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电梯直达

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发表于 2009-01-26 23:40 |只看该作者 |倒序浏览

我们知道关联数组的计算负责度为一常量，这其中的关键是因为是hash表的原因。

我一直理解的是，根据key 通过一个hash算法可以得到vlaue的存储位置。

但是今天可以一个应用中的一个dictionary 模块却不是这样子的，请大家解惑啊！

这是头文件

/*-------------------------------------------------------------------------*/
/**
   @file dictionary.h
   @author  N. Devillard
   @date Sep 2007
   @version $Revision: 1.12 $
   @brief Implements a dictionary for string variables.

   This module implements a simple dictionary object, i.e. a list
   of string/string associations. This object is useful to store e.g.
   informations retrieved from a configuration file (ini files).
*/
/*--------------------------------------------------------------------------*/

/*
    $Id: dictionary.h,v 1.12 2007-11-23 21:37:00 ndevilla Exp $
    $Author: ndevilla $
    $Date: 2007-11-23 21:37:00 $
    $Revision: 1.12 $
*/

#ifndef _DICTIONARY_H_
#define _DICTIONARY_H_

/*---------------------------------------------------------------------------
                                   Includes
 ---------------------------------------------------------------------------*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

/*---------------------------------------------------------------------------
                                   New types
 ---------------------------------------------------------------------------*/

/*-------------------------------------------------------------------------*/
/**
  @brief    Dictionary object

  This object contains a list of string/string associations. Each
  association is identified by a unique string key. Looking up values
  in the dictionary is speeded up by the use of a (hopefully collision-free)
  hash function.
 */
/*-------------------------------------------------------------------------*/
typedef struct _dictionary_ {
    int                n ;        /** Number of entries in dictionary */
    int                size ;    /** Storage size */
    char         **    val ;    /** List of string values */
    char         **  key ;    /** List of string keys */
    unsigned     *    hash ;    /** List of hash values for keys */
} dictionary ;

/*---------------------------------------------------------------------------
                              Function prototypes
 ---------------------------------------------------------------------------*/

/*-------------------------------------------------------------------------*/
/**
  @brief Compute the hash key for a string.
  @param key    Character string to use for key.
  @return 1 unsigned int on at least 32 bits.

  This hash function has been taken from an Article in Dr Dobbs Journal.
  This is normally a collision-free function, distributing keys evenly.
  The key is stored anyway in the struct so that collision can be avoided
  by comparing the key itself in last resort.
 */
/*--------------------------------------------------------------------------*/
unsigned dictionary_hash(char * key);

/*-------------------------------------------------------------------------*/
/**
  @brief Create a new dictionary object.
  @param size Optional initial size of the dictionary.
  @return 1 newly allocated dictionary objet.

  This function allocates a new dictionary object of given size and returns
  it. If you do not know in advance (roughly) the number of entries in the
  dictionary, give size=0.
 */
/*--------------------------------------------------------------------------*/
dictionary * dictionary_new(int size);

/*-------------------------------------------------------------------------*/
/**
  @brief Delete a dictionary object
  @param d dictionary object to deallocate.
  @return void

  Deallocate a dictionary object and all memory associated to it.
 */
/*--------------------------------------------------------------------------*/
void dictionary_del(dictionary * vd);

/*-------------------------------------------------------------------------*/
/**
  @brief Get a value from a dictionary.
  @param d    dictionary object to search.
  @param key    Key to look for in the dictionary.
  @param def    Default value to return if key not found.
  @return 1 pointer to internally allocated character string.

  This function locates a key in a dictionary and returns a pointer to its
  value, or the passed 'def' pointer if no such key can be found in
  dictionary. The returned character pointer points to data internal to the
  dictionary object, you should not try to free it or modify it.
 */
/*--------------------------------------------------------------------------*/
char * dictionary_get(dictionary * d, char * key, char * def);

/*-------------------------------------------------------------------------*/
/**
  @brief Set a value in a dictionary.
  @param d    dictionary object to modify.
  @param key    Key to modify or add.
  @param val    Value to add.
  @return int    0 if Ok, anything else otherwise

  If the given key is found in the dictionary, the associated value is
  replaced by the provided one. If the key cannot be found in the
  dictionary, it is added to it.

  It is Ok to provide a NULL value for val, but NULL values for the dictionary
  or the key are considered as errors: the function will return immediately
  in such a case.

  Notice that if you dictionary_set a variable to NULL, a call to
  dictionary_get will return a NULL value: the variable will be found, and
  its value (NULL) is returned. In other words, setting the variable
  content to NULL is equivalent to deleting the variable from the
  dictionary. It is not possible (in this implementation) to have a key in
  the dictionary without value.

  This function returns non-zero in case of failure.
 */
/*--------------------------------------------------------------------------*/
int dictionary_set(dictionary * vd, char * key, char * val);

/*-------------------------------------------------------------------------*/
/**
  @brief Delete a key in a dictionary
  @param d    dictionary object to modify.
  @param key    Key to remove.
  @return void

  This function deletes a key in a dictionary. Nothing is done if the
  key cannot be found.
 */
/*--------------------------------------------------------------------------*/
void dictionary_unset(dictionary * d, char * key);

/*-------------------------------------------------------------------------*/
/**
  @brief Dump a dictionary to an opened file pointer.
  @param d Dictionary to dump
  @param f Opened file pointer.
  @return void

  Dumps a dictionary onto an opened file pointer. Key pairs are printed out
  as @c [Key]=[Value], one per line. It is Ok to provide stdout or stderr as
  output file pointers.
 */
/*--------------------------------------------------------------------------*/
void dictionary_dump(dictionary * d, FILE * out);

#endif

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shake863

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发表于 2009-01-26 23:45 |只看该作者

这是源码

/*-------------------------------------------------------------------------*/
/**
   @file    dictionary.c
   @author    N. Devillard
   @date    Sep 2007
   @version    $Revision: 1.27 $
   @brief    Implements a dictionary for string variables.

   This module implements a simple dictionary object, i.e. a list
   of string/string associations. This object is useful to store e.g.
   informations retrieved from a configuration file (ini files).
*/
/*--------------------------------------------------------------------------*/

/*
    $Id: dictionary.c,v 1.27 2007-11-23 21:39:18 ndevilla Exp $
    $Revision: 1.27 $
*/
/*---------------------------------------------------------------------------
                                   Includes
 ---------------------------------------------------------------------------*/
#include "dictionnary.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

/** Maximum value size for integers and doubles. */
#define MAXVALSZ    1024

/** Minimal allocated number of entries in a dictionary */
#define DICTMINSZ    128

/** Invalid key token */
#define DICT_INVALID_KEY ((char*)-1)

/*---------------------------------------------------------------------------
                             &nbsp

rivate functions
 ---------------------------------------------------------------------------*/

/* Doubles the allocated size associated to a pointer */
/* 'size' is the current allocated size. */
static void * mem_double(void * ptr, int size)
{
    void * newptr ;
 
    newptr = calloc(2*size, 1);
    if (newptr==NULL) {
        return NULL ;
    }
    memcpy(newptr, ptr, size);
    free(ptr);
    return newptr ;
}

/*-------------------------------------------------------------------------*/
/**
  @brief Duplicate a string
  @param s String to duplicate
  @return Pointer to a newly allocated string, to be freed with free()

  This is a replacement for strdup(). This implementation is provided
  for systems that do not have it.
 */
/*--------------------------------------------------------------------------*/
static char * xstrdup(char * s)
{
    char * t ;
    if (!s)
        return NULL ;
    t = (char*)malloc(strlen(s)+1) ;
    if (t) {
        strcpy(t,s);
    }
    return t ;
}

/*---------------------------------------------------------------------------
                              Function codes
 ---------------------------------------------------------------------------*/
/*-------------------------------------------------------------------------*/
/**
  @brief    Compute the hash key for a string.
  @param    key        Character string to use for key.
  @return    1 unsigned int on at least 32 bits.

  This hash function has been taken from an Article in Dr Dobbs Journal.
  This is normally a collision-free function, distributing keys evenly.
  The key is stored anyway in the struct so that collision can be avoided
  by comparing the key itself in last resort.
 */
/*--------------------------------------------------------------------------*/
unsigned dictionary_hash(char * key)
{
    int            len ;
    unsigned    hash ;
    int            i ;

    len = strlen(key);
    for (hash=0, i=0 ; i<len ; i++) {
        hash += (unsigned)key[i] ;
        hash += (hash<<10);
        hash ^= (hash>>6) ;
    }
    hash += (hash <<3);
    hash ^= (hash >>11);
    hash += (hash <<15);
    return hash ;
}

/*-------------------------------------------------------------------------*/
/**
  @brief    Create a new dictionary object.
  @param    size    Optional initial size of the dictionary.
  @return    1 newly allocated dictionary objet.

  This function allocates a new dictionary object of given size and returns
  it. If you do not know in advance (roughly) the number of entries in the
  dictionary, give size=0.
 */
/*--------------------------------------------------------------------------*/
dictionary * dictionary_new(int size)
{
    dictionary    *    d ;

    /* If no size was specified, allocate space for DICTMINSZ */
    if (size<DICTMINSZ) size=DICTMINSZ ;

    if (!(d = (dictionary *)calloc(1, sizeof(dictionary)))) {
        return NULL;
    }
    d->size = size ;
    d->val = (char **)calloc(size, sizeof(char*));
    d->key = (char **)calloc(size, sizeof(char*));
    d->hash = (unsigned int *)calloc(size, sizeof(unsigned));
    return d ;
}

/*-------------------------------------------------------------------------*/
/**
  @brief    Delete a dictionary object
  @param    d    dictionary object to deallocate.
  @return    void

  Deallocate a dictionary object and all memory associated to it.
 */
/*--------------------------------------------------------------------------*/
void dictionary_del(dictionary * d)
{
    int        i ;

    if (d==NULL) return ;
    for (i=0 ; i<d->size ; i++) {
        if (d->key[i]!=NULL)
            free(d->key[i]);
        if (d->val[i]!=NULL)
            free(d->val[i]);
    }
    free(d->val);
    free(d->key);
    free(d->hash);
    free(d);
    return ;
}

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shake863

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/*-------------------------------------------------------------------------*/
/**
  @brief    Get a value from a dictionary.
  @param    d        dictionary object to search.
  @param    key        Key to look for in the dictionary.
  @param def    Default value to return if key not found.
  @return    1 pointer to internally allocated character string.

  This function locates a key in a dictionary and returns a pointer to its
  value, or the passed 'def' pointer if no such key can be found in
  dictionary. The returned character pointer points to data internal to the
  dictionary object, you should not try to free it or modify it.
 */
/*--------------------------------------------------------------------------*/
char * dictionary_get(dictionary * d, char * key, char * def)
{
    unsigned    hash ;
    int            i ;

    hash = dictionary_hash(key);
    for (i=0 ; i<d->size ; i++) {
        if (d->key[i]==NULL)
            continue ;
        /* Compare hash */
        if (hash==d->hash[i]) {
            /* Compare string, to avoid hash collisions */
            if (!strcmp(key, d->key[i])) {
                return d->val[i] ;
            }
        }
    }
    return def ;
}

/*-------------------------------------------------------------------------*/
/**
  @brief Set a value in a dictionary.
  @param d    dictionary object to modify.
  @param key    Key to modify or add.
  @param val    Value to add.
  @return int    0 if Ok, anything else otherwise

  If the given key is found in the dictionary, the associated value is
  replaced by the provided one. If the key cannot be found in the
  dictionary, it is added to it.

  It is Ok to provide a NULL value for val, but NULL values for the dictionary
  or the key are considered as errors: the function will return immediately
  in such a case.

  Notice that if you dictionary_set a variable to NULL, a call to
  dictionary_get will return a NULL value: the variable will be found, and
  its value (NULL) is returned. In other words, setting the variable
  content to NULL is equivalent to deleting the variable from the
  dictionary. It is not possible (in this implementation) to have a key in
  the dictionary without value.

  This function returns non-zero in case of failure.
 */
/*--------------------------------------------------------------------------*/
int dictionary_set(dictionary * d, char * key, char * val)
{
    int            i ;
    unsigned    hash ;

    if (d==NULL || key==NULL) return -1 ;
    
    /* Compute hash for this key */
    hash = dictionary_hash(key) ;
    /* Find if value is already in dictionary */
    if (d->n>0) {
        for (i=0 ; i<d->size ; i++) {
            if (d->key[i]==NULL)
                continue ;
            if (hash==d->hash[i]) { /* Same hash value */
                if (!strcmp(key, d->key[i])) {     /* Same key */
                    /* Found a value: modify and return */
                    if (d->val[i]!=NULL)
                        free(d->val[i]);
                    d->val[i] = val ? xstrdup(val) : NULL ;
                    /* Value has been modified: return */
                    return 0 ;
                }
            }
        }
    }
    /* Add a new value */
    /* See if dictionary needs to grow */
    if (d->n==d->size) {

        /* Reached maximum size: reallocate dictionary */
        d->val  = (char **)mem_double(d->val,  d->size * sizeof(char*)) ;
        d->key  = (char **)mem_double(d->key,  d->size * sizeof(char*)) ;
        d->hash = (unsigned int *)mem_double(d->hash, d->size * sizeof(unsigned)) ;
        if ((d->val==NULL) || (d->key==NULL) || (d->hash==NULL)) {
            /* Cannot grow dictionary */
            return -1 ;
        }
        /* Double size */
        d->size *= 2 ;
    }

    /* Insert key in the first empty slot */
    for (i=0 ; i<d->size ; i++) {
        if (d->key[i]==NULL) {
            /* Add key here */
            break ;
        }
    }
    /* Copy key */
    d->key[i]  = xstrdup(key);
    d->val[i]  = val ? xstrdup(val) : NULL ;
    d->hash[i] = hash;
    d->n ++ ;
    return 0 ;
}

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/*-------------------------------------------------------------------------*/
/**
  @brief    Delete a key in a dictionary
  @param    d        dictionary object to modify.
  @param    key        Key to remove.
  @return void

  This function deletes a key in a dictionary. Nothing is done if the
  key cannot be found.
 */
/*--------------------------------------------------------------------------*/
void dictionary_unset(dictionary * d, char * key)
{
    unsigned    hash ;
    int            i ;

    if (key == NULL) {
        return;
    }

    hash = dictionary_hash(key);
    for (i=0 ; i<d->size ; i++) {
        if (d->key[i]==NULL)
            continue ;
        /* Compare hash */
        if (hash==d->hash[i]) {
            /* Compare string, to avoid hash collisions */
            if (!strcmp(key, d->key[i])) {
                /* Found key */
                break ;
            }
        }
    }
    if (i>=d->size)
        /* Key not found */
        return ;

    free(d->key[i]);
    d->key[i] = NULL ;
    if (d->val[i]!=NULL) {
        free(d->val[i]);
        d->val[i] = NULL ;
    }
    d->hash[i] = 0 ;
    d->n -- ;
    return ;
}

/*-------------------------------------------------------------------------*/
/**
  @brief    Dump a dictionary to an opened file pointer.
  @param    d    Dictionary to dump
  @param    f    Opened file pointer.
  @return    void

  Dumps a dictionary onto an opened file pointer. Key pairs are printed out
  as @c [Key]=[Value], one per line. It is Ok to provide stdout or stderr as
  output file pointers.
 */
/*--------------------------------------------------------------------------*/
void dictionary_dump(dictionary * d, FILE * out)
{
    int        i ;

    if (d==NULL || out==NULL) return ;
    if (d->n<1) {
        fprintf(out, "empty dictionary\n");
        return ;
    }
    for (i=0 ; i<d->size ; i++) {
        if (d->key[i]) {
            fprintf(out, "%20s\t[%s]\n",
                    d->key[i],
                    d->val[i] ? d->val[i] : "UNDEF");
        }
    }
    return ;
}

/* Test code */
#ifdef TESTDIC
#define NVALS 20000
int main(int argc, char *argv[])
{
    dictionary    *    d ;
    char    *    val ;
    int            i ;
    char        cval[90] ;

    /* Allocate dictionary */
    printf("allocating...\n");
    d = dictionary_new(0);
    
    /* Set values in dictionary */
    printf("setting %d values...\n", NVALS);
    for (i=0 ; i<NVALS ; i++) {
        sprintf(cval, "%04d", i);
        dictionary_set(d, cval, "salut");
    }
    printf("getting %d values...\n", NVALS);
    for (i=0 ; i<NVALS ; i++) {
        sprintf(cval, "%04d", i);
        val = dictionary_get(d, cval, DICT_INVALID_KEY);
        if (val==DICT_INVALID_KEY) {
            printf("cannot get value for key [%s]\n", cval);
        }
    }
    printf("unsetting %d values...\n", NVALS);
    for (i=0 ; i<NVALS ; i++) {
        sprintf(cval, "%04d", i);
        dictionary_unset(d, cval);
    }
    if (d->n != 0) {
        printf("error deleting values\n");
    }
    printf("deallocating...\n");
    dictionary_del(d);
    return 0 ;
}
#endif
/* vim: set ts=4 et sw=4 tw=75 */

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