C++ :: Size Of Object Of Class Child?
Feb 5, 2014hiclass Parent {
};
class Child : virtual public Parent {
};
What is the size of object of Class Child in following case?
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C++ :: Size Of Object If There Is No Data Member In Class
Aug 20, 2013What is the size of object in c++ , if there is no data member in the class ?
View 3 Replies View RelatedC++ :: Class Function That Uses Instance Of Its Child Class As Argument
Mar 1, 2013I am facing a real-life problem, it can be simplified as below:
#include <iostream>
using namespace std;
class B;
class A {
public:
void f1(A a) {}
void f2(B b) {}
[Code]...
There is no problem at all with the f1(), it compiles and executes without any problem. But f2() gives compilation error. How to solve this?
The error message is: error: 'b' has incomplete type This is just to define the function f2() in a class, that uses an instance of its child class as one of its arguments.
C++ :: Using Child Class As Parameter Of A Function In Its Parent Class
Aug 27, 2014I am currently having an issue with a piece of code that I am writing in which I need to use a vector of a child class as a parameter in a function in the parent class. Below is an example of my code:
#include "child.h"
#include <vector>
class parent {
parent();
function(std::vector<child> children);
// rest of class here
}
When I do this my program doesn't compile. However if I try to forward declare, as shown in the following example, it once again refuses to compile:
#include <vector>
class child;
class parent{
parent();
function(std::vector<child> children);
// rest of class here
}
This time, it refuses to compile because it needs to know the full size of the class child in order to create the vector. How to being able to access the child is essential for my program, so what should I do?
C++ :: Function Overloading In Child Class?
Jan 17, 2014I am facing some problems while overloading base class functoin in child class. I have 2 programs as listed below.
Program 1 :
#include <iostream>
using namespace std;
class base
{
[Code].....
Compilation Errors:
child_overload.cpp: In function "int main()":
child_overload.cpp:27: error: no matching function for call to "child::func(const char [16])"
child_overload.cpp:17: note: candidates are: void child::func(double)
I thought as base class members are also as part of child class through "public" access specifier, it should access base class function, when funct() is called with a string. if I use "using base::func" in child, it works fine. But why I need that when base class memebers are part of child class?
C++ :: Reflect Child Classes From Base Class
Nov 26, 2013We want a solution in C++ that must be able to do the following:
Given a string of particular type, lets say 'A', we want to find all the types that derives from 'A'.
Instantiate new objects out of the types that are derived from 'A'.
E.g. Lets say we have a class, VehicleEntity. VehicleEntityhas child classes, PassangerCarEntity, TruckEntity, TrainEntity, BoatEntity.
We are unsure what vehicle entities there may be as the a library could be added containing more VehicleEntities. E.g. an AirplaneEntity thaterives from VehicleEntity could be added after deployment.
In the application, when a user wants to select a VehicleEntity, the user should be able to pick any of the entities deriving from VehicleEntity. This includes the PassangerCarEntity, TruckEntity, TrainEntity, BoatEntity and AirplaneEntity. The user selects an Entity, lets say AirplaneEntity, A new object of type AirplaneEntity must be instantiated.
The following is an concept example in C# of what we want to achieve in C++.
In C# the items for the dropdown list can be retrieved as follows:
Type vehicleEntityType = typeof(VehicleEntity);
List<Type> types = new List<Type>();
foreach (Assembly assembly in AppDomain.CurrentDomain.GetAssemblies())
[Code] .....
We are aware that standard C++ does not contain any Metadata on its objects, and thus it is not possible without a workaround. It does not seem possible with RTTI and boost.Mirror.
C++ :: Copying Purely Virtual Class Child
Oct 27, 2014In 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?
C++ :: How To Get Object Of Original Class From Function Of Other Class Where Other Class Object Is Member Of Original Class
Jan 21, 2013The case is like
class B{
public:
somedata;
somefunction();
}
class A{
public:
data;
function();
}
in somefunction i want a pointer to current object of class A m new to c++
C++ :: basic Polymorphism - Parent / Child Class Based Program
Oct 19, 2014I am making a very basic parent/child class based program that shows polymorphism. It does not compile due to a few syntax errors reading "function call missing argument list. Lines 76 and 77, 81 and 82, and 86 and 87.
#include<iostream>
using namespace std;
class people {
public:
virtual void height(double h) = 0;
virtual void weight(double w) = 0;
[Code] ....
C# :: Abstract Class Provide Functionality Without Affecting Child Classes?
Mar 6, 2014The 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 RelatedC# :: Object Header Size?
Dec 25, 2014In 32bit, the object header size is always 8bytes.
In 64bit, the object header size is always 16bytes.
Is this safe to assume or are there situations where the header size can be smaller/larger than the numbers above?(Haven't found anything on this, so I assume no?)
I need to know the exact size of the object header, because I need specifically pad a few classes I wrote to avoid false sharing along cache lines. Just need to make sure I have the sizes correct so I don't pad them wrong!
C++ :: Importance Of Static Object In A Class And How They Are Different From General Object
Dec 13, 2012#include "B.h"
class A {
public :
A()
{
s_b = new B();
b = new B();
[Code] ....
In my project i have seen static object as above . But not able to know what is the exact use of it and how they are different from general object .
Visual C++ :: How To Reduce Size Of Object
Feb 10, 2014I am using Visual C++ to write an app. I write CMyObject class and may allocate a lot of instances of CMyObject object, so I want to reduce the size of CMyObject class.
What I can figure out to do is:
1. I can use the following code to get the accurate size used by a single instance of CMyObject object:
CMyObject Object;
//Get the size of memory allocated for CMyObject object
int nSize = sizeof(Object);
is that correct?
2.To reduce the size of CMyObject, I have several ideas:
(1)Change member function to static member function if it is possible, since each member function will take some spaces in the instance of CMyObject.
(2)Change virtual member function to member function if it is possible, since virtual member function may take more spaces.
(3)Eliminate unnecessary member variables to reduce spaces.
(4)Finally, if (1), (2) and (3) does not work well, then change CMyObject from class to a struct that only contains some member variables, thus will eliminate the spaces allocated for constructor and destructor of a class.
C/C++ :: Object File Size Increases In Windows?
Apr 11, 2013My sample.h is
#include <string>
namespace xxx
{
class abc
[Code]....
My Question is when i compile this code in Linux platform Using g++ compiler My sample.o's Size is 1Kb.. But when the same code is compiled in Windows platform using VC++ Compiler , My sample.o's size is 42Kb..to reduce the size in windows... Is there any proble with '#include <string>' in Windows platform.
C++ :: Size Of Derived Class With Overriding Virtual Functions From Base Class?
Jan 21, 2014The 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].....
C++ :: Transfer Values Set In Privates Of Base Class By Object Of One Derived Class To Another
Apr 26, 2014I have my main.cpp like this:
#include <iostream>
#include "curve1.h"
#include "curve2.h"
using namespace std;
int main() {
Curve1 curve1Obj;
Curve2 curve2Obj;
[Code]...
Base class Score has two derived classes Curve1 and Curve2. There are two curve() functions, one is in Curve1 and other in Curve2 classes. getSize() returns the value of iSize.
My base class header score.h looks like this:
#ifndef SCORE_H
#define SCORE_H
class Score {
private:
int *ipScore;
float fAverage;
int iSize;
[Code]...
You can see that I have used curve1Obj to enter scores, calculate average and output. So if I call getSize() function with cuve1Obj, it gives the right size that I took from user in enterScores() function. Also the result is same if I call getSize() in score.cpp definition file in any of the functions (obviously).
.....
The problem is when I call curve() function of Curve2 class in main (line 23) with the object curve2Obj, it creates a new set of ipScore, fAverage and iSize (i think?) with garbage values. So when I call getSize() in curve() definition in curve2.cpp, it outputs the garbage. .....
How can I cause it to return the old values that are set in curve1.cpp?
Here is my curve2.cpp
#include <iostream>
#include "curve2.h"
using namespace std;
void Curve2::curve() {
cout << "getSize() returns: " << getSize() << endl; // out comes the garbage
}
Can I use a function to simply put values from old to new variables? If yes then how?
C++ :: Using Member Function Of A Class In Another Class And Relate It To Object In Int Main
Aug 21, 2013I am writing a program which is using SDL library. I have two different classes which one of them is Timer Class and the other is EventHandling Class.
I need to use some member functions and variables of Timer in some Eventhandling Class member functions, Although I want to define an object of Timer in int main {} and relate it to its member function that has been used in Eventhandling member function in order that it becomes easier to handle it, I mean that I want to have for example two objects of timer and two objects of Eventhandling class for two different users.
I do not know how to relate an object of a class from int main{} to its member function which is being used in another class member function.
Lets have it as a sample code:
class Timer {
private:
int x;
public:
Timer();
get_X();
start_X();
[Code] ....
C++ :: Creating One Class Object In Constructor Of Another Class
Sep 20, 2013Suppose I have two classes A and B so how to access object of class A in constructor of B's class as a parameter.
View 6 Replies View RelatedC++ :: How To Create A Class Object Inside Another Class
Feb 20, 2015My thought is that I would need to establish a variable for the class in the header and call the class within the .cpp file
//class A.h
B b;
Then in class A, to create the object and use a method from the object I would -
//class A.cpp
A::A(){
b();
}
int someAmethod(){
b.bmethod();
}
C++ :: Initializing Object Of Class Inside Another Class?
Mar 7, 2014I have a class MySeqBuildBlockModule that I am inheriting from: public SeqBuildBlock. Other than constructor and destructor, this class MySeqBuildBlockModule has a method: prep.
class MySeqBuildBlockModule: public SeqBuildBlock {
friend class SeqBuildBlockIRns;
public:
MySeqBuildBlockModule (SBBList* pSBBList0, long TI1_In, long TI2_In)// more arguements in this constructor of derived class
: SeqBuildBlock (pSBBList0)
[code]....
I would have like to intiantiate an object "myIRns_3" of a class defined in third party library
SeqBuildBlockIRns myIRns_3(pSBBList2);
and would like to access it from the prep function as:
double dEnergyAllSBBs_DK = myIRns_3.getEnergyPerRequest();
I tried to instantiate following in either private section or in constructor; but w/o any success:
SeqBuildBlockIRns myIRns_3(pSBBList2);
ERRORS encountered:
When I tried to do it inside the constructor, I get the following errors:
MySBBModule.h(113) : error C2065: 'myIRns_3' : undeclared identifier
MySBBModule.h(113) : error C2228: left of '.getEnergyPerRequest' must have class/struct/union type
MySBBModule.h(116) : error C2065: 'pSBBList' : undeclared identifier
MySBBModule.h(116) : error C2227: left of '->prepSBBAll' must point to class/struct/union
When I tried to do it in private section, I get the following errors:
MySBBModule.h(106) : error C2061: syntax error : identifier 'pSBBList2'
MySBBModule.h(113) : error C2228: left of '.getEnergyPerRequest' must have class/struct/union type
MySBBModule.h(116) : error C2065: 'pSBBList' : undeclared identifier
MySBBModule.h(116) : error C2227: left of '->prepSBBAll' must point to class/struct/union
C++ :: Declaring Object Of A Class In Another Class
Jul 14, 2014Information:
I'm using Code::Blocks v12.11.
(I'm using C++/SDL2, but I think that's of no relevance)
Problem:
I create a class named "CSprite" in a "Sprite.hpp"-file. I create a "Sprite.cpp"-file, which includes the "Sprite.hpp"-file. I define the methods of the class "CSprite" in the "Sprite.cpp"-file.
When I try to create an object of "CSprite" in the class named "CPlayer" in the file "Player.hpp" I get an error message. (<-- Looks complicated I know, the code example will be more usefull than this)
Error in the build messages:
C:UsersLinoDocuments1 Data LinoFreizeit1 ProgrammierenC++ & SDL2The Running ManCPlayer.h|30|error: 'CSprite' does not name a type|
||=== Build finished: 1 errors, 0 warnings (0 minutes, 1 seconds) ===|
Code Example:
Sprite.hpp
#ifndef _SPRITE_HPP_
#define _SPRITE_HPP_
class CSprite {
[Code] .....
What did I miss? Did I include the wrong file? Or did I Forget to include the file? Why do I get the error message?
I also tried it with a pointer declaration and the "->" Operator but I got the same error message. I know I could just write a new function to load the texture in my "CPlayer"-class but this would not really answer my question.
C++ :: Can Object Of A Class Be Assigned To Another Of Different Class?
Nov 9, 2013I fully understand that a variable of one simple data type cannot be assigned to another of a different data type in an assignment statement, except when type-conversion(i.e. casting) is employed. For structured data types (like classes), I know that the assignment operator can be overloaded; but this only addresses objects of the same type.
My problem is that I have read data from an input file into an object of one class, but I want to transfer the contents into an object of a different class in an assignment statement. Can this be realized given that the two operands of the assignment operator (=), in this case, would be of two different types?
C++ :: Size Of Empty Class
May 4, 2013This code:
#include <iostream>
class Foo {
};
int main() {
Foo foo;
std::cout << sizeof ( foo ) << std::endl;
std::cin.get();
return ( 0 );
}
produces this result: 1
Why is the size of an instance of Foo 1, although it doesn't have any member variables?
C++ :: Size Of Polymorphic Class
Nov 18, 2012I 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
C/C++ :: Size Of Class When Char Member Added
May 25, 2014Why is the size of an empty class 1? Why is the class still one when I add a char member to the class?//using turbo c++ 3.0, yes I know I'm using a very old c++ compiler and software
View 3 Replies View RelatedC++ :: Virtual Table Pointer - Size Of A Class?
Apr 22, 2015Here 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?