Ruby on Rails

Hi,

I am trying to use Fiddle to call C function in dynamic library, I used to be able to
pass a return long variable and an error message, but now only return long variable
is returned, can't get the error message, I create a very simple example to test,
this is my add.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

long add(long maxn, double delta, double conf, char *errMsg)
{
        long answer;

        errMsg = (char *) malloc(6*sizeof(char));
        answer = (long)(maxn + delta + conf);
        errMsg = "Hello!";

        return answer;
}

and add.h

#ifndef add_h
#define add_h

long add(long maxn, double delta, double conf, char *errMsg);