gscanner example

[Rudra Banerjee <bnrj rudra yahoo com>]

I tried to rewrite the example given in the page
http://www.fifi.org/doc/libgtk1.2-doc/faq-html/gtkfaq-8.html
so that it can read from a file, but its not. 
The code that i tried is:

#include <glib.h>

/* some test text to be fed into the scanner */
/*static const gchar *test_text =
( "ping = 5;\n"
  "/ * slide in some \n"
  " * comments, just for the\n"
  " * fun of it \n"
  " * /\n"
  "zonk = 0.7;\n"
  "pong = -6; \n"
  "\n"
  "# the next value is a float\n"
  "# redefine ping\n"
  "ping = - 0.5;\n" );
*/
/* define enumeration values to be returned for specific symbols */
enum {
  SYMBOL_PING = G_TOKEN_LAST + 1,
  SYMBOL_PONG = G_TOKEN_LAST + 2,
  SYMBOL_ZONK = G_TOKEN_LAST + 3
};

/* symbol array */
static const struct {
  gchar *symbol_name;
  guint  symbol_token;
} symbols[] = {
  { "Author", SYMBOL_PING, },
  { "Title", SYMBOL_PONG, },
  { "zonk", SYMBOL_ZONK, },
  { NULL, 0, },
}, *symbol_p = symbols;

static gfloat ping = 0;
static gfloat pong = 0;
static gfloat zonk = 0;

static guint
parse_symbol (GScanner *scanner)
{
  guint symbol;
  gboolean negate = FALSE;

  /* expect a valid symbol */
  g_scanner_get_next_token (scanner);
  symbol = scanner->token;
  if (symbol < SYMBOL_PING ||
      symbol > SYMBOL_ZONK)
    return G_TOKEN_SYMBOL;

  /* expect '=' */
  g_scanner_get_next_token (scanner);
  if (scanner->token != '=')
    return '=';

  /* feature optional '-' */
  g_scanner_peek_next_token (scanner);
  if (scanner->next_token == '-')
    {
      g_scanner_get_next_token (scanner);
      negate = !negate;
    }

  /* expect a float (ints are converted to floats on the fly) */
  g_scanner_get_next_token (scanner);
  if (scanner->token != G_TOKEN_FLOAT)
    return G_TOKEN_FLOAT;

  /* make sure the next token is a ';' */
  if (g_scanner_peek_next_token (scanner) != ';')
    {
      /* not so, eat up the non-semicolon and error out */
      g_scanner_get_next_token (scanner);
      return ';';
    }

  /* assign value, eat the semicolon and exit successfully */
  switch (symbol)
    {
    case SYMBOL_PING:
      ping = negate ? - scanner->value.v_float : scanner->value.v_float;
      break;
    case SYMBOL_PONG:
      pong = negate ? - scanner->value.v_float : scanner->value.v_float;
      break;
    case SYMBOL_ZONK:
      zonk = negate ? - scanner->value.v_float : scanner->value.v_float;
      break;
    }
  g_scanner_get_next_token (scanner);

  return G_TOKEN_NONE;
}

int
main (int argc, char *argv[])
{
  GScanner *scanner;
  guint expected_token;

  scanner = g_scanner_new (NULL);

  /* adjust lexing behaviour to suit our needs
   */
  /* convert non-floats (octal values, hex values...) to G_TOKEN_INT */
  scanner->config->numbers_2_int = TRUE;
  /* convert G_TOKEN_INT to G_TOKEN_FLOAT */
  scanner->config->int_2_float = TRUE;
  /* don't return G_TOKEN_SYMBOL, but the symbol's value */
  scanner->config->symbol_2_token = TRUE;

  /* load symbols into the scanner */
  while (symbol_p->symbol_name)
    {
      g_scanner_add_symbol (scanner,
                            symbol_p->symbol_name,
                            GINT_TO_POINTER (symbol_p->symbol_token));
      symbol_p++;
    }
   gint file=1;
   file=g_open("trial.bib", "r");
  /* feed in the text */
  g_scanner_input_file (scanner, file);

  /* give the error handler an idea on how the input is named */
//  scanner->input_name = "test text";

  /* scanning loop, we parse the input until its end is reached,
   * the scanner encountered a lexing error, or our sub routine came
   * across invalid syntax
   */
  do
    {
      expected_token = parse_symbol (scanner);
      
      g_scanner_peek_next_token (scanner);
    }
  while (expected_token == G_TOKEN_NONE &&
         scanner->next_token != G_TOKEN_EOF &&
         scanner->next_token != G_TOKEN_ERROR);

  /* give an error message upon syntax errors */
//  if (expected_token != G_TOKEN_NONE)
//    g_scanner_unexp_token (scanner, expected_token, NULL, "symbol",
NULL, NULL, TRUE);

  /* finsish parsing */
  g_scanner_destroy (scanner);

  /* print results */
  g_print ("ping: %s\n", ping);
  g_print ("pong: %s\n", pong);
  g_print ("zonk: %f\n", zonk);
  
  return 0;
}


what is error in it?