QSORT(3) Library Functions Manual QSORT(3)

# NAME¶

`heapsort`, `mergesort`sort functions

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 () 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 () 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 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 () is stable, that is, if two members compare as equal, their order in the sorted array is undefined. The `mergesort`() algorithm is stable.

The () 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. takes O N lg N worst-case time. Its advantage over `qsort`() is that it uses almost no additional memory; while `qsort`() does not allocate memory, it is implemented using recursion.

The function () 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, () 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:

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The size argument is zero, or, the size argument to `mergesort`() is less than “sizeof(void *) / 2”.
[]
The `heapsort`() or `mergesort`() functions were unable to allocate memory.