C++ :: Use Of Virtual Keyword In Destructors
Jan 6, 2014
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?
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Feb 19, 2014
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?
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May 15, 2013
"Destructors for a derived class object are called in the reverse order of the constructors for the object. This is a general rule that always applies. Constructors are invoked starting with the base class constructor and then the derived class constructor, whereas the destructor for the derived class is called first when an object is destroyed, followed by the base class destructor."
But why, or is it just because, so programmers know which one and modify their destructor accordingly??
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May 20, 2013
In this code:
#pragma once
#include <iostream>
class CBox // Derived class {
public:
// Constructor
explicit CBox(double lv = 1.0, double wv = 1.0, double hv = 1.0) : m_Length(lv), m_Width(wv), m_Height(hv){}
[Code] .....
Before the program ends, at return 0;
I would expect the CBox destructor to be called 3 times but it is being called 6 times? Why? Also in this code:
#pragma once
#include <iostream>
class CBox // Derived class {
public:
// Constructor
explicit CBox(double lv = 1.0, double wv = 1.0, double hv = 1.0) : m_Length(lv), m_Width(wv), m_Height(hv){}
[Code] .....
Why is the destructor called 3 times? When have you really destroyed a CBox? Doesnt emplace only create it and store it, then thats it?
[URL] .....
For pushback:
void push_back(value_type&& _Val)
{// insert by moving into element at end
if (_Inside(_STD addressof(_Val)))
{// push back an element
size_type _Idx = _STD addressof(_Val) - this->_Myfirst;
[Code] .....
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Jun 5, 2014
Every time we pass an object to a function, and when the function ends and the object is not necessary anymore the destructor is called. if it's passing by value then a copy of the object is passed. if the object has a pointer inside of it so we implement the copy constructor to create a new pointed-variable so the original pointer will not get deleted.
so far so good. But what about passing an object to a non-member function by reference?
The language says that as soon as the function ends - the object will be deleted , because we passed by ref. that means that after the function ends - the object is not usable anymore! =What does that say? that in c++ you can't pass object by ref. because it will get deleted and un-uasable??
Varifying it with a compiler shows that the object is NOT deleted after the function ends.
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Mar 5, 2015
I am in a intro C++ class and have an assignment to create a patient appointment scheduling program. I finished my code, but when I run it the destructors in each class are being called a bunch of times and the menu shows up at the bottom of the that, so the whole output looks like a mess. Identifying why the destructors are being called like this?
#include <iostream>
#include <iomanip>
#include <string>
#include <cstdlib>
#include <time.h>
using namespace std;
void ShowMenu ();
[Code] ......
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Jan 26, 2014
In c# extending the class and implementing an interface is done by : symbol.. But c# has extend keyword. What is the use of extend keyword in c#?
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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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Jun 30, 2014
for starters i hope this question wasn't posted yet.i want to write a small program that askes the user what he wants to do , and then executes the comand in system . But for some reason it doesn't quit on the key word this is the code:
Code:
#include <stdio.h>
/*a simple interaction programme that schow the system options*/
#define systemt "x1b[32m" /*changes the color to green for system output*/
#define user "x1b[0m" /*changes the color to white for user input*/
int main() {
[Code]...
Is there something wrong white the code or does the system bock me from reusing the choise string. i'll inculde the original c file as well
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Feb 14, 2014
One thing make me consider:
FistClass F1 = new FistClass ();
FistClass F2 = F1;
second line why i dont need to firstly create instance for F2 and then make reference betwwen to classes like:
FistClass F1 = new FistClass ();
FistClass F2 = new FistClass ();
F2 = F1;
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Sep 24, 2014
I'm trying to read a C code, but there are functions including CLASS word at the titles of functions. Is it a correct implementation?
For example: double CLASS getreal (int type)
What is the meaning of CLASS in titles of functions in C? I could not find such an usage in my C book?
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Aug 18, 2014
I was trying to make a tic tac toe game where the user can play against the computer
It s in borland c++ and not in c++ 11 so i wanted to convert it into c++11. My program shows error since there is nothing called conio.h in c++11. Hence I want to know if there is any alternate keyword gor the function getch() so that i could ask the user to press [ENTER].
Code:
#include<process.h>
#include<stdlib.h>
#include<string.h>
#include<iostream.h>
#include<conio.h>
int usbox,i,j,nandu=0,result,cusb,cobox,r,d;
int playl=0;
char copybox[10];
[Code] ....
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Apr 13, 2013
how can I make a class non inheritable,,, without using keyword "final" ?
class A
{
//
};
A obj; // No error
class B : public A
{
//
}; // error
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Jun 24, 2014
Is the bool keyword in C exactly like the boolean keyword in Java? why this code is getting an 'unknown type error' when I initiialze looping.
#include <stdio.h>
#include <stdlib.h>
int main()
[Code].....
If I am completely using the boolean concept wrong in C, should I just use break statements instead?
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Oct 11, 2014
In C++ by FLTK, to define a circle we use some code like this:
Circle c(Point(x,y), r);
And we can using vector_ref put and save them in a vector, like:
Vector_ref<Circle> vc;
vc.push_back(new Circle(Point(x,y),r));
Ok, those were about Circle and no problem till now!
Triangle can be defined like this for using in codes:
Graph_lib::polyline poly;
poly.add(Point(x1,y1),r1);
poly.add(Point(x2,y2),r2);
poly.add(Point(x3,y3),r3);
and this is a vector to saving them:
Vector_ref<Graph_lib::Polygon> vp;
The problem is that how to save/put triangles/polylines into that vp vector using new keyword like the circle does?
My sig: Save Cobani.
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Jan 30, 2014
I think there is no always need of keyword extern in order to declare variables globally. Is it right?
For example I can declare a variable globally in one file and use it in some other provided that I have included the last one file ( that has the declaration of the variable of course) and compile these files together :
gcc -c f1.c f2.c for example
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Nov 8, 2014
I'm working on a program that reads in a .txt file and searches through the text for a keyword. If it gets a hit on the keyword, the line number where the keyword is located and the line that contains the keyword is printed out. What I have now doesn't catch every occurance of the keyword "a".
Code:
#include <stdio.h>
#include <string.h>
int main(int argc, char **argv) {
[Code]......
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Apr 25, 2014
I am reading a file whick looks like following:
Code:
10 = NAND(1, 3)
11 = NAND(3, 6, 5)
15 = NAND(9, 6, 2, 8)
Problem: I have to find the word "NAND" and then find the numbers inside the brackets because they are the inputs to that NAND gate. I have written a code below but that code can detect the fixed number of inputs. I need a code which can detect any number of inputs (whether 2 inputs or more than two). But i don't understand how do i do that?
My code:
Code:
string input_str ("INPUT"), output_str ("OUTPUT"), nand_str("NAND");
while (getline( input_file, line ))
{
std::size_t guard_found = line.find(guard_str);
[Code].....
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Jan 6, 2014
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.
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Mar 19, 2013
#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.
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Sep 25, 2013
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..
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Jan 31, 2014
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.
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Jul 17, 2013
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.
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May 2, 2014
if we do a virtual functions(polymorphism) why we need re-declare the functions(when we create a new class derived from other)?
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Dec 29, 2014
I'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]....
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Oct 14, 2013
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()
???
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