Re: question about correct usage of gnulib

[Bastien ROUCARIES]

On Mon, May 2, 2011 at 12:02 PM, Lorenzo Bettini
<address@hidden> wrote:
> On 04/25/2011 06:36 PM, Bruno Haible wrote:
>>
>> Lorenzo Bettini wrote:
>>>
>>> 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. "
>>
>> This paragraph is correct.
>>
>>> 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?
>>
>> This will work find as long as data types defined in system headers
>> defined by
>> gnulib (such as structs, function pointers, pointers to socklen_t, etc.)
>> are
>> not exchanged between file1.cpp on one side and file2.cpp and file3.cpp on
>> the
>> other side.
>>
>> For example, if file1.cpp passes a 'struct stat' to file2.cpp through some
>> function call or global variable, then you must be aware that the 'struct
>> stat'
>> that file1.cpp sees is 64-bit safe and therefore larger than the 32-bit
>> 'struct stat' that file2.cpp sees. Similarly for 'struct sched_param' in
>> <sched.h>  and others. Typically this leads to crashes that are very hard
>> to
>> debug because the source code suggests to you that the two 'struct stat's
>> are the same when they are not.
>
> Thanks for the answer
>
> but what about libraries?
> For instance, I can live with including config.h in all .cpp library files,
> but I wouldn't add it to library header files.  Header files are not
> referring to any struct defined in system header files of gnulib... at least
> I guess (basically my library header files only use string form C++ standard
> library)...  would that be safe?

What why bruce is trying to create libposix...

Bastien

> thanks
>        Lorenzo
>
> --
> Lorenzo Bettini, PhD in Computer Science, DI, Univ. Torino
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