qsort(3C)
NAME
qsort - quick sort
SYNOPSIS
#include <stdlib.h>
void qsort(void *base, size_t nel, size_t width, int
(*compar)(const void *, const void *));
DESCRIPTION
The qsort() function is an implementation of the quick-sort
algorithm. It sorts a table of data in place. The contents
of the table are sorted in ascending order according to the
user-supplied comparison function.
The base argument points to the element at the base of the
table. The nel argument is the number of elements in the
table. The width argument specifies the size of each ele-
ment in bytes. The compar argument is the name of the com-
parison function, which is called with two arguments that
point to the elements being compared.
The function must return an integer less than, equal to, or
greater than zero to indicate if the first argument is to be
considered less than, equal to, or greater than the second
argument.
The contents of the table are sorted in ascending order
according to the user supplied comparison function.
EXAMPLES
Example 1: Program sorts.
The following program sorts a simple array:
#include <stdlib.h>
#include <stdio.h>
static int
intcompare(const void *p1, const void *p2)
{
int i = *((int *)p1);
int j = *((int *)p2);
if (i > j)
return (1);
if (i < j)
return (-1);
return (0);
}
int
main()
{
int i;
int a[10] = { 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 };
size_t nelems = sizeof (a) / sizeof (int);
qsort((void *)a, nelems, sizeof (int), intcompare);
for (i = 0; i < nelems; i++) {
(void) printf("%d ", a[i]);
}
(void) printf("\n");
return (0);
}
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| MT-Level | MT-Safe |
|_____________________________|_____________________________|
SEE ALSO
sort(1), bsearch(3C), lsearch(3C), string(3C), attributes(5)
NOTES
The comparison function need not compare every byte, so
arbitrary data may be contained in the elements in addition
to the values being compared.
The relative order in the output of two items that compare
as equal is unpredictable.
Man(1) output converted with
man2html