passing glist to func

[<revans ozarkaircraftsystems com>]

Please forgive my ignorance, but could someone explain why this doesn't
work? I want to pass a pointer to a glist to a function and modify that
glist there. The following program prints the value of "a" in function foo
then gives a Segmentation fault trying to print the value of "list" in
main.

Thanks
--------------------------
#include <glib.h>
#include <stdio.h>


void foo(GList *a)
{
  a=g_list_append(a, "text");
  a=g_list_first(a);
  printf("a=%s\n", (char *) a->data);
}

int main()
{
  GList *list=NULL;
  foo(list);
  list=g_list_first(list);
  printf("list=%s\n", (char *) list->data);
  return 0;
}