Class/Pointer Question

This is a discussion on Class/Pointer Question within the C++ Programming forums, part of the General Programming Boards category; I am making my first (semi-)usefull application: my own vector class :P I'm having some troubles with pointers: when I ...

  1. #1
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    Class/Pointer Question

    I am making my first (semi-)usefull application: my own vector class :P I'm having some troubles with pointers: when I delete them in the destructor, I get a memory leak when I run the program (Something like: "glibc detected blabal double free or corruption" and then a lot of memory addresses) If I don't delete the pointers in the destructor, everything runs fine. I am sure I don't delete somewhere else.
    Here's the class declaration:
    Code:
    template <class T>
    class myVec
    {
    	T *arrPtr;
    	T *temp;
    	int count;
    public:
    	myVec(int numElements);
    	myVec();
    	~myVec();
    
    	void addOnTop(T value);
    	void addBegin(T value);
    	void erase(int index);
    	int size() { return count; }
    	bool isEmpty();
    
    	T& operator=(const myVec &a);
    	T& operator[](int index) {if(index > (count-1)) { cout << "Memory overload!!"; } else { return arrPtr[index]; } }
    };
    And then I have a second question: if you have a class, you can declerate some variables outside public/private/protected. What I know you can't access the variables by myObj.value, but is it protected, private or something else?
    Operating Systems:
    - Ubuntu 9.04
    - XP

    Compiler: gcc

  2. #2
    Devil's Advocate SlyMaelstrom's Avatar
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    Class variables are private by default. This, by the way, is the only real difference between the class keyword and struct keyword (which is public, by default) in C++.

    ... and you'll need to provide more code for me to see why deleting in the destructor causes leaks.
    Sent from my iPadŽ

  3. #3
    ZuK
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    You have to implement a proper copy constructor and assignement operator for your class.
    Kurt

  4. #4
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    @ Kurt: I'm not finished yet!
    @ Sly:Nevermind, I found the mistake, I deleted in my Constructor :P Why Static?
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  5. #5
    Devil's Advocate SlyMaelstrom's Avatar
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    Try:
    Code:
    delete[] arrPtr;
    delete[] temp;
    Also, those lines work better in your destructor, not your default constructor.
    Sent from my iPadŽ

  6. #6
    ZuK
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    Quote Originally Posted by Ideswa
    @ Kurt: I'm not finished yet!
    I see but without them you will have multiple deletes on your data.
    Kurt

  7. #7
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    I finished my Vector class... I think.

    Code:
    #include <iostream>
    
    using namespace std;
    
    template <class T>
    class myVec
    {
    	T *arrPtr;
    	T *temp;
    	int count;
    public:
    	myVec(int numElements);
    	myVec();
    	~myVec();
    
    	void addOnTop(T value);
    	void addBegin(T value);
    	void erase(int index);
    	void erase(int begin, int end);
    	int size() { return count; }
    	bool isEmpty();
    	void assign(int num, T value);
    	void resize(int num);
    	void clear();
    	void insert(int pos, T value);
    
    	T& operator=(const myVec &a);
    	T& operator[](int index) {if(index > (count-1)) { cout << "Memory overload!!"; } else { return arrPtr[index]; } }
    };
    
    template <class T>
    myVec<T>::myVec(int numElements)
    {
    	count = numElements;
    	arrPtr = new T[count];
    	temp = new T[count];
    }
    
    template <class T>
    myVec<T>::myVec()
    {
    	count = 0;
    	arrPtr = new T[count];
    	temp = new T[count];
    }
    
    template <class T>
    myVec<T>::~myVec()
    {
    	delete arrPtr;
    	delete temp;
    }
    
    template <class T>
    void myVec<T>::addOnTop(T value)
    {
    	temp = new T[count];
    	for(int i = 0; i < count; i++)
    	{
    		temp[i] = arrPtr[i];
    	}
    	count++;
    	arrPtr = new T[count];
    	for(int i = 0; i < count; i++)
    	{
    		arrPtr[i] = temp[i];
    	}
    	arrPtr[count-1] = value;
    }
    
    template <class T>
    void myVec<T>::addBegin(T value)
    {
    	temp = new T[count];
    	for(int i = 0; i < count; i++)
    	{
    		temp[i] = arrPtr[i];
    	}
    	count++;
    	arrPtr = new T[count];
    	arrPtr[0] = value;
    	for(int i = 0; i < count; i++)
    	{
    		arrPtr[i+1] = temp[i];
    	}
    }
    
    template <class T>
    void myVec<T>::erase(int index)
    {
    	temp = new T[count-1];
    	for(int i = 0; i < index; i++)
    	{
    		temp[i] = arrPtr[i];
    	}
    	for(int i = (index+1); i < count; i++)
    	{
    		temp[i-1] = arrPtr[i];
    	}
    	count--;
    	arrPtr = new T[count];
    	for(int i = 0; i < count; i++)
    	{
    		arrPtr[i] = temp[i];
    	}
    }
    
    template <class T>
    void myVec<T>::erase(int begin, int end)
    {
    	int minus = end-begin;
    	temp = NULL;
    	temp = new T[count-minus];
    	for(int i = 0; i < begin; i++)
    	{
    		temp[i] = arrPtr[i];
    	}
    	for(int i = end; i < count; i++)
    	{
    		temp[i-minus] = arrPtr[i];
    	}
    	arrPtr = NULL;
    	count -= minus;
    	arrPtr = new T[count];
    	for(int i = 0; i < count; i++)
    	{
    		arrPtr[i] = temp[i];
    	}
    }
    
    template <class T>
    bool myVec<T>::isEmpty()
    {
    	if(count == 0)
    	{
    		return true;
    	}
    	else
    	{
    		return false;
    	}
    }
    
    template <class T>
    T& myVec<T>::operator=(const myVec &a)
    {
    	count = a.count;
    	arrPtr = new T[count];
    	for(int i = 0; i < count; i++)
    	{
    		arrPtr[i] = a.arrPtr[i];
    	}
    }
    
    template <class T>
    void myVec<T>::resize(int num)
    {
    	count = num;
    	arrPtr = new T[count];
    	for(int i = 0; i < count; i++)
    	{
    		arrPtr[i] = 0;
    	}
    }
    
    template <class T>
    void myVec<T>::assign(int num, T value)
    {
    	count = num;
    	arrPtr = new T[count];
    	for(int i = 0; i < count; i++)
    	{
    		arrPtr[i] = value;
    	}
    }
    
    template <class T>
    void myVec<T>::clear()
    {
    	count = 0;
    	arrPtr = new T[0];
    }
    
    template <class T>
    void myVec<T>::insert(int pos, T value)
    {
    	temp = new T[count+1];
    	for(int i = 0; i < pos; i++)
    	{
    		temp[i] = arrPtr[i];
    	}
    	for(int i = (pos+1); i < count; i++)
    	{
    		temp[i-1] = arrPtr[i];
    	}
    	count++;
    	arrPtr = new T[count];
    	for(int i = 0; i < count; i++)
    	{
    		if(i == pos)
    			arrPtr[i] = value;
    		else
    			arrPtr[i] = temp[i];
    	}
    }
    What do you think of it?
    Operating Systems:
    - Ubuntu 9.04
    - XP

    Compiler: gcc

  8. #8
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    Lots of memory leaks. Every time you call new (except in the constructors) you should delete the original value first.

    You are calling delete wrong, see SlyMaelstrom's example.

    >> I finished my Vector class... I think.
    There are quite a few things that need to be fixed or added, but keep going and you'll get there.

  9. #9
    C++ Witch laserlight's Avatar
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    The constructor that accepts an int argument should be declared explicit. If not, you could run into situations like:
    Code:
    myVec<int> vec = 10;
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  10. #10
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    I fixed all the bugs you pointed out, I'll expand it with other vector-like functions.
    Operating Systems:
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    Compiler: gcc

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