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<h5 class="subsubsection">2.18.4.2 Write the derived creation routine</h5>
<p>You must write a routine which will create and initialize an
entry in the hash table. This routine is passed as the
function argument to <code>bfd_hash_table_init</code>.
<p>In order to permit other hash tables to be derived from the
hash table you are creating, this routine must be written in a
standard way.
<p>The first argument to the creation routine is a pointer to a
hash table entry. This may be <code>NULL</code>, in which case the
routine should allocate the right amount of space. Otherwise
the space has already been allocated by a hash table type
derived from this one.
<p>After allocating space, the creation routine must call the
creation routine of the hash table type it is derived from,
passing in a pointer to the space it just allocated. This
will initialize any fields used by the base hash table.
<p>Finally the creation routine must initialize any local fields
for the new hash table type.
<p>Here is a boilerplate example of a creation routine.
<var>function_name</var> is the name of the routine.
<var>entry_type</var> is the type of an entry in the hash table you
are creating. <var>base_newfunc</var> is the name of the creation
routine of the hash table type your hash table is derived
from.
<pre class="example"> struct bfd_hash_entry *
<var>function_name</var> (struct bfd_hash_entry *entry,
struct bfd_hash_table *table,
const char *string)
{
struct <var>entry_type</var> *ret = (<var>entry_type</var> *) entry;
/* Allocate the structure if it has not already been allocated by a
derived class. */
if (ret == NULL)
{
ret = bfd_hash_allocate (table, sizeof (* ret));
if (ret == NULL)
return NULL;
}
/* Call the allocation method of the base class. */
ret = ((<var>entry_type</var> *)
<var>base_newfunc</var> ((struct bfd_hash_entry *) ret, table, string));
/* Initialize the local fields here. */
return (struct bfd_hash_entry *) ret;
}
</pre>
<p><strong>Description</strong><br>
The creation routine for the linker hash table, which is in
<code>linker.c</code>, looks just like this example.
<var>function_name</var> is <code>_bfd_link_hash_newfunc</code>.
<var>entry_type</var> is <code>struct bfd_link_hash_entry</code>.
<var>base_newfunc</var> is <code>bfd_hash_newfunc</code>, the creation
routine for a basic hash table.
<p><code>_bfd_link_hash_newfunc</code> also initializes the local fields
in a linker hash table entry: <code>type</code>, <code>written</code> and
<code>next</code>.
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