Array of pointers to an array of fixed size

Question

I tried to assign two fixed-size arrays to an array of pointers to them, but the compiler warns me and I don\'t understand why.

int A[5][5];
int B[5][5];
int         


        

Answer 1

Unfortunately there's a lot of crappy books/tutorials/teachers out there who will teach you wrong things....

Forget about pointer-to-pointers, they have nothing to do with arrays. Period.

Also as a rule of thumb: whenever you find yourself using more than 2 levels of indirection, it most likely means that your program design is fundamentally flawed and needs to be remade from scratch.

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To do this correctly, you would have to do like this:

A pointer to an array int [5][5] is called array pointer and is declared as int(*)[5][5]. Example:

int A[5][5];
int (*ptr)[5][5] = &A;

If you want an array of array pointers, it would be type int(*[])[5][5]. Example:

int A[5][5];
int B[5][5];
int (*arr[2])[5][5] = {&A, &B};

As you can tell this code looks needlessly complicated - and it is. It will be a pain to access the individual items, since you will have to type (*arr[x])[y][z]. Meaning: "in the array of array pointers take array pointer number x, take the contents that it points at - which is a 2D array - then take item of index [y][z] in that array".

Inventing such constructs is just madness and nothing I would recommend. I suppose the code can be simplified by working with a plain array pointer:

int A[5][5];
int B[5][5];
int (*arr[2])[5][5] = {&A, &B};
int (*ptr)[5][5] = arr[0];
...
ptr[x][y][z] = 0;

However, this is still somewhat complicated code. Consider a different design entirely! Examples:

• Make a 3D array.
• Make a struct containing a 2D array, then create an array of such structs.