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POMaintaining a unique set of elements on different criteria C++ STL
 

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    <blockquote> <p>I have to develop a component which will have a more than 100,000 instances of a class. And i want to generate a report based on the different different criteria (members) of the particular class. for example, A employee class with data fields id, names, addr, phoneno. Report generation wiil be based on</p> </blockquote> <hr> <ol> <li>names_ascending</li> <li>names_descending</li> <li>addr_ascending</li> <li>phoneno_asceding</li> <li>unique_names</li> <li>unique_addr</li> <li>unique_phoneno</li> </ol> <p>runtime iteration of instances for each call is very slow since it is a linear operation on large number of instances and requires sorting mechanism.</p> <p>So i have stored a pointers of each instances in a container on different sorted manner. But requires more memory than required. Please suggest me a better way of doing this. I have posted sample code snippet that i followed to achieve above.</p> <pre><code>class Employee { int m_id; string m_name; string m_addr; string m_phone; public: Employee(int id, string name, string addr, string phone) : m_id(id), m_name(name), m_addr(addr), m_phone(phone) { } int id() const { return m_id; } string name() const { return m_name; } string addr() const { return m_addr; } string phoneno() const { return m_phone; } }; //custom predicate for std containers struct IDComparator { bool operator() (const Employee* e1, const Employee* e2 ) { return e1-&gt;id() &lt; e2-&gt;id(); } }; struct NameComparator { bool operator() (const Employee* e1, const Employee* e2 ) { return e1-&gt;name() &lt; e2-&gt;name(); } } struct AddressComparator { bool operator() (const Employee* e1, const Employee* e2 ) { return e1-&gt;addr() &lt; e2-&gt;addr(); } }; struct PhoneComparator { bool operator() (const Employee* e1, const Employee* e2 ) { return e1-&gt;phoneno() &lt; e2-&gt;phoneno(); } }; //Class which holds huge number of employee instances class Dept { private: typedef set&lt;Employee*, IDComparator&gt; EMPID; //unnique id typedef EMPID::iterator EMPID_ITER; typedef multiset&lt;const Employee*, NameComparator&gt; EMPNAME; // for sorted names typedef EMPNAME::iterator NAME_ITER; typedef multiset&lt;const Employee*, AddressComparator&gt; EMPADDR; // for sorted addr typedef EMPADDR::iterator ADDR_ITER; typedef multiset&lt;const Employee*, PhoneComparator&gt; EMPPHONE; // for sorted phoneno typedef EMPPHONE::iterator PHONE_ITER; private: EMPID m_empids; EMPNAME m_names ; EMPADDR m_addr; EMPPHONE m_phoneno; public: Dept() { } ~Dept() { //delete the instances of employees } void add(Employee* e) { EMP_ITER iter = m_empids.insert(e).first; const Employee* empptr = &amp;*iter; m_names.insert(empptr); // adds employee pointer to name multimap m_addr.insert(empptr); // adds employee pointer to addr multimap m_phoneno.insert(empptr); // adds employee pointer to phone multimap } void print_emp_dtls() const; //prints all the emp dtls iterating though EMPID void print_unique_names() const; //iterate EMPNAME &amp; use upperbound &amp; lowerbound, prints unique names void print_asc_name() const; //iterate EMPNAME &amp; prints all names in ascending order void print_desc_name() const; //back iterate EMPNAME &amp; prints all names in descending order void print_unique_adrr() const; //iterate EMPADDR &amp; use upperbound &amp; lowerbound, prints unique address void print_asc_addr() const; //iterate EMPADDR &amp; prints all addr in ascending order void print_desc_addr() const; //back iterate EMPADDR &amp; prints all address in descending order void print_unique_phoneno() const; //iterate EMPPHONE &amp; use upperbound &amp; lowerbound,prints unique phoneno void print_asc_phoneno() const; //iterate EMPPHONE &amp; prints all phoneno in ascending order void print_desc_phoneno() const; //back iterate EMPPHONE &amp; prints all phoneno in }; </code></pre>
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