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

• 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++ for Windows, versions 1.0, 1.5, 1.51, 1.52
  • Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0

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:

Keywords : kbCRT kbVC
Version : winnt:
Platform : winnt
Issue type : kbhowto