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[PATCH v2] manual: Correct guarantee about pointers compared by qsort()
- From: Anders Kaseorg <andersk at mit dot edu>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: Andreas Schwab <schwab at suse dot de>, Paul Eggert <eggert at cs dot ucla dot edu>, OndÅej BÃlka <neleai at seznam dot cz>, libc-alpha at sourceware dot org
- Date: Thu, 11 Dec 2014 05:33:22 -0500 (EST)
- Subject: [PATCH v2] manual: Correct guarantee about pointers compared by qsort()
- Authentication-results: sourceware.org; auth=none
C99, C11, POSIX, and the glibc implementation do guarantee that the
pointers passed to the qsort comparison function lie within the array.
(Also, fix a small typographical mistake: @var{qsort} should be
@code{qsort}.)
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
---
manual/search.texi | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/manual/search.texi b/manual/search.texi
index 8aff574..662527f 100644
--- a/manual/search.texi
+++ b/manual/search.texi
@@ -164,8 +164,8 @@ To sort an array using an arbitrary comparison function, use the
@comment ISO
@deftypefun void qsort (void *@var{array}, size_t @var{count}, size_t @var{size}, comparison_fn_t @var{compare})
@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@acucorrupt{}}}
-The @var{qsort} function sorts the array @var{array}. The array contains
-@var{count} elements, each of which is of size @var{size}.
+The @code{qsort} function sorts the array @var{array}. The array
+contains @var{count} elements, each of which is of size @var{size}.
The @var{compare} function is used to perform the comparison on the
array elements. This function is called with two pointer arguments and
@@ -180,10 +180,12 @@ This can make a difference when the comparison considers only part of
the elements. Two elements with the same sort key may differ in other
respects.
-The addresses passed to the comparison function need not correspond with
-the original location of the objects, and need not even lie within the
-original array. The only way to perform a stable sort with @var{qsort}
-is to first augment the objects with a monotonic counter of some kind.
+Although the object addresses passed to the comparison function lie
+within the array, they need not correspond with the original locations
+of those objects because the sorting algorithm may swap around objects
+in the array before making some comparisons. The only way to perform
+a stable sort with @code{qsort} is to first augment the objects with a
+monotonic counter of some kind.
Here is a simple example of sorting an array of doubles in numerical
order, using the comparison function defined above (@pxref{Comparison
--
2.2.0