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<a name="How-It-Works"></a>
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<p>
Next: <a href="What-BFD-Version-2-Can-Do.html#What-BFD-Version-2-Can-Do" accesskey="n" rel="next">What BFD Version 2 Can Do</a>, Previous: <a href="History.html#History" accesskey="p" rel="prev">History</a>, Up: <a href="Overview.html#Overview" accesskey="u" rel="up">Overview</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>
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<a name="How-To-Use-BFD"></a>
<h3 class="section">1.2 How To Use BFD</h3>

<p>To use the library, include <samp>bfd.h</samp> and link with <samp>libbfd.a</samp>.	
</p>
<p>BFD provides a common interface to the parts of an object file
for a calling application. 
</p>
<p>When an application successfully opens a target file (object, archive, or
whatever), a pointer to an internal structure is returned. This pointer
points to a structure called <code>bfd</code>, described in
<samp>bfd.h</samp>.  Our convention is to call this pointer a BFD, and
instances of it within code <code>abfd</code>.  All operations on
the target object file are applied as methods to the BFD.  The mapping is
defined within <code>bfd.h</code> in a set of macros, all beginning
with &lsquo;<samp>bfd_</samp>&rsquo; to reduce namespace pollution.
</p>
<p>For example, this sequence does what you would probably expect:
return the number of sections in an object file attached to a BFD
<code>abfd</code>. 
</p>
<div class="example">
<pre class="example">#include &quot;bfd.h&quot;

unsigned int number_of_sections (abfd)
bfd *abfd;
{
  return bfd_count_sections (abfd);
}
</pre></div>

<p>The abstraction used within BFD is that an object file has:
</p>
<ul>
<li> a header,
</li><li> a number of sections containing raw data (see <a href="Sections.html#Sections">Sections</a>),
</li><li> a set of relocations (see <a href="Relocations.html#Relocations">Relocations</a>), and
</li><li> some symbol information (see <a href="Symbols.html#Symbols">Symbols</a>).
</li></ul>
<p>Also, BFDs opened for archives have the additional attribute of an index
and contain subordinate BFDs. This approach is fine for a.out and coff,
but loses efficiency when applied to formats such as S-records and
IEEE-695.
</p>


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