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

SVr4, 4.3BSD, C89, C99.

NOTES

Library routines suitable for use as the compar argument include alphasort(3) and versionsort(3). To compare C strings, the comparison function can call strcmp(3), as shown in the example below.

EXAMPLE

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

Another example is the following program, which 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 actual arguments to this function are "pointers to
       pointers to char", but strcmp(3) arguments are "pointers
       to char", hence the following cast plus dereference */

    return strcmp(* (char * const *) p1, * (char * const *) 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)

COLOPHON

This page is part of release 2.79 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


  Copyright 1993 David Metcalfe (davidprism.demon.co.uk)

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
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Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
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permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
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responsibility for errors or omissions, or for damages resulting from
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which is licensed free of charge, as they might when working
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Formatted or processed versions of this manual, if unaccompanied by
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References consulted:
    Linux libc source code
    Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
    386BSD man pages

Modified 1993-03-29, David Metcalfe
Modified 1993-07-24, Rik Faith (faithcs.unc.edu)
2006-01-15, mtk, Added example program.