qsort comparing all zeros - c

Question

I am trying to use qsort to sort an array of x-y coordinate structs pointers based on their y value, but q sort is not comparing the correct values. I am baffled at this point, can anyone see what I am doing wrong?
sort function:
23 int sortFunc(const void * firsti, const void * secondi){
24
25 const Coordinate* first = firsti;
26 const Coordinate* second = secondi;
27
28 printf("Comparing %f & %f\n", first->y, second->y);
29 if(first->y < second->y){ return 1;}
30 else if(first->y == second->y){ return 0; }
31 else{ return -1; }
32
33 }
print function:
13 void printArray(Coordinate * array[], int size){
14
15 int x;
16 for(x=0; x < size; x++){
17 printf("Point %i : %f | %f\n", x, array[x]->x, array[x]->y);
18 }
19
20 }
and calling
79 qsort(pointArray, count, sizeof(Coordinate*), sortFunc);
80 printArray(pointArray, count);
yields
Comparing 0.000000 & 0.000000
Comparing 0.000000 & 0.000000
Comparing 0.000000 & 0.000000
Comparing 0.000000 & 0.000000
Comparing 0.000000 & 0.000000
Comparing 0.000000 & 0.000000
Comparing 0.000000 & 0.000000
Point 0 : 103.253334 | -12.472327
Point 1 : -3.283118 | -3.101071
Point 2 : 9.289474 | -0.459975
Point 3 : 14.029107 | -11.844076
Point 4 : -6.465595 | 14.704790
Point 5 : -5.764663 | 8.882765
any idea what's happening?

Answer 1

Your comparison function is written as if you have an array of Coordinate structs, not an array of pointers to Coordinate structs.
Since you have an array of pointers to Coordinate structs, the comparison function will receive pointers to pointers to Coordinate structs as parameters. For this reason your comparison function should look as follows
int sortFunc(const void * firsti, const void * secondi)
{
const Coordinate* const* first = firsti;
const Coordinate* const* second = secondi;
if((*first)->y < (*second)->y){ return 1;}
else if((*first)->y == (*second)->y){ return 0; }
else{ return -1; }
}