question about correct usage of gnulib

[Lorenzo Bettini]

Hi

I've been using gnulib for some years now in my GNU packages, but I was 
wondering whether I'm using correctly, since some people reported some 
compilation errors on some architectures...

I'm using getopt module, and on that architecture the user gets this 
compilation error

g++ -DHAVE_CONFIG_H -I. -I.. -I../src/skels -I../lib -I../lib   -g -O2 
-MT yyerror.o -MD -MP -MF .deps/yyerror.Tpo -c -o yyerror.o yyerror.cc
../lib/getopt.h:194: error: redefinition of ‘struct option’
/usr/include/getopt.h:54: error: previous definition of ‘struct option’

though that source file does not use getopt, but probably gets to use 
stdlib (which is required by getopt module if I'm not wrong)... it 
probably uses stdlib header file when including C++ string header file...

now, on the manual I read

"These Gnulib substitute header files rely on <config.h> being already 
included. Furthermore <config.h> must be the first include in every 
compilation unit. This means that to all your source files and likely 
also to all your tests source files you need to add an ‘#include 
<config.h>’ at the top. Which source files are affected? Exactly those 
whose compilation includes a ‘-I’ option that refers to the Gnulib 
library directory. "

and that's something I didn't do: I was including config.h only in those 
files that rely on getopt (or on another constants set in config.h).

So the compilation problem goes away if I put config.h in all source 
files, but is that really necessary?

Would it be correct to put config.h only say in file1.cpp (and use the
‘-I’ option that refers to the Gnulib library directory for that file 
only), and not in file2.cpp and file3.cpp (where I don't use -I to refer 
to gnulib library directory), and then link all the 3 files together by 
also putting -lgnu?

or should I do something else?

thanks in advance
        Lorenzo

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Lorenzo Bettini, PhD in Computer Science, DI, Univ. Torino
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