“redefinition of 'string' as different kind of symbol”

[oscarj]

I declared a function which returns std::string in read_qacct.h

#include <string>
std::string read_qacct(std::string login, int days);

Then I include read_qacct.h in another cpp file called db2class.cpp

#include "read_qacct.h"

When I compile db2class though, the first error is

In file included from db2class.cpp:8:
./read_qacct.h:2:6: error: redefinition of 'string' as different kind of symbol
std::string read_qacct(std::string login, int days);
     ^
/usr/include/c++/4.2.1/bits/stringfwd.h:59:33: note: previous definition is here
  typedef basic_string<char>    string;

I had read_qacct.h included the same way in read_qacct.cpp where the function read_qacct was defined. I successfully compiled read_qacct.cpp. How come I got this weird error for db2class.cpp?