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Re: automatic link specification

From: AlfC
Subject: Re: automatic link specification
Date: Tue, 18 Sep 2007 07:17:43 -0000
User-agent: G2/1.0

On Sep 17, 5:51 pm, Paul Pluzhnikov <>
> AlfC <> writes:
> >> Why do you think it's a good idea to be able to do this?
> > For example, suppose  that you write a header file that uses
> > boost_filesystem internally, from them on you will need *always* to
> > compile with the option -lboost_filesystem.
> Yes. So you add it to your makefile and go on with your life.

 and then I have to mantain a makefile. ok, one gets used to this.

> > Let's say that you give your source code that is "script-like" to
> > someone else
> I have no clue what a 'script-like source code' is.

yes you do: a small code with few docen of lines, that does a simple
task, like renaming files, inspects them, do this and that .
> If she doesn't have Boost installed, the compilation will give
> awful errors about compiling.

at least it will tell what  files are missing.

> Should gcc be able to also:
>   #install_boost_if_necessary
>   #add_correct_include_flags
>   #add_correct_define_flags
> to 'automagically' resolve compilation problems as well?

yes, and make a cup of coffee,
no, I am talking about some simple task that involves gcc only, after
all I what looking for something that suggest gcc what to look for,
something that can be easily switched off or overwritten.
> > besides it is not standard, why do you think it is a *bad* idea to be
> > able to do this?
> It's a bad idea because it hides the fact that you need libboost
> inside the object file. UNIX users to do not expect this command:
>   gcc main.o
> to 'magically' search for any library besides libc.
so, after all gcc writers accepted that libc should be linked by
default, basically I am asking for something that by default links to
certain libraries.

> It's also a bad idea because UNIX linkers do not use $LIB environment
> variable to find libraries. If you need, and there are
> 4 different versions installed on the system, which one should the
> linker pick? The one in /usr/lib may not be the right one.

I understand, but that is why if implemented it should be as some
suggestion to the compiler that can be ignored if let say there are
more than one version of the file.
Following the example, what if there is more than one version of libc?
g++ won't cry, will it?

> It's also a bad idea because users will be confused when main.o
> needs one version of libboost, but foo.o needs another (possibly
> incompatible) version.

beginners are confused anyway.

> I see this on windows all the time:
>   link foo.obj bar.lib zork.lib /nodefaultlib:libc.lib
>     /nodefaultlib:libcmt.lib /nodefaultlib:libcd.lib msvcrt.lib
I didn't think about that, good point.
It seems that Windows can do it (see response from Pedro) with its
problems, gcc just can't.
ok, I just wanted to make sure I wasn't missing something with gcc.
Boost people apparently would smile if something like this is
implemented (see Pedro's link), at least it will simplify their
Getting Started page.
Don't get me wrong I still will use g++.

Thank you very much for your answer, this autolinking may be wasn't a
great idea after all.

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