Shuffle array in C

Question

I\'m looking for a function in ANSI C that would randomize an array just like PHP\'s shuffle() does. Is there such a function or do I have to write it on my own

Answer 1

Here a solution that uses memcpy instead of assignment, so you can use it for array over arbitrary data. You need twice the memory of original array and the cost is linear O(n):

void main ()
{
    int elesize = sizeof (int);
    int i;
    int r;
    int src [20];
    int tgt [20];

    for (i = 0; i < 20; src [i] = i++);

    srand ( (unsigned int) time (0) );

    for (i = 20; i > 0; i --)
    {
        r = rand () % i;
        memcpy (&tgt [20 - i], &src [r], elesize);
        memcpy (&src [r], &src [i - 1], elesize);
    }
    for (i = 0; i < 20; printf ("%d ", tgt [i++] ) );
}