STL string, iostream, and cout of class info

I'm an STL newbie, and I'm tring to write a simple program to cout a class that has an std::string in it

Here's a program that works but that doesn't use stl:

// *** compile with cl -GX test00.cpp
#include <iostream.h>
#include <string.h>

class CInfo
{
public:
  CInfo(int key, char* ref);

  friend ostream& operator<<(ostream& s, const CInfo &info);

private:
  int   m_key;
  char  m_ref[20];
};

CInfo::CInfo(int key, char* ref) : m_key(key) { strcpy(m_ref, ref); }

ostream& operator<<(ostream& s, const CInfo &info)
{
  return s << '(' << info.m_ref << ')';
}

int main(void)
{
  cout << "Reached main" << endl;
  CInfo myInfo(123456, "myRef");
  cout << myInfo << endl;
  return 0;
}


Here's the (roughly equivalent) program with std::string.  There's some strangeness with std::ostream, and I get the compiler error for the cout << myInfo << endl;

error C2678: binary '<<' : no operator defined which takes a left-hand operand of type 'class ostream_withassign' (or there is no acceptable conversion)

// *** compile with cl -GX test01.cpp
#include <iostream.h>
#include <string.h>

class CInfo
{
public:
  CInfo(int key, char* ref);

  friend ostream& operator<<(ostream& s, const CInfo &info);

private:
  int   m_key;
  char  m_ref[20];
};

CInfo::CInfo(int key, char* ref) : m_key(key) { strcpy(m_ref, ref); }

ostream& operator<<(ostream& s, const CInfo &info)
{
  return s << '(' << info.m_ref << ')';
}

int main(void)
{
  cout << "Reached main" << endl;
  CInfo myInfo(123456, "myRef");
  cout << myInfo << endl;   // <-- causes compiler error
  return 0;
}

What am I doing incorrectly?  And is the std::outstream necessary?  

TIA