Generating C code for functions of different signatures, but same implementation

Question

A situation I run into a lot in writing C code (context is scientific computation) is that I will have functions which have exactly the same body modulo minor type differences. I realize C++ offers the template feature and function overloading which allows one to have only one copy of said function and let the compiler figure out what signature you meant to use when you build.

While this is a great feature in C++, my project is in C and I furthermore do not need the full power of templating. So far what I have tried is m4 macros on a candidate source file, and this spits out respective .c files with appropriate name mangling for the different types I need. The preprocessor could therefore accomplish this as well, but I'm attempting to avoid using it in complicated ways (my code needs to be understandable for reproducibility reasons). I'm not very good with m4, so all the files have been hacks that only work in specific cases and are inapplicable in new situations.

What do other people programming in C do when this is necessary? Manually produce and maintain the different permutations of function signatures? I'm hoping that isn't the best answer, or that a tool exists to automate this dreary and error prone task.

Apologies for vagueness, let me give a toy example. Suppose I have need to add two numbers. The function might look something like this:

float add(float x,float y){
   return x+y;
}

Ok that's great for floats, but what if I need it for a wide range of types on which arithmetic is available. Ok I can do this

float add_f(float x,float y){...}
double add_lf(double x,double y){...}
unsigned int add_ui(unsigned int x, unsigned int y){...}

and so forth. If for some (probably stupid) reason I decide I need to also write the contents of the arguments to a binary file, I now have to add in the requisite file I/O code in every single function. Is there a simple way/tool to take an add function and spit out different ones with name mangling to avoid this annoying situation?

Basically in my m4 cases I would just find/replace a macro TYPE with the requisite type, and have a macro MANGLE() which mangles the functions, then I point the output to an alternate .c file. My m4 skills are lacking though.

Function pointers can help with the ultimate interface of my code, but eventually those pointers have to point to something, and then we're just enumerating all the possibilities again. I'm also unclear on how this might affect potential inlining of short functions.

Answer 1

The only thing i can think of is: make the algorithm itself independent of the type, have the user of your function create his own function to handle the type-specific parts, and make one of the parameters to your function a pointer to the "handler function".

See the definition/implementation of the qsort routine for what i mean. Qsort works for all kinds of data, but handles the data itself transparently - the only things you pass to qsort is the size of each entry, and a function pointer to a function that does the real comparison.