C++ ::  check Pointer To Class Object For Null Value?

Feb 14, 2013

lets say I have a pointer p_unit of type c_unit* (c_unit is an a.b.c.)

I have a function that returns a pointer to a new c_unit object:

c_unit * man_add_unit() {
c_unit * local_p_unit;
unsigned short int local_run_code;
print_man_add_menu();
local_run_code = get_a_run_code(); // this bit just gets user input
switch (local_run_code)

[code]....

I assign that to p_unit, then add it to a vector v_units:

p_unit = man_add_unit();
v_units.push_back(p_unit);
cout << "New unit added.
";

The whole program runs on a loop, and another thing the user can do is to print out data on c_unit objects pointed to by v_units. The problem is, in that function up there ^ I give the user the option to go back to main menu without creating a unit.

Since "local_p_unit" is declared but not assigned an initial value, I'm guessing the function would return a "null" pointer (which is what's hanging me up). If I just let this run with the above code, and go to print out the unit data, the program crashes.

I tried to make an if thing with p_unit == 0 but this always returns false and doesn't catch the "bad" unit that will subsequently cause a crash.

Btw, I have considered assigning a reference to a generic c_unit object to that there local_p_unit so it won't return null, then remove pointers to that object from v_units at the end of the loop.. But I know there's got to be a better way.

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C++ :: Which Object Draw Is Being Called In Case Of Pointer Pointing To NULL

Apr 12, 2013

[URL] ....

Which object's draw is being called?

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Nov 18, 2013

I have built LOG4CXX lib and DLL and trying to use it in my application

Loh.h
class Log
{
public:

[Code].....

In my main I am initializing Log class object and calling Debug method to log debug message to a file.

Issue I am facing is at if(CLogger::oLogger != NULL) which is always returning oLogger as NULL.

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C++ :: Calling Defined Function Pointer From Another Pointer To Class Object?

Aug 19, 2014

I am attempting to implement function pointers and I am having a bit of a problem.

See the code example below; what I want to be able to do is call a function pointer from another pointer.

I'll admit that I may not be explaining this 100% correct but I am trying to implement the code inside the main function below.

class MainObject;
class SecondaryObject;
class SecondaryObject {
public:

[Code]....

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C++ :: Pointer Class Object Vectors

Aug 4, 2013

#include <iostream>
#include <vector>
#include <string>
#include <map>
using namespace std;
struct bop {
string realname; //real name

[Code] ....

Okay, so first thing's first. The program will not compile due to lines 39-45. If I were to change those pointers into regular objects, it will not change the values of my class object. So what is the right way to do this?

I want the user to be able to input the # of employers/programmers into the system. But I cannot do that with an array of classes because when declaring an array; the array size must be constant.

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C++ :: Destructor For Class That Holds Pointer To Object

Mar 20, 2013

Lets say we have a class that holds a pointer member to another object. If I delete that pointer in the destructor I get an error (and I understand why). My question is : is it possible to overcome that without memory leaks ?

1 #include<iostream>
2 using namespace std;
3
4 class A {
5 public:
6 ~A() {
7 cout<< "~A()" <<endl;

[Code] ....

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C++ :: Copy Derived Class Object Through A Pointer To Base

Jan 14, 2015

Is there a way to copy a derived class object thru a pointer to base?

For example:

class Base { public: Base( int x ) : x( x ) {}
private: int x; };
class Derived1 : public Base { public: Derived( int z, float f ) : Base( z ), f( f ) {}
private: float f;};
class Derived2 : public Base { public: Derived( int z, string f ) : Base( z ), f( f ) {}

[Code] ....

The question is whether *B[0] would be a Derived1 object and *B[1] a Derived2 object?If not, how could I copy a derived class thru a pointer to the base class?

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C++ :: 2D Vector Check If Index Equal To Null?

Dec 2, 2014

how to check if a specific index equal to null when i try to implement it, it gives an error for example:

vector < vector <double> > v;
v[0].push_back(0);
v[0].push_back(1);
v[0].push_back(2);
v[0].push_back(3);
v[1].push_back(10);
v[1].push_back(11);
v[1].push_back(12);
v[1].push_back(13);
if(v[0][4]==NULL) {
cout<<"empty"<< endl;
}

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C++ :: Pass Object To Class Which Stores It In Container As Unique Pointer

Jul 24, 2013

class A (abstract)
class B : A
class C {
void add ( A(&*?) a )
std::vector<std::unique_ptr<A>> data; //unique_ptr<A> because A is abstract and therefore vector<A> isn't possible
}

upper situation. What is the best way to pass add an object of class B to C?

with C::add(A* a){ vector.push_back( unique_ptr<A>(a) ); }
and
int main() {
C c;
c.add( new B() );
}

This works, but i don't think it's very nice, because you could delete the pointer in main. What happens then with the unique_ptr? I could probably make C::add( std::unique_ptr<A> u_p ); but maybe it can be avoided that the "user" (in main() ) has to create the unique_ptr itself.

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Aug 12, 2013

I know what are pointer's and how to use them but there is one point i am not able to understand. Below is the example code

I understand everything in the below code except 1 thing why i am using pointer to base class object in vector int the main() Function?

Code:
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
// base class

[Code] ...

Here is the lines of code i want to understand.

Code:
vector<Employee*> employees;
employees.push_back(&emp1);
employees.push_back(&mgr1);

I know if i will not use the pointer base class function "virtual double grossPay" will be called for both base class object and derived class object and when i will use pointer with reference to the object because base class function is virtual it will look for same function in derived class and if available it will execute it.

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C# :: Getting Instance Object Is Null Compile

Dec 2, 2011

Code:

public class ColorGenetics
{
public static hk1Class jw;
public static linkedClass link;
}

[code]...

Code builds fine but compiler says I tried to use bject link w/o providing an instance. Class linkedClass has an instance of Class hk1Class set to var jw1.I had linkedClass useing the same var jw for the object instance. I changed it to jw1 thinking that would clear it up and it didn't.

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May 18, 2013

Say I have an object and 10 pointers to it in several other objects of varying class types. if the object gets deleted, those pointers have to be set to null. normally I would interconnect the object's class with the classes which have pointers to it so that it can notify them it is being deleted, and they can set their pointers to null. but this also has the burden that the classes must also notify the object when THEY are deleted since the object will need a pointer to them as well. That way the object doesn't call dereference a dangling pointer when it destructs and attempts to notify the others.

Auto pointers and shared pointers are not what I'm looking for - auto pointers delete their object when they destruct, and shared pointers do the same when no more shared pointers are pointing to it. What I'm looking for is a slick method for setting all pointers to an object to null when the object destructs.

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Apr 9, 2014

In my raytracer-project I have the following function:

bool hitObjects(Ray &ray, std::vector<Object *> &objects, Vector3& normal, Material *mat) {
double tmin = K_HUGE_VALUE;
double t;

[Code]....

When I try to run this, I only get the message "Material pointer is null". So, somehow the pointer is null after the hitObjects-function is called, even though it isn't inside that function.

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May 17, 2014

So I'm writing a small program for class, and for some reason I keep getting an error when trying to initialize head to NULL. Even threw in the namespace just to see, nothin'.

#ifndef NUMBERLIST_H
#define NUMBERLIST_H
using namespace std;

[Code].....

There's my header file. Not sure what I'm doing wrong with the constructor.

EDIT: Got it to work with nullptr, but still curious why that isn't working

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Aug 7, 2014

In jumping into C++ it says something like this: It's not necessary but when you delete a pointer it's a good idea to reset it as a null pointer. That if your code try's to dereference the pointer after being freed, your program will crash. This happens to a lot of experienced programmers.

This could corrupt users data. delete p_int;
p_int = NULL;

1. If you can deference a pointer after the memory is freed, why can't you just delete the pointer?

2. If you can do 1, how do you delete the pointer using code?

3. Every thing I've read says that free memory is handed out in a sequenced order. I don't believe that is true at all. I may be wrong. Why can't you put the data in any number of places if it will fit. Isn't the compiler smart enough to know where bytes (bits)and pieces are stored?

4. If you storing anything in free memory must use a pointer to it?

5. Can a pointer or something similar be used with stack memory?

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Dec 9, 2013

in the below program for both class pointers pointing to null. Class contains normal function executing but class contains virtual function getting segmentation fault.

#include <cstdio>
using namespace std;
class A
{

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Aug 26, 2014

Here when NonlinearSolver called the constructor,

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As an intermediate layer, the function calls boost unbounded array operator = which in turns calls std::copy which results in this error

Code:
NonlinearSolver(solver_type const & solver)
: m_gradient()
, m_function()
, m_projection() {
*this = solver;

[Code] .....

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Mar 14, 2014

struct mystruct{
int n;
};
class mscope{
public:
std::vector<mystruct> mv;

[Code] .....

So I have a vector of structs and I want to traverse it, find a struct that matches a constraint and obtain a pointer to that struct. I made a function for this purpose which takes a number and an empty pointer that will store the reference. However, after function returns the pointer becomes null. What could be causing this?

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Jan 22, 2013

getting an invalid null pointer error message after a successful build. This program is supposed to ask for firstName, lastName, age and maJor and keep doing so until the age that is input is 0 and then the program closes. Here is what I have.

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

[Code]....

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May 21, 2013

Writing this code that handles clicks with the left mouse button. But I want to be able to check for clicks within a 200x200 pixel area. Here's what I have:

void EGame::OnLButtonDown(int mX, int mY) {
int ID = mX / 200;
ID = ID + ((mY / 200) * 3);

if(grid[ID] != GRID_TYPE_NONE) {

[Code] .....

Using the width and height of the object, e.g; pX->w is width and pX->h is height ....

How would I check within the 200x200 area with mX and mY?

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Jan 21, 2013

The 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++

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C++ :: Cast Base Class Pointer To Derived Class Pointer

Feb 6, 2015

I create an instance of a base class (not derived class) and assign it to base class pointer. Then, I convert it to a pointer to a derived class and call methods on it.

why does it work, if there is a virtual table?

when will it fail?

// TestCastWin.cpp : Defines the entry point for the console application.//

#include "stdafx.h"
#include <iostream>
class B
{
public:
B(double x, double y) : x_(x), y_(y) {}
double x() const { return x_; }

[Code] ....

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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 .

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Jan 4, 2015

void myfuncion(){
int *a = new int[10];
int b[10];
int *p = b;
delete a
delete p
}

I cant delete b and/or p but how can i check it if i can use delete or not?

i want to check if the pointer is pointing on function temp variable ( those what gets deleted after function ends .

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C/C++ :: If Statement To Check Matching Word To Pointer Address Value

Jan 3, 2015

I'm having an issue coming up with an if() statement to check if a word match the one in the value of a pointer's address. So far the best I've come up with only matches the first letter of the words, you'll find it in the code below.

#include"Header.h"
int Colour(struct MyStruct *ArrayPointer, int ArraySize) //ArraySize = 3 for this run. {
int ColourCount = 0;
for (int i = 0; i < ArraySize; i++) {

[Code] ....

An example run you can see in attached pic.

I want to have an if statement that only accepts "Red" and not the occasional "Ravaged_Anus".

I'm using MVS Express 2013, .c source files, and the C++ compiler.

Attached image(s)

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Jan 25, 2014

VS 2012 / Windows 7 64 bit

class
class myclass {
public:
myclass(){/*stuff here*/}
myclass(int* p) {MyPointer = p; myclass()}

[Code] ....

it works until the myclass(int* p) calls myclass()

then the MyPointer will become CCCCCCCC (NULL value)!

is there a way to stop the second constructor from resetting the pointer value to null?

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