January 27, 1994 RADIXSORT 3

### NAME

radixsort, sradixsort - radix sort

### LIBRARY

Standard C Library (libc, -lc)

### SYNOPSIS

```int` radixsort(```const u_char **base``, int nmemb``, u_char *table``, u_int endbyte`)
```int` sradixsort(```const u_char **base``, int nmemb``, u_char *table``, u_int 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 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 0 is returned. Otherwise, -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

sort(1), qsort(3)

### HISTORY

The radixsort(``) function first appeared in 4.4BSD.