On Fri, Jan 13, 2006 at 10:47:43AM +0100, Rolf Kalbermatter wrote: > > > On Thu, Jan 12, 2006 at 09:02:42PM +0100, Rolf Kalbermatter wrote: > > > Thomas Weidenmueller wrote: > > > > > > > We've been using PCH with GCC for a long time in ReactOS, > > it's been > > > > working very well and reliable. Compiling ReactOS is *a lot* > > > > faster with > > > > PCH enabled. > > > > > > Basically what I get in MSVC 6 when modifing a header somewhere and > > > PCH is enabled is that MSVC keeps mocking about errors in the > > > headers, my change was supposed to fix. Disabling PCH (and > > > sometimes deleting the *.pch file) always fixes those issues. > > > > Unless, of course, your filesystem is samba-mounted from a linux box, > > when PCH tends to cause internal compiler errors. > > Well, I finally read a bit about how precompiled headers are supposed to work > and it seems MSVC does work in a similar way than gcc. > Basically you can only have one pch file per working unit. > > My problem was that when you create a new project in MSVC 6, PCH is by > default enabled and set to automatic but no specific header > file is filled in in the project settings. What this seems to do is taking > some (which?) header files and putting them in an > automatically generated pch file in your project output directory. Of course > for more than 1 source file in a project this is likely > each time different so build times will be even worse than without PCH. Also > it seems that header dependancy tracking isn't reliable > in such a setup. > > >From some explanations, I gathered that the only useful PCH setting in MSVC > >is as well to use one specific pch include file and even > more specifically configure one source file to create that pch file and all > others only to use it, otherwise MSVC tends to recompile > the pch file on some arbitrary conditions multiple times for different source > files, basically reverting the purpose of PCH more or > less or even make it worse. > > One thing to watch out also is that any statements in a source file before > the specifically set precompiled header file are > completely, and without any indication (well except the strange resulting > compile errors of course) ignored.
Hmm, perhaps use a CFLAGS "-include autogenerated.h" trick. Generate "autogenerated.h" by collecting all possible includes via a script on "make depend", then force it into every file with -include autogenerated.h (previously compiled to pch). Has the advantage that the magic is all in the buildsystem, no source files need to be touched. Ciao, Marcus
