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 functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here
       and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.

       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 function, 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
       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 non-zero:

	   ((char *)p - (char *)base) % width == 0
	   (char *)p >= (char *)base
	   (char *)p < (char *)base + nel * width

FUTURE DIRECTIONS

       None.

SEE ALSO

       alphasort()

       The Base Definitions volume of POSIX.1-2008, <stdlib.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy  --	Portable  Operating  System  Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013								 QSORT(3P)