Making a pool concept in c++

Question

I have a structure as

struct Employee 
{ 
 char   uName  [255]; 
 struct   Employee *  next; 
 struct   Employee *  prev; 
};

All i want to allocate memory of 100 stucture objects at a time and then use them one by one i making a linked list.If the memory is consumed fully then again i want to allocate 100 object memory

I am doing the allocation as

struct Employee * chunk=new struct Employee[100];

Now when i want to add a new node to a linked list i want to take objects from this already allocated memory.Can somebody tell how to achieve this

Employee * pEmployeeData=NULL;
for(long int i=1;i<=100;i++)
{
        pEmployeeData=EmployeePool+i;
        pEmployeeData->next=NULL;
        pEmployeeData->prev=NULL;
        InsertAtEnd(pEmployeeData);
}

where InsertAtEnd inserts the node at the end of the linked list.Please tell how to achieve this

Answer 1

I would strongly suggest that you don't try to reinvent the wheel by writing your own linked list, instead have a look at the C++ standard library which contains ready-made container types available for you to use. (for example std::vector and std::list).

Container types exist in the C++ standard library, and are used for storing collections of data/objects. for example, you could do something along the lines of

#include <iostream>
#include <vector>
#include <string>

struct Employee
{
    std::string name;
    int id;
};

int main()
{
    std::vector<Employee> my_employees;

    Employee fred = { "Fred", 1 };
    Employee bob = { "Bob", 2 };

    my_employees.push_back( fred );
    my_employees.push_back( bob );


    std::cout << my_employees[0].id << " " << my_employees[0].name << "\n"
              << my_employees[1].id << " " << my_employees[1].name << std::endl;
}

The standard containers are easy to use and to learn (You'll find plenty of internet resources which describe how to use them - and your book should also tell you!); If you're new to C++, then it's highly advisable to start out by figuring out how to use these before attempting to create your own.

Answer 2

You'd override the new and delete operators for your class.

new would have to look at any existing pools and see if there were any free objects, and if there weren't, it would then need to allocate a pool. Then, it would return memory allocated from it.

delete would need to check the pool that the provided object was allocated in. If ANY object is still allocated in it, the pool stays, otherwise, it can be deleted.

Also, since you're using C++, consider using a full blown class (though there is very little difference)