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<TITLE>The C Client Back-end</TITLE>
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<A NAME="7"><!-- Empty --></A>
<H2>7 The C Client Back-end</H2>
<A NAME="7.1"><!-- Empty --></A>
<H3>7.1 Introduction</H3>
<P> With the option <CODE>{be, c_client}</CODE> 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> The developer has to write additional code, that together with
the generated C client stubs, form a hidden Erlang node. That
additional code uses <CODE>erl_interface</CODE> functions for defining
the hidden node, and for establishing connections to other
Erlang nodes.
<A NAME="7.2"><!-- Empty --></A>
<H3>7.2 Generated Stub Files</H3>
<P> The generated stub files are:
<P>
<UL>
<LI>
For each IDL interface, a C source file, the name of which
is <CODE><Scoped Interface Name>.c</CODE>. Each operation of the
IDL interface is mapped to a C function (with scoped name)
in that file;
<BR>
</LI>
<LI>
C source files that contain functions for type conversion,
memory allocation, and data encoding/decoding;
<BR>
</LI>
<LI>
C header files that contain function prototypes and type
definitions.
<BR>
</LI>
</UL>
<P> All C functions are exported (i.e. not declared static).
<A NAME="7.3"><!-- Empty --></A>
<H3>7.3 C Interface Functions</H3>
<P> For each IDL operation a C interface function is
generated, the prototype of which is:
<P> <CODE><Return Value> <Scoped Function Name>(<Interface Object>
oe_obj, <Parameters>, CORBA_Environment *oe_env);</CODE>
<P>where
<P>
<UL>
<LI>
<CODE><Return Value></CODE> is the value to be returned as defined
by the IDL specification;
<BR>
</LI>
<LI>
<CODE><Interface Object> oe_obj</CODE> is the client interface
object;
<BR>
</LI>
<LI>
<CODE><Parameters></CODE> is a list of parameters of the
operation, defined in the same order as defined by the IDL
specdication;
<BR>
</LI>
<LI>
<CODE>CORBA_Environment *oe_env</CODE> is a pointer to the current
client environment. It contains the current file descriptor,
the current input and output buffers, etc. For details see
<A HREF="ch_c_corba_env.html#corbaenv">CORBA_Environment
C Structure</A>.
<BR>
</LI>
</UL>
<A NAME="7.4"><!-- Empty --></A>
<H3>7.4 Generating, Compiling and Linking</H3>
<P> To generate the C client stubs type the following in an
appropriate shell:
<P>
<CODE>erlc -I ICROOT/include "+{be, c_client}" File.idl</CODE>,
<P> where <CODE>ICROOT</CODE> is the root of the IC application. The
<CODE>-I ICROOT/include</CODE> is only needed if <CODE>File.idl</CODE>
refers to <CODE>erlang.idl</CODE>.
<P> When compiling a generated C stub file, the directories
<CODE>ICROOT/include</CODE> and <CODE>EICROOT/include</CODE>, have to be
specified as include directories, where <CODE>EIROOT</CODE> is the
root directory of the Erl_interface application.
<P> When linking object files the <CODE>EIROOT/lib</CODE> and
<CODE>ICROOT/priv/lib</CODE> directories have to be specified.
<A NAME="7.5"><!-- Empty --></A>
<H3>7.5 An Example</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
<CODE>/examples/c-client</CODE> directory):
<PRE>
module rmod {
interface random {
double produce();
oneway void init(in long seed1, in long seed2, in long seed3);
};
};
</PRE>
<P>Generate the C client stubs:
<PRE>
erlc '+{be, c_client}' random.idl
Erlang IDL compiler version X.Y.Z
</PRE>
<P> Six files are generated.
<P>Compile the C client stubs:
<P> Please read the <CODE>ReadMe</CODE> file att the
<CODE>examples/c-client</CODE> directory
<P>In the same
directory you can find all the code for this example.
<P> In particular you will find the <CODE>client.c</CODE> file that contains
all the additional code that must be written to obtain a complete
client.
<P> In the <CODE>examples/c-client</CODE> directory you will also find
source code for an Erlang server, which can be used for testing
the C client.
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