## NAME

`radixsort`

,
`sradixsort`

—
radix sort

## SYNOPSIS

```
#include
<limits.h>
```

`#include <stdlib.h>`

`int`

`radixsort`

(`const
u_char **base`, `int
nmemb`, `const u_char
*table`, `u_int
endbyte`);

`int`

`sradixsort`

(`const
u_char **base`, `int
nmemb`, `const u_char
*table`, `u_int
endbyte`);

## DESCRIPTION

The
`radixsort`

()
and `sradixsort`

() functions are implementations of
radix sort.

These functions sort an array of `nmemb`
pointers to byte strings. The initial member is referenced by
`base`. The byte strings may contain any values; the end
of each string is denoted by the user-specified value
`endbyte`.

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 D.E. Knuth's Algorithm R and section 5.2.5, exercise 10. They take linear time relative to the number of bytes in the strings.

## RETURN VALUES

Upon successful completion, the value 0 is returned;
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.