QSORT(3C) Standard C Library Functions QSORT(3C)
NAME
qsort,
qsort_r - quick sort
SYNOPSIS
#include <stdlib.h> void qsort(
void *base,
size_t nel,
size_t width,
int (*compar)(const void *, const void *));
void qsort_r(
void *base,
size_t nel,
size_t width,
int (*compar_arg)(const void *, const void *, void *),
void *arg);
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
comparison function need not compare every byte, so arbitrary data may
be contained in the elements in addition to the values 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. The relative order in the
output of two items that compare as equal is unpredictable.
The
qsort_r() function behaves similarly to the
qsort() function,
except that its comparison function,
compar_arg(), takes an extra
argument which is the
qsort_r() argument
arg. This allows one to avoid
global data in the comparison function, unlike with the
qsort()
function.
The
qsort() and
qsort_r() functions safely allow 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);
}
INTERFACE STABILITY
StandardMT-LEVEL MT-SafeSEE ALSO
sort(1),
bsearch(3C),
lsearch(3C),
string(3C),
attributes(7),
standards(7)illumos November 15, 2023 illumos
