hiding private member in header file

I develop my own string class. I have two files String.cpp and String.h. I can make static library and give others only header file and .lib file to hide my source code.
But in .h file one can see what my class is consisting of and simply change private to public access. So that private access specificator is just compiler trick. How can I expose only public methods? How this can be achived? I'm using VC++ .Net and like to see some code example or to get some usefull link to follow.
Thanks very much.

You can use the Pimpl (Pointer to implementation) idiom:

Code:

---

// Header file
#ifndef MICKOSTRING_H_
#define MICKOSTRING_H_

class String {
public:
  String();
  ~String();
  // Interface
private:
  struct StringImpl *pimpl;
};

#endif

---

Code:

---

// Implementation file
#include "mickostring.h"

struct StringImpl {
public:
  StringImpl();
  ~StringImpl();
public:
  // Private members of String
};

String::String()
  : pimpl ( new StringImpl )
{}

String::~String()
{
  delete pimpl;
}

---