## table of contents

QSORT(3) | Library Functions Manual | QSORT(3) |

# NAME¶

`heapsort`

, `mergesort`

—
# LIBRARY¶

library “libbsd”# SYNOPSIS¶

`#include <bsd/stdlib.h>`

`int`

`heapsort`

(`void *base`,
`size_t nmemb`, `size_t size`,
`int (*compar)(const void *, const void *)`);

`int`

`mergesort`

(`void *base`,
`size_t nmemb`, `size_t size`,
`int (*compar)(const void *, const void *)`);

# DESCRIPTION¶

The`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.
The `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
`size`. The `mergesort`

() function
behaves similarly, but *requires* that
`size` be greater than “sizeof(void *) /
2”.

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 `heapsort`

() is
*not* stable, that is, if two members compare as equal,
their order in the sorted array is undefined. The
`mergesort`

() algorithm is stable.

The `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;
while `qsort`

() does not allocate memory, it is
implemented using recursion.

The function `mergesort`

() requires
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.

Normally, `qsort`

() is faster than
`mergesort`

() is faster than
`heapsort`

(). Memory availability and pre-existing
order in the data can make this untrue.

# RETURN VALUES¶

The`heapsort`

() and `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.

# ERRORS¶

The`heapsort`

() and `mergesort`

()
functions succeed unless:
# SEE ALSO¶

sort(1), radixsort(3)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.

September 30, 2003 | Linux 4.19.0-6-amd64 |