V6 cc needs hash before whitespace before first include? - test-drb@ccmp.vtda.org

28 Feb 2019

...
  From: Phil Budne 
...
  I'm betting it was a speedup to not fork/exec
another process if it was
 going to be a null transform! 
It's worse than that! In vanilla V6, the pre-processor is built into 'cc',
not a separate command.

Here's the relevant code (from expand()):

	if (getc(ibuf1) != '#') {
		close(ibuf1[0]);
		return(file);
		}

The code to implement the directives is, ah, entertaining.

	Noel