Flushing input stream

[Kerlingen]

I've a little programming related problem and I don't know how to solve it.

A console program (lets call it "prog1.exe") has the following pseudo-code:

while not (Ctrl_Break)
{
  x = fetch_stats();     // Read some info
  writeconsole(x);       // Output the info to the console
  wait(60);              // Wait 60 seconds and repeat the whole process
}

I want to log the output of the program both to screen and to a file. So I wrote a little program ("tee.exe") which does:

while not (EndOfFile(StdIn))
{
  c = read(StdIn);     // Read one char from StdIn
  write(StdOut, c);    // Write one char to StdOut
  write(FILE, c);      // Write the same char to a file
}

In theory, executing "prog1.exe | tee.exe" would redirect all output from "prog1.exe" as input to "tee.exe", while "tee.exe" would write the input it gets to both the console and a file.

The problem is the output buffer. For performance reasons, the OS doesn't write the output of "prog1.exe" to "tee.exe" char-by-char, but waits until the output buffer is full and then writes the whole buffer to "tee.exe". Since "prog1.exe" does only output a few bytes every minute, it takes about 40 minutes before the output buffer is full and transfered to "tee.exe".

Running "prog1.exe >> output.txt" has a similar result: There is no output to the console any more und the file is also only updated when the output buffer is full.

I don't have access to "prog1.exe" or it's source code, so I can't flush the output buffer. Flushing the input buffer is not possible for some reason. The only workarounds I found for the problem describe how to flush the keyboard buffer.

Does anybody have an idea how to solve this problem?

My goal is simple:
1. See the console output in real time
2. Write the console output to a file