Using a multi-dimensional array with a generic function

Question

I've written the following generic function:

void* scramble(void* arr, int ElemSize, int n, int* indArr){
    void * res = malloc(n * ElemSize);
    int i;

    for (i = 0 ; i < n ; i++)
        memcpy((BYTE*)res+i*ElemSize, (BYTE*)arr+indArr[i]*ElemSize, ElemSize);

    return res;
}

The function gets an array, the size of each element, and number of elements in the array.
indArr is an array with indexes running from 0 to n-1 in any order.
The function returns a new array arranged according to indArr.

How can I use it to work with two dimensional arrays (or more)? I tried this, but it doesn't work:

int indArr[] = {2, 0, 1};
char names[][10] = {{"David"}, {"Daniel"}, {"Joni"}};
char **res;

res = (char**)scramble(names, sizeof(char*), 3, indArr);

for (i = 0 ; i < 3 ; i++)
    printf("%s ", res[i]);

Any thoughts? Thanks

alk · Accepted Answer · 2013-09-24T13:41:44.513

1

names is an array of arrays.

The scrambler referrs to the outer array. The elements of the latter are the "strings". The size of each string is 10.

So call the scrambler like this:

res = (char**)scramble(names, 10, 3, indArr);

or

res = (char**)scramble(names, sizeof(*names), 3, indArr);

Update:

To be able to access the single elements of the inner array do as follows:

char (*res)[10] = (char (*)[10]) scramble(names, sizeof(*names), 3, indArr);

for (int i = 0; i < 3; ++i)
  printf("res[%d] = '%s'\n", i, res[i]);

edited Sep 24 '13 at 13:41

answered Sep 24 '13 at 12:01

alk

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How do I print the strings from res? Will printf("%s", res[1]) do the trick? When I tried I didn't work – David Tzoor Sep 24 '13 at 12:08
Could you care to explain what does (*res)[10] mean? @alk – David Tzoor Sep 24 '13 at 13:06
@DavidTzoor: `char (*res)[10]` declares `res` to be a pointer to an array of 10 `char`s. – alk Sep 24 '13 at 13:40

Using a multi-dimensional array with a generic function

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