replacing malloc/free with new/delete in c++

Question

I just want to be sure.

this is my code

int * Image = (int *)malloc(sizeof(int) * m_Width/2 * m_Height);
free(Image);

if I want to use new Instead of malloc and free instead of delete. this is what i wrote

int* Image = new int[m_Width/2 * m_Height];
delete[] Image;

Is that correct?

That is indeed correct. I don't think this is worthy of an answer. — Joseph Mansfield, Feb 13 '14 at 22:54
Don't delete it, this is a good example for anyone else who has the same question. — IllusiveBrian, Feb 13 '14 at 23:01
Don't cast the result of `malloc` to `(int*)`; the cast will happen automatically. DRY. — jia103, Feb 13 '14 at 23:07
int* image = malloc(sizeof(int)* m_Width/2 * m_Height); ?? @jia103 — Gilad, Feb 13 '14 at 23:09
`malloc()` returns a `void*`. In C++, you have to type-cast it. — Remy Lebeau, Feb 13 '14 at 23:09
Sorry for any wrong info. Is the behavior different in C than C++? [This](http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc) is what I was going by. I can't believe how rusty I've gotten after working in C#. — jia103, Feb 13 '14 at 23:21

score 3 · Accepted Answer · answered Feb 13 '14 at 23:08

3

Technically, it is correct. However, this is C++ we are talking about, and the C++ way to dynamically allocate an array is to use a std:vector instead:

std::vector<int> Image(m_Width/2 * m_Height);

Or:

std::vector<int> Image;
Image.resize(m_Width/2 * m_Height);

The memory will be freed automatically when the std::vector is destructed when it goes out of scope.

answered Feb 13 '14 at 23:08

Remy Lebeau

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The original code was allocating an array of `int` values, so you would create a `std::vector` of `int` values. – Remy Lebeau Feb 13 '14 at 23:46
Yeah I was just trying to make it clear if someone like the OP was watching the answer. – MahanGM Feb 14 '14 at 09:51

score 2 · Answer 2 · answered Feb 14 '14 at 08:27

That's correct. But if you want to gain some additional semantics without getting much OOP overhead, you can use unique_ptr:

unique_ptr<int[]> Image(new int[m_Width/2 * m_Height]);
// do something with Image...
Image.Reset(); // call it if you want to free memory manually,
               // or just leave until Image is destroyed.

replacing malloc/free with new/delete in c++

2 Answers2