/usr/share/doc/libetpan-doc/API/x161.htm

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><H1
CLASS="SECT1"
><A
NAME="AEN161"
>Hash table</A
></H1
><PRE
CLASS="PROGRAMLISTING"
>#include &lt;libetpan/libetpan.h&gt;

typedef struct chash chash;

typedef struct chashcell chashiter;

typedef struct {
  char * data;
  int len;
} chashdatum;
      </PRE
><P
>      
        <B
CLASS="COMMAND"
>chash</B
> is a hash table.
        <B
CLASS="COMMAND"
>chashiter</B
> is a pointer to an element of the
        hash table.
        <B
CLASS="COMMAND"
>chashdatum</B
> is an element to be placed in
        the hash table as a key or a value. It consists in 
        data and a corresponding length.
      </P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="CHASH-NEW"
>chash_new and chash_free</A
></H2
><PRE
CLASS="PROGRAMLISTING"
>#define CHASH_COPYNONE    0
#define CHASH_COPYKEY     1
#define CHASH_COPYVALUE   2
#define CHASH_COPYALL     (CHASH_COPYKEY | CHASH_COPYVALUE)

chash * chash_new(int size, int flags);

void chash_free(chash * hash);
        </PRE
><P
>          <B
CLASS="COMMAND"
>chash_new()</B
> returns a new empty hash table
          or <B
CLASS="COMMAND"
>NULL</B
> if this
          failed. <B
CLASS="COMMAND"
>size</B
> is the initial size of the
          table used for implementation. <B
CLASS="COMMAND"
>flags</B
> can
          be a combinaison of <B
CLASS="COMMAND"
>CHASH_COPYKEY</B
> and
          <B
CLASS="COMMAND"
>CHASH_COPYVALUE</B
>.
          <B
CLASS="COMMAND"
>CHASH_COPYKEY</B
> enables copy of key, so
          that the initial value used for <B
CLASS="COMMAND"
>chash_set()</B
>
        </P
><P
>          <B
CLASS="COMMAND"
>chash_free()</B
> releases memory used by the
          hash table.
        </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="CHASH-GET"
>chash_set and chash_get</A
></H2
><PRE
CLASS="PROGRAMLISTING"
>int chash_set(chash * hash,
    chashdatum * key, chashdatum * value, chashdatum * oldvalue);

int chash_get(chash * hash,
    chashdatum * key, chashdatum * result);
        </PRE
><P
>          <B
CLASS="COMMAND"
>chash_set()</B
> adds a new element into the
          hash table. If a previous element had the same key, it is
          returns into oldvalue if <B
CLASS="COMMAND"
>oldvalue</B
> is
          different of NULL.
          Medium complexity is O(1).
        </P
><P
>          returns -1 if it fails, 0 on success.
        </P
><P
>          <B
CLASS="COMMAND"
>chash_get()</B
>returns the corresponding value
          of the given key. If there is no corresponding value, -1 is
          returned. 0 on success.
          Medium complexity is O(1).
        </P
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN191"
></A
><P
><B
>Example 2-9. chash insert and lookup</B
></P
><PRE
CLASS="PROGRAMLISTING"
>int main(void)
{
  chash * hash;
  int r;
  chashdatum key;
  chashdatum value;
  char * str1 = "my-data";
  char * str2 = "my-data";

  hash = chash_new(CHASH_DEFAULTSIZE, CHASH_COPYNONE);

  key.data = "foo";
  key.len = strlen("foo");  
  value.data = str1;
  value.data = strlen(str1) + 1;
  /* + 1 is needed to get the terminal zero in the returned string */
  r = chash_set(hash, &amp;key, &amp;value, NULL);
  if (r &lt; 0)
    goto free_hash;

  key.data = "bar";
  key.len = strlen("bar");  
  value.data = str2;
  value.data = strlen(str2) + 1;
  if (r &lt; 0)
    goto free_hash;
  
  key.data = "foo";
  key.len = strlen("foo");  
  r = chash_get(hash, &amp;key, &amp;value);
  if (r &lt; 0) {
    printf("element not found\n");
  }
  else {
    char * str;

    str = value.data;
    printf("found : %s", str);
  }
  
  chash_free(hash);

  exit(EXIT_SUCCESS);

 free_hash:
  chash_free(hash);
 err:
  exit(EXIT_FAILURE);
}
          </PRE
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="CHASH-DELETE"
>chash_delete</A
></H2
><PRE
CLASS="PROGRAMLISTING"
>int chash_delete(chash * hash,
    chashdatum * key, chashdatum * oldvalue);
        </PRE
><P
>          deletes the key/value pair given the corresponding key.
          The value is returned in old_value.
          If there is no corresponding value, -1 is returned. 0 on success.
          Medium complexity is O(1).
        </P
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN198"
></A
><P
><B
>Example 2-10. key deletion in a chash</B
></P
><PRE
CLASS="PROGRAMLISTING"
>int main(void)
{
  chash * hash;
  int r;
  chashdatum key;
  chashdatum value;
  char * str1 = "my-data";
  char * str2 = "my-data";

  hash = build_hash();
  
  key.data = "foo";
  key.len = strlen("foo");  
  chash_delete(hash, &amp;key, &amp;value);

  /* it will never be possible to lookup "foo" */
  key.data = "foo";
  key.len = strlen("foo");
  r = chash_get(hash, &amp;key, &amp;value);
  if (r &lt; 0) {
    printf("element not found\n");
  }
  else {
    char * str;

    str = value.data;
    printf("found : %s", str);
  }
  
  chash_free(hash);

  exit(EXIT_SUCCESS);

 free_hash:
  chash_free(hash);
 err:
  exit(EXIT_FAILURE);
}
          </PRE
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="CHASH-RESIZE"
>chash_resize</A
></H2
><PRE
CLASS="PROGRAMLISTING"
>int chash_resize(chash * hash, int size);
        </PRE
><P
>          <B
CLASS="COMMAND"
>chash_resize()</B
> changes the size of the
          table used for implementation of the hash table.
          returns 0 on success, -1 on failure.
        </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="CHASH-BEGIN"
>running through the chash</A
></H2
><PRE
CLASS="PROGRAMLISTING"
>chashiter * chash_begin(chash * hash);

chashiter * chash_next(chash * hash, chashiter * iter);

void chash_key(chashiter * iter, chashdatum * result);

void chash_value(chashiter iter, chashdatum * result);
        </PRE
><P
>          <B
CLASS="COMMAND"
>chash_begin()</B
> returns a pointer to the
          first element of the hash table. Returns
          <B
CLASS="COMMAND"
>NULL</B
> if there is no elements in the hash
          table.
          Complexity is O(n).
        </P
><P
>          <B
CLASS="COMMAND"
>chash_next()</B
> returns a pointer to the next
          element of the hash table. Returns <B
CLASS="COMMAND"
>NULL</B
>
          if there is no next element.
          Complexity is O(n) but n calls to chash_next() also has 
          a complexity of O(n).
        </P
><P
>          <B
CLASS="COMMAND"
>chash_key()</B
> returns the key of the given
          element of the hash table.
        </P
><P
>          <B
CLASS="COMMAND"
>chash_value</B
> returns the value of the
          given element of the hash table.
        </P
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN219"
></A
><P
><B
>Example 2-11. running through a chash</B
></P
><PRE
CLASS="PROGRAMLISTING"
>int main(void)
{
  chash * hash;
  int r;
  chashiter * iter;

  hash = build_hash();

  /* this will display all the values stored in the hash */
  for(iter = chash_begin(hash) ; iter != NULL ; iter =
    chash_next(hash, iter)) {
    chashdatum key;
    chashdatum value;
    char * str;

    chash_value(iter, &amp;value);
    str = value.data;
    printf("%s\n", str);
  }

  chash_free(hash);
}
          </PRE
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="CHASH-COUNT"
>chash_size and chash_count</A
></H2
><PRE
CLASS="PROGRAMLISTING"
>int chash_size(chash * hash);

int chash_count(chash * hash);
        </PRE
><P
>          <B
CLASS="COMMAND"
>chash_size()</B
> returns the size of the table
          used for implementation of the hash table.
          Complexity is O(1).
        </P
><P
>          <B
CLASS="COMMAND"
>chash_count()</B
> returns the number of
          elements in the hash table.
          Complexity is O(1).
        </P
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libetpan-doc 1.8.0-1 / usr / share / doc / libetpan-doc / API / x161.htm
