Why does the compiler prefer f(const void*) to f(const std::string &)?

Question

Consider the following piece of code:

#include <iostream>
#include <string>

// void f(const char *) { std::cout << "const char *"; } // <-- comment on purpose
void f(const std::string &) { std::cout << "const std::string &"; }
void f(const void *) { std::cout << "const void *"; }

int main()
{
    f("hello");
    std::cout << std::endl;
}

I compiled this program using g++ (Ubuntu 6.5.0-1ubuntu1~16.04) 6.5.0 20181026:

$ g++ -std=c++11 strings_1.cpp -Wall
$ ./a.out

const void *

Note that the comment is there on purpose to test, otherwise the compiler uses f(const char *).

So, why does the compiler pick f(const void*) over f(const std::string &)?

Answer 1

Converting to a std::string requires a "user defined conversion".

Converting to void const* does not.

User defined conversions are ordered behind built in ones.