PRB: Problems Using CFile::m_hFile When Porting MFC Apps (132290)
The information in this article applies to:
- The Microsoft Foundation Classes (MFC), when used with:
- Microsoft Visual C++ for Windows, 16-bit edition 1.0
- Microsoft Visual C++ for Windows, 16-bit edition 1.5
- Microsoft Visual C++ for Windows, 16-bit edition 1.51
- Microsoft Visual C++ for Windows, 16-bit edition 1.52
- Microsoft Visual C++, 32-bit Editions 1.0
- Microsoft Visual C++, 32-bit Editions 2.0
- Microsoft Visual C++, 32-bit Editions 2.1
- Microsoft Visual C++, 32-bit Editions 2.2
- Microsoft Visual C++, 32-bit Editions 4.0
This article was previously published under Q132290 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.
| Modification Type: | Major | Last Reviewed: | 12/9/2003 |
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| Keywords: | kbFileIO kbprb KB132290 |
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