Question

I am trying to make a c++ program with a class which holds integers on the “heap” and has only one method, pop() which returns the first item in the class and removes it. This is my code so far:

#include <iostream>
using namespace std;

class LinkList {
int *values; //pointer to integers stored in linklist
int number; // number of values stored in linklist
public:
LinkList(const int*, int); // Constructor (method declaration)
int pop(); // typically remove item from data structure (method declaration)

};

LinkList::LinkList(const int *v, int n){
number = n;
*values = *v;
int mypointer = 1;
while (mypointer<n) {
    *(values+mypointer) = *(v+mypointer);
    mypointer++;
}
}


int LinkList::pop() {
if (number>0) {
    int returnme = *values; //get the first integer in the linklist
    number--;
    values++; //move values to next address
    return returnme;
}
else {return -1;}
}



int main() {
int test[] = {1,2,3,4,5};
LinkList l1(test,5);
cout << l1.pop() << endl;
LinkList l2(test,5);
cout << l2.pop() << endl;
return 0;
}

The issue is that its failing at the line *values = *v, if i remove the 4th and 5th lines from the main method, I no longer get this issue, so its go to be a memory management thing.

What I want to do is to get values to point to a continuous bit of memory with integers in. I have tried to use arrays for this but keep just getting random memory addresses returned by pop()

Background: normal I programming in java, I’ve only be using C/C++ for 2 months, I’m using eclipse IDE in ubuntu, I can make very basic use of the debugger but currently I dont have functioning scroll bars in eclipse so I can’t do somethings if they dont fit on my screen.

Answer 1

*values = *v;

You dereference the values pointer in this line before initializing it. This is the source of the later errors, and the non-errors in the first three lines of main are simply due to luck. You have to allocate space via values = new int[n] and deallocate it in the destructor via delete[] values. std::vector does this work in a clean and exception-safe way for you.