svn commit: r247014 - head/lib/libc/stdlib

[mdf at FreeBSD.org]

On Tue, Feb 19, 2013 at 3:57 PM, Giorgos Keramidas <keramida at freebsd.org> wrote:
> Author: keramida (doc committer)
> Date: Tue Feb 19 23:57:39 2013
> New Revision: 247014
> URL: http://svnweb.freebsd.org/changeset/base/247014
>
> Log:
>   Add a sample program that shows how a custom comparison function and
>   qsort(3) can work together to sort an array of integers.
>
>   PR:             docs/176197
>   Submitted by:   Fernando, fapesteguia at opensistemas.com
>   Approved by:    gjb (mentor)
>   MFC after:      1 week
>
> Modified:
>   head/lib/libc/stdlib/qsort.3
>
> Modified: head/lib/libc/stdlib/qsort.3
> ==============================================================================
> --- head/lib/libc/stdlib/qsort.3        Tue Feb 19 23:46:51 2013        (r247013)
> +++ head/lib/libc/stdlib/qsort.3        Tue Feb 19 23:57:39 2013        (r247014)
> @@ -32,7 +32,7 @@
>  .\"     @(#)qsort.3    8.1 (Berkeley) 6/4/93
>  .\" $FreeBSD$
>  .\"
> -.Dd September 30, 2003
> +.Dd February 20, 2013
>  .Dt QSORT 3
>  .Os
>  .Sh NAME
> @@ -211,6 +211,52 @@ Previous versions of
>  did not permit the comparison routine itself to call
>  .Fn qsort 3 .
>  This is no longer true.
> +.Sh EXAMPLES
> +A sample program that sorts an array of
> +.Vt int
> +values in place using
> +.Fn qsort ,
> +and then prints the sorted array to standard output is:
> +.Bd -literal
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +
> +/*
> + * Custom comparison function that can compare 'int' values through pointers
> + * passed by qsort(3).
> + */
> +static int
> +int_compare(const void *p1, const void *p2)
> +{
> +        int *left = (int *)p1;
> +        int *right = (int *)p2;

These should be declared const int *.  And the cast shouldn't be
needed in C, since void * can be assigned to any other pointer type.

Cheers,
matthew

> +
> +        if (*left < *right)
> +                return (-1);
> +        else if (*left > *right)
> +                return (1);
> +        else
> +                return (0);
> +}
> +
> +/*
> + * Sort an array of 'int' values and print it to standard output.
> + */
> +int
> +main(void)
> +{
> +       int int_array[] = { 4, 5, 9, 3, 0, 1, 7, 2, 8, 6 };
> +       const int array_size = sizeof(int_array) / sizeof(int_array[0]);
> +       int k;
> +
> +       qsort(&int_array, array_size, sizeof(int), int_compare);
> +       for (k = 0; k < array_size; k++)
> +                printf(" %d", int_array[k]);
> +        printf("\\n");
> +        exit(EXIT_SUCCESS);
> +}
> +.Ed
>  .Sh ERRORS
>  The
>  .Fn heapsort