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• Proper way to scan a range of IP addresses

  - by Josh G

  Given a range of IP addresses entered by a user (through various means), I want to identify which of these machines have software running that I can talk to. Here's the basic process: Ping these addresses to find available machines Connect to a known socket on the available machines Send a message to the successfully established sockets Compare the response to the expected response Steps 2-4 are straight forward for me. What is the best way to implement the first step in .NET? I'm looking at the System.Net.NetworkInformation.Ping class. Should I ping multiple addresses simultaneously to speed up the process? If I ping one address at a time with a long timeout it could take forever. But with a small timeout, I may miss some machines that are available. Sometimes pings appear to be failing even when I know that the address points to an active machine. Do I need to ping twice in the event of the request getting discarded? To top it all off, when I scan large collections of addresses with the network cable unplugged, Ping throws a NullReferenceException in FreeUnmanagedResources(). !? Any pointers on the best approach to scanning a range of IPs like this?

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• How to prepare data for display on a silverlight chart using WCF RIA Services + Entity Framework

  - by Banford

  I've used WCF RIA services with Entity Framework to build a simple application which can display and updates data about school courses. This was done by following the Microsoft tutorials. Now I would like to have a chart which shows a count for how many courses are on a key stage. Example: Key Stage 3 - 20 courses Key Stage 4 - 32 courses Key Stage 5 - 12 courses Displayed on any form of chart. I have no problem binding data to the chart in XAML. My problem is that I do not know how to correct way of getting the data into that format. The generated CRUD methods are basic. I have a few thoughts about possible ways, but don't know which is correct, they are: Create a View in SQL server and map this to a separate Entity in the Entity Data Model. Generating new CRUD methods for this automatically. Customise the read method in the existing DomainService using .Select() .Distinct() etc. Don't know this syntax very well labda expressions/LINQ??? what is it? Any good quickstarts on it? Create a new class to store only the data required and create a read method for it. Tried this but didn't know how to make it work without a matching entity in the entity model. Something I am not aware of. I'm very new to this and struggling with the concepts so if there are useful blogs or documentation I've missed feel free to point me towards them. But I'm unsure of the terminology to use in my searches at the moment.

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• In Corona SDK the background image always cover other images

  - by user1446126

  I'm currently making a tower defense game with Corona SDK. However, while I'm making the gaming scene, The background scene always cover the monster spawn, I've tried background:toBack() ,however it's doesn't work.Here is my code: module(..., package.seeall) function new() local localGroup = display.newGroup(); local level=require(data.levelSelected); local currentDes = 1; monsters_list = display.newGroup() --The background local bg = display.newImage ("image/levels/1/bg.png"); bg.x = _W/2;bg.y = _H/2; bg:toBack(); --generate the monsters function spawn_monster(kind) local monster=require("monsters."..kind); newMonster=monster.new() --read the spawn(starting point) in level, and spawn the monster there newMonster.x=level.route[1][1];newMonster.y=level.route[1][2]; monsters_list:insert(newMonster); localGroup:insert(monsters_list); return monsters_list; end function move(monster,x,y) -- Using pythagoras to calauate the moving distace, Hence calauate the time consumed according to speed transition.to(monster,{time=math.sqrt(math.abs(monster.x-x)^2+math.abs(monster.y-y)^2)/(monster.speed/30),x=x, y=y, onComplete=newDes}) end function newDes() currentDes=currentDes+1; end --moake monster move according to the route function move_monster() for i=1,monsters_list.numChildren do move(monsters_list[i],200,200); print (currentDes); end end function agent() spawn_monster("basic"); end --Excute function above. timer2 = timer.performWithDelay(1000,agent,10); timer.performWithDelay(100,move_monster,-1); timer.performWithDelay(10,update,-1); move_monster(); return localGroup; end and the monster just stuck at the spawn point and stay there. but, When i comment these 3 lines of code: --local bg = display.newImage ("image/levels/1/bg.png"); --bg.x = _W/2;bg.y = _H/2; --bg:toBack(); The problem disappear Any ideas??Thanks for helping

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• What should be taught in a "Fundamentals of programming" course at university?

  - by Dervin Thunk

  I have started a new question (see here), because I think the topic is of importance in a more general form. The question is now: If you were a professor at a Computer Science Dept. in some university, what would make it into your course? This is a programming course, second term, first year computer science/computer engineering. Remember you have a limited amount of time, and students are of different levels of competence, and some may be scientists, but some will also go on to be programmers in companies of different kinds. You have to cater to all. Bonus: What language? (Although see this question for my current thoughts about this...) Maybe you want to attach a course outline from some university? See here for an even more general question about this. Answer: I can't really summarize this post... I guess it was too subjective. However, it looks like we have to cover the history of computing up to a certain extent, computer architecture (memory, registers, whatever), C, and finally some basic algos and data structures in a problem solving fashion. This will be the bare bones of the course. Thanks all. I will accept the most voted up answer to close the thread, as it should be done.

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• Creating a Linq->HQL provider

  - by Mike Q

  Hi all, I have a client application that connects to a server. The server uses hibernate for persistence and querying so it has a set of annotated hibernate objects for persistence. The client sends HQL queries to the server and gets responses back. The client has an auto-generated set of objects that match the server hibernate objects for query results and basic persistence. I would like to support using Linq to query as well as Hql as it makes the queries typesafe and quicker to build (no more typos in HQL string queries). I've looked around at the following but I can't see how to get them to fit with what I have. NHibernate's Linq provider - requires using NHibernate ISession and ISessionFactory, which I don't have LinqExtender - requires a lot of annotations on the objects and extending a base type, too invasive What I really want is something that will generate give me a nice easy to process structure to build the HQL queries from. I've read most of a 15 page article written by one of the C# developers on how to create custom providers and it's pretty fraught, mainly because of the complexity of the expression tree. Can anyone suggest an approach for implementing Linq - HQL translation? Perhaps a library that will the cleanup of the expression tree into something more SQL/HQLish. I would like to support select/from/where/group by/order by/joins. Not too worried about subqueries.

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• Socket isn't listed by netstat unless using certain ports

  - by illuzive

  I'm a computer science student with a few years of programming experience. Yesterday, while working on a project (Mac OS X, BSD sockets) at school, I encountered a strange problem. I was adding several modules to a very basic "server" (mostly a bunch of functions to set up and manage an UDP socket on a certain port). While doing this, I started the server from time to time in order to see that everything worked like it should. I've been using port 32000 during the development of the server. When I start the server and run netstat, the socket is listed as expected. > netstat -p UDP | grep 32000 udp46 0 0 *.32000 *.* However, when I run the server on other ports (random (10000 - 50000)), it's not listed by netstat. My thought was that I had somehow hard coded the port somewhere in the code, but that's not the case. The thing is - I can connect to the socket on any of the tested ports, and it reads data sent to it without any problem at all. It just doesn't get listed by netstat. What I wonder, is if anyone of you have any idea of why this happens? Note: Although this is a project at school, it's not homework. This is just something I want to understand for my own benefit.

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• Program structure in long running data processing python script

  - by fmark

  For my current job I am writing some long-running (think hours to days) scripts that do CPU intensive data-processing. The program flow is very simple - it proceeds into the main loop, completes the main loop, saves output and terminates: The basic structure of my programs tends to be like so: <import statements> <constant declarations> <misc function declarations> def main(): for blah in blahs(): <lots of local variables> <lots of tightly coupled computation> for something in somethings(): <lots more local variables> <lots more computation> <etc., etc.> <save results> if __name__ == "__main__": main() This gets unmanageable quickly, so I want to refactor it into something more manageable. I want to make this more maintainable, without sacrificing execution speed. Each chuck of code relies on a large number of variables however, so refactoring parts of the computation out to functions would make parameters list grow out of hand very quickly. Should I put this sort of code into a python class, and change the local variables into class variables? It doesn't make a great deal of sense tp me conceptually to turn the program into a class, as the class would never be reused, and only one instance would ever be created per instance. What is the best practice structure for this kind of program? I am using python but the question is relatively language-agnostic, assuming a modern object-oriented language features.

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• Distinct or group by on some columns but not others

  - by Nazadus

  I have a view that I'm trying to filter with something similar to DISTINCT on some columns but not others. I have a view like this: Name LastName Zip Street1 HouseholdID (may not be unique because it may have multiple addresses -- think of it in the logical sense as grouping persons but not physical locations; If you lookup HouseholdID 4130, you may get two rows.. or more, because the person may have mutiple mailing locations) City State I need to pull all those columns but filter on LastName,Zip, and Street1. Here's the fun part: The filter is arbitrary -- meaning I don't care which one of the duplicates goes away. This is for a mail out type thing and the other information is not used for any other reason than than to look up a specific person if needed (I have no idea why). So.. given one of the records, you can easily figure out the removed ones. As it stands now, my Sql-Fu fails me and I'm filtering in C# which is incredibly slow and is pretty much a foreach that starts with an empty list and adds the row in if the combined last name, zip, and street aren't are not in the list. I feel like I'm missing a simple / basic part of SQL that I should be understanding.

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• What would cause objectForKey: to return null with a valid string in place?

  - by theMikeSwan

  I am having an issue with NSDictionary returning null for an NSString even though the string in in the dictionary. Here is the code: - (void)sourceDidChange:(NSNotification *)aNote { NSDictionary *aDict = [aNote userInfo]; DLog(@"%@", aDict); NSString *newSourceString = [aDict objectForKey:@"newSource"]; DLog(@"%@", newSourceString); newSourceString = [newSourceString stringByReplacingOccurrencesOfString:@" " withString:@""]; DLog(@"%@", newSourceString); NSString *inspectorString = [newSourceString stringByAppendingString:@"InspectorController"]; DLog(@"%@", inspectorString); newSourceString = [newSourceString stringByAppendingString:@"ViewController"]; DLog(@"%@", newSourceString); } And I get the following log statements: 2010-04-17 23:50:13.913 CoreDataUISandbox[13417:a0f] -[RightViewController sourceDidChange:] newSource = "Second View"; 2010-04-17 23:50:13.914 CoreDataUISandbox[13417:a0f] -[RightViewController sourceDidChange:] (null) 2010-04-17 23:50:13.916 CoreDataUISandbox[13417:a0f] -[RightViewController sourceDidChange:] (null) 2010-04-17 23:50:13.917 CoreDataUISandbox[13417:a0f] -[RightViewController sourceDidChange:] (null) 2010-04-17 23:50:13.917 CoreDataUISandbox[13417:a0f] -[RightViewController sourceDidChange:] (null) As you can see the string is in the dictionary under the key newSource, yet when I call objectForKey: I get null. I have even tried the fallback option of cleaning the project. Has anyone ever run into this, or have I just forgotten something really basic?

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• routing mvc on the web

  - by generic_noob

  Hi, I was wondering if anyone could possibly provide me some advice on how i could improve the routing (and/or architecture) to each 'section' of my application. (I'm writing in PHP5, and trying to use strict MVC) Basically, I have a generic index page for the app, and that will spew out boilerplate stuff like jquery and the css etc. and it also generates the main navidation for the entire site, but i'm unsure about the best approach to connect the 'main menu' items(hyperlinks) with their associated controllers. Up until now I have been appending strings into the url and using a 'switch' statement to branch to the correct controller(and view) by extracting the strings back out of '$GET[]' to let it execute the code for the corrosponding action. for instance if i had a basic crud system for customer data, the url to edit a customers details would look like 'www.example.com/index.php?page=customer&action=edit&id=4'. I'm worried that there is a security concern by doing it this way, and i'm not sure of an alternative to branch the main 'index.php' file to the correct controller for each action once the user has clicked the link. Would it be better to use mod_rewrite to disguise the controllers names? or to create a similar system to the ASP MVC framework, where there is a seperate routing system where each url is filtered to get the associated controller? Cheers!

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• Start developing a database application using Oracle + Net Beans

  - by Ranhiru

  I have thought of creating my first database application for one of my projects using Oracle and Java. I have chosen Netbeans as my development environment. I have a few questions to getting started. Please bare with me as I'm a complete beginner to Oracle + Netbeans This will be a data intensive (yet still for a college project) database application. I do not need 1000 user concurrency or any other very advanced features but basic stuff such as triggers, stored procedures etc. Will the 11g "Express" (XE) suffice for my requirements? Do i need any Java to Oracle bridge (database connectivity driver eg. ODBC etc) for Netbeans to connect to the oracle database? If yes, what are they? Does Netbeans support Oracle databases natively? Any easy to follow guide on how do i connect to the database and insert/retrieve/display data on a J2SE application? (I know that i should Google this but if there's any guide previously followed by anyone and is considered easy, it would be greatly appreciated.)

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• What file format can I use to output a formatted text file straight from a program without having the markup be too complicated?

  - by Matt

  Premise: I am parsing a file that is quite nearly XML, but not quite. From this file I would like to extract data and output in a file that a user could open up in some program and read. To make the data reasonable, I would almost certainly need to format the text. In case it matters, I will probably be using Java to write the program. Problem: I cannot find a file format that supports formatting without having terribly complex rules and encoding problems. Attempts: I looked into a basic .txt extension first, but it does not have enough formatting advantage. I then tried a .rtf extension, but the rules for outputting text seem to be terribly complicated. It was then suggested that I used XML, but I do not understand how this file would be viewed. This appears to be probably the best solution, but I don't understand much about it. Perhaps somebody could shed some light here. In Other Words: Could somebody suggest and easy to use file format and/or shed some light on how to use XML for text formatting and viewing?

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• Referencing not-yet-defined variables - Java

  - by user2537337

  Because I'm tired of solving math problems, I decided to try something more engaging with my very rusty (and even without the rust, very basic) Java skills. I landed on a super-simple people simulator, and thus far have been having a grand time working through the various steps of getting it to function. Currently, it generates an array of people-class objects and runs a for loop to cycle through a set of actions that alter the relationships between them, which I have stored in a 2d integer array. When it ends, I go look at how much they all hate each other. Fun stuff. Trouble has arisen, however, because I would like the program to clearly print what action is happening when it happens. I thought the best way to do this would be to add a string, description, to my "action" class (which stores variables for the actor, reactor, and the amount the relationship changes). This works to a degree, in that I can print a generic message ("A fight has occurred!") with no problem. However, ideally I would like it to be a little more specific ("Person A has thrown a rock at Person B's head!"). This latter goal is proving more difficult: attempting to construct an action with a description string that references actor and reactor gets me a big old error, "Cannot reference field before it is defined." Which makes perfect sense. I believe I'm not quite in programmer mode, because the only other way I can think to do this is an unwieldy switch statement that negates the need for each action to have its own nicely-packaged description. And there must be a neater way. I am not looking for examples of code, only a push in the direction of the right concept to handle this.

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• A feeling that I'm not that good developer

  - by Karim

  Hi, Im having a strange feeling, but let me first introduce myself as a software developer. I started to program when I was still a kid, I had about 10 or 11 years. I really enjoy my work and never get bored from it. It's amazing how somebody could be paid for what he really likes to do and would be doing it anyway even for free. WHen I first started to program, I was feeling proud of what I was doing, each application I built was for me a success and after 2-3 year I had a feeling that I'm a coding guru. It was a nice feeling ;-) But the more I was in the field, the more types of software I started to develop I was starting to have a feeling that I'm completely wrong in that I'm guru. I felt that I'm not even a mediocre developer. Each new field I start to work on is giving me this feeling. Like when I once developed a device driver for a client, I saw how much I need to learn about device drivers. When I developed a video filter for an application, I saw how much do I still need to learn about DirectShow, Color Spaces, and all the theory behind that. The worst thing was when I started to learn algorithms. It was several years ago. I knew then the basic structures and algorithms like the sorting, some types of trees, some hashtables, strings etc.. and when I really wanted to learn a group of structures I learned about 5-6 new types and saw that in fact even this small group has several hundred subtypes of structures. It's depressing how little time people have in their lives to learn all this stuff. I'm now a software developer with about 10 years of experience and I still feel that I'm not a proficient developer when I think about things that others do in the industry. Is this normal what I'm experiencing or is it a sign of a destructive excessive ambition? Thanks in advance for any comments.

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• Is it a good idea to use an integer column for storing US ZIP codes in a database?

  - by Yadyn

  From first glance, it would appear I have two basic choices for storing ZIP codes in a database table: Text (probably most common), i.e. char(5) or varchar(9) to support +4 extension Numeric, i.e. 32-bit integer Both would satisfy the requirements of the data, if we assume that there are no international concerns. In the past we've generally just gone the text route, but I was wondering if anyone does the opposite? Just from brief comparison it looks like the integer method has two clear advantages: It is, by means of its nature, automatically limited to numerics only (whereas without validation the text style could store letters and such which are not, to my knowledge, ever valid in a ZIP code). This doesn't mean we could/would/should forgo validating user input as normal, though! It takes less space, being 4 bytes (which should be plenty even for 9-digit ZIP codes) instead of 5 or 9 bytes. Also, it seems like it wouldn't hurt display output much. It is trivial to slap a ToString() on a numeric value, use simple string manipulation to insert a hyphen or space or whatever for the +4 extension, and use string formatting to restore leading zeroes. Is there anything that would discourage using int as a datatype for US-only ZIP codes?

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• Integer array or struct array - which is better?

  - by MusiGenesis

  In my app, I'm storing Bitmap data in a two-dimensional integer array (int[,]). To access the R, G and B values I use something like this: // read: int i = _data[x, y]; byte B = (byte)(i >> 0); byte G = (byte)(i >> 8); byte R = (byte)(i >> 16); // write: _data[x, y] = BitConverter.ToInt32(new byte[] { B, G, R, 0 }, 0); I'm using integer arrays instead of an actual System.Drawing.Bitmap because my app runs on Windows Mobile devices where the memory available for creating bitmaps is severely limited. I'm wondering, though, if it would make more sense to declare a structure like this: public struct RGB { public byte R; public byte G; public byte B; } ... and then use an array of RGB instead of an array of int. This way I could easily read and write the separate R, G and B values without having to do bit-shifting and BitConverter-ing. I vaguely remember something from days of yore about byte variables being block-aligned on 32-bit systems, so that a byte actually takes up 4 bytes of memory instead of just 1 (but maybe this was just a Visual Basic thing). Would using an array of structs (like the RGB example` above) be faster than using an array of ints, and would it use 3/4 the memory or 3 times the memory of ints?

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• C++ Declarative Parsing Serialization

  - by Martin York

  Looking at Java and C# they manage to do some wicked processing based on special languaged based anotation (forgive me if that is the incorrect name). In C++ we have two problems with this: 1) There is no way to annotate a class with type information that is accessable at runtime. 2) Parsing the source to generate stuff is way to complex. But I was thinking that this could be done with some template meta-programming to achieve the same basic affect as anotations (still just thinking about it). Like char_traits that are specialised for the different types an xml_traits template could be used in a declaritive way. This traits class could be used to define how a class is serialised/deserialized by specializing the traits for the class you are trying to serialize. Example Thoughs: template<typename T> struct XML_traits { typedef XML_Empty Children; }; template<> struct XML_traits<Car> { typedef boost::mpl::vector<Body,Wheels,Engine> Children; }; template<typename T> std::ostream& Serialize(T const&) { // my template foo is not that strong. // but somthing like this. boost::mpl::for_each<typename XML_Traits<T>::Children,Serialize>(data); } template<> std::ostream& Serialize<XML_Empty>(T const&) { /* Do Nothing */ } My question is: Has anybody seen any projects/decumentation (not just XML) out there that uses techniques like this (template meta-programming) to emulate the concept of annotation used in languges like Java and C# that can then be used in code generation (to effectively automate the task by using a declaritive style). At this point in my research I am looking for more reading material and examples.

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• What are the skills a Drupal Developer needs?

  - by hfidgen

  I'm trying to write out a list of key Drupal competencies, mainly so I can confirm what I know, don't know and don't know I don't know. (Thanks D. Rumsfeld for that quote!) I think some of these are really broad, for instance there's quite a difference between making a functional theme and creating a theme with good SEO, load times and so on, but I'm hoping you could assume that a half decent web developer would look after that anyway. Just interested to see what people here feel is also important. Able to install Drupal on a server (pretty obvious). Able to research and install modules to meet project requirements Able to configure all the basic modules and core settings to get a site running Able to create a custom Theme from scratch which validates with good HTML/CSS and also pays attention to usability and accessibility. (Whilst still looking kick-ass). Able to use Hooks in the theme template.php to alter forms, page layout and other core functionality Can make forms from scratch using the API - with validation and posting back to the DB/email Can use Views to create blocks or pages, use php snippets as arguments, etc. Can create custom modules from scratch utilising core hooks and other hooks.

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• where does a novice begin with error logging in asp.net c# ?

  - by korben

  i'm a novice teaching myself asp.net in c# via trial and error learn by doing, unfortunately this means lots of errors! i have a custom errors page now that is basically a 404 so that site visitors don't get that ugly application error message .NET throws, but i WOULD like to be able to see what's going wrong myself as people use the site. so i'm looking to build or learn from a fairly basic error logging c# class, that will send the same information given in a browser when hitting a .NET error, send this into a TXT file and email me the error at the same time would be great i don't know where to even begin, can someone give me some pointers? an open source class that does this already that i could plugin and play with would work as well. otherwise some links or guidance on where to start reading would be great too. i sort of have a mental block on understand msdn info-dump pages though, i'm hoping to find some articles on real people talking about implementing the same thing themselves or something like that please note i'm not looking to use some extensive or complicated third party service for this, i'm hoping to learn from the process of implementing a concise customized one

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• What are the differences between mapping,binding and parsing?

  - by sfrj

  I am starting to learn web-services in java EE6. I did web development before, but never nothing related to web services. All is new to me and the books and the tutorials i find in the web are to technical. I started learning about .xsd schemas and also .xml. In that topic i feel confident, i understand what are the schemas used for and what validation means. Now my next step is learning about JAX-B(Java Api for XML Binding). I rode some about it and i did also some practice in my IDE. But i have lots of basic doubts, that make me stuck and cannot feel confident to continue to the next topic. Ill appreciate a lot if someone could explain me well my doubts: What does it mean mapping and what is a mapping tool? What does it mean binding and what is a binding tool? What does it mean parsing and what is a parsing tool? How is JAX-B related to mapping,binding and parsing? I am seeking for a good answer built by you, not just a copy paste from google(Ive already been online a few hours and only got confused).

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• Link error for user defined class type template parameter

  - by isurulucky

  Hi, I implemented a Simple STL map in C++. Factored out the comparison as a type as I was instructed to, then implemented the comparison as shown below: template <typename T> int KeyCompare<T>::operator () (T tKey1, T tKey2) { if(tKey1 < tKey2) return -1; else if(tKey1 > tKey2) return 1; else return 0; } here, tKey1 and tKet2 are the two keys I'm comparing. This worked well for all the basic data types and string. I added a template specialization to compare keys of a user defined type named Test and added a specialization as follows: int KeyCompare<Test>::operator () (Test tKey1, Test tKey2) { if(tKey1.a < tKey2.a) return -1; else if(tKey1.a > tKey2.a) return 1; else return 0; } when I run this, I get a linking error saying SimpleMap.obj : error LNK2005: "public: int __thiscall KeyCompare::operator()(class Test,class Test)" (??R?$KeyCompare@VTest@@@@QAEHVTest@@0@Z) already defined in MapTest.obj SimpleMap.obj : error LNK2005: "public: __thiscall KeyCompare::~KeyCompare(void)" (??1?$KeyCompare@VTest@@@@QAE@XZ) already defined in MapTest.obj SimpleMap.obj : error LNK2005: "public: __thiscall KeyCompare::KeyCompare(void)" (??0?$KeyCompare@VTester@@@@QAE@XZ) already defined in MapTest.obj MapTest.cpp is the test harness class in which I wrote the test case. I have used include guards as well, to stop multiple inclusions. Any idea what the matter is?? Thank you very much!!

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• Why is my simple python gtk+cairo program running so slowly/stutteringly?

  - by synapz

  My program draws circles moving on the window. I think I must be missing some basic gtk/cairo concept because it seems to be running too slowly/stutteringly for what I am doing. Any ideas? Thanks for any help! #!/usr/bin/python import gtk import gtk.gdk as gdk import math import random import gobject # The number of circles and the window size. num = 128 size = 512 # Initialize circle coordinates and velocities. x = [] y = [] xv = [] yv = [] for i in range(num): x.append(random.randint(0, size)) y.append(random.randint(0, size)) xv.append(random.randint(-4, 4)) yv.append(random.randint(-4, 4)) # Draw the circles and update their positions. def expose(*args): cr = darea.window.cairo_create() cr.set_line_width(4) for i in range(num): cr.set_source_rgb(1, 0, 0) cr.arc(x[i], y[i], 8, 0, 2 * math.pi) cr.stroke_preserve() cr.set_source_rgb(1, 1, 1) cr.fill() x[i] += xv[i] y[i] += yv[i] if x[i] > size or x[i] < 0: xv[i] = -xv[i] if y[i] > size or y[i] < 0: yv[i] = -yv[i] # Self-evident? def timeout(): darea.queue_draw() return True # Initialize the window. window = gtk.Window() window.resize(size, size) window.connect("destroy", gtk.main_quit) darea = gtk.DrawingArea() darea.connect("expose-event", expose) window.add(darea) window.show_all() # Self-evident? gobject.idle_add(timeout) gtk.main()

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• NSTask Tail -f Using objective C

  - by Bach

  I need to read the last added line to a log file, in realtime, and capture that line being added. Something similar to Tail -f. So my first attempt was to use Tail -f using NSTask. I can't see any output using the code below: NSTask *server = [[NSTask alloc] init]; [server setLaunchPath:@"/usr/bin/tail"]; [server setArguments:[NSArray arrayWithObjects:@"-f", @"/path/to/my/LogFile.txt",nil]]; NSPipe *outputPipe = [NSPipe pipe]; [server setStandardInput:[NSPipe pipe]]; [server setStandardOutput:outputPipe]; [server launch]; [server waitUntilExit]; [server release]; NSData *outputData = [[outputPipe fileHandleForReading] readDataToEndOfFile]; NSString *outputString = [[[NSString alloc] initWithData:outputData encoding:NSUTF8StringEncoding] autorelease]; NSLog (@"Output \n%@", outputString); I can see the output as expected when using: [server setLaunchPath:@"/bin/ls"]; How can i capture the output of that tail NSTask? Is there any alternative to this method, where I can open a stream to file and each time a line is added, output it on screen? (basic logging functionality)

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• CSS Clearing Floats

  - by Frank

  I'm making more of an effort to separate my html structure from presentation, but sometimes when I look at the complexity of the hacks or workarounds to make things work cross-browser, I'm amazed at huge collective waste of productive hours that are put into this. As I understand it, floats were never created for creating layouts, but because many layouts need a footer, that's how they're often being used. To clear the floats, you can add an empty div that clears both sides (div class="clear"). That is simple and works cross browser, but it adds "non-semantic" html rather than solving the presentation problem within the CSS. I realize this, but after looking at all of the solutions with their benefits and drawbacks, it seems to make more sense to go with the empty div (predictable behavior across browsers), rather than create separate stylesheets, including various css hacks and workarounds, etc. which would also need to change as CSS evolves. Is it o.k. to do this as long as you do understand what you're doing and why you're doing it? Or is it better to find the CSS workarounds, hacks and separate structure from presentation at all costs, even when the CSS presentation tools provided are not evolved to the point where they can handle such basic layout issues?

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• Using shared_ptr to implement RCU (read-copy-update)?

  - by yongsun

  I'm very interested in the user-space RCU (read-copy-update), and trying to simulate one via tr1::shared_ptr, here is the code, while I'm really a newbie in concurrent programming, would some experts help me to review? The basic idea is, reader calls get_reading_copy() to gain the pointer of current protected data (let's say it's generation one, or G1). writer calls get_updating_copy() to gain a copy of the G1 (let's say it's G2), and only one writer is allowed to enter the critical section. After the updating is done, writer calls update() to do a swap, and make the m_data_ptr pointing to data G2. The ongoing readers and the writer now hold the shared_ptr of G1, and either a reader or a writer will eventually deallocate the G1 data. Any new readers would get the pointer to G2, and a new writer would get the copy of G2 (let's say G3). It's possible the G1 is not released yet, so multiple generations of data my co-exists. template <typename T> class rcu_protected { public: typedef T type; typedef std::tr1::shared_ptr<type> rcu_pointer; rcu_protected() : m_data_ptr (new type()) {} rcu_pointer get_reading_copy () { spin_until_eq (m_is_swapping, 0); return m_data_ptr; } rcu_pointer get_updating_copy () { spin_until_eq (m_is_swapping, 0); while (!CAS (m_is_writing, 0, 1)) {/* do sleep for back-off when exceeding maximum retry times */} rcu_pointer new_data_ptr(new type(*m_data_ptr)); // as spin_until_eq does not have memory barrier protection, // we need to place a read barrier to protect the loading of // new_data_ptr not to be re-ordered before its construction _ReadBarrier(); return new_data_ptr; } void update (rcu_pointer new_data_ptr) { while (!CAS (m_is_swapping, 0, 1)) {} m_data_ptr.swap (new_data_ptr); // as spin_until_eq does not have memory barrier protection, // we need to place a write barrier to protect the assignments of // m_is_writing/m_is_swapping be re-ordered bofore the swapping _WriteBarrier(); m_is_writing = 0; m_is_swapping = 0; } private: volatile long m_is_writing; volatile long m_is_swapping; rcu_pointer m_data_ptr; };

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