Homogenizing include guards - and copyright comments

[Robert Collins]

Max Bowsher wrote:

> Off-list (presumably accidentally), Gary R. Van Sickle replied:
> 
>>I tend to think that the include guards should wrap as much of the file as
>>possible, idea being that the compiler then bypasses the most text
> 
> possible.
> 
>>But then again, rumor has it that gcc (at least) recognizes such
> 
> constructs and
> 
>>doesn't even rescan the file at all the second time, and scanning is
> 
> hardly the
> 
>>bottleneck in gcc these days....
> 
> 
> I don't think the extra copyright comments will have much of an effect on
> compilation speed. I like the layout I proposed, because it gives increased
> visual distinction between copyright boilerplate and file-specific
> interesting info.

I too like this aspect of the layout.

Additionally, recall that C / C++ compilers generally run in (at least) 
two parts: a pre-processor (cpp) that generates a single macro-expanded 
  source files, and then the actual source->(object|assembly).

The smarts of the cpp program are what drive the overhead of repeated 
includes. A naive one will scan every include fully into memory, and the 
process through the #if's. A smarter one will calculate as it goes, and 
once it hits a #if start skipping code...

My point is that a dumb one will, if header FOO is included 3 times, 
have three complete copies of FOO in memory before it's #if resolution 
pass. A smart one that only keeps one copy of FOO, and 2 copies of the 
comments is already so much faster :}....

Rob