C/C++ Arrays of multidimensional arrays

Question

I am trying to create an array of two 2D arrays as follows

Given

char twoDArr[2][3] =  {{'a','b','c'},  {'d','e','f'}};

you could do

char (*twoDArrP)[3] = twoDArr;

which yields valid results in:

cout << "twoDArr: " << twoDArr[1][2] << endl;
cout << "twoDArrP: " << twoDArrP[1][2] << endl;

My goal is to create another (static) array and/or pointer as follows

char (**threeDArr)[3] = {twoDArr, twoDArr}; //doesn't compile 

so that I can be able to access its values as:

char val = threeDArr[0][1][2];

Obviously the indices will vary

The question is what is the correct way of declaring the 3D array, i.e. the array of 2D arrays ??

I have searched for an example using this case and I cannot seem to find anything. Any help would be appreciated.

Answer 1

you need

char (*threeDArr[2])[3] = {twoDArr, twoDArr};

with your solution the "innermost" specification was the * and not an array.

Answer 2

An array of

char (*twoDArrP)[3]

of size 2 can be defined as:

char (*threeDArrP[2])[3]

which is not so clear (I'm not even sure if it's entirely correct). See cdecl.

typedef is your friend:

typedef char (*twoDArrP_type)[3];

twoDArrP_type threeDArrP[2] = {twoDArr, twoDArr};

---

This:

char (**threeDArr)[3]

as you have written, is a pointer to a pointer to an array. Not a pointer to a 2D array.