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Re: Homogenizing include guards - and copyright comments

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


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 :}....


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