C sort array of strings with qsort and strcmp - warning: incompatible pointer type

Question

I tried to sort an array of strings with qsort but got this warning:

warning: passing argument 4 of 'qsort' from incompatible pointer type

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

#define MAX_PRODUCTS   1000

int main (void) {
    int i, index = 0, isUnique;
    char products[MAX_PRODUCTS][100];
    char product[100];
    int  count[MAX_PRODUCTS];

    FILE * fp;

    fp = fopen ("one.txt", "r");

    // Read words from file and put in array if unique
    while (fscanf(fp, "%s", product) != EOF){
        isUnique = 1;
        for (i=0; i<index && isUnique; i++){
            if (strcmp(products[i], product) == 0){
                isUnique = 0;
            }   
        }

        if (isUnique) {
            strcpy(products[index], product);
            index++;
        }

        else {
            count[i - 1]++;
        }
    }

    qsort(products, MAX_PRODUCTS, sizeof(char*), strcmp);

    fclose(fp);

    return 0;
}

I also tried a custom function to compare strings but this didn't worked either. What can I do to fix it?

Answer 1

qsort is documented on the Microsoft website where it states:

compare Pointer to a user-supplied routine that compares two array elements and returns a value that specifies their relationship.

---

Use this:

int compare (const void * a, const void * b)
{
  return strcmp((char*)a, (char*)b );
}

the following way:

qsort(products, MAX_PRODUCTS, 100, compare);