writing to a buffer: help

[Rudra Banerjee <rudra banerjee aol co uk>]

Dear friends, 
Please have a look at http://fpaste.org/gvF3/
So, I am writing those values to a string and then to a file(for now!)
given that, Entries e are a structure, as, 
typedef struct {
    GtkWidget *combo, *entry1, *entryAuth, *entryEditor, *entryTitle,
            *entryPub, *entryVol, *entryIss, *entryPage, *entryMon,
            *entryNote, *entryKey, *entryYear, *entryAdd, *entryEdition,
            *entryJournal, *entrySeries, *entryBooktitle, *entryOrg,
            *entryChap, *entrySchool;
} Entries;

is there a better way of writing this; considering the fact that I have
to check if any of the entry is NULL?

My second question in this is that,
I have created a buffer from a file in a different function as

  char* buffer;
  gsize length;
  GError* error=NULL; 
  filename = gtk_file_chooser_get_filename(GTK_FILE_CHOOSER(dialog));
  g_file_get_contents(filename, &buffer, &length , &error);

I have not "g_free"-d it. Can I use the same buffer to if I want to
append the buffer from update_file.c? Or should I g_free that buffer and
reopen it?