Regarding vector::insert() and vector::size()

[katty]

Hello folks
M learning basics of vector.. i came across a doubt while writing this program

Code:

struct employee
{
  int id;
   int phone;
   
};

int main()
{

vector<employee> emp;
struct employee temp;
emp.resize(4);

for(i=0;i<4;i++)
{
temp.id =i+2;
temp.phone = i+20;
emp.insert(emp.begin()+i, temp);
}
cout<<"size="<<emp.size();  // my doubt lies here... why did size changed to 8 even though i made it as '4'
return 0;
}

And what I should do to restrict number of elements in vector
i.e if i declare size of vector is 'n' then the size should go beyond 'n'
Please guide me

[shash4evr]

when you call resize(N) method , it will create copies of objects (in your case strut) until reach the N elements.

therefore when you call size() subsequently , it will give you the size as N unless you insert elements beyond N.

if your requirement is to restrict the number of elements, then i recommend you to go for array implementation, since vector is there for to maintain variable length of elements.

like - employee* p_MyEmployees[NUM_EMP];

[charlie]

You have two good options here. You could set the size of the vector to 4, and then assign new values to each entry:

Code:

vector<employee> emp(4); // starts with 4 objects

...

// in the loop
emp[i] = temp;
// or
emp.at(i) = temp;

Or you could not set an initial size and just add elements to the vector. I would use push_back instead of insert for that:

Code:

vector<employee> emp; // starts empty

...

// in the loop
emp.push_back(temp);

I'd prefer the second version, because the first creates 4 objects and then ignores them.

[katty]

Thank You folks... now i understood how vector::insert() works