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Hello all,
I am a new programmer and I am trying to look at how two classes can interact if one class is called by another. What I am trying to do is have a control class. This control class will then make a decision in the constructor about what "sub" classes to call (they are not inherited classes so not strictly a sub class). Since I don't know ahead of time which sub classes will be called I use a pointer in my class header file. In the constructor I then make a decision about the sub classes to call, instantiate the sub classes, and set the pointer to that sub class.
Now here is the my problem; once the constructor finishes, the new sub class I made is destroyed. Later in the control class I have a function that uses the sub class pointer. The pointer works fine and all of the data is passed through the pointer and the function. My worry is that I am working off an artifact in the memory. Since the destructor is called on the sub class the pointer should be randomly pointing into space. Am I missing something about constructors/destructors and pointers? I am sure I am missing something, but I want to learn good technique and make sure I have easily modifiable code. Any help or insight is appreciated.
Below is my test code:
main file
my control class header and cpp filesCode:#include "stdafx.h" using namespace std; int main() { int kb = 0; // just a value to halt the program from closing the window { // defining a new scope to test destruction and construction int val_test = 5; // initialize the value val_test; Class1 input(0); // call class one and initialize class one's variable for (int ii = 0; ii < 10; ii++){ // loop to test this setup cout << "my value: " << ii << endl; input.set(ii); // resetting the values in class 1 } } cin >> kb; // just a halt command return 0; }
,Code:#pragma once class Class2; class Class1 { public: Class1(int a); // constructor ~Class1(void); // destructor void set(int a); // set function int & get(); // get function friend class Class2; // make class two a friend private: int b; // integer variable testing value passing Class2 *Ptr; // pointer to second class that is called from this class };
my sub class header and cpp filesCode:#include "StdAfx.h" #include "Class1.h" using namespace std; Class1::Class1(int a) { b = a; // initial assignment Class2 sub_class; // creating a class2 object Ptr = &sub_class; // setting a pointer to class2 object cout << "constructor value of class1: " << b << endl; // output statement to see the value was initialized } void Class1::set(int a) { b = a; // set the integer value cout << "Class1 stored value is: " << b << endl; // out put the set interger value cout << "Calling second sub_class" << endl; // calling the pointer to class2 Ptr->get(this); // pointer to second class passes the pointer of this object } int &Class1::get() { return b; // return a reference to this value } Class1::~Class1(void) { cout << "my control class destructor is called" << endl; // tell me when the destructor is called }
,Code:#pragma once class Class1; class Class2 { public: Class2(void); // constructor ~Class2(void); // destructor friend class Class1; // friending class 1 to see private data private: int val; // value i want passed in from class1 object int *valPtr; // pointer Class1 *Ptr; // pointer to class one object void get(Class1 *cPtr); // get function to get value from class1 object };
thanks again and I hope this is readableCode:#include "StdAfx.h" #include "Class2.h" using namespace std; Class2::Class2(void) { val = 0;// initialize the value } void Class2::get(Class1 *cPtr) { Ptr = cPtr; // set the pointer to class1 object val = Ptr->get(); // calling the class1 function get to pass the data to class 2 cout << " Sub_class value is: " << val << endl; // output what the data is } Class2::~Class2(void) { cout << "my sub_class destructor is called" << endl; // telling me when this destructor is called }
Specter
Originally Posted by Adak 
