Re: [Boost-users] boost & c-style calback issue

Hi Nikolai, thanks for your speedy reply. Nikolai N Fetissov wrote:

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Hi,

i'm facing this problem may be someone on the list do have an elegant solution

class A; class B;

class C { int operator () (A*,B*) };

typedef int (*foobar)(A*,B*); void do_something(foobar cb);

C obj; do_something(obj); *ERROR*

Object of type C is not convertible to function pointer type foobar.

...

did try boost::function ftor = obj; do_something(ftor); *ERROR*

compiler generates in both cases the following error messages cannot convert parameter 2 from 'boost::function<Signature>' to 'int (__cdecl *)(A *,B *)'

with 1> [ 1> Signature=int (A *, B *) 1> ] 1> No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called

I can't make the corresponding class B member function static due to side-effects. Any clue how to get rid of this?

You got it backwards - raw function pointer is convertible to boost::function, not the other way around (compiler is trying to tell you exactly that.) Make 'do_something' take boost::function instead.

The problem is that "do_something" is a legacy code written in plain C and it expect to get a function pointer with the signature typedef int (*foobar)(A*,B*); where A and B are struct. Making the member function that has that signature static helps solve the problem but then we do have undesirable side-effect since this operation should be instance based and not object-bases. May be someone can come out with a better approach?! Thanks Cheers Mike