I use qsort from C libary and I have datatype

Element_type **pElement and Element_type is struct typedef element_type {int ,char ....} 

example, and i call quicksor function with

qsort(*pElement,iCountElement,(size_t)sizeof(Element_type),compare);

and callback function

static int compare(const void *p1, const void *p2) {
    Element_type  *a1 = (Element_type  *)p1;
    Element_type *a2 =  (Element_type   *)p2;
    return ( (a2)->iServiceId < (a1)->iServiceId );
}

but I always get segmentation fault. Why?