#include <stdlib.h>(See libbsd(7) for include usage.)
heapsort(void *base, size_t nmemb, size_t size, int (*compar)(const void *, const void *));
size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
heapsort() function is a modified selection sort. The
mergesort() function is a modified merge sort with exponential search intended for sorting data with pre-existing order.
heapsort() function sorts an array of
nmemb objects, the initial member of which is pointed
to by base. The size of each object is specified by
behaves similarly, but requires that
size be greater than “sizeof(void *) /
The contents of the array base are sorted in ascending order according to a comparison function pointed to by 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.
The algorithm implemented by
not stable, that is, if two members compare as equal,
their order in the sorted array is undefined. The
mergesort() algorithm is stable.
heapsort() function is an
implementation of J.W.J. William's
“heapsort” algorithm, a variant of selection sorting; in
particular, see D.E. Knuth'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;
qsort() does not allocate memory, it is
implemented using recursion.
additional memory of size nmemb *
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.
qsort() is faster than
mergesort() is faster than
heapsort(). Memory availability and pre-existing
order in the data can make this untrue.
mergesort() functions return the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
mergesort() functions succeed unless:
SEE ALSO¶sort(1), radixsort(3bsd)
Williams, J.W.J, Heapsort, Communications of the ACM, 7:1, pp. 347-348, 1964.
Knuth, D.E., Sorting and Searching, The Art of Computer Programming, Vol. 3, pp. 114-123, 145-149, 1968.
McIlroy, P.M., Optimistic Sorting and Information Theoretic Complexity, Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, January 1992.
Bentley, J.L. and McIlroy, M.D., Engineering a Sort Function, Software--Practice and Experience, Vol. 23(11), pp. 1249-1265, November 1993.
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