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• Algorithm(s) for rearranging simple symbolic algebraic expressions

  - by Gabe Johnson

  Hi, I would like to know if there is a straightforward algorithm for rearranging simple symbolic algebraic expressions. Ideally I would like to be able to rewrite any such expression with one variable alone on the left hand side. For example, given the input: m = (x + y) / 2 ... I would like to be able to ask about x in terms of m and y, or y in terms of x and m, and get these: x = 2*m - y y = 2*m - x Of course we've all done this algorithm on paper for years. But I was wondering if there was a name for it. It seems simple enough but if somebody has already cataloged the various "gotchas" it would make life easier. For my purposes I won't need it to handle quadratics. (And yes, CAS systems do this, and yes I know I could just use them as a library. I would like to avoid such a dependency in my application. I really would just like to know if there are named algorithms for approaching this problem.)

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• vector::erase with pointer member

  - by matt

  I am manipulating vectors of objects defined as follow: class Hyp{ public: int x; int y; double wFactor; double hFactor; char shapeNum; double* visibleShape; int xmin, xmax, ymin, ymax; Hyp(int xx, int yy, double ww, double hh, char s): x(xx), y(yy), wFactor(ww), hFactor(hh), shapeNum(s) {visibleShape=0;shapeNum=-1;}; //Copy constructor necessary for support of vector::push_back() with visibleShape Hyp(const Hyp &other) { x = other.x; y = other.y; wFactor = other.wFactor; hFactor = other.hFactor; shapeNum = other.shapeNum; xmin = other.xmin; xmax = other.xmax; ymin = other.ymin; ymax = other.ymax; int visShapeSize = (xmax-xmin+1)*(ymax-ymin+1); visibleShape = new double[visShapeSize]; for (int ind=0; ind<visShapeSize; ind++) { visibleShape[ind] = other.visibleShape[ind]; } }; ~Hyp(){delete[] visibleShape;}; }; When I create a Hyp object, allocate/write memory to visibleShape and add the object to a vector with vector::push_back, everything works as expected: the data pointed by visibleShape is copied using the copy-constructor. But when I use vector::erase to remove a Hyp from the vector, the other elements are moved correctly EXCEPT the pointer members visibleShape that are now pointing to wrong addresses! How to avoid this problem? Am I missing something?

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• Reasonable expectation to support new Operating Systems?

  - by Neil N

  My company has a desktop app originally developed for Windows XP. The original programmer has since been fired (fired with extreme prejudice I might add). I have fixed the app various times but overall try to avoid it, it is a mess and the only real way to fix it is to completely rewrite it, which could take a year. We have been trying to "forget" about this app, and instead steer clients towards our web version, which is more up to date, easier to maintain, easier to extend, and WAY easier to support. Most clients agree, the web version is just better all around. However we have one client that insists on using the desktop app. The app required a little duct tape to get working on Vista, but now completely breaks on Windows 7. I'm not even sure WHAT all the fixes are to get it working on Win7 (the current time estimate stands at "miracle") but after both installing the RELEASE build, and running the DEBUG build from Visual Studio, the app has errors on nearly every user action, and from what I can see from a high level test run, none of them are related. Since Windows 7 did not exist when this app was developed, is my company really expected to make all the required changes to make it function as "smoothly" as it did on XP?

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• Code Organization Connundrum: Web Project With Multiple Supporting DLLs?

  - by Code Sherpa

  Hi. I am trying to get a handle on the best practice for code organization within my project. I have looked around on the internet for good examples and, so far, I have seen examples of a web project with one or multiple supporting class libraries that it references or a web project with sub-folders that follow its namespace conventions. Assuming there is no right answer, this is what I currently have for code organization: MyProjectWeb This is my web site. I am referencing my class libraries here. MyProject.DLL As the base namespace, I am using this DLL for files that need to be generally consumable. For example, my class "Enums" that has all the enumerations in my project lives there. As does class MyProjectException for all exception handling. MyProject.IO.DLL This is a grouping of maybe 20 files that handle file upload and download (so far). MyProject.Utilities.DLL ALl my common classes and methods bunched up together in one generally consumable DLL. Each class follows a "XHelper" convention such as "SqlHelper, AuthHelper, SerializationHelper, and so on... MyProject.Web.DLL I am using this DLL as the main client interface. Right now, the majority of class files here are: 1) properties (such as School, Location, Account, Posts) 2) authorization stuff ( such as custom membership, custom role, & custom profile providers) My question is simply - does this seem logical? Also, how do I avoid having to cross reference DLLs from one project library to the next? For example, MyProject.Web.DLL uses code from MyProject.Utilities.DLL and MyProject.Utilities.DLL uses code from MyProject.DLL. Is this solved by clicking on properties and selecting "Dependencies"? I tried that but still don't seem to be accessing the namespaces of the assembly I have selected. Do I have to reference every assembly I need for each class library? Responses appreciated and thanks for your patience.

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• How to import a class from default package

  - by mykhaylo

  Hi, I am using Eclipse 3.5 and I have created a project with some package structure along with the default package. I have one class in default package - Calculations.java and I want to make the use of that class in any of the package (for instance in com.company.calc). When I try to make the use of the class which is default package, its giving me compile error. Its not able to recognise the class in default package. Where is a problem? Calculations.java - source code public class Calculations{ native public int Calculate(int contextId); native public double GetProgress(int contextId); static { System.loadLibrary("Calc"); } } I can put my class in any other package. This class has some native method which is implemented in Delphi . If I put that class in any of the folder,I will have to make the change that DLL which I want to avoid(really - I can not). Thats why I put my class in the default package.

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• RichEdit VCL and URLs. Workarounds for OnPaint Issues.

  - by HX_unbanned

  So, issue is with the thing Delphi progies scare to death - Rich Edit in Windows ( XP and pre-XP versions ). Situation: I have added EM_AUTOURLDETECTION in OnCreate of form. Target - RichEdit1. Then, I have form, that is "collapsed" after showing form. RichEdit Control is sattic, visible and enabled, but it is "hidden" because form window is collapsed. I can expand and collapse form, using Button1 and changing forms Constraints and Size properties. After first time I expand form, the URL inside RichEdit1 control is highlighted. BUT - After second, third, fourth, etc... time I Collapse and Expand form, the RichEdit1 Control does not highlight URL anymore. I have tried EM_SETTEXTMODE messages, also WM_UPDATEUISTATE, also basic WM_TEXT message - no luck. It sems like this merssage really works ( enables detection ) while sending keyboard strokes ( virtual keycodes ), but not when text has been modified. Also - I am thinking to rewrite code to make RichEdit Control dynamic. Would this fix the problem? Maybe solution is to override OnPaint / OnDraw method to avoid highlight ( formatting ) losing when collapsing or expanding form? Weird is that my Embarcadero Documentation says this function must work in any moment text has been modified. Why it does not work? Any help appreciated. I am making this Community Wiki because this is common problem and togewther we cam find solution, right? :) Also - follow-ups and related Question: http://stackoverflow.com/questions/738694/override-onpaint http://stackoverflow.com/questions/478071/how-to-autodetect-urls-in-richedit-2-0 http://www.vbforums.com/archive/index.php/t-59959.html

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• How should I handle this Optimistic Concurrency error in this Entity Framework code, I have?

  - by Pure.Krome

  Hi folks, I have the following pseduo code in some Repository Pattern project that uses EF4. public void Delete(int someId) { // 1. Load the entity for that Id. If there is none, then null. // 2. If entity != null, then DeleteObject(..); } Pretty simple but I'm getting a run-time error:- ConcurrencyException: Store, Update, Insert or Delete statement affected an unexpected number of rows (0). Now, this is what is happening :- Two instances of EF4 are running inthe app at the same time. Instance A calls delete. Instance B calls delete a nano second later. Instance A loads the entity. Instance B also loads the entity. Instance A now deletes that entity - cool bananas. Instance B tries to delete the entity, but it's already gone. As such, the no-count or what not is 0, when it expected 1 .. or something like that. Basically, it figured out that the item it is suppose to delete, didn't delete (because it happened a split sec ago). I'm not sure if this is like a race-condition or something. Anyways, is there any tricks I can do here so the 2nd call doesn't crash? I could make it into a stored procedure.. but I'm hoping to avoid that right now. Any ideas? I'm wondering If it's possible to lock that row (and that row only) when the select is called ... forcing Instance B to wait until the row lock has been relased. By that time, the row is deleted, so when Instance B does it's select, the data is not there .. so it will never delete.

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• Cassandra hot keyspace structure change

  - by Pierre

  Hello. I'm currently running a 12-node Cassandra cluster storing 4TB of data, with a replication factor set to 3. For the needs of an application update, we need to change the configuration of our keyspace, and we'd like to avoid any downtime if possible. I read on a mailing list that the best way to do it is to: Kill cassandra process on one server of the cluster Start it again, wait for the commit log to be written on the disk, and kill it again Make the modifications in the storage.xml file Rename or delete the files in the data directories according to the changes we made Start cassandra Goto 1 with next server on the list My questions would be: Did I understand the process well? Is there any risk of data corruption? During the process, there will be servers with different versions of the storage.xml file in the same cluser, same keyspace. Is it a problem? Same question as above if we not only add, rename and remove ColumnFamilies, but if we change the CompareWith parameter / transform an existing column family into a super one. Or do we need to change the name? Thank you for your answers. It's the first time I'll do this, and I'm a little bit scared.

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• Boost::thread mutex issue: Try to lock, access violation

  - by user1419305

  I am currently learning how to multithread with c++, and for that im using boost::thread. I'm using it for a simple gameengine, running three threads. Two of the threads are reading and writing to the same variables, which are stored inside something i call PrimitiveObjects, basicly balls, plates, boxes etc. But i cant really get it to work, i think the problem is that the two threads are trying to access the same memorylocation at the same time, i have tried to avoid this using mutex locks, but for now im having no luck, this works some times, but if i spam it, i end up with this exception: First-chance exception at 0x00cbfef9 in TTTTT.exe: 0xC0000005: Access violation reading location 0xdddddded. Unhandled exception at 0x77d315de in TTTTT.exe: 0xC0000005: Access violation reading location 0xdddddded. These are the functions inside the object that im using for this, and the debugger is also blaming them for the exception. void PrimitiveObj::setPos(glm::vec3 in){ boost::mutex mDisposingMutex; boost::try_mutex::scoped_try_lock lock(mDisposingMutex); if ( lock) { position = in; boost::try_mutex::scoped_try_lock unlock(mDisposingMutex); } } glm::vec3 PrimitiveObj::getPos(){ boost::mutex myMutex; boost::try_mutex::scoped_try_lock lock(myMutex); if ( lock) { glm::vec3 curPos = position; boost::try_mutex::scoped_try_lock unlock(myMutex); return curPos; } return glm::vec3(0,0,0); } Any ideas?

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• SQL Express Edition, SQL Compact Editin and SQLCMD for learning purpose

  - by Mil

  Hi, I want to learn programming in SQL from some SQL tutorial sites of which I heard of here but I need some environment for executing query's. I think I have both SQL CE and SQL EE installed on my computer but I have some doubts about these DBMS and I don't know exactly how to use SQLCMD utility so I hope someone here will have time and will to explain me the following: Since running sqlcmd -S.\sqlexpress at command prompt command gives "1" prompt I assume I have SQL express installed but anyway how can I be sure what I have installed on my machine since I cannot find in installed programs SQL Express Edition name? Can I ship and use database with my C# (VC# Express) application which was created with SQL EE (embedded?)? How can use sqlcmd for learning SQL, that is by issuing commands like create, use, select..., again emphasize is on learning SQL I do not want to run scripts but use interactive command prompt like with MySQL (since I want to use SQL I would pretty much like to avoid graphical tools for DBMS)? Please tell me if you have some other advice regarding as to what should I better use in learning how to program in SQL or should I stick with the above for now. Thanks in advance.

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• What is a good programming language/environment for Linux database applications?

  - by Dkellygb

  I could use some advice on my move from the Windows world to Linux. For my business, I have used VB6 and Microsoft Access with both Access databases and SQL server in the past. The easy to use forms, report writers and programming language were perfect for CRUD apps and analysis for our small hotel/restaurant business. After using Linux at home for some time I would like to convert our small business. Our server is already a Linux box using Samba. I am happy with the OpenOffice.org applications instead of Microsoft Office. The only thing which is holding me back is a desktop database application where I can develop the forms and reports we require. Base does not seem to be up to the job yet from my experience. I would like something like VB.Net with visual studio (express) but I would like to avoid Mono – I just don’t see the point of it. (You can correct me if I’m wrong.) But a good collection of forms, controls and a good report writer would be ideal. I have looked at web based stuff like Ruby on Rails, but I think a webserver for our 5 pc network is overkill. I don’t mind running a proper database on our Ubuntu 9.10 server. I may have exposed a few prejudices above but my mind is open. Any thoughts?

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• protecting COM interfaces from exceptions

  - by rmeador

  I have several dozen objects exposed through COM interfaces, each of which with many methods, totaling a few hundred methods. These interfaces expose business objects from my app to a scripting engine. I have been given the task of protecting every single one of these methods from exceptions being thrown (to catch them and return an error using COM's Error() function, which incidentally I can find no documentation on because it's impossible to google). To my understanding, this requires that I add a try/catch around the guts of each one of these methods. The catch blocks are going to be similar or identical for each and every one of these hundreds of methods, which strongly smells of a problem (massively violates the DRY principle), but I can't think of any way to avoid changing every method. As far as I can tell, these methods are invoked directly by COM, with no intervening code that I can hook into to catch the exceptions. My current best idea is to make a macro for the catch block, but that has it's own sort of code-smell. Can anyone come up with a better approach? BTW, my app's exceptions do not derive from std::exception, so if there is some way of COM automatically handling standard exceptions, it won't help. And I sadly cannot change the existing exceptions to derive from std::exception.

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• How to set up single array or dictionary for use in multiple datasources?

  - by Roman

  I have multiple TableViewDatasources that need to display list of objects form same pool depending of certain property. E.g. object.flag1 is set- it will show up in TableView1 object.flag2 is set- it will show up in TableView2 The obvious way would be to have separate arrays for each TableView, But same object may appear in different arrays. Also I need to update objects very often or access all objects through same array. How do I setup a single dictionary or array to have all objects in one structure? To put it in another way: When table view or selection changes, application need to redraw TableViews with the new data. Application have to access the pool of objects and search through them using iterator and accessing each object and its properties. I think that this is an expensive operation and want to avoid that. Perhaps maybe by making a global pool of objects a dictionary and exposing objects properties as dictionary fields. So instead of iterating global pool of objects I could access global pool Dicitonary in a manner of database by selecting objects that has fields that match particular criteria. Anyone know any example of doing that?

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• How to mult-thread this?

  - by WilliamKF

  I wish to have two threads. The first thread1 occasionally calls the following pseudo function: void waitForThread2() { if (thread2 is not idle) { return; } notifyThread2IamReady(); while (thread2IsExclusive) { } } The second thread2 is forever in the following pseudo loop: for (;;) { Notify thread1 I am idle. while (!thread1IsReady()) { } Notify thread1 I am exclusive. Do some work while thread1 is blocked. Notify thread1 I am busy. Do some work in parallel with thread1. } What is the best way to write this such that both thread1 and thread2 are kept as busy as possible on a machine with multiple cores. I would like to avoid long delays between notification in one thread and detection by the other. I tried using pthread condition variables but found the delay between thread2 doing 'notify thread1 I am busy' and the loop in waitForThread2() on thear2IsExclusive() can be up to almost one second delay. I then tried using a volatile sig_atomic_t shared variable to control the same, but something is going wrong, so I must not be doing it correctly.

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• What do I name this class whose sole purpose is to report failure?

  - by Blair Holloway

  In our system, we have a number of classes whose construction must happen asynchronously. We wrap the construction process in another class that derives from an IConstructor class: class IConstructor { public: virtual void Update() = 0; virtual Status GetStatus() = 0; virtual int GetLastError() = 0; }; There's an issue with the design of the current system - the functions that create the IConstructor-derived classes are often doing additional work which can also fail. At that point, instead of getting a constructor which can be queried for an error, a NULL pointer is returned. Restructuring the code to avoid this is possible, but time-consuming. In the meantime, I decided to create a constructor class which we create and return in case of error, instead of a NULL pointer: class FailedConstructor : public IConstructor public: virtual void Update() {} virtual Status GetStatus() { return STATUS_ERROR; } virtual int GetLastError() { return m_errorCode; } private: int m_errorCode; }; All of the above this the setup for a mundane question: what do I name the FailedConstructor class? In our current system, FailedConstructor would indicate "a class which constructs an instance of Failed", not "a class which represents a failed attempt to construct another class". I feel like it should be named for one of the design patterns, like Proxy or Adapter, but I'm not sure which.

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• Is there a good digraph layout library callable from C++?

  - by Steve314

  The digraphs represent finite automata. Up until now my test program has been writing out dot files for testing. This is pretty good both for regression testing (keep the verified output files in subversion, ask it if there has been a change) and for visualisation. However, there are some problems... Basically, I want something callable from C++ and which plans a layout for my states and transitions but leaves the drawing to me - something that will allow me to draw things however I want and draw on GUI (wxWidgets) windows. I also want a license which will allow commercial use - I don't need that at present, and I may very well release as open source, but I don't want to limit my options ATM. The problems with GraphViz are (1) the warnings about building from source on Windows, (2) all the unnecessary dependencies for rendering and parsing, and (3) the (presumed) lack of a documented API specifically and purely for layout. Basically, I want to be able to specify my states (with bounding rectangle sizes) and transitions, and read out positions for the states and waypoints for each transition, then draw based on those co-ordinates myself. I haven't really figured out how annotations on transitions should be handled, but there should be some kind of provision for specifying bounding-box-sizes for those, associating them with transitions, and reading out positions. Does anyone know of a library that can handle those requirements? I'm not necessarily against implementing something for myself, but in this case I'd rather avoid it if possible.

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• How to easily substitute a Base class

  - by JTom

  Hi, I have the following hierarchy of classes class classOne { virtual void abstractMethod() = 0; }; class classTwo : public classOne { }; class classThree : public classTwo { }; All classOne, classTwo and classThree are abstract classes, and I have another class that is defining the pure virtual methods class classNonAbstract : public classThree { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; And right now I need it differently...I need it like class classNonAbstractOne : public classOne { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; class classNonAbstractTwo : public classTwo { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; and class classNonAbstractThree : public classThree { void abstractMethod(); // Couple of new methods void doIt(); void doItToo(); }; But all the nonAbstract classes have the same new methods, with the same code...and I would like to avoid copying all the methods and it's code to every nonAbstract class. How could I accomplish that? Hopefully it's understandable...

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• Can a stateless WCF service benefit from built-in database connection pooling?

  - by vladimir

  I understand that a typical .NET application that accesses a(n SQL Server) database doesn't have to do anything in particular in order to benefit from the connection pooling. Even if an application repeatedly opens and closes database connections, they do get pooled by the framework (assuming that things such as credentials do not change from call to call). My usage scenario seems to be a bit different. When my service gets instantiated, it opens a database connection once, does some work, closes the connection and returns the result. Then it gets torn down by the WCF, and the next incoming call creates a new instance of the service. In other words, my service gets instantiated per client call, as in [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerCall)]. The service accesses an SQL Server 2008 database. I'm using .NET framework 3.5 SP1. Does the connection pooling still work in this scenario, or I need to roll my own connection pool in form of a singleton or by some other means (IInstanceContextProvider?). I would rather avoid reinventing the wheel, if possible.

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• Are Fortran control characters (carriage control) still implemented in compilers?

  - by CmdrGuard

  In the book Fortran 95/2003 for Scientists and Engineers, there is much talk given to the importance of recognizing that the first column in a format statement is reserved for control characters. I've also seen control characters referred to as carriage control on the internet. To avoid confusion, by control characters, I refer to the characters "1, a blank (i.e. \s), 0, and +" as having an effect on the vertical spacing of output when placed in the first column (character) of a FORMAT statement. Also, see this text-only web page written entirely in fixed-width typeface : Fortran carriage-control (because nothing screams accuracy and antiquity better than prose in monospaced font). I found this page and others like it to be not quite clear. According to Fortran 95/2003 for Scientists and Engineers, failure to recall that the first column is reserved for carriage control can lead to horrible unintended output. Paraphrasing Dave Barry, type the wrong character, and nuclear missiles get fired at Norway. However, when I attempt to adhere to this stern warning, I find that gfortran has no idea what I'm talking about. Allow me to illustrate my point with some example code. I am trying to print out the number Pi: PROGRAM test_format IMPLICIT NONE REAL :: PI = 2 * ACOS(0.0) WRITE (*, 100) PI WRITE (*, 200) PI WRITE (*, 300) PI 100 FORMAT ('1', "New page: ", F11.9) 200 FORMAT (' ', "Single Space: ", F11.9) 300 FORMAT ('0', "Double Space: ", F11.9) END PROGRAM test_format This is the output: 1New page: 3.141592741 Single Space: 3.141592741 0Double Space: 3.141592741 The "1" and "0" are not typos. It appears that gfortran is completely ignoring the control character column. My question, then, is this: Are control characters still implemented in standards compliant compilers or is gfortran simply not standards compliant? For clarity, here is the output of my gfortran -v Using built-in specs. Target: powerpc-apple-darwin9 Configured with: ../gcc-4.4.0/configure --prefix=/sw --prefix=/sw/lib/gcc4.4 --mandir=/sw/share/man --infodir=/sw/share/info --enable-languages=c,c++,fortran,objc,java --with-gmp=/sw --with-libiconv-prefix=/sw --with-ppl=/sw --with-cloog=/sw --with-system-zlib --x-includes=/usr/X11R6/include --x-libraries=/usr/X11R6/lib --disable-libjava-multilib --build=powerpc-apple-darwin9 --host=powerpc-apple-darwin9 --target=powerpc-apple-darwin9 Thread model: posix gcc version 4.4.0 (GCC)

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• Exiting from the Middle of an Expression Without Using Exceptions

  - by Jon Purdy

  Is there a way to emulate the use of flow-control constructs in the middle of an expression? Is it possible, in a comma-delimited expression x, y, for y to cause a return? Edit: I'm working on a compiler for something rather similar to a functional language, and the target language is C++. Everything is an expression in the source language, and the sanest, simplest translation to the destination language leaves as many things expressions as possible. Basically, semicolons in the target language become C++ commas. In-language flow-control constructs have presented no problems thus far; it's only return. I just need a way to prematurely exit a comma-delimited expression, and I'd prefer not to use exceptions unless someone can show me that they don't have excessive overhead in this situation. The problem of course is that most flow-control constructs are not legal expressions in C++. The only solution I've found so far is something like this: try { return x(), // x(); (1 ? throw Return(0) : 0); // return 0; } catch (Return& ret) { return ref.value; } The return statement is always there (in the event that a Return construct is not reached), and as such the throw has to be wrapped in ?: to get the compiler to shut up about its void result being used in an expression. I would really like to avoid using exceptions for flow control, unless in this case it can be shown that no particular overhead is incurred; does throwing an exception cause unwinding or anything here? This code needs to run with reasonable efficiency. I just need a function-level equivalent of exit().

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• I've made something that might be useful to the community. Now what?

  - by Chris McCall

  If the specifics are important, I made a cruisecontrol.net publisher plugin that notifies a series of phone numbers via voice, announcing the current state of the build. It uses Twilio to do so. I'd like to avoid getting hung up on the specifics of what it is I've made, as I have this question a lot, with a number of little hobby one-offs. What's the state of the art as far as making my hobby output available to the world at large? There seem to be a lot of options for open-source project hosting, community features, and what role to take in all of this. It's a little bewildering. What I'm looking for is to put this out into the wild for free and basically take a hands-off approach from there. Is that realistic? Which project hosting service can I use for free to allow developers to at least download the code, report issues and collaborate with each other to improve the product? What snags have you run into that could make me regret this decision? I'm interested in war stories, advice and guidance on making this little product available to the community where it can be used.

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• Java assignment issues - Is this atomic?

  - by Bob

  Hi, I've got some questions about Java's assigment. Strings I've got a class: public class Test { private String s; public synchronized void setS(String str){ s = s + " - " + str; } public String getS(){ return s; } } I'm using "synchronized" in my setter, and avoiding it in my getter, because in my app, there are a tons of data gettings, and very few settings. Settings must be synchronized to avoid inconsistency. My question is: is getting and setting a variable atomic? I mean, in a multithreaded environment, Thread1 is about to set variable s, while Thread2 is about to get "s". Is there any way the getter method could get something different than the s's old value or the s's new value (suppose we've got only two threads)? In my app it is not a problem to get the new value, and it is not a problem to get the old one. But could I get something else? What about HashMap's getting and putting? considering this: public class Test { private Map<Integer, String> map = Collections.synchronizedMap(new HashMap<Integer, String>()); public synchronized void setMapElement(Integer key, String value){ map.put(key, value); } public String getValue(Integer key){ return map.get(key); } } Is putting and getting atomic? How does HashMap handle putting an element into it? Does it first remove the old value and put the now one? Could I get other than the old value or the new value? Thanks in advance!

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• How to get resultset with stored procedure calls over two linked servers?

  - by räph

  I have problems filling a temporary table with the resultset from a procedure call on a linked server, in which again a procedure on another server is called. I have a Stored Procedure sproc1 with the following code, which calls another procedure sproc2 on a linked server. SET @sqlCommand = 'INSERT INTO #tblTemp ( ModuleID, ParamID) ' + '( SELECT * FROM OPENQUERY(' + @targetServer + ', ' + '''SET FMTONLY OFF; EXEC ' + @targetDB + '.usr.sproc2 ' + @param + ''' ) )' exec ( @sqlCommand ) Now in the called sproc2 I again call a third procedure sproc3 on another linked server, which returns my resultset. SET @sqlCommand = 'EXEC ' + @targetServer +'.database.usr.sproc3 ' + @param exec ( @sqlCommand ) The whole thing doen't work, as I get an SQL error 7391 The operation could not be performed because OLE DB provider "%ls" for linked server "%ls" was unable to begin a distributed transaction. I already checked the hints at this microsoft article, but without success. But maybe, I can change the code in sproc1. Would there be some alternative to the temp table and the open query? Just calling stored procedures from server A to B to C and returning the resultset is working (I do this often in the application). But this special case with the temp table and openquery doesn't work! Or is it just not possible what I am trying to do? The microsft article states: Check the object you refer on the destination server. If it is a view or a stored procedure, or causes an execution of a trigger, check whether it implicitly references another server. If so, the third server is the source of the problem. Run the query directly on the third server. If you cannot run the query directly on the third server, the problem is not actually with the linked server query. Resolve the underlying problem first. Is this my case? PS: I can't avoid the architecture with the three servers.

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• How to Elegantly convert switch+enum with polymorphism

  - by Kyle

  I'm trying to replace simple enums with type classes.. that is, one class derived from a base for each type. So for example instead of: enum E_BASE { EB_ALPHA, EB_BRAVO }; E_BASE message = someMessage(); switch (message) { case EB_ALPHA: applyAlpha(); case EB_BRAVO: applyBravo(); } I want to do this: Base* message = someMessage(); message->apply(this); // use polymorphism to determine what function to call. I have seen many ways to do this which all seem less elegant even then the basic switch statement. Using dyanimc_pointer_cast, inheriting from a messageHandler class that needs to be updated every time a new message is added, using a container of function pointers, all seem to defeat the purpose of making code easier to maintain by replacing switches with polymorphism. This is as close as I can get: (I use templates to avoid inheriting from an all-knowing handler interface) class Base { public: template<typename T> virtual void apply(T* sandbox) = 0; }; class Alpha : public Base { public: template<typename T> virtual void apply(T* sandbox) { sandbox->applyAlpha(); } }; class Bravo : public Base { public: template<typename T> virtual void apply(T* sandbox) { sandbox->applyBravo(); } }; class Sandbox { public: void run() { Base* alpha = new Alpha; Base* bravo = new Bravo; alpha->apply(this); bravo->apply(this); delete alpha; delete bravo; } void applyAlpha() { // cout << "Applying alpha\n"; } void applyBravo() { // cout << "Applying bravo\n"; } }; Obviously, this doesn't compile but I'm hoping it gets my problem accross.

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• How to get XML element/attribute name in SQL Server 2005

  - by OG Dude

  Hi, I have a simple procedure in SQL Server 2005 which takes some XML as input. The element attributes correspond to field names in tables. I'd like to be able to determine <elementName>, <attribNameX> dynamically as to avoid having to hardcode them into the procedure. How can I do this? The XML looks like this: <ROOT> <elementName attribName1 = "xxx" attribName2 = "yyy"/> <elementName attribName1 = "aaa" attribName2 = "bbb"/> ... </ROOT> The stored procedure like this: CREATE PROC dbo.myProc ( @XMLInput varchar(1000) ) AS BEGIN SET NOCOUNT ON DECLARE @XMLDocHandle int EXEC sp_xml_preparedocument @XMLDocHandle OUTPUT, @XMLInput SELECT someTable.someCol FROM dbo.someTable JOIN OPENXML (@XMLDocHandle, '/ROOT/elementName',1) WITH (attrib1Name int, attrib2Name int) AS XMLData ON someTable.attribName1 = XMLData.attribName1 AND someTable.attribName2 = XMLData.attribName2 EXEC sp_xml_removedocument @XMLDocHandle END GO The question has been asked here before but maybe there is a cleaner solution. Additionally, I'd like to pass the tablename as a parameter as well - I read some stuff arguing that this is bad style - so what would be a good solution for having a dynamic tablename? Thanks a lot in advance, /David

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