Map::using size() and looping [closed]

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//employee is class with public members salary and nname
    int main()
    {
        map<int,employee> employees;

        employee e1;
        strcpy(e1.nname,"aaa");
        e1.salary=25000;

        employee e2;
        strcpy(e2.nname,"ccc");
        e2.salary=26000;
        employees[1]=e1;
        employees[2]=e2;

        employee e3;
        strcpy(e3.nname,"bbb");
        e3.salary=26000;

       employees[5]=e3;

       employee ee;

       cout<<employees.size()<<endl;

       for(int i=0;i<employees.size();i++)
        {
            ee=employees[i];
            cout<<ee.nname<<endl;
        }

    o/p:     3               -      //so i=3       displays employees[0],1,2,3
             aaa             -      //i=
             ccc             -
                             -       //2 blank lines
                             -    // <---why blank line cming ,ok cause no data but why it 
             bbb             -      //executed 4th and 5th time and we got 
                                    //  employees[5] -----              bbb?????
                                    //when i printed value of"i" i got from 0 to 5!!!
--------------
can any1 explain thanx in advance

---

You are displaying employees[i], where i= 0,1,2,3,4,5.
Why are you displaying 6 entries if employees.size() == 3 prior to entering the for-loop?

The answer is, that when i==0, you are adding an entry to the map at employees[0]. (This is because map::operator[] returns a reference, and if the entry does not exist, it creates one).

So now, employees.size() equals 4. Calling employees[1],[2] does not alter the map, but because the size is 4, you are also accessing employees[3], which in turn adds an entry to the map (and so on for employees[4]).
This stops when you reach employees[5], because it exists in the map and the map does not grow anymore.

If you want to iterate through the map entries, use an iterator.

map<int, employee>::iterator it;
for (it = employees.begin(); it != employees.end(); ++it)
{
   ee = it->second;
   cout<< ee.nname << endl;
}

PS- Please, make your code readable.

---

OK, let's try this with a more controlled example:

#include <iostream>
#include <map>
#include <string>
using namespace std;

int main()
{
        map<int,string> db;

        db[1] = string("index = 1");
        db[2] = string("index = 2");
        db[5] = string("index = 5");

        for (size_t i = 0; i < db.size(); i++)
        {
                cout << i << " : " << db[i] << endl;
                cout << "size is : " << db.size() << endl;
        }

        return 0;
}

Now, the problem here is that when you access the db[0], db[3] and db[4], you are actually adding elements into the map.

0 : 
size is : 4
1 : index = 1
size is : 4
2 : index = 2
size is : 4
3 : 
size is : 5
4 : 
size is : 6
5 : index = 5
size is : 6

You may also have another problem. Your class employee might have a broken default constructor, that isn't initializing the string attribute correctly.