It''s hard to search for this topic, because a lot of sites concerning C++ templates use the word C... sorry. If I want to do something as (seemingly) simple as writing a reusable linked list implementation, how would I go about it in C? I realize that I could just use void* for all of my nodes, and just cast them, but is there some slick way using typedefs and macros, etc., to allow for an unknown type that can be determined at runtime?

I didn''t see a delete button, but I saw it under edit (finally)... I deleted them, but I think they''re still there.

Sorry.

What the hell, I''ll bite.

First off, unlike templates in C++, your system will be evaluated at runtime (templates are evaluated at compile time). The system will actually have a lot in common with implementing OO in C (so you might as well do it, too). Consider the following C++ fragment:

template < typename T >void SomeFunction( const T & t ){  t.generic_method();}

This application of templates requires a means for determining that the actual type instantiating the template (T) has the method generic_method. This is trivial in C++ because the code is fully expanded and then passed to the compiler, which simply looks into the symbol table. Since your system would be evaluated at runtime, you''d have to store an explicit symbol table which would be searched.

Furthermore, since neither C nor C++ is introspective (there is no way to programmatically query an entity as to its properties), you''ll need to use specific tokens as associative indices to indicate the existence of a certain function in an object''s interface. This could simply be the function name (an entry with the key "find" indicates the existence of a function find()).

C is not inherently object-oriented and doesn''t support inheritance, so all your objects must actually be of one type in C, but masquerade as being of different types. This is the hard part. You need to store a generic reference to all your objects (void *), but supply a conversion mechanism to recover the original object complete with type. This suggests typecasting, and would be easy if the function-style typecast could be assigned to a function pointer. Unfortunately it can''t, AFAICT.

This is such an intrinsic problem that I am unable to think of a workaround or solution. So you''re SOL.

Wasn''t that fun!

I'm actually being forced to take C programming at school, only because it is a prerequisite for all of the other computer science classes I already have that are transferring (CSI, CSII, CSIII, etc...) You'd think since I have the classes that it is a prereq for... nevermind. In any case, I talked them into at least letting me skip to *ADVANCED* C, which is still a joke.

We are supposedly covering linked lists this week, and since I have already known how to do those for 10 years or so, I figured I would try to spice things up just for fun.

My point is, I CAN'T USE C++... I just wanted something "fun".



[edited by - smitty1276 on February 16, 2004 10:19:27 PM]

I tried the define thing, and I kept getting weird errors... maybe I''ll try again. It was just a quick attempt and I didn''t really do any trouble shooting.

Thanks for the responses.