Why conditionally include config.h?
Hey list, Why do many autoconfiscated projects bracket inclusion of the generated config.h with #if HAVE_CONFIG_H / #endif. Assuming the build environment was configured, why shouldn't the source just always unconditionally include config.h? I mean if it isn't there, typically that means the user didn't configure first which ought to be an error anyways, no? -- Kip Warner -- Software Engineer OpenPGP encrypted/signed mail preferred http://www.thevertigo.com signature.asc Description: This is a digitally signed message part ___ Autoconf mailing list Autoconf@gnu.org https://lists.gnu.org/mailman/listinfo/autoconf
Re: Why conditionally include config.h?
On 09/13/2012 05:22 PM, Kip Warner wrote: Hey list, Why do many autoconfiscated projects bracket inclusion of the generated config.h with #if HAVE_CONFIG_H / #endif. Bad copy-and-paste habits. Probably because historically, libtool prided itself on being usable even without autoconf, and therefore libtool headers have to use HAVE_CONFIG_H. Projects that use libtool would then copy libtool's habits, even when they use autoconf, and the practice has spread to projects that don't even use libtool. Assuming the build environment was configured, why shouldn't the source just always unconditionally include config.h? I mean if it isn't there, typically that means the user didn't configure first which ought to be an error anyways, no? Yep, you are exactly right, which is why gnulib doesn't use HAVE_CONFIG_H, and even provides a syntax check rule that you can copy into your project to also avoid it yourself. -- Eric Blake ebl...@redhat.com+1-919-301-3266 Libvirt virtualization library http://libvirt.org signature.asc Description: OpenPGP digital signature ___ Autoconf mailing list Autoconf@gnu.org https://lists.gnu.org/mailman/listinfo/autoconf
Re: Why conditionally include config.h?
On 14 September 2012 02:43, Eric Blake ebl...@redhat.com wrote: On 09/13/2012 05:22 PM, Kip Warner wrote: Hey list, Why do many autoconfiscated projects bracket inclusion of the generated config.h with #if HAVE_CONFIG_H / #endif. Bad copy-and-paste habits. I've seen some packages where same sources are used with multiple build systems (typically autotools in more unixy systems and visual studio project files on Windows) and it's actually needed to weed out config.h include when building with system that does not provide it. But more often #ifdef HAVE_CONFIG_H is just idiom copied from some other project. For example, in our freeciv project, this would need cleanup. It used to be possible to build without autotools and fc_config.h (for systems lacking autotools support those ancient times), and thus #ifdefs are used. However, if one would try to build without HAVE_CONFIG_H defined today, it would go horribly wrong. - ML ___ Autoconf mailing list Autoconf@gnu.org https://lists.gnu.org/mailman/listinfo/autoconf
Re: Why conditionally include config.h?
On Thu, 13 Sep 2012, Kip Warner wrote: Why do many autoconfiscated projects bracket inclusion of the generated config.h with #if HAVE_CONFIG_H / #endif. Assuming the build environment was configured, why shouldn't the source just always unconditionally include config.h? I mean if it isn't there, typically that means the user didn't configure first which ought to be an error anyways, no? Since subsequent responses are not yet adequate ... It is not necessary to have a configuration header when Autoconf is used. If a configuration header is not used, then all definitions appear on the compiler command line and HAVE_CONFIG_H is not defined. However, it is a bug for #if HAVE_CONFIG_H to be used in any installed header file because it might apply to any package, including some other package. Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer,http://www.GraphicsMagick.org/ ___ Autoconf mailing list Autoconf@gnu.org https://lists.gnu.org/mailman/listinfo/autoconf
Re: Why conditionally include config.h?
Marko Lindqvist cazf...@gmail.com writes: On 14 September 2012 02:43, Eric Blake ebl...@redhat.com wrote: On 09/13/2012 05:22 PM, Kip Warner wrote: Why do many autoconfiscated projects bracket inclusion of the generated config.h with #if HAVE_CONFIG_H / #endif. Bad copy-and-paste habits. I've seen some packages where same sources are used with multiple build systems (typically autotools in more unixy systems and visual studio project files on Windows) and it's actually needed to weed out config.h include when building with system that does not provide it. But more often #ifdef HAVE_CONFIG_H is just idiom copied from some other project. I believe the #ifdef wrapper used to be recommended by the Autoconf manual way back, many moons ago (2.13 days at the latest), because it was how the transition from defining things via -D on the command line to using a header was handled. It goes along with the definition of @DEFS@, which previously (and by previously I mean a long time ago) used to contain all the results of configure as -D flags to the compiler, but which was replaced by just -DHAVE_CONFIG_H if you used the AC_CONFIG_HEADERS (or its earlier versions) macro. So, in other words, you could transition your package that was assuming -D flags on the compiler command line to using a config.h header by adding that #ifdef code to the source files, and then it would work with either Autoconf method: either a config.h file or direct -D flags on the compiler command line. I suspect the above is what's happening when you see this in really old projects, and in newer projects it's copy and paste from older projects. -- Russ Allbery (r...@stanford.edu) http://www.eyrie.org/~eagle/ ___ Autoconf mailing list Autoconf@gnu.org https://lists.gnu.org/mailman/listinfo/autoconf
