Vector of Login Records

1. Consider that we have a text file "last.txt, which is the output generated by running the command "last -w" on lilina.
2. For each record, we are only interested in the login name and duration between login/logout, so we define a class CLogin:

   class CLogin {
   public:
       string  name;
       int     minute;
   
       CLogin(string s, int m): name(s), minute(m) {}
       CLogin(string s, string m): name(s) {
           // minute = stoi(m.substr(0,2))*60 + stoi(m.substr(3,2));
           // g++ on lilina is too old, otherwise you should have stoi().
           minute = atoi(m.substr(0,2).c_str())*60 + atoi(m.substr(3,2).c_str());
   
       }
       friend ostream& operator<<(ostream& output, const CLogin& a) {
           output << a.name << ' ' << a.minute;
           return output;
       }
   };

3. Assume that we have a function getLogin() which reads data from a text file and returns a vector of CLogin objects. Each CLogin object consists of two data members: a login name and the minutes of the login session.

   vector<CLogin> getLogin(const char* fn = "last.txt") {
       ifstream infile(fn);
       string line;
       vector<CLogin> logins;
       while (getline(infile, line)) {
           string name;
           string duration;
           int nStart, nLength;
           name = line.substr(0, line.find(" "));
           nStart = line.find("(")+1;
           nLength = line.find(")") - nStart;
           duration = line.substr(nStart, nLength);
   #ifdef _DEBUG
           cout << name << duration << endl;
   #endif
           logins.push_back( CLogin(name, duration) );
       }
       return logins;
   };

4. You may test getLogin() with the following main program:

   int main()
   {
       vector<CLogin> logins = getLogin();
       for (size_t i=0; i<logins.size(); ++i) {
           cout << logins[i] << endl;
       }
       return 0;
   }

5. The output may look like:

   solomon 44
   s109321059 8
   s109321059 7
   s109321059 0
   s110321005 12
   solomon 30
   solomon 20
   klim 8
   s108321022 251
   s108321022 5

6. The above output is not good, because the same user has several login records. We want to aggregate them into a single record. Now you are requested to develop a loginCount() function, which will return a vector of CCount. CCount is similar to CLogin, but the second data member, which is an integer, will store the login counts instead of durations.

   class CCount {
   public:
       string  name;
       int     count;
   
       CCount(string s, int c=0): name(s), count(c) {}
   
       friend ostream& operator<<(ostream& output, const CCount& a) {
           output << a.name << ' ' << a.count;
           return output;
       }
   };

7. This vector will be shorter than the previous one, because each user will only have a corresponding record.
   • To generate a new vector which accumulates the occurrence of each user, you may check whether a login name exists in the vector or not.
   • If it already exists, simply increment the corresponding count by 1.
   • If not, append a new entry with this name, and initialize the count as 1.
8. You may test your loginCount() with the following main program:

   vector<CLogin> loginCount(vector<CLogin>& logins);
   
   int main()
   {
       vector<CLogin> logins = getLogin("/home/solomon/CPP/last.txt");
       vector<CCount> counts = loginCount(logins);
       for (size_t i=0; i<counts.size(); ++i) {
           cout << counts[i] << endl;
       }
       return 0;
   }
   

9. The output may look like:

   solomon 133
   s109321059 27
   s110321005 36
   klim 20
   s108321022 36
   s110321529 21
   s110321063 77
   s107321058 60
   s109321020 15
   s110321071 12