separate-array-of-pointers technique

separate-array-of-pointers technique

what is separate-array-of-pointers technique? when and where can it be used?
here I will explain it.
separate-array-of-pointers is a array of pointers each of which points at one element of another array.when we sort a array  whose elements may be a large structure,it may be useful. As the array is sorted ,it will spend much time. Beause a lot of data will be copied back and forth.we can exploite separate-array-of-pointers technique.

/**/ /*
* demonstrate the use of separate-array-of-pointers technique.
*  
*/
#include  < stdio.h >
#include  < stdlib.h >

struct employee {
       char name[20];
       long emp_id;
       } ;
int  emp_pointer_name_compare( const   void   * e1p, const   void   * e2p)
{
  const struct employee **e1,**e2;
  e1=(const struct employee* *) (e1p); //it is hard to understand?
  e2=(const struct employee* *) (e2p);
  return strcmp((*e1)->name,(*e2)->name);
     
      
}
/**/ /*
int emp_name_compare(const void *e1p,const void * e2p)
{
  const struct employee *e1,*e2;
  e1=(const struct employee* ) (e1p); //it is hard to understand?
  e2=(const struct employee* ) (e2p);
  return strcmp(e1->name,e2->name);
}*/
int  main()
{
struct employee employees[10];
struct employee *pemployees[10];
char buf[BUFSIZ];
int i,nep;
for(nep=0;nep<3 &&fgets(buf,BUFSIZ,stdin)!=NULL;nep++)
{
             sscanf(buf,"%s %ld\n",&employees[nep].name,
                                   &employees[nep].emp_id);
             pemployees[nep]=&employees[nep];                     
                                   
}   
qsort(pemployees,nep,sizeof(struct employee *),emp_pointer_name_compare);

/**//*qsort(employees,nep,sizeof(struct employee),emp__name_compare);*/

printf("Sorted by name:");
for(i=0;i<nep;i++)
{
 printf("%s %ld \n",pemployees[i]->name,pemployees[i]->emp_id);
} 
scanf("%d",&i);
return 0;    
}