mirror of https://github.com/mkerrisk/man-pages
118 lines
3.5 KiB
Groff
118 lines
3.5 KiB
Groff
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" References consulted:
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.\" Linux libc source code
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.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
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.\" 386BSD man pages
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.\"
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.\" Modified 1993-03-29, David Metcalfe
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.\" Modified 1993-07-24, Rik Faith (faith@cs.unc.edu)
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.\" 2006-01-15, mtk, Added example program.
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.\"
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.TH QSORT 3 2003-11-15 "" "Linux Programmer's Manual"
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.SH NAME
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qsort \- sorts an array
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.SH SYNOPSIS
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.nf
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.B #include <stdlib.h>
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.sp
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.BI "void qsort(void *" base ", size_t " nmemb ", size_t " size ,
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.BI " int(*" compar ")(const void *, const void *));"
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.fi
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.SH DESCRIPTION
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The
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.BR qsort ()
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function sorts an array with \fInmemb\fP elements of
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size \fIsize\fP.
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The \fIbase\fP argument points to the start of the
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array.
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.PP
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The contents of the array are sorted in ascending order according to a
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comparison function pointed to by \fIcompar\fP, which is called with two
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arguments that point to the objects being compared.
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.PP
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The comparison function must return an integer less than, equal to, or
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greater than zero if the first argument is considered to be respectively
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less than, equal to, or greater than the second.
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If two members compare
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as equal, their order in the sorted array is undefined.
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.SH "RETURN VALUE"
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The
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.BR qsort ()
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function returns no value.
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.SH "CONFORMING TO"
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SVr4, 4.3BSD, C89, C99.
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.SH NOTES
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Library routines suitable for use as the
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.I compar
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argument include
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.BR alphasort (3)
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and
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.BR versionsort (3).
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To compare C strings, the comparison function can call
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.BR strcmp (3),
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as shown in the example below.
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.SH EXAMPLE
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For one example of use, see the example under
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.BR bsearch (3).
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Another example is the following program,
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which sorts the strings given in its command-line arguments:
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.sp
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.nf
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <string.h>
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#include <assert.h>
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static int
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cmpstringp(const void *p1, const void *p2)
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{
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/* The actual arguments to this function are "pointers to
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pointers to char", but strcmp(3) arguments are "pointers
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to char", hence the following cast plus dereference */
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return strcmp(* (char * const *) p1, * (char * const *) p2);
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}
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int
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main(int argc, char *argv[])
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{
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int j;
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assert(argc > 1);
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qsort(&argv[1], argc \- 1, sizeof(char *), cmpstringp);
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for (j = 1; j < argc; j++)
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puts(argv[j]);
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exit(EXIT_SUCCESS);
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}
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.fi
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.SH "SEE ALSO"
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.BR sort (1),
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.BR alphasort (3),
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.BR strcmp (3),
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.BR versionsort (3)
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