HdA>
   > appli  log
   >
   > leaves me with a file of 0 length, whereas without redirection:
   >
   > appli < input
   >
   > results are written to the screen.
HdA>

   Somewhere in the documentation for your C++ compiler, it will say what
   the buffering behaviour of the standard output stream is.  To quote
   from the ISO C standard :

    "When opened [...] the standard input and standard output streams are
     fully buffered if and only if the stream can be determined not to
     refer to an interactive device."

   In other words, the buffering changes according to whether the RTL can
   determine whether the standard output is a device or a file.  In the
   former case it is a file, and the standard output is fully buffered.  A
   fully buffered stream doesn't empty its buffers (by calling the OS/2
   DosWrite function) until the buffer is full.

   In the latter case, it is an interactive device (i.e. the console), and
   the standard output can be either unbuffered or line buffered.  The
   standard doesn't specify which.  Different C++ compilers choose
   different options.  IBM VisualAge C++ chooses line buffering, which
   means that the standard output stream buffer isn't written (via
   DosWrite) until a NewLine character is written (or the buffer is full,
   or other implementation-defined conditions occur).

   So in the former case, if you haven't written BUFSIZ characters to
   standard output before your program fails, they won't have been
   actually written (via DosWrite) and will be lost.

   There are three solutions :

    1.  Output to standard error instead (it is _never_ fully buffered).

    2.  Use `setvbuf' to make the standard output line buffered
        unconditionally (making it unbuffered is overkill and redundant
        considering that you are probably writing a whole line at a time
        anyway).

    3.  Use `fflush' to flush the contents of the stream buffer after
        every `printf' statement.

   > JdeBP <
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