Create 2D array with "new"?

Question

I want to create a 2D array like the following.

char **dog = new char[480][640];

But it errors:

error C2440: 'initializing' : cannot convert from 'char (*)[640]' to 'char ** '
        Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

what do I need to do using "new"? (not using calloc, malloc or char dog[480][640];)

`char (*p)[640] = new char[480][640];` Note that a 2D array of `T` is not the same as an array of pointers to arrays of `T`. Oh, and rather use `std::vector` than raw `new`. Cheers & hth., — Cheers and hth. - Alf, Dec 04 '11 at 00:50
@Mooing Duck: that covers 640x350 and 640x480 resolutions, but it does look a bit odd to mix `vector` and `array` that way. I think I'd use just `vector` all the way, forget about the micro-optimization possible with `array`, and as an added bonus get code that works with more current compilers. Cheers, — Cheers and hth. - Alf, Dec 04 '11 at 02:32

score 6 · Accepted Answer · answered Dec 04 '11 at 00:45

6

Something like this:

char **dog = new char *[480];
for (int i = 0; i < 480; i++)
    dog[i] = new char[640];

And the same when deleting, but then the loop first.

answered Dec 04 '11 at 00:45

Some programmer dude

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KCH · Answer 2 · 2011-12-04T01:07:31.673

5

If you want to get memory from heap, you can use it this way:

// declaration
char *dog = new char[640*480];

// usage
dog[first_index * 640 + second_index] = 'a';

// deletion
delete[] dog;

edited Dec 04 '11 at 01:07

answered Dec 04 '11 at 00:51

KCH

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I think an indexing scheme like this is almost always preferable to handling 2d arrays directly. – pg1989 Dec 04 '11 at 00:52
how much more overhead is there in a 2D array vs 1D array? does it slow things down? – jdl Dec 04 '11 at 00:57
@jdl: shouldn't be any overhead, but this is faster for some things, and more error-prone in others. – Mooing Duck Dec 04 '11 at 02:03

score 0 · Answer 3 · answered Dec 04 '11 at 00:44

0

You're creating a pointer to a pointer by using **. I'm not sure you want that, you probably want a normal pointer (*).

answered Dec 04 '11 at 00:44

Tom van der Woerdt

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Create 2D array with "new"?

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