Re: [Boost-users] boost::function, boost::bind question

From: Philippe Després (pdespres_at_[hidden])
Date: 2005-03-16 11:57:29

ok thanks a lot. I do not like NR either but I did not find a good C++ 
alternative yet...

Ben Hutchings wrote:
> Philippe Després wrote:
> 
>> Hello,
>>
>> I am using Numerical Recipes routines and I am trying to call this 
>> function
> 
> 
> I wouldn't advise using any of that source code.  It's not good C++ code 
> and the licence fees could get expensive.  See 
> <http://www.accu.org/cgi-bin/accu/rvout.cgi?from=0ti_n&file=n003134a> 
> for more information.
> 
>> void mrqmin(Vec_I_DP &x, Vec_I_DP &y, Vec_I_DP &sig, Vec_IO_DP &a,
>>     Vec_I_BOOL &ia, Mat_O_DP &covar, Mat_O_DP &alpha, DP &chisq,
>>     void funcs(const DP, Vec_I_DP &, DP &, Vec_O_DP &), DP &alamda);
>>
>>
>> and I would like to call it with funcs being a member function pointer 
>> of one of my class.  I can declare the member as static but then I 
>> cannot access member variable, which is the goal here.
> 
> 
> You can access static member variables.
> 
>  > Someone suggested to use boost to solve the problem.
> <snip>
> 
> Boost doesn't have a solution to this problem.  Boost.Bind and 
> Boost.Function help you to adapt functions, but they produce function 
> objects that are of no use with a function that requires a function 
> pointer, such as the C-style code found in Numerical Recipes.  Functions 
> that call-back through function pointers should always pass through an 
> arbitrary context pointer.  This allows you to define a static member 
> function like this:
> 
> void my_class::my_callback(void * context, other args...)
> {
>     static_cast<my_class *>(context)->real_callback(other args...);
> }
> 
> and then pass &my_callback and this as arguments to the other function. 
>  However, it looks like mrqmin doesn't even pass through any context, so 
> this won't help you.  An alternative is to copy this into a static 
> member variable - or, in a multithreaded application, into TLS - before 
> making the call.  Then you would define your call-back function like this:
> 
> void my_class::my_callback(args...)
> {
>     static_cast<my_class *>(current_instance_)->real_callback(args...);
> }
> 
> Ben.
> 
> 
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-- 
Philippe Després
Associate Specialist
UCSF Physics Research Lab
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