Sometimes it is a useful sin, many data structure libraries for C use this for:

1) genericity 2) (extreme) speed

It's (unfortunately) impossible for C to equal C++ templates in this: write once, use for multiple datatypes (without macros).

For people who like copy pasting, generic macros is on the horizon for C11, which is rapidly being implemented (and mostly works) for Clang and GCC, the most important compilers. Read more about it here: http://www.robertgamble.net/2012/01/c11-generic-selections.h...

Simply put, it allows to create a small "shim"-macro that detects the type of the input parameters and redirect to an actual function based on type.

What's wrong with that? It allows you to write type-safe sort-of-generic data structures. It's certainly better than 'generic' data structures that work on void*'s.