C++ :: Memory Address Of Class Member Variables?
Jun 22, 2013
Suppose I have two classes, MyClassX and MyClassY, each with two member variables, as defined below. I create an object instance of each class, and then create a pointer to each member variable for each object:
Code:
class MyClassX
{
public:
int a;
double b;
MyClassX(int _a, double _b)
[code]....
After converting the hexadecimal to decimal, it appears that with MyClassX, pxb is 8 bytes from pxa, whereas for MyClassY, pya is only 4 bytes from pyb. This makes sense for MyClassY, because the first member variable to be stored is an int, and so will occupy 4 bytes. However, why should this be any different for MyClassX, which also has an int as the first member variable, so shouldn't this also occupy 4bytes?
The reason I have come across this problem is that I am looking into streaming objects to memory and then loading them again. (I know boost can do this, but I am trying it out myself from scratch.) Therefore, this is causing an issue, because I cannot just assume that the size of memory occupied by an object is just the sum of the sizes of its member variables. MyClassX is 8 bytes larger than MyClassY, even though the intuition is that it should only occupy 4 bytes more due to a double being replaced by an int.
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Apr 2, 2014
How to get relative memory address of members of Class or Structure ? I want to auto scan the members of Class/Struct, and show the address/value like the "watch window" in debug mode of popular C/C++ IDE software.
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Mar 21, 2012
Code:
class CObjects {
int m_CurrentTime;
int m_Steps;
AStarList* OPEN;
AStarList* CLOSED;
std::vector<AStarNode *>solution;
[code]....
CCB is derived from CrowdEntity and in turn is derived from CObjects Inside CObjects, I declared AStarList *OPEN; Why would howmany become garbage (cdcdcdcd) when I reference it in GetBestNode()
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Apr 8, 2015
C++
Create a Triangle class that has the following member variables:
side1 - a double
side2 - a double
side 3 - a double perimeter area
The class should have the following member functions:
- default constructor that sets the value of all 3 sides of a triangle to 0.0
- a constructor with arguments that accepts values for the three sides of a triangle (member variables) as arguments
- setDimensions - a function that allows the value of the three sides to be entered by the user through the keyboard
- testSides - a function that determines if the 3 values entered can actually be the sides of a triangle. If they do not create a triangle, print the values entered and an appropriate message
--The sum of any two side lengths of a triangle must always be greater than the length of the third side: so side 1 + side 2 > side 3 and side 1 + side 3 > side 2 and side 2 + side 3 > side 1 ( all three must be true for the 3 values to make a triangle)
- getSide1 - a function that returns the value of side 1, getSide2 - a function that returns the value of side 2, getSide3 - a function that returns the value of side 3
- getArea - a function that returns the area of a triangle: The formula for the area of a triangle (when the height is not known) is: A = sqrt (p(p-side1)(p-side2)(p-side3)) where p = (side1+side2+side3)/2
- getPerimeter - a function that returns the perimeter of a triangle: Perimeter = side1 + side2+ Side 3
- A displayTriangleInfo function that displays side1, side2, side3, area, and perimeter for a triangle object.
After testing your code for a single object, create an array of 5 triangles. Use a for loop and the setDimensions function to allow the user to set the values for the 3 sides of a triangle, test the vales entered to determine if the 3 create a triangle. If they do create a triangle than use the getArea and getPerimeter functions to calculate the Area and Perimeter for the triangle and use the displayTriangleInfo function to display all of the data for that triangle. If the three values do not create a triangle then print the 3 numbers entered and an appropriate message. In either case the loop should then move on and get the data for the next triangle from the user.
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Feb 22, 2013
I have two classes, a Package class and a Person class. The Package class has two Person objects has member variables, a Sender and a Receiver. While overloading the << operator for the Package class so that it will make an output label from everything in the Package class. Here is my code...
class Package{
public:
Person Sender;
Person Reciever;
int weight;
double cost;
friend ostream &operator<<(ostream &out, Package &pack);
[Code] .....
So my problem is on that last output line, I am unable to call Sender.getName()... etc. Is there a proper syntax so that I can access the members of the Person class while overloading the << operator for the Package class?
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Oct 23, 2013
I want to take address of a member function in c++. How to do this.
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Nov 20, 2012
I have written a C program without variable. And I want to print the value at that memory location.How to print that value?
code is like:-
int main()
{
printf("Enter value:");
scanf("%d",1245024);
/* how to print the value here */
return 0;
}
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Jun 25, 2013
#include <iostream>
#include <vector>
using namespace std;
int main() {
int * ptr;
vector<int> data;
data.resize( 1000 );
[Code] ....
So I need container that doesn't rellocate their address, It doesn't need to be like vector that everything is in a single pointer such as
int * a = new int[2000];
I have a pointer pointing to a member of a container and it needs to remain valid... doing
vector<int *> Array;
// allocating
for( int i = 0; i < 1000; ++ i ){
Code] ...
Waste of time, allocating them and deallocate them seem to take some time too
a List is also not efficient enough because I access them based on index
It is not a int it is pointing to but a texture, for the sake of simpler example I pick int
So is there a container that doesn't change member address and allocate when it needs to expand ?
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Jan 14, 2014
I am working on something that requires the memory address of my computers workload.. collect the trace files? and what trace file as well..
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Sep 30, 2013
Pointers point to an address in memory. What if I used 3 pointers: 2 to mark the first/last nodes, and the third to mark the current node being referenced? I would wrap it in a class (to make the memory management automatic, of course), but is this practical?? maybe some pseudo code will get the juices flowing:
template<class type>
class supercondensed_list{
public:
supercondensed_list();
~supercondensed_list();
[code].....
Any things I should take into consideration? I'm not exactly the most experienced with pointers, and manually managing memory, but I think it's worth trying. If this works, then my programs should, in theory, be 100% memory efficient.
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Sep 9, 2013
I've recently been reading tutorials on arrays and their aquaintance with memory addresses. So, I completely understand how an array's name, when defined, is a constant pointer to its first element's address.
My problem, however, lies with characters, and how they are basically arrays except with a null terminator for the last index. What I've come to undestand, is that, when defining a character variable, each 'character' has a memory address it is associated with.
For example:
char name[] = {"Hello"}; // | 'H' | 'e' | 'l' | 'l' | 'o' | '/0' |
An address holds the value of 'H'.
An address holds the value of 'e'.
An address holds the value of 'l' and so on.
I have come to believe this is false, however. Mainly from a simple std::cout command.
std::cout << &name << std::endl; // attempt 1
std::cout << &name[0] << std::endl; // attempt 2
The first attempt, as I assumed, should print the address of the first element.
The second attempt, as I assumed, did not. I figured, &names[0] would print the address of the first element, which should have been the same as &names.
So, this brings me to my question, are characters formed of constant addresses, or are the address of individual characters not reachable?
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Apr 29, 2013
What I'm trying to do is:
int *p;
someType memoryLocation;
cout<<"Enter your memory location: ";
cin >> memoryLocation;
p = memoryLocation;
cout << *p;
I was just messing around with some code, and was curious to if this was possible.
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Jun 30, 2014
The results of my code is supposed to be very simple: return the 2 integers and then their sum. However, it's doing returning the first value, then an address in memory(rather than the 2nd value), and then the 2nd value(rather than the sum). Here is the code:
#include <stdio.h>
#include <stdlib.h>
struct calculator{
double num1;
double num2;
double result;
[Code] .....
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Sep 12, 2013
I made a text file. I can do all File I/O functions in c. no problem! except that "I want to get the memory address of the beginning of that File", so that I can access each character of the file by incrementing memory address.
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Jun 3, 2013
I have an integer pointer and i want its address without allocating memory,
main() {
int *a;
cout<<a;
}
This is giving 00000000 and its but obvious. Now if i use address of a (&a) along with *a,
main() {
int *a;
cout<<a;
cout<<&a;
}
'cout<<a' gives me a constant address but 'cout<<&a' gives me different address.
what is the reason behind & and why behaviour of 'cout<<a' changes when using with &.
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Jan 2, 2013
A special hardware unit with some storage in it is connected to your computer and is memory-mapped so that its storage is accessible in the address range 0x55500000 – 0x555fffff. You want to interface this hardware unit to your C++ program so that dynamic memory is allocated in this hardware unit, not in your computer’s memory. Implement a class MyHardwareMemAllocator which has the following function.
void * allocMemoryInMyHardware(int numberOfBytesToAllocate);
which returns a pointer to the allocated memory chunk, or null if unable to allocate.
C library calls like malloc are not allowed.
1) How to allocate memory from given address range.
2) How to check whether this required memory space is available or not for allocating
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Jul 8, 2014
When declaring char array[10], memory is allocated for 10 1-bit memory locations. Is extra memory allocated for storing the address of array[0]? In expressions, is array equivalent to a pointer constant or is it an identifier for a memory cell containing the address of array[0]? In other words, is array a variable or an alias for &array[0]?
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Jul 26, 2012
Try to implement overloading << operator. If I done it void then everything work fine (see comment out) if I make it class of ostream& then the operator return to me some memory address.
Code:
#ifndef Point_HPP // anti multiply including gates
#define Point_HPP
#include <sstream>
class Point {
private:// declaration of private data members
double x;// X coordinate
double y;// Y coordinate
[Code] .....
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Nov 10, 2013
my clsLocalStudent inherits from clsStudent. How to i set my accounts information (accountNumber, accountHolderID . . . . .)?
Code:
#include <iostream>
#include "clsInterest.h"
#include "clsDate.h"
[Code]......
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Feb 18, 2014
I'm struggling with the whole stack/heap thing. I totally see the need to create objects on the free store to outlive functions, however, I don't see the purpose of "new" when working with classes.
Code:
class Person{
public:
Person(std::string strName, int number);
~Person(void);
Resource r;
[Code] .....
Now, what is the difference? Why would I need to create a Resource on the free store? Both variables named r live until the destructor runs, right?
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May 21, 2013
For static variables when the memory will be allocated? During compilation or linking or loading time? In below program i am getting error :
(Error C2099: initializer is not a constant in microsoft visual studio) .
If i initialize x = 10 or any constant it works , why?
Code:
main() {
int i=10;
static int x = i;//error ?
if(x==i)
printf("Equal");
[Code] .....
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Sep 30, 2014
I have created a windows form project in visual studio so that I can use a windows form to interact with the game class that I'm creating, but I'm running into some problems.
For one thing, I would like to be able to call Image::FromFile() one time only during initialization, and store the result in a member variable (called mBGImage). From what I can tell, the variable needs to be of type String^ (this caret symbol is new to me, but I understand it is the "managed code" version of the standard pointer, which would look like String*).
When I try to compile the following code (located in my header file) I get the error :
"error C3265: cannot declare a managed 'mBGImage' in an unmanaged 'BSG::BSGame'".
How can I store the result of Image::FromFile() permanently in my class?
When I try to declare a global variable of type "Image^", I get "error C3145: global or static variable may not have managed type System:rawing::Image ^"
#include "stdafx.h"
using namespace System;
using namespace System::ComponentModel;
using namespace System::Collections;
using namespace System::Windows::Forms;
[Code] ......
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Jan 16, 2013
i want to write a program that can access to variables and methods of another program. I ques for access to variables need to read memory, but about methods?how i can use methods and call them?
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May 23, 2014
I'm playing around and wrote a tiny program.
Code:
char bracketin[] = "thisgetsbracketed.txt";
char bracketout[] = "bracketed.txt";
char testwalk[10] = "12345678";
[Code]....
I'm incrementing the pointer to buffer 150 bytes beyond its reserved 50. I see testwalk, followed by bracketout, followed by bracketin printed by the overflow on buffer.
The memory locations are ordered descending from their call order. Why is this the case?
One would think that they would be written in ascending order as I call them. I can only assume that they're compiled bottom up - where could I read about this process?
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Oct 7, 2014
How to initialize a static member of a class with template, which type is related to a nested class?
This code works (without nested class):
#include<iostream>
using namespace std;
struct B{
B(){cout<<"here"<<endl;}
};
template<typename Z>
[Code] ,....
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Aug 21, 2013
I 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] ....
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