What does star sign(*) in `std::string(*)(int)`

Question

Here is code, I don't understand star sign(*) in std::string(*)

using boost::algorithm::join;
using boost::adaptors::transformed;
auto tostr = static_cast<std::string(*)(int)>(std::to_string);

Here is original code

Answer 1

It's a pointer to function accepting int parameter and returning std::string - exactly what std::to_string does.

As @PeteBecker pointed out, the cast there is needed because there are actuall multiple overloads for to_string, accepting different arguments (ints, doubles, shorts, etc). The cast allows the compiler to pick one of them.