Re: [boost] [Test] boost_unit_test_framework and main()

From: Douglas Gregor (doug.gregor_at_[hidden])
Date: 2007-05-15 09:33:39

On May 15, 2007, at 3:33 AM, Jürgen Hunold wrote:
> An'n Dingsdag 15 Mai 2007 hett Vladimir Prus schreven:
>> I believe this is intentional change made in Boost.Test for 1.34,  
>> in the
>> interest of making Linux (where 'main' can be in shared library) and
>> Windows (where 'main' cannot be in shared library), uniform.
>
> Yes, that was the intention

I understand the reasoning---uniformity of behavior across  
platforms---but I believe this change was a mistake. My rationale  
follows.

When linking on Windows, if both a DLL and a static library are  
available, which one does the linker choose?

>> However, you'd need to ask Gennadiy how to your tests work now.
>
> Just #define BOOST_TEST_DYN_LINK

For the shared library tests.

For the static library tests, I don't define BOOST_TEST_DYN_LINK, and  
I put the .a file directly on the link line instead of using -L and -l.

>
> Taking a look at libs/test/build/Jamfile.v2 reveals
>     : usage-requirements
>                    <define>BOOST_TEST_NO_AUTO_LINK=1
>                    <link>shared:<define>BOOST_TEST_DYN_LINK=1
>
> which Boost.Build applies automagically ;-))

Users of Boost.Build are isolated from this change are isolated from  
the effects of this change due to usage-requirements. usage- 
requirements are very cool, but they hide the fact that this change  
causes real trouble for people not using Boost.Build. The very simple  
line

        g++ mytest.cpp -I $BOOST_HDRDIR -L $BOOST_ROOT/lib - 
lboost_unit_test_framework-gcc33-mt-d

fails to link. That's bad for at least two reasons: (1) it's the  
first line that someone is likely to write when trying out the unit  
test framework, and it's not going to work; (2) it's the line that  
most non-BBv2 build systems would produce, because using -L and -l  
are the common ways to link against a static library in the Unix  
world. Not the *only* way, but the common way. There also doesn't  
seem to be any documentation that tells users that this change was  
made, or how to link to the Boost unit test framework on a *nix system.

We've already had some user confusion on this change, e.g.,

        http://lists.boost.org/boost-users/2007/05/27716.php

where I stole the link line above. As I was typing this note, I see  
another note requesting assistance on getting this library to link.  
Not a good sign.
        
I think we should revert this change for 1.34.1, so that main()  
appears in both the static and the shared library. This makes the  
simple use cases (which used to work!) work again.

        - Doug