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

qsort() 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.

base points to the element at the base of the table. nel is the number of elements in the table. width specifies the size of each element in bytes. compar 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.

The contents of the table are sorted in ascending order according to the user supplied comparison function.

EXAMPLE

The following program sorts a simple array:

static int intcompare(i,j)
int ∗i, ∗j;
{
        return(∗i − ∗j);
}
main()
{
        int a[10];
        int i;
        a[0] = 9;
        a[1] = 8;
        a[2] = 7;
        a[3] = 6;
        a[4] = 5;
        a[5] = 4;
        a[6] = 3;
        a[7] = 2;
        a[8] = 1;
        a[9] = 0;
        qsort((char ∗) a, 10, sizeof(int), intcompare);
        for (i=0; i<10; i++) printf(" %d",a[i]);
        printf("\n");
}

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 5.1 — Last change: 13 Jul 1990

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