QSORT(3P)                 POSIX Programmer's Manual                QSORT(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       qsort — sort a table of data

SYNOPSIS         top

       #include <stdlib.h>

       void qsort(void *base, size_t nel, size_t width,
           int (*compar)(const void *, const void *));

DESCRIPTION         top

       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         top

       The qsort() function shall not return a value.

ERRORS         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top



       The comparison function need not compare every byte, so arbitrary
       data may be contained in the elements in addition to the values being

RATIONALE         top

       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



SEE ALSO         top


       The Base Definitions volume of POSIX.1‐2008, stdlib.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- 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 Standard is the referee document. The original
       Standard can be obtained online at .

       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 .

IEEE/The Open Group                 2013                           QSORT(3P)