| .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
| .\" |
| .\" %%%LICENSE_START(VERBATIM) |
| .\" Permission is granted to make and distribute verbatim copies of this |
| .\" manual provided the copyright notice and this permission notice are |
| .\" preserved on all copies. |
| .\" |
| .\" Permission is granted to copy and distribute modified versions of this |
| .\" manual under the conditions for verbatim copying, provided that the |
| .\" entire resulting derived work is distributed under the terms of a |
| .\" permission notice identical to this one. |
| .\" |
| .\" Since the Linux kernel and libraries are constantly changing, this |
| .\" manual page may be incorrect or out-of-date. The author(s) assume no |
| .\" responsibility for errors or omissions, or for damages resulting from |
| .\" the use of the information contained herein. The author(s) may not |
| .\" have taken the same level of care in the production of this manual, |
| .\" which is licensed free of charge, as they might when working |
| .\" professionally. |
| .\" |
| .\" Formatted or processed versions of this manual, if unaccompanied by |
| .\" the source, must acknowledge the copyright and authors of this work. |
| .\" %%%LICENSE_END |
| .\" |
| .\" 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 (faith@cs.unc.edu) |
| .\" 2006-01-15, mtk, Added example program. |
| .\" Modified 2012-03-08, Mark R. Bannister <cambridge@users.sourceforge.net> |
| .\" and Ben Bacarisse <software@bsb.me.uk> |
| .\" Document qsort_r() |
| .\" |
| .TH QSORT 3 2021-03-22 "" "Linux Programmer's Manual" |
| .SH NAME |
| qsort, qsort_r \- sort an array |
| .SH SYNOPSIS |
| .nf |
| .B #include <stdlib.h> |
| .PP |
| .BI "void qsort(void *" base ", size_t " nmemb ", size_t " size , |
| .BI " int (*" compar ")(const void *, const void *));" |
| .BI "void qsort_r(void *" base ", size_t " nmemb ", size_t " size , |
| .BI " int (*" compar ")(const void *, const void *, void *)," |
| .BI " void *" arg ");" |
| .fi |
| .PP |
| .RS -4 |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .RE |
| .PP |
| .BR qsort_r (): |
| .nf |
| _GNU_SOURCE |
| .fi |
| .SH DESCRIPTION |
| The |
| .BR qsort () |
| function sorts an array with \fInmemb\fP elements of |
| size \fIsize\fP. |
| The \fIbase\fP argument points to the start of the |
| array. |
| .PP |
| The contents of the array are sorted in ascending order according to a |
| comparison function pointed to by \fIcompar\fP, which is called with two |
| arguments that point to the objects being compared. |
| .PP |
| 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. |
| .PP |
| The |
| .BR qsort_r () |
| function is identical to |
| .BR qsort () |
| except that the comparison function |
| .I compar |
| takes a third argument. |
| A pointer is passed to the comparison function via |
| .IR arg . |
| In this way, the comparison function does not need to use global variables to |
| pass through arbitrary arguments, and is therefore reentrant and safe to |
| use in threads. |
| .SH RETURN VALUE |
| The |
| .BR qsort () |
| and |
| .BR qsort_r () |
| functions return no value. |
| .SH VERSIONS |
| .BR qsort_r () |
| was added to glibc in version 2.8. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR qsort (), |
| .BR qsort_r () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| .BR qsort (): |
| POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD. |
| .SH NOTES |
| To compare C strings, the comparison function can call |
| .BR strcmp (3), |
| as shown in the example below. |
| .SH EXAMPLES |
| For one example of use, see the example under |
| .BR bsearch (3). |
| .PP |
| Another example is the following program, |
| which sorts the strings given in its command-line arguments: |
| .PP |
| .EX |
| #include <stdio.h> |
| #include <stdlib.h> |
| #include <string.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(*(const char **) p1, *(const char **) p2); |
| } |
| |
| int |
| main(int argc, char *argv[]) |
| { |
| if (argc < 2) { |
| fprintf(stderr, "Usage: %s <string>...\en", argv[0]); |
| exit(EXIT_FAILURE); |
| } |
| |
| qsort(&argv[1], argc \- 1, sizeof(char *), cmpstringp); |
| |
| for (int j = 1; j < argc; j++) |
| puts(argv[j]); |
| exit(EXIT_SUCCESS); |
| } |
| .EE |
| .SH SEE ALSO |
| .BR sort (1), |
| .BR alphasort (3), |
| .BR strcmp (3), |
| .BR versionsort (3) |