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Q132290: PRB: Problems Using CFile::m_hFile When Porting MFC Apps

Article: Q132290
Product(s): Microsoft C Compiler
Version(s): winnt:1.0,2.0,2.1,2.2,4.0
Operating System(s): 
Keyword(s): kbFileIO kbMFC kbVC100 kbVC150 kbVC200 kbVC400 kbprb kbGrpDSMFCATL
Last Modified: 29-JUL-2001

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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 
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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

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