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• Opinions regarding C++ programming practice

  - by Sagar

  I have a program that I am writing, not too big. Apart from the main function, it has about 15 other functions that called for various tasks at various times. The code works just fine all in one file, and as it is right now. However, I was wondering if anyone had any advice on whether it is smarter/more efficient/better programming to put those functions in a separate file different from where main is, or whether it even matters at all. If yes, why? If no, why not? I am not new at C++, but definitely not an expert either, so if you think this question is stupid, feel free to tell me so. Thanks for your time!

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• Efficient way to maintain a sorted list of access counts in Python

  - by David

  Let's say I have a list of objects. (All together now: "I have a list of objects.") In the web application I'm writing, each time a request comes in, I pick out up to one of these objects according to unspecified criteria and use it to handle the request. Basically like this: def handle_request(req): for h in handlers: if h.handles(req): return h return None Assuming the order of the objects in the list is unimportant, I can cut down on unnecessary iterations by keeping the list sorted such that the most frequently used (or perhaps most recently used) objects are at the front. I know this isn't something to be concerned about - it'll make only a miniscule, undetectable difference in the app's execution time - but debugging the rest of the code is driving me crazy and I need a distraction :) so I'm asking out of curiosity: what is the most efficient way to maintain the list in sorted order, descending, by the number of times each handler is chosen? The obvious solution is to make handlers a list of (count, handler) pairs, and each time a handler is chosen, increment the count and resort the list. def handle_request(req): for h in handlers[:]: if h[1].handles(req): h[0] += 1 handlers.sort(reverse=True) return h[1] return None But since there's only ever going to be at most one element out of order, and I know which one it is, it seems like some sort of optimization should be possible. Is there something in the standard library, perhaps, that is especially well-suited to this task? Or some other data structure? (Even if it's not implemented in Python) Or should/could I be doing something completely different?

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• C++ inheritance and member function pointers

  - by smh

  In C++, can member function pointers be used to point to derived (or even base) class members? EDIT: Perhaps an example will help. Suppose we have a hierarchy of three classes X, Y, Z in order of inheritance. Y therefore has a base class X and a derived class Z. Now we can define a member function pointer p for class Y. This is written as: void (Y::*p)(); (For simplicity, I'll assume we're only interested in functions with the signature void f() ) This pointer p can now be used to point to member functions of class Y. This question (two questions, really) is then: Can p be used to point to a function in the derived class Z? Can p be used to point to a function in the base class X?

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• Why is sqrt() not a method on Float?

  - by KaptajnKold

  In Ruby everything is an object. That's why I don't understand why we have the Math module. It seems to me that most (all?) of the functions in the Math module should have been methods on the numeric types like Integer, Float and so on. E.g. instead of Math.sqrt(5) it would make more sense to have 5.sqrt The same goes for sin, cos, tan, log10 and so on. Does anyone know why all these functions ended up in the Math module?

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• Function Composition in C++

  - by Channel72

  There are a lot of impressive Boost libraries such as Boost.Lambda or Boost.Phoenix which go a long way towards making C++ into a truly functional language. But is there a straightforward way to create a composite function from any 2 or more arbitrary functions or functors? If I have: int f(int x) and int g(int x), I want to do something like f . g which would statically generate a new function object equivalent to f(g(x)). This seems to be possible through various techniques, such as those discussed here. Certainly, you can chain calls to boost::lambda::bind to create a composite functor. But is there anything in Boost which easily allows you to take any 2 or more functions or function objects and combine them to create a single composite functor, similar to how you would do it in a language like Haskell?

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• Is there any performance issue using Row_Number to implement table paging in Sql Server 2008?

  - by majkinetor

  I want to implement table paging using this method: SET @PageNum = 2; SET @PageSize = 10; WITH OrdersRN AS ( SELECT ROW_NUMBER() OVER(ORDER BY OrderDate, OrderID) AS RowNum ,* FROM dbo.Orders ) SELECT * FROM OrdersRN WHERE RowNum BETWEEN (@PageNum - 1) * @PageSize + 1 AND @PageNum * @PageSize ORDER BY OrderDate ,OrderID; Is there anything I should be aware of ? Table has millions of records. Thx. EDIT: After using suggested MAXROWS method for some time (which works really really fast) I had to switch back to ROW_NUMBER method because of its greater flexibility. I am also very happy about its speed so far (I am working with View having more then 1M records with 10 columns). To use any kind of query I use following modification: PROCEDURE [dbo].[PageSelect] ( @Sql nvarchar(512), @OrderBy nvarchar(128) = 'Id', @PageNum int = 1, @PageSize int = 0 ) AS BEGIN SET NOCOUNT ON Declare @tsql as nvarchar(1024) Declare @i int, @j int if (@PageSize <= 0) OR (@PageSize > 10000) SET @PageSize = 10000 -- never return more then 10K records SET @i = (@PageNum - 1) * @PageSize + 1 SET @j = @PageNum * @PageSize SET @tsql = 'WITH MyTableOrViewRN AS ( SELECT ROW_NUMBER() OVER(ORDER BY ' + @OrderBy + ') AS RowNum ,* FROM MyTableOrView WHERE ' + @Sql + ' ) SELECT * FROM MyTableOrViewRN WHERE RowNum BETWEEN ' + CAST(@i as varchar) + ' AND ' + cast(@j as varchar) exec(@tsql) END If you use this procedure make sure u prevented sql injection.

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• c++ exercise question

  - by Djecua

  in need of help on a C++ program that will help a deli owner help her customers.Prompt the user for the number of bagels.if then calculate the customers payment two ways. first it finds the price of the smallest multiple of 13 bagels that is closet to the customer's order. it then calculates the price of the customer's order so that the customer's payment is the smallest amount possible with the customer getting the exact number of bagels ordered. if the first method is the smallest amount the program outputs the number of bagels the customer will receive along with the dollar amount owed and the dollar amount saved. otherwise just print the number of bagels received the dollar amount owed $ 3.80 for a dozen bagels (13 bagels) half a dozen(6 bagels) sing bagel cost $.50 owner of the deli is a honest merchant, customers always get the best price on an order, even if they get more bagels than ordered, for example a customer that orders 10 bagels would pay $ 4.60 (2.60 for a half dozen bagels plus $2.00 for 4 single bagels.merchant gives her customer 13 bagels saving the customer $0.80 If someone can example to me how would i design to give customer extra bagels and how to calculate cost.

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• Django, javascript and code ruse problem

  - by dragoon

  Hi, I have some sort of a design problem with my Django AJAX application. I have a template where I initialize js variable from django context variable like so: var test = "{{ test }}"; This variable is than used in a number of js functions that are needed for interface to work properly. So now I'm trying to reuse some content from this page in another page that loads it dynamically on some user interaction using jQuery.load(..), and I don't see any way how I can initialize that variable, so js functions don't work now. Is there any solution for this or may be I'm doing it wrong? Thanks.

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• Calling a function that has 'Activity' as an argument.

  - by Andrew

  I have stripped down my functions for simplicity: public static int countLines(String fileName, Activity activity) throws IOException { BufferedReader in = new BufferedReader(new InputStreamReader(activity.getAssets().open(fileName))); return 3; } I am calling it from here: private CharSequence RandomRead() throws IOException { int numberLines = countLines("data.txt", ??????); return "Success" } In the call to countLines("data.txt", ??????), what do I put as the argument for the Activity? I've Googled all night and I can find no examples of an actual call to a function where Activity is an argument. (Lots of examples actually using 'activity', but no calls to the example functions). Thanks!

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• Adding the text area input to a list with jquery

  - by amylynn83

  I am making a shopping list app. When an item is added to the text input, it should be converted into a list item with a class of "tile" and added to the beginning of the list with a class of ".shopping_item_list". Here is my HTML: <section> <h1 class="outline">Shopping List Items</h1> <ul class="shopping_item_list"> <li class="tile">Flowers<span class="delete">Delete</span></li> </ul> </section> My jQuery: $("input[name='shopping_item']").change(function() { var item = $(this).val(); $("<li class='tile'>+ item +</li>").prependTo(".shopping_item_list"); $(".tile").removeClass("middle"); $(".shopping_item_list li:nth-child(3n+2)").addClass("middle"); }); This isn't working, and I can't figure out why. I'm new to jQuery. Also, I need to add the "delete" span to the list item and am not sure how. Thanks for any help you can offer! Edited to add: Thanks to the feedback here, I was able to make it work with: $("input[name='shopping_item']").change(function() { var item = $(this).val(); $("<li class='tile'>" + item + "<span class='delete'>Delete</span>" + " </li>").prependTo(".shopping_item_list"); $(".tile").removeClass("middle"); $(".shopping_item_list li:nth-child(3n+2)").addClass("middle"); }); However, in my jquery, I have functions for the classes "tile" and "delete" that are not working for newly added items. // hide delete button $(".delete").hide(); // delete square $(".tile").hover(function() { $(this).find(".delete").toggle(); }); $(".tile").on("click", ".delete", function() { $(this).closest("li.tile").remove(); $(".tile").removeClass("middle"); $(".shopping_item_list li:nth-child(3n+2)").addClass("middle"); }); // cross off list $(".tile").click(function() { $(this).toggleClass("deleteAction"); }); The new items, which have these classes applied aren't using these functions at all. Do I need to add the functions below the add item? Does the order in which they appear in my js file matter? Do I need to add some kind of function?

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• code folding in Visual Studio for F#

  - by Yin Zhu

  I find that I tend to write long source files in F#. Some open source projects in F# also have long source files, e.g. FPersec and F# for excel. So it would be very helpful if code folding (even very limited support) is available in VS for F#. E.g. in a module, we can fold out functions that are stable, only leave functions that are subject to change unfold. Is this feature easy to be supported, e.g. by a third party vendor?

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• Perl: How do I extract certain bits from a byte and then covert these bits to a hex value?

  - by Siegfried Hepp

  I need to extract certain bits of a byte and covert the extract bits back to a hex value. Example (the value of the byte is 0xD2) : 76543210 bit position 11010010 is 0xD2 Bit 0-3 defines the channel which is 0010b is 0x2 Bit 4-5 defines the controller which is 01b is 0x1 Bit 6-7 defines the port which is 11b is 0x3 I somehow need to get from the byte is 0xD2 to channel is 0x2, controller is 0x1, port is 0x3 I googled allot and found the functions pack/unpack, vec and sprintf. But I'm scratching by head how to use the functions to achieve this. Any idea how to achieve this in Perl ?

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• how to set windows 7 resolution to 16:9 in virtualbox running in ubuntu 12.04 as a host?

  - by Gabriele

  I have installed Virtualbox in Ubuntu 12.04, and I created a virtual guest with Windows 7 64bit. Guest additions were also installed. It works fine, but I can't set the resolution to anything higher than 1600 x 1200, whereas my screen is 1920x1080. Here's my system specifications: Intel(R) Core(TM) i7-3632QM CPU @ 2.20GHz AMD Radeon 7650 VGA 8 Gb RAM DDR3 Moreover, if I try to enhable 3D acceleration in the settings of my guest, when I expand to full screen it aborts... Thanks in advance Gabriele

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• Seperate compilation in C++

  - by Pat Murray

  Suppose you are creating a class with multiple .cpp files (which each contain the implementation of a member function) and have the class' declaration in a .h file. Also, each .cpp file includes the .h file via the include directive. I was told that if you change the implementation of any of the member functions (.cpp files) that you will have to recompile every .cpp file in order to run the program. That is, if I had 5 member functions (each implemented in a .cpp file) and I changed the implementation of 1 of the .cpp files I would have to compile the 1 .cpp file I changed AND the 4 other .cpp files I didn't change in order to correctly run my program. My question, if the previous statement is true, is why is the statement is true? Any insight on this concept would be helpful.

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• Cross-reference of computers having virtualization technology [closed]

  - by msorens

  When considering obtaining a new computer one of my prerequisites is the ability to load Windows 8 in a virtual machine (using VirtualBox). A prerequisite for that is that the host computer have virtualization technology. I located an Intel cross reference of chips having virtualization technology but I am trying to find a "higher level" cross reference between computer models and virtualization technology availability, skipping the extra step of having to first look up what CPU chip is in a machine, then cross-referencing that on Intel's list.

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• Parsing a comma-separated list

  - by alex

  I have a comma-separated list of values, for example: strins s = "param1=true;param2=4;param3=2.0f;param4=sometext;"; I need a functions: public bool ExtractBool(string parameterName, string @params); public int ExtractInt(string parameterName, string @params); public float ExtractFloat(string parameterName, string @params); public string ExtractString(string parameterName, string @params); Is there a special functions in .net that can help me with csl ? PS: parameter names are equal within a list.

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• How To Refactor If-else Code Segment?

  - by LostInLib

  I'm developing win8(metro style) application with Html5-js-jquery. I have this code segment; GetBoutiqueDetail: function (boutiqueId, options) { if (IsUserLogin()) { //different job A } else { ShowLoginPanel(undefined); } }, GetProductDetail: function (boutiqueId, productId, options) { if (IsUserLogin()) { //different job B } else { ShowLoginPanel(undefined); } }, AddBasket: function (productId, productVariantId, quantity, options) { if (IsUserLogin()) { //different job C } else { ShowLoginPanel(undefined); } },.... .And ~20 functions should check if user login or not. I should call functions like similar to "Library.GetBoutiqueDetail();" So my question is simple, how can I refactor that code to remove these if-else sections ?

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• interactive lua prompt in opengl application

  - by anon

  Okay, so when I run lua, I get something like: lua Lua 5.1.4 Copyright (C) 1994-2008 Lua.org, PUC-Rio > Now, I want a prompt like this, 1) in a GUI application I've written. My GUI application can provide functions like: get_input_from_screen(); and write_this_crap_out_to_screen(); and more functions I can write as necessary I also know how to embed a lua interpreter in my C++ code (short tutorial on the web) What I don't know .. is how to connect the input/output of a lua interpreter with my GUI stuff. Any help/links apreciated. Thanks!

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• CGridView Filter doesn't work when you add more than one button to the CButtonColumn

  - by era

  I have a CGridView as follows, <?php $this->widget('zii.widgets.grid.CGridView', array( 'id'=>'order-grid', 'dataProvider'=>$model->search(), 'filter'=>$model, 'columns'=>array( 'order_id', //'ordered_datetime', 'customer_id', 'status', //'delivery_address', array( 'class'=>'CButtonColumn', 'template' => '{view} {rollback} {receive}{pack} {dispatch}{delivered}', 'htmlOptions'=>array('width'=>'250px'), 'buttons'=>array( 'receive'=>array( 'id'=>'receive', 'name'=>'receive', 'url'=>'$this->grid->controller->createUrl("/shop/order/admin&received=true", array("id"=>$data->order_id,"asDialog"=>1,"gridId"=>$this->grid->id))', 'type'=>'submit', 'imageUrl'=>'/mdg/images/Receive1.png', 'visible'=>'($data->status=="pending")?true:false;' ), 'rollback'=>array( 'id'=>'rollback', 'name'=>'rollback', 'url'=>'$this->grid->controller->createUrl("/shop/order/admin&rollback=true", array("id"=>$data->order_id,"asDialog"=>1,"gridId"=>$this->grid->id))', 'imageUrl'=>'/mdg/images/rollback.jpg', 'visible'=>'($data->status=="pending")?false:true;' ), ), ), ), )); ? And When I add one more button to the buttons array, the filter doesnt work. Any Idea why that is? It's Great if anyone can help.. Thanks!

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• Get the first and last posts in a thread

  - by Grampa

  I am trying to code a forum website and I want to display a list of threads. Each thread should be accompanied by info about the first post (the "head" of the thread) as well as the last. My current database structure is the following: threads table: id - int, PK, not NULL, auto-increment name - varchar(255) posts table: id - int, PK, not NULL, auto-increment thread_id - FK for threads The tables have other fields as well, but they are not relevant for the query. I am interested in querying threads and somehow JOINing with posts so that I obtain both the first and last post for each thread in a single query (with no subqueries). So far I am able to do it using multiple queries, and I have defined the first post as being: SELECT * FROM threads t LEFT JOIN posts p ON t.id = p.thread_id ORDER BY p.id LIMIT 0, 1 The last post is pretty much the same except for ORDER BY id DESC. Now, I could select multiple threads with their first or last posts, by doing: SELECT * FROM threads t LEFT JOIN posts p ON t.id = p.thread_id ORDER BY p.id GROUP BY t.id But of course I can't get both at once, since I would need to sort both ASC and DESC at the same time. What is the solution here? Is it even possible to use a single query? Is there any way I could change the structure of my tables to facilitate this? If this is not doable, then what tips could you give me to improve the query performance in this particular situation?

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• Running exec inside function

  - by None

  How can you use the python exec keyword inside functions?

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• Ruby integer to string key

  - by Gene

  A system I'm building needs to convert non-negative Ruby integers into shortest-possible UTF-8 string values. The only requirement on the strings is that their lexicographic order be identical to the natural order on integers. What's the best Ruby way to do this? We can assume the integers are 32 bits and the sign bit is 0. This is successful: (i >> 24).chr + ((i >> 16) & 0xff).chr + ((i >> 8) & 0xff).chr + (i & 0xff).chr But it appears to be 1) garbage-intense and 2) ugly. I've also looked at pack solutions, but these don't seem portable due to byte order. FWIW, the application is Redis hash field names. Building keys may be a performance bottleneck, but probably not. This question is mostly about the "Ruby way".

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• How to extract a single function from a source file

  - by Adam Matan

  Hi, I'm working on a small academic research about extremely long and complicated functions in the Linux kernel. I'm trying to figure out if there is a good reason to write 600 or 800 lines-long functions. For that purpose, I would like to find a tool that can extract a function from a .c file, so I can run some automated tests on the function. For example, If I have the function cifs_parse_mount_options() within the file connect.c, I'm seeking a solution that would roughly work like: extract /fs/cifs/connect.c cifs_parse_mount_options and return the 523 lines of code(!) of the function, from the opening braces to the closing braces. Of course, any way of manipulating existing software packages like gcc to do that, would be most helpful too. Thanks, Udi EDIT : The answers to Regex to pull out C function prototype declarations? convinced me that matching function declaration by regex is far from trivial.

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• jQuery, Forms, Browser Refreshes

  - by Eric Cope

  I have a large form with some fields values dependent on previous elements. I use jquery's .trigger event to trigger the dependent field's update functions. When I refresh the page (click reload or click back), the previous values selected are still there, but the dependent fields are not reflecting the other element's values. How can I trigger the update functions upon refresh? I saw a way to prevent the browser from using the form's cached values. I'd rather use the cached values and update the elements dependent on the elements with cached values.

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• Missing something with Reader monad - passing the damn thing around everywhere

  - by Richard Huxton

  Learning Haskell, managing syntax, have a rough grasp of what monads etc are about but I'm clearly missing something. In main I can read my config file, and supply it as runReader (somefunc) myEnv just fine. But somefunc doesn't need access to the myEnv the reader supplies, nor do the next couple in the chain. The function that needs something from myEnv is a tiny leaf function. So - how do I get access to the environment in a function without tagging all the intervening functions as (Reader Env)? That can't be right because otherwise you'd just pass myEnv around in the first place. And passing unused parameters through multiple levels of functions is just ugly (isn't it?). There are plenty of examples I can find on the net but they all seem to have only one level between runReader and accessing the environment.

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