QSORT(3) Library Functions Manual QSORT(3)NAME
qsort - quicker sort
SYNOPSIS
qsort(base, nel, width, compar)
char *base;
int (*compar)( );
DESCRIPTION
Qsort is an implementation of the quicker-sort algorithm. The first argument is a pointer to the base of the data; the second is the num-
ber of elements; the third is the width of an element in bytes; the last is the name of the comparison routine to be called with two argu-
ments which are pointers to the elements being compared. The routine must return an integer less than, equal to, or greater than 0 accord-
ing as the first argument is to be considered less than, equal to, or greater than the second.
SEE ALSO sort(1)QSORT(3)
Check Out this Related Man Page
QSORT(3P) POSIX Programmer's Manual QSORT(3P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAME
qsort - 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 implementa-
tion may reorder elements of the array between calls to the comparison function, but shall not alter the contents of any individual ele-
ment.
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.
The contents of the array shall be sorted in ascending order according to a comparison function. The compar 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.
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
compared.
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 Technol-
ogy -- 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(3P)