External, read from process or read from socket?

[Dar Scott]

I'm down to making some evaluation applications.

I want to make some test stacks that interface to some existing and 
some new programs and services running on several W2K systems in a 
distributed control system.  Communication among these use some 
multithreaded C++ libraries.  The test stack needs to communicate 
the same way.
I'm considering three approaches for the glue:

1.  Calls to externals.

2.  TCP/IP to a separate go-between process (program or service).

3.  Read and write from and to a console app started with "open 
process".

Any warnings?  Good experiences or bad?

Dar Scott