Here's an example of what a platform-specific getload.c might look like,
in skeleton form:

/* to get data types and such: */
#include "ttyload.h"

/* general headers that are likely to be used on most systems: */
#include <stdio.h>		/* for perror */
#include <stdlib.h>		/* for exit() */

/* and here's the core function: */
void	getload(load_list *loadavgs)
{
    /* to store data from the load average retrieval routine: */
    sometype	theload[3];
    /* to store the return value of same: */
    int		ret;

    if((ret = someroutineforgettingload(theload)) < 0)
    {
    	perror("thatroutineIcalled() failed");
	exit(1);
    }

    /* so the caller can know how we did with getting the load, and
     * report on problems there: */
    loadavgs->numloads	= ret;

    /* and these all should be in integer form as one 1024'th of the
     * actual load average...  On most platforms, you'll probably have
     * to do this math (but some may not require it, depending on how
     * the routine for getting the load average actually works): */
    loadavgs->one_minute	= theload[0] * 1024;
    loadavgs->five_minute	= theload[1] * 1024;
    loadavgs->fifteen_minute	= theload[2] * 1024;

    /* no need to "return()" anything, because we exit() on fatal
     * errors, and return information about our success level beyond
     * that with numloads. */
}