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  • Risking the exception anti-pattern.. with some modifications

    - by Sridhar Iyer
    Lets say that I have a library which runs 24x7 on certain machines. Even if the code is rock solid, a hardware fault can sooner or later trigger an exception. I would like to have some sort of failsafe in position for events like this. One approach would be to write wrapper functions that encapsulate each api a: returnCode=DEFAULT; try { returnCode=libraryAPI1(); } catch(...) { returnCode=BAD; } return returnCode; The caller of the library then restarts the whole thread, reinitializes the module if the returnCode is bad. Things CAN go horribly wrong. E.g. if the try block(or libraryAPI1()) had: func1(); char *x=malloc(1000); func2(); if func2() throws an exception, x will never be freed. On a similar vein, file corruption is a possible outcome. Could you please tell me what other things can possibly go wrong in this scenario?

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  • Delegates in Action -Help

    - by Amutha
    I am learning delegates.I am very curious to apply delegates to the following chain-of-responsibility pattern. Kindly help me the way to apply delegates to the following piece. Thanks in advance.Thanks for your effort. #region Chain of Responsibility Pattern namespace Chain { public class Player { public string Name { get; set; } public int Score { get; set; } } public abstract class PlayerHandler { protected PlayerHandler _Successor = null; public abstract void HandlePlayer(Player _player); public void SetupHandler(PlayerHandler _handler) { _Successor = _handler; } } public class Employee : PlayerHandler { public override void HandlePlayer(Player _player) { if (_player.Score <= 100) { MessageBox.Show(string.Format("{0} is greeted by Employee", _player.Name)); } else { _Successor.HandlePlayer(_player); } } } public class Supervisor : PlayerHandler { public override void HandlePlayer(Player _player) { if (_player.Score >100 && _player.Score<=200) { MessageBox.Show(string.Format("{0} is greeted by Supervisor", _player.Name)); } else { _Successor.HandlePlayer(_player); } } } public class Manager : PlayerHandler { public override void HandlePlayer(Player _player) { if (_player.Score > 200) { MessageBox.Show(string.Format("{0} is greeted by Manager", _player.Name)); } else { MessageBox.Show(string.Format("{0} got low score", _player.Name)); } } } } #endregion #region Main() void Main() { Chain.Player p1 = new Chain.Player(); p1.Name = "Jon"; p1.Score = 100; Chain.Player p2 = new Chain.Player(); p2.Name = "William"; p2.Score = 170; Chain.Player p3 = new Chain.Player(); p3.Name = "Robert"; p3.Score = 300; Chain.Employee emp = new Chain.Employee(); Chain.Manager mgr = new Chain.Manager(); Chain.Supervisor sup = new Chain.Supervisor(); emp.SetupHandler(sup); sup.SetupHandler(mgr); emp.HandlePlayer(p1); emp.HandlePlayer(p2); emp.HandlePlayer(p3); } #endregion

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  • What's the smartest way to organize SVN for translated versions of the same project?

    - by brandonjp
    I apologize because I know this has been covered over and over again, but I'm trying to understand the smartest way to cleverly use subversion to our benefit. (*Note: I know our method is not the BEST way to handle localized versions, but external factors are forcing us to work this way on current projects) We have a fairly static website in English...html, css, js, etc. After the site comes back from the translator we will have 5 variations of the same code (this week...then potentially 25 more in the future!). So we'll soon have a folder for EN, FR, SP, DE, etc. Most files (css, js, img) will remain exactly the same; and html files (structure, id's, classes) will only vary based on the localized text inside the elements. Is there any way to use clever SVN folder structuring that would help us out in the event that if a small change is needed, we don't have to manually change the files in each and every translated version of the site? Thanks! --bp

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  • Overriding properties of child view controller vs setting them via parent view controller

    - by robinjam
    If you want to modify the default behaviour of a View Controller by changing the value of one of its properties, is it considered better form to instantiate the class and set its property directly, or subclass it and override the property? With the former it would become the parent View Controller's responsibility to configure its children, whereas with the latter the children would effectively configure themselves. EDIT: Some more information: The class I am referring to is FetchedTableViewController, a subclass of UITableViewController that I made to display the results of a Core Data fetch operation. There are two places I want to display the results of a fetch, and they each have different fetch requests. I'm trying to decide whether it's better to create a subclass for each one, and override the fetchRequest property, or make it the responsibility of the parent controller to set the fetchRequest property for its children.

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  • C++ interpreter conceptual problem

    - by Jan Wilkins
    I've built an interpreter in C++ for a language created by me. One main problem in the design was that I had two different types in the language: number and string. So I have to pass around a struct like: class myInterpreterValue { myInterpreterType type; int intValue; string strValue; } Objects of this class are passed around million times a second during e.g.: a countdown loop in my language. Profiling pointed out: 85% of the performance is eaten by the allocation function of the string template. This is pretty clear to me: My interpreter has bad design and doesn't use pointers enough. Yet, I don't have an option: I can't use pointers in most cases as I just have to make copies. How to do something against this? Is a class like this a better idea? vector<string> strTable; vector<int> intTable; class myInterpreterValue { myInterpreterType type; int locationInTable; } So the class only knows what type it represents and the position in the table This however again has disadvantages: I'd have to add temporary values to the string/int vector table and then remove them again, this would eat a lot of performance again. Help, how do interpreters of languages like Python or Ruby do that? They somehow need a struct that represents a value in the language like something that can either be int or string.

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  • best practice on precedence of variable declaration and error handling in C

    - by guest
    is there an advantage in one of the following two approaches over the other? here it is first tested, whether fopen succeeds at all and then all the variable declarations take place, to ensure they are not carried out, since they mustn't have had to void func(void) { FILE *fd; if ((fd = fopen("blafoo", "+r")) == NULL ) { fprintf(stderr, "fopen() failed\n"); exit(EXIT_FAILURE); } int a, b, c; float d, e, f; /* variable declarations */ /* remaining code */ } this is just the opposite. all variable declarations take place, even if fopen fails void func(void) { FILE *fd; int a, b, c; float d, e, f; /* variable declarations */ if ((fd = fopen("blafoo", "+r")) == NULL ) { fprintf(stderr, "fopen() failed\n"); exit(EXIT_FAILURE); } /* remaining code */ } does the second approach produce any additional cost, when fopen fails? would love to hear your thoughts!

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  • What are the common programming mistakes in Python?

    - by Paul McGuire
    I was about to tag the recent question in which the OP accidentally shadowed the builtin operator module with his own local operator.py with the "common-mistakes" tag, and I saw that there are a number of interesting questions posted asking for common mistakes to avoid in Java, Ruby, Scala, Clojure, .Net, jQuery, Haskell, SQL, ColdFusion, and so on, but I didn't see any for Python. For the benefit of Python beginners, can we enumerate the common mistakes that we have all committed at one time or another, in the hopes of maybe steering a newbie or two clear of them? (In homage to "The Princess Bride", I call these the Classic Blunders.) If possible, a little supporting explanation on what the problem is, and the generally accepted resolution/workaround, so that the beginning Pythoner doesn't read your answer and say "ok, that's a mistake, how do I fix it?"

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  • User upload file above web root with php

    - by Chris
    I have a website where local bands can have a profile page, I'm implementing an upload system so that they can add songs to their profile. I want to make sure that clever visitors to my website cannot download their songs. I was thinking about uploading them to above the folder for my domain so that they cannot be accessed directly. Is this a good idea and/or possible? If not, what do you suggest I do to try and avoid users downloading songs. I'm already using a flash player to try and prevent downloads.

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  • SOAP - Why do I need to query for the values for an update?

    - by Phill Pafford
    I'm taking over a project and wanted to understand if this is common practice using SOAP. The process that is currently in place I have to query all the values before I do an update cause I need to pass back all the values that are not being updated. Does this sound right? Example Values: fname=phill lname=pafford address=123 main phone:222-555-1212 So if I just wanted to update the phone number I need to query for the record, get all the values and submit these values for an update. Example Update Values: fname=phill lname=pafford address=123 main phone:111-555-1212 I just want to know if this is common practice or should I change the functionality of this?

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  • Best architecture for accessing secondary database

    - by fearofawhackplanet
    I'm currently developing an app which will use a Linq to SQL (or possibly EF) data access layer. We already have a database which holds all our Contacts information, but there is currently no API around this. I need to interact with this DB from the new app to retrieve contact details. I can think of two ways I could do this - 1) Develop a suite of web services against the contacts database 2) Write a Linq to SQL (or EF) DAL and API against the contacts database I will probably be developing several further apps in the future which will also need access to the Contacts data. Which would generally be the prefered method? What are the points I need to consider? Am I even asking a sensible question, or am I missing something obvious?

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  • Increasing your efficiency during programming

    - by Tom
    Yeah, yeah, I know, it is a little bit of offtopic, but let's try. So, I want to increase my efficiency during my programming as much as possible to programme as fast and sensibly as possiblle. What do you do before starting coding? Drink a lot of coffee, energy drinks? Do you listen to music during programming or you keep quite? Share your ideas.

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  • Method hiding with interfaces

    - by fearofawhackplanet
    interface IFoo { int MyReadOnlyVar { get; } } class Foo : IFoo { int MyReadOnlyVar { get; set; } } public IFoo GetFoo() { return new Foo { MyReadOnlyVar = 1 }; } Is the above an acceptable way of implementing a readonly/immutable object? The immutability of IFoo can be broken with a temporary cast to Foo. In general (non-critical) cases, is hiding functionality through interfaces a common pattern? Or is it considered lazy coding? Or even an anti-pattern?

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  • Best way to handle input from a keyboard "wedge"

    - by Mykroft
    I'm writing a C# POS (point of sale) system that takes input from a keyboard wedge magcard reader. This means that any data it reads off of a mag stripe is entered as if it were typed on the keyboard very quickly. Currently I'm handling this by attaching to the KeyPress event and looking for a series of very fast key presses that contain the card swipe sentinel characters. Is there a better way to deal with this sort of input? Edit: The device does simply present the data as keystrokes and doesn't interface through some other driver. Also We use a wide range of these types of devices so ideally a method should work independent of the specific model of wedge being used. However if there is no other option I'll have to make do.

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  • How to organize code using an optional assembly reference?

    - by apoorv020
    I am working on a project and want to optionally use an assembly if available. This assembly is only available on WS 2008 R2, and my ideal product whould be a common binary for both computers with and without the assembly. However, I'm primarily developing on a Windows 7 machine, where I cannot install the assembly. How can I organize my code so that I can (with minimum changes) build my code on a machine without the assembly and secondly, how do I ensure that I call the assembly functions only when it is present. (NOTE : The only use of the optional assembly is to instantiate a class in the library and repeatedly call a (single) function of the class, which returns a boolean. The assembly is fsrmlib, which exposes advanced file system management operations on WS08R2.) I'm currently thinking of writing a wrapper class, which will always return true if the assembly is not present. Is this the right way to go about doing this?

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  • how to wrap a function that only takes individual elements to make it take a list

    - by stevejb
    Hello, Say I have a function handed to me that I cannot change and must use as is. This function takes several objects in the form of oldFunction( object1, object2, object3, ...) where ... are other arguments. I want to write a wrapper to take a list of objects. My idea was this. sjb.ListWrapper <- function(myList,...) { lLen <- length(myList) myStr <- "" for( i in 1:lLen) { myStr <- paste(myStr, "myList[[", i , "]],",sep="") } myCode <- paste("oldFunction(", myStr, "...)") eval({myCode}) } However, the issue is that I want to use this from Sweave and I need the output of oldFunction to be printed. What is the right way to do this? Thanks.

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  • Using free function as pseudo-constructors to exploit template parameter deduction

    - by Poita_
    Is it a common pattern/idiom to use free functions as pseudo-constructors to avoid having to explicitly specify template parameters? For example, everyone knows about std::make_pair, which uses its parameters to deduce the pair types: template <class A, class B> std::pair<A, B> make_pair(A a, B b) { return std::pair<A, B>(a, b); } // This allows you to call make_pair(1, 2), // instead of having to type pair<int, int>(1, 2) // as you can't get type deduction from the constructor. I find myself using this quite often, so I was just wondering if many other people use it, and if there is a name for this pattern?

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  • What is the best way to organize directories within a large grails application?

    - by egervari
    What is the best way to organize directories within a large grails application? In a typical Spring application, we'd have myproject/domain/ and myproject/web/controllers and myproject/services Since grails puts these artifacts in their own directories... and then just uses the same base project package for everything, what is the best practice? Use the same sub package name for domain objects, controllers, services too? Ken

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  • How to avoid repetition when working with primitive types?

    - by I82Much
    I have the need to perform algorithms on various primitive types; the algorithm is essentially the same with the exception of which type the variables are. So for instance, /** * Determine if <code>value</code> is the bitwise OR of elements of <code>validValues</code> array. * For instance, our valid choices are 0001, 0010, and 1000. * We are given a value of 1001. This is valid because it can be made from * ORing together 0001 and 1000. * On the other hand, if we are given a value of 1111, this is invalid because * you cannot turn on the second bit from left by ORing together those 3 * valid values. */ public static boolean isValid(long value, long[] validValues) { for (long validOption : validValues) { value &= ~validOption; } return value != 0; } public static boolean isValid(int value, int[] validValues) { for (int validOption : validValues) { value &= ~validOption; } return value != 0; } How can I avoid this repetition? I know there's no way to genericize primitive arrays, so my hands seem tied. I have instances of primitive arrays and not boxed arrays of say Number objects, so I do not want to go that route either. I know there are a lot of questions about primitives with respect to arrays, autoboxing, etc., but I haven't seen it formulated in quite this way, and I haven't seen a decisive answer on how to interact with these arrays. I suppose I could do something like: public static<E extends Number> boolean isValid(E value, List<E> numbers) { long theValue = value.longValue(); for (Number validOption : numbers) { theValue &= ~validOption.longValue(); } return theValue != 0; } and then public static boolean isValid(long value, long[] validValues) { return isValid(value, Arrays.asList(ArrayUtils.toObject(validValues))); } public static boolean isValid(int value, int[] validValues) { return isValid(value, Arrays.asList(ArrayUtils.toObject(validValues))); } Is that really much better though? Any thoughts in this matter would be appreciated.

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  • Interface and base class mix, the right way to implement this

    - by Lerxst
    I have some user controls which I want to specify properties and methods for. They inherit from a base class, because they all have properties such as "Foo" and "Bar", and the reason I used a base class is so that I dont have to manually implement all of these properties in each derived class. However, I want to have a method that is only in the derived classes, not in the base class, as the base class doesn't know how to "do" the method, so I am thinking of using an interface for this. If i put it in the base class, I have to define some body to return a value (which would be invalid), and always make sure that the overriding method is not calling the base. method Is the right way to go about this to use both the base class and an interface to expose the method? It seems very round-about, but every way i think about doing it seems wrong... Let me know if the question is not clear, it's probably a dumb question but I want to do this right.

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