C++ string to C-string conversion

// strings and c-strings
// tested with g++ (Debian 6.3.0-18+deb9u1) 6.3.0 20170516 under Debian Stretch
#include <iostream>
#include <string>

using std::cout;
using std::endl;

std::string mk_str() {
  return ">Karl-Heinz-Rumpelstilzchen-Koopmann-van-Wijdenvouwrden-123&456*&^%#:";
}

int main ()
{
  std::string str = mk_str();  // initial string
  const char* cstr = str.c_str();  // notice the `const` qualifier

  cout << "--- TEST ---" << endl;
  cout << "  string = '" << str << "'" << endl;
  cout << "c-string = '" << cstr << "'" << endl;

  for(std::size_t i = 0; i <= str.length(); ++i)
    printf("char %3d = '%c'\n", int(cstr[i]), cstr[i]);

  cout << "--- END TEST ---" << endl;
  return 0;
}