qsort , qsort_r , heapsort , mergesort - sort functions
and heapsort ();
functions sort an array of Fa nmemb objects, the initial member of which is pointed to by Fa base . The size of each object is specified by Fa size . The mergesort ();
function behaves similarly, but requires that Fa size be greater than ``sizeof(void *) / 2''
The contents of the array Fa base are sorted in ascending order according to a comparison function pointed to by Fa compar , which requires two arguments pointing to the objects being compared.
The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.
function behaves identically to qsort (,);
except that it takes an additional argument, Fa thunk , which is passed unchanged as the first argument to function pointed to Fa compar . This allows the comparison function to access additional data without using global variables, and thus qsort_r ();
is suitable for use in functions which must be reentrant.
The algorithms implemented by
and heapsort ();
are not stable, that is, if two members compare as equal, their order in the sorted array is undefined. The mergesort ();
algorithm is stable.
and qsort_r ();
functions are an implementation of C.A.R. Hoare's ``quicksort'' algorithm, a variant of partition-exchange sorting; in particular, see An D.E. Knuth Ns 's "Algorithm Q" . Quicksort takes O N lg N average time. This implementation uses median selection to avoid its O N**2 worst-case behavior.
function is an implementation of An J.W.J. William Ns 's ``heapsort'' algorithm, a variant of selection sorting; in particular, see An D.E. Knuth Ns 's "Algorithm H" . Heapsort takes O N lg N worst-case time. Its only advantage over qsort ();
is that it uses almost no additional memory; while qsort ();
does not allocate memory, it is implemented using recursion.
requires additional memory of size Fa nmemb * Fa size bytes; it should be used only when space is not at a premium. The mergesort ();
function is optimized for data with pre-existing order; its worst case time is O N lg N; its best case is O N.
is faster than mergesort ();
is faster than heapsort (.);
Memory availability and pre-existing order in the data can make this untrue.
Rv -std heapsort mergesort
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Created 1996-2023 by Maxim Chirkov
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