Here is the code,
Code:
class A {
public:
virtual void foo(){}
};
class B : public A {
[Code] ....
Obviously when you call pA->foo, it will call foo defined in B. But foo defined in B is private. It is not supposed to be called outside the class B. So it looks like virtual breaks encapsulation.
I want to define a base class A which allows different type of logging (file stream, console, etc). In the meantime, I want a class B to to be able to call A's print function (i.e. derived class C's print function which defines the logging method). However, I don't want to make A's print function to be public because it will only be called by B.
class A {
protected:
virtual void print(void);
};
[Code] .....
I have been reading up about object oriented programming recently and have come across 'Encapsulation, Polymorphism and Inheritance' as i understand it so far all OOP programs should use these three concepts. So i started thinking how do i get these concepts into my program as i am using WPF C# and i could not really find much good info about how these concepts apply to WPF programs.
Or do these concepts just not work with WPF programs?
what is main Difference between Encapsulation and Data Abstraction?
View 2 Replies View RelatedI am working on a code and first i need to initialize the array depending on the size (min size 3x3, maximum size 9x9). The initialized array will descend in order. Note that it seems like a simple code and seems to work for any size from 3x3 to 7x7, but for some reason i get a strange output in the last few rows for 8x8 and 9x9. Not sure why. The second part to my problem is the very last digit of 0. I did hard code to define it but i would like to make it a character like an underscore...what is the easy way to do this?
* Implements the Game of Fifteen (generalized to d x d).
*
* Usage: ./fifteen d
*
* whereby the board's dimensions are to be d x d,
* where d must be in [MIN,MAX]
*
* Note that usleep is obsolete, but it offers more granularity tha sleep and is simpler to use than nanosleep; `man usleep` for more.
#define _XOPEN_SOURCE 500
#include <cs50.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
// board's minimal dimension
#define MIN 3
[Code] .....
For my c++ we're suppose to write a program that prints out a check. It's suppose to translate the numeric value of the dollars to worded strings.
Header File:
#ifndef CHECKWRITING_H
#define CHECKWRITING_H
#include <string>
[Code]....
I'm trying to make a percentage counter inside a loop, printing each completed percent of the loop as it goes. I've managed to write such code, but when I run it the percentage output breaks down (becomes negative!) for large loops. I have an example below.
Code:
#include <iostream>
#include <sstream>
#include <string>
#include <stdlib.h>
#include <stdio.h>
using namespace std ;
int main() {
[code].....
Compiling and running the above yields the output:
Code:
...1% ...2% ...3% ...4% ...5% ...6% ...7% ...8% ...9% ...10% ...11% ...12% ...13% ...14% ...15% ...16% ...17% ...18% ...19% ...20% ...21% ...-21% ...-20% ...-19% ...-18% ...-17% ...-16% ...-15% ...-14% ...-13% ...-12% ...-11% ...-10% ...-9% ...-8% ...-7% ...-6% ...-5% ...-4% ...-3% ...-2% ...-1% ...0% ...1% ...2% ...3% ...4% ...5% ...6% ...7% ...8% ...9% ...10% ...11% ...12% ...13% ...14% ...15% ...16% ...17% ...18% ...19% ...20% ...21% ...-21% ...-20% ...-19% ...-18% ...-17% ...-16% ...-15% ...-14% ...-13% ...-12% ...-11% ...-10% ...-9% ...-8% ...-7% ...-6% ...-5% ...-4% ...-3% ...-2% ...-1% ...0% ...1% ...2% ...3% ...4% ...5% ...6% ...7% ...8% ...9% ...10% ...11% ...12% ...13% ...14%...100%
If I change the value of N to 1e7 instead of 1e8, the output is correct however!
Code:
...1% ...2% ...3% ...4% ...5% ...6% ...7% ...8% ...9% ...10% ...11% ...12% ...13% ...14% ...15% ...16% ...17% ...18% ...19% ...20% ...21% ...22% ...23% ...24% ...25% ...26% ...27% ...28% ...29% ...30% ...31% ...32% ...33% ...34% ...35% ...36% ...37% ...38% ...39% ...40% ...41% ...42% ...43% ...44% ...45% ...46% ...47% ...48% ...49% ...50% ...51% ...52% ...53% ...54% ...55% ...56% ...57% ...58% ...59% ...60% ...61% ...62% ...63% ...64% ...65% ...66% ...67% ...68% ...69% ...70% ...71% ...72% ...73% ...74% ...75% ...76% ...77% ...78% ...79% ...80% ...81% ...82% ...83% ...84% ...85% ...86% ...87% ...88% ...89% ...90% ...91% ...92% ...93% ...94% ...95% ...96% ...97% ...98% ...99%...100%
when i uncomment statements in the following ,it works perfectly fine for infix to postfix conversion.although comments are simple cout statements,, execution with cout statements as comments breaks in b/w.I have found this particularly with a^b-c.DevCPP is also showing similar behavior. I can't understand what's going on.I am working on code blocks.
#include<iostream>
#include<cstdio>
#include<conio.h>
using namespace std;
char stk[15];
[code]....
Using cin.sync() works great so far, but my program still breaks if you copy something with multiple lines into the console.
string test = "";
while(true) {
cin.sync();
getline(cin, test );
cout << endl << "test: " << test << endl;
}
However, if you were to copy this:
1
2
3
and paste it into the program, the output would be1
2
3
test: 1
test: 2
And if you press enter one more time:1
2
3
test: 1
test: 2
test: 3
The 3 finally pops out.
class Parent{
public:
virtual int width();
virtual int height();
int area(){return width()*height();};
[Code] ....
I have questions about multiple inheritance and virtual methods. I have a class called solid. All objects of this class have hitboxes and can collide with others. I have the following methods:
void testCollision(something begin, something end);
/* This method takes a container's begin and end iterators to test if the object collides with any other object of the list of all the solids currently in the game area. Each time there is a collision, it calls collide(other) and other.collide(*this) */
virtual bool collide(solid& other);
/* This method always returns false and does nothing */
This class will be inherited by another class which will have overloads for a few specific collisions. For example:
class player : public solid{
public:
bool collide(projectile& other);
bool collide(enemy& other);
bool collide(wall& other);
};
My question is quite simple actually. If I have a loop which calls testCollision() with all elements in the list of all solids (a list of pointers to solids to be exact) and there is a collision between the player and a projectile, will testCollision call player::colide(projectile& other) or will it call solid::collide(solid& other). And in any case, did I understand how to use the virtual keyword? If I'm right, it should call the player::colide method if it's there for the specific type, else it will call the solid::colide which only returns 0, ignoring collision.
have a look at the following code :
class Base
{
public:
virtual ~Base()
{
cout << "Calling ~Base()" << endl;
[Code]...
Now this program produces the following result:
Calling ~Derived()
Calling ~Base()
i was reading online and got stuck here. i am unable to understand why 'calling ~Base()' is been printed here? when we reached delete pbase; in int main() it goes to Base class first and finds that its destructor is virtual so it goes to Derive class and finds another destructor and executes it but why does it prints ~Base() in any case?
#include <iostream>
using namespace std;
struct A {
virtual void f() { cout<<"A
"; }
};
[code]...
I would expect that both examples 2 & 3 will give me the same result.I tried to figure it out but I could not. Both are references of a base class type, that get a derived object.
Q1 : why is the difference between them ?
As I see it, its kind of a mix between pointer - which in case of virtual method that was override in derived class - would give me the derived method (e.g. "B") and between regular object - which in case of virtual method that was override - would give me the specific method (Still "B"). So, example 2 "use" it as a regular object and example 3, "use" it as pointer.
Q2 : How should I refer to it ? I am using VS2008.
How to put virtual keyword in the function of the base class. Will the function still be over-written properly? What will happen if I
(1) call function from base class pointer
(2) call function from derived class pointer
(3) call function from derived class object
If the virtual keyword is present, the over-written version will be called in all cases, am I mistaken?
have a look-
class Base
{
private:
{
[Code].....
my question is why we can't directly call the member function of the desired class instead of using virtual function.
***********same program using virtual keyword*******************
class Base
{
private:
{
[Code].....
Why we generally prefer the 2nd one i.e with virtual keyword. why we can't directly call the member function of the desired class instead of using virtual function...make me understand this point..
I was reading about the CRTP, and I can't for the life of me understand it's advantages over virtual functions.
Unless you're coding embedded systems, and can't afford the few extra bytes for the vptr, or coding something requiring high-performance, where every nanosecond counts, I just don't see why the CRTP is so attractive. It just adds more text and forces every user class that wants to use the CRTP'd hierarchy to become a template class.
I tried implementing my Functor hierarchy with the CRTP instead of virtual functions...All it did was clutter my files with angle brackets and made the whole thing look very ugly.
if we do a virtual functions(polymorphism) why we need re-declare the functions(when we create a new class derived from other)?
View 10 Replies View RelatedI'm just playing around with C++ and I'm trying to make a sort of virtual pet game. I know its not the best looking code but I'm trying. But as of right now I'm trying to be able to animate the game a little . For example , if a user decides to "pet" their "pet" I want the pets mouth to open from '_' to ^o^ like this:
() ()
('_') -> () ()
(^o^) and switch back and forth.
Here's my code:
#include <iostream>
#include <cstring>
using namespace std;
void Greeting()
[code]....
I try the functions pointers too, but without success. I understand the objects are the way for work with class's. until here fine. But why i can't change the virtual functions from an object? is there anyway for do it? Ican't do, outside of classfunctions, these code:
#include <iostream>
using namespace std;
class test {
public:
virtual void created(){};
[Code] ....
How i can validate these line:
void a::created()
???
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?
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]....
I've got the following code with output. I can't figure out myself why it's what printed out there. I believe, it has something to deal with overloading/overriding/virtual functions implementations in C++:
class Base{
public: virtual void f(int);
virtual void f(double);
}
[Code].....
Thus here're my conclusions:
1) in line
d.f(1.0);
for some reason compiler preferred casting double->int of the argument and then call to 'Derived::f(int)'.
2)in line
pb->f(1.0);
for some reason compiler preferred call to 'Base::f(double);'. 'Base' is static type of pb, but the dynamic type is 'Derived'.
I believe the answer has to deal with the fact whether virtual table contains in addition to functions' names also the types of arguments they accept. AFAIK, vTable doesn't include such info.
I want to overload pure virtual function from 3rd party SDK class to put my debug messages like that:
errorStatus aXsaction(){printf(_T("
abort transaction"));transactionManager->abortTransaction();}
#define transactionManager->abortTransaction() aXsaction()
But compiler complains on the minus sign:
error C2008: '-' : unexpected in macro definition
Is it possible to trick the compiler?
I recall when I first started playing with C++ I was told that you should never use virtual functions unless you absolutely cannot think of a better way to do whatever you are attempting. This is something I have tried to stick to over the years - and indeed is probably why I have never used inheritance or polymorphism much in my own programmes.
However, I notice through a great deal of the code examples offered to questions here and even over on StackOverflow that commentators show no hesitation to recommend code that involves virtual functions. More so, I have even seen several instances here where - what I was taught as, but they may well have a different official name - 'pure virtual functions' (those with definitions inside a class of something like virtual int function_name(void)=0) are demonstrated and I was very clearly taught to avoid those like the plague.
I was wondering therefore has the official thinking changed since the middle nineties on when - and even whether - to use virtual functions in your programmes?
Is it possible to do something like this:
class A //parent {
public:
virtual void DoSomething() = 0;
};
class B : public A //child {
public:
void DoSomething(string s) override;
}
Where the child member function overrides and changes the parents member function.
I need to pass an array of key states to the Controller class' Update() function but don't want to send it to every class derived from Object (like Controller).
Is this possible or do I have to overload the original Update() member function (but I would need to define the method in Object then (i.e remove the pure virtual function (=0)))
I have an AbstractAgent base class that manages a background thread. The actual work done in the background thread is accomplished through a pure virtual function call.
Here's the problem: because the base class is initialized prior to the derived class, there is a race condition in which the pure virtual call might occur before the derived class is initialized. Likewise, on teardown the derived class might deconstruct before the base class destructor has a chance to stop the thread.
I'd like to know if there are any well-known patterns for dealing with this problem. All I can think of is providing start() and stop() methods which can be called from the most-derived class's constructor/destructor, but that strikes me as inelegant.