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  • Serializing persistent/functional data structures

    - by Rob
    Persistent data structures depend on the sharing of structure for efficiency. For an example, see here. How can I preserve the structure sharing when I serialize the data structures and write them to a file or database? If I just naively traverse the datastructures, I'll store the correct values, but I'll lose the structure sharing. I'd like to be able to save data-structures with shared components to a file, restore them, and still have most of the structure shared in the restored data.

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  • The program fails to display `cout` when it is run

    - by Jeff - FL
    Hello, I justed started a C++ course & I wrote, compiled, debugged & ran my first program: // This program calculates how much a little league team spent last year to purchase new baseballs. #include <iostream> using namespace std; int baseballs; int cost; int total; int main() { baseballs, cost, total; // Get the number of baseballs were purchased. cout << "How many baseballs were purchased? "; cin >> baseballs; // Get the cost of baseballs purchased. cout << "What was the cost of each baseball purchased? "; cin >> cost; // Calculate the total. total = baseballs * cost; // Display the total. cout << "The total amount spent $" << total << endl; return 0; } The only probelm that I encountered was that when I ran the program it failed to display the total amount spent (cout). Could someone please explain why? Thanks Jeff H - Sarasota, FL

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  • Writing an auto-memoizer in Scheme. Help with macro and a wrapper.

    - by kunjaan
    I am facing a couple of problems while writing an auto-memoizer in Scheme. I have a working memoizer function, which creats a hash table and checks if the value is already computed. If it has been computed before then it returns the value else it calls the function. (define (memoizer fun) (let ((a-table (make-hash))) (?(n) (define false-if-fail (?() #f)) (let ((return-val (hash-ref a-table n false-if-fail))) (if return-val return-val (begin (hash-set! a-table n (fun n)) (hash-ref a-table n))))))) Now I want to create a memoize-wrapper function like this: (define (memoize-wrapper function) (set! function (memoizer function))) And hopefully create a macro called def-memo which defines the function with the memoize-wrapper. eg. the macro could expand to (memoizer (define function-name arguments body ...) or something like that. So that I should be able to do : (def-memo (factorial n) (cond ((= n 1) 1) (else (* n (factorial (- n 1)))))) which should create a memoized version of the factorial instead of the normal slow one. My problem is that the The memoize-wrapper is not working properly, it doesnt call the memoized function but the original function. I have no idea how to write a define inside of the macro. How do I make sure that I can get variable lenght arguments and variable length body? How do I then define the function and wrap it around with the memoizer? Thanks a lot.

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  • Unmanaged Struct Instance in Managed Class

    - by HeHasMoments
    Hi, I've got a fairly specific problem i've been struggling with for a couple of days. I'm using a native C++, one of the methods takes a ptr to a struct containing fixed size char arrays. e.g. struct userData { char data1[10]; char data2[10]; }; method: short AddItem(long id, userData* data); I'm trying to call to call this from Managed VC++ but I need to have an instance of userData I can keep hold of in my managed class. Can anyone help with how to achieve this? Thanks

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  • functional, bind1st and mem_fun

    - by Neil G
    Why won't this compile? #include <functional> #include <boost/function.hpp> class A { A() { typedef boost::function<void ()> FunctionCall; FunctionCall f = std::bind1st(std::mem_fun(&A::process), this); } void process() {} }; Errors: In file included from /opt/local/include/gcc44/c++/bits/stl_function.h:712, from /opt/local/include/gcc44/c++/functional:50, from a.cc:1: /opt/local/include/gcc44/c++/backward/binders.h: In instantiation of 'std::binder1st<std::mem_fun_t<void, A> >': a.cc:7: instantiated from here /opt/local/include/gcc44/c++/backward/binders.h:100: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:103: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:106: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:111: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:117: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h: In function 'std::binder1st<_Operation> std::bind1st(const _Operation&, const _Tp&) [with _Operation = std::mem_fun_t<void, A>, _Tp = A*]': a.cc:7: instantiated from here /opt/local/include/gcc44/c++/backward/binders.h:126: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' In file included from /opt/local/include/boost/function/detail/maybe_include.hpp:13, from /opt/local/include/boost/function/detail/function_iterate.hpp:14, from /opt/local/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:47, from /opt/local/include/boost/function.hpp:64, from a.cc:2: /opt/local/include/boost/function/function_template.hpp: In static member function 'static void boost::detail::function::void_function_obj_invoker0<FunctionObj, R>::invoke(boost::detail::function::function_buffer&) [with FunctionObj = std::binder1st<std::mem_fun_t<void, A> >, R = void]': /opt/local/include/boost/function/function_template.hpp:913: instantiated from 'void boost::function0<R>::assign_to(Functor) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' /opt/local/include/boost/function/function_template.hpp:722: instantiated from 'boost::function0<R>::function0(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' /opt/local/include/boost/function/function_template.hpp:1064: instantiated from 'boost::function<R()>::function(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' a.cc:7: instantiated from here /opt/local/include/boost/function/function_template.hpp:153: error: no match for call to '(std::binder1st<std::mem_fun_t<void, A> >) ()'

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  • How to implement a list fold in Java

    - by Peter Kofler
    I have a List and want to reduce it to a single value (functional programing term "fold", Ruby term "inject"), like Arrays.asList("a", "b", "c") ... fold ... "a,b,c" As I am infected with functional programing ideas (Scala), I am looking for an easier/shorter way to code it than sb = new StringBuilder for ... { append ... } sb.toString

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  • Use of unassigned local variable 'xxx'

    - by Tomislav
    I'm writing a database importer from our competitors to ours database:) I have a code generator which create Methods form import to our database like public void Test_Import_Customer_1() // variables string conn; string sqlSelect; string sqlInsert; int extID; string name; string name2; DateTime date_inserted; sqlSelect="select id,name,date_inserted from table_competitors_1"; oledbreader reader = new GetOledbRader(sqlString,conn); while (reader.read()) { name=left((string)myreader["name"],50); //limitation of my field date_inserted=myreader["date_inserted"]; sqlInsert=string.Format("insert into table(name,name2,date_inserted)values '{0}', '{1}', {2})",name,name2,date_inserted); //here is the problem name2 "Use of unassigned local variable" ExecuteSQL(sqlInsert) } As different companies database has different fields i can not set value to each variable and there is a big number of tables to go one variable to next. like sqlSelect_Company_1 = "select name,date_inserted from table_1"; sqlSelect_Company_2 = "select name,name2 from table_2"; is there a way to override the typing of each variable one by one with default values?

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  • Difference between var and Class class in object creation

    - by Divine
    Its a silly question, however shocked to see different behaviors. Learning a lot. Lets say I have two classes below Class A { public void Display() { } } Class B : A { public void Display() { } } Class C : B { public void Display() { } } Class Final { static void Main() { var c = new C(); // B c = new C(); //My doubt is, both of the above gives different results. May I know B c = new C() creates object of B or C? What I understood is, it creates object of B. Then why we say "new C()"? I agree with C c = new C(); But I thought, B b = new C(); creates object of B. Where we use this style? Only when utilizing runtime polymorphism? (Overriding methods)? } }

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  • Web-Application development startup advice

    - by rpr
    Dear programmers of StackOverflow, recently me and two of my friends from college started a software company. We are developing web-applications using GWT-Spring-Hibernate and other helper frameworks. In a couple of months, we managed to set up a stable back-end and produced some demo programs for CRM solutions. Our area of interest is CRM where we can combine the flexibility of our back-end with the slick looking GWT based GUIs. Unfortunately we live in a third world country (well, kind of two and a half :) and no one here gives our work enough credit, or really cares about the advantages of web-apps. We are stuck at the moment because our current clients do not want to pay that much money for just "putting their local app on the web". Since we can not find satisfying work here, we have decided to work online/international. I was wondering if you guys know a good freelance kind of sites where we can throw ourselves into the market.. Also a question from frustration, to those who are in the field or knowledgeable/interested about web based CRM, how much would you ask/pay for lets say a web app which will keep track of all the patients of a multi-branch clinic also allowing the patients to access to view their own records? Including tiered authorization, logging etc.. Many thanks in advance for your responses!

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  • Convert any Form Video into RGB24 Media

    - by BALA
    how to convert YUY2,YUV, RGB565 and More Video subtype into RGB24 Subtype Video in DirectShow + VC++ can u understand my question? I have a Upstream filter its output is in YUY2 Format but i need to convert it into RGB24 Format. Is there any inbuilt Filters in DirectShow or we have to convert it through my code. i have already added ColorSpaceConverter But it is not Connecting with Smart Tee Input Pin.

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  • Loading xml with encoding UTF 16 using XDocument

    - by Sangram
    Hi, I am trying to read the xml document using XDocument method . but i am getting an error when xml has <?xml version="1.0" encoding="utf-16"?> When i removed encoding manually.It works perfectly. I am getting error " There is no Unicode byte order mark. Cannot switch to Unicode. " i tried searching and i landed up here-- Why does C# XmlDocument.LoadXml(string) fail when an XML header is included? But could not solve my problem. My code : XDocument xdoc = XDocument.Load(path); Any suggestions ?? thank you.

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  • F# replace ref variable with something fun

    - by Stephen Swensen
    I have the following F# functions which makes use of a ref variable to seed and keep track of a running total, something tells me this isn't in the spirit of fp or even particular clear on its own. I'd like some direction on the clearest (possible fp, but if an imperative approach is clearer I'd be open to that) way to express this in F#. Note that selectItem implements a random weighted selection algorithm. type WeightedItem(id: int, weight: int) = member self.id = id member self.weight = weight let selectItem (items: WeightedItem list) (rand:System.Random) = let totalWeight = List.sumBy (fun (item: WeightedItem) -> item.weight) items let selection = rand.Next(totalWeight) + 1 let runningWeight = ref 0 List.find (fun (item: WeightedItem) -> runningWeight := !runningWeight + item.weight !runningWeight >= selection) items let items = [new WeightedItem(1,100); new WeightedItem(2,50); new WeightedItem(3,25)] let selection = selectItem items (new System.Random())

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  • VS 2008 Code Snippet Indentation

    - by Daniel
    In VS 2008, there are XML code snippets that seem to be pretty awesome :) However, it seems that the snippets we created do not indent properly. For example if we have the following code: { ... { ... { InsertSnippet here. We get something like: { ... { ... { FirstLineofSnippet SecondLineOfSnippet ThirdLineOfSnippet Is there any way to make it so that all lines keep the same indentation?

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  • Best way to implement nested loops in a view in asp.net mvc 2

    - by Junior Ewing
    Hi, Trying to implement some nested loops that are spitting out good old nested html table data. So the question is; What is the best way to loop through lists and nested lists in order to produce easily maintainable code. It can get quite narly quite fast when working with multiple nested tables or lists. Should I make use of a HTML helper, or make something with the ViewModel to simplify this? A requirement is if there are no children at a node there should be an empty row on that spot with some links for creation and into other parts of the system.

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  • Applying a function to a custom type in F#

    - by Frederik Wordenskjold
    On my journey to learning F#, I've run into a problem I cant solve. I have defined a custom type: type BinTree = | Node of int * BinTree * BinTree | Empty I have made a function which takes a tree, traverses it, and adds the elements it visits to a list, and returns it: let rec inOrder tree = seq{ match tree with | Node (data, left, right) -> yield! inOrder left yield data; yield! inOrder right | Empty -> () } |> Seq.to_list; Now I want to create a function, similar to this, which takes a tree and a function, traverses it and applies a function to each node, then returns the tree: mapInOrder : ('a -> 'b) -> 'a BinTree -> 'b BinTree This seems easy, and it probably is! But I'm not sure how to return the tree. I've tried this: let rec mapInOrder f tree = match tree with | Node(data, left, right) -> mapInOrder f left Node(f(data), left, right) mapInOrder f right | Empty -> () but this returns a unit. I havent worked with custom types before, so I'm probably missing something there!

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  • How can programmers get the quiet working environment they need? [closed]

    - by Richard
    We have an open plan office with all our programmers, web designers and client service team. Problem is my programmer team has to put up with dance music and wailing guitars all day due to the fact that designers and client services team think this makes the office a better environment. When I turn it off (by blocking the streaming of music on the router, he-he-he) they complain that its so quiet and dull. How do I explain to them that programmers need a calm quiet environment without coming across like a really annoying geek? Any other thoughts or ideas appreciated.

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  • Team Foundation Server 2010 Unmapping

    - by LeeHull
    Any idea how to unmap a project? Here is what I am trying to do, I changed the location of a source control, completely removed it from TFS source control.. but now it is showing up wanting to add it.. And the other issue I'm having is.. when I try to Map the new project, it is giving this error.. thing is, I've completely deleted the files off my local PC, and I'm wanting to map and get latest version from source control, but giving error trying to map, rather not change the location, how do I remove the old binding and the project, when it was already deleted using TfsDeleteProject.exe

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  • VS 2010 Web.config transformations for debugging

    - by Dirk
    I’m a fan of the new VS 2010 Web.config transformations. I use this feature for deployment purposes and wondered if it is possible to use them for debugging too. I think of using them in the IDE: I want to create different built configuration (with linked transformation configurations); choose one of them; start the web site in the IDE and debug the different configuration this way.

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