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<p>Usually, Boost.Build handles implicit dependendies completely
automatically. For example, for C++ files, all <code class="literal">#include</code>
statements are found and handled. The only aspect where user help
might be needed is implicit dependency on generated files.</p>
<p>By default, Boost.Build handles such dependencies within one
main target. For example, assume that main target "app" has two
sources, "app.cpp" and "parser.y". The latter source is converted
into "parser.c" and "parser.h". Then, if "app.cpp" includes
"parser.h", Boost.Build will detect this dependency. Moreover,
since "parser.h" will be generated into a build directory, the
path to that directory will automatically added to include
path.</p>
<p>Making this mechanism work across main target boundaries is
possible, but imposes certain overhead. For that reason, if
there's implicit dependency on files from other main targets, the
<code class="literal"><implicit-dependency></code> [ link ] feature must
be used, for example:</p>
<pre class="programlisting">
lib parser : parser.y ;
exe app : app.cpp : <implicit-dependency>parser ;
</pre>
<p>
The above example tells the build system that when scanning
all sources of "app" for implicit-dependencies, it should consider
targets from "parser" as potential dependencies.
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