API for iterating the g_hash_table

[Tony Yat-Tung Cheung]

Hi,

Is there any API for iterating GHashTable?

I only see the the g_hash_table_foreach() here. But sometimes people may 
like to iterate through a hash table and stop the iteration when certain 
conditions are met.

Currently, there is g_hash_table_size(), we could easily add iteration 
by providing the following two new APIs,

gconstpointer g_hash_table_get_key(GHashTable *hash_table, int pos);
gconspointer g_hash_table_get_value(GHashTable *hash_table, int pos);
The two APIs allows one to iterate the hash table, for example,

for (i = 0; i  g_hash_table_size(hash_table); i++) {
 gconstpointer value = g_hash_table_get_value(hash_table, i);
 /* Do some processing here */
 if (is_match(value))
   return TRUE;
}
Should we add the APIs?

Regards,
Tony Cheung
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glib API for iterating the g_hash_table

[Tony Yat-Tung Cheung]

Hi,

Is there any API for iterating GHashTable?

I only see the the g_hash_table_foreach() here. But sometimes people may
like to iterate through a hash table and stop the iteration when certain
conditions are met.
Currently, there is g_hash_table_size(), we could easily add iteration
by providing the following two new APIs,
gconstpointer g_hash_table_get_key(GHashTable *hash_table, int pos);
gconspointer g_hash_table_get_value(GHashTable *hash_table, int pos);
The two APIs allows one to iterate the hash table, for example,

for (i = 0; i  g_hash_table_size(hash_table); i++) {
 gconstpointer value = g_hash_table_get_value(hash_table, i);
 /* Do some processing here */
 if (is_match(value))
   return TRUE;
}
Should we add the APIs?

Regards,
Tony Cheung
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[EMAIL PROTECTED]
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Re: API for iterating the g_hash_table

[Tony Yat-Tung Cheung]

Sven Neumann wrote:

  Hi,

Tony Yat-Tung Cheung [EMAIL PROTECTED] writes:

  
  
Currently, there is g_hash_table_size(), we could easily add iteration
by providing the following two new APIs,

gconstpointer g_hash_table_get_key(GHashTable *hash_table, int pos);
gconspointer g_hash_table_get_value(GHashTable *hash_table, int pos);

The two APIs allows one to iterate the hash table, for example,

for (i = 0; i  g_hash_table_size(hash_table); i++) {
  gconstpointer value = g_hash_table_get_value(hash_table, i);

  /* Do some processing here */
  if (is_match(value))
return TRUE;
}

  
  
This looks rather akward since it exposes internals like the position
of an element in the hash table. If this functionality is actually
needed (do you have a use case?), then it should be an extended
version of g_hash_table_foreach() that stops traversal when the
callback function returns TRUE (just like g_tree_foreach).


Sven
  

Yes, the proposed API may expose too much implementation details in
some views. For perfect API, one may want to use an iterator, instead
of an integer index. Then APIs will become,
gconstpointer g_hash_table_get_key(GHashTable *hash_table, GHashTableIterator iterator);
gconspointer g_hash_table_get_value(GHashTable *hash_table, GHashTableIterator iterator);
It's certainly an improvement for g_hash_table_foreach() to stop
traversal when the callback function returns TRUE. We should have this,
except that it breaks the current API. Even with it, sometimes the user
may also want to do more than just stopping the trasversal. He/she may
also want to get the current node, return a special value from the
current function...etc. I think the most convenient API is an iterator,
either in a simple integer index or an iterator structure.

Thanks.

Tony Cheung

Re: API for iterating the g_hash_table

[Tony Yat-Tung Cheung]

[EMAIL PROTECTED] wrote:

  
I only see the the g_hash_table_foreach() here. But sometimes people may 
like to iterate through a hash table and stop the iteration when certain 
conditions are met.

  
  
It is rather trivial to construct a GList of hash table keys (or
values) using g_hash_table_foreach. Of course it's only useful on
a table whose contents change never or seldom because the list
has to be updated on each change. Anyway, here's what I use. I
was too lazy to make Append_key() the right type.

void append_key(void *k, void *v, GList **keys)
{
}

GList *get_hash_keys(GHashTable *hash)
{
GList *keys = NULL;

g_hash_table_foreach(hash, append_key, keys);
return keys;
}


--Daniel
  

Hi Daniel,

Good suggestion.

Apart from your suggestion, we may also use a GList together with a
GHashTable. When inserting a node into the GHashTable, we also insert
the element to the GList. It's a bit more trouble and less efficient,
but it works for simple cases. Until we have add new APIs for iterating
through the GHashTable, I am afraid we have to do this way...

Thanks.

Regards,
Tony Cheung