Question

Firstly, I had a snippet as following:

struct D
{

  int sum;

  D():sum(0){accum();}

  void incre(int arg){sum+=arg;}

  void accum()
  {
    int arr[]={1,2,3,4,5};

    std::for_each(arr,arr+ sizeof(arr)/sizeof(int),
                  std::bind1st(std::mem_fun(&D::incre),this));

    cout << sum <<endl;
  }
};

int main()
{
  D();
}

It compiled properly.But after my changing the member function incre to

void incre(int &  arg){sum+=arg;}

it produced errors, like

typename _Operation::result_type std::binder1st<_Operation>::operator()
    (typename _Operation::second_argument_type&) const [with _Operation = 
    std::mem_fun1_t<void, D, int&>]’ cannot be overloaded

Do you have any ideas about what is going on? I’ll appreciate any help.

Answer 1

The problem is that internally, mem_fun tries to set as its argument type a const reference to the argument type of the member function. If you make then function take in a reference, then it tries to create a reference to a reference, which is illegal in C++. This is a known defect in the library and is being remedied by the new bind function that will appear in C++0x.