how to specify a pointer to an overloaded function?

Question

I want to pass an overloaded function to the std::for_each() algorithm. e.g.:

class A {
  void f(char c);
  void f(int i);

  void scan(const std::string& s)
  { std::for_each(s.begin(), s.end(), f); }
};

I'd expect the compiler to resolve f() by the iterator type. Apparently, it (gcc 4.1.2) doesn't do it. So, how can I specify which f() I want?

thanks a lot

Answer 1

You can use static_cast<>() to specify which f to use according to the function signature implied by the function pointer type:

// Uses the void f(char c); overload
std::for_each(s.begin(), s.end(), static_cast<void (*)(char)>(&f));
// Uses the void f(int i); overload
std::for_each(s.begin(), s.end(), static_cast<void (*)(int)>(&f)); 

Or, you can also do this:

// The compiler will figure out which f to use according to
// the function pointer declaration.
void (*fpc)(char) = &f;
std::for_each(s.begin(), s.end(), fpc); // Uses the void f(char c); overload
void (*fpi)(int) = &f;
std::for_each(s.begin(), s.end(), fpi); // Uses the void f(int i); overload

If f is a member function, then you need to use mem_fun, or for your case, use the solution presented in this Dr. Dobb's article.

Answer 2

Not to answer your question, but am I the only one that finds

for ( int i = 0; i < s.size(); i++ ) {
   f( s[i] );
}

both simpler and shorter than the for_each alternative suggested by in silico in this case?