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Q29852: HOWTO: Use fopen() to Append Data to File Terminated w/ CTRL+Z

Article: Q29852
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbCRT kbVC
Last Modified: 22-JUL-2001

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The information in this article applies to:

- The C Run-Time (CRT), included with:
   - Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax 
   - Microsoft C/C++ for MS-DOS, version 7.0 
   - Microsoft Visual C++, versions 1.0, 1.5, 1.51, 1.52 
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, versions 1.0, 2.0, 2.1, 4.0 
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SUMMARY
=======

When data need to be appended to a stream file that is terminated with the
CTRL+Z end-of-file (EOF) marker (ASCII 1Ah), use fopen() with an access mode of
"a+" to open the stream. This will ensure that all data appended to the stream
are accessible after the stream is closed.

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

If fopen() is called with the "a+" mode, the operations of reading from and
writing to the opened stream file are valid. Before any data are appended, the C
Run-time reads the file and deletes the end-of-file marker. However, if fopen()
is called with the "a" mode, only the operation of writing to the opened file is
valid. The C Run-time must seek to the end of the file and append characters
after the end-of-file marker, CTRL+Z.

When displaying the contents of a text file, the MS-DOS and Windows NT TYPE
commands stop upon encountering a CTRL+Z character. Certain editors such as
Edlin and WordStar also ignore all characters after the first CTRL+Z in a file.
Consequently, if text is appended after the CTRL+Z end-of-file marker, it may
not be viewable.

Additional query words:

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Keywords          : kbCRT kbVC 
Technology        : kbVCsearch kbAudDeveloper kbCRT
Version           : winnt:
Issue type        : kbhowto

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