pointer to array of pointers! how to delete?

Question

so I have a pointer that points to an array of pointers!

    int **matrixPtr;
    matrixPtr = new int*[5];
    for(i=0; i<5; ++i){
        matrixPtr[i]= new int[5];
    }

I'm wondering if this is the proper way to free up the memory!

    for(i=0; i<5; ++i){
        delete [] matrixPtr[i];
    }
    delete [] matrixPtr;

Thanks!

You are right. How many times you "new", that's how many times you need to delete them — SwiftMango
– SwiftMango, Commented Sep 10, 2013 at 5:19
While not an answer to the question, please do consider using std::array or std::vector to make your life easier by avoiding new and delete altogether. — Marc Claesen
– Marc Claesen, Commented Sep 10, 2013 at 5:23
It's an assignment for a data structures class so I can't change the implementation...... — Matt
– Matt, Commented Sep 10, 2013 at 5:28
Why so afraid of manual allocation? It is not suggested but does not mean you cannot do it! — SwiftMango
– SwiftMango, Commented Sep 10, 2013 at 5:31

Wagner Patriota · Accepted Answer · 2013-09-10 05:21:47Z

7

No problem. It's right! You deallocated in the reverse order that you allocated! I don't even think there's another way to do that.

answered Sep 10, 2013 at 5:21

Wagner Patriota

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5 Comments

Arne Mertz Over a year ago

The best way would be to avoid manual allocation all together.

Michael Haidl Over a year ago

@ArneMertz and no one further will ever understand how memory handling is done right. I don't think that avoiding manual allocations is "the best way". Understanding allocation procedures is "the best way".

Wagner Patriota Over a year ago

@ArneMertz. Use C++11 or C++14 does not disencourage us to use manual allocation. It depends on the purpose of the developer. You could say "there is another way IF YOU WANT to avoid manual allocation", but it's not the "best way"... it's just "one way"! But I liked your point of view! +1 ;-)

juanchopanza Over a year ago

@kronos if you really need to understand manual memory allocation, then yes, you have to try it out. But this should only be advanced level stuff, because you would only need it to implement safe, easy to use components. The problem is that this kind of thing is often done at the beginning of the C++ learning process, when it can do more harm than good.

Arne Mertz Over a year ago

@WagnerPatriota C++ encourages the use of encapsulation to put the perils of manual resource management into their own classes. C++11/14 just provide handy standard library classes so one does not have to roll their own. However, coping with resource management and something else (e.g. some business logic) violates the SRP.

Arne Mertz · Accepted Answer · 2013-09-10 05:28:22Z

2

Yes and no. Yes, it's the right way to manually free the memory if you have to allocate it manually like you did.

But no, you should avoid manual allocation and deallocation of memory. If you are stuck with C++03 and without any smart pointers, you should use a vector of vectors. In C++11 you have more options, namely smart pointers and std::array, the latter only if you know the size of the inner or outer dimension or both at compiletime. In C++14 std::dynarray could become an option, too.

answered Sep 10, 2013 at 5:28

Arne Mertz

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2 Comments

Matt Over a year ago

yeah my instructor is requiring it be done this way else I would use something more practical!

Arne Mertz Over a year ago

@Matt Of course, if it's just for the sake of learning memory management, then this is the way to go.

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