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Re: automatic link specification

From: Paul Pluzhnikov
Subject: Re: automatic link specification
Date: Mon, 17 Sep 2007 17:51:44 -0700
User-agent: Gnus/5.1006 (Gnus v5.10.6) XEmacs/21.4 (Jumbo Shrimp, linux)

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.

> 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.

> , she should know implementation details about some
> library called boost_filesystem that she never heard about and worst ,

No, she doesn't. She only needs to know that your source depends
on the Boost library, and therefore she should install 'boost-devel'
package, and use the Makefile you supplied to build your sources.

> the compilation gives awful errors messages about linking

If she doesn't have Boost installed, the compilation will give
awful errors about compiling. Should gcc be able to also:


to 'automagically' resolve compilation problems as well?

> 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.

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.

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. 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

Clearly, the user of this command is begging the linker to "just
please, please link that damned executable so I can go on with
my life".

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