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<a name="Outer-macros-1"></a>
<h3 class="section">7.1 Outer macros</h3>

<a name="index-Macros_002c-outer"></a>
<p>Outer macros provide a shorthand way of invoking macro definitions in
the source language; they are not expanded by <small>FWEB</small>.  Outer macros are
defined by &lsquo;<samp>@d</samp>&rsquo; (see <a href="ATd.html#ATd">ATd</a>) or &lsquo;<samp>@D</samp>&rsquo;
(see <a href="ATD_005f.html#ATD_005f">ATD_</a>).  They may be placed in any definition part.  <small>FTANGLE</small>
collects them during phase 1; during phase 2, they are simply copied in
order of their appearance to the beginning of the output file.  This is
most useful for C or C++ codes; it&rsquo;s a quick way of typing
&lsquo;<samp>#define</samp>&rsquo; when the positioning of the &lsquo;<samp>#define</samp>&rsquo; is
unimportant.
</p>
<p>As an example,
</p>
<div class="example">
<pre class="example">@c
@
@d YES 1
@d NO 0
@a
main()
{}

@
@d BUF_LEN 100
@a
...
</pre></div>

<p>The keyword into which the &lsquo;<samp>@d</samp>&rsquo; is translated is
language-dependent; it is controlled by the style-file parameter
&lsquo;<samp>outer_def</samp>&rsquo;. See <a href="Miscellaneous-params.html#Miscellaneous-params">Miscellaneous params</a>.
</p>
<p>Outer macros can be undefined by &lsquo;<samp>@u</samp>&rsquo;.  The translation is
controlled by the style-file parameter &lsquo;<samp>outer_undef</samp>&rsquo;.
See <a href="Miscellaneous-params.html#Miscellaneous-params">Miscellaneous params</a>.
</p>
<p>The default behavior, in which the outer macro definitions are just
copied to the top of the output file, is fine for simple applications.
However, often C programmers prefer to maintain their macro definitions
in a header file such as <samp>test.h</samp>.  One way of accomplishing this is to
redirect <small>FTANGLE</small>&rsquo;s output from the command line, as in
&lsquo;<samp>ftangle test -=test.h</samp>&rsquo;, then use an &lsquo;<samp>@O</samp>&rsquo; command immediately
after the first &lsquo;<samp>@a</samp>&rsquo; in the <code>web</code> file to open up
<samp>test.c</samp>.  A more complicated variant of this allows additional
information to be placed into the header file, as in the following example:
</p>
<div class="example">
<pre class="example">@c
@* INTRO.
We assume command-line redirection into \.{test.h} (`\.{-=test.h}').

@d A 1 // This will go into \.{test.h}.

@a
@&lt;Header material@&gt;@; // Also goes into \.{test.h}.
@O test.c // Remaining unnamed sections go into \.{test.c}.

@ Header material may be defined as needed throughout the code, but
with this design it will all go into \.{test.h}.

@&lt;Header material@&gt;=

@&lt;Includes@&gt;@;
@&lt;Typedefs@&gt;@;
@&lt;Global variables@&gt;@;

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