On Tue, Sep 7, 2010 at 20:02, Ian Lance Taylor <iant@xxxxxxxxxx> wrote: > Tom Browder <tom.browder@xxxxxxxxx> writes: > >> The cpp manual states: >> >> <quote> >> CPP optimizes even further. It remembers when a header file has a >> wrapper `#ifndef'. If a subsequent `#include' specifies that header, >> and the macro in the `#ifndef' is still defined, it does not bother to >> rescan the file at all. >> </quote> >> >> Does that mean (1) the file is reopened but not scanned, or (2) does >> it mean the file is not even opened? It seems that (1) is probably >> the correct answer, but I'm looking for confirmation. > > I believe that the file is not even opened. > >> It makes a slight difference efficiency-wise, and there is a cpp >> "#pragma once" that will definitely avoid reopening the header after >> the first time it's read. > > #pragma once is considered to be obsolete, because the default behaviour > is simpler. Thank you, Ian. Regards, -Tom
