Program crashes when allocating memory for object array

Question

My code is something like this in C++

MyObject* someObject;

void makeArray(int sizeArray)
{
    someObject = (MyObject*) malloc(sizeof(MyObject) * sizeArray);
}

Now this compiles without any errors or warnings, but when I run the program it instantly crashes. I have also tried to hardcode the array in, and I do have enough memory for it. I haven't used malloc too much, so I probably have something coded wrong, but if that's the problem, what is it?

don't use `malloc` in C++ unless you're overloading operator `new` — Iosif Murariu, Jun 14 '14 at 09:14
@EdHeal Eh, yes? See [_C++11 Style_](http://channel9.msdn.com/Events/GoingNative/GoingNative-2012/Keynote-Bjarne-Stroustrup-Cpp11-Style). — , Jun 14 '14 at 09:18
(There are exceptions, of course. For example, when dealing with a crappy API or when implementing the C++ standard library.) — , Jun 14 '14 at 09:28

score 3 · Answer 1 · edited Jun 20 '20 at 09:12

3

Memory allocation is not construction

You should not use malloc when you are creating objects that have a non-trivial constructor, mainly because malloc will not call any constructor; it will merely allocate memory, nothing more.

In C++, you use operator new to allocate memory and construct the object:

MyObject* someObject;

void makeArray(int sizeArray) {
    someObject = new MyObject[sizeArray];
}

^{Note: For every new you shall have a matching delete, please remember to use delete[] someObject when you are done.}

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The C++ way of doing things is to use std::vector which will handle memory management, and object construction/destruction for you:

std::vector<MyObject> vec (sizeArray); // create a vector with `sizeArray` elements

If you "must" use pointers please don't use raw-pointers, instead you should use smart-pointers if those are available under your implementation:

What is a smart pointer and when should I use one?

edited Jun 20 '20 at 09:12

Community

1
1

answered Jun 14 '14 at 09:15

Filip Roséen - refp

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In was in earlier versions of C++ – Ed Heal Jun 14 '14 at 09:16
2

I would argue that the right solution is to use `std::vector` in C++Anything. As for Ed's comment, the point is that you make it sound as if you couldn't dynamically allocate an array with `new` before C++11. (not my down-vote BTW) – juanchopanza Jun 14 '14 at 09:17
- `new` was in the earlier versions of C++ – Ed Heal Jun 14 '14 at 09:18
@juanchopanza - It depends. Sometimes using new is useful when performing custom memory allocations – Ed Heal Jun 14 '14 at 09:20
@EdHeal opsie, weird typo: **fixed**! – Filip Roséen - refp Jun 14 '14 at 09:21
@juanchopanza added wording regarding `std::vector`, thanks. – Filip Roséen - refp Jun 14 '14 at 09:21

score 1 · Answer 2 · answered Jun 14 '14 at 09:15

1

Why are you using malloc in C++? new is what you should be using

i.e.

someObject = new MyObject[sizeArray];

then use delete[] to delete it!

answered Jun 14 '14 at 09:15

Ed Heal

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I didn't downvote, but think the better recommendation is to use a `std::vector<>`. – πάντα ῥεῖ Jun 14 '14 at 09:19
@πάνταῥεῖ - It is an answer to the question and is correct. Seems rather harsh to downvote but I will bear it in mind. – Ed Heal Jun 14 '14 at 09:21
I told you I didn't downvote! I just put a comment with some criticism. – πάντα ῥεῖ Jun 14 '14 at 09:22
@πάνταῥεῖ - I took your comment to mean that the person that downvoted was due to me not mentioning vector – Ed Heal Jun 14 '14 at 09:24

Program crashes when allocating memory for object array

2 Answers2

Memory allocation is not construction

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