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  • How to have a policy class implement a virtual function?

    - by dehmann
    I'm trying to design a policy-based class, where a certain interface is implemented by the policy itself, so the class derives from the policy, which itself is a template (I got this kind of thinking from Alexandrescu's book): #include <iostream> #include <vector> class TestInterface { public: virtual void test() = 0; }; class TestImpl1 { public: void test() {std::cerr << "Impl1" << std::endl;} }; template<class TestPolicy> class Foo : public TestInterface, TestPolicy { }; Then, in the main() function, I call test() on (potentially) various different objects that all implement the same interface: int main() { std::vector<TestInterface*> foos; foos.push_back(new Foo<TestImpl1>()); foos[0]->test(); delete foos[0]; return 0; } It doesn't compile, though, because the following virtual functions are pure within ‘Foo<TestImpl1>’: virtual void TestInterface::test() I thought TestInterface::test() is implemented because we derive from TestImpl1?

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  • "Undefined Symbols" when inheriting from stdexcept classes

    - by Austin Hyde
    Here is an exception defined in <stdexcept>: class length_error : public logic_error { public: explicit length_error(const string& __arg); }; Here is my exception: class rpn_expression_error : public logic_error { public: explicit rpn_expression_error(const string& __arg); }; Why do I get this error when <stdexcept> does not? Undefined symbols: rpn_expression_error::rpn_expression_error(/*string*/ const&), referenced from: ... ld: symbol(s) not found

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  • Refactoring a C# derived class with method dependancies

    - by drelihan
    Hi Folks, I want to get your opinion on this. I have a class which is derived from a base class. I don't have control over the code in the base class and it is critical to the system that I derive from it. In my class I inherite two methods that are critical to the system and are used in pretty much every function, many times. I intend to refactor this derived class and extract some classes from it - this won't be a problem. What I'm not sure about is, is it worth extracting class if I have to constantly make call backs to my main class to access the two methods (or public wrappers to the methods)??? Thanks

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  • Why can't sub-packages see package private classes?

    - by Polaris878
    Okay so, I have this project structure: package A.B class SuperClass (this class is marked package private) package A.B.C class SubClass (inherits from super class) I'd rather not make SuperClass publicly visible... It is really just a utility class for this specific project (A.B). It seems to me that SubClass should be able to see SuperClass, because package A.B.C is a subpackage of A.B... but this is not the case. What would be the best way to resolve this issue? I don't think it makes sense to move everything in A.B.C up to A.B or move A.B down to A.B.C... mainly because there will probably be an A.B.D which inherits from stuff in A.B as well... I'm a bit new to Java, so be nice :D (I'm a C++ and .NET guy)

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  • How to use derived class shared variables in shared methods of base class

    - by KoolKabin
    Hi guys, I am trying to add shared members in derived classes and use that values in base classes... I have base class DBLayer public shared function GetDetail(byval UIN as integer) dim StrSql = string.format("select * from {0} where uin = {1}", tablename, uin) .... end function end class my derived class class User inherits dblayer public shared tabledname as string = "users" end class class item inherits dblayer public shared tabledname as string = "item" end class class category inherits dblayer public shared tabledname as string = "category" end class currently there is error using the tablename variable of derived class in base class but i want to use it... coz i dun know other techniques... if other solutions are better then u can post it or u can say how can i make it work? confused...

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  • Can a class inherit from LambdaExpression in .NET? Or is this not recommended?

    - by d.
    Consider the following code (C# 4.0): public class Foo : LambdaExpression { } This throws the following design-time error: Foo does not implement inherited abstract member System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) There's absolutely no problem with public class Foo : Expression { } but, out of curiosity and for the sake of learning, I've searched in Google System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) and guess what: zero results returned (when was the last time you saw that?). Needless to say, I haven't found any documentation on this method anywhere else. As I said, one can easily inherit from Expression; on the other hand LambdaExpression, while not marked as sealed (Expression<TDelegate> inherits from it), seems to be designed to prevent inheriting from it. Is this actually the case? Does anyone out there know what this method is about? EDIT (1): More info based on the first answers - If you try to implement Accept, the editor (C# 2010 Express) automatically gives you the following stub: protected override Expression Accept(System.Linq.Expressions.ExpressionVisitor visitor) { return base.Accept(visitor); } But you still get the same error. If you try to use a parameter of type StackSpiller directly, the compiler throws a different error: System.Linq.Expressions.Compiler.StackSpiller is inaccessible due to its protection level. EDIT (2): Based on other answers, inheriting from LambdaExpression is not possible so the question as to whether or not it is recommended becomes irrelevant. I wonder if, in cases like this, the error message should be Foo cannot implement inherited abstract member System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) because [reasons go here]; the current error message (as some answers prove) seems to tell me that all I need to do is implement Accept (which I can't do).

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  • How to design this class hierarchy?

    - by devoured elysium
    I have defined an Event class: Event and all the following classes inherit from Event: AEvent BEvent CEvent DEvent Now, with the info I gather from all these Event classes, I will make a chart. With AEvent and BEvent, I will generate points for that chart, while with CEvent and DEvent I will paint certain regions of the chart. Now, how should I signal this in my class hierarchy? Should I make AEvent and BEvent inherit from PointEvent while CEvent and DEvent inherit from RegionEvent, being that both RegionEvent and PointEvent inherit from Event? Should I add a field with an Enum to Event with 2 values, Point and Region, and each of the child classes set their value to it? Should I use some kind of pattern here? Which one? Thanks.

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  • XSLT: Is there a way to "inherit" canned functionality?

    - by Ian Boyd
    i am once again having to cobble together a bit of XSLT into order to turn generated XML into (rather than simply generating HTML). i'm having huge deja-vu this time again. i'm once again having to solve again basic problems, e.g.: how to convert characters into valid html entity references how to preserve whitespace/carriage returns when converting to html how to convert to HTML as opposed to xhtml how to convert dates from xml format into presentable format how to tear apart strings with substring This is all stuff that i've solved many times before. But every time i come back to XSLT i have to start from scratch, re-inventing the wheel every time. If it were a programming language i would have a library of canned functions and procedures i can call. i would have subroutines to perform the commonly repeated tasks. i would inherit from a base class that already implements the ugly boilerplate stuff. Is there any way in XSLT to grow, expand and improve the ecosystem with canned code?

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  • Inherit from Type class of .Net

    - by Miguel Angelo
    Is there any point at all on inheriting from Type class in .Net? i.e. What could be the meaning of doing so? I am asking this because of this text in MSDN documentation: Notes to Inheritors When you inherit from Type, you must override the following members... list of members. MSDN doc for Type: http://msdn.microsoft.com/en-us/library/system.type.aspx ok, that is actually saying that anyone can inherit from Type... but they dont say why would you ever want to do that. Thanks!

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  • Python Django vs ASP.NET MVC

    - by eddyc05
    Hey guys ! i'm fairly new at web development scene and i was wondering if you guys can help me break up the pros and cons of using python django vs asp.net mvc besides the maturity level of its framework. I have intermediate experience with JAVA. As of right now, i'm leaning towards python but i just wanted to make sure i am making the right choice. I find myself limited with books available on asp.net web developments. I am aware that there is the storefront example on the official asp.net site. However, that tutorial was a little hard for me to follow. I've done a research around and was hoping python could be my next available choice. There are more tutorials available online for python anyways. What do you guys think??

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  • How to implement Xml Serialization with inherited classes in C#

    - by liorafar
    I have two classes : base class name Component and inheritd class named DBComponent [Serializable] public class Component { private string name = string.Empty; private string description = string.Empty; } [Serializable] public class DBComponent : Component { private List<string> spFiles = new List<string>(); // Storage Procedure Files [XmlArrayItem("SPFile", typeof(string))] [XmlArray("SPFiles")] public List<string> SPFiles { get { return spFiles; } set { spFiles = value; } } public DBComponent(string name, string description) : base(name, description) { } } [Serializable] public class ComponentsCollection { private static ComponentsCollection instance = null; private List<Component> components = new List<Component>(); public List<Component> Components { get { return components; } set { components = value; } } public static ComponentsCollection GetInstance() { if (ccuInstance == null) { lock (lockObject) { if (instance == null) PopulateComponents(); } } return instance; } private static void PopulateComponents() { instance = new CCUniverse(); XmlSerializer xs = new XmlSerializer(instance.GetType()); instance = xs.Deserialize(XmlReader.Create("Components.xml")) as ComponentsCollection; } } } I want read\write from a Xml file. I know that I need to implement the Serialization for DBComponent class otherwise it will not read it.But i cannot find any simple article for that. all the articles that I found were too complex for this simple scenario. The Xml file looks like this: <?xml version="1.0" encoding="utf-8" ?> <ComponentsCollection> <Components> <DBComponent Name="Tenant Historical Database" Description="Tenant Historical Database"> <SPFiles> <SPFile>Setup\TenantHistoricalSP.sql</SPFile> </SPFiles> </DBComponent> <Component Name="Agent" Description="Desktop Agent" /> </Components> </ComponentsCollection> Can someone please give me a simple example of how to read this kind of xml file and what should be implemented ? Thanks Lior

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  • Adding STI to Existing Table...

    - by keruilin
    I want to add STI to an existing table using a custom type column. Let's call this taste_type whose corresponding model is Fruit. In the Fruit model I have: set_inheritance_column :taste_type In my migration to add STI I have: class AddSTI < ActiveRecord::Migration def self.up add_column :fruits, :taste_type, :string, :limit => 100, :null => false Fruit.reset_column_information Fruit.find_by_id(1).update_attributes({:taste_type => 'Sour'}) end def self.down remove_column :fruits, :taste_type end end When I run the migration, I get the following error: Mysql::Error: Column 'taste_type' cannot be null: ... Any idea what's going? I can get the migration to run if I comment the set_inheritance_column in the Fruit model, then uncomment it after I run the migration. Obviously, I don't want to do this, however.

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  • Call the cast operator of template base class within the derived class

    - by yoni
    I have a template class, called Cell, here the definition: template <class T> class OneCell { ..... } I have a cast operator from Cell to T, here virtual operator const T() const { ..... } Now i have derived class, called DCell, here template <class T> class DCell : public Cell<T> { ..... } I need to override the Cell's cast operator (insert a little if), but after I need to call the Cell's cast operator. In other methods it's should be something like virtual operator const T() const { if (...) { return Cell<T>::operator const T; } else throw ... } but i got a compiler error error: argument of type 'const int (Cell::)()const' does not match 'const int' What can I do? Thank you, and sorry about my poor English.

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  • ruby restrict attr_accessor in subclass

    - by Arivarasan
    I want restrict the access of superclass's method in subclass class Parent attr_accessor :first_name, :last_name def initialize(first_name, last_name) @first_name, @last_name = first_name, last_name end def full_name @first_name + " " + @last_name end end class Son < Parent attr_accessor :first_name def initialize(parent, first_name) @first_name = first_name @last_name = parent.last_name end def full_name @first_name + " " + @last_name end end p = Parent.new("Bharat", "Chipli") puts p.full_name s = Son.new(p, "Harry") s.last_name= "Smith" puts s.full_name here i am getting son's full name as "Harry Smith", but i want "Harry Chipli"

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  • Javascript static method intheritance

    - by Matteo Pagliazzi
    I want to create a javascript class/object that allow me to have various method: Model class Model.all() » static method Model.find() » static method Model delete() » instance method Model save() » instance method Model.create() » static that returns a new Model instance For static method I can define them using: Model.staticMethod(){ method } while for instance method is better to use: function Model(){ this.instanceMethod = function(){} } and then create a new instance or using prototype? var m = function Model(){ } m.prototype.method() = function(){ } Now let's say that I want to create a new class based on Model, how to inherit not only its prototypes but also its static methods?

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  • PHP syntax for referencing self with late static binding

    - by Chris
    When I learned PHP it was pretty much in procedural form, more recently I've been trying to adapt to the OOP way of doing things. Hoever the tutorials I've been following were produced before PHP 5.3 when late static binding was introduced. What I want to know is how do I reference self when calling a function from a parent class. For example these two methods were written for a User class which is a child of DatabaseObject. Right now they're sitting inside the User class, but, as they're used in other child classes of DatabaseObject I'd like to promote them to be included inside DatabaseObject. public static function find_all() { global $database; $result_set = self::find_by_sql("select * from ".self::$table_name); return $result_set; } and: protected function cleaned_attributes() { global $database; $clean_attributes = array(); foreach($this->attributes() as $key => $value) { $clean_attributes[$key] = $database->escape_value($value); } return $clean_attributes; } So I have three questions: 1) How do I change the self:: reference when I move it to the parent. Is it static:: or something similar? 2) When calling the function from my code do I call it in the same way, as a function of the child class eg User::find_all() or is there a change there also? 3) Is there anything else I need to know before I start chopping bits up?

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  • Problems Allocating Objects of Derived Class Where Base Class has Abstract Virtual Functions

    - by user1743901
    I am trying to get this Zombie/Human agent based simulation running, but I am having problems with these derived classes (Human and Zombie) who have parent class "Creature". I have 3 virtual functions declared in "Creature" and all three of these are re-declared AND DEFINED in both "Human" and "Zombie". But for some reason when I have my program call "new" to allocate memory for objects of type Human or Zombie, it complains about the virtual functions being abstract. Here's the code: definitions.h #ifndef definitions_h #define definitions_h class Creature; class Item; class Coords; class Grid { public: Creature*** cboard; Item*** iboard; int WIDTH; int HEIGHT; Grid(int WIDTHVALUE, int HEIGHTVALUE); void FillGrid(); //initializes grid object with humans and zombies void Refresh(); //calls Creature::Die(),Move(),Attack(),Breed() on every square void UpdateBuffer(char** buffer); bool isEmpty(int startx, int starty, int dir); char CreatureType(int xcoord, int ycoord); char CreatureType(int startx, int starty, int dir); }; class Random { public: int* rptr; void Print(); Random(int MIN, int MAX, int LEN); ~Random(); private: bool alreadyused(int checkthis, int len, int* rptr); bool isClean(); int len; }; class Coords { public: int x; int y; int MaxX; int MaxY; Coords() {x=0; y=0; MaxX=0; MaxY=0;} Coords(int X, int Y, int WIDTH, int HEIGHT) {x=X; y=Y; MaxX=WIDTH; MaxY=HEIGHT; } void MoveRight(); void MoveLeft(); void MoveUp(); void MoveDown(); void MoveUpRight(); void MoveUpLeft(); void MoveDownRight(); void MoveDownLeft(); void MoveDir(int dir); void setx(int X) {x=X;} void sety(int Y) {y=Y;} }; class Creature { public: bool alive; Coords Location; char displayletter; Creature() {Location.x=0; Location.y=0;} Creature(int i, int j) {Location.setx(i); Location.sety(j);} virtual void Attack() =0; virtual void AttackCreature(Grid G, int attackdirection) =0; virtual void Breed() =0; void Die(); void Move(Grid G); int DecideSquare(Grid G); void MoveTo(Grid G, int dir); }; class Human : public Creature { public: bool armed; //if armed, chances of winning fight increased for next fight bool vaccinated; //if vaccinated, no chance of getting infected int bitecount; //if a human is bitten, bite count is set to a random number int breedcount; //if a human goes x steps without combat, will breed if next to a human int starvecount; //if a human does not eat in x steps, will die Human() {displayletter='H';} Human(int i, int j) {displayletter='H';} void Attack(Grid G); void AttackCreature(Grid G, int attackdirection); void Breed(Grid G); //will breed after x steps and next to human int DecideAttack(Grid G); }; class Zombie : public Creature { public: Zombie() {displayletter='Z';} Zombie(int i, int j) {displayletter='Z';} void Attack(Grid G); void AttackCreature(Grid G, int attackdirection); void Breed() {} //does nothing int DecideAttack(Grid G); void AttackCreature(Grid G, int attackdirection); }; class Item { }; #endif definitions.cpp #include <cstdlib> #include "definitions.h" Random::Random(int MIN, int MAX, int LEN) //constructor { len=LEN; rptr=new int[LEN]; //allocate array of given length for (int i=0; i<LEN; i++) { int random; do { random = rand() % (MAX-MIN+1) + MIN; } while (alreadyused(random,LEN,rptr)); rptr[i]=random; } } bool Random::alreadyused(int checkthis, int len, int* rptr) { for (int i=0; i<len; i++) { if (rptr[i]==checkthis) return 1; } return 0; } Random::~Random() { delete rptr; } Grid::Grid(int WIDTHVALUE, int HEIGHTVALUE) { WIDTH = WIDTHVALUE; HEIGHT = HEIGHTVALUE; //builds 2d array of creature pointers cboard = new Creature**[WIDTH]; for(int i=0; i<WIDTH; i++) { cboard[i] = new Creature*[HEIGHT]; } //builds 2d array of item pointers iboard = new Item**[WIDTH]; for (int i=0; i<WIDTH; i++) { iboard[i] = new Item*[HEIGHT]; } } void Grid::FillGrid() { /* For each creature pointer in grid, randomly selects whether to initalize as zombie, human, or empty square. This methodology can be changed to initialize different creature types with different probabilities */ int random; for (int i=0; i<WIDTH; i++) { for (int j=0; j<HEIGHT; j++) { Random X(1,100,1); //create a single random integer from [1,100] at X.rptr random=*(X.rptr); if (random < 20) cboard[i][j] = new Human(i,j); else if (random < 40) cboard[i][j] = new Zombie(i,j); else cboard[i][j] = NULL; } } //at this point every creature pointer should be pointing to either //a zombie, human, or NULL with varying probabilities } void Grid::UpdateBuffer(char** buffer) { for (int i=0; i<WIDTH; i++) { for (int j=0; j<HEIGHT; j++) { if (cboard[i][j]) buffer[i][j]=cboard[i][j]->displayletter; else buffer[i][j]=' '; } } } bool Grid::isEmpty(int startx, int starty, int dir) { Coords StartLocation(startx,starty,WIDTH,HEIGHT); switch(dir) { case 1: StartLocation.MoveUp(); if (cboard[StartLocation.x][StartLocation.y]) return 0; case 2: StartLocation.MoveUpRight(); if (cboard[StartLocation.x][StartLocation.y]) return 0; case 3: StartLocation.MoveRight(); if (cboard[StartLocation.x][StartLocation.y]) return 0; case 4: StartLocation.MoveDownRight(); if (cboard[StartLocation.x][StartLocation.y]) return 0; case 5: StartLocation.MoveDown(); if (cboard[StartLocation.x][StartLocation.y]) return 0; case 6: StartLocation.MoveDownLeft(); if (cboard[StartLocation.x][StartLocation.y]) return 0; case 7: StartLocation.MoveLeft(); if (cboard[StartLocation.x][StartLocation.y]) return 0; case 8: StartLocation.MoveUpLeft(); if (cboard[StartLocation.x][StartLocation.y]) return 0; } return 1; } char Grid::CreatureType(int xcoord, int ycoord) { if (cboard[xcoord][ycoord]) //if there is a creature at location xcoord,ycoord return (cboard[xcoord][ycoord]->displayletter); else //if pointer at location xcoord,ycoord is null, return null char return '\0'; } char Grid::CreatureType(int startx, int starty, int dir) { Coords StartLocation(startx,starty,WIDTH,HEIGHT); switch(dir) { case 1: StartLocation.MoveUp(); if (cboard[StartLocation.x][StartLocation.y]) return (cboard[StartLocation.x][StartLocation.y]->displayletter); case 2: StartLocation.MoveUpRight(); if (cboard[StartLocation.x][StartLocation.y]) return (cboard[StartLocation.x][StartLocation.y]->displayletter); case 3: StartLocation.MoveRight(); if (cboard[StartLocation.x][StartLocation.y]) return (cboard[StartLocation.x][StartLocation.y]->displayletter); case 4: StartLocation.MoveDownRight(); if (cboard[StartLocation.x][StartLocation.y]) return (cboard[StartLocation.x][StartLocation.y]->displayletter); case 5: StartLocation.MoveDown(); if (cboard[StartLocation.x][StartLocation.y]) return (cboard[StartLocation.x][StartLocation.y]->displayletter); case 6: StartLocation.MoveDownLeft(); if (cboard[StartLocation.x][StartLocation.y]) return (cboard[StartLocation.x][StartLocation.y]->displayletter); case 7: StartLocation.MoveLeft(); if (cboard[StartLocation.x][StartLocation.y]) return (cboard[StartLocation.x][StartLocation.y]->displayletter); case 8: StartLocation.MoveUpLeft(); if (cboard[StartLocation.x][StartLocation.y]) return (cboard[StartLocation.x][StartLocation.y]->displayletter); } //if function hasn't returned by now, square being looked at is pointer to null return '\0'; //return null char } void Coords::MoveRight() {(x==MaxX)? (x=0):(x++);} void Coords::MoveLeft() {(x==0)? (x=MaxX):(x--);} void Coords::MoveUp() {(y==0)? (y=MaxY):(y--);} void Coords::MoveDown() {(y==MaxY)? (y=0):(y++);} void Coords::MoveUpRight() {MoveUp(); MoveRight();} void Coords::MoveUpLeft() {MoveUp(); MoveLeft();} void Coords::MoveDownRight() {MoveDown(); MoveRight();} void Coords::MoveDownLeft() {MoveDown(); MoveLeft();} void Coords::MoveDir(int dir) { switch(dir) { case 1: MoveUp(); break; case 2: MoveUpRight(); break; case 3: MoveRight(); break; case 4: MoveDownRight(); break; case 5: MoveDown(); break; case 6: MoveDownLeft(); break; case 7: MoveLeft(); break; case 8: MoveUpLeft(); break; case 0: break; } } void Creature::Move(Grid G) { int movedir=DecideSquare(G); MoveTo(G,movedir); } int Creature::DecideSquare(Grid G) { Random X(1,8,8); //X.rptr now points to 8 unique random integers from [1,8] for (int i=0; i<8; i++) { int dir=X.rptr[i]; if (G.isEmpty(Location.x,Location.y,dir)) return dir; } return 0; } void Creature::MoveTo(Grid G, int dir) { Coords OldLocation=Location; Location.MoveDir(dir); G.cboard[Location.x][Location.y]=this; //point new location to this creature G.cboard[OldLocation.x][OldLocation.y]=NULL; //point old location to NULL } void Creature::Die() { if (!alive) { delete this; this=NULL; } } void Human::Breed(Grid G) { if (!breedcount) { Coords BreedLocation=Location; Random X(1,8,8); for (int i=0; i<8; i++) { BreedLocation.MoveDir(X.rptr[i]); if (!G.cboard[BreedLocation.x][BreedLocation.y]) { G.cboard[BreedLocation.x][BreedLocation.y])=new Human(BreedLocation.x,BreedLocation.y); return; } } } } int Human::DecideAttack(Grid G) { Coords AttackLocation=Location; Random X(1,8,8); int attackdir; for (int i=0; i<8; i++) { attackdir=X.rptr[i]; switch(G.CreatureType(Location.x,Location.y,attackdir)) { case 'H': break; case 'Z': return attackdir; case '\0': break; default: break; } } return 0; //no zombies! } int AttackRoll(int para1, int para2) { //outcome 1: Zombie wins, human dies //outcome 2: Human wins, zombie dies //outcome 3: Human wins, zombie dies, but human is bitten Random X(1,100,1); int roll= *(X.rptr); if (roll < para1) return 1; else if (roll < para2) return 2; else return 3; } void Human::AttackCreature(Grid G, int attackdirection) { Coords AttackLocation=Location; AttackLocation.MoveDir(attackdirection); int para1=33; int para2=33; if (vaccinated) para2=101; //makes attackroll > para 2 impossible, never gets infected if (armed) para1-=16; //reduces chance of zombie winning fight int roll=AttackRoll(para1,para2); //outcome 1: Zombie wins, human dies //outcome 2: Human wins, zombie dies //outcome 3: Human wins, zombie dies, but human is bitten switch(roll) { case 1: alive=0; //human (this) dies return; case 2: G.cboard[AttackLocation.x][AttackLocation.y]->alive=0; return; //zombie dies case 3: G.cboard[AttackLocation.x][AttackLocation.y]->alive=0; //zombie dies Random X(3,7,1); //human is bitten bitecount=*(X.rptr); return; } } int Zombie::DecideAttack(Grid G) { Coords AttackLocation=Location; Random X(1,8,8); int attackdir; for (int i=0; i<8; i++) { attackdir=X.rptr[i]; switch(G.CreatureType(Location.x,Location.y,attackdir)) { case 'H': return attackdir; case 'Z': break; case '\0': break; default: break; } } return 0; //no zombies! } void Zombie::AttackCreature(Grid G, int attackdirection) { int reversedirection; if (attackdirection < 9 && attackdirection>0) { (attackdirection<5)? (reversedirection=attackdirection+4):(reversedirection=attackdirection-4); } else reversedirection=0; //this should never happen //when a zombie attacks a human, the Human::AttackZombie() function is called //in the "reverse" direction, utilizing that function that has already been written Coords ZombieLocation=Location; Coords HumanLocation=Location; HumanLocation.MoveDir(attackdirection); if (G.cboard[HumanLocation.x][HumanLocation.y]) //if there is a human there, which there should be G.cboard[HumanLocation.x][HumanLocation.y]->AttackCreature(G,reversedirection); } void Zombie::Attack(Grid G) { int attackdirection=DecideAttack(G); AttackCreature(G,attackdirection); } main.cpp #include <cstdlib> #include <iostream> #include "definitions.h" using namespace std; int main(int argc, char *argv[]) { Grid G(500,500); system("PAUSE"); return EXIT_SUCCESS; }

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  • Conversion of pointer-to-pointer between derived and base classes?

    - by Mike Mueller
    Regarding the following C++ program: class Base { }; class Child : public Base { }; int main() { // Normal: using child as base is allowed Child *c = new Child(); Base *b = c; // Double pointers: apparently can't use Child** as Base** Child **cc = &c; Base **bb = cc; return 0; } GCC produces the following error on the last assignment statement: error: invalid conversion from ‘Child**’ to ‘Base**’ My question is in two parts: Why is there no implicit conversion from Child** to Base**? I can make this example work with a C-style cast or a reinterpret_cast. Using these casts means throwing away all type safety. Is there anything I can add to the class definitions to make these pointers cast implicitly, or at least phrase the conversion in a way that allows me to use static_cast instead?

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  • Inheriting from the web client class

    - by robUK
    Hello, C# 2008 I am not sure how much work there is to inheriting from the web client class. Currently I am using it in my project. And I can't change to anything else. The customer would like to have a timeout after a certain period of time. The web client doesn't have this. So rather than re-invent the wheel, I am thinking of inheriting from the web client and adding this property. Do you think this is a suitable solution? Could it mean more work just to add this. What is the easiest way to go about this? Many thanks,

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  • Linq 2 SQL Store inherited classes - not mapped to tables in the database

    - by user348672
    Hi. I'm trying to introduce the Linq2SQL technique into the project and have encountered the following issue: I've created ORM classes based on the Northwind database. In some other application I create several classes derived from the Linq2SQL classes. I'm able to add such a class to EntitySet but the application fails to submit changes. Is there any way around this? Sample code(MyClass is derived from the Order): DataClasses1DataContext northwind = new DataClasses1DataContext(); Product chai = northwind.Products.Single(p => p.ProductName == "Chai"); Product tofu = northwind.Products.Single(p => p.ProductName == "Tofu"); Order myOrder = new Order(); myOrder.OrderDate = DateTime.Now; myOrder.RequiredDate = DateTime.Now.AddDays(1); myOrder.Freight = 34; Order_Detail myItem1 = new Order_Detail(); myItem1.Product = chai; myItem1.Quantity = 12345; Order_Detail myItem2 = new Order_Detail(); myItem2.Product = tofu; myItem2.Quantity = 3; myOrder.Order_Details.Add(myItem1); myOrder.Order_Details.Add(myItem2); Customer myCustomer = northwind.Customers.Single(c => c.CompanyName == "B's Beverages"); MyClass newOrder = new MyClass(); newOrder.OrderDate = DateTime.Now; newOrder.RequiredDate = DateTime.Now.AddDays(31); newOrder.Freight = 35; Order_Detail myItem3 = new Order_Detail(); myItem3.Product = tofu; myItem3.Quantity = 3; newOrder.Order_Details.Add(myItem3); myCustomer.Orders.Add(myOrder); myCustomer.Orders.Add(newOrder); As I said I'm able to add the newOrder object but unable to submit into the database.

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  • Can I create a custom class that inherits from a strongly typed DataRow?

    - by Calvin Fisher
    I'm working on a huge, old project with a lot of brittle code, some of which has been around since the .NET 1.0 era, and it has been and will be worked on by other people... so I'd like to change as little as possible. I have one project in my solution that contains DataSet.xsd. This project compiles to a separate assembly (Data.dll). The database schema includes several tables arranged more or less hierarchically, but the only way the tables are actually linked together is through joins. I can get, e.g. DepartmentRow and EmployeeRow objects from the autogenerated code. EmployeeRow contains information from the employee's corresponding DepartmentRow through a join. I'm making a new report to view multiple departments and all their employees. If I use the existing data access scheme, all I will be able to get is a spreadsheet-like output where each employee is represented on one line, with department information repeated over and over in its appropriate columns. E.g.: Department1...Employee1... Department1...Employee2... Department2...Employee3... But what the customer would like is to have each department render like a heading, with a list of employees beneath each. E.g.: - Department1... Employee1... Employee2... + Department2... I'm trying to do this by inheriting hierarchical objects from the autogenerated Row objects. E.g.: public class Department : DataSet.DepartmentRow { public List<Employee> Employees; } That way I could nest the data in the report by using a collection of Department objects as the DataSource, each of which will put its list of Employees in a subreport. The problem is that this gives me a The type Data.DataSet.DepartmentRow has no constructors defined error. And when I try to make a constructor, e.g. public class Department : DataSet.DepartmentRow { private Department() { } public List<Employee> Employees; } I get a 'Data.DataSet.DepartmentRow(System.Data.DataRowBuilder)' is inaccessible due to its protection level. error in addition to the first one. Is there a way to accomplish what I'm trying to do? Or is there something else I should be trying entirely?

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  • c# inheriting generic collection and serialization...

    - by Stecy
    Hi, The setup: class Item { private int _value; public Item() { _value = 0; } public int Value { get { return _value; } set { _value = value; } } } class ItemCollection : Collection<Item> { private string _name; public ItemCollection() { _name = string.Empty; } public string Name { get {return _name;} set {_name = value;} } } Now, trying to serialize using the following code fragment: ItemCollection items = new ItemCollection(); ... XmlSerializer serializer = new XmlSerializer(typeof(ItemCollection)); using (FileStream f = File.Create(fileName)) serializer.Serialize(f, items); Upon looking at the resulting XML I see that the ItemCollection.Name value is not there! I think what may be happening is that the serializer sees the ItemCollection type as a simple Collection thus ignoring any other added properties... Is there anyone having encountered such a problem and found a solution? Regards, Stécy

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  • Why does a function that takes IEnumerable<interface> not accept IEnumerable<class>?

    - by Matt Whitfield
    Say, for instance, I have a class: public class MyFoo : IMyBar { ... } Then, I would want to use the following code: List<MyFoo> classList = new List<MyFoo>(); classList.Add(new MyFoo(1)); classList.Add(new MyFoo(2)); classList.Add(new MyFoo(3)); List<IMyBar> interfaceList = new List<IMyBar>(classList); But this produces the error: `Argument '1': cannot convert from 'IEnumerable<MyFoo>' to 'IEnumerable<IMyBar>' Why is this? Since MyFoo implements IMyBar, one would expect that an IEnumerable of MyFoo could be treated as an IEnumerable of IMyBar. A mundane real-world example being producing a list of cars, and then being told that it wasn't a list of vehicles. It's only a minor annoyance, but if anyone can shed some light on this, I would be much obliged.

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  • C# visually subclass datagridview control VS2005

    - by DRapp
    Maybe its something stupid, but I'm having a problem with a subclass of a DataGridView Control in VS2005 C#. I know I can subclass from almost anything by doing public class MyDataGridView : DataGridView {} no problem, and I put in some things / elements I want applicable globally. Now, I take this gridview and put into a custom user control that will contain other controls too. So I have something like created by the visual designer. I grab some buttons, label, and my derived "MyDataGridView" on it. public partial class MyCompoundDGVPlus : UserControl So, now, I can visually draw, move, change all sorts of settings as needed, no problem. Now, I want this "MyCompoundDGVPlus" class as the basis for other classes, of which I will manipulate settings specific, but want all to have the same look / feel, and otherwise similar flow, hence the derivations. I've even set the "modifiers" setting to public, so I SHOULD be able to modify any of the properties of the controls at any derived level. So, now, I create a new subclass of "MyFirstDetailedDGVPlus" derived from "MyCompoundDGVPlus". Ok visually, all the label, button, datagridview appear. However, now I want to specifically define the columns of the datagridview here in this class visually, but its locked. However, the LABEL on the form, I CAN get all the property settings.... What am I missing.

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