Simple function overloading in C (extended)

overload.h.in

#ifndef OVERLOAD__FN__H
#define OVERLOAD__FN__H

#ifndef VA_NARGS
/* Count variadic macro arguments (1-10 arguments, extend as needed)
 */
#define VA_NARGS_IMPL(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, N, ...) N
#define VA_NARGS(...) VA_NARGS_IMPL(__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)
#endif

/* Simple name mangling of function _FN_ based on arity
 */
#define ___FN__impl2(n, ...) ___FN__impl__ ## n(__VA_ARGS__)
#define ___FN__impl(n, ...) ___FN__impl2(n, __VA_ARGS__)
#define _FN_(...) ___FN__impl(VA_NARGS(__VA_ARGS__), __VA_ARGS__)

#endif // OVERLOAD__FN__H

overload.sh

#!/bin/bash

usage="Usage: $0 FUNCTION..."

if [ $# -lt 1 ]; then
    echo $usage
    exit 0
fi

for fn in "$@"; do
    echo "Generating overload_$fn.h"
    sed s/_FN_/$fn/g overload.h.in > overload_$fn.h
done

overload_sum.c

#include <stdio.h>
#include "overload_sum.h"

int sum(int a, int b)
{
    return a + b;
}

int sum(int a, int b, int c)
{
    return a + b + c;
}

double sum(double a, double b, double c, double d)
{
    return a + b + c + d;
}

int main(void)
{
    printf("%d\n", sum(1, 2));
    printf("%d\n", sum(1, 2, 3));
    printf("%g\n", sum(1, 2, 3, 4));

    return 0;
}