Newbie problem with the String class

[Martin Wiebusch]

Hi, I'm new to KDevelop. I was trying to write a simple C++ program
(that "Hello world" stuff). It looks like that:

#include <iostream.h>
#include <stdlib.h>
#include <String.h>

int main(int argc, char** argv)
{
  String s = "Hello world";

  cout << s << endl;
  return EXIT_SUCCESS;
}

Now, when I select "Compile file" everything works fine, but when I
select "Make" or "Rebuild all" I get following error messages:

undefined reference to 'String::String(char const *)'
undefined reference to 'String::~String(void)'
undefined reference to 'String::~String(void)'

(Yes, I get the last one twice) There ist a file "String.h" in the
directory /usr/include/g++/ and in that file the String class and the
above mentioned constructor and destructor are defined. 

Has anyone an idea of what's going wrong there?