[CMake] How to guarntee the sequence of build if no target can be used

[Alexander Neundorf]

On Monday 01 June 2009, Dong Tiger wrote:
> 2009/5/29 Alexander Neundorf <a.neundorf-work at gmx.net>
>
> > On Thursday 28 May 2009, idlecat511 at gmail.com wrote:
> > > Hi,
> > >
> > > This situation is:
> > >
> > > foo.h is generated from foo.x. And foo.h is included by bar.h. And then
> > > bar.h is included by a lot of c files. So actually every c files
> >
> > including
> >
> > > bar.h depends on foo.h.
> > > But the file number is so big that I don't want to add dependency for
> >
> > each
> >
> > > one.
> > >
> > > How can I specify foo.x is generated before all the c files being
> >
> > compiled?
> >
> > > It seems add_custom_target works but it will regenerate foo.h every
> > > time even the foo.x is not modified.
> >
> > You should use
> > add_custom_command(OUTPUT <fullpath>/foo.h
> >                   ... )
> >
> > and then list that generated file as a source file for your target:
> >
> > add_library(blub <fullpath>/foo.h foo.c bar.c ...)
>
> I know by this way, if foo.h is changed, blub will be rebuilt. But what I
> need is foo.h is guaranteed to be up to date before foo.o is built.  I am
> not sure if this command is relevant to this. Will cmake try to make sure
> all the src files are up to date before compiling any .c files?

Yes.

> > This should make sure that everything is up to date.
> >
> > The header-file dependency scanning does in general not work for
> > generated files, you need to list the generated file as source file for
> > the targets which need it.
>
> Another problem is that I am trying to avoid adding dependencies for these
> generated files manually because in my project, there are many generated
> head files and quite a few .c files including them. I just want to make
> sure the head files are generated before any .c compilation.
> ADD_CUSTOM_TARGET can do this but it will regenerate the head files even
> they are up-to-date.

There should be no need to do this if you use add_custom_command()

Alex