qsort(3C) Standard C Library Functions 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 element in bytes. The compar argument is the name of the comparison 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.
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("
");
return(0);
}
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
|MT-Level |MT-Safe |
+-----------------------------+-----------------------------+
SEE ALSO
sort(1), bsearch(3C), lsearch(3C), string(3C), attributes(5), standards(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.
SunOS 5.10 6 Dec 2004 qsort(3C)
