Imagine if there is an abstract class with a method (say output or print) which would be inherited by a few other classes. Later objects are created using the inherited classes, and the user wishes to call the above method twice, for eg (i) output/print to screen and (ii) output/print to a file. What is the best way to achieve that.
View 6 RepliesI did know that the size of a class is increased by 4 bytes (32bit compiler) if the class has a virtual function. I wrote one program and it is giving strange output. I am using linux g++ compiler.
The program and output is as below
Code:
#include<iostream>
using namespace std;
class Base {
public:
void fun() {
[Code] ....
output=4
Code:
#include<iostream>
using namespace std;
class Base {
public:
virtual void fun() {
[Code] .....
Output is 16
I have an abstract base class - let's call it MyInterface - and a class that most classes in my program inherit from, let's call it MyBaseclass.
Let's assume that all my objects inherit MyBaseclass, some of which also inherit MyInterface. Now I want to collect objects in a container class, MyContainerclass. The container class is only interested in objects that implement MyInterface.
Now I know that all objects that inherit MyInterface also inherit MyBaseclass, but the compiler doesn't know that. MyContainerclass wants to call methods in MyBaseclass, but it collects pointers to MyInterface classes. I can't make MyInterface inherit MyBaseclass, because I will be using classes that I don't want to change (they are part of a framework) that already inherit MyContainerclass. IOW, I can't use virtual inheritance to get a nice inheritance diamond.
To sum up, I want to create a container class that:
1. Collects objects that implement MyInterface.
2. Calls MyBaseclass methods on the collected objects.
two more questions
Code:
#ifndef PERFECTSIM_PARSER
#define PERFECTSIM_PARSER
#include <string>
#include <d3dx9.h>
#include <sstream>
#include <iostream>
#include "tinyxml inyxml.h"
using namespace std;
template<class T>
class GetValue {
protected:
virtual T get(TiXmlNode* pParent);
[code].....
1) Can't instantiate abstract class of GetVector3.
2) Don't you think the coding is very redundant ?
I need to create a vector of pointers and hold the book objects in it. then i have a virtual function in my books which is a pure virtual in LibraryItems. When i try to add the books object in my code, i understand that since the scope runs out there is no object that is added. so when i run print it gives me an error.
#include<iostream>
#include "books.h"
#include "library.h"
#include <vector>
using namespace std;
int main(int argc, char * argv[]) {
vector<LibraryItems* >libraryInfo;
[Code] .....
I have this header file called Shape.h containing these function declarations. and a Shape.cpp which contains the body of the function. I am not showing it since it is not needed.
//This is from Shapes.h header file
#ifndef SHAPES_H
#define SHAPES_H
#include <iostream>
[Code]....
I have this unfinished Main.cpp because the third line "JuanSanchez::Circle *pCar = new Circle; " is giving me a compiler error "error C2061: syntax error : identifier 'Circle' "
#include "Shapes.h"
int main()
{
const int arrayIndex = 4;
JuanSanchez::Shape *myShape[arrayIndex];
JuanSanchez::Circle *pCar = new Circle;
}
What Could be causing this error?
I have the following code:
class Element {
public:
..
virtual unsigned NumberOfNodes() = 0;
[Code] ....
Is it possible to implement this better? All the element stuff can be static, but this is not possible with the abstract class. I want to have Mesh independent of a specific element. With the code above, if I have multiple meshes I have one instance of an element, e.g., Triangle for each mesh. Although they are all exactly the same.
I am working on a project that requires me to create objects from a abstract class that has 2 child classes (that need to be derived). Any examples on how to do this? I looked online and the examples were pretty vague. the main error that I am getting is when I make a temp object with & in front of it (such as Employee &genericEmp) it throws a must be initialized error.
View 6 Replies View RelatedI want to create an abstract base class having a member function that can accept a templatized structure as its parameter, something that according to C++'s rules can't be done for a good reason.
That good reason it is because an abstract base class is intended to provide interface rules to the classes that will derive from it and should not deal with data.
But how would you go about doing something like the following which is probably a reasonable design decision?
template<typename T>
class Matrix { /* ... */ };
class iFile {
public:
virtual ~iFile() {} = 0;
virtual void Process(const Matrix<T>&) = 0;
[Code] .....
I am making a snake game just to give some context.
//LevelObject.hpp
class LevelObject {
public:
virtual void Update() = 0;
virtual void Draw(Canvas& canvas) = 0;
protected:
Vector3 location_;
[Code] ....
The problem I have is with the Size constructor and the abstract class LevelObject which size is a member of.
The compiler error I get is:
C:Program Files (x86)ProgrammingProjectsUniversityprg_interactivesnakey_takeysrc..inc..incPlayer.hpp|17|warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 [enabled by default]|
C:Program Files (x86)ProgrammingProjectsUniversityprg_interactivesnakey_takeysrc..inc..inc..incPlayer.hpp|17|warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 [enabled by default]|
[Code] .....
However I do invoke the copy constructor when I pass a variable of type size to the constructor in this line:
size_ = Size(s);
But the problem is that its complaining that the abstract class LevelObject doesn't invoke the constructor, which it shouldn't.
I have an abstract class called Mbase and from it derived two classes: Sparse and Dense. Now I have an array in which its elements can be either Sparse or Dense. So, I delcared the array to have pointers to Mbase class. For example:
PHP Code:
Mbase** A;
Sparse* A1 = new Sparse;
Dense* A2 = new Dense;
A[1] = dynamic_cast<Mbase*>(A1);
A[2] = dynamic_cast<Mbase*>(A2);
Now, I have operator + defined in Sparse and Dense. but when I do
PHP Code:
A[1]+A[2]
I get that operator + is not defined for Mbase class. So, I tried to define it in the Mbase class
PHP Code:
class Mbase{
public:
void put()=0;
double get()=0;
Mbase operator +(Mbase A);
}
However, the last code does not compile complaining that it cannot declare a class of type abstract in Mbase operator +(Mbase A). I think this is because I am returning Mbase instance.
I have an abstract class named Terrain, and a class named RoadMap, which supposed to hold an N*N array of Terrains. But I'm not sure what type should the RoadMap class hold:
Code:
#ifndef TERRAIN_H
#define TERRAIN_H
class Terrain {
[Code] ....
I can't use an array of refernces here, so I tried this:
Code: Terrain** terrain; and then I thought this was the way to go:
Code: Terrain (*terrain)[]; But now I'm not sure.
The N*N matrix size supposed to be determined according to a given input... What type should I use there?
As i have one Abstract base class say MyBase.
It have parameterized constructor with string value it have abstract method call.And I also have One child class say MyChild.
It does not have any constructor only one have public method and i want to call that parameterized constructor of base class onto child class.
how to call the methods of the class.I have an object call v which is an array and I don't how to call the methods of the class. The error is here:
v.readDates(v[a]);
#include "Date.h"
#include <iostream>
using namespace std;
int main(){
int a;
cout << " HOW MANY DATES DO YOU HAVE? " << endl;
[code]....
I'm using lua 5.2.2 with luabind 0.9.
I'd like to be able to add additional class-methods through lua for any classes that I've bound in c++, but I'm unsure how to do it.
The problem is that luabind uses a function as the __index-metamethod for any bound classes instead of a table, so I don't see a way to access the class-methods at all.
e.g., I'm binding my classes like this:
luabind::module(lua) [
luabind::class_<testClass>("TestClass")
.def(luabind::constructor<>())
.def("TestFunc",&TestFunc)
];
What I essentially want to do is to add a lua-function to the list of methods for this class, and be able to overwrite existing ones:
local t = tableOfClassMethods
local r = t.TestFunc -- Reference to the c++-function we've bound
t.SomeFunction = function(o) end -- New function for all objects of this class
t.TestFunc = function(o) end -- Should overwrite the c++-function of the same name
I'm trying to implement a decision tree that gets doubles as input (in this sample code just random numbers) and returns a boolean value. At the nodes, I'd like to use various operators that can have different input and return types. I've implemented an abstract base class for the nodes and I'm deriving the specific nodes from it. In the code below, I've included only a few derived classes. Building the tree (randomly) is no problem. However, I'm looking for a clever way to evaluate the tree. I think that uncommenting the lines in bold print would in principle do it. However, this is not possible because "value" is not a member of the base class. The type of "value" is different in the derived classes, so I cannot simply declare it in the base class.
"Node.h"
#pragma once
class NodeBase{
public:
NodeBase* Child_1;
NodeBase* Child_2;
virtual void evaluate() = 0;
[Code] ....
A have two classes, one inheriting the other, and the parent class being abstract (I plan on adding more child classes in the future). For reasons I won't bother mentioning, I'm making use of an STL container as a way for me to access all of the child objects in the heap. I've done so by making use of a map, with key type int and value type being a pointer to the parent class:
//PARENT.H
class Parent {
protected:
static int n;
static std::map<int, Parent*> map;
public:
virtual void pureVirtual() = 0;
[code]....
The Problem:In line 5 of Parent.cpp, initializing the value of the element to new Child won't work, as according to the compiler, the Child class hasn't been declared yet, and including Child.h into the Parent.h only opens an even bigger can of worms.I also can't initialize it as new Parent, seeing as the parent class is an abstract one.
The Question:Is there a way I can initialize the static map properly. Making the Parent class abstract is not an option.
For example, in a header file A.h, I define an abstract class,
Code:
// A.h
class A {
public:
virtual void foo() = 0;
private:
static int _x;
};
How'd I initialize static member data _x?Normally, we initialize a static member data in a cpp file. However, there is not cpp file for A.h. If I intialize _x in header file, there will be linker errors like mulitple defined symbols. What is appropriate way to do that?
Creating the methods for class List
main.cpp Code: #include "List.h"
int main( )
{
List la; // create list la
la.push_front( "mom" );
la.push_back( "please" );
la.push_back( "send" );
la.push_back( "money" );
la.push_front( "hi" );
cout << "
la contains:
" << la << '
[code]...
I need to override a few methods in FILE class so i defined few methods as
EnCrpt * fp;
fp * fopen(const char * filename, const char * mode);
int fwrite(const void * p,int length,int readLenth,FILE * fpp = NULL);
int fread(void * p,int length,int readLenth,FILE * fpp = NULL);
int fseek(FILE * fpp = NULL,long offset, int whence);
long ftell(FILE * fpp = NULL);
int feof(FILE * fpp = NULL);
int fflush(FILE * fpp = NULL);
int fclose(FILE * fpp = NULL);
I will call fread method in my encrypted file class .. similar to other methods.. is this correct ? can NULL file pointer create issue ?
Because i have so many place where FILE class called i don't want to change everywhere to call encrypted file class so i am override these methods to encrypted file class instead of standrd FILE class
I am given 2 methods and they want me to create a stand alone class for sql that will change the sql string.
my question is how can i take these 2 methods and make one class out of them that will used on various other forms.
#1
public string AuthenticateWithDB(CUiPontisDatabaseSpecification pdb, string sUserId, string sPassword,
bool bCreatePersistentCookie)
#2
public static void ChangeConnection(Util.ODBC.ODBCDSN odbcInfo, CPonDatabaseVendorType dbType, string uid, string password)
they want it so they can use it like
CUiHttpSessionManager.SimpleDataConnectionString = SomeNewClass.CreateSimpleDataConnectionString()
where some new class is my new class
The abstract class can provide more functionality without affecting child classes.If we add any method to the interface ,then will it affect all the child classes ?
View 2 Replies View RelatedThere is any method to compile a method of a class separately from the other methods and the main.
View 1 Replies View RelatedThe only difficulty im having is creating a class and methods & being able to access them from my win form app. Can i get a few tips on the do's and donts of creating classes / methods and accessing them from form app.
This is what i have put together so far.
public partial class Form1 : Form {
private Image[] dicePics;
private int[] diceNum;
private Random randomize;
public Form1() {
InitializeComponent();
[code]....
I develop add-ons for MS Flight Simulator and I use the poorly documented SDK for this. The SDK provides a .h file in which an interface class is defined (with pure virtual methods only), something like this:
Code:
class IPanelCCallback {
public:
virtual IPanelCCallback* QueryInterface (PCSTRINGZ pszInterface) = 0;
virtual bool ConvertStringToProperty (PCSTRINGZ keyword, SINT32* pID) = 0;
virtual bool ConvertPropertyToString (SINT32 id, PPCSTRINGZ pKeyword) = 0;
};
In my code, I use this interface like this:
Code:
IPanelCCallback* pCallBack = panel_get_registered_c_callback("fs9gps");
...
SINT32 id;
pCallBack->ConvertStringToProperty(propertyName, &id);
Everything works fine, but I don't understand why... I thought the linker would stop with an "undefined symbol" error because the IPanelCCallback methods, such as ConvertStringToProperty, are declared as pure virtual but defined nowhere, and I don't use any library for linking. With such an interface class, I thought I would have to defined a subclass of IPanelCCallback and define the ConvertStringToProperty method.
I am writing my program on C++ language. I have one promblem. I need to set signal handler for my process. As the signal is related with the process on system level I have faced the problem.
My program consists several classes. They are connected together. But it doesn't metter in this case. The problem is that I need to access to member and methods of the class from my signal handler. For instance , I have class named Foo at it has some members and methods.
So from my handler I need to call its function and change members.
I understand that compiler should know that this class instances will exist during all program execution.
I have tried to set static member class Foo instance in another class , but this didn't solve the problem.
What is correct approach to do this. How to correctly implement signal handling in such case.
Here is example of my code
Code:
class MyContainer{
private:
std::vector<Foo> container;
public:
int removeFromContainer(Foo* aFoo) {
[Code] .....