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Re: question about correct usage of gnulib

From: Simon Josefsson
Subject: Re: question about correct usage of gnulib
Date: Wed, 11 May 2011 14:56:47 +0200
User-agent: Gnus/5.110018 (No Gnus v0.18) Emacs/23.2 (gnu/linux)

Lorenzo Bettini <address@hidden> writes:

> On 05/03/2011 01:11 PM, Lorenzo Bettini wrote:
>> On 05/02/2011 02:59 PM, Bastien ROUCARIES wrote:
>>> 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...
>> does this mean that it is not safe to use gnulib as above?
> what I meant is "is it not safe to use gnulib in a library"?

I'm not sure I understand the question fully -- but gnulib is safe to
use in a library, add a #include <config.h> to all your .c or .cpp files
as the first non-comment and non-whitespace line.  You shouldn't include
config.h from any header file.


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