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• Processor, OS : 32bit, 64 bit

  - by Sandbox

  I am new to programming and come from a non-CS background (no formal degree). I mostly program winforms using C#. I am confused about 32 bit and 64 bit.... I mean, have heard about 32 bit OS, 32 bit processor and based on which a program can have maximum memory. How it affects the speed of a program. There are lot more questions which keep coming to mind. I tried to go through some Computer Organization and Architecture books. But, either I am too dumb to understand what is written in there or the writers assume that the reader has some CS background. Can someone explain me these things in a plain simple English or point me to something which does that. EDIT: I have read things like In 32-bit mode, they can access up to 4GB memory; in 64-bit mode, they can access much much more....I want to know WHY to all such things. BOUNTY: Answers below are really good....esp one by Martin. But, I am looking at a thorough explanation, but in plain simple English.

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• Using memset on structures in C++

  - by garry

  Hey guys. I am working on fixing older code for my job. It is currently written in C++. They converted static allocation to dynamic but didn't edit the memsets/memcmp/memcpy. This is my first programming internship so bare with my newbe-like question. The following code is in C, but I want to have it in C++ ( I read that malloc isn't good practice in C++). I have two scenarios: First, we have f created. Then you use &f in order to fill with zero. The second is a pointer *pf. I'm not sure how to set pf to all 0's like the previous example in C++. Could you just do pf = new foo instead of malloc and then call memset(pf, 0, sizeof(foo))? struct foo { ... } f; memset( &f, 0, sizeof(f) ); //or struct foo { ... } *pf; pf = (struct foo*) malloc( sizeof(*pf) ); memset( pf, 0, sizeof(*pf) );

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• JQuery transition animation

  - by kk-dev11

  This program randomly selects two employees from a json-object Employees array, winnerPos is already defined. For better user experience I programmed these functions to change pictures one by one. The animation stops when the randomly selected person is shown on the screen. The slideThrough function will be triggered when the start button is pressed. function slideThrough() { counter = 0; start = true; clearInterval(picInterval); picInterval = setInterval(function () { changePicture(); }, 500); } function changePicture() { if (start) { if (counter > winnerPos) { setWinner(); start = false; killInterval(); } else { var employee = Employees[counter]; winnerPic.fadeOut(200, function () { this.src = 'img/' + employee.image; winnerName.html(employee.name); $(this).fadeIn(300); }); counter++; } } } The problem is the animation doesn't work smoothly. At first it works, but not perfect. The second time the transition happens in an irregular way, i.e. different speed and fadeIn/fadeOut differs from picture to picture. Could anyone help me to fine-tune the transition?

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• Is there a way in VS2008 (c#) to see all the possible exception types that can originate from a meth

  - by Matt

  Is there a way in VS2008 IDE for c# to see all the possible exception types that can possibly originate from a method call or even for an entire try-catch block? I know that intellisense or the object browser tells me this method can throw these types of exceptions but is there another way than using the object browser everytime? Something more accessible when coding? Furthermore, I don't think intellisense or the object browser do anything more than read the XML code comments. Shouldn't it be possible to scan a class's source and find all the exception types that can be thrown. (Forget path-ing based on method input, just scan the code for exception types) Am I wrong? Extending this idea, you should be able to hover over the 'try' or 'catch' keywords and present a tooltip with all the types of exceptions that can be thrown. My question boils down to, does a VS2008 add on like this exist? Does VS2010 do this perhaps? If not, could you implement it the way I've described, by scanning the class code for thrown exception types and would people find it useful. Exceptions bubble up so you have to scan every bit of code every method call, which I guess could be impractical, though I suppose you could build an index the first time and increase your speed that way. (It might be a cool little project....)

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• php / phpDoc - @return instance of $this class ?

  - by searbe

  How do I mark a method as "returns an instance of the current class" in my phpDoc? In the following example my IDE (Netbeans) will see that setSomething always returns a foo object. But that's not true if I extent the object - it'll return $this, which in the second example is a bar object not a foo object. class foo { protected $_value = null; /** * Set something * * @param string $value the value * @return foo */ public function setSomething($value) { $this->_value = $value; return $this; } } $foo = new foo(); $out = $foo->setSomething(); So fine - setSomething returns a foo - but in the following example, it returns a bar..: class bar extends foo { public function someOtherMethod(){} } $bar = new bar(); $out = $bar->setSomething(); $out->someOtherMethod(); // <-- Here, Netbeans will think $out // is a foo, so doesn't see this other // method in $out's code-completion ... it'd be great to solve this as for me, code completion is a massive speed-boost. Anyone got a clever trick, or even better, a proper way to document this with phpDoc?

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• Speeding up a group by date query on a big table in postgres

  - by zaius

  I've got a table with around 20 million rows. For arguments sake, lets say there are two columns in the table - an id and a timestamp. I'm trying to get a count of the number of items per day. Here's what I have at the moment. SELECT DATE(timestamp) AS day, COUNT(*) FROM actions WHERE DATE(timestamp) >= '20100101' AND DATE(timestamp) < '20110101' GROUP BY day; Without any indices, this takes about a 30s to run on my machine. Here's the explain analyze output: GroupAggregate (cost=675462.78..676813.42 rows=46532 width=8) (actual time=24467.404..32417.643 rows=346 loops=1) -> Sort (cost=675462.78..675680.34 rows=87021 width=8) (actual time=24466.730..29071.438 rows=17321121 loops=1) Sort Key: (date("timestamp")) Sort Method: external merge Disk: 372496kB -> Seq Scan on actions (cost=0.00..667133.11 rows=87021 width=8) (actual time=1.981..12368.186 rows=17321121 loops=1) Filter: ((date("timestamp") >= '2010-01-01'::date) AND (date("timestamp") < '2011-01-01'::date)) Total runtime: 32447.762 ms Since I'm seeing a sequential scan, I tried to index on the date aggregate CREATE INDEX ON actions (DATE(timestamp)); Which cuts the speed by about 50%. HashAggregate (cost=796710.64..796716.19 rows=370 width=8) (actual time=17038.503..17038.590 rows=346 loops=1) -> Seq Scan on actions (cost=0.00..710202.27 rows=17301674 width=8) (actual time=1.745..12080.877 rows=17321121 loops=1) Filter: ((date("timestamp") >= '2010-01-01'::date) AND (date("timestamp") < '2011-01-01'::date)) Total runtime: 17038.663 ms I'm new to this whole query-optimization business, and I have no idea what to do next. Any clues how I could get this query running faster?

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• jQuery trigger custom event synchronously?

  - by Miguel Angelo

  I am using the jQuery trigger method to call an event... but it behaves inconsistently. Sometimes it call the event, sometimes it does not. <a href="#" onclick=" $(this).trigger('custom-event'); window.location.href = 'url'; return false; ">text</a> The custom-event has lots of listeners added to it. It is as if the trigger method is not synchronous, allowing the window.location.href be changed before executing the events. And when window.location.href is changed a navigation occurs, interrupting everything. How can I trigger events synchronously? Using jQuery 1.8.1. Thanks! EDIT I have found that the event, when called has a stack trace like this: jQuery.fx.tick (jquery-1.8.1.js:9021) tick (jquery-1.8.1.js:8499) jQuery.Callbacks.self.fireWith (jquery-1.8.1.js:1082) jQuery.Callbacks.fire (jquery-1.8.1.js:974) jQuery.speed.opt.complete (jquery-1.8.1.js:8991) $.customEvent (myfile.js:28) This proves that jQuery trigger method is asynchronous. Oohhh my... =\

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• Scan file contents into an array of a structure.

  - by ZaZu

  Hello, I have a structure in my program that contains a particular array. I want to scan a random file with numbers and put the contents into that array. This is my code : ( NOTE : This is a sample from a bigger program, so I need the structure and arrays as declared ) The contents of the file are basically : 5 4 3 2 5 3 4 2 #include<stdio.h> #define first 500 #define sec 500 struct trial{ int f; int r; float what[first][sec]; }; int trialtest(trial *test); main(){ trial test; trialtest(&test); } int trialtest(trial *test){ int z,x,i; FILE *fin; fin=fopen("randomfile.txt","r"); for(i=0;i<5;i++){ fscanf(fin,"%5.2f\t",(*test).what[z][x]); } fclose(fin); return 0; } But the problem is, whenever this I run this code, I get this error : (25) : warning 508 - Data of type 'double' supplied where a pointer is required I tried adding do{ for(i=0;i<5;i++){ q=fscanf(fin,"%5.2f\t",(*test).what[z][x]); } }while(q!=EOF); But that didnt work either, it gives the same error. Does anyone have a solution to this problem ?

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• Refetching a previously visited page

  - by user613665

  All, I am having a field day with page refetching. Any help or pointer will be greatly appreciated!! The behavior is a bit specific to mobile browser. Problem: I have two pages and created a shortcut link to pg#1 in the home page. Through a form submit button, user is taken from pg#1 to pg#2. All that is working fine. Now once I am on pg#2. I will leave the browser and click the shortcut later. The browser will stay on pg#2 and won't go to pg#1 even though the path in URLS is different between the two views. It is almost like Django decides that since I have already visited view#1, it doesn't need to fetch it again. This problem or behavior doesn't happen if I move the same code that handle the two views and the templates to a bare bone test project. Setup: I am using django-registration, context session. I am not using any HTML caching tag. I already have DEBUG turned on in my settings.py. Are there other ways that I can tell what the server is doing. Thanks in advance. pdxMobile Update: Here is the code snippets. def sendmsg(request): if request.method =='POST': messages.add_message(request, messages.INFO, "Hello world") return redirect ('rcvmsg') return render_to_response('sendMsg.html',RequestContext(request)) def rcvmsg(request): '''view that receives the msg.''' printMsg ='Didnt get a message' if messages: thisMsg = messages.get_messages(request) for rcvMsg in thisMsg: printMsg = rcvMsg return render_to_response('rcvMsg.html',{'print_msg':printMsg},RequestContext(request)) URL: url(r'^rcvMsg/','mydomain.mainApp.views.rcvmsg',name='rcvmsg'), (r'^sendMsg/code','mydomain.mainApp.views.sendmsg'),

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• C# / this. and List<T>

  - by user3533030

  I am having trouble understanding how to initialize a List of objects and use it with methods inside of a class. I understand the mechanics of the List, but not how to initialize it inside a method and use it later. For example, I want to have a class that creates the List when it is constructed. Then, I want to use a method of that class to add elements to the list. The elements in the list are objects defined by the SolidWorks API. So, to construct the List, I used... public class ExportPoints : Exporter { public List<SldWorks.SketchPoint> listOfSketchPoints; public ExportPoints(SldWorks.SldWorks swApp, string nameSuffix) : base(swApp, nameSuffix) { List<SldWorks.SketchPoint> listOfSketchPoints = new List<SldWorks.SketchPoint>(); } public void createListOfFreePoints() { try { [imagine more code here] this.listOfSketchPoints.Add(pointTest); } catch (Exception e) { Debug.Print(e.ToString()); return; } } This fails during execution as if the listOfSketchPoints was never initialized as a List. So, I tried a hack and this worked: public ExportPoints(SldWorks.SldWorks swApp, string nameSuffix) : base(swApp, nameSuffix) { List<SldWorks.SketchPoint> listOfSketchPoints = new List<SldWorks.SketchPoint>(); this.listOfSketchPoints = listOfSketchPoints; } This approach creates the behavior that I want. However, it seems that I lack some understanding as to why this is necessary. Shouldn't it be possible to "initialize" a List that is a property of your object with a constructor? Why would you need to create the list, then assign the pointer of that new List to your property?

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• PHP: How to know if a user is currently downloading a file?

  - by metrobalderas

  I'm developing a quick rapidshare-like site where the user can download files. First, I created a quick test setting headers and using readfile() but then I found in the comments section there's a way to limit the speed of the download, which is great, here's the code: $local_file = 'file.zip'; $download_file = 'name.zip'; // set the download rate limit (=> 20,5 kb/s) $download_rate = 20.5; if(file_exists($local_file) && is_file($local_file)) { header('Cache-control: private'); header('Content-Type: application/octet-stream'); header('Content-Length: '.filesize($local_file)); header('Content-Disposition: filename='.$download_file); flush(); $file = fopen($local_file, "r"); while(!feof($file)) { // send the current file part to the browser print fread($file, round($download_rate * 1024)); // flush the content to the browser flush(); // sleep one second sleep(1); } fclose($file);} else { die('Error: The file '.$local_file.' does not exist!'); } But now my question is, how to limit the number of downloads at the same time? How can I check there's still a connection with some user's IP? Thanks.

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• Best Approach for Checking and Inserting Records

  - by nevets1219

  In one of our existing C programs which purpose is: Open connection to DB for record in all_record: if record contain certain data: if record is NOT in table A: // see #1 insert record information into table A and B // see #2 Close connection to DB select field from table where field=XXX 2 inserts This is typically done every X months to sync everything up or so I'm told. I've also been told that this process takes roughly a couple of days. There is (currently) at most 2.5million records (though not necessarily all 2.5m will be inserted). One of the table contains 10 fields and the other 5 fields. There isn't much to be done about iterating through the records since that part can't be changed at the moment. What I would like to do is speed up the part where I query MySQL. I'm not sure if I have left out any important details -- please let me know! I'm also no SQL expert so feel free to point out the obvious. I thought about: Putting all the inserts into a transaction (at the moment I'm not sure how important it is for the transaction to be all-or-none or if this affects performance) Using Insert X Where Not Exists Y LOAD DATA INFILE (but that would require I create a (possibly) large temp file) I read that (hopefully someone can confirm) I should drop indexes so they aren't re-calculated. mysql Ver 14.7 Distrib 4.1.22, for sun-solaris2.10 (sparc) using readline 4.3

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• AS3 TextField is blank, doesn't accept any of my settings??

  - by Andy Melichar

  Having a strange issue with assigning a TextField to a movie clip. nameFormat = new TextFormat(); nameFormat.size = 14; nameFormat.color = "0x000000"; nameFormat.border = true; nameFormat.font = "Arial"; charName = new TextField(); charName.defaultTextFormat = nameFormat; charName.text = value.charname; charName.x = 92.5; charName.y = 6.5; charName.width = 205; charName.height = 21; thechars[value.charid].addChild(charName); If I trace charName.text it traces correctly, but when the containing movieclip is displayed, it is always blank and none of my settings (borders, background color, etc..) show up. I'm placing several of these movieclips into another movieclip, which is then added to a scroller as such: scrollContent.addChild(thechars[newvalue.charid]); theScroller.source = scrollContent; The strange thing is that I am using the exact same method to drop a button into each of the 'thechars' and it shows up and works fine. AND... if I hover my mouse over the spot where the textField should be, I can see my mouse change from a pointer to a text cursor, so the textFields are showing up, they are just blank? Help?

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• How to delete Drawn Line in java?

  - by Jeyjey

  Hello Folks, well this is my code: import javax.swing.; import javax.; import java.awt.; import java.awt.Color; import java.awt.Graphics.; import java.awt.event.*; import javax.swing.UIManager; public class SimpleGUI extends JFrame{ public SimpleGUI(){ this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE) ; } public void go(){ Drawpanel = new Mypanel(); JFrame frame = new JFrame("Chasing Line"); frame.getContentPane().add(BorderLayout.CENTER, Drawpanel); frame.setSize(300,300); frame.setVisible(true); Drawpanel.addMouseMotionListener(new java.awt.event.MouseMotionAdapter() { public void mouseMoved(java.awt.event.MouseEvent evt) { DrawpanelMouseMoved(evt); } }); } public void DrawpanelMouseMoved(java.awt.event.MouseEvent evt) { xpos=evt.getX(); ypos=evt.getY(); System.out.println("Coordinates : X :"+ xpos+"Y: "+ypos); Drawpanel.paintImage(xpos,ypos); } class Mypanel extends JPanel{ public void paintImage(int xpost,int ypost){ Graphics d = getGraphics(); d.setColor(Color.black); d.drawLine(xpost, 0, xpost, this.getHeight()); d.setColor(Color.red); d.drawLine(0, ypost, this.getWidth(),ypost); this.validate(); } } // end the inner class public static void main(String[] args){ try { UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel"); } catch(Exception e) { System.err.println("Look and feel not set"); } SimpleGUI win = new SimpleGUI(); win.go(); } Mypanel Drawpanel; private int xpos=0; private int ypos=0; } // close SimpleGUI class The problem is how can i delete the old lines?, i mea,make only the current x and y lines appear on the screen, make the intersection between both lines "follow" the mouse pointer. thanks for any reply.

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• Singleton pattern in C++

  - by skydoor

  I have a question about the singleton pattern. I saw two cases concerning the static member in the singleton class. First it is an object, like this class CMySingleton { public: static CMySingleton& Instance() { static CMySingleton singleton; return singleton; } // Other non-static member functions private: CMySingleton() {} // Private constructor ~CMySingleton() {} CMySingleton(const CMySingleton&); // Prevent copy-construction CMySingleton& operator=(const CMySingleton&); // Prevent assignment }; One is an pointer, like this class GlobalClass { int m_value; static GlobalClass *s_instance; GlobalClass(int v = 0) { m_value = v; } public: int get_value() { return m_value; } void set_value(int v) { m_value = v; } static GlobalClass *instance() { if (!s_instance) s_instance = new GlobalClass; return s_instance; } }; What's the difference between the two cases? Which one is correct?

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• Game design flaw, need help investigating

  - by Snake

  I am not sure if I will be able to get help here but I would give it a shot. The problem is I dont know where the problem is. I have a cards game, in which when you "human" play by dragging a card, then at the end of card being dragged, a handler using postExecute is called with delay of 0.5 sec to start the next player in turn (which is a bot) The bot chooses the color and plays it and at the end of the animation (the card moving to the middle) a handler is started for the next bot and so on. Once the play reaches again to the human player, it waits for his touchs to drag the crad and start the cycle again. The problem that in production, sometimes I am getting errors. The error is resulting in somehow messing up the sequence which ends up with players having more cards than others. After investigation, I found that the transition from human to bot is the problem. Somehow, the transition is happening twice (meaning handler calling post execute twice and the bot is playing twice and everything is messed up). Its been mutliple months and I can't reproduce it (to fix it) and I cna't figure out why this is happeneing? ANY IDEA how I can go after it? How can I get more info about or how can I solve something like that? any pointer would help me

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• Fit into div in CSS

  - by Teodoris

  Hello everyone my menu bar can't fit into my <div> area at different browser. I have checked with Opera and Chrome it looks fine but with Explorer and Firefox my menu can't fit. And my menu is in this <div> tag: .page { width: 964px; margin-left: auto; margin-right: auto; background-image:url(../images2/images/orta_alan_bg_GOLGE.png); background-repeat:repeat-y; } Here is my menu: ul#menu { padding: 0 0 2px; position: relative; margin: 0; text-align: center; } ul#menu li { display: inline; list-style: none; font-family: 'Museo300Regular'; font-size:17px; font-style:normal; } ul#menu li a { background-image:url(../../images2/images/menu_bg_normal.jpg); background-repeat: repeat; padding: 5px 19px 5px; font-weight: normal; text-decoration: none; line-height: 2.8em; background-color: #e8eef4; color: #FEFEFF; border-radius: 4px 4px 0 0; -webkit-border-radius: 4px 4px 0 0; -moz-border-radius: 4px 4px 0 0; cursor:pointer; } So what is the problem why it can't fit into with Explorer and Firefox? I attach an image you can understand what I mean Here is the Chrome and Opera it can fit

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• Convert one delphi code line to c++

  - by user1332636

  How can I write that line in c++? This is the code in delphi type TSettings = record sFileName: String[50]; siInstallFolder: Byte; bRunFile: Boolean; ... end; .. var i: dword; sZdData: PChar; Settings :Tsettings; begin .... ZeroMemory(@Settings, sizeof(Tsettings)); settings := Tsettings(Pointer(@sZdData[i])^); // this code to c++ c++ code (hope the rest is OK) struct TSettings{ char sFileName[50]; byte siInstallFolder; bool bRunFile; ... } Settings; ... DWORD i; LPBYTE sZdData; ZeroMemory(&Settings, sizeof(TSettings)); Settings = ????? // im failing here i dunno what to do // i need same as in delphi code above

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• Why does this CSS button mess with <a> tags?

  - by Ian McCullough

  Here is my CSS button { border: 0 none; cursor: pointer; padding: 0 15px 0 0; text-align: center; height: 30px; line-height: 30px; width: auto; } button a { color:white; text-decoration:none; } button.rounded { background: transparent url(/images/button/btn_right.png) no-repeat scroll right top; clear: left; font-size: 0.8em; } button span { display: block; padding: 0 0 0 15px; position: relative; white-space: nowrap; height: 30px; line-height: 30px; } button.rounded span { background: transparent url(/images/button/btn_left.png) no-repeat scroll left top; color: #FFFFFF; } button.rounded:hover { background-position: 100% -30px; } button.rounded:hover span { background-position: 0% -30px; } button::-moz-focus-inner { border: none; } Here is the code for my "button" with a link in it. <button class="rounded"><span><a href="profile.php">Profile</a></span></button> The issue is it does not link to the href when i click on it. Anyone know why?

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• multiple dependent android projects in eclipse

  - by lope

  Hi there! I just started to play with android dev and java+eclipse is pretty new to me. I managed to create simple project and run it on my device. Now I want to create simple game (more of them actually) and I would love to use shared code base for all of them (game loop, initialization, etc..). Problem is that I have no idea how to correctly do this. I created android project called engine with all basic stuff that I need and made it work on device. Now I tried to create another project in same workspace called mygame. Main class (activity) of mygame is MyGameApp which inherits from EngineApp (main activity of my engine project) which inherits from Activity. I added engine project into required projects in mygame build path tab in properties. Problem is that when I try to run this project it crashes on ClassNotFoundException trying to find my MyGameApp class. Any help (or pointer to some articles that explain how this is done) is greatly appreciated. few hours of googling didn't help much :/

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• explain notifier.c from the Linux kernel

  - by apollon

  I'm seeking to fully understand the following code snippet from kernel/notifier.c. I have read and built simple link lists and think I get the construct from K&R's C programming. The second line below which begins with the 'int' appears to be two items together which is unclear. The first is the (*notifier_call) which I believe has independent but related significance with the second containing a 'notifier block' term. Can you explain how it works in detail? I understand that there is a function pointer and multiple subscribers possible. But I lack the way to tie these facts together, and could use a primer or key so I exactly understand how the code works. The third line looks to contain the linking structure, or recursive nature. Forgive my terms, and correct them as fit as I am a new student of computer science terminology. struct notifier_block { int (*notifier_call)(struct notifier_block *, unsigned long, void *); struct notifier_block *next; int priority; };

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• Conceptual data modeling: Is RDF the right tool? Other solutions?

  - by paprika

  I'm planning a system that combines various data sources and lets users do simple queries on these. A part of the system needs to act as an abstraction layer that knows all connected data sources: the user shouldn't [need to] know about the underlying data "providers". A data provider could be anything: a relational DBMS, a bug tracking system, ..., a weather station. They are hooked up to the query system through a common API that defines how to "offer" data. The type of queries a certain data provider understands is given by its "offer" (e.g. I know these entities, I can give you aggregates of type X for relationship Y, ...). My concern right now is the unification of the data: the various data providers need to agree on a common vocabulary (e.g. the name of the entity "customer" could vary across different systems). Thus, defining a high level representation of the entities and their relationships is required. So far I have the following requirements: I need to be able to define objects and their properties/attributes. Further, arbitrary relations between these objects need to be represented: a verb that defines the nature of the relation (e.g. "knows"), the multiplicity (e.g. 1:n) and the direction/navigability of the relation. It occurs to me that RDF is a viable option, but is it "the right tool" for this job? What other solutions/frameworks do exist for semantic data modeling that have a machine readable representation and why are they better suited for this task? I'm grateful for every opinion and pointer to helpful resources.

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• How does a java compiler resolve a non-imported name

  - by gexicide

  Consider I use a type X in my java compilation unit from package foo.bar and X is not defined in the compilation unit itself nor is it directly imported. How does a java compiler resolve X now efficiently? There are a few possibilities where X could reside: X might be imported via a star import a.b.* X might reside in the same package as the compilation unit X might be a language type, i.e. reside in java.lang The problem I see is especially (2.). Since X might be a package-private type, it is not even required that X resides in a compilation unit that is named X.java. Thus, the compiler must look into all entries of the class path and search for any classes in a package foo.bar, it then must read every class that is in package foo.bar to check whether X is included. That sounds very expensive. Especially when I compile only a single file, the compiler has to read dozens of class files only to find a type X. If I use a lot of star imports, this procedure has to be repeated for a lot of types (although class files won't be read twice, of course). So is it advisable to import also types from the same package to speed up the compilation process? Or is there a faster method for resolving an unimported type X which I was not able to find?

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• When are temporaries created as part of a function call destroyed?

  - by Michael Mrozek

  Is a temporary created as part of an argument to a function call guaranteed to stay around until the called function ends, even if the temporary isn't passed directly to the function? There's virtually no chance that was coherent, so here's an example: class A { public: A(int x) : x(x) {printf("Constructed A(%d)\n", x);} ~A() {printf("Destroyed A\n");} int x; int* y() {return &x;} }; void foo(int* bar) { printf("foo(): %d\n", *bar); } int main(int argc, char** argv) { foo(A(4).y()); } If A(4) were passed directly to foo it would definitely not be destroyed until after the foo call ended, but instead I'm calling a method on the temporary and losing any reference to it. I would instinctively think the temporary A would be destroyed before foo even starts, but testing with GCC 4.3.4 shows it isn't; the output is: Constructed A(4) foo(): 4 Destroyed A The question is, is GCC's behavior guaranteed by the spec? Or is a compiler allowed to destroy the temporary A before the call to foo, invaliding the pointer to its member I'm using?

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• C Map String to Function

  - by Scriptonaut

  So, I'm making a Unix minishell, and have come to a roadblock. I need to be able to execute built-in functions, so I made a function: int exec_if_built_in(char **args) It takes an array of strings(the first being the command, and the rest being arguments). For non built-in commands I simply use something like execvp, however I need to find a way to map the first string to a function. I was thinking of making two arrays, one of strings, and another with their corresponding function pointers. However, since many of these functions will be different(return and accept different things), this approach won't work. I also thought of making an array of structs with a name property and a function pointer property, however once again due to the varied nature of the functions I'll be using, this won't work. So, what's the best way to execute a function based on the input of a string? How do I map a string to a certain function? I'm not very familiar with function pointers so I may be missing something. Thank you guys for the help :)

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