C++ :: Graph Class - How To Provide Virtual Iterators
May 29, 2013
I have a 'Graph' class, which has derived classes for Adjacency Matrix and Adjacency List representations.
How do I provide iterators for traversing vertices and edges, when the iterator classes would have different implementations for the different derived classes ?
The following way is the only one I can think of, but seems quite cumbersome.
Code:
class Base {
public:
class BaseIterator {
};
virtual const BaseIterator& begin();
virtual const BaseIterator& end();
[Code] .....
Or is there a pattern for doing this that I'm not aware of ? Would composition be a better idea here compared to polymorphism ? I mean, I can think like..a Graph can 'have' several representation 'objects' within it.
All the involved classes are templates,not sure if that makes the situation different.
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Mar 6, 2014
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 ?
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Mar 27, 2013
i want to know how i can solve this question? do i need to create a class or write the program codes.
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Jan 21, 2014
The compiler creates virtual table for the base class and also for the derived class whether we override it or not.
That means each class has separate virtual table. when we get the size of the each class with out any data members... the size of base is -- 4 bytes(64 bit) and the size of derived is -- 1
The size of base class 4 is correct since it creates the virtual pointer internally and its size is member data + virtual pointer, but it in this case I have included any data members so it has given 4 byts.
But why in case of derived is 1 byte, since it the derived class has overridden the virtual function from base, this will also contains the virtual pointer which will be pointing to derived class Vtable, it the size of the class suppose to be 4 instead of 1 byte.
#include<iostream>
class A{
public:
[Code].....
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Dec 27, 2012
class Parent{
public:
virtual int width();
virtual int height();
int area(){return width()*height();};
[Code] ....
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Mar 27, 2015
I am trying to create a platformer and is stuck on a problem regarding my virtual class Entity. I wish to use it to create stuff like the Player and Enemy class(es). But how to do the parameter for my collision check function. Below is my Entity- and player class.
There might be a better way to check CC with a lot of different objects, this is my first attempt.
This is the error I am getting: "error C2664: 'bool Player::CollisionCheck(Hostile)' : cannot convert argument 1 from 'Player' to 'Hostile'"
#ifndef ENTITY_H
#define ENTITY_H
#include <SFMLGraphics.hpp>
class Entity {
public:
Entity();
Entity(sf::Vector2f position, sf::Vector2f size, sf::Color fillColor, sf::Color outlineColor);
[Code] ....
and in Hostile I would (I guess) use
bool CollisionCheck(Player p);
But if I try for example to use Player in the CC in player.h it will complain that the function doesn't have an overload for that. Hostile is just a example class name right now, it isn't implemented yet. I am trying to use Player, but if possible wish to be able to have a different class depending on what kind of entity it is. The entity will probably also be the players projectiles and so on.
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Feb 17, 2013
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?
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May 4, 2013
How can I access the virtual base class? This is a practice exercise from c++ primer plus 6.
The problem is that the name becomes No Name instead of the name specified when creating the gunslinger, I don't know how I can call the virtual base class explicitly
Output,
#ifndef PERSON_H_
#define PERSON_H_
#include <string>
#include <iostream>
#include <cstdlib>
using std::string;
class person
[code]....
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Mar 20, 2013
Below is simplified code consists of two classes, namely Parent and Child.
Child is inherited from Parent.
All member functions of class Parent are declared virtual, and they have been overridden in the class Child.
Code 1:
#include <cstdlib>
#include <iostream>
using namespace std;
#define QUANTITY 5
class Parent {
[Code] ....
The output of the code:
Child::showID() -- ID is 1804289383
Child::showID() -- ID is 846930886
Child::showID() -- ID is 1681692777
Child::showID() -- ID is 1714636915
Child::showID() -- ID is 1957747793
Parent::operator=() invoked.
Child::showID() -- ID is 1804289383
Child::showID() -- ID is 846930886
Child::showID() -- ID is 1714636915
Child::showID() -- ID is 1714636915
Child::showID() -- ID is 1957747793
Question:
Why is Parent::operator= invoked instead of Child::operator= ..?
Isn't it already declared virtual and hence would be overridden..?
I need to invoke Child::operator= instead. How to achieve this?
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Oct 27, 2014
In short, this is what I have
class A{
A(){}
virtual void pure() = 0;
}
[Code] .....
I need a2 to be a deep copy of a1, but if I understand it correctly, then a2 should just be a pointer copy of a1. How do I make a2 be a different instance of B?
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Apr 22, 2015
Here is an example,
Code:
class A {
public:
virtual void foo(){}
virtual void foo2(){}
virtual void foo3(){}
};
int main() {
A a;
int ret = sizeof(A);
return 0;
}
Basically object a contains a virtual table pointer which is of size 4 bytes. Since class A should have a virtual table which contains three pointers pointing to foo, foo2,foo3 separately. So the virtual table should be of size 12 bytes. I wonder where is virtual table located in memory?
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Jul 11, 2012
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.
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Aug 26, 2013
Assume this class:
class GenericTrafficLight {
public:
virtual enum LightState;
void setLightState(LightState newState) {
currentState = newState;
}
private:
LightState currentState;
};
And this deriving class:
class FuturisticTrafficLight : public GenericTrafficLight {
public:
enum LightState {
LIGHT_STATE_RED = 0,
LIGHT_STATE_YELLOW = 1,
LIGHT_STATE_CYAN = 2,
LIGHT_STATE_GREEN = 3
};
};
This yields this error: "C2911 (...) cannot be declared or defined in the current scope" in the deriving class's enum definition.
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Mar 16, 2013
Let's look at this simplified code, it gives compilation error
#include <iostream>
using namespace std;
class A {
public:
void showInfo() { cout << " This is an instance of A" << endl; }
[Code] ....
Without using pointer, how to make this works?
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May 8, 2014
Given an array of angles A = [0 30 60 90 120 150 180 210 240 270 300 330 360]
Write a program that will generate the data set of angles automatically and provide three columns; sin(angle), cos(angle), tan(angle). Make this program as compact and readable as possible.
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May 6, 2014
I need to do a code that gave me Original string, uppercase string, lowercase string, reverse string (if letter is upper then convert to lower, and if lower then convert it to upper) and uppercase first (first character of each word in uppercase).
I need to do it in functions but i dont know hot to use strings. The program should provide the option to save the outputs in a file.
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Sep 27, 2013
I want some people to see my C++ program, enter inputs (they can enter number 1, 2, 3, etc) as CIN, and then the program runs as it would if they were sitting in my place.
I have seen a few places which try to do this e.g.
[URL]
The problem is the CIN is not fully featured. For example in the first website you have to enter the input before you run the program. So that would not work for a program where CIN was being done all the time.
So I can get a domain, ask them to telnet into the Linux shell and compile and run my c++ Demo program. Is that the best way? Thats the worst case. I send them the .cpp file and they'll have to run and compile it on their own machine.
The best case is that they click on a link, get an online console and interact with it like they would with a real input/output c++ interface.how this can be done?
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Dec 25, 2014
I'm having problem getting the values for iterators. This code:
auto sum = inputVec.begin() + itLast;
gave this error: no match for 'operator+'
#include <iostream>
#include <vector>
#include <iterator>
using namespace std;
int main(){
vector<int> inputVec;
[Code] .....
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Feb 6, 2013
Do stream iterators, such as std::istreambuf_iterator<char>, read a chunk of bytes internally, or do they read the stream one byte at a time?
Because I am thinking to write a BufferedFile class which uses an std::vector<char>.
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May 20, 2013
In this code:
vector<int> mydata(100);
mydata[2] = 999;
In statement 2 does that call the iterator to access the 3rd position and set its value to 999?
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Oct 13, 2013
Assuming I have a list of pointers to a generic type T:
#include <vector>
//...
list<T*> myList;
Now assuming I want to go on the list, and if T's type is matched to the type I'm looking for, then cast it to this type and do something. List shown here:
list<T*>:: const_iterator iter= myList.begin();
for(; iter!=myList.end(); ++iter){
if( typeid(*iter)==typeid(Something*)) //RUN-TIME ERROR
dynamic_cast<Something*>(*iter)->DoSomething();
}
how do I fix this run-time error?
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Jun 15, 2014
When using an iterator with a std container (list / vector etc) sometimes it's possible to modify the container (e.g. delete an item) yet still carry on using the iterator - whereas in other cases, modifying the container immediately invalidates any open iterators on it. Is there an easy way to know which containers fall into which category? (or does it vary from one compiler to another?)
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Oct 8, 2014
I am working on very large code.
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Oct 9, 2014
I am working on very large code. I got a segmentation fault when trying to use one cpp file and tried to locate the error using Valgrind
Since the code is very large, I will only post a short portion of it below. I think the problem may come because triann is a vector defined in the header class, so triann[tri] is causing problems?
void ADe::aNe(int v, set<int> &nei)
{
for(set<int>::iterator iter = vert2tri[v].begin(); iter != vert2tri[v].end(); iter++)
{
[Code].....
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Jul 5, 2012
I'm working on writing some classes around a ROM hardware addon card. The classes expose the data on the ROM as a container with iterators, much like a vector or a list.
The classes don't have any data themselves, since all the data is on the ROM.
I'm having some dillemma's as to how to approach/implement the classes. If you were to write somethign like this... Or were using something like this written by someone else.... How would you expect this to be done ?
1) Make all the member functions static, make a private constructor to prevent making instances. This works, but may look a bit weird...
Code:
for (auto it = RomTable::begin(); it != RomTable::end(); ++it)
2) expect users to make a (dummy) instance, then use it as a regular container. this might be a bit counter intuitive since the class has no datamembers.
3) create a single instance, expect users to use that everywhere. make the constructor inaccessible. Some C++ 'purists' might perceive this as global data and thus not a good solution ?
Additionally. Do I need to provide both a const_iterator and an iterator ? There's nothing to be modified, so I'm guessing an iterator isn't needed (?) Or will some STL stuff not work without an iterator ? I'm obviously not fussed about the STL functions that make changes to the container to not work (like sort, fill, swap...)
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Jul 18, 2012
So i made an STL compatible container.And to make this work I had to make my own iterator (derived from std::iterator).
What is the portable (if any) and "well behaved" thing to do in case of usage anomalies.such as iterating an iterator too far, or passing an invalid index to a operator[]
Looking at how VC++ does things in something like std::array or std::vector.
Code:
iterator_type& operator+=(difference_type offset)
{// increment by integer
#if _ITERATOR_DEBUG_LEVEL == 2
if (size < index + offset)
{// report error
[Code] .....
lots of names starting with underscores, so it's implementation specific. Is there even a "well behaved" thing to do ? Or is any such work always going to be compiler specific?
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