QSORT(P) POSIX Programmer's Manual QSORT(P)NAMEqsort - sort a table of data
SYNOPSIS
#include <stdlib.h>
void qsort(void *base, size_t nel, size_t width,
int (*compar)(const void *, const void *));
DESCRIPTION
The qsort() function shall sort an array of nel objects, the initial
element of which is pointed to by base. The size of each object, in
bytes, is specified by the width argument. If the nel argument has the
value zero, the comparison function pointed to by compar shall not be
called and no rearrangement shall take place.
The application shall ensure that the comparison function pointed to by
compar does not alter the contents of the array. The implementation
may reorder elements of the array between calls to the comparison func‐
tion, but shall not alter the contents of any individual element.
When the same objects (consisting of width bytes, irrespective of their
current positions in the array) are passed more than once to the com‐
parison function, the results shall be consistent with one another.
That is, they shall define a total ordering on the array.
The contents of the array shall be sorted in ascending order according
to a comparison function. The compar argument is a pointer to the com‐
parison 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.
RETURN VALUE
The qsort() function shall not return a value.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The comparison function need not compare every byte, so arbitrary data
may be contained in the elements in addition to the values being com‐
pared.
RATIONALE
The requirement that each argument (hereafter referred to as p) 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:
((char *)p - (char *)base) % width == 0
(char *)p >= (char *)base
(char *)p < (char *)base + nel * width
FUTURE DIRECTIONS
None.
SEE ALSO
The Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>
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 .
IEEE/The Open Group 2003 QSORT(P)
