Inspired by Minecraft (like countless other people out there) I decided to give a clone a try to see how this can be accomplished. My last few adventures into the 3D world went through C++ but that always presented me with a problem: The C++ code I write does not scale well to computer games. This time I thought I can probably try to work around the problem by forcing myself to simple C.
This worked really well up to the point where I needed two kinds of lists. One that accepted floats and another one that works with arbitrary pointers.
The C++ way for this is obvious: use templates. That's also one of the best features in C++ and works surprisingly well for the (I imagine) great hack it is. However in C we don't have that but the closest to templates in C (or code generation in general) is the preprocessor.
A warning upfront: all these examples use very generic names. This is a very bad idea. If you want to use something like this in your own code, make sure to prefix all macros, functions, types etc. with a unique prefix. (For instance instead of CAT name it MYLIB_CAT).
Abusing the Preprocessor
Generally there are two ways to do code generation for C. One involves external tools that create new C files, the other involves the C preprocessor which is normally intended to expand macros, include other files or remove comments before the compiler goes over your code.
I normally like to avoid tools that generate new C files for the very simple reason that these usually generate ugly looking code I then have to look at which is annoying or at least require yet another tool in my toolchain which causes headaches when compiling code on more than on operating system. A simple Python script that generates a C file sounds simple, but it stops being simple if you also want that thing to be part of your windows installation where Python is usually not available or works differently.
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Armin Ronacher's Thoughs and Writings
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