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diff --git a/man/man3/qsort.3 b/man/man3/qsort.3 new file mode 100644 index 000000000..16e8b1b65 --- /dev/null +++ b/man/man3/qsort.3 @@ -0,0 +1,157 @@ +'\" t +.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" 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 (date) "Linux man-pages (unreleased)" +.SH NAME +qsort, qsort_r \- sort an array +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <stdlib.h> +.P +.BI "void qsort(void " base [. size " * ." nmemb "], size_t " nmemb ", \ +size_t " size , +.BI " int (*" compar ")(const void [." size "], \ +const void [." size ])); +.BI "void qsort_r(void " base [. size " * ." nmemb "], size_t " nmemb ", \ +size_t " size , +.BI " int (*" compar ")(const void [." size "], \ +const void [." size "], void *)," +.BI " void *" arg ");" +.fi +.P +.RS -4 +Feature Test Macro Requirements for glibc (see +.BR feature_test_macros (7)): +.RE +.P +.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. +.P +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. +.P +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. +.P +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 ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR qsort (), +.BR qsort_r () +T} Thread safety MT-Safe +.TE +.SH STANDARDS +.TP +.BR qsort () +C11, POSIX.1-2008. +.SH HISTORY +.TP +.BR qsort () +POSIX.1-2001, C89, SVr4, 4.3BSD. +.TP +.BR qsort_r () +glibc 2.8. +.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). +.P +Another example is the following program, +which sorts the strings given in its command-line arguments: +.P +.\" SRC BEGIN (qsort.c) +.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 (size_t j = 1; j < argc; j++) + puts(argv[j]); + exit(EXIT_SUCCESS); +} +.EE +.\" SRC END +.SH SEE ALSO +.BR sort (1), +.BR alphasort (3), +.BR strcmp (3), +.BR versionsort (3) |