Linked List Operations C++ - c++

Question

I've got a linked list data base using templates which compiles fine and lets me print out a list of all states and lets me search for a person and print all that persons data (since these methods work, I left them out below to save space).
Below I have a print_people_in_state method, what I need to be able to do is to (given a user input of state) print out the info on all the people from that particular state. However right now when I run it, nothing happens. How can I fix this?
If you want to run the code yourself here is a link to the file that I named data.txt (http://rabbit.eng.miami.edu/class/een118/labs/152/dbfile1.txt)
#include <iostream>
#include <string>
#include <string.h>
#include <fstream>
using namespace std;
struct person
{
int dob,ss_number;
string fname, lname,state;
person()
{ }
person(int a, int b, string c, string d, string e)
{dob=a; ss_number=b; fname=c; lname=d; state=e;}
};
struct state
{
string sname;
person*P;
state()
{}
state(string a)
{sname=a;}
};
template<typename T>struct Link
{
T*data;
Link*extradata;
Link*next;
Link()
{}
Link(T*a,Link<T>*C=NULL)
{
data=a;
next=C;
}
};
template<typename T>
struct List
{int length;
Link<T>*Head,*tail;
List(Link<T>*h=NULL, Link<T>*t=NULL)
{
Head=h;
tail=t;
length=0;
}
void add(T*object)
{
{ if (Head == NULL && tail == NULL)
{ Link<T> * newlink = new Link<T>(object);
Head = newlink;
tail = Head; }
else
{ Link<T> * newlink = new Link<T>(object);
tail->next = newlink;
tail=newlink;} }
}
void print_people_in_state(string search)
{
Link<state>*temp=Head;
if(temp!==NULL)
{
if(temp->data->P->state==search)
{
cout<<temp->data->P->fname<<endl;
}
// temp=temp->next;
}}
};
List<person>*person_from_file(string file)//reads file
{
List<person>* newlist=new List<person>();
// Link<T> * head=NULL;
// Link<T> * temp=NULL;
ifstream fin;
fin.open("data.txt");
if (fin.fail())
cout<<"file not found\n";
if (!fin.fail())
{
while(true)
{
int a,b;
string c,d,e;
fin>>a>>b>>c>>d>>e;
if (fin.fail())break;
person * p=new person(a,b,c,d,e);
newlist->add(p);
}
}
else
cout<<"Can't open file";
fin.close();
return newlist;
}
List<state>*state_from_file(string file)//reads file
{
List<state>* newlist=new List<state>();
// Link<T> * head=NULL;
// Link<T> * temp=NULL;
ifstream fin;
fin.open("data.txt");
if (fin.fail())
cout<<"file not found\n";
if (!fin.fail())
{
while(true)
{
int a,b;
string c,d,e;
fin>>a>>b>>c>>d>>e;
if (fin.fail())break;
state * s=new state(e);
newlist->add(s);
}
}
else
cout<<"Can't open file";
fin.close();
return newlist;
}
int main()
{List<person>*A = person_from_file("data.txt");
List<state> *B= state_from_file("data.txt");
B->print_people_in_state("TX");
return 0;
}

Answer 1

You can simplify Link and List. You can read the file once and fill both lists at the same time. In fact, you don't really need a separate list for states, its usage is confusing.
template<typename T>class Link
{
public:
Link(T *data) { Data = data; Next = NULL; }
T *Data;
Link<T> *Next;
};
template<typename T>struct List
{
int Count;
Link<T> *Head, *Tail;
List() { Head = NULL; Tail = NULL; Count = 0; }
Link<T>* AddData(T *data)
{
Link<T> *node = new Link<T>(data);
Count++;
if (Head == NULL)
{
Head = Tail = node;
}
else
{
Tail->Next = node;
Tail = node;
}
return node;
}
};
int main()
{
List<person> *list = new List<person>;
ifstream fin("data.txt");
while (fin)
{
int a, b;
string c, d, e;
fin >> a >> b >> c >> d >> e;
list->AddData(new person(a, b, c, d, e));
}
Link<person> *node = list->Head;
while (node)
{
if (node->Data->state == "TX")
cout << node->Data->fname << endl;
node = node->Next;
}
return 0;
}