How to get number of arrays in a multidimensional array

Question

I have a multidimensional array consisting of several sub arrays. Is it possible to count the number of sub-arrays in the array?

Answer 1

If the array is declared on the stack, then you can get the number of elements by using the sizeof() function:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int a[3][4];

    fprintf(stdout, "size of a in bytes: %zu\n", sizeof(a));
    fprintf(stdout, "size of a[0][0] in bytes: %zu\n", sizeof(a[0][0]));
    fprintf(stdout, "number of elements in a: %zu\n", sizeof(a)/sizeof(a[0][0]));

    int b[3][4][5];

    fprintf(stdout, "size of b in bytes: %zu\n", sizeof(b));
    fprintf(stdout, "size of b[0][0][0] in bytes: %zu\n", sizeof(b[0][0][0]));
    fprintf(stdout, "number of elements in b: %zu\n", sizeof(b)/sizeof(b[0][0][0]));

    return EXIT_SUCCESS;
}

To compile:

$ gcc -Wall stack_array_test.c -o stack_array_test

Results:

$ ./stack_array_test
size of a in bytes: 48
size of a[0][0] in bytes: 4
number of elements in a: 12
size of b in bytes: 240
size of b[0][0][0] in bytes: 4
number of elements in b: 60

Knowing this, you could modify the denominator to get sizes of elements at different dimension indices. I'll leave that as an exercise.

Now, if your array is declared dynamically — on the heap — then you cannot use this technique.

You could create a struct to mimic a vector, which stores the pointers, along with a size_t representing the number of elements. You could extend this idea to keep a vector of vectors, or a vector of vectors of vectors, and so on. Getting the number of "subarrays" would be a matter of looking up the size parameter of each nested vector and keeping a running tally.

Answer 2

Yes, it is possible to count the number of sub-arrays in the array?

Here is example written in PHP

    <?php
    function getArrayCount(array $arr, $include_empty_arr = true, &$count = 0) {

        foreach ($arr as $a) {

            if (is_array($a)) {

                $include_empty_array_flag = ($include_empty_arr) ? $include_empty_arr : (!empty($a));

                if ($include_empty_array_flag) {
                    $count++;
                }

                getArrayCount($a, $include_empty_arr, $count);
            }
        }

        return $count;
    }

    $my_arr = array(array('1', '2'), array('3', '4', array()), array('44', array(array(707, 808, 909, 180), 77, 88, 99, 100)), array('5', '6', '7', array('8', '9', '10', array())));

    //if you want to count empty sub-array too, then simply call the function getArrayCount($my_arr);
    echo "Number of sub-arrays : " . getArrayCount($my_arr);
    //will output 
    //Number of sub-arrays : 9
    //if you want to count sub-arrays which are not empty, then simply call the function getArrayCount($my_arr, false); with an additional boolean flag parameter
    echo "<br/>Number of sub-arrays (exclude empty arrays) : " . getArrayCount($my_arr, false);
    //will output 
    //Number of sub-arrays (exclude empty arrays) : 7
    ?>