From 8ff74efcc11a77e221808293ed390faf6dea86fe Mon Sep 17 00:00:00 2001 From: Paul Eggert Date: Thu, 1 Feb 2024 11:52:46 -0800 Subject: [PATCH] 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. --- manual/search.texi | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff --git a/manual/search.texi b/manual/search.texi index ffaadc46f5..db577a5332 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 -- 2.40.1