Specifying AM_CPPFLAGS from within configure.ac

[Matthew Walker]

Hi,

I would like to know how I should go about specifying AM_CPPFLAGS from 
within my configure.ac.

I read Norman Gray and Alexandre Duret-Lutz's discussion from this 
mailing list on this topic 
(http://www.mail-archive.com/address@hidden/msg10024.html) but could 
not understand quite what I was supposed to do.

The library that I'm working on has an "--enable--full-debug" mode, and 
I would like to ensure that the compiler spits out all the warnings it 
can by specifing CPPFLAGS=-Wall.  I have, however, read that setting 
CPPFLAGS is a bad thing to do because users should be able to alter that 
variable to their hearts content.

I understand that I should instead specify the automake variable 
AM_CPPFLAGS.  Now from what I could understand from the Norman and 
Alex's discussion, it is possible to do this in configure.ac rather than 
having to change every single one of the (many) makefiles.  It has 
something to do with AC_SUBST, but that's where I become lost.

Any help will be very much appreciated.  I am _very_ much a newbie to 
autoconf/automake and I apologize sincerely if this is a stupid question.

Thank you for your thoughts,

Matthew Walker