[fpc-pascal] redirecting stdout

[Bernd]

is it possible to redirect stdout so that everytime I call writeln()
the output is sent to a function that accepts a string instead of
stdout?

I have googled for some hours now and looked into the CRT unit but I
somehow cannot figure out how this mechanism is supposed to work. I
understand that somehow I have to change a few (which ones?) pointers
in a textrec record to some functions that I provide but I have no
clue how this all is supposed to work.

What exactly happens when I write to stdout, which functions are
called and in which order and where and how can I hook into this whole
thing to receive the string that has been written?

I need some holding hands now, a simple "look how crt does it" won't
help because I first need to understand the concept of what is going
on with this textrec variable.

Say I have a procedure foo

procedure foo(s: ansistring);
begin
   // some code to send this string somewhere else
end;

What are the absolute minimum needed things (no extra bells and
whistles) that I have to do so that foo() will be called on every call
to writeln() and receives the string?

Is there any documentation about this that i should have read before
asking this question? I could not find anything, at least not online,
maybe because it is all old pre-www turbopascal knowledge that can be
only found in books, and everything the CRT unit does (i don't even
know what exactly it does and what it is used for, I only know that it
seems to somehow amongst other things messes around with stdout/stdin)
seems to be undocumented voodoo magic to me.


Bernd