Deletion problem

[BeyondTheEye]

I've created a class, Category.

#ifndef CATEGORY_H_INCLUDED
#define CATEGORY_H_INCLUDED

#include <string>
using std::string;

enum Type {Integer, Double, Bool, String, Date, Time};

class Category
{
    public:
        Category() : itsType(String) {}
        Category(Type type) : itsType(type) {}
        Category(string name) : itsName(name) {}
        Category(Type type, string name) : itsName(name), itsType(type) {}
        ~Category() {}

        void operator=(const Category& rCat) {itsName = rCat.itsName; itsType = rCat.itsType;}

        const Type& GetType() const {return itsType;}
        const string& GetName() const {return itsName;}

    private:
        string itsName;
        Type itsType;
};

#endif // CATEGORY_H_INCLUDED

Used in main.cpp.

#include <iostream>
using namespace std;

#include "Category.h"

int main()
{
    Category test(String, string("Test"));
    Category* pCat = new Category;
    pCat[0] = test;
    cout << "Name: " << pCat[0].GetName() << endl;
    cout << "Type: " << pCat[0].GetType() << endl;
    delete [] pCat; //Crashes the program
    //delete pCat; //Works fine

    return 0;
}

The problem is indicated in main().
When I use delete [] pCat the program crashes.
When I do the same using delete pCat , it doesn't.
If there's more than 1 Category in the array, the problem doesn't occur...

I've tried doing the same with int, which works fine. I can't seem to figure out why it doesn't work for Category..

Any input is welcome.

[mrnutty]

The proper use of delete and delete []

int *Num = new int;
int *Array = new int[5];

delete Num; //good
delete [] Num; //Bad -- undefined 
delete [] Array; //good
delete Array; //bad --undefined

As you can see, you have :

Category* pCat = new Category;

Which should follow up with a

delete pCat;

You are using an array notation bracket, i.e [] on pCat, and that
is probably why it lead you to think you should use delete [] pCat,
but in fact, if you know abut pointers, pCat[0] is the same as *pCat.

Also (1) pCat[0].GetType() is the same as (2) (*pCat).GetType and (3) pCat->GetType.
Use the option (3), as it is more clear, that pCat is not an array of a class object and "prettier."

[BeyondTheEye]

The proper use of delete and delete []

int *Num = new int;
int *Array = new int[5];

delete Num; //good
delete [] Num; //Bad -- undefined 
delete [] Array; //good
delete Array; //bad --undefined

As you can see, you have :

Category* pCat = new Category;

Which should follow up with a

delete pCat;

You are using an array notation bracket, i.e [] on pCat, and that
is probably why it lead you to think you should use delete [] pCat,
but in fact, if you know abut pointers, pCat[0] is the same as *pCat.

Also (1) pCat[0].GetType() is the same as (2) (*pCat).GetType and (3) pCat->GetType.
Use the option (3), as it is more clear, that pCat is not an array of a class object and "prettier."

I would normally go with option (3). However, I was using the class in a program with a self-written form of Vector, and it kept crashing upon destruction of the object.
I was hoping there was a way around just leaving the [] out, since it means an extra if-condition in the Vector-class...

Guess that's an anwser though, unless there's a specific reason why the deletion goes wrong.

[mrnutty]

" I was using the class in a program with a self-written form of Vector, and it kept crashing upon destruction of the object."

Mind showing your constructor and destructor?

[BeyondTheEye]

#define DEFAULTSIZE 0

template <class T>
class Array
{
    public:
        //Public constructor
        Array() {itsSize = DEFAULTSIZE; itsElements = 0;}
        //Copy constructor
        Array(const Array&);
        //Destructor
        ~Array() {if(itsSize > 1) delete [] itsElements; else if(itsSize == 1) delete itsElements;}
        //Previous destructor
        //~Array() {if(itsSize) delete [] itsElements;
    private:
        //Private constructor
        Array(int size) {itsSize = size; itsElements = new T[itsSize];}
        //Private variables
        int itsSize;
        T* itsElements;
};

I modified the destructor to prevent the crashing. The old destructor is commented out under it.

[mrnutty]

Normally with destructor and constructor,
you should do something like ,

Array(){
  mainArray = new Type[0];
}
~Array(){
  delete [] mainArray;
}

Here is a complete example.

#include <iostream>
#include <string> 
 
using std::cout;
using std::string;
using std::endl;

template<typename Type>
class Array
{
	typedef unsigned int uInt;
private:
	uInt len;
	Type * mainArray;
public:
	Array(){
		mainArray = new Type[0];
		len = 0;
	}
	Array(uInt Sz, Type val){
		mainArray = new Type[Sz];
		len = Sz;
		for(uInt i = 0; i < Sz; i++)
			mainArray[i] = val;
	}
	~Array(){
		//Its able to delete a null pointer, i.e if(len == 0);
		delete [] mainArray; 
	}
	bool isEmpty() {
		return len == 0; 
	}
	uInt Size(){
		return len; 
	}
	bool Print(int col)
	{
		if(!len) 
			return false;

		for(uInt i = 0; i < len; i++) {
			if(i && i % col == 0) 
				cout << endl;			
			cout<<mainArray[i]<<" ";
		}
		
		return true;
	}
	
};

int main()
{  
	Array<int> Numbers;
	Array<float> Numerics(12,10);

	cout<<"Numbers size is : " << Numbers.Size() << endl;
	cout<<"Numerics size is: "<< Numerics.Size() << endl;
	
	if(Numbers.Print(4))
		;
	else cout<<"Nothing to print in Numbers\n";

	cout<<endl;

	if(Numerics.Print(4))
		;
	else cout<<"Nothing to print in Numerics\n";
	
	cout<<"\n\n";


	return 0;
}

[BeyondTheEye]

Thanks for the info. I'll go and change that..

EDIT:
Seems to still give crashes. If I use delete [] mainArray on my Category class it still crashes

[mrnutty]

Can you post your whole code if its not too big.

[BeyondTheEye]

Same problem as in the first post, without a dynamic array. I've never had it with any other class, so I'd assume Category is the problem, not the Array class.

[BeyondTheEye]

Figured it out. It appears new Type isn't quite the same as new Type[1]

[mrnutty]

Figured it out. It appears new Type isn't quite the same as new Type[1]

Yep, if you look closely, you would have seen that on my post.