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  • How to implement a simple auto-complete functionality?

    - by Kaarel
    I'd like to implement a simple class (in Java) that would allow me to register and deregister strings, and on the basis of the current set of strings auto-complete a given string. So, the interface would be: void add(String) void remove(String) String complete(String) What's the best way to do this in terms of algorithms and data-structures?

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  • Can I use a filehandle instead of a filename for creating DBM files?

    - by Dancrumb
    I'm using MLDBM to persist some Perl data structures and I'm wondering if there's an alternative to the following: tie %hash, "MLDBM", $dbm_file, O_CREAT | O_RDWR, 0644; Primarily, I'd like to be able to use STDOUT, rather than a known file name. This could then be redirected to a file on the shell-side. I've been searching with keywords like "tie", "DBM" and "filehandle", but the hits tend to talk about tying filehandles to things, as opposed to things to filehandles. Any suggestions?

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  • How are the concepts of process and threads implementated in Linux kernel?

    - by Shan
    Can any one explain how are the concepts of process and threads implemented in Linux kernel ? I am looking for an intuitive explanation with some C snippets ( and important data structures) that clearly distinguishes between the two. I am just looking for the key implementation ideas I should get hold off. Essentially, I want to understand them and implement something similar in an embedded target (not supporte by any OS) in C language.

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  • Finding where varables have been declared in what file?

    - by robUK
    Hello, GNU Emacs 23.1.1 I am maintaining someones code. There are many files and directories for the headers and source files. I am wondering if there is a easy way to use emacs that when I highlight a variable name I can go straight to where it is declared? Some of the structures I am working in are declared in other header files, rather than go searching for them, I just want to be taken straight to them. Many thanks for any suggestions,

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  • Book on C++ for understanding advanced concepts

    - by Invincible
    What is good book for industry level C++ programming? I am not looking for a beginners C++ book that talks about datatypes and control structures. I am looking for a more advanced book. For example, how to build system applications using C++. Any kind of guidance will be very helpful.

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  • Functional Programming Equivalent of Design Patterns Book?

    - by JasonFruit
    Is there a functional-programming equivalent to the Gang of Four Design Patterns book? That is, is there a book that explains and gives examples of how commonly-needed code structures are implemented functionally? I think seeing that would give me a better idea of how to go about using in practice the functional concepts whose theory I understand.

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  • How long is a CS degree good for?

    - by Recursion
    I came upon a comment on another forum today and one user responding to another suggested that a CS degree is really only good for one through two years at the most, and after that its as if you never had it. Is this really true? is this what employers think? When I did CS I never learned anything new, we learned fundamentals like data structures, algorithms, time complexity, OS fundamentals, language characteristics. Most of this stuff has been around for the past 20 years or so.

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  • Parsing Huge XML Files in PHP

    - by Ian
    I'm trying to parse the dmoz content/structures xml files into mysql, but all existing scripts to do this are very old and don't work well. How can I go about opening a large (+1GB) xml file in php for parsing?

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  • i have question about job

    - by davit-datuashvili
    hi i will explain my situation i am study algorithms and data structures and i know many thing practical and others most thoereticaly and trying to implement in practise i want to get job where i will study more quickly i am interested if i have chance to start job when i have not expierence? thanks please advise what to do

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  • C: Convert A ? B : C into if (A) B else C

    - by tur1ng
    I was looking for a tool that can convert C code expressions for the form: a = (A) ? B : C; into the 'default' syntax with if/else statements: if (A) a = B else a = C Does someone know a tool that's capable to do such a transformation? I work with GCC 4.4.2 and create a preprocessed file with -E but do not want such structures in it.

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  • Variable Length Array

    - by corinaf
    Hello, I would like to know how a variable length array is managed (what extra variables or data structures are kept on the stack in order to have variable length arrays). Thanks a lot.

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  • Premature-Optimization and Performance Anxiety

    - by James Michael Hare
    While writing my post analyzing the new .NET 4 ConcurrentDictionary class (here), I fell into one of the classic blunders that I myself always love to warn about.  After analyzing the differences of time between a Dictionary with locking versus the new ConcurrentDictionary class, I noted that the ConcurrentDictionary was faster with read-heavy multi-threaded operations.  Then, I made the classic blunder of thinking that because the original Dictionary with locking was faster for those write-heavy uses, it was the best choice for those types of tasks.  In short, I fell into the premature-optimization anti-pattern. Basically, the premature-optimization anti-pattern is when a developer is coding very early for a perceived (whether rightly-or-wrongly) performance gain and sacrificing good design and maintainability in the process.  At best, the performance gains are usually negligible and at worst, can either negatively impact performance, or can degrade maintainability so much that time to market suffers or the code becomes very fragile due to the complexity. Keep in mind the distinction above.  I'm not talking about valid performance decisions.  There are decisions one should make when designing and writing an application that are valid performance decisions.  Examples of this are knowing the best data structures for a given situation (Dictionary versus List, for example) and choosing performance algorithms (linear search vs. binary search).  But these in my mind are macro optimizations.  The error is not in deciding to use a better data structure or algorithm, the anti-pattern as stated above is when you attempt to over-optimize early on in such a way that it sacrifices maintainability. In my case, I was actually considering trading the safety and maintainability gains of the ConcurrentDictionary (no locking required) for a slight performance gain by using the Dictionary with locking.  This would have been a mistake as I would be trading maintainability (ConcurrentDictionary requires no locking which helps readability) and safety (ConcurrentDictionary is safe for iteration even while being modified and you don't risk the developer locking incorrectly) -- and I fell for it even when I knew to watch out for it.  I think in my case, and it may be true for others as well, a large part of it was due to the time I was trained as a developer.  I began college in in the 90s when C and C++ was king and hardware speed and memory were still relatively priceless commodities and not to be squandered.  In those days, using a long instead of a short could waste precious resources, and as such, we were taught to try to minimize space and favor performance.  This is why in many cases such early code-bases were very hard to maintain.  I don't know how many times I heard back then to avoid too many function calls because of the overhead -- and in fact just last year I heard a new hire in the company where I work declare that she didn't want to refactor a long method because of function call overhead.  Now back then, that may have been a valid concern, but with today's modern hardware even if you're calling a trivial method in an extremely tight loop (which chances are the JIT compiler would optimize anyway) the results of removing method calls to speed up performance are negligible for the great majority of applications.  Now, obviously, there are those coding applications where speed is absolutely king (for example drivers, computer games, operating systems) where such sacrifices may be made.  But I would strongly advice against such optimization because of it's cost.  Many folks that are performing an optimization think it's always a win-win.  That they're simply adding speed to the application, what could possibly be wrong with that?  What they don't realize is the cost of their choice.  For every piece of straight-forward code that you obfuscate with performance enhancements, you risk the introduction of bugs in the long term technical debt of the application.  It will become so fragile over time that maintenance will become a nightmare.  I've seen such applications in places I have worked.  There are times I've seen applications where the designer was so obsessed with performance that they even designed their own memory management system for their application to try to squeeze out every ounce of performance.  Unfortunately, the application stability often suffers as a result and it is very difficult for anyone other than the original designer to maintain. I've even seen this recently where I heard a C++ developer bemoaning that in VS2010 the iterators are about twice as slow as they used to be because Microsoft added range checking (probably as part of the 0x standard implementation).  To me this was almost a joke.  Twice as slow sounds bad, but it almost never as bad as you think -- especially if you're gaining safety.  The only time twice is really that much slower is when once was too slow to begin with.  Think about it.  2 minutes is slow as a response time because 1 minute is slow.  But if an iterator takes 1 microsecond to move one position and a new, safer iterator takes 2 microseconds, this is trivial!  The only way you'd ever really notice this would be in iterating a collection just for the sake of iterating (i.e. no other operations).  To my mind, the added safety makes the extra time worth it. Always favor safety and maintainability when you can.  I know it can be a hard habit to break, especially if you started out your career early or in a language such as C where they are very performance conscious.  But in reality, these type of micro-optimizations only end up hurting you in the long run. Remember the two laws of optimization.  I'm not sure where I first heard these, but they are so true: For beginners: Do not optimize. For experts: Do not optimize yet. This is so true.  If you're a beginner, resist the urge to optimize at all costs.  And if you are an expert, delay that decision.  As long as you have chosen the right data structures and algorithms for your task, your performance will probably be more than sufficient.  Chances are it will be network, database, or disk hits that will be your slow-down, not your code.  As they say, 98% of your code's bottleneck is in 2% of your code so premature-optimization may add maintenance and safety debt that won't have any measurable impact.  Instead, code for maintainability and safety, and then, and only then, when you find a true bottleneck, then you should go back and optimize further.

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  • SQL University: What and why of database refactoring

    - by Mladen Prajdic
    This is a post for a great idea called SQL University started by Jorge Segarra also famously known as SqlChicken on Twitter. It’s a collection of blog posts on different database related topics contributed by several smart people all over the world. So this week is mine and we’ll be talking about database testing and refactoring. In 3 posts we’ll cover: SQLU part 1 - What and why of database testing SQLU part 2 - What and why of database refactoring SQLU part 3 - Tools of the trade This is a second part of the series and in it we’ll take a look at what database refactoring is and why do it. Why refactor a database To know why refactor we first have to know what refactoring actually is. Code refactoring is a process where we change module internals in a way that does not change that module’s input/output behavior. For successful refactoring there is one crucial thing we absolutely must have: Tests. Automated unit tests are the only guarantee we have that we haven’t broken the input/output behavior before refactoring. If you haven’t go back ad read my post on the matter. Then start writing them. Next thing you need is a code module. Those are views, UDFs and stored procedures. By having direct table access we can kiss fast and sweet refactoring good bye. One more point to have a database abstraction layer. And no, ORM’s don’t fall into that category. But also know that refactoring is NOT adding new functionality to your code. Many have fallen into this trap. Don’t be one of them and resist the lure of the dark side. And it’s a strong lure. We developers in general love to add new stuff to our code, but hate fixing our own mistakes or changing existing code for no apparent reason. To be a good refactorer one needs discipline and focus. Now we know that refactoring is all about changing inner workings of existing code. This can be due to performance optimizations, changing internal code workflows or some other reason. This is a typical black box scenario to the outside world. If we upgrade the car engine it still has to drive on the road (preferably faster) and not fly (no matter how cool that would be). Also be aware that white box tests will break when we refactor. What to refactor in a database Refactoring databases doesn’t happen that often but when it does it can include a lot of stuff. Let us look at a few common cases. Adding or removing database schema objects Adding, removing or changing table columns in any way, adding constraints, keys, etc… All of these can be counted as internal changes not visible to the data consumer. But each of these carries a potential input/output behavior change. Dropping a column can result in views not working anymore or stored procedure logic crashing. Adding a unique constraint shows duplicated data that shouldn’t exist. Foreign keys break a truncate table command executed from an application that runs once a month. All these scenarios are very real and can happen. With the proper database abstraction layer fully covered with black box tests we can make sure something like that does not happen (hopefully at all). Changing physical structures Physical structures include heaps, indexes and partitions. We can pretty much add or remove those without changing the data returned by the database. But the performance can be affected. So here we use our performance tests. We do have them, right? Just by adding a single index we can achieve orders of magnitude performance improvement. Won’t that make users happy? But what if that index causes our write operations to crawl to a stop. again we have to test this. There are a lot of things to think about and have tests for. Without tests we can’t do successful refactoring! Fixing bad code We all have some bad code in our systems. We usually refer to that code as code smell as they violate good coding practices. Examples of such code smells are SQL injection, use of SELECT *, scalar UDFs or cursors, etc… Each of those is huge code smell and can result in major code changes. Take SELECT * from example. If we remove a column from a table the client using that SELECT * statement won’t have a clue about that until it runs. Then it will gracefully crash and burn. Not to mention the widely unknown SELECT * view refresh problem that Tomas LaRock (@SQLRockstar on Twitter) and Colin Stasiuk (@BenchmarkIT on Twitter) talk about in detail. Go read about it, it’s informative. Refactoring this includes replacing the * with column names and most likely change to application using the database. Breaking apart huge stored procedures Have you ever seen seen a stored procedure that was 2000 lines long? I have. It’s not pretty. It hurts the eyes and sucks the will to live the next 10 minutes. They are a maintenance nightmare and turn into things no one dares to touch. I’m willing to bet that 100% of time they don’t have a single test on them. Large stored procedures (and functions) are a clear sign that they contain business logic. General opinion on good database coding practices says that business logic has no business in the database. That’s the applications part. Refactoring such behemoths requires writing lots of edge case tests for the stored procedure input/output behavior and then start to refactor it. First we split the logic inside into smaller parts like new stored procedures and UDFs. Those then get called from the master stored procedure. Once we’ve successfully modularized the database code it’s best to transfer that logic into the applications consuming it. This only leaves the stored procedure with common data manipulation logic. Of course this isn’t always possible so having a plethora of performance and behavior unit tests is absolutely necessary to confirm we’ve actually improved the codebase in some way.   Refactoring is not a popular chore amongst developers or managers. The former don’t like fixing old code, the latter can’t see the financial benefit. Remember how we talked about being lousy at estimating future costs in the previous post? But there comes a time when it must be done. Hopefully I’ve given you some ideas how to get started. In the last post of the series we’ll take a look at the tools to use and an example of testing and refactoring.

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  • Master Data

    - by david.butler(at)oracle.com
    Let's take a deeper look at what we mean when we talk about 'Master' data. In its most general sense, master data is data that exists in more than one operational application. These are the applications that automate business processes. These applications require significant amounts of data to function correctly.  This includes data about the objects that are involved in transactions, as well as the transaction data itself.  For example, when a customer buys a product, the transaction is managed by a sales application.  The objects of the transaction are the Customer and the Product.  The transactional data is the time, place, price, discount, payment methods, etc. used at the point of sale. Many thousands of transactional data attributes are needed within the application. These important data elements are local to the applications and have no bearing on other applications. Harmonization and synchronization across applications is not necessary. The Customer and Product objects of the transaction also have a large number of attributes. Customer for example, includes hierarchies, hierarchical and matrixed relationships, contacts, classifications, preferences, accounts, identifiers, profiles, and addresses galore for 'ship to', 'mail to'; 'service at'; etc. Dozens of attributes exist for individuals, hundreds for organizations, and thousands for products. This data has meaning beyond any particular application. It exists in many applications and drives the vital cross application enterprise business processes. These are the processes that define and differentiate the organization. At every decision point, information about the objects of the process determines the direction of the process flow. This is the nature of the data that exists in more than one application, and this is why we call it 'master data'. Let me elaborate. Parties Oracle has developed a party schema to model all participants in your daily business operations. It models people, organizations, groups, customers, contacts, employees, and suppliers. It models their accounts, locations, classifications, and preferences.  And most importantly, it models the vast array of hierarchical and matrixed relationships that exist between all the participants in your real world operations.  The model logically separates people and organizations from their relationships and accounts.  This separation creates flexibility unmatched in the industry and accounts for the fact that the Oracle schema for Customers, Suppliers, and Accounts is a true superset of the wide variety of commercial and homegrown customer models in existence. Sites Sites are places where business is conducted. They can be addresses, clusters such as retail malls, locations within a cluster, floors within a building, places where meters are located, rooms on floors, etc.  Fully understanding all attributes of a site is key to many business processes. Attributes such as 'noise abatement policy' at a point of delivery, or the size of an oven in a business kitchen drive day-to-day activities such as delivery schedules or food promotions. Typically this kind of data is siloed in departments and scattered across applications and spreadsheets.  This leads to conflicting information and poor operational efficiencies. Oracle's Global Single Schema can hold all site attributes in one place and enables a single version of authoritative site information across the enterprise. Products and Services The Oracle Global Single Schema also includes a number of entities that define the products and services a company creates and offers for sale. Key entities include Items organized into Catalogs and Price Lists. The Catalog structures provide for the ability to capture different views of a product such as engineering, manufacturing, and service which are based on a unified product model. As a result, designers, manufacturing engineers, purchasers and partners can work simultaneously on a common product definition. The Catalog schema allows for unlimited attributes, combines them into meaningful groups, and maps them to catalog categories to track these different types of information. The model also maps an unlimited number of functional structures for each item. For example, multiple Bills of Material (BOMs) can be constructed representing requirements BOM, features BOM, and packaging BOM for an item. The Catalog model also supports hierarchical information about each item and all standard Global Data Synchronization attributes. Business Processes Utilizing Linked Data Entities Each business entity codified into a centralized master data environment significantly improves the efficiency of the automated business processes that use the consolidated data.  When all the key business entities used by an organization's process are so consolidated, the advantages are multiplied.  The primary reason for business process breakdowns (i.e. data errors across application boundaries) is eliminated. All processes are positively impacted and business process automation is itself automated.  I like to use the "Call to Resolution" business process as an example to help illustrate this important point. It involves call center applications, service applications, RMA applications, transportation applications, inventory applications, etc. Customer, Site, Product and Supplier master data must all be correct and consistent across these applications.  What's more, the data relationships between customer and product, and product and suppliers must be right. This is the minimum quality needed to insure the business process flows without error. But that is not the end of the story. Critical master data attributes such as customer loyalty, profitability, credit worthiness, and propensity to buy can optimize the call center point of contact component of the process. Critical product information such as alternative parts or equivalent products can optimize the resolution selected by the process. A comprehensive understanding of the 'service at' location can help insure multiple trips are avoided in the process. Full supplier information on reliability, delivery delays, and potential alternates can prevent supplier exceptions and play a significant role in optimizing the process.  In other words, these master data attributes enable the optimization of the "Call to Resolution" enterprise business process. Master data supports and guides business process flows. Thus the phrase 'Master Data' is indeed appropriate. MDM is the software that houses, manages, and governs the master data that resides in all applications and controls the enterprise business processes. A complete master data solution takes a data model that holds fully attributed master data entities and their inter-relationships. Oracle has this model. Oracle, with its deep understanding of application data is the logical choice for managing all your master data within the enterprise whether or not your organization actually runs any Oracle Applications.

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  • How can I compare two directories to compare missing files, when the directories don't have the same structure?

    - by David Dean
    I've been sent a HDD of new and updated files from an organisation that we are working with, but we already have most of the files sitting on our servers, and would like to update our local versions to match theirs. Normally, this would be a job for something like rsync, but our problem is that the directory structure they provide is very poorly organised and we've had to rearrange their files in the past to work best with our systems. So, my question is: How can I find out which files in the set they have provided are new or different to the versions that we have, when the directory structures are different? Once that question is answered, we can update the changed files, and work out where to put the new files on our system, probably somewhat manually.

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  • Windows Server 2008 R2 Server Core with AD Role having GUI Admin Console

    - by Robert Koritnik
    I would like to setup a machine with Windows Server 2008 R2 Server Core and install following server roles: Active Directory Domain Services Active Directory Federation Services Active Directory Lightweight Directory Services (I'm not sure whether I actually need this one - see note below) I'm obviously going to install Enterprise Edition. Question Can I have an AD administration graphical user interface to manage Active Directory on Server Core machine? I would really like to have it, because I'm not so keen to do stuff using power-shell, because I've never managed AD as well, so a GUI would be much more helpful, because I could at least visualize it a bit better and maybe understand AD structures. Note: I'm setting up development environment machine as well and installing Sharepoint Foundation 2010 on in so it would use this AD machine.

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  • Apply SharePoint template to existing site?

    - by johnnyb10
    I have several similar SharePoint sites (running on WSS 3) and I have saved one of the sites as a template. I now want to make a different site (which already exists) have the same structure as this site--the same lists, document libraries, views, etc. I know I can delete the existing site and then recreate it based on this template, but is there a way to apply this template to my existing site, so that it gets rid of its existing lists, etc., and replaces them with the ones from the template? I don't have any content in the site, and I don't want to keep any of the existing structures, so I don't care if anything gets swept away. I may need to do this with a bunch of sites in the future, so being able to apply the template rather than recreating from scratch might be very helpful.

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  • Website requests not reaching IIS?

    - by pete the pagan-gerbil
    To start off with a confession, I am not a server admin - just a developer tasked with getting to the root of a problem. Please be gentle! I have an intranet ASP.NET website running in IIS on a virtual machine. The website is not accessed very often (the last IIS log file was modified nearly six months ago). Both the IP address and Host header value are now failing to return the website, and the IIS log still doesn't show any more recent activity. The virtual machine was moved to a different physical location a few months ago, and the IP address for it has changed. Could this be what has broken access to the site? What else should I be checking to solve this? I don't have totally unrestricted access to the building's network settings, structures, etc. I would be grateful for any advice, even if I can't use it myself it'll improve my knowledge of what's going on behind the scenes!

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  • Coding exercise for Linux Systems Admin?

    - by Prashanth Sundaram
    Hello All, I am preparing for a Systems Admin(linux) role for a big company(top 10 companies) and one of the requisite is knowledge of a language like perl, python or Ruby. I have a phone interview which involves sharing a editor with the interviewer, now what kind of coding exercise can I expect on a phone interview or a regular interview? I have used shell for most of my day-to-day tasks and occasionally Perl and python for bigger tasks. Now I don't expect them to ask Write a script that sync's AD users to LDAP? I don't think data structures, algorithms or sorting questions apply to me role? Can you give me any examples of SysAdmin related coding questions?

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  • Memory consumption of each accept() call on server running on Windows 2008 [migrated]

    - by Atul
    I've written a simple and small server application on Windows 2008 that just accepts connections and does nothing else. I am doing memory footprint assessment of socket calls, What I found that each connection (after accept()) consumes at least 2.5 KB of memory. Interestingly, the memory is not consumed by the process that has accept() call but it consumed by a OS process. I believe it might be because of data structures being created inside OS for each connection. Now, I have two key questions: Is it possible by any means to reduce this memory footprint (by changing any parameters, configuration etc) ? If yes how ? (Because 2K for each connection would be too much if we planning server to accept millions of connections) If my server is intended to accept million connections, is it good idea to use Windows 2008 ? or shall I switch to some other OS? Please advice me.

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