NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part2/17917

Internet Message Format | 1996-08-05 | 2.8 KB

Path: library.erc.clarkson.edu!rpi!not-for-mail
From: [e-mail] (J. Kanze)
Newsgroups: comp.lang.c++,comp.lang.c++.moderated
Subject: Re: Dynamic class definitions in C++: possible?
Date: 17 Apr 1996 15:13:49 -0000
Organization: GABI Software, Sarl.
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References: <4ko91f$[e-mail]> <4koodt$[e-mail]>
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X-Original-Date: 17 Apr 1996 14:42:11 GMT

In article <4koodt$[e-mail]> [e-mail] (John
Lockwood) writes:

|> [e-mail] (Kyle F. Downey) wrote:

|> >1) load a C++ class definition from a file
|> >2) convert it to an internal format
|> >3) use the class just as you would a compiled class

|> >This would allow you to add a class at run-time based on a
|> >text/user-supplied definition.

|> Why not rethink the problem?

|> 1) Read some data from a file.
|> 2) Do something with this data using the rich language features that
|> C++ offers (polymorphism, templates, etc).
|> 3) Make your program work just as if you'd implemented it using
|> some wierd JAVA-inspired idea.

|> I'm not trying to be intentionally dense here.  If there are problems
|> that can only be solved in the way you've outlined and not in the way
|> I have, I'd be interested if you or others would chime in.

There is one frequent use for this sort of thing: upgrading the software
of an installation without stopping it.  For example, if you want a
telephone switch to handle a new type of terminal, you write the code
for the new class (which derives from the class `Terminal' already known
to the system), then add it to a running system.

Coplien discusses several (very) non-portable solutions to do this.
Under most systems, however, I would see if something along the lines of
implemening a command to load a DLL in the original software wouldn't
work.  If this is possible, then all you should have to do to add a new
type is to link the code as a DLL, then load it.  (I am also supposing
here that any static variables in the DLL will be constructed when the
DLL is loaded.  One static variable would contain all of the pertinate
information concerning the new terminal type, and would register itself
with the existing software in its constructor.)
--
James Kanze           ([phone]          email: [e-mail]
GABI Software, Sarl., 8 rue des Francs Bourgeois, 67000 Strasbourg, France
Conseils en informatique industrielle --
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