二维指针数组

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] .