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  • Why do HDFS clusters have only a single NameNode?

    - by grautur
    I'm trying to understand better how Hadoop works, and I'm reading The NameNode is a Single Point of Failure for the HDFS Cluster. HDFS is not currently a High Availability system. When the NameNode goes down, the file system goes offline. There is an optional SecondaryNameNode that can be hosted on a separate machine. It only creates checkpoints of the namespace by merging the edits file into the fsimage file and does not provide any real redundancy. Hadoop 0.21+ has a BackupNameNode that is part of a plan to have an HA name service, but it needs active contributions from the people who want it (i.e. you) to make it Highly Available. from http://wiki.apache.org/hadoop/NameNode So why is the NameNode a single point of failure? What is bad or difficult about having a complete duplicate of the NameNode running as well?

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  • Declarative Transactions in Node.js

    - by James Kingsbery
    Back in the day, it was common to manage database transactions in Java by writing code that did it. Something like this: Transaction tx = session.startTransaction(); ... try { tx.commit(); } catch (SomeException e){ tx.rollback(); } at the beginning and end of every method. This had some obvious problems - it's redundant, hides the intent of what's happening, etc. So, along came annotation-driven transactions: @Transaction public SomeResultObj getResult(...){ ... } Is there any support for declarative transaction management in node.js?

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  • Fastest way to parse big json android

    - by jem88
    I've a doubt that doesn't let me sleep! :D I'm currently working with big json files, with many levels. I parse these object using the 'default' android way, so I read the response with a ByteArrayOutputStream, get a string and create a JSONObject from the string. All fine here. Now, I've to parse the content of the json to get the objects of my interest, and I really can't find a better way that parse it manually, like this: String status = jsonObject.getString("status"); Boolean isLogged = jsonObject.getBoolean("is_logged"); ArrayList<Genre> genresList = new ArrayList<Genre>(); // Get jsonObject with genres JSONObject jObjGenres = jsonObject.getJSONObject("genres"); // Instantiate an iterator on jsonObject keys Iterator<?> keys = jObjGenres.keys(); // Iterate on keys while( keys.hasNext() ) { String key = (String) keys.next(); JSONObject jObjGenre = jObjGenres.getJSONObject(key); // Create genre object Genre genre = new Genre( jObjGenre.getInt("id_genre"), jObjGenre.getString("string"), jObjGenre.getString("icon") ); genresList.add(genre); } // Get languages list JSONObject jObjLanguages = jsonObject.getJSONObject("languages"); Iterator jLangKey = jObjLanguages.keys(); List<Language> langList = new ArrayList<Language>(); while (jLangKey.hasNext()) { // Iterate on jlangKey obj String key = (String) jLangKey.next(); JSONObject jCurrentLang = (JSONObject) jObjLanguages.get(key); Language lang = new Language( jCurrentLang.getString("id_lang"), jCurrentLang.getString("name"), jCurrentLang.getString("code"), jCurrentLang.getString("active").equals("1") ); langList.add(lang); } I think this is really ugly, frustrating, timewaster, and fragile. I've seen parser like json-smart and Gson... but seems difficult to parse a json with many levels, and get the objects! But I guess that must be a better way... Any idea? Every suggestion will be really appreciated. Thanks in advance!

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  • Why don't more companies hire remotely?

    - by James
    I keep hearing about the desperate recruiting efforts of companies in tech hubs such as SF and NYC. However, every time I'm contacted by a startup I'm told the position is on-site and working remotely isn't possible. Let me clarify that these are tech startups. They should be very comfortable with the idea of using technology to get things done and connect teams together. With the housing market the way it is, many of us can't relocate even if we wanted to pay the higher cost of living. Why are so many companies still stuck in the industrial mindset of butts in seats?

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  • Lucene best practice

    - by Dragos
    I am trying to understand how Lucene should be used. From what I have read, creating an IndexReader is costly, so using a Search Manager shoulg be the right choice. However, a SearchManager should be produced by a NRTManager(which, by the way, should replace the IndexWriter for every add or delete operation performed). But in order to have a NRTManager, I should first have an IndexWriter, and here comes my problem. The documentation says: an IndexWriter is thread-safe the constructor of this class takes a Directory object, so it seems creating an instace should be costly(as in the case of an IndexReader) all changes are buffered and flushed periodically(so they seem to encourage using a single instance) but: the changes, although flushed will only be visible after commit or close after finished making updates(add/delete), the instance should be closed I also found this: http://stackoverflow.com/questions/5374419/forgot-to-close-the-lucene-indexwriter-after-adding-documents-to-the-index where it is said that not closing a writer might ruin everything So what am I really supposed to do? Is having a single IndexWriter instance a good idea(make only commit and never close it)? EDIT: What is more, if I use NRTManager, how can I make acommit`? Is it even possible?

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  • At what point does "constructive" criticism of your code become unhelpful?

    - by user15859
    I recently started as a junior developer. As well as being one of the least experienced people on the team, I'm also a woman, which comes with all sorts of its own challenges working in a male-dominated environment. I've been having problems lately because I feel like I am getting too much unwarranted pedantic criticism on my work. Let me give you an example of what happened recently. Team lead was too busy to push in some branches I made, so he didn't get to them until the weekend. I checked my mail, not really meaning to do any work, and found that my two branches had been rejected on the basis of variable names, making error messages more descriptive, and moving some values to the config file. I don't feel that rejecting my branch on this basis is useful. Lots of people were working over the weekend, and I had never said that I would be working. Effectively, some people were probably blocked because I didn't have time to make the changes and resubmit. We are working on a project that is very time-sensitive, and it seems to me that it's not helpful to outright reject code based on things that are transparent to the client. I may be wrong, but it seems like these kinds of things should be handled in patch type commits when I have time. Now, I can see that in some environments, this would be the norm. However, the criticism doesn't seem equally distributed, which is what leads to my next problem. The basis of most of these problems was due to the fact that I was in a codebase that someone else had written and was trying to be minimally invasive. I was mimicking the variable names used elsewhere in the file. When I stated this, I was bluntly told, "Don't mimic others, just do what's right." This is perhaps the least useful thing I could have been told. If the code that is already checked in is unacceptable, how am I supposed to tell what is right and what is wrong? If the basis of the confusion was coming from the underlying code, I don't think it's my responsibility to spend hours refactoring a whole file that someone else wrote (and works perfectly well), potentially introducing new bugs etc. I'm feeling really singled out and frustrated in this situation. I've gotten a lot better about following the standards that are expected, and I feel frustrated that, for example, when I refactor a piece of code to ADD error checking that was previously missing, I'm only told that I didn't make the errors verbose enough (and the branch was rejected on this basis). What if I had never added it to begin with? How did it get into the code to begin with if it was so wrong? This is why I feel so singled out: I constantly run into this existing problematic code, that I either mimic or refactor. When I mimic it, it's "wrong", and if I refactor it, I'm chided for not doing enough (and if I go all the way, introducing bugs, etc). Again, if this is such a problem, I don't understand how any code gets into the codebase, and why it becomes my responsibility when it was written by someone else, who apparently didn't have their code reviewed. Anyway, how do I deal with this? Please remember that I said at the top that I'm a woman, and I'm sure these guys don't usually have to worry about decorum when they're reviewing other guys' code, but honestly that doesn't work for me, and it's causing me to be less productive. I'm worried that if I talk to my manager about it, he'll think I can't handled the environment, etc.

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  • What companies do what I'm interested in?

    - by Alex
    I'm a systems guy. People change their concentrations to avoid taking operating systems, while I took it during my first semester after transferring. I'm taking compilers and networks now, and I think they're awesome. And yet there are so many job postings looking for people to do work in things like web development, and so few postings looking for people to work in kernel hacking or network engineering. What sorts of companies do these things? I'm currently awaiting a contract in the mail for an internship with VMWare, so I'm not out of a job for the summer. Still, I'd like to companies do these things.

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  • Should I use multiple column primary keys or add a new colum?

    - by Covar
    My current database design makes use of a multiple column primary key to use existing data (that would be unique anyway) instead of creating an additional column assigning each entry an arbitrary key. I know that this is allowed, but was wondering if this is a practice that I might want to use cautiously and possibly avoid (much like goto in C). So what are some of the disadvantages I might see in this approach or reasons I might want a single column key?

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  • What is the ideal laptop for creative coding applications?

    - by Jason
    Hi, I am a creative coder using C++(cinder and OpenFrameworks) I am looking to upgrade from my MacBook, which slowed down to about 3fps this morning. My project involves particles systems and fluids reacting to audio analysis data and computer vision data in real-time. SD or HD? no biggie. I have asked many people what computer I need. Ideally, I want a MacBook Pro. But is that enough power? I've been told that I need a desktop for what I am doing though I'd rather stay portable I've been told that I should go PC linux to get the most power but I'd rather stay mac I've been told that RAM is more of bottleneck than processor speed I've been told that the Graphics Card is more important than CPU and that code optimizations such as using trees over lists, proper threading, sending tasks to the GPU make a bigger difference than the hardware!!! what's true?! what do I need? Any suggestions are greatly appreciated

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  • Building a Map based WebApp fast?

    - by NLemay
    I want to build a WebApp which is basically a map with points of interest, filters, and a list of those points. Something really similar to AirBnB, or any other map based app. Of course, I could just take Google Maps API and build what's around. But I guess a lot of people already did that, and may be I could use their work to make mine faster. Here's what I need : Adding multiples POI A list of POI that are showed on the map A way to filter POI Most have a behavior to handle a lot of POI Can works on mobile and tablet I already know one template that can do nearly all of this, it is call Bootleaf. But I would like to know if you know others that might work better.

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  • Tomcat + Spring + CI workflow

    - by ex3v
    We're starting our very first project with Spring and java web stack. This project will be mainly about rewriting quite large ERP/CRM from Zend Framework to Java. Important factor in my question is that I come from php territory, where things (in terms of quality) tend to look different than in java world. Fatcs: there will be 2-3 developers, at least one of developers uses Windows, rest uses Linux, there is one remote linux-based machine, which should handle test and production instances, after struggling with buggy legacy code, we want to introduce good programming and development practices (CI, tests, clean code and so on) client: internal, frequent business logic changes, scrum, daily deployments What I want to achieve is good workflow on as many development stages as possible (coding - commiting - testing - deploying). The problem is that I've never done this before, so I don't know what are best practices to do this. What I have so far is: developers code locally, there is vagrant instance on every development machine, managed by puppet. It contains the same linux, jenkins and tomcat versions as production machine, while coding, developer deploys to vagrant machine, after local merge to test branch, jenkins on vagrant handles tests, when everything is fine, developer pushes commits and merges jenkins on remote machine pulls commit from test branch, runs tests and so on, if everything looks green, jenkins deploys to test tomcat instance Deployment to production is manual (altough it can be done using helping scripts) when business logic is tested by other divisions and everything looks fine to client. Now, the real question: does above make any sense? Things that I'm not sure about: Remote machine: won't there be any problems with two (or even three, as jenkins might need one) instances of same app on tomcat? Using vagrant to develop on php environment is just vise. Isn't this overkill while using Tomcat? I mean, is there higher probability that tomcat will act the same on every machine? Is there sense of having local jenkins on vagrant?

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  • Do you know any studies on relation of productivity of a programmer and the workstation used?

    - by Tomasz Blachowicz
    I was wondering if there are any studies (formal or not-so-formal) that show correlation between a developer productivity and the workstation used to develop software. It is often heard as argument that the high spec workstations increase the productivity (or the low spec machines impact productivity to the greater extent). To me it sound reasonable, however I'd like to verify the statement with some studies if such exists. Can you help me with that?

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  • How to understand Linux kernel source code for a beginner?

    - by user16867
    I am a student interested in working on Memory Management, particularly the page replacement component of the linux kernel. What are the different guides that can help me to begin understanding the kernel source? I have tried to read the book Understanding the Linux Virutal Memory Manager by Mel Gorman and Understanding the Linux Kernel by Cesati and Bovet, but they do not explain the flow of control through the code. They only end up explaining various data structures used and the work various functions perform. This makes the code more confusing. My project deals with tweaking the page replacement algorithm in a mainstream kernel and analyse its performance for a set of workloads. Is there a flavor of the linux kernel that would be easier to understand(if not the linux-2.6.xx kernel)?

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  • How important is it for a programmer to know how to implement a QuickSort/MergeSort algorithm from memory?

    - by John Smith
    I was reviewing my notes and stumbled across the implementation of different sorting algorithms. As I attempted to make sense of the implementation of QuickSort and MergeSort, it occurred to me that although I do programming for a living and consider myself decent at what I do, I have neither the photographic memory nor the sheer brainpower to implement those algorithms without relying on my notes. All I remembered is that some of those algorithms are stable and some are not. Some take O(nlog(n)) or O(n^2) time to complete. Some use more memory than others... I'd feel like I don't deserve this kind of job if it weren't because my position doesn't require that I use any sorting algorithm other than those found in standard APIs. I mean, how many of you have a programming position where it actually is essential that you can remember or come up with this kind of stuff on your own?

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  • How safe is it to rely on thirdparty Python libs in a production product?

    - by skyler
    I'm new to Python and come from the write-everything-yourself world of PHP (at least this is how I always approached it). I'm using Flask, WTForms, Jinja2, and I've just discovered Flask-Login which I want to use. My question is about the reliability of using thirdparty libraries for core functionality in a project that is planned to be around for several years. I've installed these libraries (via pip) into a virtualenv environment. What happens if these libraries stop being distributed? Should I back up these libraries (are they eggs)? Can I store these libraries in my project itself, instead of relying on pip to install them in a virtualenv? And should I store these separately? I'm worried that I'll rely on a library for core functionality, and then one day I'll download an incompatible version through pip, or the author or maintainer will stop distributing it and it'll no longer be available. How can I protect against this, and ensure that any thirdparty libraries that I use in my projects will always be available as they are now?

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  • Should I use parentheses in logical statements even where not necessary?

    - by Jeff Bridgman
    Let's say I have a boolean condition a AND b OR c AND d and I'm using a language where AND has a higher order of operation precedent than OR. I could write this line of code: If (a AND b) OR (c AND d) Then ... But really, that's equivalent to: If a AND b OR c AND d Then ... Are there any arguments in for or against including the extraneous parentheses? Does practical experience suggest that it is worth including them for readability? Or is it a sign that a developer needs to really sit down and become confident in the basics of their language?

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  • Unicode license

    - by Eric Grange
    Unicode Terms of use (http://www.unicode.org/copyright.html) state that any software that uses their data files (or a modification of it) should carry the Unicode license references. It seems to me that most Unicode libraries have functions to check if a character is a digit, a letter, a symbol, etc. ans so will contain a modification of the Unicode Data Files (usually in the form of tables). Does that mean the license applies and all applications that use such Unicode libraries should carry the license? I've checked around, and it appears very few Unicode software do carry the license, though arguable most of those that didn't carry the license were from companies that were members of the Unicode consortium (do they get license exemption?). Some (f.i. Mozilla) are only "Liaison Members", and while their software do not carry the license (AFAICT), they do obviously rely on data derived from those data files. Is Mozilla in breach of the license? Should we carry the license in all apps that include any form of advanced Unicode support? (ie. are bound to rely on the Unicode data files) Or is there some form of broad exemption? (since very very few software out there carries the license)

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  • Organization standards for large programs

    - by Chronicide
    I'm the only software developer at the company where I work. I was hired straight out of college, and I've been working here for several years. When I started, eveeryone was managing their own data as they saw fit (lots of filing cabinets). Until recently, I've only been tasked with small standalone projects to help with simple workflows. In the beginning of the year I was asked to make a replacement for their HR software. I used SQL Server, Entity Framework, WPF, along with MVVM and Repository/Unit of work patterns. It was a huge hit. I was very happy with how it went, and it was a very solid program. As such, my employer asked me to expand this program into a corporate dashboard that tracks all of their various corporate data domains (People, Salary, Vehicles/Assets, Statistics, etc.) I use integrated authentication, and due to the initial HR build, I can map users to people in positions, so I know who is who when they open the program, and I can show each person a customized dashboard given their work functions. My concern is that I've never worked on such a large project. I'm planning, meeting with end users, developing, documenting, testing and deploying it on my own. I'm part way through the second addition, and I'm seeing that my code is getting disorganized. It's still programmed well, I'm just struggling with the organization of namespaces, classes and the database model. Are there any good guidelines to follow that will help me keep everything straight? As I have it now, I have folders for Data, Repositories/Unit of Work, Views, View Models, XAML Resources and Miscellaneous Utilities. Should I make parent folders for each data domain? Should I make separate EF models per domain instead of the one I have for the entire database? Are there any standards out there for organizing large programs that span multiple data domains? I would appreciate any suggestions.

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  • VBScript and Xpath excluding duplicates [closed]

    - by Malachi
    I am trying to pull names from an XML Document using a vbscript. XML Document structure <Aliases> <Alias PartyType="DF" CaseID="000000" NameType=""> Name Name</Alias> <Alias PartyType="DF" CaseID="000000" NameType=""> Name Name</Alias> <Alias PartyType="DF" CaseID="000000" NameType=""> Name Name</Alias> ... </Aliases> the XML File might have 100 rows with the same name coming from several different CaseID's because for this part of my vbscript I am trying to pull all the different Names from all cases, but here is the issue, I don't want to return duplicates. is there a way to do this with an xPath Expression or should I try to do this with VBScript? EDIT I am pretty sure that I am going to have to do this with VBScript. Would it be Faster and more efficient to solve this issue in VBScript, xPath, or in populating the XML I am retrieving information from ( this might prove more difficult than the other two options ) I am also asking a Similar question on stackoverflow

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  • Single responsibility principle - am I overusing it?

    - by Tarun
    For reference - http://en.wikipedia.org/wiki/Single_responsibility_principle I have a test scenario where in one module of application is responsible for creating ledger entries. There are three basic tasks which could be carried out - View existing ledger entries in table format. Create new ledger entry using create button. Click on a ledger entry in the table (mentioned in first pointer) and view its details in next page. You could nullify a ledger entry in this page. (There are couple more operation/validations in each page but fore sake of brevity I will limit it to these) So I decided to create three different classes - LedgerLandingPage CreateNewLedgerEntryPage ViewLedgerEntryPage These classes offer the services which could be carried out in those pages and Selenium tests use these classes to bring application to a state where I could make certain assertion. When I was having it reviewed with on of my colleague then he was over whelmed and asked me to make one single class for all. Though I yet feel my design is much clean I am doubtful if I am overusing Single Responsibility principle

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  • If you develop on multiple operating systems, is it better to have multiple computers + displays?

    - by dan
    I develop for iOS and Linux. My preferred OS is Ubuntu. Now my software shop (me and a partner) is developing for Windows too. Now the question is, is it more efficient to have multiple workstations, one for each target OS? Efficiency and productivity is a higher priority than saving money. I have a 3.4Ghz i7 desktop workstation running Ubuntu and virtualized Windows with two displays, and I'm putting together an even more powerful i7 Hackintosh with 16GB RAM (to replace my weak 2.2Ghz i5 Macbook Pro). My specific dilemma is whether I should sell the first computer and triple boot on the second one, or buy two more displays and run both desktop systems simultaneously. Would appreciate answers from developers who write software for multiple OSes. Running guest OSes in VirtualBox on one system not ideal, because in my experience performance is seriously degraded under virtualization. So the choice is between dual/triple booting on one system vs having two systems, one for OSX+iOS/Windows (dual boot) and the other for Ubuntu (which I prefer to use as my main OS). For much of our work, I write a server-side application in Linux and a client for iOS (or for Windows or OS X) simultaneously.

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  • How seriously would an employer take a job application from an applicant studying at the Open University [closed]

    - by user866190
    I ask the question because I am considering applying to a traditional bricks and mortar university to do mathematics, computer science or software engineering. However I am in my late twenties and have a young family so I am seriously considering going down the Open University route and working in the software development industry at the same time. If I do attend Open University, I will definitely study Mathematics. I fell in love with PHP and the common web technologies a few years back and it has slowly progressed into learning C++, Java and also Python. If I spent the next year increasing my knowledge of those languages whilst studying at the Open University, would an employee consider a self taught programmer who is 20% of the way through a Bsc in Mathematics?

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  • Understanding Application binary interface (ABI)

    - by Tim
    I am trying to understand the concept of Application binary interface (ABI). From The Linux Kernel Primer: An ABI is a set of conventions that allows a linker to combine separately compiled modules into one unit without recompilation, such as calling conventions, machine interface, and operating-system interface. Among other things, an ABI defines the binary interface between these units. ... The benefits of conforming to an ABI are that it allows linking object files compiled by different compilers. From Wikipedia: an application binary interface (ABI) describes the low-level interface between an application (or any type of) program and the operating system or another application. ABIs cover details such as data type, size, and alignment; the calling convention, which controls how functions' arguments are passed and return values retrieved; the system call numbers and how an application should make system calls to the operating system; and in the case of a complete operating system ABI, the binary format of object files, program libraries and so on. I was wondering whether ABI depends on both the instruction set and the OS. Are the two all that ABI depends on? What kinds of role does ABI play in different stages of compilation: preprocessing, conversion of code from C to Assembly, conversion of code from Assembly to Machine code, and linking? From the first quote above, it seems to me that ABI is needed for only linking stage, not the other stages. Is it correct? When is ABI needed to be considered? Is ABI needed to be considered during programming in C, Assembly or other languages? If yes, how are ABI and API different? Or is it only for linker or compiler? Is ABI specified for/in machine code, Assembly language, and/or of C?

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  • Searching for entity awareness in 3D space algorithm and data structure

    - by Khanser
    I'm trying to do some huge AI system just for the fun and I've come to this problem. How can I let the AI entities know about each other without getting the CPU to perform redundant and costly work? Every entity has a spatial awareness zone and it has to know what's inside when it has to decide what to do. First thoughts, for every entity test if the other entities are inside the first's reach. Ok, so it was the first try and yep, that is redundant and costly. We are working with real time AI over 10000+ entities so this is not a solution. Second try, calculate some grid over the awareness zone of every entity and test whether in this zones are entities (we are working with 3D entities with float x,y,z location coordinates) testing every point in the grid with the indexed-by-coordinate entities. Well, I don't like this because is also costly, but not as the first one. Third, create some multi linked lists over the x's and y's indexed positions of the entities so when we search for an interval between x,y and z,w positions (this interval defines the square over the spatial awareness zone) over the multi linked list, we won't have 'voids'. This has the problem of finding the nearest proximity value if there isn't one at the position where we start the search. I'm not convinced with any of the ideas so I'm searching for some enlightening. Do you people have any better ideas?

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  • How much C/C++ knowledge is needed for Objective-C/iPhone development?

    - by BFree
    First, a little background. I'm a .Net developer (C#) and have over 5 years experience in both web development and desktop applications. I've been wanting to look into iPhone development for some time now, but for one reason or another always got side tracked. I finally have a potential project on the horizon, and I'm now going full steam ahead learning this stuff. My question is this: I haven't done any C/C++ programming since my schooling days, I've been living in managed land ever since. How much knowledge if any is needed to be successful as an iOS developer? Obviously memory management is something that I'll have to be conscious about (although with iOS 5 there seems to be something called ARC which should make my life easier), but what else? I'm not just talking about the C API (for example, in order to get the sin of a number, I call the sin() function), that's what Google is for. I'm talking about fundamental C/C++ idioms that the average C# developer is unaware of.

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