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  • Reversible numerical calculations in Prolog

    - by user8472
    While reading SICP I came across logic programming chapter 4.4. Then I started looking into the Prolog programming language and tried to understand some simple assignments in Prolog. I found that Prolog seems to have troubles with numerical calculations. Here is the computation of a factorial in standard Prolog: f(0, 1). f(A, B) :- A > 0, C is A-1, f(C, D), B is A*D. The issues I find is that I need to introduce two auxiliary variables (C and D), a new syntax (is) and that the problem is non-reversible (i.e., f(5,X) works as expected, but f(X,120) does not). Naively, I expect that at the very least C is A-1, f(C, D) above may be replaced by f(A-1,D), but even that does not work. My question is: Why do I need to do this extra "stuff" in numerical calculations but not in other queries? I do understand (and SICP is quite clear about it) that in general information on "what to do" is insufficient to answer the question of "how to do it". So the declarative knowledge in (at least some) math problems is insufficient to actually solve these problems. But that begs the next question: How does this extra "stuff" in Prolog help me to restrict the formulation to just those problems where "what to do" is sufficient to answer "how to do it"?

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  • Indices instead of pointers in STL containers?

    - by zvrba
    Due to specific requirements [*], I need a singly-linked list implementation that uses integer indices instead of pointers to link nodes. The indices are always interpreted with respect to a vector containing the list nodes. I thought I might achieve this by defining my own allocator, but looking into the gcc's implementation of , they explicitly use pointers for the link fields in the list nodes (i.e., they do not use the pointer type provided by the allocator): struct _List_node_base { _List_node_base* _M_next; ///< Self-explanatory _List_node_base* _M_prev; ///< Self-explanatory ... } (For this purpose, the allocator interface is also deficient in that it does not define a dereference function; "dereferencing" an integer index always needs a pointer to the underlying storage.) Do you know a library of STL-like data structures (i am mostly in need of singly- and doubly-linked list) that use indices (wrt. a base vector) instead of pointers to link nodes? [*] Saving space: the lists will contain many 32-bit integers. With two pointers per node (STL list is doubly-linked), the overhead is 200%, or 400% on 64-bit platform, not counting the overhead of the default allocator.

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  • Rtti data manipulation and consistency in Delphi 2010

    - by Coco
    Has anyone an idea, how I can make TValue using a reference to the original data? In my serialization project, I use (as suggested in XML-Serialization) a generic serializer which stores TValues in an internal tree-structure (similar to the MemberMap in the example). This member-tree should also be used to create a dynamic setup form and manipulate the data. My idea was to define a property for the Data: TDataModel <T> = class {...} private FData : TValue; function GetData : T; procedure SetData (Value : T); public property Data : T read GetData write SetData; end; The implementation of the GetData, SetData Methods: procedure TDataModel <T>.SetData (Value : T); begin FData := TValue.From <T> (Value); end; procedure TDataModel <T>.GetData : T; begin Result := FData.AsType <T>; end; Unfortunately, the TValue.From method always makes a copy of the original data. So whenever the application makes changes to the data, the DataModel is not updated and vice versa if I change my DataModel in a dynamic form, the original data is not affected. Sure I could always use the Data property before and after changing anything, but as I use lot of Rtti inside my DataModel, I do not realy want to do this anytime. Perhaps someone has a better suggestion?

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  • How can I have sub-elements of a complex/mixed type with unrestricted order and count?

    - by mbmcavoy
    I am working with XML where some elements will contain text with additional markup. This is similar to this example at W3Schools. However, I need the markup tags to be able to appear in any order and possibly more than once. To modify their example for illustration: <letter> Dear Mr.<name>John Smith</name>. Your order <orderid>1032</orderid> will be shipped on <shipdate>2001-07-13</shipdate>. Thank you, <name>Bob Adams</name> </letter> None of the options presented by W3Schools (on the page following the linked example) allow this XML due to the second <name> element. Their explanation of the "indicators" and my testing are consistent. <xs:sequence> - violates the element order <xs:choice> - more than one kind of element is used. <xs:all> - maxOccurs is restricted to "1". This seems like it should be basic, after all, XHTML allows such things. How do I define my schema to allow this?

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  • Circular dependency with generics

    - by devoured elysium
    I have defined the following interface: public interface IStateSpace<State, Action> where State : IState where Action : IAction<State, Action> // <-- this is the line that bothers me { void SetValueAt(State state, Action action); Action GetValueAt(State state); } Basically, an IStateSpace interface should be something like a chess board, and in each position of the chess board you have a set of possible movements to do. Those movements here are called IActions. I have defined this interface this way so I can accommodate for different implementations: I can then define concrete classes that implement 2D matrix, 3D matrix, graphs, etc. public interface IAction<State, Action> { IStateSpace<State, Action> StateSpace { get; } } An IAction, would be to move up(this is, if in (2, 2) move to (2, 1)), move down, etc. Now, I'll want that each action has access to a StateSpace so it can do some checking logic. Is this implementation correct? Or is this a bad case of a circular dependence? If yes, how to accomplish "the same" in a different way? Thanks

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  • Namespace constraint with generic class decleration

    - by SomeGuy
    Good afternoon people, I would like to know if (and if so how) it is possible to define a namespace as a constraint parameter in a generic class declaration. What I have is this: namespace MyProject.Models.Entities <-- Contains my classes to be persisted in db namespace MyProject.Tests.BaseTest <-- Obvious i think Now the decleration of my 'BaseTest' class looks like so; public class BaseTest<T> This BaseTest does little more (at the time of writing) than remove all entities that were added to the database during testing. So typically I will have a test class declared as: public class MyEntityRepositoryTest : BaseTest<MyEntity> What i would LIKE to do is something similar to the following: public class BaseTest<T> where T : <is of the MyProject.Models.Entities namespace> Now i am aware that it would be entirely possible to simply declare a 'BaseEntity' class from which all entities created within the MyProject.Models.Entities namespace will inherit from; public class BaseTest<T> where T : MyBaseEntity but...I dont actually need to, or want to. Plus I am using an ORM and mapping entities with inheritance, although possible, adds a layer of complexity that is not required. So, is it possible to constrain a generic class parameter to a namespace and not a specific type ? Thank you for your time.

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  • Flash compiler error 1061: Call to a possibly undefined method run... but run exists!

    - by Zane Geiger
    So I've been working on making a game in Processing but I think Flash would be a better way to get more people playing it, so I've decided to learn Flash. The problem is that I keep getting really stupid errors on incredibly simple things. For instance, I want to make a 'Block' object to use in a platform game. So I make a new .as file, name it Block.as, and define the Block class within it like so: package { public class Block { public function Block() { // constructor code } public function run() { } } } I don't want to add the code yet, I just want to ensure that this works. So in my main timeline code, I try to create an instance of the Block object and execute its run method: var block1:Block = new Block(); block1.run(); Every time it gives me this inane error: Scene 1, Layer 'Layer 1', Frame 1, Line 2 1061: Call to a possibly undefined method run through a reference with static type Block. What undefined method!? It's defined RIGHT THERE in Block.as. The class file is even in the same folder and everything. I'm getting REALLY annoyed at how poorly Flash handles such a ridiculously simple project. Does anyone know why Flash hates me?

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  • ISO C++ forbids declaration of 'QPushButton' with no type in QT Creator

    - by Mohit Deshpande
    I am running QT Creator on a Linux Ubuntu 9.10 machine. I just got started with QT Creator, and I was going through the tutorials when this error popped up while I was trying to build my project: "ISO C++ forbids declaration of 'QPushButton' with no type". This problem appears in my header file: #ifndef MAINWINDOW_H #define MAINWINDOW_H #include <QtGui/QWidget> namespace Ui { class MainWindow; } class MainWindow : public QWidget { Q_OBJECT public: MainWindow(QWidget *parent = 0); ~MainWindow(); public slots: void addContact(); void submitContact(); void cancel(); private: Ui::MainWindow *ui; QPushButton *addButton; QPushButton *submitButton; QPushButton *cancelButton; QLineEdit *nameLine; QTextEdit *addressText; QMap<QString, QString> contacts; QString oldName; QString oldAddress; }; #endif // MAINWINDOW_H

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  • Rails select box in form decides on create action in controller?

    - by dannymcc
    Hi Everyone? I am trying to add a select box to the base of my create form that decides if an action runs from the controller...if that makes any sense? Basically the application creates a project in FreeagentCentral whenever a new project is made: def create @company = Company.find(params[:kase][:company_id]) @kase = @company.kases.create!(params[:kase]) respond_to do |format| params[:send_to_freeagent] ? @kase.create_freeagent_project(current_user) #flash[:notice] = 'Case was successfully created.' flash[:notice] = fading_flash_message("Case was successfully created.", 5) format.html { redirect_to(@kase) } format.xml { render :xml => @kase, :status => :created, :location => @kase } end end and within my form I have: <%= check_box_tag :send_to_freeagent, 1 % Create project in Freeagent? What I would like to happen, is if the select box is checked the project is sent to Freeagent. If not, the case just gets created locally as normal but without the Freeagent data being sent. If I use the above code, I get an exception caught error: SyntaxError in KasesController#new controllers/kases_controller.rb:114: syntax error, unexpected '\n' Any idea what I am doing wrong, also is it possible to make the check boxes checked as default? Thanks, Danny

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  • mysterical error

    - by Görkem Buzcu
    i get "customer_service_simulator.exe stopped" error, but i dont know why? this is my c programming project and i have limited time left before deadline. the code is: #include <stdio.h> #include <stdlib.h> #include<time.h> #define FALSE 0 #define TRUE 1 /*A Node declaration to store a value, pointer to the next node and a priority value*/ struct Node { int priority; //arrival time int val; //type int wait_time; int departure_time; struct Node *next; }; Queue Record that will store the following: size: total number of elements stored in the list front: it shows the front node of the queue (front of the queue) rear: it shows the rare node of the queue (rear of the queue) availability: availabity of the teller struct QueueRecord { struct Node *front; struct Node *rear; int size; int availability; }; typedef struct Node *niyazi; typedef struct QueueRecord *Queue; Queue CreateQueue(int); void MakeEmptyQueue(Queue); void enqueue(Queue, int, int); int QueueSize(Queue); int FrontOfQueue(Queue); int RearOfQueue(Queue); niyazi dequeue(Queue); int IsFullQueue(Queue); int IsEmptyQueue(Queue); void DisplayQueue(Queue); void sorteddequeue(Queue); void sortedenqueue(Queue, int, int); void tellerzfunctionz(Queue *, Queue, int, int); int main() { int system_clock=0; Queue waitqueue; int exit, val, priority, customers, tellers, avg_serv_time, sim_time,counter; char command; waitqueue = CreateQueue(0); srand(time(NULL)); fflush(stdin); printf("Enter number of customers, number of tellers, average service time, simulation time\n:"); scanf("%d%c %d%c %d%c %d",&customers, &command,&tellers,&command,&avg_serv_time,&command,&sim_time); fflush(stdin); Queue tellerarray[tellers]; for(counter=0;counter<tellers;counter++){ tellerarray[counter]=CreateQueue(0); //burada teller sayisi kadar queue yaratiyorum } for(counter=0;counter<customers;counter++){ priority=1+(int)rand()%sim_time; //this will generate the arrival time sortedenqueue(waitqueue,1,priority); //here i put the customers in the waiting queue } tellerzfunctionz(tellerarray,waitqueue,tellers,customers); DisplayQueue(waitqueue); DisplayQueue(tellerarray[0]); DisplayQueue(tellerarray[1]); // waitqueue-> printf("\n\n"); system("PAUSE"); return 0; } /*This function initialises the queue*/ Queue CreateQueue(int maxElements) { Queue q; q = (struct QueueRecord *) malloc(sizeof(struct QueueRecord)); if (q == NULL) printf("Out of memory space\n"); else MakeEmptyQueue(q); return q; } /*This function sets the queue size to 0, and creates a dummy element and sets the front and rear point to this dummy element*/ void MakeEmptyQueue(Queue q) { q->size = 0; q->availability=0; q->front = (struct Node *) malloc(sizeof(struct Node)); if (q->front == NULL) printf("Out of memory space\n"); else{ q->front->next = NULL; q->rear = q->front; } } /*Shows if the queue is empty*/ int IsEmptyQueue(Queue q) { return (q->size == 0); } /*Returns the queue size*/ int QueueSize(Queue q) { return (q->size); } /*Shows the queue is full or not*/ int IsFullQueue(Queue q) { return FALSE; } /*Returns the value stored in the front of the queue*/ int FrontOfQueue(Queue q) { if (!IsEmptyQueue(q)) return q->front->next->val; else { printf("The queue is empty\n"); return -1; } } /*Returns the value stored in the rear of the queue*/ int RearOfQueue(Queue q) { if (!IsEmptyQueue(q)) return q->rear->val; else { printf("The queue is empty\n"); return -1; } } /*Displays the content of the queue*/ void DisplayQueue(Queue q) { struct Node *pos; pos=q->front->next; printf("Queue content:\n"); printf("-->Priority Value\n"); while (pos != NULL) { printf("--> %d\t %d\n", pos->priority, pos->val); pos = pos->next; } } void enqueue(Queue q, int element, int priority){ if(IsFullQueue(q)){ printf("Error queue is full"); } else{ q->rear->next=(struct Node *)malloc(sizeof(struct Node)); q->rear=q->rear->next; q->rear->next=NULL; q->rear->val=element; q->rear->priority=priority; q->size++; } } void sortedenqueue(Queue q, int val, int priority) { struct Node *insert,*temp; insert=(struct Node *)malloc(sizeof(struct Node)); insert->val=val; insert->priority=priority; temp=q->front; if(q->size==0){ enqueue(q, val, priority); } else{ while(temp->next!=NULL && temp->next->priority<insert->priority){ temp=temp->next; } //printf("%d",temp->priority); insert->next=temp->next; temp->next=insert; q->size++; if(insert->next==NULL){ q->rear=insert; } } } niyazi dequeue(Queue q) { niyazi del; niyazi deli; del=(niyazi)malloc(sizeof(struct Node)); deli=(niyazi)malloc(sizeof(struct Node)); if(IsEmptyQueue(q)){ printf("Queue is empty!"); return NULL; } else { del=q->front->next; q->front->next=del->next; deli->val=del->val; deli->priority=del->priority; free(del); q->size--; return deli; } } void sorteddequeue(Queue q) { struct Node *temp; struct Node *min; temp=q->front->next; min=q->front; int i; for(i=1;i<q->size;i++) { if(temp->next->priority<min->next->priority) { min=temp; } temp=temp->next; } temp=min->next; min->next=min->next->next; free(temp); if(min->next==NULL){ q->rear=min; } q->size--; } void tellerzfunctionz(Queue *a, Queue b, int c, int d){ int i; int value=0; int priority; niyazi temp; temp=(niyazi)malloc(sizeof(struct Node)); if(c==1){ for(i=0;i<d;i++){ temp=dequeue(b); sortedenqueue((*(a)),temp->val,temp->priority); } } else{ for(i=0;i<d;i++){ while(b->front->next->val==1){ if((*(a+value))->availability==1){ temp=dequeue(b); sortedenqueue((*(a+value)),temp->val,temp->priority); (*(a+value))->rear->val=2; } else{ value++; } } } } } //end of the program

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  • Visual C++ doesn't operator<< overload

    - by PierreBdR
    I have a vector class that I want to be able to input/output from a QTextStream object. The forward declaration of my vector class is: namespace util { template <size_t dim, typename T> class Vector; } I define the operator<< as: namespace util { template <size_t dim, typename T> QTextStream& operator<<(QTextStream& out, const util::Vector<dim,T>& vec) { ... } template <size_t dim, typename T> QTextStream& operator>>(QTextStream& in,util::Vector<dim,T>& vec) { .. } } However, if I ty to use these operators, Visual C++ returns this error: error C2678: binary '<<' : no operator found which takes a left-hand operand of type 'QTextStream' (or there is no acceptable conversion) A few things I tried: Originaly, the methods were defined as friends of the template, and it is working fine this way with g++. The methods have been moved outside the namespace util I changed the definition of the templates to fit what I found on various Visual C++ websites. The original friend declaration is: friend QTextStream& operator>>(QTextStream& ss, Vector& in) { ... } The "Visual C++ adapted" version is: friend QTextStream& operator>> <dim,T>(QTextStream& ss, Vector<dim,T>& in); with the function pre-declared before the class and implemented after. I checked the file is correctly included using: #pragma message ("Including vector header") And everything seems fine. Doesn anyone has any idea what might be wrong?

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  • jQuery: one-liner for removing all children but one

    - by user1352530
    HTML code is: <li> <a href="#" /> <ul> <li> <a href="#"/> </li> </ul> </li> I want to delete any node under $(this) = li that is not a link. If there are more than one link, just the first one is saved, and if there are links inside the ul tag, they are not included because they are descendants and no childrens. Something like this (I am cloning and outputting html): $(this).clone().remove('not(a:first)').html(); //Assuming remove looks for "a" as a first child Does not work, so I try with this: $(this).clone().children().remove('not(a:first)').parent().html(); Does not work so I try with this: $(this).clone().remove('not(>a:first)').html(); I need the original element as a reference after removal for chaining more operations EDIT: Ok! Second one works with a little syntax correction as some appointed (:not( instead of not() but I would like to know if there is any other solution similar to the third line so I don't have to do children().remove().parent(). Thank you!

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  • How do the major C# DI/IoC frameworks compare?

    - by Slomojo
    At the risk of stepping into holy war territory, What are the strengths and weaknesses of these popular DI/IoC frameworks, and could one easily be considered the best? ..: Ninject Unity Castle.Windsor Autofac StructureMap Are there any other DI/IoC Frameworks for C# that I haven't listed here? In context of my use case, I'm building a client WPF app, and a WCF/SQL services infrastructure, ease of use (especially in terms of clear and concise syntax), consistent documentation, good community support and performance are all important factors in my choice. Update: The resources and duplicate questions cited appear to be out of date, can someone with knowledge of all these frameworks come forward and provide some real insight? I realise that most opinion on this subject is likely to be biased, but I am hoping that someone has taken the time to study all these frameworks and have at least a generally objective comparison. I am quite willing to make my own investigations if this hasn't been done before, but I assumed this was something at least a few people had done already. Second Update: If you do have experience with more than one DI/IoC container, please rank and summarise the pros and cons of those, thank you. This isn't an exercise in discovering all the obscure little containers that people have made, I'm looking for comparisons between the popular (and active) frameworks.

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  • Codeigniter Inserting Multidimensional Array as rows in MySQL

    - by RisingSun
    Please Refer to this question I asked Codeigniter Insert Multiple Rows in SQL To restate <tr> <td><input type="text" name="user[0][name]" value=""></td> <td><input type="text" name="user[0][address]" value=""><br></td> <td><input type="text" name="user[0][age]" value=""></td> <td><input type="text" name="user[0][email]" value=""></td> </tr> <tr> <td><input type="text" name="user[1][name]" value=""></td> <td><input type="text" name="user[1][address]" value=""><br></td> <td><input type="text" name="user[1][age]" value=""></td> <td><input type="text" name="user[1][email]" value=""></td> </tr> .......... Can Be Inserted into MySQL as this foreach($_POST['user'] as $user) { $this->db->insert('mytable', $user); } This results in multiple MySQL queries. Is it possible to optimise it further, so that the insert occurs in one query Something like this insert multiple rows via a php array into mysql but taking advantage of codeigniters simpler syntax. Thanks

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  • NHibernate query against the key field of a dictionary (map)

    - by Carl Raymond
    I have an object model where a Calendar object has an IDictionary<MembershipUser, Perms> called UserPermissions, where MembershipUser is an object, and Perms is a simple enumeration. This is in the mapping file for Calendar as <map name="UserPermissions" table="CalendarUserPermissions" lazy="true" cascade="all"> <key column="CalendarID"/> <index-many-to-many class="MembershipUser" column="UserGUID" /> <element column="Permissions" type="CalendarPermission" not-null="true" /> </map> Now I want to execute a query to find all calendars for which a given user has some permission defined. The permission is irrelevant; I just want a list of the calendars where a given user is present as a key in the UserPermissions dictionary. I have the username property, not a MembershipUser object. How do I build that using QBC (or HQL)? Here's what I've tried: ISession session = SessionManager.CurrentSession; ICriteria calCrit = session.CreateCriteria<Calendar>(); ICriteria userCrit = calCrit.CreateCriteria("UserPermissions.indices"); userCrit.Add(Expression.Eq("Username", username)); return calCrit.List<Calendar>(); This constructed invalid SQL -- the WHERE clause contained WHERE membership1_.Username = @p0 as expected, but the FROM clause didn't include the MemberhipUsers table. Also, I really had to struggle to learn about the .indices notation. I found it by digging through the NHibernate source code, and saw that there's also .elements and some other dotted notations. Where's a reference to the allowed syntax of an association path? I feel like what's above is very close, and just missing something simple.

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  • Changing Apache2.2.11 httpd.conf has no effect

    - by Adrian
    Hi, Hopefully someone can help here. I recently installed wampserver ver 2.0 with Apache ver 2.2.11. My issue is, I have some large php scripts which timeout at the default 5 min (300 sec) browser limit (I'm using ie8). It is critcal I get this limit extended. I have tried changing the httpd.conf file to include the following: TimeOut 1200 My objective was to set the timeout at 1200 seconds, or 20 min. I had just chosen a random location to place this directive within the httpd.conf file as I cannot locate any documentation to suggest it belongs in a specific place within the file. Regardless, the changes I make appear in the httpd.conf file that can be found in the system tray for wampserver, however they have no effect - the browser still times out after 5 minutes. I thought perhaps I had the capitals incorrect, so I changed to: Timeout 1200 This change had no effect either. Can someone please help, this is very frustrating. Maybe the command can only be used within a specific module? If so, I have no idea which one, nor do I know the syntax to specify this. Regards Adrian.

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  • Java - How to declare table[i][j] elements as instance variables?

    - by JDelage
    All, I am trying to code a Connect4 game. For this, I have created a P4Game class and a P4Board class which represents the i X j dimensions of the Connect4 board. In P4Game, I have the following: public class P4Game{ //INSTANCE VARIABLES private int nbLines; private int nbColumns; private P4Board [][] position; //CONSTRUCTOR public P4Game(int nbLines, int nbColumns){ this.nbColumns = nbColumns; this.nbLines = nbLines; P4Board [][] position = new P4Board [nbLines][nbColumns]; //Creates the table to receive the instances of the P4Board object.*/ for (int i=0; i<nbLines; i++){ for (int j=0; j<nbColumns; j++){ this.position[i][j] = new P4Board(i,j); //Meant to create each object at (line=i, column=j) } } } This causes a NullPointerException in the nested loops where I mention this.position[i][j]. I reference those objects in other methods of this class so I need them to be instance variables. I suppose the exception is due to the fact that I have not listed the table element position[i][j] as an instance variable at the beginning of the class. my question to people here is (1) is my assumption correct, and if so (2) what would be the syntax to declare instance variables of this form? Thank you all for your help with what I realize is a very basic question. Hopefully it will also benefit other newbies. Cheers, JDelage

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  • Special Characters in JS, how to use "/" character

    - by user1461222
    I've vbulletin 4.2.0 i added an special button to it's editor with this article; http://www.vbulletinguru.com/2012/add-a-new-toolbar-button-to-ckeditor-tutorial/ The thing i want to do is add an syntax highlighter code with this button. When i use below code it's working fine; CKEDITOR.plugins.add( 'YourPluginName', { init: function( editor ) { editor.addCommand( 'SayHello', { exec : function( editor ) { editor.insertHtml( "Hello from my plugin" ); } }); editor.ui.addButton( 'YourPluginName', { label: 'My Button Tooltip', command: 'SayHello', icon: this.path + 'YourPluginImage.png' } ); } } ); so i changed this code to this, because i wannt to add specific text like below; CKEDITOR.plugins.add( 'DKODU', { init: function( editor ) { editor.addCommand( 'SayHello', { exec : function( editor ) { editor.insertHtml( '[kod=delphi][/kod]' ); } }); editor.ui.addButton( 'DKODU', { label: 'My Button Tooltip', command: 'SayHello', icon: this.path + 'star.png' } ); } } ); after update the code when i press the button nothings happen, i checked with google and this site but i couldn't figure it out i think i made mistake with some special characters but i couldn't find what's the problem. If i made some mistakes when i publish this question forgive me and also forgive me for my bad english, thanks.

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  • How to easily map c++ enums to strings

    - by Roddy
    I have a bunch of enum types in some library header files that I'm using, and I want to have a way of converting enum values to user strings - and vice-versa. RTTI won't do it for me, because the 'user strings' need to be a bit more readable than the enumerations. A brute force solution would be a bunch of functions like this, but I feel that's a bit too C-like. enum MyEnum {VAL1, VAL2,VAL3}; String getStringFromEnum(MyEnum e) { switch e { case VAL1: return "Value 1"; case VAL2: return "Value 2"; case VAL1: return "Value 3"; default: throw Exception("Bad MyEnum"); } } I have a gut feeling that there's an elegant solution using templates, but I can't quite get my head round it yet. UPDATE: Thanks for suggestions - I should have made clear that the enums are defined in a third-party library header, so I don't want to have to change the definition of them. My gut feeling now is to avoid templates and do something like this: char * MyGetValue(int v, char *tmp); // implementation is trivial #define ENUM_MAP(type, strings) char * getStringValue(const type &T) \ { \ return MyGetValue((int)T, strings); \ } ; enum eee {AA,BB,CC}; - exists in library header file ; enum fff {DD,GG,HH}; ENUM_MAP(eee,"AA|BB|CC") ENUM_MAP(fff,"DD|GG|HH") // To use... eee e; fff f; std::cout<< getStringValue(e); std::cout<< getStringValue(f);

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  • Connect Rails model to non-rails database

    - by the_snitch
    I'm creating a new web application (Rails 3 beta), of which pieces of it will access data from a legacy mysql database that a current php application is using. I do not wish to modify the legacy db schema, I just want to be able to read/write to it, as well as the rails application having it's own database using activerecord for the newer stuff. I'm using mysql for the rails app, so I have the adapter installed. How is the best way to do this? For example, I want contacts to come from the old database. Should I create a contacts controller, and manually call sql to get the variables for the views? Or should I create a Contact model, and define attributes that match the fields in the database, and am I able to use it like Contact.mail_address to have it call "SELECT mailaddr FROM contacts WHERE id=Contact.id". Sorry, I've never done much in Rails outside of the standard stuff that is documented well. I'm not sure of what the best approach would be. Ideally, I want the contacts to be presented to my rails application as native as possible, so that I can expose them RESTfully for API access. Any suggestions and code examples would be much appreciated

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  • Can some tell me why I am seg faulting in this simple C program?

    - by user299648
    I keep on getting seg faulted after I end my first for loop, and for the life of me I don't why. The file I'm scanning is just 18 strings in 18 lines. I thinks the problem is the way I'm mallocing the double pointer called picks, but I don't know exactly why. I'm am only trying to scanf strings that are less than 15 chars long, so I don't see the problem. Can someone please help. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_LENGTH 100 int main( int argc,char *argv[] ) { char* string = malloc( 15*sizeof(char) ); char** picks = malloc(15*sizeof(char*)); FILE* pick_file = fopen( argv[l], "r" ); int num_picks; for( num_picks=0 ; fgets( string, MAX_LENGTH, pick_file ) != NULL ; num_picks++ ) { scanf( "%s", picks+num_picks ); } //this is where i seg fault int x; for(x=0; x<num_picks;x++) printf("s\n", picks+x); }

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  • Java: how do I get a class literal from a generic type?

    - by Tom
    Typically, I've seen people use the class literal like this: Class<Foo> cls = Foo.class; But what if the type is generic, e.g. List? This works fine, but has a warning since List should be parameterized: Class<List> cls = List.class So why not add a <?>? Well, this causes a type mismatch error: Class<List<?>> cls = List.class I figured something like this would work, but this is just a plain ol' a syntax error: Class<List<Foo>> cls = List<Foo>.class How can I get a Class<List<Foo>> statically, e.g. using the class literal? I could use @SuppressWarnings("unchecked") to get rid of the warnings caused by the non-parameterized use of List in the first example, Class<List> cls = List.class, but I'd rather not. Any suggestions? Thanks!

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  • memcmp,strcmp,strncmp in C

    - by el10780
    I wrote this small piece of code in C to test memcmp() strncmp() strcmp() functions in C. Here is the code that I wrote: #include <stdio.h> #include <stdlib.h> #include <string.h> int main(int argc, char** argv) { char *word1="apple",*word2="atoms"; if (strncmp(word1,word2,5)==0) printf("strncmp result.\n"); if (memcmp(word1,word2,5)==0) printf("memcmp result.\n"); if (strcmp(word1,word2)==0) printf("strcmp result.\n"); } Can somebody explain me the differences because I am confused with these three functions?My main problem is that I have a file in which I tokenize its line of it,the problem is that when I tokenize the word "atoms" in the file I have to stop the process of tokenizing.I first tried strcmp() but unfortunately when it reached to the point where the word "atoms" were placed in the file it didn't stop and it continued,but when I used either the memcmp() or the strncmp() it stopped and I was happy.But then I thought,what if there will be a case in which there is one string in which the first 5 letters are a,t,o,m,s and these are being followed by other letters.Unfortunately,my thoughts were right as I tested it using the above code by initializing word1 to "atomsaaaaa" and word2 to atoms and memcmp() and strncmp() in the if statements returned 0.On the other hand strcmp() it didn't.It seems that I must use strcmp(). I have done google searches but I got more confused as I have seen sites and other forums to define these three differently.If it is possible for someone to give me correct explanations/definitions so I can use them correctly in my source code,I would be really grateful.

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  • Ad distribution problem: an optimal solution?

    - by Mokuchan
    I'm asked to find a 2 approximate solution to this problem: You’re consulting for an e-commerce site that receives a large number of visitors each day. For each visitor i, where i € {1, 2 ..... n}, the site has assigned a value v[i], representing the expected revenue that can be obtained from this customer. Each visitor i is shown one of m possible ads A1, A2 ..... An as they enter the site. The site wants a selection of one ad for each customer so that each ad is seen, overall, by a set of customers of reasonably large total weight. Thus, given a selection of one ad for each customer, we will define the spread of this selection to be the minimum, over j = 1, 2 ..... m, of the total weight of all customers who were shown ad Aj. Example Suppose there are six customers with values 3, 4, 12, 2, 4, 6, and there are m = 3 ads. Then, in this instance, one could achieve a spread of 9 by showing ad A1 to customers 1, 2, 4, ad A2 to customer 3, and ad A3 to customers 5 and 6. The ultimate goal is to find a selection of an ad for each customer that maximizes the spread. Unfortunately, this optimization problem is NP-hard (you don’t have to prove this). So instead give a polynomial-time algorithm that approximates the maximum spread within a factor of 2. The solution I found is the following: Order visitors values in descending order Add the next visitor value (i.e. assign the visitor) to the Ad with the current lowest total value Repeat This solution actually seems to always find the optimal solution, or I simply can't find a counterexample. Can you find it? Is this a non-polinomial solution and I just can't see it?

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  • Can someone tell me what this Java class does? I/O related

    - by anon
    I am relatively new to Java and trying to learn the I/O syntax. Could someone give me a general overview of what this code does? Thanks!! import java.io.*; public class FileReader { private String openFile=""; private String saveFile=""; FileReader(openFile, saveFile) { this.openFile=openFile; this.saveFile=saveFile; } public String process(){ System.out.println(this.openFile); System.out.println(this.saveFile); BufferedReader open=null; FileReader openFR=null; FileWriter save=null; int counter=0; String output=""; if(openFile.equals("")){ return "No open file specifified\n"; } if(this.saveFile.equals("")){ return "No save file specified\n"; } try { openFR = new FileReader(this.openFile); open = new BufferedReader(openFR); } catch (FileNotFoundException e) { return ("Open file no longer exists\n"); } try { save = new FileWriter(saveFile); } catch (IOException e){ return ("Error saving the file\n"); } try{ String temp = open.readLine(); while(temp != null){ temp = open.readLine(); counter++; save.write(output + "\n"); } } catch (IOException e){ e.getStackTrace(); return ("Error reading open file"); } try { save.flush(); } catch (IOException e) { e.printStackTrace(); return ("Error writing save file"); } return "Operation completed successfully"; } }

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