Dynamically allocate contiguous memory for a "rectangular 2d array", without using VLAs

Question

This is one of those questions where there are so many answers, and yet none do the specific thing.

I tried to look at all of these posts — 1 2 3 4 5 6 7 8 9 — and every time the solution would be either using VLAs, using normal arrays with fixed dimensions, or using pointer to pointer.

What I want is to allocate:

• dynamically (using a variable set at runtime)
• rectangular ("2d array") (I don't need a jagged one. And I guess it would be impossible to do it anyway.)
• contiguous memory (in #8 and some other posts, people say that pointer to pointer is bad because of heap stuff and fragmentation)
• no VLAs (I heard they are the devil and to always avoid them and not to talk to people who suggest using them in any scenario).

So please, if there is a post I skipped, or didn't read thoroughly enough, that fulfils these requirements, point me to it.
Otherwise, I would ask of you to educate me about this and tell me if this is possible, and if so, how to do it.

Answer 1

You can dynamically allocate a contiguous 2D array as

int (*arr)[cols] = malloc( rows * sizeof (int [cols]) );

and then access elements as arr[i][j].

If your compiler doesn’t support VLAs, then cols will have to be a constant expression.