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 Ibase 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 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() 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);
}

INTERFACE STABILITY

Standard

MT-LEVEL
MT-Safe

SEE ALSO

sort(1), bsearch(3C), lsearch(3C), string(3C), attributes(7), standards(7)

OmniOS October 11, 2020 OmniOS