This 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?
I have a doubt related Size of empty structure. I know the answer of empty structure is "0".
How and why the Result got ZERO..??
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].....
I 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
hiclass Parent {
};
class Child : virtual public Parent {
};
What is the size of object of Class Child in following case?
What is the size of object in c++ , if there is no data member in the class ?
View 3 Replies View RelatedWhy 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 RelatedHere 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?
I wanted to add that the template argument is needed because its a "special case" but if that doesn't work what would be the next best way to solve this problem. I want to be able to declare the const size of the array outside the class far removed from it actually. I'm actually going off this page
[URL] .....
Heres the code
#include <iostream>
template <int F>
class C
{
[Code]....
A file is created but its empty. And when I first create an entry and then display all the entries, it does nothing.
#include<iostream>
#include<fstream>
#include<iomanip>
#include<string>
using namespace std;
class comp {
[Code] ....
We have been assigned to create an iTunes library. Everything compiles in my other .h file but my main is not happy with my object declaration. It keeps stating "primary expression before '{'". Here is my main code:
#include<iostream>
#include<string>
#include<fstream>
#include"myTunes.h"
using namespace std;
//function protocols
void read(string);
[Code] ......
what is the empty state of queue?
View 5 Replies View RelatedIt has been a few years since I have had to do this, but I need to declare a method in my base class, but produce no code for it. Then when this library is used by my second project I will derive a class from this base class and put the code into it there. How is this possible? I used to know how but do not remember how now.
The library is a static library designed for linking with both 32bit and 64bit Windows applications to handle a lot of the tedious stuff with Windows programming. The method in question handles specific command inputs. However, since each program that uses this library will have different uses for these commands, I want to leave it up to the user to code their own handling, but require it to be coded in the derived class.
So this is my working code with sql i want convert it so i can read it from xml, basiccl i need to fill empty list with xml column BrivDat..
var connStr = @"Data Source=(LocalDB)v11.0;" +
@"AttachDbFilename=C:dbaseAdaPlus.mdf;Integrated Security=True";
List<DateTime> Holidays = new List<DateTime>();
using (SqlConnection conn = new SqlConnection(connStr))
using (SqlCommand cmdd = new SqlCommand("select * from Brivdienas", conn))
[Code] ......
I am writing a c++ program in Linux.. I am reading a line from commandline at run time using "getline(std::cin,str);". now, what i want is if i left the commandline as idle (terminal as idle), then i want to know that the commandline is empty... is it possible ???
View 4 Replies View RelatedSo I was wondering if I were to empty the elements of a stack into a queue, but i only wanted to empty the even numbers or the odd ones. What would the if statement be to accomplish this. Im guessing for even it would be something like if(number % 2!=0)? What about for odd?
View 2 Replies View RelatedI wrote a template function which use dynamic array as parameter. But if parameter is a empty array, it have compile error.
code:
#include <iostream>
int arry[] = {1,2,3};
int empty_arry[] = {};
[Code]....
compile error:
[zengchao@cmcc-server2 ]$g++ test.cpp
test.cpp: In function ‘int main(int, char**)’:
test.cpp:16: error: no matching function for call to ‘array_parameter(int [0])’
I started making something for my class and the thing im getting stuck with is this function:
void ucitajOdgovore(string asocijacija[21]){
int brojac=0;
ifstream fajl;
string putanja;
/*srand(time(NULL)); int random=(rand() %5) +1;
switch(random){
[Code] ....
In the main, i pass real string array "asocijacije" in function which i use in it, and when i use it after this fun. i get an empty array. Its like it didnt happend and i cant see where i went wrong.
program im creating that is a Mediastore. I have 3 forms one start form where you choose which form you wanna go to Lager or Kassa are the two choices. in these forms i have 1 listbox each that share the same Data. In my Listboxes i have objects of a class called produkts that consist of 3 variables Name,SerialNumber and Price. When i have added these objects to my listbox and they are showing i wanna be able to use my "go back" button to go back to my orginal form where i choose which form i wanna go to and then go to eather my Lager form or my Kassa form and the items are supposed to still there however that is not happening for some reason.
public Lager()
{
InitializeComponent();
}
[Code].....
Change the frame window size according to font size increases.
View 3 Replies View RelatedI must take an old MFC project in VC++ 6.0 and make changes.
The problem is text size in screen is different from size in print preview.
for example with this font
Code:
CFont f50;
f50.CreateFont(100,0,0,0,FW_BOLD,0,0,0,DEFAULT_CHARSET,OUT_DEFAULT_PRECIS,
CLIP_DEFAULT_PRECIS,DEFAULT_QUALITY,FF_DONTCARE,"Frutiger LT Std 45 Light");
And this text
Code:
s=_T("Let's try to calculate the size of this text");
and with MM_LOMETRIC map mode
GetTextExtent() returns me:
On screen: (1595,99)
Ink printer + print preview: (1589,100)
PDFCreator + print preview: (1580,100)
comparing with screen size the height is bigger but lenght is smaller. I don't understand.
I can understand that different printers process the fonts in different way and then to have different lenghts. That's not the problem. The problem is I need to simulate in screen the same behaviour i will have on printer because these texts are being aligned in the document, and I don't want to see that the text si aligned different in text than in paper.
What can I do to render the text on screen with the same size I will have on the printer? Print preview is doing it. Should I change the font parameters? is something related with pixels per inch?
I am new to c++ and have started creating a dummy program to perform a simple task of writing a few strings to the console, which are first generated using random generation. When I execute the code, an extra line for each generated object appears in the console.
int gemNum;
cout << "This program calculates the value and type of gems
";
cout << "Please enter the number of gems: ";
cin >> gemNum;
vector<int> gemVector(gemNum);
vector<int> gemCollection = fillGemCollection(gemNum);
vector<int> gemSort = sortGems(gemCollection);
vector<string> gemResult = finalGemValue(gemNum, gemSort);
for(int i = 0; i<gemResult.size();i++){
string gemString = gemResult[i];
cout << gemString << endl;
}
This program calculates the value and type of gems..Please enter the number of gems: 4
10 hematite
40 carnelian
60 onyx
120 silver pearl
Press "e" and enter to end program
This problem is best explained by looking at its output below. I stored 15 different values but when retrieved some are wrong.
#include <iostream>
using namespace std;
class A {
public:
int ** pointer;
[Code] ....
I need to store and retrieve the 15 different values correctly. How to solve this? The main thing is, I need to store the pointer in class A objects.
I have tried to implement a much simplified version of boost::compressed_pair.What follows is a partially specialized EBO_pair<T1, T2> class template, written in C++11.The first type T1 is constrained to not be empty.The second type T2 may or may not be empty.
#pragma once
#include <memory>
#include <type_traits>
#include <utility>
namespace dsa
}
[code]...
Edit: added non-member swap() function template.
I made two dimensional array to represent my (game) inventory. Slot is empty if its value is 0 and 1 if not.
Now i need to find if i can put new item in my inventory that can take up 4x2 slots. I tried this but it doesn't work as i expected:
#include <iostream>
int main() {
const int inventorySlotRows = 5;
const int inventorySlotColumns = 5;
int arr[inventorySlotRows][inventorySlotColumns] =
[Code] .....
I have two classes, one class requests another class to populate a vector with some data using getAvailableStreams() method:
vector<AutoRefPtr<ManifestStream> > availableStreams;
std::cout << "now asking for streams." << std::endl;
manifest->getAvailableStreams(&availableStreams);
std::cout << "got so many streams: " << availableStreams.size() << std::endl;
The other class passes another pre-populated vector back:
virtual RESULT getAvailableStreams(std::vector< AutoRefPtr<ManifestStream> >* availableStreams) {
availableStreams = static_cast<std::vector< AutoRefPtr<ManifestStream> >* >(myStreams); //myStreams contains 1 stream
I'm also adding a stream here directly just for testing purposes:
ManifestStream stream2;
availableStreams->push_back(AutoRefPtr<ManifestStream>(&stream2));
std::cout << "calling getAvailableStreams. Giving so many streams: " << myStreams->size() << ", " <<
availableStreams->size() << std::endl;
return result_OK;
}
If I run the code, I can see the following logs:
Now asking for streams. Calling getAvailableStreams.
Giving so many streams: 2, 2
got so many streams: 0
Why am I getting 0 streams when I exist the method? I just had 2 streams in availableStreams while I was inside the method, where have they disappeared?