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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<title>
Data Structures
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<div class="SECT1">
<h1 class="SECT1">
<a name="Z29">Data Structures</a>
</h1>
<p>
glib implements many common data structures, so you don't
have to reinvent the wheel every time you want a linked
list. This section covers glib's implementation of linked
lists, sorted binary trees, N-ary trees, and hash tables.
</p>
<div class="SECT2">
<h2 class="SECT2">
<a name="Z30">Lists</a>
</h2>
<p>
glib provides generic single and doubly linked lists,
<span class="STRUCTNAME">GSList</span> and <span class=
"STRUCTNAME">GList</span>, respectively. These are
implemented as lists of <span class="STRUCTNAME">
gpointer</span>; you can use them to hold integers with
the <tt class="FUNCTION">GINT_TO_POINTER</tt> and <tt
class="FUNCTION">GPOINTER_TO_INT</tt> macros. <span
class="STRUCTNAME">GSList</span> and <span class=
"STRUCTNAME">GList</span> have identical API's, except
that there is a <tt class="FUNCTION">
g_list_previous()</tt> function and no <tt class=
"FUNCTION">g_slist_previous()</tt>. This section will
discuss <span class="STRUCTNAME">GSList</span> but
everything also applies to the doubly linked list.
</p>
<p>
In the glib implementation, the empty list is simply a
<span class="STRUCTNAME">NULL</span> pointer. It's always
safe to pass <span class="STRUCTNAME">NULL</span> to list
functions since it's a valid list of length 0. Code to
create a list and add one element might look like this:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
GSList* list = NULL;
gchar* element = g_strdup("a string");
list = g_slist_append(list, element);
</pre>
</td>
</tr>
</table>
<p>
glib lists have a noticeable Lisp influence; the empty
list is a special "nil" value for that reason. <tt class=
"FUNCTION">g_slist_prepend()</tt> works much like <tt
class="APPLICATION">cons</tt>---it's a constant-time
operation that adds a new cell to the front of the list.
</p>
<p>
Notice that you must replace the list passed to
list-modifying functions with their return value, in case
the head of the list changes. glib will handle memory
issues, deallocating and allocating list links as needed.
</p>
<p>
For example, the following code would remove the
above-added element and empty the list:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
list = g_slist_remove(list, element);
</pre>
</td>
</tr>
</table>
<p>
<span class="STRUCTNAME">list</span> is now <span class=
"STRUCTNAME">NULL</span>. You still have to free <span
class="STRUCTNAME">element</span> yourself, of course. To
clear an entire list, use <tt class="FUNCTION">
g_slist_free()</tt>, which removes all the links in one
fell swoop. <tt class="FUNCTION">g_slist_free()</tt> has
no return value because it would always be <span class=
"STRUCTNAME">NULL</span>, and you can simply assign that
value to your list if you like. Obviously, <tt class=
"FUNCTION">g_slist_free()</tt> frees only the list cells;
it has no way of knowing what to do with the list
contents.
</p>
<p>
To access a list element, you refer to the <span class=
"STRUCTNAME">GSList</span> struct directly:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
gchar* my_data = list->data;
</pre>
</td>
</tr>
</table>
<p>
To iterate over the list, you might write code like this:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
GSList* tmp = list;
while (tmp != NULL)
{
printf("List data: %p\n", tmp->data);
tmp = g_slist_next(tmp);
}
</pre>
</td>
</tr>
</table>
<p>
<a href="z29.html#FL-LISTCHANGING">Figure 13</a> shows
the basic functions for changing <span class=
"STRUCTNAME">GSList</span> contents. For all of these,
you must assign the return value to your list pointer in
case the head of the list changes. Note that glib does <i
class="EMPHASIS">not</i> store a pointer to the tail of
the list, so prepending is a constant-time operation,
while append, insert, and remove are proportional to the
list's size.
</p>
<p>
In particular, this means that constructing a list using
<tt class="FUNCTION">g_slist_append()</tt> is a <i class=
"EMPHASIS">terrible</i> idea; use <tt class="FUNCTION">
g_slist_prepend()</tt> and then call <tt class=
"FUNCTION">g_slist_reverse()</tt> if you need items in a
particular order. If you anticipate frequently appending
to a list, you can also keep a pointer to the last
element. The following code can be used to perform
efficient appends:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
void
efficient_append(GSList** list, GSList** list_end, gpointer data)
{
g_return_if_fail(list != NULL);
g_return_if_fail(list_end != NULL);
if (*list == NULL)
{
g_assert(*list_end == NULL);
*list = g_slist_append(*list, data);
*list_end = *list;
}
else
{
*list_end = g_slist_append(*list_end, data)->next;
}
}
</pre>
</td>
</tr>
</table>
<p>
To use this function, you would store the list and its
end somewhere, and pass their address to <tt class=
"FUNCTION">efficient_append()</tt>:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
GSList* list = NULL;
GSList* list_end = NULL;
efficient_append(&list, &list_end, g_strdup("Foo"));
efficient_append(&list, &list_end, g_strdup("Bar"));
efficient_append(&list, &list_end, g_strdup("Baz"));
</pre>
</td>
</tr>
</table>
<p>
Of course you have to be careful not to use any list
functions that might change the end of the list without
updating <span class="STRUCTNAME">list_end</span>.
</p>
<div class="FIGURE">
<a name="FL-LISTCHANGING"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-LISTCHANGING.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_append</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>, gpointer <tt
class="PARAMETER"><i>data</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_prepend</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>, gpointer <tt
class="PARAMETER"><i>data</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_insert</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>, gpointer <tt
class="PARAMETER"><i>data</i></tt>, gint <tt class=
"PARAMETER"><i>position</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_remove</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>, gpointer <tt
class="PARAMETER"><i>data</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 13. Changing linked list contents</b>
</p>
</div>
<p>
For accessing list elements, the functions in <a href=
"z29.html#FL-LISTACCESS">Figure 14</a> are provided. None
of these change the list's structure. <tt class=
"FUNCTION">g_slist_foreach()</tt> applies a <span class=
"STRUCTNAME">GFunc</span> to each element of the list. A
<span class="STRUCTNAME">GFunc</span> is defined as
follows:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
typedef void (*GFunc)(gpointer data, gpointer user_data);
</pre>
</td>
</tr>
</table>
<p>
Used in <tt class="FUNCTION">g_slist_foreach()</tt>, your
<span class="STRUCTNAME">GFunc</span> will be called on
each <span class="STRUCTNAME">list->data</span> in
<span class="STRUCTNAME">list</span>, passing the <span
class="STRUCTNAME">user_data</span> you provided to <tt
class="FUNCTION">g_slist_foreach()</tt>. <tt class=
"FUNCTION">g_slist_foreach()</tt> is comparable to
Scheme's "map" function.
</p>
<p>
For example, you might have a list of strings, and you
might want to be able to create a parallel list with some
transformation applied to the strings. Here is some code,
using the <tt class="FUNCTION">efficient_append()</tt>
function from an earlier example:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
typedef struct _AppendContext AppendContext;
struct _AppendContext {
GSList* list;
GSList* list_end;
const gchar* append;
};
static void
append_foreach(gpointer data, gpointer user_data)
{
AppendContext* ac = (AppendContext*) user_data;
gchar* oldstring = (gchar*) data;
efficient_append(&ac->list, &ac->list_end,
g_strconcat(oldstring, ac->append, NULL));
}
GSList*
copy_with_append(GSList* list_of_strings, const gchar* append)
{
AppendContext ac;
ac.list = NULL;
ac.list_end = NULL;
ac.append = append;
g_slist_foreach(list_of_strings, append_foreach, &ac);
return ac.list;
}
</pre>
</td>
</tr>
</table>
<p>
glib and GTK+ use the "function pointer and user data"
idiom heavily. If you have functional programming
experience, this is much like using lambda expressions to
create a <i class="FIRSTTERM">closure</i>. (A closure
combines a function with an <i class="FIRSTTERM">
environment</i>---a set of name-value bindings. In this
case the "environment" is the user data you pass to <tt
class="FUNCTION">append_foreach()</tt>, and the "closure"
is the combination of the function pointer and the user
data.)
</p>
<div class="FIGURE">
<a name="FL-LISTACCESS"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-LISTACCESS.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_find</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>, gpointer <tt
class="PARAMETER"><i>data</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_nth</tt></code>(GSList* <tt class=
"PARAMETER"><i>list</i></tt>, guint <tt class=
"PARAMETER"><i>n</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">gpointer <tt class=
"FUNCTION">g_slist_nth_data</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>, guint <tt class=
"PARAMETER"><i>n</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_last</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">gint <tt class=
"FUNCTION">g_slist_index</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>, gpointer <tt
class="PARAMETER"><i>data</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">g_slist_foreach</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>, GFunc <tt class=
"PARAMETER"><i>func</i></tt>, gpointer <tt class=
"PARAMETER"><i>user_data</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 14. Accessing data in a linked list</b>
</p>
</div>
<p>
There are some handy list-manipulation routines, listed
in <a href="z29.html#FL-LISTMANIP">Figure 15</a>. With
the exception of <tt class="FUNCTION">
g_slist_copy()</tt>, all of these affect the lists
in-place. Which means you must assign the return value
and forget about the passed-in pointer, just as you do
when adding or removing list elements. <tt class=
"FUNCTION">g_slist_copy()</tt> returns a newly-allocated
list, so you can continue to use both lists and must free
both lists eventually.
</p>
<div class="FIGURE">
<a name="FL-LISTMANIP"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-LISTMANIP.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">guint <tt class=
"FUNCTION">g_slist_length</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_concat</tt></code>(GSList* <tt
class="PARAMETER"><i>list1</i></tt>, GSList* <tt
class="PARAMETER"><i>list2</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_reverse</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_copy</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 15. Manipulating a linked list</b>
</p>
</div>
<p>
Finally, there are some provisions for sorted lists,
shown in <a href="z29.html#FL-LISTSORTED">Figure 16</a>.
To use these, you must write a <span class="STRUCTNAME">
GCompareFunc</span>, which is just like the comparison
function in the standard C <tt class="FUNCTION">
qsort()</tt>. Using glib types, this becomes:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
typedef gint (*GCompareFunc) (gconstpointer a, gconstpointer b);
</pre>
</td>
</tr>
</table>
<p>
If <span class="STRUCTNAME">a < b</span>, the function
should return a negative value; if <span class=
"STRUCTNAME">a > b</span> a positive value; if <span
class="STRUCTNAME">a == b</span> it should return 0.
</p>
<p>
Once you have a comparison function, you can insert an
element into an already-sorted list, or sort an entire
list. Lists are sorted in ascending order. You can even
recycle your <span class="STRUCTNAME">GCompareFunc</span>
to find list elements, using <tt class="FUNCTION">
g_slist_find_custom()</tt>. (A word of caution: <span
class="STRUCTNAME">GCompareFunc</span> is used
inconsistently in glib; sometimes it glib expects an
equality predicate instead of a <tt class="FUNCTION">
qsort()</tt>-style function. However, the usage is
consistent within the list API.)
</p>
<p>
Be careful with sorted lists; misusing them can rapidly
become very inefficient. For example, <tt class=
"FUNCTION">g_slist_insert_sorted()</tt> is an O(n)
operation, but if you use it in a loop to insert multiple
elements the loop runs in exponential time. It's better
to simply prepend all your elements, then call <tt class=
"FUNCTION">g_slist_sort()</tt>.
</p>
<div class="FIGURE">
<a name="FL-LISTSORTED"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-LISTSORTED.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_insert_sorted</tt></code>(GSList*
<tt class="PARAMETER"><i>list</i></tt>, gpointer <tt
class="PARAMETER"><i>data</i></tt>, GCompareFunc <tt
class="PARAMETER"><i>func</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_sort</tt></code>(GSList* <tt
class="PARAMETER"><i>list</i></tt>, GCompareFunc <tt
class="PARAMETER"><i>func</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GSList* <tt class=
"FUNCTION">g_slist_find_custom</tt></code>(GSList*
<tt class="PARAMETER"><i>list</i></tt>, gpointer <tt
class="PARAMETER"><i>data</i></tt>, GCompareFunc <tt
class="PARAMETER"><i>func</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 16. Sorted lists</b>
</p>
</div>
</div>
<div class="SECT2">
<h2 class="SECT2">
<a name="Z31">Trees</a>
</h2>
<p>
There are two different kinds of tree in glib; <span
class="STRUCTNAME">GTree</span> is your basic balanced
binary tree, useful to store key-value pairs sorted by
key; <span class="STRUCTNAME">GNode</span> stores
arbitrary tree-structured data, such as a parse tree or
taxonomy.
</p>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z32">GTree</a>
</h3>
<p>
To create and destroy a <span class="STRUCTNAME">
GTree</span>, use the constructor-destructor pair
displayed in <a href="z29.html#FL-TREECONSTRUCT">Figure
17</a>. <span class="STRUCTNAME">GCompareFunc</span> is
the same <tt class="FUNCTION">qsort()</tt>-style
comparison function described for <span class=
"STRUCTNAME">GSList</span>; in this case it's used to
compare keys in the tree.
</p>
<div class="FIGURE">
<a name="FL-TREECONSTRUCT"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-TREECONSTRUCT.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">GTree* <tt class=
"FUNCTION">g_tree_new</tt></code>(GCompareFunc <tt
class="PARAMETER"><i>
key_compare_func</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">g_tree_destroy</tt></code>(GTree* <tt
class="PARAMETER"><i>tree</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 17. Creating and destroying balanced binary
trees</b>
</p>
</div>
<p>
Functions for manipulating the contents of the tree are
shown in <a href="z29.html#FL-TREEMANIP">Figure 18</a>.
All very straightforward; <tt class="FUNCTION">
g_tree_insert()</tt> overwrites any existing value, so
be careful if the existing value is your only pointer
to a chunk of allocated memory. If <tt class=
"FUNCTION">g_tree_lookup()</tt> fails to find the key,
it returns <span class="STRUCTNAME">NULL</span>,
otherwise it returns the associated value. Both keys
and values have type <span class="STRUCTNAME">
gpointer</span>, but the <tt class="FUNCTION">
GPOINTER_TO_INT()</tt> and <tt class="FUNCTION">
GPOINTER_TO_UINT()</tt> macros allow you to use
integers instead.
</p>
<div class="FIGURE">
<a name="FL-TREEMANIP"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-TREEMANIP.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">g_tree_insert</tt></code>(GTree* <tt
class="PARAMETER"><i>tree</i></tt>, gpointer <tt
class="PARAMETER"><i>key</i></tt>, gpointer <tt
class="PARAMETER"><i>value</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">g_tree_remove</tt></code>(GTree* <tt
class="PARAMETER"><i>tree</i></tt>, gpointer <tt
class="PARAMETER"><i>key</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">gpointer <tt class=
"FUNCTION">g_tree_lookup</tt></code>(GTree* <tt
class="PARAMETER"><i>tree</i></tt>, gpointer <tt
class="PARAMETER"><i>key</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 18. Manipulating <span class="STRUCTNAME">
GTree</span> contents</b>
</p>
</div>
<p>
There are two functions which give you an idea how
large the tree is, shown in <a href=
"z29.html#FL-TREESIZE">Figure 19</a>.
</p>
<div class="FIGURE">
<a name="FL-TREESIZE"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-TREESIZE.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">gint <tt class=
"FUNCTION">g_tree_nnodes</tt></code>(GTree* <tt
class="PARAMETER"><i>tree</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">gint <tt class=
"FUNCTION">g_tree_height</tt></code>(GTree* <tt
class="PARAMETER"><i>tree</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 19. Determining the size of a <span class=
"STRUCTNAME">GTree</span></b>
</p>
</div>
<p>
Using <tt class="FUNCTION">g_tree_traverse()</tt> (<a
href="z29.html#FL-TREETRAVERSE">Figure 20</a>) you can
walk the entire tree. To use it, you provide a <span
class="STRUCTNAME">GTraverseFunc</span>, which is
passed each key-value pair and a <span class=
"STRUCTNAME">data</span> argument you give to <tt
class="FUNCTION">g_tree_traverse()</tt>. Traversal
continues as long as the <span class="STRUCTNAME">
GTraverseFunc</span> returns <span class="STRUCTNAME">
FALSE</span>; if it ever returns <span class=
"STRUCTNAME">TRUE</span> then traversal stops. You can
use this to search the tree by value. Here is the
definition of <span class="STRUCTNAME">
GTraverseFunc</span>:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
typedef gint (*GTraverseFunc)(gpointer key, gpointer value, gpointer data);
</pre>
</td>
</tr>
</table>
<p>
<span class="STRUCTNAME">GTraverseType</span> is an
enumeration; there are four possible values. Here are
their meanings with respect to <span class=
"STRUCTNAME">GTree</span>.
</p>
<ul>
<li>
<p>
<span class="STRUCTNAME">G_IN_ORDER</span> first
recurses the left child of the node (the "lower"
key according to your <span class="STRUCTNAME">
GCompareFunc</span>), then calls the traversal
function on the key-value pair of the current node,
then recurses the right child. This traversal is in
order from lowest to highest, according to your
<span class="STRUCTNAME">GCompareFunc</span>.
</p>
</li>
<li>
<p>
<span class="STRUCTNAME">G_PRE_ORDER</span> calls
the traversal function on the key-value pair of the
current node, then recurses the left child, then
recurses the right child.
</p>
</li>
<li>
<p>
<span class="STRUCTNAME">G_POST_ORDER</span>
recurses the left child, then recurses the right
child, and finally calls the traversal function on
the current node's key-value pair.
</p>
</li>
<li>
<p>
<span class="STRUCTNAME">G_LEVEL_ORDER</span> is
only meaningful for <span class="STRUCTNAME">
GNode</span>, it is not allowed with <span class=
"STRUCTNAME">GTree</span>.
</p>
</li>
</ul>
<div class="FIGURE">
<a name="FL-TREETRAVERSE"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-TREETRAVERSE.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">g_tree_traverse</tt></code>(GTree* <tt
class="PARAMETER"><i>tree</i></tt>, GTraverseFunc
<tt class="PARAMETER"><i>traverse_func</i></tt>,
GTraverseType <tt class="PARAMETER"><i>
traverse_type</i></tt>, gpointer <tt class=
"PARAMETER"><i>data</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 20. Traversing <span class="STRUCTNAME">
GTree</span></b>
</p>
</div>
</div>
<div class="SECT3">
<h3 class="SECT3">
<a name="Z33">GNode</a>
</h3>
<p>
A <span class="STRUCTNAME">GNode</span> is an N-way
tree, implemented as a doubly linked list with parent
and child lists. Thus, most list operations have
analogues in the <span class="STRUCTNAME">GNode</span>
API. You can also walk the tree in various ways. Here's
the declaration for a node:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
typedef struct _GNode GNode;
struct _GNode
{
gpointer data;
GNode *next;
GNode *prev;
GNode *parent;
GNode *children;
};
</pre>
</td>
</tr>
</table>
<p>
There are macros to access <span class="STRUCTNAME">
GNode</span> members, shown in <a href=
"z29.html#ML-NODEACCESS">Figure 21</a>. As with <span
class="STRUCTNAME">GList</span>, the <span class=
"STRUCTNAME">data</span> member is intended to be used
directly. These macros return the <span class=
"STRUCTNAME">next</span>, <span class="STRUCTNAME">
prev</span>, and <span class="STRUCTNAME">
children</span> members respectively; they also check
whether their argument is <span class="STRUCTNAME">
NULL</span> before dereferencing it, and return <span
class="STRUCTNAME">NULL</span> if it is.
</p>
<div class="FIGURE">
<a name="ML-NODEACCESS"></a>
<div class="FUNCSYNOPSIS">
<a name="ML-NODEACCESS.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF"><tt class="FUNCTION">
g_node_prev_sibling</tt></code>(<tt class=
"PARAMETER"><i>node</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF"><tt class="FUNCTION">
g_node_next_sibling</tt></code>(<tt class=
"PARAMETER"><i>node</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF"><tt class="FUNCTION">
g_node_first_child</tt></code>(<tt class=
"PARAMETER"><i>node</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 21. Accessing <span class="STRUCTNAME">
GNode</span> members</b>
</p>
</div>
<p>
To create a node, the usual <tt class="FUNCTION">
_new()</tt> function is provided (<a href=
"z29.html#FL-NODENEW">Figure 22</a>). <tt class=
"FUNCTION">g_node_new()</tt> creates a childless and
parentless node containing <span class="STRUCTNAME">
data</span>. Typically <tt class="FUNCTION">
g_node_new()</tt> is used only to create the root node;
convenience macros are provided which automatically
create new nodes as needed.
</p>
<div class="FIGURE">
<a name="FL-NODENEW"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-NODENEW.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">GNode* <tt class=
"FUNCTION">g_node_new</tt></code>(gpointer <tt
class="PARAMETER"><i>data</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 22. Creating a <span class="STRUCTNAME">
GNode</span></b>
</p>
</div>
<p>
To build a tree the fundamental operations shown in <a
href="z29.html#FL-NODEBUILD">Figure 23</a> are used.
Each operation returns the just-added node, for
convenience when writing loops or recursing the tree.
Unlike <span class="STRUCTNAME">GList</span>, it is
safe to ignore the return value.
</p>
<div class="FIGURE">
<a name="FL-NODEBUILD"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-NODEBUILD.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">GNode* <tt class=
"FUNCTION">g_node_insert</tt></code>(GNode* <tt
class="PARAMETER"><i>parent</i></tt>, gint <tt
class="PARAMETER"><i>position</i></tt>, GNode* <tt
class="PARAMETER"><i>node</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GNode* <tt class=
"FUNCTION">g_node_insert_before</tt></code>(GNode*
<tt class="PARAMETER"><i>parent</i></tt>, GNode*
<tt class="PARAMETER"><i>sibling</i></tt>, GNode*
<tt class="PARAMETER"><i>node</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GNode* <tt class=
"FUNCTION">g_node_prepend</tt></code>(GNode* <tt
class="PARAMETER"><i>parent</i></tt>, GNode* <tt
class="PARAMETER"><i>node</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 23. Building a <span class="STRUCTNAME">
GNode</span> tree</b>
</p>
</div>
<p>
The convenience macros shown in <a href=
"z29.html#ML-NODECONV">Figure 24</a> are implemented in
terms of the fundamental operations. <tt class=
"FUNCTION">g_node_append()</tt> is analagous to <tt
class="FUNCTION">g_node_prepend()</tt>; the rest take a
<span class="STRUCTNAME">data</span> argument,
automatically allocate a node for it, and call the
corresponding basic operation.
</p>
<div class="FIGURE">
<a name="ML-NODECONV"></a>
<div class="FUNCSYNOPSIS">
<a name="ML-NODECONV.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF"><tt class="FUNCTION">
g_node_append</tt></code>(<tt class=
"PARAMETER"><i>parent</i></tt>, <tt class=
"PARAMETER"><i>node</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF"><tt class="FUNCTION">
g_node_insert_data</tt></code>(<tt class=
"PARAMETER"><i>parent</i></tt>, <tt class=
"PARAMETER"><i>position</i></tt>, <tt class=
"PARAMETER"><i>data</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF"><tt class="FUNCTION">
g_node_insert_data_before</tt></code>(<tt class=
"PARAMETER"><i>parent</i></tt>, <tt class=
"PARAMETER"><i>sibling</i></tt>, <tt class=
"PARAMETER"><i>data</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF"><tt class="FUNCTION">
g_node_prepend_data</tt></code>(<tt class=
"PARAMETER"><i>parent</i></tt>, <tt class=
"PARAMETER"><i>data</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF"><tt class="FUNCTION">
g_node_append_data</tt></code>(<tt class=
"PARAMETER"><i>parent</i></tt>, <tt class=
"PARAMETER"><i>data</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 24. Building a <span class="STRUCTNAME">
GNode</span></b>
</p>
</div>
<p>
To remove a node from the tree, there are two functions
shown in <a href="z29.html#FL-NODEDESTROY">Figure
25</a>. <tt class="FUNCTION">g_node_destroy()</tt>
removes the node from a tree, destroying it and all its
children. <tt class="FUNCTION">g_node_unlink()</tt>
removes a node and makes it into a root node; i.e., it
converts a subtree into an independent tree.
</p>
<div class="FIGURE">
<a name="FL-NODEDESTROY"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-NODEDESTROY.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">g_node_destroy</tt></code>(GNode* <tt
class="PARAMETER"><i>root</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">g_node_unlink</tt></code>(GNode* <tt
class="PARAMETER"><i>node</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 25. Destroying a <span class="STRUCTNAME">
GNode</span></b>
</p>
</div>
<p>
There are two macros for detecting the top and bottom
of a <span class="STRUCTNAME">GNode</span> tree, shown
in <a href="z29.html#ML-NODEEXTREMA">Figure 26</a>. A
root node is defined as a node with no parent or
siblings. A leaf node has no children.
</p>
<div class="FIGURE">
<a name="ML-NODEEXTREMA"></a>
<div class="FUNCSYNOPSIS">
<a name="ML-NODEEXTREMA.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF"><tt class="FUNCTION">
G_NODE_IS_ROOT</tt></code>(<tt class=
"PARAMETER"><i>node</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF"><tt class="FUNCTION">
G_NODE_IS_LEAF</tt></code>(<tt class=
"PARAMETER"><i>node</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 26. Predicates for <span class=
"STRUCTNAME">GNode</span></b>
</p>
</div>
<p>
You can ask glib to report useful information about a
<span class="STRUCTNAME">GNode</span>, including the
number of nodes it contains, its root node, its depth,
and the node containing a particular data pointer.
These functions are shown in <a href=
"z29.html#FL-NODEPROPERTIES">Figure 27</a>.
</p>
<p>
<span class="STRUCTNAME">GTraverseType</span> was
introduced earlier, with respect to <span class=
"STRUCTNAME">GTree</span>; here are the possible values
for <span class="STRUCTNAME">GNode</span>:
</p>
<ul>
<li>
<p>
<span class="STRUCTNAME">G_IN_ORDER</span> first
recurses the leftmost child of the node, then
visits the node itself, then recurses the rest of
the node's children. This isn't very useful; mostly
it is intended for use with <span class=
"STRUCTNAME">GTree</span>.
</p>
</li>
<li>
<p>
<span class="STRUCTNAME">G_PRE_ORDER</span> visits
the current node, then recurses each child in
turn.
</p>
</li>
<li>
<p>
<span class="STRUCTNAME">G_POST_ORDER</span>
recurses each child in order, then visits the
current node.
</p>
</li>
<li>
<p>
<span class="STRUCTNAME">G_LEVEL_ORDER</span> first
visits the node itself; then each of the node's
children; then the children of the children; then
the children of the children of the children; and
so on. That is, it visits each node of depth 0,
then each node of depth 1, then each node of depth
2, etc.
</p>
</li>
</ul>
<p>
<span class="STRUCTNAME">GNode</span>'s tree-traversal
functions have a <span class="STRUCTNAME">
GTraverseFlags</span> argument. This is a bitfield used
to change the nature of the traversal. Currently there
are only three flags---you can visit only leaf nodes,
only non-leaf nodes, or all nodes:
</p>
<ul>
<li>
<p>
<span class="STRUCTNAME">G_TRAVERSE_LEAFS</span>
means to traverse only leaf nodes.
</p>
</li>
<li>
<p>
<span class="STRUCTNAME">
G_TRAVERSE_NON_LEAFS</span> means to traverse only
non-leaf nodes.
</p>
</li>
<li>
<p>
<span class="STRUCTNAME">G_TRAVERSE_ALL</span> is
simply a shortcut for <span class="STRUCTNAME">
(G_TRAVERSE_LEAFS |
G_TRAVERSE_NON_LEAFS)</span>.
</p>
</li>
</ul>
<div class="FIGURE">
<a name="FL-NODEPROPERTIES"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-NODEPROPERTIES.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">guint <tt class=
"FUNCTION">g_node_n_nodes</tt></code>(GNode* <tt
class="PARAMETER"><i>root</i></tt>, GTraverseFlags
<tt class="PARAMETER"><i>flags</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GNode* <tt class=
"FUNCTION">g_node_get_root</tt></code>(GNode* <tt
class="PARAMETER"><i>node</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">gboolean <tt class=
"FUNCTION">g_node_is_ancestor</tt></code>(GNode*
<tt class="PARAMETER"><i>node</i></tt>, GNode* <tt
class="PARAMETER"><i>descendant</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">guint <tt class=
"FUNCTION">g_node_depth</tt></code>(GNode* <tt
class="PARAMETER"><i>node</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GNode* <tt class=
"FUNCTION">g_node_find</tt></code>(GNode* <tt
class="PARAMETER"><i>root</i></tt>, GTraverseType
<tt class="PARAMETER"><i>order</i></tt>,
GTraverseFlags <tt class="PARAMETER"><i>
flags</i></tt>, gpointer <tt class="PARAMETER"><i>
data</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 27. <span class="STRUCTNAME">GNode</span>
Properties</b>
</p>
</div>
<p>
The remaining <span class="STRUCTNAME">GNode</span>
functions are straightforward; most of them are simply
operations on the node's list of children. <a href=
"z29.html#FL-NODEACCESSORS">Figure 28</a> lists them.
There are two function typedefs unique to <span class=
"STRUCTNAME">GNode</span>:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
typedef gboolean (*GNodeTraverseFunc) (GNode* node, gpointer data);
typedef void (*GNodeForeachFunc) (GNode* node, gpointer data);
</pre>
</td>
</tr>
</table>
<p>
These are called with a pointer to the node being
visited, and the user data you provide. A <span class=
"STRUCTNAME">GNodeTraverseFunc</span> can return <span
class="STRUCTNAME">TRUE</span> to stop whatever
traversal is in progress; thus you can use <span class=
"STRUCTNAME">GNodeTraverseFunc</span> in combination
with <tt class="FUNCTION">g_node_traverse()</tt> to
search the tree by value.
</p>
<div class="FIGURE">
<a name="FL-NODEACCESSORS"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-NODEACCESSORS.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">g_node_traverse</tt></code>(GNode* <tt
class="PARAMETER"><i>root</i></tt>, GTraverseType
<tt class="PARAMETER"><i>order</i></tt>,
GTraverseFlags <tt class="PARAMETER"><i>
flags</i></tt>, gint <tt class="PARAMETER"><i>
max_depth</i></tt>, GNodeTraverseFunc <tt class=
"PARAMETER"><i>func</i></tt>, gpointer <tt class=
"PARAMETER"><i>data</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">guint <tt class=
"FUNCTION">g_node_max_height</tt></code>(GNode* <tt
class="PARAMETER"><i>root</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">
g_node_children_foreach</tt></code>(GNode* <tt
class="PARAMETER"><i>node</i></tt>, GTraverseFlags
<tt class="PARAMETER"><i>flags</i></tt>,
GNodeForeachFunc <tt class="PARAMETER"><i>
func</i></tt>, gpointer <tt class="PARAMETER"><i>
data</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">
g_node_reverse_children</tt></code>(GNode* <tt
class="PARAMETER"><i>node</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">guint <tt class=
"FUNCTION">g_node_n_children</tt></code>(GNode* <tt
class="PARAMETER"><i>node</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GNode* <tt class=
"FUNCTION">g_node_nth_child</tt></code>(GNode* <tt
class="PARAMETER"><i>node</i></tt>, guint <tt
class="PARAMETER"><i>n</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GNode* <tt class=
"FUNCTION">g_node_last_child</tt></code>(GNode* <tt
class="PARAMETER"><i>node</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GNode* <tt class=
"FUNCTION">g_node_find_child</tt></code>(GNode* <tt
class="PARAMETER"><i>node</i></tt>, GTraverseFlags
<tt class="PARAMETER"><i>flags</i></tt>, gpointer
<tt class="PARAMETER"><i>data</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">gint <tt class=
"FUNCTION">g_node_child_position</tt></code>(GNode*
<tt class="PARAMETER"><i>node</i></tt>, GNode* <tt
class="PARAMETER"><i>child</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">gint <tt class=
"FUNCTION">g_node_child_index</tt></code>(GNode*
<tt class="PARAMETER"><i>node</i></tt>, gpointer
<tt class="PARAMETER"><i>data</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GNode* <tt class=
"FUNCTION">g_node_first_sibling</tt></code>(GNode*
<tt class="PARAMETER"><i>node</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">GNode* <tt class=
"FUNCTION">g_node_last_sibling</tt></code>(GNode*
<tt class="PARAMETER"><i>node</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 28. Accessing a <span class="STRUCTNAME">
GNode</span></b>
</p>
</div>
</div>
</div>
<div class="SECT2">
<h2 class="SECT2">
<a name="Z34">Hash Tables</a>
</h2>
<p>
<span class="STRUCTNAME">GHashTable</span> is a simple
hash table implementation, providing an associative array
with constant-time lookups. To use the hash table, you
must provide a <span class="STRUCTNAME">GHashFunc</span>,
which should return a positive integer when passed a hash
key:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
typedef guint (*GHashFunc) (gconstpointer key);
</pre>
</td>
</tr>
</table>
<p>
Each returned <span class="STRUCTNAME">guint</span>
(modulus the size of the table) corresponds to a "slot"
or "bucket" in the hash; <span class="STRUCTNAME">
GHashTable</span> handles collisions by storing a linked
list of key-value pairs in each slot. Thus, the <span
class="STRUCTNAME">guint</span> values returned by your
<span class="STRUCTNAME">GHashFunc</span> must be fairly
evenly distributed over the set of possible <span class=
"STRUCTNAME">guint</span> values, or the hash table will
degenerate into a linked list. Your <span class=
"STRUCTNAME">GHashFunc</span> must also be fast, since it
is used for every lookup.
</p>
<p>
In addition to <span class="STRUCTNAME">GHashFunc</span>,
a <span class="STRUCTNAME">GCompareFunc</span> is
required to test keys for equality. Somewhat
unpleasantly, <span class="STRUCTNAME">GHashTable</span>
does not use <span class="STRUCTNAME">GCompareFunc</span>
in the same way <span class="STRUCTNAME">GSList</span>
and <span class="STRUCTNAME">GTree</span> do, although
the function signature is the same. Here <span class=
"STRUCTNAME">GCompareFunc</span> is expected to be an
equality operator, returning <span class="STRUCTNAME">
TRUE</span> if its arguments are equal. It should <i
class="EMPHASIS">not</i> be a <span class="STRUCTNAME">
qsort()</span>-style comparison function. The key
comparison function is used to find the correct key-value
pair when hash collisions result in more than one pair in
the same hash slot.
</p>
<p>
To create and destroy a <span class="STRUCTNAME">
GHashTable</span>, use the constructor and destructor
listed in <a href="z29.html#FL-HASHNEW">Figure 29</a>.
Remember that glib has no way of knowing how to destroy
the data contained in your hash table; it only destroys
the table itself.
</p>
<div class="FIGURE">
<a name="FL-HASHNEW"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-HASHNEW.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">GHashTable* <tt class=
"FUNCTION">g_hash_table_new</tt></code>(GHashFunc <tt
class="PARAMETER"><i>hash_func</i></tt>, GCompareFunc
<tt class="PARAMETER"><i>
key_compare_func</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">
g_hash_table_destroy</tt></code>(GHashTable* <tt
class="PARAMETER"><i>hash_table</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 29. <span class="STRUCTNAME">
GHashTable</span></b>
</p>
</div>
<p>
Ready-to-use hash and comparison functions are provided
for the most common keys: integers, pointers, and
strings. These are listed in <a href=
"z29.html#FL-HASHFUNCS">Figure 30</a>. The functions for
integers accept a pointer to a <span class="STRUCTNAME">
gint</span>, rather than the <span class="STRUCTNAME">
gint</span> itself. If you pass <span class="STRUCTNAME">
NULL</span> as the hash function argument to <tt class=
"FUNCTION">g_hash_table_new()</tt>, <tt class="FUNCTION">
g_direct_hash()</tt> is used by default. If you pass
<span class="STRUCTNAME">NULL</span> as the key equality
function, then simple pointer comparison is used
(equivalent to <span class="STRUCTNAME">
g_direct_equal()</span>, but without a function call).
</p>
<div class="FIGURE">
<a name="FL-HASHFUNCS"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-HASHFUNCS.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">guint <tt class=
"FUNCTION">g_int_hash</tt></code>(gconstpointer <tt
class="PARAMETER"><i>v</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">gint <tt class=
"FUNCTION">g_int_equal</tt></code>(gconstpointer <tt
class="PARAMETER"><i>v1</i></tt>, gconstpointer <tt
class="PARAMETER"><i>v2</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">guint <tt class=
"FUNCTION">g_direct_hash</tt></code>(gconstpointer
<tt class="PARAMETER"><i>v</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">gint <tt class=
"FUNCTION">g_direct_equal</tt></code>(gconstpointer
<tt class="PARAMETER"><i>v1</i></tt>, gconstpointer
<tt class="PARAMETER"><i>v2</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">guint <tt class=
"FUNCTION">g_str_hash</tt></code>(gconstpointer <tt
class="PARAMETER"><i>v</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">gint <tt class=
"FUNCTION">g_str_equal</tt></code>(gconstpointer <tt
class="PARAMETER"><i>v1</i></tt>, gconstpointer <tt
class="PARAMETER"><i>v2</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 30. Pre-written hashes/comparisons</b>
</p>
</div>
<p>
Manipulating the hash is simple. The routines are
summarized in <a href="z29.html#FL-HASHMANIP">Figure
31</a>. Insertions do <i class="EMPHASIS">not</i> copy
the key or value; these are entered into the table
exactly as you provide them, overwriting any pre-existing
key-value pair with the same key ("same" is defined by
your hash and equality functions, remember). If this is a
problem, you must do a lookup or remove before you
insert. Be especially careful if you dynamically allocate
keys or values.
</p>
<p>
The simple <tt class="FUNCTION">
g_hash_table_lookup()</tt> returns the value it finds
associated with <span class="STRUCTNAME">key</span>, or
<span class="STRUCTNAME">NULL</span> if there is no
value. Sometimes this won't do. For example, <span class=
"STRUCTNAME">NULL</span> may be a valid value in itself.
If you're using strings as keys, especially dynamically
allocated strings, knowing that a key is in the table
might not be enough; you might want to retrieve the exact
<span class="STRUCTNAME">gchar*</span> the hash table is
using to represent key <span class="STRUCTNAME">
"foo"</span>. A second lookup function is provided for
cases like these. <tt class="FUNCTION">
g_hash_table_lookup_extended()</tt> returns <span class=
"STRUCTNAME">TRUE</span> if the lookup succeeded; if it
returns <span class="STRUCTNAME">TRUE</span>, it places
the key and value it found in the locations it's given.
</p>
<div class="FIGURE">
<a name="FL-HASHMANIP"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-HASHMANIP.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">
g_hash_table_insert</tt></code>(GHashTable* <tt
class="PARAMETER"><i>hash_table</i></tt>, gpointer
<tt class="PARAMETER"><i>key</i></tt>, gpointer <tt
class="PARAMETER"><i>value</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">g_hash_table_remove</tt></code>(GHashTable
* <tt class="PARAMETER"><i>hash_table</i></tt>,
gconstpointer <tt class="PARAMETER"><i>
key</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">gpointer <tt class=
"FUNCTION">g_hash_table_lookup</tt></code>(GHashTable
* <tt class="PARAMETER"><i>hash_table</i></tt>,
gconstpointer <tt class="PARAMETER"><i>
key</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">gboolean <tt class=
"FUNCTION">
g_hash_table_lookup_extended</tt></code>(GHashTable*
<tt class="PARAMETER"><i>hash_table</i></tt>,
gconstpointer <tt class="PARAMETER"><i>
lookup_key</i></tt>, gpointer* <tt class="PARAMETER">
<i>orig_key</i></tt>, gpointer* <tt class=
"PARAMETER"><i>value</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 31. Manipulating <span class="STRUCTNAME">
GHashTable</span></b>
</p>
</div>
<p>
<span class="STRUCTNAME">GHashTable</span> keeps an
internal array whose size is a prime number. It also
keeps a count of the number of key-value pairs stored in
the table. If the average number of pairs per available
slot drops below 0.3 (or so), the array is made smaller;
if it goes above 3, the array is made larger to reduce
collisions. Resizing happens automatically whenever you
insert or remove pairs from the table. This ensures the
hash table's memory use is optimal. Unfortunately, it is
inefficient to rebuild the hash table over and over if
you're doing a large number of insertions or removals. To
solve the problem, the hash table can be <i class=
"FIRSTTERM">frozen</i>, meaning that resizing is
temporarily suppressed. When you're done adding and
removing items, you simply <i class="FIRSTTERM">thaw</i>
the table, resulting in a single optimal-size
calculation. (Be careful though; a frozen table can end
up with many hash collisions if you add large quantities
of data. This should be fine as long as you thaw before
you do any lookups.) The functions are in <a href=
"z29.html#FL-HASHFREEZE">Figure 32</a>.
</p>
<div class="FIGURE">
<a name="FL-HASHFREEZE"></a>
<div class="FUNCSYNOPSIS">
<a name="FL-HASHFREEZE.SYNOPSIS"></a>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="FUNCSYNOPSISINFO">
#include <glib.h>
</pre>
</td>
</tr>
</table>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">
g_hash_table_freeze</tt></code>(GHashTable* <tt
class="PARAMETER"><i>hash_table</i></tt>);</code>
</p>
<p>
<code><code class="FUNCDEF">void <tt class=
"FUNCTION">g_hash_table_thaw</tt></code>(GHashTable*
<tt class="PARAMETER"><i>hash_table</i></tt>);</code>
</p>
</div>
<p>
<b>Figure 32. Freezing and thawing <span class=
"STRUCTNAME">GHashTable</span></b>
</p>
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