QSORT(3C)QSORT(3C)NAMEqsort - 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 argu‐
ment specifies the size of each element in bytes. The compar argument
is the name of the comparison function, which is called with two argu‐
ments 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.
USAGE
The qsort() function safely allows concurrent access by multiple
threads to disjoint data, such as overlapping subtrees or tables.
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 attributes:
┌────────────────────┬─────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼─────────────────┤
│Interface Stability │ Standard │
├────────────────────┼─────────────────┤
│MT-Level │ MT-Safe │
└────────────────────┴─────────────────┘
SEE ALSOsort(1), bsearch(3C), lsearch(3C), string(3C), attributes(5), stan‐
dards(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 com‐
pared.
The relative order in the output of two items that compare as equal is
unpredictable.
Dec 6, 2004 QSORT(3C)
