structures with the same name are messed up

[Jonathan Wakely]

On 25 April 2014 12:21, Gyorgy Kovesdi wrote:
> On 2014. April 25. 12:53:54 Markus Trippelsdorf wrote:
>> You're violating the "one definition rule". It states that you can
>> define the same struct in different translation units, provided it
>> consist of the same sequence of tokens, otherwise the behavior is
>> undefined as in your example.
>
> Ok, you are right.
> But my problem is that those definitions come from two independent sources
> using the same library and do not know each other.

C++ namespaces exist to avoid this problem.

> I do not see a solution to solve it, but at least detecting this situation
> would be useful.
>
> nm -C a.o b.o
>
> a.o:
> 0000000000000000 T test_a(int)
> 0000000000000000 W Checker<test>::mySize()
>
> b.o:
> 0000000000000000 T test_b(int)
> 0000000000000000 W Checker<test>::mySize()
>
> There are two different functions having the same name and parameter list: why
> the linker do not send at least a warning message about it? If I define such
> (e.g. other test_a() function again) then it results in a linker error. Why
> those mySize() functions not?

Because test_a is not a template.  It is normal for template
instantiations to be defined in multiple files, and the linker is
required to only keep one of the definitions (This is the Borland
model described at
http://gcc.gnu.org/onlinedocs/gcc/Template-Instantiation.html). It is
your job to ensure those definitions are the same.

You can try the Gold linker's --detect-odr-violations option to get a
warning about this kind of error.