qsort(3p) — Linux manual 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
       corresponding 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.1‐2017 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(3p)

       The Base Definitions volume of POSIX.1‐2017, stdlib.h(0p)

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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               2017                         QSORT(3P)

Pages that refer to this page: stdlib.h(0p), alphasort(3p), bsearch(3p)

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