Re: CFLAGS/LDFLAGS vs. --with

[Braden McDaniel]

On 8/6/09 4:36 PM, Murray S. Kucherawy wrote:
> What is the general wisdom when deciding whether to add support for a new 
> "--with" vs. just encouraging use of CFLAGS/LDFLAGS on the command line?
>
> In particular I'm talking about openssl here.  I have a package that needs it.  
> Several systems come stock with an older version in /usr and then people 
> install a newer one in /usr/local or perhaps someplace weird like /usr/pkg.  Is 
> it more common or correct to tell people to do:
>
> ./configure CFLAGS=-I/usr/pkg/include LDFLAGS=-L/usr/pkg/lib
>
> ...or add support for a "--with-openssl" that adds additional variables during 
> compilation pointing to the one the user wants my package to use?
>
> Unless I'm missing something (which is possible because I'm still learning autoconf), adding the 
> "--with" will mean I can't use AC_CHECK_HEADERS to search for various openssl includes 
> and will have to do my own tests for the required headers, libraries and functions.  Or is it 
> possible to arrange that AC_CHECK_HEADERS applies its work to the additional path provided via the 
> "--with"?  I didn't see such a capability described in the info pages, but I may not have 
> looked in the right place.

If all your --with argument would be doing is dumbly appending 
"/include" and "/lib" for -I and -L flags, I don't see the point.

The advantage of training the user add the appropriate -I and -L flags 
to CPPFLAGS (not CFLAGS) and LDFLAGS, respectively, is that this is 
knowledge that's reusable for any conventionally constructed package. 
It is also a strategy that can succeed in getting things working without 
any special knowledge from the package maintainer--something that can be 
very useful in general.

Braden