<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- This file documents the BFD library.

Copyright (C) 1991 - 2013 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License" and "Funding
Free Software", the Front-Cover texts being (a) (see below), and with
the Back-Cover Texts being (b) (see below).  A copy of the license is
included in the section entitled "GNU Free Documentation License".

(a) The FSF's Front-Cover Text is:

A GNU Manual

(b) The FSF's Back-Cover Text is:

You have freedom to copy and modify this GNU Manual, like GNU
     software.  Copies published by the Free Software Foundation raise
     funds for GNU development. -->
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
<head>
<title>Untitled Document: Write the Derived Creation Routine</title>

<meta name="description" content="Untitled Document: Write the Derived Creation Routine">
<meta name="keywords" content="Untitled Document: Write the Derived Creation Routine">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link href="index.html#Top" rel="start" title="Top">
<link href="BFD-Index.html#BFD-Index" rel="index" title="BFD Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="Deriving-a-New-Hash-Table-Type.html#Deriving-a-New-Hash-Table-Type" rel="up" title="Deriving a New Hash Table Type">
<link href="Write-Other-Derived-Routines.html#Write-Other-Derived-Routines" rel="next" title="Write Other Derived Routines">
<link href="Define-the-Derived-Structures.html#Define-the-Derived-Structures" rel="prev" title="Define the Derived Structures">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.indentedblock {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
div.smalllisp {margin-left: 3.2em}
kbd {font-style:oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nocodebreak {white-space:nowrap}
span.nolinebreak {white-space:nowrap}
span.roman {font-family:serif; font-weight:normal}
span.sansserif {font-family:sans-serif; font-weight:normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
<a name="Write-the-Derived-Creation-Routine"></a>
<div class="header">
<p>
Next: <a href="Write-Other-Derived-Routines.html#Write-Other-Derived-Routines" accesskey="n" rel="next">Write Other Derived Routines</a>, Previous: <a href="Define-the-Derived-Structures.html#Define-the-Derived-Structures" accesskey="p" rel="prev">Define the Derived Structures</a>, Up: <a href="Deriving-a-New-Hash-Table-Type.html#Deriving-a-New-Hash-Table-Type" accesskey="u" rel="up">Deriving a New Hash Table Type</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="BFD-Index.html#BFD-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Write-the-derived-creation-routine"></a>
<h4 class="subsubsection">2.18.4.2 Write the derived creation routine</h4>
<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>
<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>
<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>
<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>
<p>Finally the creation routine must initialize any local fields
for the new hash table type.
</p>
<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.
</p>

<div class="example">
<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></div>
<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>
<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>.
</p>
<hr>
<div class="header">
<p>
Next: <a href="Write-Other-Derived-Routines.html#Write-Other-Derived-Routines" accesskey="n" rel="next">Write Other Derived Routines</a>, Previous: <a href="Define-the-Derived-Structures.html#Define-the-Derived-Structures" accesskey="p" rel="prev">Define the Derived Structures</a>, Up: <a href="Deriving-a-New-Hash-Table-Type.html#Deriving-a-New-Hash-Table-Type" accesskey="u" rel="up">Deriving a New Hash Table Type</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="BFD-Index.html#BFD-Index" title="Index" rel="index">Index</a>]</p>
</div>


</body>
</html>