Safe array deletion

Question

I'm new to C++ and i'm not absolutely sure how to deal with arrays and pointers in a safe way. In my class I got a member called items:

Item * items;

in my class method called read() I open a file and read the items from this file. I allocate the space accordingly:

items = new Item[item_count];

item_count is given as a variable in the file and is read in advance before creating any items. In the deconstructor in my class I release the memory like this again:

delete[] items;

But if i call the method read() twice before my deconstructor is executed the memory for the first array will not be released properly. I would like to release it in the read method in advance before allocating new memory. But how do I check if some memory is already allocated for the array items?

EDIT: I know there are many other possibilities out there with more 'modern' approachs and more comfortable solutions. But in this case we where explicitly told to use pointers and arrays (education purpose only).

Answer 1

In modern C++, "the safe way" is to avoid raw pointers and raw arrays entirely.

Declare your variable like this:

std::vector<Item> items;

Allocate the space like this:

items.resize(item_count);

In the deconstructor in your class, no code is necessary to release this memory. It's handled automatically.

The reuse of items that you describe in your question will work.

Answer 2

Unless you have some strong reason not to do so, just use std::vector for arrays in C++:

#include <vector>  // for std::vector

....
std::vector<Item> items;

In this way, you don't have to explicitly call delete[] to release vector items' resources; it's just done automatically thanks to vector's (and Items') destructors.

This helps building code that is structurally incapable of leaking resources.

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You can create a vector of itemCount Items using something like:

std::vector<Item> items(itemCount);

or you could dynamically resize the vector using its resize() method, e.g.:

items.resize(itemCount);