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Re: Problem with PFE approach [Was: Faster compilation speed] (Daniel Berlin)  wrote on 17.08.02 in <>:

> On Sat, 17 Aug 2002, Timothy J. Wood wrote:
> >
> > On Saturday, August 17, 2002, at 08:04  PM, Daniel Berlin wrote:
> >
> > > On Sat, 17 Aug 2002, Timothy J. Wood wrote:
> > >
> > >>
> > >>    So, another problem with PFE that I've noticed after working with
> > >> it
> > >> for a while...
> > >>
> > >>    If you put all your commonly used headers in a PFE, then changing
> > >> any
> > >> of these headers causes the PFE header to considered changed.  And,
> > >> since this header is imported into every single file in your project,
> > >> you end up in a situation where changing any header causes the entire
> > >> project to be rebuilt.
> > >
> > > Um, this header should *not* be explicitly included in the files.
> > > It's *prefix* header.
> >
> >    I'm not saying that I'm #including it in my sources.  What I'm saying
> > is that the IDE knows that all my files depend upon it (they all end up
> > including it due to it being the prefix header, regardless of whether
> > it is listed or not).  This means that they may have depedencies on the
> > its contents and must be rebuilt if it or any header it includes
> > changes.
> No, they shouldn't have any dependencies on it's contents. They should

That would be seriously broken ...

> include what they normally include.  The fact that the prefix header stores
> the compiler state should prevent these includes from doing anything (since
> it'll know it's already processed that header) when it is present.
> Any build system that makes the files depend on the prefix header is
> broken, and needs to be fixed.

... unless you have some mechanism to prevent them from being influenced  
by any change in any header which is used in the prefix header but which  
they do not include normally.

What mechanism would that be?

The dependency chain is *exactly* the same as if the prefix header was  
normally included at the start of every source file.

MfG Kai

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