C++ :: Add Variable Address To Void Pointer Inside Of Class?

Dec 1, 2013

How can I add the variable adress to a void pointer inside of a class?

class variant2 {
private:
void *Vvariant=NULL;
public:
template<typename b>
variant & operator = (b *adress)

[Code] ....

if possible i want avoid the '&' when i assign the variable address.(variant2 f=varname;//like you see i don't use the '&')
for the moment i just need put the address to Variant pointer. but i receive several errors .

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C :: Initialize A Pointer Variable With A Knowing Address?

Dec 28, 2013

I need to initialize a pointer variable with a knowing address. See code below, ptr is the final destination and value of ptr_address contains the address value, so I need to do something like ptr = *ptr_address.

Code:

int *ptr;
int *ptr_address;
int address;
address = 0x10000005;
ptr_address = &(address);
ptr = *ptr_address;

The problem is that compiler gives the following warning message:

warning: assignment makes pointer from integer without a cast [enabled by default]

Is my code wrong or there is any other way to do it without receiving this compiler warning?

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Visual C++ :: Access Variable Inside Class From Other Class

Nov 9, 2013

I am trying to access a variable from another class through another class but it is not returning its "instance"?

Example:
Class View

Code:
...
V3D_Viewer viewer;
...
Class MainWindow

Code:
...
viewer* myView;
myView = new viewer();
...
Class Test

Code:
...
MainWindow window;
window.myView->setBackgroundColor(WHITE);
...

I am new to c++ references and pointers,

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C++ :: Variable Inside A Class - How To Manage Memory Allocation

Jul 30, 2014

recently I developed a class header only in C++ to deal with byte arrays. Since I developed programs in other languages that had some libraries to dial with byte arrays, I developed one that the syntax is very similar to other languages.

Since I'm not very familiar with memory management, I was concerned about somethings I've read about (ex: memory fragmentation).

Here is a very simple example of my practice:

class ByteArray {
public:
ByteArray(size_t size) {
buffer = (int8_t*)malloc(size);
}

[Code].....

The class is intended to be used as part of comunication protocol in a webserver, byte arrays are created and destroyed a lot. Should I use pools? Is there a better practice? Am I doing everything wrong (laugh)?

For those who wants to see the entire class: [URL]

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C++ :: Logical Error - Change Value Inside Void Statement

Jul 16, 2013

I've encountered a slight logical error in my code

/*
Lab06_pensionplans.cpp
Purpose :
- Create a simple financial application to calculate retirement plans
*/
#include <iostream>
#include <cstdlib>
using namespace std;
void displayMenu() {
system("cls");

[Code] ....

Look at case 2, which the user supposed to key in a new input, the problem is the value will never got into main function, I don't know what should I modify with the function.

Figured out I need to change the

void changeData(int startingAge, int numOfYears,
double lumpSumAmount, double yearlyAmount, double interestRate )

into

void changeData(int &startingAge, int &numOfYears,
double &lumpSumAmount, double &yearlyAmount, double &interestRate )

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C++ :: Defining Classes And Using Them Inside Void Main Function

May 18, 2013

This is a program I developed in which we had to define a class named BOOK with the data members and member functions as shown in the program..We have to:

(i) Make the user enter the values in the array BOOK.
(ii) Display the details that the user entered.
(iii) Search for a book from the array upon its Bno and display its details.
(iv) Search for a book from the array upon its Bname and display its details.

PROGRAM:

#include<iostream.h>
#include<conio.h>
#include<stdio.h>
#include<string.h>
class BOOK {
private:
int Bno;
char Bname[20];

[Code] .....

But while running it the compiler gives the errors as:

Line 43 to 48: Illegal character '' (0x5c)
Line 69: Undefined symbol 'Display'
Line 88: 'BOOK::Bno' is not accessible.
Line 89:'BOOK::Bname' is not accessible.
Line 90:'BOOK::Author' is not accesible.
Line 91:'BOOK::Price' is not accesible.
Line 108:'BOOK::Bno' is not accessible.
Line 109:'BOOK::Bname' is not accessible.
Line 110:'BOOK::Author' is not accesible.
Line 111:'BOOK::Price' is not accesible.
from 43 to 48..the line feed was also used at many other places but there it was not given as an error so why here?
Line 69: I defined the Display() function outside the class since it contained control structures, so what's the error then?

About the lines the rest of the error( the "not accessible" ones) I know these data members are not accessible because they are in private visibility mode. But then how to make them accessible? (Without putting them in public because it was a part of the question to create the data members in private).

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C++ :: How To Convert Void Pointer To Int / Double / String Pointer

Mar 7, 2013

I have a function:

const void insertStuff(const void *key, const int value){
// I want to convert the void pointer into one
// of three types of pointers(int, string, or double)
switch(value){
case 0:
int *intPtr = key;

[Code] .....

But this causes an error of: "crosses initialization of int*intPtr"

What's the correct way of implementing this?

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C++ :: Create Assignment Operator For A Class That Uses Pointer For Its Private Variable?

Mar 30, 2013

i am trying to create the assignment operator for a class that uses a pointer for it's private variable. The error is saying expected constructor, deconstructor, or type conversion before "operator. (which is the assignment operator. I have tried everything i could think of or find online and nothing has worked. below is the code for the assignment operator in the .h file and the .cpp file.

//Assignment constructor
indexList &operator=(const indexList <T> &rhs);
template <class T>
indexList<T>::indexList operator=(const indexList <T> &rhs) {
if(this != &rhs) {
numberOfElements = rhs.numberOfElements;

[Code]...

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Visual C++ :: Access Violation Reading Void Assigned Dynamically Allocated Value Inside Function

Sep 16, 2013

Why the void pointer passed to testb doesn't continue pointing to the allocated integer after the function call returns.

Code:
#include <stdio.h>
#include <iostream>
void* testa() {
return new int(1);

[Code] ....

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C/C++ :: Assign One Variable Address To Another Variable

Feb 3, 2014

I've been experimenting with pointers and am getting the below error.

'error: cannot convert 'int**' to 'int*' in assignment'

I thought it was ok to assign a variable address to another variable. Line 18 is where I get the error.

I am trying to show the progression of memory as I increment it as I have done on line 17 and again, I don't know why I don't see a progression through memory locations when output to the console on line 20.

Here's the code:
#include <iostream>
#include <cstring>
#include <cstdlib>
using namespace std;
int main() {

int *tt = new int;
int *p = new int;

[Code] .....

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C++ :: How To Declare Variable For All Void

Jul 25, 2013

How to declare variable for all void() as I have another void s in my C++ program. I want to have a variable that can use for all the void and not only in a simple void.Is it possible?

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C :: Dereferencing Of Void Pointer

Apr 14, 2014

I could understand void pointers I created the following program:

Code:
#include <stdio.h>
#include <string.h>
int main(void) {

char word[] = "Zero";
int number = 0;
void *ptr = NULL;

[Code] .....

The program works fine, however i really want to fully understand what is going on with the dereferencing of the void pointer, for example: With the following code:

Code:
ptr = &number;
*((int *)ptr) = 1;

Why can't you just do:

Code:
ptr = &number;
*(int *)ptr = 1;

And again with this code, (i'm guessing it's becuase its a pointer to a pointer?):

Code:
ptr = &word;
strcpy(ptr,"One");

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C :: Printing From Void Pointer

May 26, 2014

Code:
int main() {
List* newList= lst_new();
names* nama;
char* data;
int x=1;

[Code] ....

I cant seem to be able to print a string.. the functions lst_next() lst_first() return void*.

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C++ :: Void Pointer As A Parameter

Mar 14, 2013

I want to have a function that has a pointer to an int/double/string so I thought I'd use a void pointer like so:

int someFnc(int a, int b, const void *key){
// take care of converting key into appropriate type in here
}

And when I want to use this function I'd like to be able to do something like this:

main{
...
int myKey;
someFnc(1,2,myKey);
]

But I get a compiler error telling me:

invalid conversion from 'int' to 'const void' -[fpermissive]

Do I need to convert myKey into a void pointer before passing it as an argument?

Why does passing myKey like this work?

someFnc(1,2,&myKey);

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C/C++ :: How To Use Void Pointer Functions

Sep 27, 2014

int (*cInts)(void*,void*);
cInts= &compareInts;

int x=(cInts)(2,5); //This wont work. I tried a bunch of other things
printf(x);

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C++ :: Variable Or Field Entered Void

Jan 16, 2012

I am experiencing some errors with my first c++ program. im getting some compilation errors that i cannot figure out.

In file included from w2.cpp:7:
Fraction.h:17: error: variable or field 'enter' declared void
Fraction.h:17: error: expected primary-expression before 'struct'
Fraction.h:18: error: variable or field 'display' declared void
and so on ..........

Code:
#include "fraction.h"
//using namespace std;
/*
int main() {
struct Fraction fraction;
cout << "Fraction Simplifier" << endl;
cout << "===================" << endl;
enter(&fraction);

[Code] .....

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C++ :: Delegate Class - Support Void Class Function With No Parameters

Jun 22, 2013

I'm trying to write a simple Delegate class with a Bind() and Invoke() function. For now it only needs to support a void class function with no parameters. I've searched around and found quite a few exmaples, though, those class are heavily templated and I lose track trying to simplify it.

So far my code is following:

Code:
#include <windows.h>
class Test {
public:
void DoSomething() {
MessageBox(NULL, L"Test::DoSomething!", NULL, 0);

[Code] ....

The part I am having difficulty with is assigning &Test::DoSomething to the m_Callback variable.

&tObject::DoSomething works, yet _Callback which I pass &Test::DoSomething to does not work.

Also, why does the following line work:

Code:
m_Callback = &Wrapper<tObject, &tObject::DoSomething>;

When wrapper is like:

Code:
template<class tObject, void (tObject::*Func)()>
void Wrapper(void* Object)

Should it not be Wrapper<class-typename, parameter-1>(parameter-2) // This currently creates an error

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C++ :: Void Pointer Argument In A Function?

Jun 11, 2014

Why does the following code compile and execute without any error? I mean, the function compareid should get 2 arguments so why does the compiler not complaining, is it because of the type of arguments?

Code:
#include <stdio.h>
int compareid(void* info, int value); // ansi declaration
int compareid(void* info, int value)

[Code] .....

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C++ :: Reference Pointer - Void Exchange

Mar 15, 2012

#include "vehicle.h"
...
void exchange(vehicle *&v1, vehicle *&v2) {
vehicle *tmp = v2;
v2=v1;
v1=tmp;
}

Is it right?

How about: void exchange(vehicle *v1, vehicle *v2){...}

What is the difference between *&v1 and *v1 ?

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C/C++ :: Address Of Integer Variable

Nov 25, 2014

Consider the below initialization of x.

int x = 0x01234567;

If x is stored in RAM as given below, what would be the address x in both case?

(if image is invisible please follow this link)

Assume that size of integer is 4 byte.

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C :: Variable Or Field Declared Void And Other Errors

Mar 29, 2014

I'm creating a payroll program and here is my code

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define REPORTHEADING1 " Employee Pay Hours Gross Tax Net
"
#define REPORTHEADING2 " Name Rate Worked Pay Due Pay
}

[code]....

The errors I get are: variable or field PrintSummaryReport declared void in function voidPrintSummaryReport... cannot convert FILE to const car for argument to int printf(const char*...) which is for the following lines

Code:

printf(reportFile,REPORTLINEFORMAT1,fullName,payrate,regHours,gross,fedtax,
ssitax,netpay);
printf(reportFile,REPORTLINEFORMAT2,ovtHours,statetax,deferred);

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C++ :: Error - Variable Or Field Declared Void

Sep 17, 2014

Why I am getting this error

error: variable or field createBinaryFile declared void

void createBinaryFile(std::fstream&, std::ifstream&);

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C/C++ :: Getting Variable Or Field Declared Void And Other Errors

Mar 28, 2014

I'm creating a payroll program and here is my code

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define REPORTHEADING1 " Employee Pay Hours Gross Tax Net
"
#define REPORTHEADING2 " Name Rate Worked Pay Due Pay

[code]....

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C :: Display Address Of A Pointer

Jan 31, 2014

I've got a problem with a piece of code that it doesn't seem to work anymore.

Code:
#include <stdio.h>
#include <conio.h>
main () {

[Code] ..... i

I chose a to be 5 and it displays the following:

"Type a value for a:
5
5 in octal is: 5
5 in hexadecimal is: 5

Process returned 23 <0x17> execution time : 1.031 s".I first saw this when trying to display the address of a pointer. Am i missing something? I used to run this code on dev-c++ successfully but after a day or so of practice, it's not working anymore. I switched from dev-c++ to code blocks.

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C :: Sorted List - Why Value Of Void Pointer Change

Feb 16, 2014

I have a the following in a header file.

Code:

struct SortedList{
void * data;
struct SortedList * next;
struct SortedList * previous;
int (*compareFunc)(void *, void *);
void (*destructor)(void *);

[Code] ....

In a .c file, I implemented the SLCreate function.

Code:
SortedListPtr SLCreate(CompareFuncT cf, DestructFuncT df){
struct SortedList item;
item.data = NULL;
item.next = (struct SortedList *) malloc(sizeof(struct SortedList));

[Code] ....

In main.c, I try to do the following:

Code:
SortedListPtr list = SLCreate(&compareInts, &destroy);

A bunch other code that does not alter list or it's contents at all.

struct SortedList item = (*list);
void * data = item.data;
if (data != NULL) {
printf(Why did data become not null???
"); }

How come my variable data became not null anymore when I haven't altered it at all....

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C++ :: Output Address Of Variable In Binary?

Sep 24, 2014

How can I output the address of a variable in binary?

#include <iostream>
#include <sstream>
#include <string>
using namespace std;

[Code] ....

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