Bug in Microport stdio

[Larry V. Streepy]

In article <123 at gaia.UUCP> jon at gaia.UUCP (Jonathan Corbet) writes:
>I have found what appears to be an obnoxious bug in the standard I/O
>library for Microport unix.  Rather than let other folks out there track
>it down themselves, I thought I would pass it on:
>
>Essentially, the problem is this: when you fopen() a file for "r+" access,
>read from the file, then attempt to write, the data written gets lost.  This
>happens even if you are careful to do a fseek() like the manual says.  
>This breaks certain software, such as netnews.  The solution I have found
>is to get the current position with ftell(), close and reopen the file,
>fseek() to the position of interest, then do the write.
>
>   [text of test program removed]
>
>Jonathan Corbet
>{hao | nbires}!gaia!jon

This problem also manifests itself on the AT&T PC6300+.  I had the same
problem bringing up netnews (i.e. the ACTIVE file wasn't being updated).

The problem can be worked around in a slightly more efficient manner.
After opening the file set the stream to unbuffered via setbuf(3S).
as an example:

      if( (fp = fopen( "file_to_open", "r+" )) == NULL ) {
         /* handle error */
      }
      else setbuf( fp, (char *)NULL );
      
      /* rest of code */

When I applied this to the test program Jonathan supplied it worked fine.

Larry V. Streepy, Jr.                      "Waiting is"
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