The exercise 15.41 in book of c++ primer 4th [closed]

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class Query{
    friend Query operator&(const Query&,const Query&);
    friend Query operator|(const Query&,const Query&);
    friend Query operator~(const Query&);
public:
    Query(const string&);           //build a new WordQuery ??
    Query(const Query&c):p(c.p),use(c.use){++*use;}
    ~Query(){delQuery();}
    Query operator=(const Query&c);
    set<TextQuery::line_no> eval(const TextQuery&c) const{return p->eval(c);}
    ostream& display(ostream&s) const {return p->display(s);}
private:
    Query(QueryBase *query):p(query),use(new size_t(1)){}
    QueryBase *p;
    size_t* use;
    void delQuery(){
        if(--*use==0)
            delete p;
            delete use;
    }
};

class WordQuery:public QueryBase{
    friend class Query;
    WordQuery(const string& s):QueryWord(s){}  //Query use the WordQuery constructor
    set<lineno> eval(const TextQuery&t) const
    {return t.run_query(QueryWord);}
    ostream& display(ostream& os) const
    {return os<<QueryWord;}
    string QueryWord;
};

I invoke it in expression Query q=Query(s1) & Query(s2) | Query(s3);

ERRORS:"TextQueryADVANCE.cpp:(.text+0x15ba): undefined reference to `Query::Query(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
"

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It appears that you put the prototype for the constructor, but you didn't actually put an implementation.

You put: Query(const string&);, which says that there is a constructor somewhere that takes a string and creates a Query with it. However, somewhere you actually have to put something that does that.

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This is a linker error. It seems you have not provided an implementation for Query(const string&).