Re: file offsets used by fseek and ftell

[John W. Eaton]

On 23-Jan-2004, John W. Eaton <address@hidden> wrote:

| On 23-Jan-2004, Alois Schloegl <address@hidden> wrote:
| 
| | The origin for introducing the STREAMPOS object was the ability to 
| | access files larger than 4GBytes. If the issue becomes a question 
| | whether octave should support, (1) access to files larger than 4GB or 
| | (2) FTELL returning a numeric value, I second the later.
| 
| If you (or someone) can show me a *portable* way to get the file
| position as an integer, then we can convert it back.  The motivation
| for the change is to be able to support large files *and* allow Octave
| to compile with future C++ systems that don't necessarily have
| streampos/streamoff as a simple integer.

Here is a portable fix for the problem.  Unfortunately, there is only
== or != for comparison, so I don't see how to use a better search
method.  Obviously this is a bit of a kluge, but it is portable.

jwe


Index: src/file-io.cc
===================================================================
RCS file: /usr/local/cvsroot/octave/src/file-io.cc,v
retrieving revision 1.149
diff -u -r1.149 file-io.cc
--- src/file-io.cc      22 Jan 2004 22:10:28 -0000      1.149
+++ src/file-io.cc      23 Jan 2004 18:27:38 -0000
@@ -638,7 +638,7 @@
 from the beginning of the file @var{fid}.\n\
 @end deftypefn")
 {
-  octave_value retval = streamoff_array (dim_vector (1, 1), -1);
+  octave_value retval = -1;
 
   int nargin = args.length ();
 
@@ -647,7 +647,27 @@
       octave_stream os = octave_stream_list::lookup (args(0), "ftell");
 
       if (! error_state)
-       retval = streamoff_array (dim_vector (1, 1), os.tell ());
+       {
+         std::streamoff tell_pos = os.tell ();
+
+         if (! error_state)
+           {
+             std::streamoff show_pos (-1);
+
+             long position = -1;
+
+             while (position < LONG_MAX)
+               {
+                 if (show_pos == tell_pos)
+                   break;
+
+                 show_pos++;
+                 position++;
+               }
+
+             retval = position;
+           }
+       }
     }
   else
     print_usage ("ftell");