C++ :: Pointer-based Data Loading From A (text) File

I have two classes, productListType and buyerListType, that are each basically linked lists. To create the linked list for an object of productListType, I successfully wrote a non-class function createProductList to read the product data from a text file. The class definition for buyerListType has a data member productBoughtRecord that is of type productListType to aggregate the details of the products purchased by a particular buyer during transactions. I decided to make productBoughtRecord a pointer since the contents of this data member would wax and wane over the course of several transactions, depending on the amount and frequency of payments made by the buyer. I have provided a rough sketch of the class below:

class buyerListType
{
public:
setCustomerInfo( ....., productListType* p);
.
.
.
private:
productListType* productBoughtRecord;
.
.
};

I'm similarly trying to write a non-class function createBuyerList to load the record of customers from a text file. How do I determine what the value of the formal parameter p in member function setCustomerInfo is, in order to be able to set the data member productBoughtRecord? take into consideration that an object of class buyerListType would have multiple buyers with varying amounts of products purchased.