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• How do I change the class of an object to a subclass of its current class in C++?

  - by Jared P

  I have an array of pointers to a base class, so that I can make those pointers point to (different) subclasses of the base class, but still interact with them. (really only a couple of methods which I made virtual and overloaded) I'm wondering if I can avoid using the pointers, and instead just make an array of the base class, but have some way to set the class to the subclass of my choosing. I know there must be something there specifying the class, as it needs to use that to look up the function pointer for virtual methods. By the way, the subclasses all have the same ivars and layout. Note: the design is actually based on using a template argument instead of a variable, due to performance increases, so really the abstract base class is just the interface for the subclasses, which are all the same except for their compiled code. Thanks

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• How can I compare the performance of log() and fp division in C++?

  - by Ventzi Zhechev

  Hi, I’m using a log-based class in C++ to store very small floating-point values (as the values otherwise go beyond the scope of double). As I’m performing a large number of multiplications, this has the added benefit of converting the multiplications to sums. However, at a certain point in my algorithm, I need to divide a standard double value by an integer value and than do a *= to a log-based value. I have overloaded the *= operator for my log-based class and the right-hand side value is first converted to a log-based value by running log() and than added to the left-hand side value. Thus the operations actually performed are floating-point division, log() and floating-point summation. My question whether it would be faster to first convert the denominator to a log-based value, which would replace the floating-point division with floating-point subtraction, yielding the following chain of operations: twice log(), floating-point subtraction, floating-point summation. In the end, this boils down to whether floating-point division is faster or slower than log(). I suspect that a common answer would be that this is compiler and architecture dependent, so I’ll say that I use gcc 4.2 from Apple on darwin 10.3.0. Still, I hope to get an answer with a general remark on the speed of these two operators and/or an idea on how to measure the difference myself, as there might be more going on here, e.g. executing the constructors that do the type conversion etc. Cheers!

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• Howto disable the emacs site-start files permanently?

  - by elemakil

  When solving this problem I figured out that I need to disable the site-wise init files in order to get my emacs + CEDET running (everything works nicely when starting emacs using emacs --no-site-file but is broken without the additional argument). I'd like to disable the site-wise init files permanently but as I'm using several different approaches/methods when launching emacs (launcher/panel/terminal) I don't think aliasing it in my .zshrc won't work. I require a method to permanently disable all site-start files. Is there any easy way to achieve this? Thanks!

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• Asynchronous SQL Operations

  - by Paul Hatcherian

  I've got a problem I'm not sure how best to solve. I have an application which updates a database in response to ad hoc requests. One request in particular is quite common. The request is an update that by itself is quite simple, but has some complex preconditions. For this request the business layer first requests a set of data from the data layer. The business logic layer evaluated the data from the database and parameters from the request, from this the action to be performed is determined, and the request's response message(s) are created. The business layer now executes the actual update command that is the purpose of the request. This last step is the problem, this command is dependent on the state of the database, which might have changed since the business logic ran. Locking down the data read in this operation across several round-trips to the database doesn't seem like a good idea either. Is there a 'best-practice' way to accomplish something like this? Thanks!

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• Django: do I need to do HttpResponseRedirect to render a simple string after a POST?

  - by AP257

  I've got a mobile app that makes POST requests to a Django site. I want to return a simple string (not a template-based page) after the app makes the POST request, saying 'Success' or 'Failure' as appropriate. However I know that after a POST request in Django you're supposed to do a HttpResponseRedirect. But, do I really need to redirect to another page and write a new function to handle it, all to output a string? And if so, how do I pass the success/failure status of the app in the HttpResponseRedirect, since it's only supposed to take one argument? Thanks!

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• Strange behaviour when collapsing lines in XML bound WPF Datagrid

  - by Flossn

  i am using a wpf datagrid with a xml file as DataContext. All working good except for iterating thorough the table and collapsing individual rows. There are several checkboxes where the user can decide which kinds of rows he wants to see, dependent on their error level string. If a checkbox is checked, some of the rows are collapsed, others not. You need to uncheck the checkbox and check it again to collapse the ones of the first try and some of the others. If you recheck it again more rows are collapsed every time. I guess it has something to do with how much of the list is actually visible and how much not because of the window size. Thanks in advance. foreach (DataGridRow r in rows) { bool showRow = true; var tb = Datagrid.GetCell(dataGridEvents, r, 2).Content; string level = ((TextBlock)tb).Text; switch (level) { case "Warning": showRow = checkBoxWarnings.IsChecked.HasValue ? checkBoxWarnings.IsChecked.Value : false; break; case "Critical": showRow = checkBoxCritical.IsChecked.HasValue ? checkBoxCritical.IsChecked.Value : false; break; case "OK": showRow = checkBoxOK.IsChecked.HasValue ? checkBoxOK.IsChecked.Value : false; break; case "Unknown": showRow = checkBoxUnknown.IsChecked.HasValue ? checkBoxUnknown.IsChecked.Value : false; break; } r.Visibility = showRow ? Visibility.Visible : Visibility.Collapsed; }

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• Whether to put method code in a VB.Net data storage class, or put it in a separate class?

  - by Alan K

  TLDR summary: (a) Should I include (lengthy) method code in classes which may spawn multiple objects at runtime, (b) does doing so cause memory usage bloat, (c) if so should I "outsource" the code to a class that is loaded only once and have the class methods call that, or alternatively (d) does the code get loaded only once with the object definition anyway and I'm worrying about nothing? ........ I don't know whether there's a good answer to this but if there is I haven't found it yet by searching in the usual places. In my VB.Net (2010 if it matters) WinForms project I have about a dozen or so class objects in an object model. Some of these are pretty simple and do little more than act as data storage repositories. The ones further up the object model, however, have an increasing number of methods. There can be a significant number of higher level objects in use though the exact number will be runtime dependent so I can't be more precise than that. As I was writing the method code for one of the top level ones I noticed that it was starting to get quite lengthy. Memory optimisation is something of a lost art given how much memory the average PC has these days but I don't want to make my application a resource hog. So my questions for anyone who knows .Net way better than I do (of which there will be many) are: Is the code loaded into memory with each instance of the class that's created? Alternatively is it loaded only once with the definition of the class, and all derived objects just refer to that definition? (I'm not really sure how that could be possible given that, for example, event handlers can be assigned dynamically, but no harm asking.) If the answer to the first one is yes, would it be more efficient to write the code in a "utility" object which is loaded only once and called from the real class' methods? Any thoughts appreciated.

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• Mathematica & J/Link: Memory Constraints?

  - by D-Bug

  I am doing a computing-intensive benchmark using Mathematica and its J/Link Java interface. The benchmark grinds to a halt if a memory footprint of about 320 MB is reached, since this seems to be the limit and the garbage collector needs more and more time and will eventually fail. The Mathematica function ReinstallJava takes the argument command line. I tried to do ReinstallJava[CommandLine -> "java -Xmx2000m ..."] but Mathematica seems to ignore the -Xmx option completely. How can I set the -Xmx memory option for my java program? Where does the limit of 320 MB come from? Any help would be greatly appreciated.

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• How can I determine the "correct" number of steps in a questionnaire where branching is used?

  - by Mike Kingscott

  I have a potential maths / formula / algorithm question which I would like help on. I've written a questionnaire application in ASP.Net that takes people through a series of pages. I've introduced conditional processing, or branching, so that some pages can be skipped dependent on an answer, e.g. if you're over a certain age, you will skip the page that has Teen Music Choice and go straight to the Golden Oldies page. I wish to display how far along the questionnaire someone is (as a percentage). Let's say I have 10 pages to go through and my first answer takes me straight to page 9. Technically, I'm now 90% of the way through the questionnaire, but the user can think of themselves as being on page 2 of 3: the start page (with the branching question), page 9, then the end page (page 10). How can I show that I'm on 66% and not 90% when I'm on page 9 of 10? For further information, each Page can have a number of questions on that can have one or more conditions on them that will send the user to another page. By default, the next page will be the next one in the collection, but that can be over-ridden (e.g. entire sets of pages can be skipped). Any thoughts? :-s

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• C# dll import function correctly

  - by poco

  I am trying to import a function from a c dll into C#. The c function looks like this unsigned short write_buffer( unsigned short device_number, unsigned short word_count, unsigned long buffer_link, unsigned short* buffer) my attempt at a C# import looks like this [DllImport("sslib32.dll", CharSet = CharSet.Ansi, SetLastError = true)] private static extern ushort write_buffer(ushort deviceNumber, ushort wordCount, UInt32 bufferLink, IntPtr buffer) In C# i have a Dictionary of messages that i would like to pass to this function. The Dictionary looks like this: Dictionary<string, List<ushort>> msgs I am a bit confused how to make a make a proper call to pass msgs as the buffer. deviceNumber is 2, wordCount is 32, and buffLink is 0. So i know the call should look something like this write_buffer(2,32,0, msgs[key]); Obviously i am getting an invalid argument for the IntPtr. What is the proper way to make this call?

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• Explicitly persist states in Workflow 4.0 rather than everything.

  - by jlafay

  I have ran into an issue with my SQL instance store attached to a WorkflowApplication that is running. When I exit my application I'm calling an Unload() on the WF app to persist it. I didn't think about it during design time, but it does makes sense, it's persisting an arg that was passed in to the WorkflowApplication constructor when instanced. When the application runs, everything in the workflow works as expected. When I call Unload() I get an unhandled exception that states that the arg is not serializable and needs [DataContractAttribute]. What's passed into the workflow is my applications custom logger object that I wrote so that the WF can log to disk in a uniform way that I prefer. How do I prevent the workflow app from persisting this one argument and persist everything else? I'm sure something can be done with extensions but I'm having a hard time finding info on them or finding persistence examples for my scenario.

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• TFS merging for users that are used to VSS

  - by JacksonD

  I just migrated a team of 7 developers from VSS to TFS. I migrated all of their code into a DEV folder which I then branched into a QA folder (which I branched into a PROD folder). The developers usually don't work on the same files, but there are some shared utility classes. All of the code is for a large ASP.NET web site. When the developers are ready to merge from DEV to QA, they only want to merge their changes. For example, let's say that Developer1 has been working on a project for the last 3 months and he's ready to merge all of his code into QA. However, Developer2 has been working on a different project for the last 2 months which is not ready to be merged. Developer1 and Developer2's changes are not in any way dependent on each other, but they are not separated into different folder structures and they each regularly do a get latest. There doesn't seem to be a way for developer1 to only merge his changes without also merging all of developer2's changes. Currently, developer1 is going through the Pending Changes window and 'Undoing Pending Changes' for all of Developer2's changes, but this is time consuming. They could merge each file individually, but this is also time consuming. Is there an easier way? I am going to have a coronary if I hear one more person explain how much easier it was to work in VSS.

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• JavaScript eval() with `this`

  - by mojuba

  If I define a JavaScript code snippet in my HTML, like so: <div id=myElem onMyUpdate="alert('Update called for ' + this.id)">... then what is the most elegant way of evaluating it from within JavaScript with this properly assigned? What I came up with so far is something like this: if (elem.hasAttribute('onMyUpdate')) (function () { eval(elem.getAttribute('onMyUpdate')) }).call(elem); which looks terrible (to me), but works. Any better/more elegant alternatives? MDN says there used to be the second argument to eval() for doing just that but it's deprecated now; MDN then suggests to use operator with() instead, which, if you follow the link provided, turns out to be made deprecated by the latest standard. Dead end, in other words. (As a side note, StackOverflow ignores the word this in search terms and thus it may miss relevant answers - is there a way of telling it not to?) Edit: I forgot to mention: no jQuery please, just vanilla JavaScript

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• WIX: How to register an Application to a URL Protocol?

  - by NOP slider

  In WIX 3.5 you can register file types easily: <ProgId Id="MyApp.File" Description="MyApp File" Icon="MyAppEXE" IconIndex="0"> <Extension Id="ext" ContentType="application/x-myapp-file"> <Verb Id="open" Command="&amp;Open" TargetFile="MyAppEXE" Argument="&quot;%1&quot;"/> </Extension> </ProgId> What if I want to register an URL protocol, as specified here? Obviously, it has no extension so where would I put the Verb tag? Or should I use another approach? Thanks.

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• Equivalent of object using literal notation

  - by brz dot net

  See following class: function availItem(xs, s, m, l, xl) { this.xs = xs; this.s = s; this.m = m; this.l = l; this.xl = xl; } How can I declare the above class using JSON? I think It should be in following manner but problem is to pass argument. var availItem = { xs : xs, s : s, m : m, l : l, xl : xl } I want to use both in same manner like var obj =new availItem(xs,s,b,l,xl);

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• How can unit testing make parameter validation redundant?

  - by Johann Gerell

  We have a convention to validate all parameters of constructors and public functions/methods. For mandatory parameters of reference type, we mainly check for non-null and that's the chief validation in constructors, where we set up mandatory dependencies of the type. The number one reason why we do this is to catch that error early and not get a null reference exception a few hours down the line without knowing where or when the faulty parameter was introduced. As we start transitioning to more and more TDD, some team members feel the validation is redundant. Uncle Bob, who is a vocal advocate of TDD, strongly advices against doing parameter validation. His main argument seems to be "I have a suite of unit tests that makes sure everything works". But I can for the life of it just not see in what way unit tests can prevent our developers from calling these methods with bad parameters in production code. Please, unit testers out there, if you could explain this to me in a rational way with concrete examples, I'd be more than happy to seize this parameter validation!

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• How to print size_t variable portably?

  - by ArunSaha

  I have a variable of type size_t, and I want to print it using printf(). What format specifier do I use to print it portably? In 32-bit machine, %u seems right. I compiled with g++ -g -W -Wall -Werror -ansi -pedantic, and there was no warning. But when I compile that code in 64-bit machine, it produces warning. size_t x = <something>; printf( "size = %u\n", x ); warning: format '%u' expects type 'unsigned int', but argument 2 has type 'long unsigned int' The warning goes away, as expected, if I change that to %lu. The question is, how can I write the code, so that it compiles warning free on both 32- and 64- bit machines? Edit: I guess one answer might be to "cast" the variable into an unsigned long, and print using %lu. That would work in both cases. I am looking if there is any other idea. (C, C++)

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• rake test and test_structure.sql

  - by korinthe

  First of all, I have to run "rake RAILS_ENV=test ..." to get the test suites to hit my test DB. Annoying but ok to live with. However when I do so, I get a long stream of errors like so: > rake RAILS_ENV=test -I test test:units psql:/path/to/project/db/test_structure.sql:33: ERROR: function "armor" already exists with same argument types [and many more] It looks like some DB definitions are getting unnecessarily reloaded. I can't find any mention of this on Google, so I was wondering whether others have seen this? I am using a PostgreSQL database with the following in my environment.rb: config.active_record.schema_format = :sql and using Rails 2.3.5 with rake 0.8.7.

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• Handling the distinction between undefined- and null-parameters in JavaScript

  - by Jakob

  I know very well that null and undefined are distinct in JavaScript. However, I can't seem to decide whether or not use that fact when my own functions are passed one of those as its argument. Or, expressed in a different way, should myFoo(undefined) return the same thing as myFoo(null) or is everything fine if it doesn't? Or, in yet another case, since myBar(1, 2, 3) is the same thing as myBar(1, 2, 3, undefined, undefined), should myBar(1, 2, 3, null, null) return the same thing as myBar(1, 2, 3)? I feel that there's potential for confusion in both cases and that a library should probably follow a convention when handling null/undefined. I'm not really asking for personal opinions (so please express those as comments rather than answers). I'm asking if anyone knows if there is a best practice that one should stick to when it comes to handling this distinction. References to external sources are very welcome!

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• Limiting a search to records from last_request_at...

  - by bgadoci

  I am trying to figure out how to display a count for records that have been created in a table since the last_request_at of a user. In my view I am counting the notes of a question with the following code: <% unless @questions.empty? %> <% @questions.each do |question| %> <%= h(question.notes.count) %> end end This is happening in the /views/users/show.html.erb file. Instead of counting all the notes for the question, I would only like to count the notes that have been created since the users last_request_at datetime. I don't neccessarily want to scope notes to display this 'new notes' count application wide, just simply in this one instance. To accomplish I am assuming I need to create a variable in the User#show action and call it in the view but not really sure how to do that. Other information you may need: class Note < ActiveRecord::Base belongs_to :user belongs_to :question end class Question < ActiveRecord::Base has_many :notes, :dependent => :destroy belongs_to :user end

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• C++ toLowerCase Function won't work - Access violation

  - by misaizdaleka

  Hi, I have a simple function which takes an array of characters as an argument, and converts all the characters to lower case. However, I get a weird access violation error. Here's the code: void toLower(char *rec) { int i=0; while (rec[i]!='\0') { if (rec[i]>='A' && rec[i]<='Z') rec[i]='a'+rec[i]-'A'; //this is where I get an error - assigning the //the value to rec[i] is the problem i++; } } Can you tell me what's my mistake? Thanks

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• How to print a variable in reversed byte order in Perl?

  - by jth

  Hi, I'am trying to convert the variable $num into its reverse byte order and print it out. This is what I have done so far: my $num=0x5514ddb7; my $s=pack('I!',$num); print "$s\n"; He prints it out as some non-printable characters and in a hex editor it looks right, but how can I get it readable on the console? Already tried print sprintf("%#x\n",$s); but he complains about an non-numeric argument, so I think pack returns a string. Any ideas how can I print out `0xb7dd1455 on the console, based on $num?

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• C++ wrapper for C library

  - by Maximilien

  Hi, Recently I found a C library that I want to use in my C++ project. This code is configured with global variables and writes it's output to memory pointed by static pointers. When I execute my project I would like 2 instances of the C program to run: one with configuration A and one with configuration B. I can't afford to run my program twice, so I think there are 2 options: Make a C++ wrapper: The problem here is that the wrapper-class should contain all global/static variables the C library has. Since the functions in the C library use those variables I will have to create very big argument-lists for those functions. Copy-paste the C library: Here I'll have to adapt the name of every function and every variable inside the C library. Which one is the fastest solution? Are there other possibilities to run 2 instances of the same C source? Thanks, Max

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• Java: How to get Unicode name of a character (or its type category)?

  - by java.is.for.desktop

  Hello, everyone! The Character class in Java defines methods which check a given char argument for equality with certain Unicode chars or for belonging to some type category. These chars and type categories are named. As stated in given javadoc, examples for named chars are HORIZONTAL TABULATION, FORM FEED, ...; example for named type categories are SPACE_SEPARATOR, PARAGRAPH_SEPARATOR, ... However, being byte or int values instead of enums, the name of these types are "hidden" at runtime. So, is there a possibility to get characters' and/or type categories' names at runtime?

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• C++ new line not translating

  - by m3n

  First off, I'm a complete beginner at C++. I'm coding something using an API, and would like to pass text containing new lines to it, and have it print out the new lines at the other end. If I hardcode whatever I want it to print out, like so printInApp("Hello\nWorld"); it does come out as separate lines in the other end, but if I retrieve the text from the app using a method that returns a const char then pass it straight to printInApp (which takes const char as argument), it comes out as a single line. Why's this and how would I go about to fix it?

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