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<h1>7 The C Client Back-end</h1>
<h3><a name="id73982">7.1
Introduction</a></h3>
<p>With the option <span class="code">{be, c_client}</span> the IDL Compiler generates
C client stubs according to the IDL to C mapping, on top of the
Erlang distribution and gen_server protocols.</p>
<p>The developer has to write additional code, that together with
the generated C client stubs, form a hidden Erlang node. That
additional code uses <span class="code">erl_interface</span> functions for defining
the hidden node, and for establishing connections to other
Erlang nodes.</p>
<h3><a name="id74007">7.2
Generated Stub Files</a></h3>
<p>The generated stub files are:</p>
<ul>
<li>
<p>For each IDL interface, a C source file, the name of which
is <span class="code"><Scoped Interface Name>.c</span>. Each operation of the
IDL interface is mapped to a C function (with scoped name)
in that file;</p>
</li>
<li>
<p>C source files that contain functions for type conversion,
memory allocation, and data encoding/decoding;</p>
</li>
<li>
<p>C header files that contain function prototypes and type
definitions.</p>
</li>
</ul>
<p>All C functions are exported (i.e. not declared static).</p>
<h3><a name="id74057">7.3
C Interface Functions</a></h3>
<p>For each IDL operation a C interface function is
generated, the prototype of which is:</p>
<p><span class="code"><Return Value> <Scoped Function Name>(<Interface Object> oe_obj, <Parameters>, CORBA_Environment *oe_env);</span></p>
<p>where</p>
<ul>
<li>
<p><span class="code"><Return Value></span> is the value to be returned as defined
by the IDL specification;</p>
</li>
<li>
<p><span class="code"><Interface Object> oe_obj</span> is the client interface
object;</p>
</li>
<li>
<p><span class="code"><Parameters></span> is a list of parameters of the
operation, defined in the same order as defined by the IDL
specification;</p>
</li>
<li>
<p><span class="code">CORBA_Environment *oe_env</span> is a pointer to the current
client environment. It contains the current file descriptor,
the current input and output buffers, etc. For details see
<span class="bold_code"><a href="ch_c_corba_env.html#corbaenv">CORBA_Environment C Structure</a></span>.</p>
</li>
</ul>
<h3><a name="id74134">7.4
Generating, Compiling and Linking</a></h3>
<p>To generate the C client stubs type the following in an
appropriate shell:</p>
<p><span class="code">erlc -I ICROOT/include "+{be, c_client}" File.idl</span>,</p>
<p>where <span class="code">ICROOT</span> is the root of the IC application. The
<span class="code">-I ICROOT/include</span> is only needed if <span class="code">File.idl</span>
refers to <span class="code">erlang.idl</span>.</p>
<p>When compiling a generated C stub file, the directories
<span class="code">ICROOT/include</span> and <span class="code">EICROOT/include</span>, have to be
specified as include directories, where <span class="code">EIROOT</span> is the
root directory of the Erl_interface application.</p>
<p>When linking object files the <span class="code">EIROOT/lib</span> and
<span class="code">ICROOT/priv/lib</span> directories have to be specified. </p>
<h3><a name="id74198">7.5
An Example</a></h3>
<p>In this example the IDL specification file "random.idl" is used
for generating C client stubs (the file is contained in the IC
<span class="code">/examples/c-client</span> directory):</p>
<div class="example"><pre>
module rmod {
interface random {
double produce();
oneway void init(in long seed1, in long seed2, in long seed3);
};
}; </pre></div>
<p>Generate the C client stubs:</p>
<div class="example"><pre>
erlc '+{be, c_client}' random.idl
Erlang IDL compiler version X.Y.Z </pre></div>
<p>Six files are generated. </p>
<p>Compile the C client stubs:</p>
<p>Please read the <span class="code">ReadMe</span> file att the
<span class="code">examples/c-client</span> directory</p>
<p>In the same
directory you can find all the code for this example.</p>
<p>In particular you will find the <span class="code">client.c</span> file that contains
all the additional code that must be written to obtain a complete
client. </p>
<p>In the <span class="code">examples/c-client</span> directory you will also find
source code for an Erlang server, which can be used for testing
the C client.</p>
</div>
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