Q146445: PRB: istream::seekg() Does Not Reset EOF State

Article: Q146445
Product(s): Microsoft C Compiler
Version(s): 4.0
Operating System(s): 
Keyword(s): kbCompiler kbCPPonly kbVC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600
Last Modified: 30-JUL-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- The C/C++ Compiler (CL.EXE), included with:
   - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

The istream::seekg() function does not reset the EOF (end of file) state when
the stream pointer is already at EOF.

RESOLUTION
==========

To work around this problem, call ios::clear() for the stream before calling
istream::seekg().

STATUS
======

This behavior is by design.

MORE INFORMATION
================

You don't need to call clear(), if the stream pointer is not already at EOF.

Sample Code
-----------

  /* Compile options needed: None
  */ 

  // Input: A file with the name test.txt containing some characters.

  #include <fstream.h>
  #include <assert.h>

  void main()
  {
    fstream in("test.txt", ios::in);

    char c;
    int i = 0;

    // Count characters in file
    while (in.get(c))
       ++i;

    assert(in.eof());

    // Reset read pointer to beginning of file
    in.clear();
    in.seekg(0, ios::beg);

    // Check that file can now be read.
    // Fails without the in.clear() statement above.
    assert(!in.eof());
  }

Additional query words:

======================================================================
Keywords          : kbCompiler kbCPPonly kbVC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : 4.0
Issue type        : kbprb

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.