Subj : Re: How to pass class-member function to pthread_create(....)?
To   : comp.programming.threads
From : Torsten Robitzki
Date : Mon Jul 18 2005 11:04 pm

Vyacheslav Kononenko wrote:

> 
> Torsten Robitzki wrote:
> 
>>Vyacheslav Kononenko wrote:
>>
>>
>>>Chris Thomasson wrote:
>>>
>>>
>>>>>>Unfortunately extern "C" is necessary if your interested in creating
>>>>>>"correct code"...
>>>>>
>>>>>The problem is using extern "C" does _NOT_ make 100% correct code
>>>>>either. It could be safer to do that. But could be safer is different
>>>>>than correct/incorrect statements showed here.
>>>>
>>>>I would argue that it is "correct" to use extern "C" for the functions you
>>>>pass to a pthreads library; pthreads is a C library after all...
>>>
>>>
>>>extern "C" does not gurantee that your C++ function would be correctly
>>>callable from any C code.
>>
>>So what's the point of declaring a function extern "C" other then make
>>it callable from C?
> 
> But make it callable from C is different than guarantee that _ANY_ C
> code compiled by _ANY_ C compiler or C++ compiler in C mode with _ANY_
> set of options will call extern "C" function correctly, isn't it?

One can't make it callable from every C compiler, but from every sane C 
compiler on your platform. Extern "C" is a feature of your C++ compiler 
and if that compiler don't behave like it it's requested by your 
platform ABI it's prety pointless.

>>It might work. But why would one gamble and depend on something that
>>might work if there is an easy approach that is required to work because
>>there are specifications that guaranties that this approach will work?
> 
> 
> There is no such specifications that the problem. You have to know that
> your C library compiler code is compatible with C++ compiler generated
> code anyway. And you can know if it is safe to call extern "C++"
> linkage from the C library as well.

I would expect a compiler that can't generate code with the requested 
linkage to issue an error.

regards
Torsten

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