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• Question about best practices and Macros from the book 'C++ Coding Standards'

  - by Victor T.

  From Herb Sutter and Andrei Alexandrescu's 'C++ Coding Standards', Item 16: Avoid Macros under Exceptions for this guideline they wrote: For conditional compilation (e.g., system-dependent parts), avoid littering your code with #ifdefs. Instead, prefer to organize code such that the use of macros drives alternative implementations of one common interface, and then use the interface throughout. I'm having trouble understanding exactly what they mean by this. How can you drive alternate implementations without the use of #ifdef conditional compile macro directives? Can someone provide an example to help illustrate what's being proposed by the above paragraph? Thanks

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• Are Scala "continuations" just a funky syntax for defining and using Callback Functions?

  - by Alex R

  And I mean that in the same sense that a C/Java for is just a funky syntax for a while loop. I still remember when first learning about the for loop in C, the mental effort that had to go into understanding the execution sequence of the three control expressions relative to the loop statement. Seems to me the same sort of effort has to be applied to understand Continuations (in Scala and I guess probably other languages). And then there's the obvious follow-up question... if so, then what's the point? It seems like a lot of pain (language complexity, programmer errors, unreadable programs, etc) for no gain.

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• How does struts 1.X ActionForm handle pure html checkbox list?

  - by BlueDolphin

  I am dealing with an old application which uses struts 1.2. And for some reason, we are using pure html form to submit to struts action. For example: for the content output of testAction.do, I try to submit to itself. item 1 item 2 Then I associate an form bean TestForm with testAction. I am not sure how to specify the properties in the form so that it take the value from myitem1 after user click "submit" I tried to add getMyitem1(), setMyitem1(String[] items), getSelectedMyitem1(), setSelectedMyitem1(String[] items) Those set methods are only called when page are loaded. I guess my understanding of ActionForm in struts 1.x must be wrong. Please advise, thanks.

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• ARC, worth it or not?

  - by MSK

  When I moved to Objective C (iOS) from C++ (and little Java) I had hard time understanding memory management in iOS. But now all this seems natural and I know retain, autorelease, copy and release stuff. After reading about ARC, I am wondering is there more benefits of using ARC or it is just that you dont have to worry about memory management. Before moving to ARC I wanted to know how worth is moving to ARC. XCode has "Convert to Objective C ARC" menu. Is the conversion is that simple (nothing to worry about)? Does it help me in reducing my apps memory foot-print, memory leaks etc (somehow ?) Does it has much testing impact on my apps ? What are non-obvious advantages? Any Disadvantage os moving to it?

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• MPI4Py Scatter sendbuf Argument Type?

  - by Noel

  I'm having trouble with the Scatter function in the MPI4Py Python module. My assumption is that I should be able to pass it a single list for the sendbuffer. However, I'm getting a consistent error message when I do that, or indeed add the other two arguments, recvbuf and root: File "code/step3.py", line 682, in subbox_grid i = mpi_communicator.Scatter(station_range, station_data) File "Comm.pyx", line 427, in mpi4py.MPI.Comm.Scatter (src/ mpi4py_MPI.c:44993) File "message.pxi", line 321, in mpi4py.MPI._p_msg_cco.for_scatter (src/mpi4py_MPI.c:14497) File "message.pxi", line 232, in mpi4py.MPI._p_msg_cco.for_cco_send (src/mpi4py_MPI.c:13630) File "message.pxi", line 36, in mpi4py.MPI.message_simple (src/ mpi4py_MPI.c:11904) ValueError: message: expecting 2 or 3 items Here is the relevant code snipped, starting a few lines above 682 mentioned above. for station in stations #snip--do some stuff with station station_data = [] station_range = range(1,len(station)) mpi_communicator = MPI.COMM_WORLD i = mpi_communicator.Scatter(station_range, nsm) #snip--do some stuff with station[i] nsm = combine(avg, wt, dnew, nf1, nl1, wti[i], wtm, station[i].id) station_data = mpi_communicator.Gather(station_range, nsm) I've tried a number of combinations initializing station_range, but I must not be understanding the Scatter argument types properly. Does a Python/MPI guru have a clarification this?

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• Question about mysql indexes on low to medium cardinality columns

  - by Kevin J

  I have a general question about the way that database indexing works, particularly in mysql. Let's say I have a table with a million rows with a column "ClientID" that is distributed relatively equally among 30 values. Thus, this column is very low cardinality (30) relative to the primary key (1 million). Now, I understand that you shouldn't create indexes on low cardinality fields. However, in this case, queries are only ever done with one of the 30 clientIDs. Thus, wouldn't creating an index on ClientID be helpful, as the search space is automatically reduced to 1/30th what it normally would be? Or is my understanding of how the index works flawed? Thanks

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• Magento layout override!

  - by Farid

  Hi, I'm kind of new to the Magento, so forgive me for my stupid question! As I understand the whole concept of Magento is base on overriding the basic components that's are available with in the Magento. So based on my understanding I've decided to update the layout of onepage checkout in Magento. I've created my own layout and in the config file set that my layout updates the checkout module layout. But the problem is it's actually does not update the base layout, it replaces it self with base layout! Should it be act like this or am I wrong?!

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• Sqlalchemy layout with WSGI application

  - by TheDude

  I'm working on writing a small WSGI application using Bottle and SqlAlchemy and am confused on how the "layout" of my application should be in terms of SqlAlchemy. My confusion is with creating engines and sessions. My understanding is that I should only create one engine with the 'create_engine' method. Should I be creating an engine instance in the global namespace in some sort of singleton pattern and creating sessions based off of it? How have you done this in your projects? Any insight would be appreciated. The examples in the documentation dont seem to make this entirely clear (unless I'm missing something obvious). Any thoughts?

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• gcc problem with explicit template instantiation?

  - by steve jaffe

  It is my understanding that either a declaration or typedef of a specialization ought to cause a template class to be instantiated, but this does not appear to be happening with gcc. E.g. I have a template class, template class Foo {}; I write class Foo<double>; or typedef Foo<double> DoubleFoo; but after compilation the symbol table of the resulting object file does not contain the members of Foo. If I create an instance: Foo<double> aFoo; then of course the symbols are all generated. Has anyone else experienced this and/or have an explanation?

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• Handling ID's with db4o and ASP.NET MVC2

  - by Craig McGuff

  So, i'm looking at the TekPub sample for ASP.NET MVC2 (http://mvcstarter.codeplex.com/) using DB4o and there are a bunch of templates to create controllers etc, the generated code looks like: public ActionResult Details(int id) { var item = _session.Single<Account>(x=>x.ID == id); return View(item); } Now, my understanding is that using DB4o or a simliar object database that ID's are not required, so how/what exactly do I pass to enable this kind of templated code to function? UPDATE: Both answers were useful, I have modifed the templates to use GUID as the ID. I will add any relevant code/notes here once I see how it works out.

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• I need help translating this portion of the ECMAScript grammar?

  - by ChaosPandion

  I've been working on my own implementation of ECMAScript for quite some time now. I have basically done everything by hand to help gain a deep understanding of the process. Repeated attempts to analyze and understand this portion of the grammar have failed so I've been working on the run time instead. Now I am at a point were I will be working on object literals so I really need to polish my syntactic analyzer. Can anyone put this in terms a language parser novice could understand? My biggest source of confusion is the following: new MemberExpression Arguments This is supposed to be a member expression, but this seemingly conflicts with the following: NewExpression : MemberExpression new NewExpression Is a new expression a member expression or a left hand side expression? To be honest I am having trouble laying out the proper C# classes for the concrete grammar. MemberExpression : PrimaryExpression FunctionExpression MemberExpression [ Expression ] MemberExpression . IdentifierName new MemberExpression Arguments NewExpression : MemberExpression new NewExpression CallExpression : MemberExpression Arguments CallExpression Arguments CallExpression [ Expression ] CallExpression . IdentifierName LeftHandSideExpression : NewExpression CallExpression

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• EXC_BAD_ACCESS when not using self.

  - by chris

  I got nabbed by the following bug again and would like some clarification to exactly why it is a bug. I have a simple UITableView that loads some data: // myclass.h @property (nonatomic, retain) NSArray *myData // myclass.m @synthesize myData; - (void) viewDidLoad { ... myData = someDataSource // note the lack of self } - (UITableViewCell *) cellForRowAtIndexPath ... { ... cell.textLabel.text = [self.myData objectAtIndex:indexPath.row]; // EXC_BAD_ACCESS } The table first loads fine, but when scrolling up enough that one of the cells is totally out of the view I then get the EXC_BAD_ACCESS error. Am I missing something in regards to @property retain. My understanding is that it releases anything that the pointer was previously pointing to before the reassignment. If I am correct then why would not using self. cause any problems? Thanks for the help.

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• abstract class MouseAdapter vs. interface

  - by Stefano Borini

  I noted this (it's a java.awt.event class). public abstract class MouseAdapter implements MouseListener, MouseWheelListener, MouseMotionListener { .... } Then you are clearly forced to extend from this adapter public class MouseAdapterImpl extends MouseAdapter {} the class is abstract and implements no methods. Is this a strategy to combine different interfaces into a single "basically interface" ? I assume in java it's not possible to combine different interfaces into a single one without using this approach. In other words, it's not possible to do something like this in java public interface MouseAdapterIface extends MouseListener, MouseWheelListener, MouseMotionListener { } and then eventually public class MouseAdapterImpl implements MouseAdapterIface {} Is my understanding of the point correct ? what about C# ?

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• Arrays & Pointers

  - by Thomas

  Hi, Looking for some help with arrays and pointers and explanation of what I am trying to do. I want to create a new array on the heap of type Foo* so that I may later assign objects that have been created else where to this array. I am having troubles understanding what I am creating exactly when I do something like the following. Foo *(*f) = new Foo*[10]; Also once I have created my array how do I access each element for example. (f + 9)->fooMember(); ?????? Thanks in advance.

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• Which Java modules get Spring Security

  - by HDave

  I have a classic Java SOA application, with a web UI module, web services module, a service module (Java API), a domain module and a persistence module. In a sense, each of these modules has their own public API. My understanding of Spring Security is that I can use web filters to handle the security of the web gui and web services, and method level security (via annotations) for the service module. My question is this: should I bother to add method level security to the domain module and the persistence module or is that considered overkill?

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• Refactor or Rewrite

  - by Rick J

  Hmm I have a application in flex (codebase around 20K lines) ... its sort of a social network meets digg kind of thing, I need to add more features to it. This is my first ever flex project. Now im in a dilemma as to whether to refactor or rewrite the application. Im having a lot of trouble understanding the existing code (there is no documentation and the original developer is missing!!). Anyone faced with such a dilemma before? any opinions on what i should do?

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• How do I get a right outer join in L2E?

  - by Dan

  I have two tables that I set up through the VS Entity Data Model Diagram tool. I'm trying to do a right outer join and it doesn't return results from the 2nd table. I have set up a 0..1 to MANY relationship from the diagram tool. When I run a Linq-To-Entities query, it still defaults to an INNER JOIN. From my understanding of entities, if I set up the relationship using VS, when I join the tables, it should automagically figure out the join syntax based on the relationship I supply. It doesn't seem to be doing that. I am using EF v1 (not Linq-to-Sql). Query I'm running: from s in SomeTable join t in SomeOtherTable on s.ID equals t.ID select new { s.MyFieldName, t.MyOtherFieldName }

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• OWL inferencing question

  - by user439170

  I am using the Jena semantic web framework version 2.6.3. I have code that creates a model with owl inferencing and then adds the following triples: [:bnode-3 rdf:type owl:Restriction] [:bnode-3 owl:onProperty :offspringOf] [:bnode-3 owl:someValuesFrom :Person] [:bnode-3 rdfs:subClassOf :Person] bnode-3 is supposed to be a restriction class which, for example, would contain :joe if :bob is a :Person and the following triple were asserted: [:joe :offspringOf :bob]. Then, since the restriction class is a subclass of Person, :joe would also be a person. And, in fact, this works. Whats confusing to me is that after I assert just the 4 triples at the top of this post, the inferencer creates a blank node which is a Person. In other words, the following triple is now in the model: [_:b0 rdf:type :Person] I don't understand why it would do this. Any help in understanding this would be greatly appreciated. Thanks. Kent.

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• Favouriting things in a database - most efficient method of keeping track?

  - by a2h

  I'm working on a forum-like webapp where I'd like to allow users to favourite an item so that they can keep track of it, and also so that others can see how many times an item's been favourited. The problem is, I'm unsure on the best practices for databases, which includes this situation. I have two ideas in my head on how to do this: Add an extra column to the user table and store things like so: "|2|5|73|" Add an extra table with at least two columns, one for referencing an item, the other for referencing a user. I feel uncomfortable about going for the second method as it involves an extra table, and potentially more queries would be required. Perhaps these beliefs aren't an issue, as I have little understanding of databases beyond simply working with table layouts and basic queries.

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• MDX: How To Aggregate Hierarchy Level Members With Same Name

  - by Dave Frautnick

  Greetings, I am new to MDX, and am having trouble understanding how to perform an aggregation on a hierarchy level with members that have the same names. This query is particular to Microsoft Analysis Services 2000 cubes. I have a given hierarchy dimension with levels defined as follows: [Segment].[Flow].[Segment Week] Within the [Segment Week] level, I have the following members: [Week- 1] [Week- 2] [Week- 3] ... [Week- 1] [Week- 2] [Week- 3] The members have the same names, but are aligned with a different [Flow] in the parent level. So, the first occurrence of the [Week- 1] member aligns with [Flow].[A] while the second occurrence of [Week- 1] aligns with [Flow].[B]. What I am trying to do is aggregate all the members within the [Segment Week] level that have the same name. In SQL terms, I want to GROUP BY the member names within the [Segment Week] level. I am unsure how to do this. Thank you. Dave

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• How to determine whether a .NET exception is being handled?

  - by romkyns

  We're investigating a coding pattern in C# in which we'd like to use a "using" clause with a special class, whose Dispose() method does different things depending on whether the "using" body was exited normally or with an exception. To the best of my understanding, the CLR keeps track of the current exception being handled until it's been consumed by a "catch" handler. However it's not entirely clear whether this information is exposed in any way for the code to access. Do you know whether it is, and if so, how to access it? For example: using (var x = new MyObject()) { x.DoSomething(); x.DoMoreThings(); } class MyObject : IDisposable { public void Dispose() { if (ExceptionIsBeingHandled) Rollback(); else Commit(); } } This looks almost like System.Transactions.TransactionScope, except that success/failure is not determined by a call to x.Complete(), but rather based on whether the using body was exited normally.

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• What simple methods are there to wrap a c++ based object model with a COM interface

  - by Rich

  I have a pre-existing c++ object model which represents the business layer tier of an application. I want to be able to expose the object model to applications written in other languages i.e vbscript, VB, javascript etc. I believe the best way of doing this is to wrap the business objects with a COM layer. What fast and effective methods are there for doing this. Any advice, links to practical "How to" documentation would be very much appreciated. Because I'm starting a bounty on this , here's a few extra guidelines for potential bounty hunters :- 1)I've decided on an ATL approach 2)I'm now specifically looking for links to really good "how to and quickly" documentation on wrapping a pre-existing c++ object model to make it useable by a scripting language like javascript 3) Something with small working examples showing me what code needs to be added to what files, e.g what goes into the cpp , idl and hpp/h etc. It' must include an example I can compile test and change to get a better understanding.

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• Installing a condition handler in Common Lisp

  - by Paul Nathan

  The HTTP library Drakma on CLISP generates an error USOCKET:UNSUPPORTED due to a bug in Drakma+CLISP. However, it turns out that the CONTINUE restart seems to work fine. Therefore, I spent some time with CLtL and other references trying to determine how to write a restart handler. (defun http-request (url param) (handler-bind ((USOCKET:UNSUPPORTED #'(lambda (x) (invoke-restart 'continue))))) (drakma:http-request url :method :post :parameters param)) According to my best understanding, the above code should trap the error USOCKET:UNSUPPORTED. It doesn't; it seems to ignore the error binder. How do I fix this?

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• PHP namespaces and using the \ prefix in declaration

  - by Jason McCreary

  The following throws an error stating Exception can no be redeclared. namespace \NYTD\ReadingListBackend; class Exception extends \Exception { } However, removing the \ prefix in the namespace declaration does not: namespace NYTD\ReadingListBackend; I recently adopted PHP namespaces. My understanding is that namespaces prefixed with \ are a fully qualified name. So why can't I use the prefix in the namespace declaration? I can when referencing (e.g. new \NYTD\ReadingListBackend\Exception). Would appreciate a full explanation as I couldn't find anything in the docs.

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• Creating a project, from Makefile to static/dynamic libraries in UNIX

  - by Sasha

  Guys, would you describe a few things about c++ building blocks, on unix. I want to create an application that links against static libs and dynamic libs (.so). Question 1: How do I create static library using gcc/g++ ?How do I make my app link against it. Question 2: How to specify it in the makefile, linking against static and dynamic libs, assuming that both libraries have header files Summary: I have been using makefiles and libraries for years, written by someone else. Thus every time I modified it, I simply cut-and-pasted things around, without really understanding it. Now I want to get down to the ground and understand the building/linking/Creating Makfile process in-depth. What is a good book describing these concepts in intimate details? Thanks

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