Turbo Pascal, Capture Writeln using stream?

Question

I've got a legacy TP5 program. It compiles and runs OK using TP7. I'd like to capture and log some of the write / writeln statements. I can do a global search-and-replace for write and writeln, so I don't mind code changes like that. It does use some formated output: write(r:4:2) so I'd like to keep that.

I don't know any way to capture write/writeln other than writing to a file, then reading each line back and writing it again :~( But it occured to me that that is very like writing to a stream (introduced in Tp5.5), then streaming copies to multiple outputs.

Has anyone done this before? Is it possible? Is there another way?

Answer 1

Afaik it is possible, and commonly done in FPC and Delphi, TP's successors. The only trouble is that the TEXTREC isn't exported by TP, so you have to copy it from sources to somewhere.

The textrec has a bunch of procedure variables (like function pointers in C) that you can set to your own functions to process I/O. Setting these variables is what Assign() does.

The problem is finding the room to store the state (e.g. the pointer to the stream) though. IIRC the TP textrec is tighter than Delphi's.

Anyway, search for a unit StreamIO by Peter Below. This is a FPC/Delphi unit that you will have to adopt, but at least it demonstrates the principles. It would be better to simply migrate to something newer anyway. Maybe SWAG has a TP equivalent too.