'\" te
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.TH QSORT 3C "Dec 6, 2004"
.SH NAME
qsort \- quick sort
.SH SYNOPSIS
.LP
.nf
#include <stdlib.h>

\fBvoid\fR \fBqsort\fR(\fBvoid *\fR\fIbase\fR, \fBsize_t\fR \fInel\fR, \fBsize_t\fR \fIwidth\fR,
     \fBint (*\fR\fIcompar\fR)(const void *, const void *));
.fi

.SH DESCRIPTION
.sp
.LP
The \fBqsort()\fR 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.
.sp
.LP
The \fIbase\fR argument points to the element at the base of the table.  The
\fInel\fR argument is the number of elements in the table.  The \fIwidth\fR
argument specifies the size of each element in bytes.  The \fIcompar\fR
argument is the name of the comparison function, which is called with two
arguments that point to the elements being compared.
.sp
.LP
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.
.sp
.LP
The contents of the table are sorted in ascending order according to the user
supplied comparison function.
.SH USAGE
.sp
.LP
The \fBqsort()\fR function safely allows concurrent access by  multiple threads
to disjoint data, such as overlapping subtrees or tables.
.SH EXAMPLES
.LP
\fBExample 1 \fRProgram sorts.
.sp
.LP
The following program sorts a simple array:

.sp
.in +2
.nf
#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("\en");
    return (0);
}
.fi
.in -2

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.sp
.LP
\fBsort\fR(1), \fBbsearch\fR(3C), \fBlsearch\fR(3C), \fBstring\fR(3C),
\fBattributes\fR(5), \fBstandards\fR(5)
.SH NOTES
.sp
.LP
The comparison function need not compare every byte, so arbitrary data may be
contained in the elements in addition to the values being compared.
.sp
.LP
The relative order in the output of two items that compare as equal is
unpredictable.