C中的qsort（）函数中的cmpfunc

Question

Can someone explain me cmpfunc which is used in the qsort function? What are a and b in this function and what are they pointing to?

int cmpfunc(const void *a, const void *b)
{
    return(*(int*)a - *(int*)b);
}

Answer 1

a and b in cmpfunc are pointers to const void type. cmpfunc can accept pointer to elements of array of any data type.
void * pointer can't be dereferenced, therefore a cast int * is needed before dereferencing.

Answer 2

In this inputs are *void and you need to comaper integers in your case. So you will need to convert types. That's why there are

     *(int *) a

it can be float type

     *(float *) a 

and so on other type...

you can find this implementation :

 int cmpfunc(const void *a, const void *b)
 {
  if(*(int *)a  <  *(int *)b) return -1;
  if(*(int *)a  == *(int *)b) return 0;
  if(*(int *)a  >  *(int *)b) return 1; 
}