NAME

qsort - sorts an array

SYNOPSIS

#include <stdlib.h>

void qsort(void *base, size_t nmemb, size_t size,

int(*compar)(const void *, const void *));

DESCRIPTION

The qsort() function sorts an array with nmemb elements of size size. The base argument points to the start of the array.

The contents of the array are sorted in ascending order according to a comparison function pointed to by compar, which is called with two arguments that point to the objects being compared.

The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second. If two members compare as equal, their order in the sorted array is undefined.

RETURN VALUE

The qsort() function returns no value.

CONFORMING TO

SVID 3, POSIX, 4.3BSD, ISO 9899

NOTE

Library routines suitable for use as the compar argument include strcmp() (see below), alphasort(), and versionsort().

EXAMPLE

For one example of use, see the example under bsearch(3).

The following example program sorts the strings given in its command-line arguments:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>
static int
cmpstringp(const void *p1, const void *p2)
{

    /* The arguments to this function are "pointers to

       pointers to char", but strcmp() arguments are "pointers

       to char", hence the following cast plus dereference */

    return strcmp(* (char **) p1, * (char **) p2);
}
int
main(int argc, char *argv[])
{

    int j;

    assert(argc > 1);

    qsort(&argv[1], argc - 1, sizeof(char *), cmpstringp);

    for (j = 1; j < argc; j++)

        puts(argv[j]);

    exit(EXIT_SUCCESS);
}

SEE ALSO

sort(1), alphasort(3), strcmp(3), versionsort(3)