Functions with variable lenght arguments in Arduino

I was reading about variable length arguments for functions in the C programming language and I thought, “hey, will this thing work on an Arduino?”.. well, it turns out that yes, it’s working great!

But, what are functions with a variable length? Well, the standard C printf function is a good example (not available on Arduino of course). You can call it with how many arguments you want, for example:

printf("%d", 5);
printf("%d %d", 5, 7);

So, how can we make this with the Arduino? Here is an example, using the same example from here, just ported into Arduino code:

#include <stdarg.h>
#include <stdio.h>

/* this function will take the number of values to average
   followed by all of the numbers to average */
float average ( int num, ... )
{
    va_list arguments;                     
    float sum = 0;

    /* Initializing arguments to store all values after num */
    va_start ( arguments, num );           
    /* Sum all the inputs; we still rely on the function caller to tell us how
     * many there are */
    for ( int x = 0; x < num; x++ )        
    {
        sum += va_arg ( arguments, double ); 
    }
    va_end ( arguments );                  // Cleans up the list

    return sum / num;                      
}


void setup() {
  Serial.begin(9600);
}

void loop() {
  float avg = average( 3, 12.2, 22.3, 4.5 );
  Serial.println(avg);
  avg = average( 5, 3.3, 2.2, 1.1, 5.5, 3.3 );
  Serial.println(avg);
  
  delay(1000);
}