# radixsort man page

radixsort, sradixsort — radix sort

## Library

library “libbsd”

## Synopsis

#include <limits.h>

#include <bsd/stdlib.h>

*int*

radixsort(`const unsigned char **base`, `int nmemb`, `const unsigned char *table`, `unsigned endbyte`);

*int*

sradixsort(`const unsigned char **base`, `int nmemb`, `const unsigned char *table`, `unsigned endbyte`);

## Description

The radixsort() and sradixsort() functions are implementations of radix sort.

These functions sort an `nmemb` element array of pointers to byte strings, with the initial member of which is referenced by `base`. The byte strings may contain any values. End of strings is denoted by character which has same weight as user specified value `endbyte`. `endbyte` has to be between 0 and 255.

Applications may specify a sort order by providing the `table` argument. If non-NULL, `table` must reference an array of UCHAR_MAX + 1 bytes which contains the sort weight of each possible byte value. The end-of-string byte must have a sort weight of 0 or 255 (for sorting in reverse order). More than one byte may have the same sort weight. The `table` argument is useful for applications which wish to sort different characters equally, for example, providing a table with the same weights for A-Z as for a-z will result in a case-insensitive sort. If `table` is NULL, the contents of the array are sorted in ascending order according to the ASCII order of the byte strings they reference and `endbyte` has a sorting weight of 0.

The sradixsort() function is stable, that is, if two elements compare as equal, their order in the sorted array is unchanged. The sradixsort() function uses additional memory sufficient to hold `nmemb` pointers.

The radixsort() function is not stable, but uses no additional memory.

These functions are variants of most-significant-byte radix sorting; in particular, see Algorithm R and section 5.2.5, exercise 10. They take linear time relative to the number of bytes in the strings.

's## Return Values

The radixsort() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable **errno** is set to indicate the error.

## Errors

- [EINVAL]
- The value of the
`endbyte`element of`table`is not 0 or 255.

Additionally, the sradixsort() function may fail and set **errno** for any of the errors specified for the library routine malloc(3).

## See Also

Knuth, D.E., Sorting and Searching, *The Art of Computer Programming*, Vol. 3, pp. 170-178, 1968.

Paige, R., Three Partition Refinement Algorithms, *SIAM J. Comput.*, No. 6, Vol. 16, 1987.

McIlroy, P., Computing Systems, *Engineering Radix Sort*, Vol. 6:1, pp. 5-27, 1993.

## History

The radixsort() function first appeared in 4.4BSD.

## Referenced By

sradixsort(3) is an alias of radixsort(3).