DOCUMENT:Q132290  29-JUL-2001  [visualc]
TITLE   :PRB: Problems Using CFile::m_hFile When Porting MFC Apps
PRODUCT :Microsoft C Compiler
PROD/VER:winnt:1.0,2.0,2.1,2.2,4.0
OPER/SYS:
KEYWORDS:kbFileIO kbMFC kbVC100 kbVC150 kbVC200 kbVC400 kbprb kbGrpDSMFCATL

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

 - The Microsoft Foundation Classes (MFC), used with:
    - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51, 1.52 
    - Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 2.2, 4.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

When you port MFC applications that use CFile from Windows version 3.1 to
Windows NT or Windows 95, you may encounter problems related to use of the
m_hFile member variable.

CAUSE
=====

In all versions of MFC, CFile:: m_hFile is defined as a UINT. In the 16-bit
versions of MFC (versions 2.0 and 2.5x), m_hFile is a HANDLE that is created
from a call to the C Runtime Library (CRT) function _dos_open(). In this case,
other CRT functions that use the handle, such as _eof(), work correctly.

In the 32-bit versions of MFC (versions 2.1 and 3.x), m_hFile is a handle that is
created from a call to the Win32 function CreateFile(), which is incompatible
with the C Runtime functions. In this case, you need to use the Win32 API
function set.

RESOLUTION
==========

If your MFC application must use functions outside of the CFile class to obtain
the functionality you need, note these differences and use compatible
functions.

To obtain a C run-time file handle and set it to point to the operating system
file handle m_hFile, you can use the _open_osfhandle() function. The handle
returned by that function is compatible with _eof() and other C Runtime Library
functions.

REFERENCES
==========

Please see your online documentation for more information on compatible
functions.

Additional query words: 4.00 4.0 95 2.00 2.10 2.50 2.51 2.52 3.00 3.10 3.20 m_hFile

======================================================================
Keywords          : kbFileIO kbMFC kbVC100 kbVC150 kbVC200 kbVC400 kbprb kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:1.0,2.0,2.1,2.2,4.0
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 2001.