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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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