Cross-process interaction under C++

Please help, how can I organize the process-process data exchange (in Windows, if that matters)?

I have process1.exe which calls process2.exe with a few command line arguments. I want to track "progress" of process2 from process1 (say, some int value). It (that int value) can be accessed from process1 permanently or each X ms - doesn't matter.

Will be useful any solution: WinApi or Qt.

Thank you everybody! All answers are very useful! :) Many thanks!!

OTOH:

• stdin/stdout redirection
• Named pipe (CreateNamedPipe)
• Anonymous pipe (CreatePipe)
• Sockets (socket, connect, bind)
• Shared memory (CreateFileMapping, MapViewOfFile)
• Windows messages (e.g. WM_APP)

Pick one - Windows messages or shared memory may be the easier ones.