thanks in advance...

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• Why can't decimal numbers be represented exactly in binary?

  - by Barry Brown

  There have been several questions posted to SO about floating-point representation. For example, the decimal number 0.1 doesn't have an exact binary representation, so it's dangerous to use the == operator to compare it to another floating-point number. I understand the principles behind floating-point representation. What I don't understand is why, from a mathematical perspective, are the numbers to the right of the decimal point any more "special" that the ones to the left? For example, the number 61.0 has an exact binary representation because the integral portion of any number is always exact. But the number 6.10 is not exact. All I did was move the decimal one place and suddenly I've gone from Exactopia to Inexactville. Mathematically, there should be no intrinsic difference between the two numbers -- they're just numbers. By contrast, if I move the decimal one place in the other direction to produce the number 610, I'm still in Exactopia. I can keep going in that direction (6100, 610000000, 610000000000000) and they're still exact, exact, exact. But as soon as the decimal crosses some threshold, the numbers are no longer exact. What's going on? Edit: to clarify, I want to stay away from discussion about industry-standard representations, such as IEEE, and stick with what I believe is the mathematically "pure" way. In base 10, the positional values are: ... 1000 100 10 1 1/10 1/100 ... In binary, they would be: ... 8 4 2 1 1/2 1/4 1/8 ... There are also no arbitrary limits placed on these numbers. The positions increase indefinitely to the left and to the right.

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• Clarification of atomic memory access for different OSs

  - by murrekatt

  I'm currently porting a Windows C++ library to MacOS as a hobby project as a learning experience. I stumbled across some code using the Win Interlocked* functions and thus I've been trying to read up on the subject in general. Reading related questions here in SO, I understand there are different ways to do these operations depending on the OS. Interlocked* in Windows, OSAtomic* in MacOS and I also found that compilers have builtin (intrinsic) operations for this. After reading gcc builtin atomic memory access, I'm left wondering what is the difference between intrinsic and the OSAtomic* or Interlocked* ones? I mean, can I not choose between OSAtomic* or gcc builtin if I'm on MacOS when I use gcc? The same if I'd be on Windows using gcc. I also read that on Windows Interlocked* come as both inline and intrinsic versions. What to consider when choosing between intrinsic or inline? In general, are there multiple options on OSs what to use? Or is this again "it depends"? If so, what does it depend on? Thanks!

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• Rails: Getting rid of generic "X is invalid" validation errors

  - by DJTripleThreat

  I have a sign-up form that has nested associations/attributes whatever you want to call them. My Hierarchy is this: class User < ActiveRecord::Base acts_as_authentic belongs_to :user_role, :polymorphic => true end class Customer < ActiveRecord::Base has_one :user, :as => :user_role, :dependent => :destroy accepts_nested_attributes_for :user, :allow_destroy => true validates_associated :user end class Employee < ActiveRecord::Base has_one :user, :as => :user_role, :dependent => :destroy accepts_nested_attributes_for :user, :allow_destroy => true validates_associated :user end I have some validation stuff in these classes as well. My problem is that if I try to create and Customer (or Employee etc) with a blank form I get all of the validation errors I should get plus some Generic ones like "User is invalid" and "Customer is invalid" If I iterate through the errors I get something like: user.login can't be blank User is invalid customer.whatever is blah blah blah...etc customer.some_other_error etc etc Since there is at least one invalid field in the nested User model, an extra "X is invalid" message is added to the list of errors. This gets confusing to my client and so I'm wondering if there is a quick way to do this instead of having to filer through the errors myself.

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• IKImageView, Buttons work intermittently in 10.5 but ok in 10.6

  - by markhunte

  Hi all, In IB,I have connected some buttons to a IKImageView. Using its received Action 'ZoomIn:', 'ZoomOut:','ZoomImageToActualSize:' When I build for 10.6 I have no issues these work as expected. But in 10.5 (ppc), they sometimes work as expected and sometimes do not. I have even tried it programatically. But I get the same results. It is intermittent with each build after I have made some small change in IB that I need. But not changes that should affect how the view acts. The only buttons that seem to work through out are 'ZoomImageToFit' and the rotate ones. When the do not work as expected, I see no change to the current image in the view, but when my app (/s, I have had this issue before in different apps) changes the image The view reflects the last request from a button. So for example when it does not work. An image is displayed, I click the 'ZoomImageToActualSize:' button, nothing happens. I load a new image and it is displayed at Actual size. Example when it does work. An image is displayed, I click the 'ZoomImageToActualSize:' button, It is displayed at Actual size. By the way, I know I can reset the view default , before I load a new image. Also if I run the 10.5 app in 10.6, it works ok, but as above I get intermittent results with the same build on multible 10.5 machines. Does anyone know what is going on, is this a known bug? Thanks for any help. MH

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• RegisterStartupScript doesn't appear to be working on page postback within update panel

  - by Jen

  OK - so am working on a system that uses a custom datepicker control (I know there are other ones out there.. but for consistency would like to understand why my current issue is happening and fix it). So its a custom user control with a textbox and on Page_PreRender does this: protected void Page_PreRender(object sender, EventArgs e) { string clientScript = @" $(function(){ $('#" + this.Date1.ClientID + @"').datepicker({dateFormat: 'dd/mm/yy', constrainInput: true}); });"; Page.ClientScript.RegisterStartupScript(this.GetType(), this.ClientID, clientScript, true); //Type t = this.GetType(); //if (!Page.ClientScript.IsStartupScriptRegistered(t, this.ClientID)) //{ // Page.ClientScript.RegisterStartupScript(t, this.ClientID, clientScript, true); //} } Ignore commented out stuff - that was me trying something different - didn't help. My issue is that this all works fine when I load the page. But if I select something from a dropdownlist causing a page postback - when I click into my date fields they stop working. As in I should be able to click into the textbox and a nice calendar control appears. But after postback there is no nice calendar control appearing! It's currently all wrapped (in the hosting page) inside an update panel. So I comment out the update panel stuff and the dates are working after page postback. So it appears to be something related to that update panel. Any suggestions please? Thanks!!

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• jQuery.ajax() + empty JSON object = parse error

  - by roosteronacid

  I get a parse error when using jQuery to load some JSON data. Here's a snippet of my code: jQuery.ajax({ dataType: "json", success: function (json) { jQuery.each(json, function () { alert(this["columnName"]); }); } }); I get no errors when parsing a non-empty JSON object. So my guess is that the problem is with my serializer. Question is: how do I format an empty JSON object which jQuery won't consider malformed? This is what I've tried so far, with no success: {[]} {[null]} {} {null} {"rows": []} {"rows": null} {"rows": {}} UPDATE: I can understand that I've been somewhat vague--let me try and clarify: Parsing of the JSON object is not the issue here--JQuery is - I think. jQuery throws a parse-error (invokes the error function). It seems like jQuery's internal JSON validation is not accepting any of the before mentioned objects. Not even the valid ones. Output of the error function is: XMLHttpRequest: XMLHttpRequest readyState=4 status=200 textStatus: parsererror errorThrown: undefined This goes for all of the before mentioned objects.

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• Add an item to the Finder/Save dialog sidebar

  - by Clinton Blackmore

  I'm working on a script where a user logs into a guest account on OS and is prompted for their network credentials in order to mount their network home folder (while they benefit from working on a local user folder). As the guest folder is deleted when users log out, I want to discourage them from saving anything there. I would like to replace the items on the Finder and Open/Save sidebar lists (such as "Desktop", username, "Documents", etc) with ones that would save into their network home folder. It is possible to do this using AppleScript or Cocoa APIs, or do I need to modify a plist and restart the Finder? [Ack. Looking into ~/Library/Preferences/com.apple.sidebars.plist, it isn't at all clear how I'd populate it.] Similar Questions: AppleScript: adding mounted folder to Finder Sidebar? suggests using fstab; this code will most likely run as a user and really, automounting at that point would be too late. How do you programmatically put folder icons on the Finder sidebar, given that you have to use a custom icon for the folder? Says there is no Cocoa API, but that you can use a carbon-style LSSharedFileList API that is only documented in a single header file. Does anyone know of some example code to add an item to the Finder sidebar?

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• error: invalid type argument of '->' (have 'struct node')

  - by Roshan S.A

  Why cant i access the pointer "Cells" like an array ? i have allocated the appropriate memory why wont it act like an array here? it works like an array for a pointer of basic data types. #include<stdio.h> #include<stdlib.h> #include<ctype.h> #define MAX 10 struct node { int e; struct node *next; }; typedef struct node *List; typedef struct node *Position; struct Hashtable { int Tablesize; List Cells; }; typedef struct Hashtable *HashT; HashT Initialize(int SIZE,HashT H) { int i; H=(HashT)malloc(sizeof(struct Hashtable)); if(H!=NULL) { H->Tablesize=SIZE; printf("\n\t%d",H->Tablesize); H->Cells=(List)malloc(sizeof(struct node)* H->Tablesize); should it not act like an array from here on? if(H->Cells!=NULL) { for(i=0;i<H->Tablesize;i++) the following lines are the ones that throw the error { H->Cells[i]->next=NULL; H->Cells[i]->e=i; printf("\n %d",H->Cells[i]->e); } } } else printf("\nError!Out of Space"); } int main() { HashT H; H=Initialize(10,H); return 0; } The error I get is as in the title-error: invalid type argument of '->' (have 'struct node').

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• Type classe, generic memoization

  - by nicolas

  Something quite odd is happening with y types and I quite dont understand if this is justified or not. I would tend to think not. This code works fine : type DictionarySingleton private () = static let mutable instance = Dictionary<string*obj, obj>() static member Instance = instance let memoize (f:'a -> 'b) = fun (x:'a) -> let key = f.ToString(), (x :> obj) if (DictionarySingleton.Instance).ContainsKey(key) then let r = (DictionarySingleton.Instance).[key] r :?> 'b else let res = f x (DictionarySingleton.Instance).[key] <- (res :> obj) res And this ones complains type DictionarySingleton private () = static let mutable instance = Dictionary<string*obj, _>() static member Instance = instance let memoize (f:'a -> 'b) = fun (x:'a) -> let key = f.ToString(), (x :> obj) if (DictionarySingleton.Instance).ContainsKey(key) then let r = (DictionarySingleton.Instance).[key] r :?> 'b else let res = f x (DictionarySingleton.Instance).[key] <- (res :> obj) res The difference is only the underscore in the dictionary definition. The infered types are the same, but the dynamic cast from r to type 'b exhibits an error. 'this runtime coercition ... runtime type tests are not allowed on some types, etc..' Am I missing something or is it a rough edge ?

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• Which pdf elements could cause crashes?

  - by Felixyz

  This is a very general question but it's based on a specific problem. I've created a pdf reader app for the iPad and it works fine except for certain pdf pages which always crash the app. We now found out that the very same pages cause Safari to crash as well, so as I had started to suspect the problem is somewhere in Apple's pdf rendering code. From what I have been able to see, the crashing pages cause the rendering libraries to start allocating memory like mad until the app is killed. I have nothing else to help me pinpoint what triggers this process. It doesn't necessarily happen with the largest documents, or the ones with the most shapes. In fact, we haven't found any parameter that helps us predict which pages will crash and which not. Now we just discovered that running the pages through a consumer program that lets you merge docs gets rid of the problem, but I haven't been able to detect which attribute or element it is that is the key. Changing documents by hand is also not an option for us in the long run. We need to run an automated process on our server. I'm hoping someone with deeper knowledge about the pdf file format would be able to point me in a reasonable direction to look for document features that could cause this kind of behavior. All I've found so far is something about JBIG2 images, and I don't think we have any of those.

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• Auditing front end performance on web application

  - by user1018494

  I am currently trying to performance tune the UI of a company web application. The application is only ever going to be accessed by staff, so the speed of the connection between the server and client will always be considerably more than if it was on the internet. I have been using performance auditing tools such as Y Slow! and Google Chrome's profiling tool to try and highlight areas that are worth targeting for investigation. However, these tools are written with the internet in mind. For example, the current suggestions from a Google Chrome audit of the application suggests is as follows: Network Utilization Combine external CSS (Red warning) Combine external JavaScript (Red warning) Enable gzip compression (Red warning) Leverage browser caching (Red warning) Leverage proxy caching (Amber warning) Minimise cookie size (Amber warning) Parallelize downloads across hostnames (Amber warning) Serve static content from a cookieless domain (Amber warning) Web Page Performance Remove unused CSS rules (Amber warning) Use normal CSS property names instead of vendor-prefixed ones (Amber warning) Are any of these bits of advice totally redundant given the connection speed and usage pattern? The users will be using the application frequently throughout the day, so it doesn't matter if the initial hit is large (when they first visit the page and build their cache) so long as a minimal amount of work is done on future page views. For example, is it worth the effort of combining all of our CSS and JavaScript files? It may speed up the initial page view, but how much of a difference will it really make on subsequent page views throughout the working day? I've tried searching for this but all I keep coming up with is the standard internet facing performance advice. Any advice on what to focus my performance tweaking efforts on in this scenario, or other auditing tool recommendations, would be much appreciated.

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• List of Big-O for PHP functions?

  - by Kendall Hopkins

  After using PHP for a while now, I've noticed that not all PHP built in functions as fast as expected. Consider the below two possible implementations of a function that finds if a number is prime using a cached array of primes. //very slow for large $prime_array $prime_array = array( 2, 3, 5, 7, 11, 13, .... 104729, ... ); $result_array = array(); foreach( $array_of_number => $number ) { $result_array[$number] = in_array( $number, $large_prime_array ); } //still decent performance for large $prime_array $prime_array => array( 2 => NULL, 3 => NULL, 5 => NULL, 7 => NULL, 11 => NULL, 13 => NULL, .... 104729 => NULL, ... ); foreach( $array_of_number => $number ) { $result_array[$number] = array_key_exists( $number, $large_prime_array ); } This is because in_array is implemented with a linear search O(n) which will linearly slow down as $prime_array grows. Where the array_key_exists function is implemented with a hash lookup O(1) which will not slow down unless the hash table gets extremely populated (in which case it's only O(logn)). So far I've had to discover the big-O's via trial and error, and occasionally looking at the source code. Now for the question... I was wondering if there was a list of the theoretical (or practical) big O times for all* the PHP built in functions. *or at least the interesting ones For example find it very hard to predict what the big O of functions listed because the possible implementation depends on unknown core data structures of PHP: array_merge, array_merge_recursive, array_reverse, array_intersect, array_combine, str_replace (with array inputs), etc.

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