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