2D array of pointers

Question

I'm working an application which required the below thinngs.

const char List1[2][10] = {"Stack","Overflow"};
const char List2[2][10] = {"Goo","Gle"};
const char List3[2][10] = {"Face","Book"};
const char List4[2][10] = {"Pizza","Hutt"};

Now I've to store List1,..,List4 into another array as explained below.

char **var_name[2][2] = { &List1, &List2, &List3, &List4};

What I should called to "var_name"? & Is it right way?

Also If I want to print "Book" using XYZ, then how I can print it?

Answer 1

List1 is an array of two arrays of 10 const char. So &List1 is a pointer to an array of two arrays of 10 char. If var_name is an array of those, it is an array of pointers to an array of two arrays of 10 const char. You can build a declaration for that piece by piece:

• var_name is an array…: var_name[].
• … of pointers: *var_name[].
• …to an array of two…: (*var_name[])[2].
• …arrays of 10…: (*var_name[])[2][10].
• … const char: const char (*var_name[])[2][10].

Then you can define and initialize it:

char (*var_name[])[2][10] = { &List1, &List2, &List3, &List4};

"Book" is in element 1 of List3, which is in element 2 of var_name, so you can refer to it with (*var_name[2])[1].

Note that this requires the *, because var_name[i] is a pointer. This follows the sample code you gave where the array is initialized with &List1. It is more common to use a pointer to the first element of an array instead of a pointer to the array. (The addresses in memory are the same, but the types are different.)

Suppopse we want to eliminate this unnecessary pointer level and initialize var_name with { List1, List2, List3, List4 }. As usual in C, those arrays will be automatically converted to pointers to their first elements. The first element of each of those arrays is an array of 10 const char. So we will be initializing var_name with pointers to arrays of 10 const char.

Thus, var_name will be an array of pointers to arrays of 10 const char. Again, we can build the declaration piece by piece:

• var_name is an array…: var_name[].
• … of pointers…: *var_name[].
• … to arrays of 10…: (*var_name[])[10].
• … const char…: const char (*var_name[])[10].

Then the definition and initialization is:

const char (*var_name[])[10] = { List1, List2, List3, List4 };

Now the elements of List3 are pointed to by var_name[2], so we can refer to "Book" with var_name[2][1].