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authorPaul Eggert <eggert@cs.ucla.edu>2024-02-01 11:52:46 -0800
committerPaul Eggert <eggert@cs.ucla.edu>2024-02-01 17:54:21 -0800
commite7b90e6e605cf236d4bd79e4930cd6a46f9932c7 (patch)
tree1fb3fa98e0a6e91b266d2b3971253669bd45d554 /manual
parent275607a07fb2a60757ba47ec3f1f4e645ad19bb1 (diff)
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stdlib: fix qsort example in manual
* manual/search.texi (Comparison Functions, Array Sort Function): Sort an array of long ints, not doubles, to avoid hassles with NaNs. Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Diffstat (limited to 'manual')
-rw-r--r--manual/search.texi21
1 files changed, 12 insertions, 9 deletions
diff --git a/manual/search.texi b/manual/search.texi
index ffaadc4..db577a5 100644
--- a/manual/search.texi
+++ b/manual/search.texi
@@ -35,19 +35,22 @@ second, zero if they are ``equal'', and positive if the first argument
is ``greater''.
Here is an example of a comparison function which works with an array of
-numbers of type @code{double}:
+numbers of type @code{long int}:
@smallexample
int
-compare_doubles (const void *a, const void *b)
+compare_long_ints (const void *a, const void *b)
@{
- const double *da = (const double *) a;
- const double *db = (const double *) b;
+ const long int *la = a;
+ const long int *lb = b;
- return (*da > *db) - (*da < *db);
+ return (*la > *lb) - (*la < *lb);
@}
@end smallexample
+(The code would have to be more complicated for an array of @code{double},
+to handle NaNs correctly.)
+
The header file @file{stdlib.h} defines a name for the data type of
comparison functions. This type is a GNU extension.
@@ -183,16 +186,16 @@ 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
+Here is a simple example of sorting an array of @code{long int} in numerical
order, using the comparison function defined above (@pxref{Comparison
Functions}):
@smallexample
@{
- double *array;
- int size;
+ long int *array;
+ size_t nmemb;
@dots{}
- qsort (array, size, sizeof (double), compare_doubles);
+ qsort (array, nmemb, sizeof *array, compare_long_ints);
@}
@end smallexample