for_each（for_each（））？

Question

This works, for_each passes vectors

std::vector<int> v(10, 1);
std::vector< std::vector<int> > vv(10, v);
auto vvit = vv.begin();

std::for_each(vvit, vv.end(), f);

to function f which applies for_each anew to work with inner vector ints

void f(const std::vector<int>& v) {std::for_each(v.begin(), v.end(), def);}

but for_each within for_each

std::for_each(vvit, vv.end(), std::for_each((*vvit).begin(), (*vvit).end(), def));

and function for just ints

void def(const int& i) { std::cout << i; }

does not. (Nor with bind, if I tried correctly.) The compiler says that the def function cannot apply the right conversion ie from vector allocator (the vector's position pointer?) to const int&, something the former example achieves with the vector-separating function f.

Is this complicated or trivial?

Answer 1

Easiest solution is to pass for_each in a lambda:

std::for_each(vvit, vv.end(), [f](std::vector<int> const& v)
  { std::for_each(v.begin(), v.end(), f); } );

But what's wrong with

for (auto const& v : vv) {
  for (int i : v) {
    f(i);
  }
}