Extracting all values from a GLib GTree

Question

I've built a GLib GTree which contains key/value pairs where the key is a character (e.g. 'a') and the value is the frequency by which that character appears in a string. For example, if the string was 'aaa' then the only element in the tree would be: 'a' => 3.

What I want to do is iterate over the tree and keep a count of the number of characters with a given frequency, i.e. where the value of the key/value pair matches.

The pseudocode would be something like:

frequency_count = 0
while (current_element = get_next_element)
  if (current_element->value == desired_frequency)
    frequency_count = frequency_count + 1

Is there a way to do this with a GTree? The only function I can find is g_tree_foreach(), but that requires me to pass a callback function that returns TRUE to stop traversing the tree, and I don't want to stop traversal until I've visited every element. Am I supposed to use the gpointer user_data parameter of the callback function to pass in the frequency count and desired frequency values?

Answer 1

Am I supposed to use the gpointer user_data parameter of the callback function to pass in the frequency count and desired frequency values?

Yes.

Example:

typedef struct
{
  guint desired_frequency;
  guint n_matches;
} MatchData;

static gboolean
n_nodes_matching_frequency_cb (gpointer key,
                               gpointer value,
                               gpointer user_data)
{
  MyTreeElement *element = value;
  MatchData *data = user_data;

  if (element->value == data->desired_frequency)
    data->n_matches++;

  return FALSE;
}

guint
n_nodes_matching_frequency (GTree *tree,
                            guint  desired_frequency)
{
  MatchData data = { desired_frequency, 0 };
  g_tree_foreach (tree, n_nodes_matching_frequency_cb, &data);
  return data.n_matches; 
}