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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 

.TH "QSORT" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"

.\" qsort 

.SH NAME

qsort \- sort a table of data

.SH SYNOPSIS

.LP

\fB#include <stdlib.h>

.br

.sp

void qsort(void *\fP\fIbase\fP\fB, size_t\fP \fInel\fP\fB, size_t\fP

\fIwidth\fP\fB,

.br

\ \ \ \ \ \  int (*\fP\fIcompar\fP\fB)(const void *, const void *));

.br

\fP

.SH DESCRIPTION

.LP

The \fIqsort\fP() function shall sort an array of \fInel\fP objects,

the initial element of which is pointed to by

\fIbase\fP. The size of each object, in bytes, is specified by the

\fIwidth\fP argument. If the \fInel\fP argument has the value

zero, the comparison function pointed to by \fIcompar\fP shall not

be called and no rearrangement shall take place.

.LP

The application shall ensure that the comparison function pointed

to by \fIcompar\fP does not alter the contents of the array.

The implementation may reorder elements of the array between calls

to the comparison function, but shall not alter the contents of

any individual element.

.LP

When the same objects (consisting of width bytes, irrespective of

their current positions in the array) are passed more than

once to the comparison function, the results shall be consistent with

one another. That is, they shall define a total ordering on

the array.

.LP

The contents of the array shall be sorted in ascending order according

to a comparison function. The \fIcompar\fP argument is a

pointer to the comparison function, which is called with two arguments

that point to the elements being compared. The application

shall ensure that the function returns an integer less than, equal

to, or greater than 0, if the first argument is considered

respectively less than, equal to, or greater than the second. If two

members compare as equal, their order in the sorted array is

unspecified.

.SH RETURN VALUE

.LP

The \fIqsort\fP() function shall not return a value.

.SH ERRORS

.LP

No errors are defined.

.LP

\fIThe following sections are informative.\fP

.SH EXAMPLES

.LP

None.

.SH APPLICATION USAGE

.LP

The comparison function need not compare every byte, so arbitrary

data may be contained in the elements in addition to the

values being compared.

.SH RATIONALE

.LP

The requirement that each argument (hereafter referred to as \fIp)\fP

to the comparison function is a pointer to elements of

the array implies that for every call, for each argument separately,

all of the following expressions are nonzero:

.sp

.RS

.nf

\fB((char *)p - (char *)base) % width == 0

(char *)p >= (char *)base

(char *)p < (char *)base + nel * width

\fP

.fi

.RE

.SH FUTURE DIRECTIONS

.LP

None.

.SH SEE ALSO

.LP

The Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<stdlib.h>\fP

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group. In the

event of any discrepancy between this version and the original IEEE and

The Open Group Standard, the original IEEE and The Open Group Standard

is the referee document. The original Standard can be obtained online at

http://www.opengroup.org/unix/online.html .