Removing Duplicates from an Array using C [duplicate]

Answer 1

You could utilise qsort from stdlib.h to ensure your array is sorted into ascending order to remove the need for a nested loop.

Note that qsort requires a pointer to a function (int_cmp in this instance), i've included it below.

This function, int_array_unique returns the duplicate free array 'in-place' i.e. it overwrites the original and returns the length of the duplicate free array via the pn pointer

/**
 * Return unique version of int array (duplicates removed)
 */
int int_array_unique(int *array, size_t *pn)
{
    size_t n = *pn;

    /* return err code 1 if a zero length array is passed in */
    if (n == 0) return 1;

    int i;
    /* count the no. of unique array values */
    int c=0;

    /* sort input array so any duplicate values will be positioned next to each
     * other */
    qsort(array, n, sizeof(int), int_cmp);

    /* size of the unique array is unknown at this point, but the output array
     * can be no larger than the input array. Note, the correct length of the
     * data is returned via pn */
    int *tmp_array = calloc(n, sizeof(int));

    tmp_array[c] = array[0];
    c++;

    for (i=1; i a
    and positive if a > b */
    return *ia  - *ib;
}