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A few suggestions for autoheader

From: Nicholas Wourms
Subject: A few suggestions for autoheader
Date: Thu, 16 Oct 2003 15:58:49 -0400
User-agent: Mozilla/5.0 (Windows; U; Win 9x 4.90; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax)


I think that maximum control over the format of the generated template is very desirable if not crucial, especially if it is an installed file. However the convenience of autoheader is just too good to go without. So, in the spirit of that, I have a few suggestions about how to make the various AH_* macros more extensible:

1) Allow another (optional) argument which would define the ordinal of placement for the cpp macro template, placing it before any cpp macros without ordinal definitions. The ones without ordinal definitions will revert to the default ordering scheme currently being used. Of course, one could really go farther building on this idea, but for now I just wanted to keep it simple.
AH_TEMPLATE([FOO1], [Define to 1 if foo1], [1])
AH_TEMPLATE([FOO2], [Define to 1 if foo2])
AH_TEMPLATE([FOO3], [Define to 1 if foo3], [2])
would be placed like:
/* Define to 1 if foo1 */
#undef FOO1

/* Define to 1 if foo3 */
#undef FOO3

/* Define to 1 if foo2*/
#undef FOO2

2)Often times you might want to group a set of cpp macros together under one comment, so something analogous to the relationship between AC_CHECK_FUNC and AC_CHECK_FUNCS would be ideal. So tentatively this functionality would be in the form of AC_DEFINES, AH_TEMPLATE, and AH_VERBATIMS.
[At least one of the following should be defined if blah... ])
would look like:
/* At least one of the following should be defined if blah... */
#undef FOO1
#undef FOO2
#undef FOO3

3)There are instances of packages installing autoheader generated files into global include subdirectories (i.e. cyrus snmp). This can be a real pain if, as a developer, you are building against two packages, both of which have installed config.h files and made them public. This inevitably leads to the definition and redefinition the same cpp macro (thus causing lots of gcc noise and errors if they conflict). To mitigate this, I suggest another new autoconf macro, AH_IFNDEF. The idea is that given AH_IFNDEF without any args in, autoheader will guard each cpp macro by wrapping it like so:
#ifndef <macro name>
# undef <macro name>
#endif /* !<macro name> */
If given a list of cpp macro name(s) as argument(s), AH_IFNDEF will only guard those specific cpp macro(s) in the list. This is useful since it could really save a lot of unnecessary tedious AH_VERBATIM redundancy. Of course it is left as an exercise to the developer using the package as to which config.h comes first, but you get the point. The basic idea is to make installed config.h's as sanitary as possible.

Working with m4 often give me a headache, not to mention I'm really terrible at it. So, I hope someone finds one or all of these ideas interesting and can actually do the m4 programming needed to bring them to fruition.


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