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qsort
=====

Syntax
------

     #include <stdlib.h>
     
     void qsort(void *base, size_t numelem, size_t size,
                int (*cmp)(const void *e1, const void *e2));

Description
-----------

This function sorts the given array in place.  BASE is the address of
the first of NUMELEM array entries, each of size SIZE bytes.  `qsort'
uses the supplied function CMP to determine the sort order for any two
elements by passing the address of the two elements and using the
function's return address.

The return address of the function indicates the sort order:

Negative
     Element E1 should come before element E2 in the resulting array.

Positive
     Element E1 should come after element E2 in the resulting array.

Zero
     It doesn't matter which element comes first in the resulting array.

Return Value
------------

None.

Example
-------

     typedef struct {
       int size;
       int sequence;
     } Item;
     
     int qsort_helper_by_size(void *e1, void *e2)
     {
       return ((Item *)e2)->size - ((Item *)e1)->size;
     }
     
     Item list[100];
     
     qsort(list, 100, sizeof(Item), qsort_helper_by_size);
     
     int qsort_stringlist(void *e1, void *e2)
     {
       return strcmp(*(char **)e1, *(char **)e2);
     }
     
     char *slist[10];
     
     /* alphabetical order */
     qsort(slist, 10, sizeof(char *), qsort_stringlist);