Example to demonstrate using a C99 preprocessor macro to execute a variadict function without having to explicitly pass the argument list size.

ArgsExample.cpp

// arg_helper.h
#ifndef ARG_HELPER_H
#define ARG_HELPER_H

#include <stdarg.h>

/** 
 * Using MSVC?
 */
#define IS_MSVC _MSC_VER && !__INTEL_COMPILER

/**
 * Define the macros to determine variadic argument lengths up to 20 arguments. The MSVC 
 * preprocessor handles variadic arguments a bit differently than the GNU preprocessor,
 * so we account for that here. 
 */
#if IS_MSVC
  #define MSVC_HACK(FUNC, ARGS) FUNC ARGS
  #define APPLY(FUNC, ...) MSVC_HACK(FUNC, (__VA_ARGS__))
  #define VA_LENGTH(...) APPLY(VA_LENGTH_, 0, ## __VA_ARGS__, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
#else
  #define VA_LENGTH(...) VA_LENGTH_(0, ## __VA_ARGS__, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
#endif

/**
 * Strip the processed arguments to a length variable.
 */
#define VA_LENGTH_(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19, _20, N, ...) N
  
#endif // ARG_HELPER_H

// ----

// mymath.h
#ifndef MY_MATH_H
#define MY_MATH_H

#include "arg_helper.h"

/**
 * Use the VA_LENGTH macro to determine the length of the variadict args to
 * pass in as the first parameter, and forward along the arguments after that.
 */
#define ExecVF(Func, ...) Func(VA_LENGTH(__VA_ARGS__), __VA_ARGS__)

namespace my {
  namespace math {
    
    template<class T> 
    extern T Min(int count, T value, ...) {
      va_list args;
      va_start(args, value);
    
      T min = value;
      for (int i = 0; i < count-1; ++i) {
        T next = va_arg(args, T);
        min = min < next ? min : next;
      }
      va_end(args);
      
      return min;
    }
    
  };
  
};

#endif // MY_MATH_H

// ----

// main.cpp
#include <cstdio>
#include "mymath.h"

int main() {
  int min = ExecVF(my::math::Min<int>, 5, 2, 20, -3, 66, 0, 34);
  printf("min: %d\n", min);
  
  return 0;
}

// Output
// min: -3