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<div class="navheader"><table width="100%" summary="Navigation header"><tr><td width="20%" align="left"><a accesskey="p" href="deps.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="relx.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="ports"></a>Chapter 8. NIFs and port drivers</h2></div></div></div><p>Erlang.mk can not only build Erlang projects, but also the C code
that some projects come with, like NIFs and port drivers.</p><p>There are two ways to build the C code: using a custom Makefile,
or making Erlang.mk do it directly. The C code will be built
as needed when you run <code class="literal">make</code>.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_c_source_code_location_and_erlang_environment"></a>8.1. C source code location and Erlang environment</h2></div></div></div><p>The C source code should be located in the <span class="emphasis"><em>$(C_SRC_DIR)</em></span> directory.
It defaults to <span class="emphasis"><em>c_src/</em></span>. Should you need to modify it, all you
need to do is to set the variable in your Makefile before including
Erlang.mk:</p><pre class="programlisting">C_SRC_DIR = $(CURDIR)/my_nif_source</pre><p>When this directory exists, Erlang.mk will automatically create a
file named <span class="emphasis"><em>$(C_SRC_ENV)</em></span>. This file defaults to <span class="emphasis"><em>$(C_SRC_DIR)/env.mk</em></span>.
This can also be changed:</p><pre class="programlisting">C_SRC_ENV = $(C_SRC_DIR)/erlang_env.mk</pre><p>It contains a few variable definitions for the environment used for the build:</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">
<code class="literal">ERTS_INCLUDE_DIR</code>
</span></dt><dd>
Path to the ERTS include files (<span class="emphasis"><em>erl_driver.h</em></span>, <span class="emphasis"><em>erl_nif.h</em></span> and more).
</dd><dt><span class="term">
<code class="literal">ERL_INTERFACE_INCLUDE_DIR</code>
</span></dt><dd>
Path to the Erl_Interface include files (<span class="emphasis"><em>ei.h</em></span> and related).
</dd><dt><span class="term">
<code class="literal">ERL_INTERFACE_LIB_DIR</code>
</span></dt><dd>
Path to the Erl_Interface static libraries.
</dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_using_a_custom_makefile"></a>8.2. Using a custom Makefile</h2></div></div></div><p>Erlang.mk will automatically run <code class="literal">make</code> if it detects a Makefile
in <span class="emphasis"><em>$(C_SRC_DIR)/Makefile</em></span>.</p><p>The Makefile should have at least two targets: a default target
(which can be anything, for example <code class="literal">all</code>) which is invoked when
building the C code, and a <code class="literal">clean</code> target invoked when cleaning
it.</p><p>You can include the <span class="emphasis"><em>env.mk</em></span> file to benefit from the Erlang
environment detection:</p><pre class="programlisting">include env.mk</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="_using_erlang_mk_directly"></a>8.3. Using Erlang.mk directly</h2></div></div></div><p>You don’t need to write a Makefile to build C source code, however.
Erlang.mk comes with rules to build both shared libraries and
executables, using the source files it finds in <span class="emphasis"><em>$(C_SRC_DIR)</em></span>.</p><p>By default, Erlang.mk will create a shared library. To change
this and create an executable instead, put this in your Makefile
before including Erlang.mk:</p><pre class="programlisting">C_SRC_TYPE = executable</pre><p>The generated file name varies depending on the type of project
you have (shared library or executable) and on the platform you
build the project on.</p><p>For shared libraries, the generated file name will be
<span class="emphasis"><em>$(C_SRC_OUTPUT)$(C_SRC_SHARED_EXTENSION)</em></span>, with the default
being <span class="emphasis"><em>$(CURDIR)/priv/$(PROJECT)</em></span> followed by the extension:
<code class="literal">.dll</code> on Windows, <code class="literal">.so</code> everywhere else.</p><p>For executables, the generated file name is
<span class="emphasis"><em>$(C_SRC_OUTPUT)$(C_SRC_EXECUTABLE_EXTENSION)</em></span>, with the same
default except for the extension: <code class="literal">.exe</code> on Windows, and otherwise
nothing.</p><p>Erlang.mk sets appropriate compile and linker flags by default.
These flags vary depending on the platform, and can of course
be overriden.</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">
<code class="literal">CC</code>
</span></dt><dd>
The compiler to be used.
</dd><dt><span class="term">
<code class="literal">CFLAGS</code>
</span></dt><dd>
C compiler flags.
</dd><dt><span class="term">
<code class="literal">CXXFLAGS</code>
</span></dt><dd>
C++ compiler flags.
</dd><dt><span class="term">
<code class="literal">LDFLAGS</code>
</span></dt><dd>
Linker flags.
</dd><dt><span class="term">
<code class="literal">LDLIBS</code>
</span></dt><dd>
Libraries to link against.
</dd></dl></div><p>The source files are automatically gathered from the contents
of <span class="emphasis"><em>$(C_SRC_DIR)</em></span>. Erlang.mk looks for <span class="emphasis"><em>.c</em></span>, <span class="emphasis"><em>.C</em></span>, <span class="emphasis"><em>.cc</em></span> and <span class="emphasis"><em>.cpp</em></span>
source files. You can define the variable <code class="literal">SOURCES</code> to manually
list the files to compile.</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="deps.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="code.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="relx.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> </td></tr></table></div>
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