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  • variables in abstract classes C++

    - by wyatt
    I have an abstract class CommandPath, and a number of derived classes as below: class CommandPath { public: virtual CommandResponse handleCommand(std::string) = 0; virtual CommandResponse execute() = 0; virtual ~CommandPath() {} }; class GetTimeCommandPath : public CommandPath { int stage; public: GetTimeCommandPath() : stage(0) {} CommandResponse handleCommand(std::string); CommandResponse execute(); }; All of the derived classes have the member variable 'stage'. I want to build a function into all of them which manipulates 'stage' in the same way, so rather than defining it many times I thought I'd build it into the parent class. I moved 'stage' from the private sections of all of the derived classes into the protected section of CommandPath, and added the function as follows: class CommandPath { protected: int stage; public: virtual CommandResponse handleCommand(std::string) = 0; virtual CommandResponse execute() = 0; std::string confirmCommand(std::string, int, int, std::string, std::string); virtual ~CommandPath() {} }; class GetTimeCommandPath : public CommandPath { public: GetTimeCommandPath() : stage(0) {} CommandResponse handleCommand(std::string); CommandResponse execute(); }; Now my compiler tells me for the constructor lines that none of the derived classes have a member 'stage'. I was under the impression that protected members are visible to derived classes? The constructor is the same in all classes, so I suppose I could move it to the parent class, but I'm more concerned about finding out why the derived classes aren't able to access the variable. Also, since previously I've only used the parent class for pure virtual functions, I wanted to confirm that this is the way to go about adding a function to be inherited by all derived classes.

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  • What do you name the "other" kind of view-model in an MVVM project?

    - by DanM
    With MVVM, I think of a view-model as a class that provides all the data and commands that a view needs to bind to. But what happens when I have a database entity object, say a Customer, and I want to build a class that shapes or flattens the Customer class for use in a data grid. For example, maybe this special Customer object would have a property TotalOrders, which is actually calculated using a join with a collection of Order entities. My question is, what do I call this special Customer class? In other situations, I'd be tempted to call it a CustomerViewModel, but I feel like "overloading" the notion of a view-model like this would be confusing in an MVVM project. What would you suggest?

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  • Arraylist can't compare objects after they are loaded from disk

    - by Zka
    To make it easy, lets say I have an arraylist allBooks containing class "books" and an arraylist someBooks containing some but not all of the "books". Using contains() method worked fine when I wanted to see if a book from one arraylist was also contained in another. The problem was that this isn't working anymore when I save both of the Arraylists to a .bin file and load them back once the program restarts. Doing the same test as before, the contains() returns false even if the compared objects are the same (have the same info inside). I solved it by overloading the equals method and it works fine, but I want to know why did this happen?

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  • How to make "int" parse blank strings?

    - by Alex B
    I have a parsing system for fixed-length text records based on a layout table: parse_table = [\ ('name', type, length), .... ('numeric_field', int, 10), # int example ('textc_field', str, 100), # string example ... ] The idea is that given a table for a message type, I just go through the string, and reconstruct a dictionary out of it, according to entries in the table. Now, I can handle strings and proper integers, but int() will not parse all-spaces fields (for a good reason, of course). I wanted to handle it by defining a subclass of int that handles blank strings. This way I could go and change the type of appropriate table entries without introducing additional kludges in the parsing code (like filters), and it would "just work". But I can't figure out how to override the constructor of a build-in type in a sub-type, as defining constructor in the subclass does not seem to help. I feel I'm missing something fundamental here about how Python built-in types work. How should I approach this? I'm also open to alternatives that don't add too much complexity.

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  • Unable to Get values from Web Form to a PHP Class to Display

    - by kentrenholm
    I am having troubles getting the value from my variables submitted via a web form using a PHP class file. Here is my structure of the web page: Order Form Page Process.php Page Book.php Page I can easily get the user data entered (on Order Form Page), process, and display it on the Process.php page. The issue is that I must create a Book class and print the details of the data using the Book class. I have an empty constructor printing out "created" so I know my constructor is being called. I also am able to print the word "title" so I know I can print to the screen by using the Book class. My issue is that I can't get values in my variables in the Book class. Here is my variable declaration: private $title; Here is my printDetails function: public function printDetails () { echo "Title: " . $this->title . "<br />"; } Here is my new instance of the book class: $bookNow = new book; Here are my get and set functions: function __getTitle($title) { return $this->$title; } function __setTitle($title,$value) { $this->$title = $value; } I do have four other variables that I'm looking to display as well. Each of those have their own variable declaration, a line in printDetails, and their own setter and getter. Lastly, I also have a call to the Book class in my process PHP. It looks like this: function __autoload($book) { include $book . '.php'; } $bookNow = new book(); Any help, much appreciated. It must be something so very small (I'm hoping).

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  • IList<T> vs IEnumerable<T>. What is more efficient IList<T> or IEnumerable<T>

    - by bigb
    What is more efficient way to make methods return IList<T> or IEnumerable<T>? IEnumerable<T> it is immutable collection but IList<T> mutable and contain a lot of useful methods and properties. To cast IList<T> to IEnumerable<T> it is just reference copy: IList<T> l = new List<T>(); IEnumerable<T> e = l; To cast IEnumerable<T> to List<T> we need to iterate each element or to call ToList() method: IEnumerable<T>.ToList(); or may pass IEnumerable<T> to List<T> constructor which doing the same iteration somewhere within its constructor. List<T> l = new List<T>(e); Which cases you think is more efficient? Which you prefer more in your practice?

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  • C++ Word-Number to int

    - by Andrew
    I'm developing a program that makes basic calculations using words instead of numbers. E.g. five + two would output seven. The program becomes more complex, taking input such as two_hundred_one + five_thousand_six (201 + 5006) Through operator overloading methods, I split each number and assign it to it's own array index. two would be [0], hundred is [1], and one is [2]. Then the array recycles for 5006. My problem is, to perform the actual calculation, I need to convert the words stored in the array to actual integers. I have const string arrays such as this as a library of the words: const string units[] = { "", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; const string teens[] = { "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" }; const string tens[] = { "", "", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety" }; If my 'token' array has stored in it two hundred one in index 0, 1, and 2, I'm not sure what the best way to convert these to ints would involve.

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  • What next generation low level language is the best bet to migrate the code base ?

    - by e-satis
    Let's say you have a company running a lot of C/C++, and you want to start planning migration to new technologies so you don't end up like COBOL companies 15 years ago. For now, C/C++ runs more than fine and there is plenty dev on the market for it. But you want to start thinking about it now, because given the huge running code base and the data sensitivity, you feel it can take 5-10 years to move to the next step without overloading the budget and the dev teams. You have heard about D, starting to be quite mature, and Go, promising to be quite popular. What would be your choice and why?

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  • Making a PHP object behave like an array?

    - by Mark Biek
    I'd like to be able to write a PHP class that behaves like an array and uses normal array syntax for getting & setting. For example (where Foo is a PHP class of my making): $foo = new Foo(); $foo['fooKey'] = 'foo value'; echo $foo['fooKey']; I know that PHP has the _get and _set magic methods but those don't let you use array notation to access items. Python handles it by overloading __getitem__ and __setitem__. Is there a way to do this in PHP? If it makes a difference, I'm running PHP 5.2.

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  • Returning JSON or XML for Exceptions in Jersey

    - by Dominic
    My goal is to have an error bean returned on a 404 with a descriptive message when a object is not found, and return the same MIME type that was requested. I have a look up resource, which will return the specified object in XML or JSON based on the URI (I have setup the com.sun.jersey.config.property.resourceConfigClass servlet parameter so I dont need the Accept header. My JAXBContextResolver has the ErrorBean.class in its list of types, and the correct JAXBContext is returned for this class because I can see in the logs). eg: http://foobar.com/rest/locations/1.json @GET @Path("{id}") @Produces({MediaType.APPLICATION_JSON, MediaType.APPLICATION_XML}) public Location getCustomer(@PathParam("id") int cId) { //look up location from datastore .... if (location == null) { throw new NotFoundException("Location" + cId + " is not found"); } } And my NotFoundException looks like this: public class NotFoundException extends WebApplicationException { public NotFoundException(String message) { super(Response.status(Response.Status.NOT_FOUND). entity(new ErrorBean( message, Response.Status.NOT_FOUND.getStatusCode() ) .build()); } } The ErrorBean is as follows: @XmlRootElement(name = "error") public class ErrorBean { private String errorMsg; private int errorCode; //no-arg constructor, property constructor, getter and setters ... } However, I'm always getting a 204 No Content response when I try this. I have hacked around, and if I return a string and specify the mime type this works fine: public NotFoundException(String message) { super(Response.status(Response.Status.NOT_FOUND). entity(message).type("text/plain").build()); } I have also tried returning an ErrorBean as a resource. This works fine: {"errorCode":404,"errorMsg":"Location 1 is not found!"}

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  • Having troubles inheriting base class

    - by Nick
    When I inherit the base class, it's telling me there is no such class This is enhanced.h: class enhanced: public changeDispenser // <--------where error is occuring { public: void changeStatus(); // Function: Lets the user know how much of each coin is in the machine enhanced(int); // Constructor // Sets the Dollar amount to what the User wants void changeLoad(int); // Function: Loads what change the user requests into the Coin Machine int dispenseChange(int); // Function: Takes the users amount of cents requests and dispenses it to the user private: int dollar; }; This is enhanced.cpp: #include "enhanced.h" #include <iostream> using namespace std; enhanced::enhanced(int dol) { dollar = dol; } void enhanced::changeStatus() { cout << dollar << " dollars, "; changeDispenser::changeStatus(); } void enhanced::changeLoad(int d) { dollar = dollar + d; //changeDispenser::changeLoad; } This is changeDispenser.h: class changeDispenser { public: void changeStatus(); // Function: Lets the user know how much of each coin is in the machine changeDispenser(int, int, int, int); // Constructor // Sets the Quarters, Dimes, Nickels, and Pennies to what the User wants void changeLoad(int, int, int, int); // Function: Loads what change the user requests into the Coin Machine int dispenseChange(int); // Function: Takes the users amount of cents requests and dispenses it to the user private: int quarter; int dime; int nickel; int penny; }; I didn't include the driver file or the changeDispenser imp file, but in the driver, these are included #include "changeDispenser.h" #include "enhanced.h"

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  • DCI: How to implement Context with Dependency Injection?

    - by ciscoheat
    Most examples of a DCI Context are implemented as a Command pattern. When using Dependency Injection though, it's useful to have the dependencies injected in the constructor and send the parameters into the executing method. Compare the Command pattern class: public class SomeContext { private readonly SomeRole _someRole; private readonly IRepository<User> _userRepository; // Everything goes into the constructor for a true encapsuled command. public SomeContext(SomeRole someRole, IRepository<User> userRepository) { _someRole = someRole; _userRepository = userRepository; } public void Execute() { _someRole.DoStuff(_userRepository); } } With the Dependency injected class: public class SomeContext { private readonly IRepository<User> _userRepository; // Only what can be injected using the DI provider. public SomeContext(IRepository<User> userRepository) { _userRepository = userRepository; } // Parameters from the executing method public void Execute(SomeRole someRole) { someRole.DoStuff(_userRepository); } } The last one seems a bit nicer, but I've never seen it implemented like this so I'm curious if there are any things to consider.

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  • Ideal way/architecture to deliver large data over Web Services

    - by zengr
    We are trying to design 6 web services, which will serve another client component. The client component requires data from the web service we are implementing. Now, the problem is, there is not 1 WS we are implementing, there is one WS which the client component hits, this initiates a series (5 more) of WSs which gather data from their respective data stores and finally provide the data back to the original WS, which then delivers the data back to the client component. So, if the requested data becomes huge, then, this will be a serious problem for our internal communication channel. So, what do you guys suggest? What can be done to avoid overloading of the communication channel between the internal WS and at the same time, also delivering the data to the client component.

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  • Double use of variables?

    - by Vaccano
    I have read that a variable should never do more than one thing. Overloading a variable to do more than one thing is bad. Because of that I end up writing code like this: (With the customerFound variable) bool customerFound = false; Customer foundCustomer = null; if (currentCustomer.IsLoaded) { if (customerIDToFind = currentCustomer.ID) { foundCustomer = currentCustomer; customerFound = true; } } else { foreach (Customer customer in allCustomers) { if (customerIDToFind = customer.ID) { foundCustomer = customer; customerFound = true; } } } if (customerFound) { // Do something } But deep down inside, I sometimes want to write my code like this: (Without the foundCustomer variable) Customer foundCustomer = null; if (currentCustomer.IsLoaded) { if (customerIDToFind = currentCustomer.ID) { foundCustomer = currentCustomer; } } else { foreach (Customer customer in allCustomers) { if (customerIDToFind = customer.ID) { foundCustomer = customer; } } } if (foundCustomer != null) { // Do something } Does this secret desires make me an evil programmer? (i.e. is the second case really bad coding practice?)

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  • Could someone help me debug my app (not very big)?

    - by Alex
    Not sure if this kind of help is accepted to ask for here, tell me if it isn't. It has to get done before tomorrow, it's not entirerly finished but it should work somewhat ok by now. I'm trying to use the Eclipse debugger (not very used to it). I have my top-level or main class, which is Game, in which I have a constructor and a main method. In the main method I create a new "Game", initiating the constructor. public static void main(String[] args){ Game chess = new Game(); } public Game(){ Board board = new Board(); That's the first thing the debugger reacts to: Thread [main] (Suspended) ClassNotFoundException(Object).<init>() line: 20 [local variables unavailable] ClassNotFoundException(Throwable).<init>(String, Throwable) line: 217 ClassNotFoundException(Exception).<init>(String, Throwable) line: not available ClassNotFoundException.<init>(String) line: not available URLClassLoader$1.run() line: not available AccessController.doPrivileged(PrivilegedExceptionAction<T>, AccessControlContext) line: not available [native method] Launcher$ExtClassLoader(URLClassLoader).findClass(String) line: not available Launcher$ExtClassLoader.findClass(String) line: not available Launcher$ExtClassLoader(ClassLoader).loadClass(String, boolean) line: not available Launcher$AppClassLoader(ClassLoader).loadClass(String, boolean) line: not available Launcher$AppClassLoader.loadClass(String, boolean) line: not available Launcher$AppClassLoader(ClassLoader).loadClass(String) line: not available Game.<init>() line: 15 Game.main(String[]) line: 11 Line 11 is the one line in my main method, line 15 is the instantiation of "board".

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  • Is it possible to have a variadic function in C with no non-variadic parameter?

    - by Tim
    I have the following function: void doStuff(int unusedParameter, ...) { va_list params; va_start(params, unusedParameter); /* ... */ va_end(params); } As part of a refactor, I'd like to remove the unused parameter without otherwise changing the implementation of the function. As far as I can tell, it's impossible to use va_start when you don't have a last non-variadic parameter to refer to. Is there any way around this? Background: It is in fact a C++ program, so I could use some operator-overloading magic as suggested here, but I was hoping not to have to change the interface at this point. The existing function does its work by requiring that the variable argument list be null-terminated, and scanning for the NULL, therefore it doesn't need a leading argument to tell it how many arguments it has.

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  • What is a truly empty std::vector in C++?

    - by RyanG
    I've got a two vectors in class A that contain other class objects B and C. I know exactly how many elements these vectors are supposed to hold at maximum. In the initializer list of class A's constructor, I initialize these vectors to their max sizes (constants). If I understand this correctly, I now have a vector of objects of class B that have been initialized using their default constructor. Right? When I wrote this code, I thought this was the only way to deal with things. However, I've since learned about std::vector.reserve() and I'd like to achieve something different. I'd like to allocate memory for these vectors to grow as large as possible because adding to them is controlled by user-input, so I don't want frequent resizings. However, I iterate through this vector many, many times per second and I only currently work on objects I've flagged as "active". To have to check a boolean member of class B/C on ever iteration is silly. I don't want these objects to even BE there for my iterators to see when I run through this list. Is reserving the max space ahead of time and using push_back to add a new object to the vector a solution to this?

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  • Why operator= returns reference not const reference

    - by outmind
    The original question is related to overloading operator= and I like to share my findings as it was nontrivial for me to find them. I cannot imagine reasonable example to use (a=b) as lvalue. With the help of IRC and google I've found the next article: http://msdn.microsoft.com/en-us/magazine/cc301415.aspx it provides two examples. (a=b)=c f(T& ); f(a=b) but both a bit not good, as first violate associativity and I believe that it is bad practice. The second one give me the same feeling. Could you provide more good examples why it should be non constant?

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  • Using new (this) to reuse constructors

    - by Brandon Bodnar
    This came up recently in a class for which I am a teaching assistant. We were teaching the students how to do copy constructors in c++, and the students who were originally taught java asked if you can call one constructor from another. I know the answer to this is no, as they are using the pedantic flag for their code in class, and the old standards do not have support for this. I found on Stackoverflow and other sites a suggestion to fake this using new (this) such as follows class MyClass { private: int * storedValue; public: MyClass(int initialValue = 0) { storedValue = new int(initialValue); } ~ MyClass() { delete storedValue; } MyClass(const MyClass &b) { new (this) MyClass(*(b.storedValue)); } int value() { return *storedValue; } }; This is really simple code, and obviously does not save any code by reusing the constructor, but it is just for example. My question is if this is even standard compliant, and if there are any edge cases that should be considered that would prevent this from being sound code?

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  • problem with a string's format in c++ while doing tcp communication

    - by james t
    hi, i am building a simple c++ client, i am splitting the info i get from the server to frames, and pass each frame to a function that processes it, i split the frame into lines using Poco::StringTokenizer tokenizer(frame, "\n"); i take the first line of the tokenizer which represents the type of frame StmpCommand command(tokenizer[0]); a StmpCommand is an enum with the different types of messages and the constructor works as follows : StmpCommand(std::string command): commandType_() { bool x=command=="CONNECTED"; std::cout<<x<<std::endl; if ("SUBSCRIBE" == command) commandType_ = SUBSCRIBE; else if ("UNSUBSCRIBE" == command) commandType_ = UNSUBSCRIBE; else if ("SEND" == command) commandType_ = SEND; else if ("BEGIN" == command) commandType_ = BEGIN; else if ("COMMIT" == command) commandType_ = COMMIT; else if ("CONNECT" == command) commandType_ = CONNECT; else if ("MESSAGE" == command) commandType_ = MESSAGE; else if ("RECEIPT" == command) commandType_ = RECEIPT; else if ("CONNECTED" == command) commandType_ = CONNECTED; else if ("DISCONNECT" == command) commandType_ = DISCONNECT; else if ("ERROR" == command) commandType_ = ERROR; else { std::cerr<<"Error in building StmpCommand object, unknown type - "<<command<<std::endl; } } the first frame i am trying to proccess is a CONNECTED frame therefor i try to create a StmpCommand with CONNECTED as the constructor's only argument and for some reason i am getting an : Error in building StmpCommand object, unknown type - CONNECTED i am clearly passing a string containing CONNECTED but i'm guessing there is something else there that isn't allowing the condition else if ("CONNECTED" == command) to hap

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  • Confusion about pointers and their memory addresses

    - by TimothyTech
    alright, im looking at a code here and the idea is difficult to understand. #include <iostream> using namespace std; class Point { public : int X,Y; Point() : X(0), Y(0) {} }; void MoveUp (Point * p) { p -> Y += 5; } int main() { Point point MoveUp(&point) cout <<point.X << point.Y; return 0; } Alright, so i believe that a class is created and X and Y are declared and they are put inside a constructor a method is created and the argument is Point * p, which means that we are going to stick the constructor's pointer inside the function; now we create an object called point then call our method and put the pointers address inside it? isnt the pointers address just a memory number like 0x255255? and why wasnt p ever declared? (int * p = Y) what is a memory addres exactly? that it can be used as an argument?

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  • Adobe After Efects Plugin With Cocoa (Overriding malloc)

    - by mustISignUp
    Messing about a bit, i have a working Adobe After Effects plugin with a bit of Obj-c / Cocoa in it (NSArray and custom objects - not ui stuff). The SDK guide states:- Always use After Effects memory allocation functions. In low-memory conditions (such as during RAM preview), it’s very important that plug-ins not compete with After Effects for OS memory, and deal gracefully with out-of-memory conditions. Failing to use our functions can cause lock-ups, crashes, and tech support calls. Don’t do that. If you’re wrapping existing C++ code, overloading new and delete to use our functions will save substantial reimplementation. On Windows, derive all classes from a common base class which implements new and delete. so my question.. is something compatible with the above statement possible in Obj-c?

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  • Can I include a view in Kohana 3 that is not within `application/views`?

    - by alex
    I am building a staff area for a website, which is completely different to the main brochure style site. I have 2 Kohana systems setup. I realise they can both share the same system and modules folder. Now, with the second one, I want to make the main template view a view in a different folder. I tried this in my base controller $this->template = DOCROOT . '../~new2/application/views/template.php'; But Kohana is looking for it in its own views folder as evident by the error I received. I even put a var_dump(file_exists($this->template)); // true to be sure it was finding the correct file. Is there a way to add a template file that is not within the views folder, without hacking the core Kohana code (and if I'm lucky not extending and overloading the view class).

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  • C++ Type error with Object versus Object reference

    - by muddybruin
    I have the following function (which worked in Visual Studio): bool Plane::contains(Vector& point){ return normalVector.dotProduct(point - position) < -doubleResolution; } When I compile it using g++ version 4.1.2 , I get the following error: Plane.cpp: In member function âvirtual bool Plane::contains(Vector&)â: Plane.cpp:36: error: no matching function for call to âVector::dotProduct(Vector)â Vector.h:19: note: candidates are: double Vector::dotProduct(Vector&) So as you can see, the compiler thinks (point-position) is a Vector but it's expecting Vector&. What's the best way to fix this? I verified that this works: Vector temp = point-position; return normalVector.dotProduct(temp) < -doubleResolution; But I was hoping for something a little bit cleaner. I heard a suggestion that adding a copy constructor might help. So I added a copy constructor to Vector (see below), but it didn't help. Vector.h: Vector(const Vector& other); Vector.cpp: Vector::Vector(const Vector& other) :x(other.x), y(other.y), z(other.z), homogenous(other.homogenous) { }

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  • Analog of Java Form Layout in Qt

    - by Narek
    Once I have programmed GUI with Java and have used Form Layouts. Form layout (if I am not mistaken that is from SWT library) made possible to give right, left, top and bottom adges of any GUI element (widget) with respect to other widgets in the same widget (parent widget) or with respect to the adges of parent widget. So it was possible to control the future of widgets that are inside of another one, when that "another widget" is being resized. In Qt I have find the QFormLayout which is similar to Java one, but seems I can't handle with widgets as flexible in terms of relative positioning, as it was with Java's Form Layout. So are there any other means to give a widget position with respect to the others (without overloading resizeEvent function) as that was in Java? Thanks.

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