diff options
| author | Anders Kaseorg <andersk@MIT.EDU> | 2014-07-02 21:17:50 -0400 |
|---|---|---|
| committer | Ondřej Bílka <neleai@seznam.cz> | 2014-12-10 16:24:44 +0100 |
| commit | f5f46d51f75083e27fae79cee6cd7707888faba3 (patch) | |
| tree | 5a31623e034dfa63c27d713ec8b189e380cde710 /manual | |
| parent | b987c89126b84b06c22b13c2827499bc9d9e5e88 (diff) | |
manual: Remove incorrect claim that qsort() can be stabilized
Under certain conditions on the size of the array and its items,
qsort() may fall back to an in-place quicksort if it cannot allocate
memory for a temporary array with malloc(). This algorithm is not a
stable sort even if the comparison function is written in the
described manner.
Fixes #10672.
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Diffstat (limited to 'manual')
| -rw-r--r-- | manual/search.texi | 9 |
1 files changed, 4 insertions, 5 deletions
diff --git a/manual/search.texi b/manual/search.texi index 509a54313a..8aff57433a 100644 --- a/manual/search.texi +++ b/manual/search.texi @@ -180,11 +180,10 @@ 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. -If you want the effect of a stable sort, you can get this result by -writing the comparison function so that, lacking other reason -distinguish between two elements, it compares them by their addresses. -Note that doing this may make the sorting algorithm less efficient, so -do it only if necessary. +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. Here is a simple example of sorting an array of doubles in numerical order, using the comparison function defined above (@pxref{Comparison |