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copied!<p>In C anyway you an do it the way cfront used to do it in the early days of C++ when the C++ code was translated into C. But you need to be quite disciplined and do all the grunt work manually.</p> <p>Your 'classes' have to be initialized using a function that performs the constructor's work. this will include initializing a pointer to a table of polymorphic function pointers for the virtual functions. Virtual function calls have to be made through the vtbl function pointer (which will point to a structure of function pointers - one for each virtual function).</p> <p>The virtual function structure for each derived calss needs to be a super-set of the one for the base class.</p> <p>Some of the mechanics of this might be hidden/aided using macros.</p> <p>Miro Samek's first edition of <a href="http://www.state-machine.com/resources/index.htm" rel="nofollow noreferrer">"Practical Statecharts in C/C++"</a> has an Appendix A - "C+ - Object Oriented Programming in C" that has such macros. It looks like this was dropped from the second edition. Probably because it's more trouble than it's worth. Just use C++ if you want to do this...</p> <p>You should also read <a href="http://www.pearsonhighered.com/educator/product/Inside-the-C-Object-Model/9780201834543.page" rel="nofollow noreferrer">Lippman's "Inside the C++ Object Model"</a> which goes into gory details about how C++ works behind the scenes, often with snippets of how things might work in C.</p> <hr> <p>I think I see what you're after. Maybe.</p> <p>How can something like this work:</p> <pre><code>typedef struct foo { int a; } foo; void doSomething( foo f); // note: f is passed by value typedef struct bar { foo base; int b; } bar; int main() { bar b = { { 1 }, 2}; doSomething( b); // how can the compiler know to 'slice' b // down to a foo? return 0; } </code></pre> <p>Well you can't do that as simply as that without language support - you'd need to do some things manually (that's what it means to not have language support):</p> <pre><code> doSomething( b.base); // this works </code></pre>

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