Array of pointers to multidimensional arrays

Question

i have some bidimensional arrays like:

int shape1[3][5] =  {1,0,0,
             1,0,0,
             1,0,0,
             1,0,0,
             1,0,0};
int shape2[3]         


        

Answer 1

First of all, the first array bound refers to the outermost array dimension, so you should probably declare shape1 as:

int shape1[5][3] =  {1,0,0,
                     1,0,0,
                     1,0,0,
                     1,0,0,
                     1,0,0};

and similarly for shape2.

[EDIT: I've changed the type of shapes below to correspond to Robert Barnes' answer -- we don't want the outermost subscript to be included in this type!]

The slightly strange-looking typename you need is:

int (*shapes[])[3] = { shape1, shape2 };

This allows the element at row 4, column 1 of shape2 to be addressed using

shapes[1][3][0]

Breakdown of subexpressions and their C types:

shapes            // has type "int (*x[2])[3]" (decays to "(**x)[3]")
shapes[1]         // has type "int (*x)[3]"
shapes[1][3]      // has type "int x[3]" (decays to "int *x")
shapes[1][3][0]   // has type "int x"

(Note that a dummy x has been included in the types above to make them clearer -- in fact this identifier is not part of the type.)

A rule of thumb for decoding C/C++ types is "starting from the variable name, read right when you can and left when you hit a closing parenthesis." So the decoded typename for shapes is:

An array of pointers to an array of 3 integers.

In general it's much nicer to use typedefs for these complicated types, as dirkgently suggests.