Re: Promoting unsigned long int to long int

pereges <Broli00@xxxxxxxxx> writes:

btw can i sort an array of pointers with qsort function ??

Yes, you can.

I tried the
following but failed miserably as it reutrned the same unsorted list :


int cmp_coord_x(const void *vpa, const void *vpb)
{
const vector *va = vpa;
const vector *vb = vpb;

The array is an array of vector *. The void * you get in the compare
points to an array element -- it is a void * but it points to a vector
**. This is in the FAQ. If you don't mind a cast:

const vector *va = *(const vector *const *)vpa;
const vector *vb = *(const vector *const *)vpb;

return (va->coord[0] < va->coord[0] ? -1 : vb->coord[0] > vb->coord[0]);

You have your va's and vb's mixed up. I think you wanted:

return (va->coord[0] < vb->coord[0] ? -1 : va->coord[0] > vb->coord[0]);

}

int cmp_coord_y(const void *vpa, const void *vpb)
{
const vector *va = vpa;
const vector *vb = vpb;

return (va->coord[1] < va->coord[1] ? -1 : vb->coord[1] > vb-
coord[1]);
}

int cmp_coord_z(const void *vpa, const void *vpb)
{
const vector *va = vpa;
const vector *vb = vpb;

return (va->coord[2] < va->coord[2] ? -1 : vb->coord[2] > vb-
coord[2]);
}

/* axis is used as criterion on how we sort the array */
if (axis == 0)
{
qsort(parent_vpa, sizeof parent_vpa/ sizeof *parent_vpa,
sizeof *parent_vpa, cmp_coord_x);
}
if (axis == 1)
{
qsort(parent_vpa, sizeof parent_vpa/ sizeof *parent_vpa,
sizeof *parent_vpa, cmp_coord_y);
}
if (axis == 2)
{
qsort(parent_vpa, sizeof parent_vpa/ sizeof *parent_vpa,
sizeof *parent_vpa, cmp_coord_z);
}

I'd use an array of function pointers and write:

qsort(parent_vpa, sizeof parent_vpa / sizeof *parent_vpa,
sizeof *parent_vpa, cmp_coord[axis]);

the array would be:

typedef int compare_function(const void *, const void *);
compare_function *cmp_coord[] = {
cmp_coord_x, cmp_coord_y, cmp_coord_z
};

(not compiled so beware syntax errors).

--
Ben.
.