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

The function you are looking for is already present in the standard C library. Its name is qsort. Random sorting can be implemented as:

int rand_comparison(const void *a, const void *b)
{
    (void)a; (void)b;

    return rand() % 2 ? +1 : -1;
}

void shuffle(void *base, size_t nmemb, size_t size)
{
    qsort(base, nmemb, size, rand_comparison);
}

The example:

int arr[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };

srand(0); /* each permutation has its number here */

shuffle(arr, 10, sizeof(int));

...and the output is:

3, 4, 1, 0, 2, 7, 6, 9, 8, 5