Using JudySL

The JudySL functions provide a way to use string values as indexes into a Judy array. In JudySL arrays, elements are sorted lexicographically (case-sensitive) by indexes:

void * JudySLArray ["Toto, I don't think we're in Kansas any more"];

Since an initial (empty) JudySL array is represented by a null pointer, you can make JudySL arrays multi-dimensional:

void * JudySLArray [char *][char *]...;

The table below shows the JudySL functions. For more information, see the JudySL(3X) man page.

JudySL sorting example

You can find the code for this example and others on the Judy web site: http://devresource.hp.com/judy/

// JudySort.c// Judy demonstration code:  Judy equivalent of sort -u.  While Judy is not// primarily intended as a sorting algorithm, in many cases it's faster to// store values in a Judy array and read them back in sorted order than to sort// them using standard algorithms.//// Usage:  <program> <file-to-sort>//// Code and comments are included if you want to modify the program to output// duplicates as an exercise.//// Note:  If an input line is longer than BUFSIZ, it's broken into two or more// lines.#include <sys/types.h>#include <stdio.h>#include <unistd.h>#include <string.h>#include <errno.h>#include "Judy.h"main (int argc, char ** argv){    Pvoid_t  PJArray = (Pvoid_t) NULL;  // Judy array.    PPvoid_t PPValue;                   // Judy array element.    char     Index [BUFSIZ];            // string to sort.    char *   Pc;                        // place in Index.    FILE *   fpin;                      // to read file.    JError_t JError;                    // Judy error structure// CHECK FOR REQUIRED INPUT FILE PARAMETER:    if (argc != 2)    {        (void) fprintf (stderr, "Usage: %s <file-to-sort>\n", argv[0]);        (void) fputs   ("Uses each line as a JudySL index.\n", stderr);        exit (1);    }// OPEN INPUT FILE:    if ((fpin = fopen (argv[1], "r")) == (FILE *) NULL)    {        (void) fprintf (stderr, "%s: Cannot open file \"%s\": %s "                        "(errno = %d)\n", argv[0], argv[1], strerror (errno),                        errno);        exit (1);    }// INPUT/STORE LOOP://// Read each input line (up to Index size) and save the line as an index into a// JudySL array.  If the line doesn't overflow Index, it ends with a newline,// which must be removed for sorting comparable to sort(1).    while (fgets (Index, sizeof (Index), fpin) != (char *) NULL)    {        if ((Pc = strchr (Index, '\n')) != (char *) NULL)            *Pc = '\0';                         // trim at newline.        if ((PPValue = JudySLIns (& PJArray, Index, &JError))             == PPJERR)        {            fprintf(stderr, "File: '%s', line: %d: Judy error: %d\n",                    __FILE__, __LINE__, JU_ERRNO(&JError));            exit (1);        }// To modify the program to output duplication counts, like uniq -d, or to emit// multiple copies of repeated strings:#ifdef notdef        ++(*((ulong_t *) PPValue));#endif    }// PRINT SORTED STRINGS://// To output all strings and not just the unique ones, output Index multiple// times = *((ulong_t *) PPValue).    Index[0] = '\0';                            // start with smallest string.    for (PPValue  = JudySLFirst (PJArray, Index, &JError);         PPValue != (PPvoid_t) NULL;         PPValue  = JudySLNext  (PJArray, Index, &JError))    {        (void) puts (Index);                    // see comment above.    }    exit (0);    /*NOTREACHED*/} // main()

In summary