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  • What header file is where the boost libray define its own primitive data type?

    - by ronghai
    Recently, I try to use the boost::spirit::qi binary endian parser to parse some binary data depends on the endianness of the Platform. There is a simple example, like following: Using declarations and variables: using boost::spirit::qi::little_word; using boost::spirit::qi::little_dword; using boost::spirit::qi::little_qword; boost::uint16_t us; boost::uint32_t ui; boost::uint64_t ul; Basic usage of the little endian binary parsers: test_parser_attr("\x01\x02", little_word, us); assert(us == 0x0201); test_parser_attr("\x01\x02\x03\x04", little_dword, ui); assert(ui == 0x04030201); test_parser_attr("\x01\x02\x03\x04\x05\x06\x07\x08", little_qword, ul); assert(ul == 0x0807060504030201LL); test_parser("\x01\x02", little_word(0x0201)); test_parser("\x01\x02\x03\x04", little_dword(0x04030201)); test_parser("\x01\x02\x03\x04\x05\x06\x07\x08", little_qword(0x0807060504030201LL)); It works very well. But my questions come, why do we need use some data types like boost::uint16_t, boost::uint32_t here? Can I use unsigned long or unsigned int here? And if I want to parse double or float data type, what boost data type should I use? And please tell me where is boost define the above these types? Thanks a lot.

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  • How to program critical section for reader-writer systems?

    - by Srinivas Nayak
    Hi, Lets say, I have a reader-writer system where reader and writer are concurrently running. 'a' and 'b' are two shared variables, which are related to each other, so modification to them needs to be an atomic operation. A reader-writer system can be of the following types: rr ww r-w r-ww rr-w rr-ww where [ r : single reader rr: multiple reader w : single writer ww: multiple writer ] Now, We can have a read method for a reader and a write method for a writer as follows. I have written them system type wise. rr read_method { read a; read b; } ww write_method { lock(m); write a; write b; unlock(m); } r-w r-ww rr-w rr-ww read_method { lock(m); read a; read b; unlock(m); } write_method { lock(m); write a; write b; unlock(m); } For multiple reader system, shared variable access doesn't need to be atomic. For multiple writer system, shared variable access need to be atomic, so locked with 'm'. But, for system types 3 to 6, is my read_method and write_method correct? How can I improve? Sincerely, Srinivas Nayak

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  • Whats wrong with my cookies?

    - by William
    For some reason This php script won't echo my cookie variable: <?php require 'connection.php'; require 'variables.php'; $name = $_POST['name']; $pass = $_POST['pass']; if(($name == $admin_name) && ($pass == $admin_pass)){ setcookie($forum_url."name",$name,time()+604800); setcookie($forum_url."pass",$pass,time()+604800); } else echo 'Failed'; ?> heres the html that gets sent to admin_login.php <form method=post action=admin_login.php> <div id="formdiv"> <div class="fieldtext1">Name</div> <div class="fieldtext1">Pass</div> <input type="text" name=name size=25 /> <input type="password" name=pass size=25 /> </div> <input type=submit value="Submit" id="submitbutton"> </form> here is the index, where I want the info echoed <?php echo $_COOKIE[$forum_url."name"]; ?> What am I doing wrong?

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  • Configuring zend to use gmail smtp: Windows Apache dev-environment: "Could not open socket" error - repeatedly - going mad

    - by confused
    My dev environment is Win XP SP2 / Apache 2.something PHP 5.something_or_other My prod env is Linux Ubuntu / Apache 2.something_else PHP 5.something_or_other_else The code is all Zend Framework Version: 1.11.1 I can telnet to: smtp.gmail.com 465 from the PC. I have Mercury configured on my PC to use gmail as it's smtp host and it works just fine. (MercuryC SMTP Client). Mercury is set to use port 465 and SSL on smtp.gmail.com -- No problem. Zend mail works just fine on my production environment using the production mail server to send out mail. It's the same basic application.ini but with different values in the mail variables. On my local PC dev setup, my application.ini contains: (same values as I use in Mercury) mail.templatePath = APPLICATION_PATH "/emails" mail.sender.name = "myAccount" mail.sender.email = "[email protected]" mail.host = smtp.gmail.com mail.smtp.auth = "login" mail.smtp.username = "[email protected]" mail.smtp.password = "myPassWord" mail.smtp.ssl = "ssl" mail.smtp.port = 465 I have been doing trial and error for hours trying to get a single email out with no success. In every case, regardless of server or port settings it throws an error and reports: Could not open socket. Both Apache and Mercury Core are exceptions in my Windows Firewall config. Mercury seems to be having no problem. I have searched stackoverflow before posting this and have been googling for hours -- with no success. I am slowly losing my mind I would be very much obliged for any tip as to what might be wrong. Thanks for reading. =================== BTW When I use the SAME application.ini values on my local PC as on the production host, I get the same "Could not open socket" error. Those values are: mail.templatePath = APPLICATION_PATH "/emails" mail.sender.name = "otherUser" mail.sender.email = "[email protected]" mail.host = smtp.otherServer.com mail.smtp.auth = "login" mail.smtp.username = "[email protected]" mail.smtp.password = "otherPAssWord" mail.smtp.ssl = "ssl" mail.smtp.port = 465 I know these work in the production (Ubuntu) environment. I'm utterly baffled.

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  • How to implement "business rules" in Rails?

    - by Zabba
    What is the way to implement "business rules" in Rails? Let us say I have a car and want to sell it: car = Cars.find(24) car.sell car.sell method will check a few things: does current_user own the car? check: car.user_id == current_user.id is the car listed for sale in the sales catalog? check: car.catalogs.ids.include? car.id if all o.k. then car is marked as sold. I was thinking of creating a class called Rules: class Rules def initialize(user,car) @user = user @car = car end def can_sell_car? @car.user_id == @user.id && @car.catalogs.ids.include? @car.id end end And using it like this: def Car def sell if Rules.new(current_user,self).can_sell_car ..sell the car... else @error_message = "Cannot sell this car" nil end end end As for getting the current_user, I was thinking of storing it in a global variable? I think that whenever a controller action is called, it's always a "fresh" call right? If so then storing the current user as a global variable should not introduce any risks..(like some other user being able to access another user's details) Any insights are appreciated! UPDATE So, the global variable route is out! Thanks to PeterWong for pointing out that global variables persist! I've now thinking of using this way: class Rules def self.can_sell_car?(current_user, car) ......checks.... end end And then calling Rules.can_sell_car?(current_user,@car) from the controller action. Any thoughts on this new way?

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  • Polymorphic Queue

    - by metdos
    Hello Everyone, I'm trying to implement a Polymorphic Queue. Here is my trial: QQueue <Request *> requests; while(...) { QString line = QString::fromUtf8(client->readLine()).trimmed(); if(...)){ Request *request=new Request(); request->tcpMessage=line.toUtf8(); request->decodeFromTcpMessage(); //this initialize variables in request using tcpMessage if(request->requestType==REQUEST_LOGIN){ LoginRequest loginRequest; request=&loginRequest; request->tcpMessage=line.toUtf8(); request->decodeFromTcpMessage(); requests.enqueue(request); } //Here pointers in "requests" do not point to objects I created above, and I noticed that their destructors are also called. LoginRequest *loginRequest2=dynamic_cast<LoginRequest *>(requests.dequeue()); loginRequest2->decodeFromTcpMessage(); } } Unfortunately, I could not manage to make work Polymorphic Queue with this code because of the reason I mentioned in second comment.I guess, I need to use smart-pointers, but how? I'm open to any improvement of my code or a new implementation of polymorphic queue. Thanks.

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  • How to override the default init.tcl

    - by Sean Murphy
    I'm working on a project where I want to make use of TCL as the command interpreter. I have a working c library object which I can load from within the tcl shell but my problem is finding a way to automatically do this while starting a tclsh. Essentially my ultimate goal is to be able to run a script and have it load my library and run some initial startup tcl code before dropping me back to the tclsh command prompt in interactive mode. e.g. tclsh -f myscript.tcl --then-switch-to-interactive or EXPORT TCLINIT=myscript.tcl tclsh The basic goal is to avoid having to distribute tclsh but rather rely in local user installations of tcl. All I would like to distribute is my library, a startup script and a shell command to launch the tclsh with the library preloaded. I've tried using the environment variables TCLINIT and TCL_LIBRARY but they seem to have no effect. The only workable solutions I've found so far are to add "source myscript.tcl" to either the end of /usr/share/tcltk/tcl8.5.init.tcl or ~/.tclshrc However both of these "solutions" are non perfect as they require modification of the default users workspace. It strikes me that there must be a way to handle this in TCL, but my research so far hasn't yielded anything. Does anyone have any suggestions?

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  • How do you rotate a sprite around its center by caclulating a new x and y position?

    - by Sam152
    I'm using Dark GDK and C++ to create a simple 2d game. I'm rotating an object but it rotates from the top left corner of the sprite. I have the following variables available: PlayerX PlayerY PlayerWidth PlayerHeight RotateAngle (360 x 0) Is there an algorithm that will modify the pivot point of the sprite, preferable to the center? Here is a small code sample: void Player::Move( void ) { if ( checkLeft() ) { PlayerX -= PlayerSpeed; if ( PlayerX < 0 ) PlayerX = 0; } if ( checkRight() ) { PlayerX += PlayerSpeed ; if ( PlayerX > 800 - PlayerWidth ) PlayerX = 800 - PlayerWidth; } if ( checkUp()) { PlayerY -= PlayerSpeed; if ( PlayerY < 0 ) PlayerY = 0; } if ( checkDown()) { PlayerY += PlayerSpeed; if ( PlayerY > 600 - PlayerHeight) PlayerY = 600 - PlayerHeight; } RotateAngle += 5; if(RotateAngle > 360) RotateAngle -=360; dbRotateSprite(Handle,RotateAngle); dbSprite ( 1 , PlayerX , PlayerY , Handle ); } Edit I'm considering opening up some reputation for this question, I have yet to be provided with an answer that works for me. If someone can provide an actual code sample that does the job, I'd be very happy. The problem with Blindy's answer is that no matter how much I simply translate it back or forth, the spirte still rotates around the top left hand corner and moving it somewhere rotating around the top left corner, then moving it back to the same position accomplishes nothing. Here is what I believe to be going on: Just so there is no confusion I have created a an image of what is going on. The left shows what is actually happening and the right shows what I need to happen.

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  • Form not sending full data

    - by gAMBOOKa
    I have a form with over 50 input fields. The input fields are divided into 5 jquery jabs within the form container. Here's a sample of what it looks like: <form action="admin/save" method="post" enctype="multipart/form-data"> <input type="hidden" name="type" value="department" /> <input type="hidden" name="id" value="21" /> <div id="tabs"> <ul> <li><a href="#tab-1">Tab 1</a><li> <li><a href="#tab-2">Tab 2</a><li> <li><a href="#tab-3">Tab 3</a><li> </ul> <div id="tab-1"> <label>Name</label> <input type="text" name="user-name" /> </div> <div id="tab-2"> <label>Address</label> <input type="text" name="user-address" /> </div> <div id="tab-3"> <label>Phone</label> <input type="text" name="user-phone" /> </div> </div> <input type="submit" value="Send" /> </form> I'm using PHP's Kohana framework, so admin maps to a controller, and save maps to the method action_save. When I output the $_POST variables in action_save, only 'type' and 'id' show up, all the other fields don't seem to submit their data. What could I be doing wrong?

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  • JSF 2.0 Dynamic Views

    - by Robe Eleckers
    Hello, I'm working on a web project which uses JSF 2.0, PrimeFaces and PrettyFaces as main frameworks / libraries. The pages have the following (common) structure: Header, Content, Footer. Header: The Header always contains the same menu. This menu is a custom component, which generates a recursive html <ul><li> list containing <a href="url"> html links, this is all rendered with a custom renderer. The link looks like 'domain.com/website/datatable.xhtml?ref=2'. Where the ref=2 used to load the correct content from the database. I use prettyfaces to store this request value in a backingbean. Question 1: Is it ok to render the <a href> links myself, or should I better add an HTMLCommandLink from my UIComponent and render that in the encodeBegin/End? Question 2: I think passing variables like this is not really the JSF 2.0 style, how to do this in a better way? Content: The content contains dynamic data. It can be a (primefaces) datatable, build with dynamic data from the database. It can also be a text page, also loaded from the database. Or a series of graphs. You got the point, it's dynamic. The content is based on the link pressed in the header menu. If the content is of type datatable, then I put the ref=2 variable to a DataTableBean (via prettyfaces), which then loads the correct datatable from the database. If the content is of type chart, I'll put it on the ChartBean. Question 3: Is this a normal setup? Ideally I would like to update my content via Ajax. I hope it's clear :)

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  • How to mult-thread this?

    - by WilliamKF
    I wish to have two threads. The first thread1 occasionally calls the following pseudo function: void waitForThread2() { if (thread2 is not idle) { return; } notifyThread2IamReady(); while (thread2IsExclusive) { } } The second thread2 is forever in the following pseudo loop: for (;;) { Notify thread1 I am idle. while (!thread1IsReady()) { } Notify thread1 I am exclusive. Do some work while thread1 is blocked. Notify thread1 I am busy. Do some work in parallel with thread1. } What is the best way to write this such that both thread1 and thread2 are kept as busy as possible on a machine with multiple cores. I would like to avoid long delays between notification in one thread and detection by the other. I tried using pthread condition variables but found the delay between thread2 doing 'notify thread1 I am busy' and the loop in waitForThread2() on thear2IsExclusive() can be up to almost one second delay. I then tried using a volatile sig_atomic_t shared variable to control the same, but something is going wrong, so I must not be doing it correctly.

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  • How to make a big switch control structure with variable check values?

    - by mystify
    For example, I have a huge switch control structure with a few hundred checks. They're an animation sequence, which is numbered from 0 to n. Someone said I can't use variables with switch. What I need is something like: NSInteger step = 0; NSInteger i = 0; switch (step) { case i++: // do stuff break; case i++: // do stuff break; case i++: // do stuff break; case i++: // do stuff break; } The point of this is, that the animation system calls a method with this big switch structure, giving it a step number. I want to be able to simply cut-copy-paste large blocks and put them in a different position inside the switch. for example, the first 50 blocks to the end. I could do that easily with a huge if-else structure, but it would look ugly and something tells me switch is much faster. How to?

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  • ASP.NET MVC Paging for a search form

    - by James Alexander
    I've read several different posts on paging w/ in MVC but none describe a scenario where I have something like a search form and then want to display the results of the search criteria (with paging) beneath the form once the user clicks submit. My problem is that, the paging solution I'm using will create <a href="..."> links that will pass the desired page like so: http://mysite.com/search/2/ and while that's all fine and dandy, I don't have the results of the query being sent to the db in memory or anything so I need to query the DB again. If the results are handled by the POST controller action for /Search and the first page of the data is rendered as such, how do I get the same results (based on the form criteria specified by the user) when the user clicks to move to page 2? Some javascript voodoo? Leverage Session State? Make my GET controller action have the same variables expected by the search criteria (but optional), when the GET action is called, instantiate a FormCollection instance, populate it and pass it to the POST action method (there-by satisfying DRY)? Can someone point me in the right direction for this scenario or provide examples that have been implemented in the past? Thanks!

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  • curl: downloading from dynamic url

    - by adam n
    I'm trying to download an html file with curl in bash. Like this site: http://www.registrar.ucla.edu/schedule/detselect.aspx?termsel=10S&subareasel=PHYSICS&idxcrs=0001B+++ When I download it manually, it works fine. However, when i try and run my script through crontab, the output html file is very small and just says "Object moved to here." with a broken link. Does this have something to do with the sparse environment the crontab commands run it? I found this question: http://stackoverflow.com/questions/1279340/php-ssl-curl-object-moved-error but i'm using bash, not php. What are the equivalent command line options or variables to set to fix this problem in bash? (I want to do this with curl, not wget) Edit: well, sometimes downloading the file manually (via interactive shell) works, but sometimes it doesn't (I still get the "Object moved here" message). So it may not be a a specifically be a problem with cron's environment, but with curl itself. the cron entry: * * * * * ~/.class/test.sh >> ~/.class/test_out 2>&1 test.sh: #! /bin/bash PATH=/usr/local/bin:/usr/bin:/bin:/sbin cd ~/.class course="physics 1b" url="http://www.registrar.ucla.edu/schedule/detselect.aspx?termsel=10S<URL>subareasel=PHYSICS<URL>idxcrs=0001B+++" curl "$url" -sLo "$course".html --max-redirs 5 As I was searching around on google, someone suggested that the problem might happen because there are parameters in the url. (Because it is a dynamic url?)

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  • OOP 101 - quick question.

    - by R Bennett
    I've used procedural for sometime now and trying to get a better understanding of OOP in Php. Starting at square 1 and I have a quick question ot get this to gel. Many of the basic examples show static values ( $bob-name = "Robert";) when assigning a value, but I want to pass values... say from a form ( $name = $_POST['name']; ) class Person { // define properties public $name; public $weight; public $age; public function title() { echo $this->name . " has submitted a request "; } } $bob = new Person; // want to plug the value in here $bob->name = $name; $bob->title(); I guess I'm getting a little hung up in some areas as far as accessing variables from within the class, encapsulation & "rules", etc., can $name = $_POST['name']; reside anywhere outside of the class or am I missing an important point? Thanks

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  • DataGridView not displaying a row after it is created

    - by joslinm
    Hi, I'm using Visual Studio 10 and I just created a Database using SQL Server CE. Within it, I made a table CSLDataTable and that automatically created a CSLDataSet & CSLDataTableTableAdapter. The three variables were automatically created in my MainWindow.cs class: cSLDataSet cSLDataTableTableAdapter cSLDataTableBindingSource I have added a DataGridView in my Form called dataGridView and datasource cSLDataTableBindingSource. In my MainWindow(), I tried adding a row as a test: public MainWindow() { InitializeComponent(); CSLDataSet.CSLDataTableRow row = cSLDataSet.CSLDataTable.NewCSLDataTableRow(); row.File_ = "file"; row.Artist = "artist11"; row.Album = "album"; row.Save_Structure = "save"; row.Sent = false; row.Error = true; row.Release_Format = "release"; row.Bit_Rate = "bitrate.."; row.Year = "year"; row.Physical_Format = "format"; row.Bit_Format = "bitformat"; row.File_Path = "File!!path"; row.Site_Origin = "what"; cSLDataSet.CSLDataTable.Rows.Add(row); cSLDataSet.AcceptChanges(); cSLDataTableTableAdapter.Fill(cSLDataSet.CSLDataTable); cSLDataTableTableAdapter.Update(cSLDataSet); dataGridView.Refresh(); dataGridView.Update(); } In regards to the DataSet methods I tried calling, I had been trying to find a "correct" way to interact with the adapter, dataset, and datatable to successfully show the row, but to no avail. I'm rather new to using SQL Server CE Database, and read a lot of the MSDN sites & thought I was on the right track, but I've had no luck. The DataGridView shows the headers correctly, but that new row does not show up.

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  • javascript plugin - singleton pattern?

    - by Adam Kiss
    intro Hello, I'm trying to develop some plugin or/*and* object in javascript, which will control some properties over some object. It will also use jQuery, to ease development. idea This is in pseudocode to give you an idea, since I can't really describe it in english with the right words, it's impossible to go and use google to find out what I want to use (and learn). I will have plugin (maybe object?) with some variables and methods: plugin hideshow(startupconfig){ var c, //collection add: function(what){ c += what; }, do: function(){ c.show().hide().stop(); //example code } } and I will use it this way (or sort-of): var p = new Plugin(); p .add($('p#simple')) .add($('p#simple2')) .do(); note I'm not really looking for jQuery plugin tutorials - it's more like usage of singleton pattern in document in javascript, jQuery is mentione only because it will be used to modify dom and simplify selectors, jQuery plugin maybe just for that one little function add. I'm looking for something, that will sit on top of my document and call functions from itselft based on timer, or user actions, or whatever. problems I don't really know where to start with construction of this object/plugin I'm not really sure how to maintain one variable, which is collection of jQuery objects (something like $('#simple, #simple2');) I would maybe like to extedn jQuery with $.fn.addToPlugin to use chaining of objects, but that should be simple (really just each( p.add($(this)); )) I hope I make any sense, ideas, links or advices appreciated.

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  • Intel IA-32 Assembly

    - by Kay
    I'm having a bit of difficulty converting the following java code into Intel IA-32 Assembly: class Person() { char name [8]; int age; void printName() {...} static void printAdults(Person [] list) { for(int k = 0; k < 100; k++){ if (list[k].age >= 18) { list[k].printName(); } } } } My attempt is: Person: push ebp; save callers ebp mov ebp, esp; setup new ebp push esi; esi will hold name push ebx; ebx will hold list push ecx; ecx will hold k init: mov esi, [ebp + 8]; mov ebx, [ebp + 12]; mov ecx, 0; k=0 forloop: cmp ecx, 100; jge end; if k>= 100 then break forloop cmp [ebx + 4 * ecx], 18 ; jl auxloop; if list[k].age < 18 then go to auxloop jmp printName; printName: auxloop: inc ecx; jmp forloop; end: pop ecx; pop ebx; pop esi; pop ebp; Is my code correct? NOTE: I'm not allowed to use global variables.

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  • PHP - Best practice to retain form values across postback

    - by Adam
    Hello, Complete PHP novice here, almost all my previous work was in ASP.NET. I am now working on a PHP project, and the first rock I have stumbled upon is retaining values across postback. For the most simple yet still realistic example, i have 10 dropdowns. They are not even databound yet, as that is my next step. They are simple dropdowns. I have my entire page inclosed in a tag. the onclick() event for each dropdown, calls a javascript function that will populate the corrosponding dropdowns hidden element, with the dropdowns selected value. Then, upon page reload, if that hidden value is not empty, i set the selected option = that of my hidden. This works great for a single postback. However, when another dropdown is changed, the original 1'st dropdown loses its value, due to its corrosponding hidden value losing its value as well! This draws me to look into using querystring, or sessions, or... some other idea. Could someone point me in the right direction, as to which option is the best in my situation? I am a PHP novice, however I am being required to do some pretty intense stuff for my skill level, so I need something flexable and preferribly somewhat easy to use. Thanks! -----edit----- A little more clarification on my question :) When i say 'PostBack' I am referring to the page/form being submitted. The control is passed back to the server, and the HTML/PHP code is executed again. As for the dropdowns & hiddens, the reason I used hidden variables to retain the "selected value" or "selected index", is so that when the page is submitted, I am able to redraw the dropdown with the previous selection, instead of defaulting back to the first index. When I use the $_POST[] command, I am unable to retrieve the dropdown by name, but I am able to retrieve the hidden value by name. This is why upon dropdown-changed event, I call javascript which sets the selected value from the dropdown into its corrosponding hidden.

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  • How do I apply a "template" or "skeleton" of code in C# here?

    - by Scott Stafford
    In my business layer, I need many, many methods that follow the pattern: public BusinessClass PropertyName { get { if (this.m_LocallyCachedValue == null) { if (this.Record == null) { this.m_LocallyCachedValue = new BusinessClass( this.Database, this.PropertyId); } else { this.m_LocallyCachedValue = new BusinessClass( this.Database, this.Record.ForeignKeyName); } } return this.m_LocallyCachedValue; } } I am still learning C#, and I'm trying to figure out the best way to write this pattern once and add methods to each business layer class that follow this pattern with the proper types and variable names substituted. BusinessClass is a typename that must be substituted, and PropertyName, PropertyId, ForeignKeyName, and m_LocallyCachedValue are all variables that should be substituted for. Are attributes usable here? Do I need reflection? How do I write the skeleton I provided in one place and then just write a line or two containing the substitution parameters and get the pattern to propagate itself? EDIT: Modified my misleading title -- I am hoping to find a solution that doesn't involve code generation or copy/paste techniques, and rather to be able to write the skeleton of the code once in a base class in some form and have it be "instantiated" into lots of subclasses as the accessor for various properties. EDIT: Here is my solution, as suggested but left unimplemented by the chosen answerer. // I'll write many of these... public BusinessClass PropertyName { get { return GetSingleRelation(ref this.m_LocallyCachedValue, this.PropertyId, "ForeignKeyName"); } } // That all call this. public TBusinessClass GetSingleRelation<TBusinessClass>( ref TBusinessClass cachedField, int fieldId, string contextFieldName) { if (cachedField == null) { if (this.Record == null) { ConstructorInfo ci = typeof(TBusinessClass).GetConstructor( new Type[] { this.Database.GetType(), typeof(int) }); cachedField = (TBusinessClass)ci.Invoke( new object[] { this.Database, fieldId }); } else { var obj = this.Record.GetType().GetProperty(objName).GetValue( this.Record, null); ConstructorInfo ci = typeof(TBusinessClass).GetConstructor( new Type[] { this.Database.GetType(), obj.GetType()}); cachedField = (TBusinessClass)ci.Invoke( new object[] { this.Database, obj }); } } return cachedField; }

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  • proper use of volatile keyword

    - by luke
    I think i have a pretty good idea about the volatile keyword in java, but i'm thinking about re-factoring some code and i thought it would be a good idea to use it. i have a class that is basically working as a DB Cache. it holds a bunch of objects that it has read from a database, serves requests for those objects, and then occasionally refreshes the database (based on a timeout). Heres the skeleton public class Cache { private HashMap mappings =....; private long last_update_time; private void loadMappingsFromDB() { //.... } private void checkLoad() { if(System.currentTimeMillis() - last_update_time > TIMEOUT) loadMappingsFromDB(); } public Data get(ID id) { checkLoad(); //.. look it up } } So the concern is that loadMappingsFromDB could be a high latency operation and thats not acceptable, So initially i thought that i could spin up a thread on cache startup and then just have it sleep and then update the cache in the background. But then i would need to synchronize my class (or the map). and then i would just be trading an occasional big pause for making every cache access slower. Then i thought why not use volatile i could define the map reference as volatile private volatile HashMap mappings =....; and then in get (or anywhere else that uses the mappings variable) i would just make a local copy of the reference: public Data get(ID id) { HashMap local = mappings; //.. look it up using local } and then the background thread would just load into a temp table and then swap the references in the class HashMap tmp; //load tmp from DB mappings = tmp;//swap variables forcing write barrier Does this approach make sense? and is it actually thread-safe?

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  • ajax to php to curl and back..

    - by pfunc
    I am trying to make an ajax call to a php script. The php script calls an rss feed using curl, gets the data, and returns the data to the funciton. I keep getting an error "Warning: Wrong parameter count for curl_error() in" .... Here is my php code:1 $ch = curl_init() or die(curl_error()); curl_setopt($ch, CURLOPT_URL, $feed); curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); $data1 = curl_exec($ch) or die(curl_error()); echo $data1; and the ajax call: $.ajax({ url: "getSingleFeed.php", type: "POST", data: "feedURL=" + window.feedURL, success: function(feed){ alert(feed); }}); I tested all the variables, they are being passed correctly, I can echo them out. But this line: $data1 = curl_exec($ch) or die(curl_error()); is what is giving me the error. I am doing the same thing with curl on other pages, just without ajax, and it is working fine. Is there anything special I need to do with ajax to do this?

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  • image not displaying in midlet

    - by user316843
    Hello all,am new here. i have a slight problem; PLease look at the following code and tell me if am doing something wrong because the image is not displaying. i have made it really small so it should fit but its not displaying. i have images displaying in other screens but this main midlet would not. Here is the code: import java.io.IOException; import javax.microedition.midlet.*; import javax.microedition.lcdui.*; /** * @author jay */ public class WShop extends MIDlet implements CommandListener { /* Declare display variables*/ private Form mainForm; private Display display; private Command OK,Exit,wView, mView, myView; /* */ Categories categories = new Categories(this); Image image; public WShop() { /* initialize Screen and Command buttons that will be used when the application starts in the class constructor*/ mainForm = new Form("Wind Shopper"); OK = new Command("OK", Command.OK, 2); Exit = new Command("Exit", Command.EXIT, 0); wview= new Command("wview", Command.OK, 0); mview= new Command("mview", Command.OK, 0); try { /* retrieving the main image of the application*/ image = Image.createImage("/main.png"); } catch (IOException ex) { ex.printStackTrace(); } mainForm.addCommand(OK); mainForm.addCommand(Exit); mainForm.addCommand(wView); mainForm.addCommand(mView); mainForm.setCommandListener(this); } public void startApp() { /* checks to see if the display is currently empty and then sets it to the current screen */ if (display == null) { display = Display.getDisplay(this); } display.setCurrent(mainForm); } /* paused state of the application*/ public void pauseApp() { } /* Destroy Midlet state*/ public void destroyApp(boolean unconditional) { } Thanks in advance.

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  • Pointer problem in C for char*

    - by egebilmuh
    Hi guys, i use pointer for holding name and research lab property. But when i print the existing Vertex ,when i print the vertex, i cant see so -called attributes properly. For example though real value of name is "lancelot" , i see it as wrong such as "asdasdasdasd" struct vertex { int value; char*name; char* researchLab; struct vertex *next; struct edge *list; }; void GRAPHinsertV(Graph G, int value,char*name,char*researchLab) { //create new Vertex. Vertex newV = malloc(sizeof newV); // set value of new variable to which belongs the person. newV->value = value; newV->name=name; newV->researchLab=researchLab; newV->next = G->head; newV->list = NULL; G->head = newV; G->V++; } /*** The method creates new person. **/ void createNewPerson(Graph G) { int id; char name[30]; char researchLab[30]; // get requeired variables. printf("Enter id of the person to be added.\n"); scanf("%d",&id); printf("Enter name of the person to be added.\n"); scanf("%s",name); printf("Enter researc lab of the person to be added\n"); scanf("%s",researchLab); // insert the people to the social network. GRAPHinsertV(G,id,name,researchLab); } void ListAllPeople(Graph G) { Vertex tmp; Edge list; for(tmp = G->head;tmp!=NULL;tmp=tmp->next) { fprintf(stdout,"V:%d\t%s\t%s\n",tmp->value,tmp->name,tmp->researchLab); } system("pause"); }

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  • Can PHP dissect its own syntax?

    - by Nathan Long
    Can PHP dissect its own syntax? For example, I'd like to write a function that takes in an input like $object->attribute and says to itself: OK, he's giving me $foo->bar, which means he must think that $foo is an object that has a property called bar. Before I try accessing bar and potentially get a 'Trying to get property of non-object' error, let me check whether $foo is even an object. The end goal is to echo a value if it is set, and fail silently if not. I want to avoid repetition like this: <input value="<? if(is_object($foo) && is_set($foo->bar)){ echo $foo->bar; }?> "/> ...and to avoid writing a function that does the above, but has to have the object and attribute passed in separately, like this: <input value="<? echoAttribute($foo,'bar') ?>" /> ...but to instead write something which: preserves the object-attribute syntax is flexible: can also handle array keys or regular variables Like this: <input value="<? echoIfSet($foo->bar); ?> /> <input value="<? echoIfSet($baz['buzz']); ?> /> <input value="<? echoIfSet($moo); ?> /> But this all depends on PHP being able to tell me "what kind of thing am I asking for when I say $object->attribute or $array[$key]", so that my function can handle each according to its own type. Is this possible?

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