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Editorial Team
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Asked: 2026-05-17T15:54:27+00:00

How can I add extra flag variables (like CPPFLAGS) that will apply to all

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How can I add extra flag variables (like CPPFLAGS) that will apply to all makefiles? Currently, we’re using CPPFLAGS, but that is supposed to be reserved as a user variable and I would like to reserve it. I’d prefer not to use AM_CPPFLAGS because I would like to reserve that for specific Makefile.amS. What I want is something like GLOBAL_CPPFLAGS that I could set in configure.ac and have it applied to everything. It would also be nice if there were a way to explicitly ignore the flag.

I think what I need to do is to write my own make rule, but how would I make that available in all subfolders without copying it into every Makefile.am?

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  1. Editorial Team

    You’re correct in not using CPPFLAGS. That’s a user variable. What I’d do is something like this:

    In the root of your source dir, create a file called common.am and define whatever you need in there:

    ## common.am
AM_CPPFLAGS = -DFOO

    I know you said you didn’t want to use AM_CPPFLAGS, but hear me out. In your individual subdirectories, include $(top_srcdir)/common.am and extend or override AM_CPPFLAGS as needed:

    ## bar/Makefile.am
include $(top_srcdir)/common.am
AM_CPPFLAGS += -DBAR

    If you want to override, use = instead of +=:

    ## baz/Makefile.am
include $(top_srcdir)/common.am
AM_CPPFLAGS = -DBAZ
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