/*
 * call-seq:
 *    res.ftype( column_number )
 *
 * Returns the data type associated with _column_number_.
 *
 * The integer returned is the internal +OID+ number (in PostgreSQL)
 * of the type. To get a human-readable value for the type, use the
 * returned OID and the field's #fmod value with the format_type() SQL 
 * function:
 * 
 *   # Get the type of the second column of the result 'res'
 *   typename = conn.
 *     exec( "SELECT format_type($1,$2)", [res.ftype(1), res.fmod(1)] ).
 *     getvalue( 0, 0 )
 * 
 * Raises an ArgumentError if _column_number_ is out of range.
 */
static VALUE
pgresult_ftype(VALUE self, VALUE index)
{
        PGresult* result = get_pgresult(self);
        int i = NUM2INT(index);
        if (i < 0 || i >= PQnfields(result)) {
                rb_raise(rb_eArgError, "invalid field number %d", i);
        }
        return INT2NUM(PQftype(result, i));
}