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<H1><A NAME="SECTION02340000000000000000"></A><A NAME="1558"></A>
<BR>
Writing the Client
</H1>
<P>
We will write the client in the main hello/ subdirectory.
The main program will be written in C.
File hello.c is as follows:
<P>
<BR>
<PRE CLASS="verbatim">#include <stdio.h>
#include "Hello_World.h"
int main(int argc, char** argv)
{
Hello_World h = Hello_World__create();
char* msg = Hello_World_getMsg(h);
printf("%s\n", msg);
Hello_World_deleteRef(h);
free(msg);
}
</PRE></td></tr></table></blockquote>
<P>
This code creates the Hello_World object, calls the getMsg() method,
prints the ubiquitous saying, decrements the reference count for
the object, and frees the message string.
<P>
There are a few details worth noting here. The C bindings
generate function names by combining packages, classes, and method names
with underscores (e.g. <TT>Hello_World_getMsg()</TT>. Whenever you
see double underscores<A NAME="1561"></A> in Babel generated symbols, they indicate something
built-in to (and sometimes specific to) the language binding.
The <TT>_create()</TT> method is built-in to every instantiatable class
defined in SIDL, triggering the creation of Babel internal data structures
as well as the constructor of the actual object implementation.
<P>
To generate<A NAME="1563"></A> the C glue code necessary to call the library,
we run the Babel tool again, this time specifying C as the target language:
<P>
<BLOCKQUOTE>
<TT> <TT>%</TT> <TT><B>babel -client=C hello.sidl</B></TT>
<BR>
</TT></BLOCKQUOTE>or simply
<BLOCKQUOTE>
<TT> <TT>%</TT> <TT><B>babel -cC hello.sidl</B></TT>
<BR>
</TT></BLOCKQUOTE>
<P>
The ``<TT>-cC</TT>'' flag,
or its equivalent long-form ``<TT>-client=C</TT>'', tells the
Babel code generator to create only the C stub calling code,
not the entire library implementation.
The library libhello.so already contains the
necessary IOR, skeleton, and implementation object files.
We compile the hello program using the following GNU Make
Makefile:<A NAME="1572"></A>
<P>
<BR>
<PRE CLASS="verbatim">.c.o:
gcc -I$(HOME)/babel/include -Ilib -c $<
include babel.make
OBJS = hello.o ${STUBSRCS:.c=.o}
hello: ${OBJS}
gcc ${OBJS} -o $@ \
-Rlib -Llib -lhello \
-R$(HOME)/babel/lib -L$(HOME)/babel/lib -lsidl
clean:
${RM} *.o hello
</PRE></td></tr></table></blockquote>
<P>
Note that the ``-R'' flags tell the dynamic library loader where to find the
hello and sidl shared libraries.
You could achieve the same behavior through environment
variables such as <TT>LD_LIBRARY_PATH</TT>.
On some machines and compilers (notably linux-gcc-3.0) the -R flag
is no longer supported, so you will have to modify the
appropriate environment variable to find the shared library.
<P>
Finally, we make the executable and run it:
<P>
<BLOCKQUOTE>
<TT> <TT>%</TT> <TT><B>make hello</B></TT>
<BR><TT>%</TT> <TT><B>./hello</B></TT>
<BR>
Hello World
</TT></BLOCKQUOTE>
<P>
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<br><br>babel-0.10.2<br>users_guide Last Modified 2005-03-23<br><br><a href="http://www.llnl.gov/CASC/components">http://www.llnl.gov/CASC/components</a><br><a href="mailto:components@llnl.gov">components@llnl.gov</a>
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