Proper way of deleting a char** array

Question

I have a dynamically allocated char** array as a private member in one of my classes.

The first allocation occurs according to number of words

client_interests = new char* [n];

Later each index of the array is allocated according to length of the word + 1

char[i] = new char [strlen(word)+1];

Would this be the proper way of deallocating the memory of this member (the classes dtor is calling this function)?

void Client::deallocate()
{
    int i;
    for (i = 0; i < n; i ++) //loops through each word
    {
        delete [] client_interests[i]; //each word is an array of characters, hence delete [] is used
    }
    delete [] client_interests; //deallocating the pointer
    client_interests = NULL;
}

Thaks!

Honestly, using a `std::vector` would be the most "proper" way of dealing with this outright. — WhozCraig, Aug 18 '14 at 10:52
possible duplicate of [2-Dimensional array deallocation](http://stackoverflow.com/questions/10220322/2-dimensional-array-deallocation) — PrR3, Aug 18 '14 at 10:52
Yes, I know - but this is the assignment that was given to us, we have to use c type strings. — Medvednic, Aug 18 '14 at 10:53
Your code seems not to have any errors, although `std::vector` is much much **much far** better solution. — ikh, Aug 18 '14 at 11:00
You want to check whether `client_interests` is null before the loop; otherwise, calling the function a second time will do bad things with a null pointer. (Alternatively, do this work directly in the destructor, so there's no danger of calling it twice). Also, make sure you're following the [Rule of Three](http://stackoverflow.com/questions/4172722) (which standard containers would give you automatically). — Mike Seymour, Aug 18 '14 at 11:25

score 2 · Answer 1 · answered Aug 18 '14 at 10:57

2

Yes, if you absolutely cannot use std::vector<std::string>, then your way of deallocating things is correct.

answered Aug 18 '14 at 10:57

anderas

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score 2 · Accepted Answer · answered Aug 18 '14 at 10:58

2

Your code is correct. Since you allocate using new [], de-allocating with delete [] as you do is required. Also, obviously de-allocating in reverse order - inner arrays first, then outer array - is also required.

answered Aug 18 '14 at 10:58

Jordan Samuels

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How about `for (i = n-1; i >= 0; --i)` if you *really* want reverse order? ;) – fredoverflow Aug 18 '14 at 11:08
@FredOverflow If you like, but it's not necessary and maybe not as readable. The reverse order need only apply to outer/inner, not to the individual inner allocations themselves, as they are independent. That said, if there are additional semantics and exception-safety concerns, it may be appropriate to do as you say. – Jordan Samuels Aug 18 '14 at 11:36

score 1 · Answer 3 · answered Aug 18 '14 at 11:03

1

Yes this is the correct way of deallocating the 2d array.

delete []

is used to deallocate an array, and you are doing it correctly as you first deallocate the inner arrays and than the outer array.

answered Aug 18 '14 at 11:03

Taimour

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Proper way of deleting a char** array

3 Answers3