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<H1><A NAME="SECTION03250000000000000000"></A>
<A NAME="6608"></A>
<BR>
Calling Methods from C++
</H1>
Since C++ is an object-oriented language, there is a lot less programmer
overhead in using SIDL from the C++ perspective than from non-OO
languages such as C or FORTRAN 77.
<P>
<A NAME="6609"></A><A NAME="6610"></A>
<A NAME="6611"></A><A NAME="6612"></A>
<A NAME="6613"></A>
<P>
<BR><P></P>
<DIV ALIGN="CENTER">
<A NAME="tbl:cxx:features"></A>
<DIV ALIGN="CENTER">
<A NAME="6615"></A>
<TABLE CELLPADDING=3 BORDER="1">
<CAPTION><STRONG>Table 7.2:</STRONG>
SIDL Features Mapped onto C++</CAPTION>
<TR><TH ALIGN="CENTER"><SPAN CLASS="textbf">SIDL Feature</SPAN></TH>
<TH ALIGN="LEFT" VALIGN="TOP" WIDTH=342><SPAN CLASS="textbf">C++ Implementation</SPAN></TH>
</TR>
<TR><TD ALIGN="CENTER">packages</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=342>C++ namespaces (no name transformations)</TD>
</TR>
<TR><TD ALIGN="CENTER">version numbers</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=342>ignored</TD>
</TR>
<TR><TD ALIGN="CENTER">interface</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=342>C++ class (called "stub", serves as a proxy to the implementation)</TD>
</TR>
<TR><TD ALIGN="CENTER">class</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=342>C++ class (called "stub", serves as a proxy to the implementation)</TD>
</TR>
<TR><TD ALIGN="CENTER">methods</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=342>C++ member functions; uses base method name when overloading; no name
mangling;
NOTE: Member functions beginning with a leading underscore
"_" may be Babel internals, or specific to C++ binding.</TD>
</TR>
<TR><TD ALIGN="CENTER">static methods</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=342>Static C++ member functions; uses base method name when overloading;
no name mangling;
even works for dynamically loaded object's exceptions
thrown and caught using C++ exception handling.</TD>
</TR>
<TR><TD ALIGN="CENTER">reference counting</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=342>SIDL C++ stubs can be treated as smart-pointers.
Constructors, destructors, and operators are overloaded
so that explicit
calls to <TT>addRef()</TT> or <TT>deleteRef()</TT>
are rarely needed.</TD>
</TR>
<TR><TD ALIGN="CENTER">casting</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=342>Assignment operators are overloaded to handle safe
casting up and down the inheritance hierarchy.
User should never call <TT>dynamic_cast<>()</TT> on a
SIDL object since the stubs inheritance hierarchy
does not follow the SIDL inheritance hierarchy.
Attempted downcasts using assignment should be checked
by a call to (<TT>_is_nil()</TT>, or <TT>_not_nil()</TT>).</TD>
</TR>
<TR><TD ALIGN="CENTER">instance creation</TD>
<TD ALIGN="LEFT" VALIGN="TOP" WIDTH=342>Use static member function "<TT>_create</TT>". The
default constructor for a C++ stub creates the
equivalent of a NULL pointer. Works only
with non-abstract classes.</TD>
</TR>
</TABLE>
</DIV>
</DIV>
<BR>
<P>
These proxy classes (we call "stubs") serve as the firewall
between the application in C++ and Babel's internal workings.
As one would expect, the proxy classes maintain minimal state so that,
unlike C or FORTRAN 77, there is no special context argument added to
non-static member functions.
<P>
Below are examples using standard classes. The first is an example of creating
an object of the base class and its association to the base interface.
<P>
<BR>
<PRE CLASS="verbatim">sidl::BaseClass object = sidl::BaseClass::_create();
sidl::BaseInterface interface = object;
</PRE></td></tr></table></blockquote>
<P>
Here is an example call to the addSearchPath in the SIDL.Loader class:
<P>
<BR>
<PRE CLASS="verbatim">std::string s("/try/looking/here");
sidl::Loader::addSearchPath( s );
</PRE></td></tr></table></blockquote>
<P>
Examples of calls to SIDL overloaded methods are based on the
<TT>overload_sample.sidl</TT> file shown in Section <A HREF="node107.html#sec:overloading">5.6</A>.
Recall that the file describes three versions of the <TT>getValue</TT> method.
The first takes no arguments, the second takes an integer argument, and the
third takes a boolean. Each is called in the code snippet below:
<P>
<BR>
<PRE CLASS="verbatim">
bool b1, bresult;
int i1, iresult, nresult;
Overload::Sample t = Overload::Sample::_create();
nresult = t.getValue();
bresult = t.getValue(b1);
iresult = t.getValue(i1);
</PRE></td></tr></table></blockquote>
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