Help - std::string

["Jim Gifford" <jim@xxxxxxxxx>]

Here is the error message I receive. What am I doing wrong??

make  all-am
make[1]: Entering directory `/usr/src/cone-0.52/maildir'
Compiling maildirsearch.c
Compiling maildirsearchC.cpp
In file included from maildirsearchC.cpp:7:
maildirsearch.h:95: error: syntax error before `;' token
maildirsearch.h:97: error: syntax error before `;' token
maildirsearch.h:103: error: `string' undeclared in namespace `std'
maildirsearch.h:103: error: parse error before `)' token
maildirsearch.h: In member function `int mail::Search::setString(...)':
maildirsearch.h:105: error: `String' undeclared (first use this function)
maildirsearch.h:105: error: (Each undeclared identifier is reported only
once
   for each function it appears in.)
maildirsearch.h:105: error: `s' undeclared (first use this function)
make[1]: *** [maildirsearchC.o] Error 1
make[1]: Leaving directory `/usr/src/cone-0.52/maildir'
make: *** [all] Error 2

Code
#include <string.h>

namespace mail {

class Search {

        struct maildir_searchengine sei;

        std::string String;

        std::vector<unsigned> rbuf;

 public:
        Search();
        virtual ~Search();

        int setString(std::string s)
        {
                String=s;
                return maildir_search_start(&sei, s.c_str());
        }

        void reset()
        {
                maildir_search_reset(&sei);
        }


        void operator<<(char c) { maildir_search_step(&sei, c); }

        operator bool() { return maildir_search_found(&sei); }

        bool operator !() { return ! operator bool(); }

 private:
        Search(const Search &); // UNDEFINED

        Search &operator=(const Search &); // UNDEFINED

};