On Thu, Jan 24, 2019 at 12:31 PM Paul Smith <psmith@xxxxxxx> wrote: > > On Thu, 2019-01-24 at 12:10 -0600, Peng Yu wrote: > > So only the following in the gcc manual go to CPPFLAGS. All other > > options go to other GNU Make variables. > > > > Preprocessor Options > > -Aquestion=answer -A-question[=answer] -C -dD -dI -dM -dN > > -Dmacro[=defn] -E -H -idirafter dir -include file -imacros file > > -iprefix file -iwithprefix dir -iwithprefixbefore dir -isystem > > dir -imultilib dir -isysroot dir -M -MM -MF -MG -MP -MQ -MT > > -nostdinc -P -fdebug-cpp -ftrack-macro-expansion > > -fworking-directory -remap -trigraphs -undef -Umacro -Wp,option > > -Xpreprocessor option -no-integrated-cpp > > I don't think you can really make that statement: it depends on your > environment. > > As I said, one idea behind using a separate variable is that there may > be other tools that you want to use which also take preprocessor > arguments. It's not uncommon (or at least was not in the past) for > other tools to use the preprocessor to process source code for other > reasons than compilation; those other tools would need the -I and -D > options (and -U although that's rarely used). However, most of the > less standard flags above will not be recognized by most of these other > tools and could cause them to throw errors. > > There's no one-size-fits-all definition, IMO. The answer to all your > questions is, "it depends on what you want to do". If you have no > reason to ever use the preprocessor separately maybe you don't need a > separate CPPFLAGS at all. > > There's just a general rule-of-thumb: > * preprocessor options go into CPPFLAGS > * options that can be used with BOTH C compilers and C linkers go into > CFLAGS > * options that can be used with BOTH C++ compilers and C++ linkers go > into CXXFLAGS > * options that can be used ONLY with linkers, but not compilers, go > into LDFLAGS, except -l which goes into LDLIBS. > > Is there a particular reason you want to be so precise about this? There is quite a confusion about how to use make variables. Different sources give different bits of advice. I'd like to make it clear about it. -- Regards, Peng
