C++ error could not convert from pointer to pointer

Question

I am asked to write a function that read from a file and input it's data in a doubly linked list . But every time I try to run the program , a compiling error is displayed with the following :

[Error] could not convert 'I1' from 'opening(World&)::Individual*' to 'Individual'
[Error] could not convert 'I2' from 'opening(World&)::Individual*' to 'Individual'

This is the content of the file :

FName1#LName1#Age1#male#University1,FName2#LName2#Age2#male#University2
FName1#LName1#Age1#male#University1,FName3#LName3#Age3#male#University3
FName7#LName7#Age7#female#University7,FName1#LName1#Age1#male#University1
FName7#LName7#Age7#female#University7,FName2#LName2#Age2#male#University2
FName6#LName6#Age6#female#University6,FName7#LName7#Age7#female#University7
FName4#LName4#Age4#male#University4,FName6#LName6#Age6#female#University6
FName4#LName4#Age4#male#University4,FName5#LName5#Age5#male#University5
FName5#LName5#Age5#male#University5,FName6#LName6#Age6#female#University6

That's my code :

#include <iostream>
#include <fstream>
#include <string.h>
#include <string.h>

using namespace std;

 struct Friend;
 struct World ;
 struct Individual;

struct Friend{
    Individual *self;
    Friend *next;
};

struct Individual{
    string FirstName,
    LastName,
    University;
    int Age;
    bool gender;
    Friend *myFriends;    // used as an adjacency list to enumerate all friends
    Individual *next;     // usedfor the doubly linked list denoted by World
    Individual *previous; // used for the doubly linked list denoted by World
};


struct World {
    Individual *Head, *Tail;
};
 World * InitializeList()
{
    return NULL;
}



void InsertInWorld(World & network, Individual I) {

    Individual* tmp = new Individual;
    if (tmp == NULL)
    {
        exit(1);
    }
    tmp->FirstName = I.FirstName;
    tmp->LastName = I.LastName;
    tmp->University = I.University;
    tmp->Age = I.Age;
    tmp->gender = I.gender;
    tmp->myFriends->next = NULL;
    tmp->myFriends->self = NULL;
    tmp->next = NULL;
    tmp->previous = NULL;

    if (network.Head == NULL || network.Tail==NULL) {
        network.Head = tmp;
        network.Tail = tmp;
        return;
    }
    else
    {
        tmp->next = network.Head;
        network.Head->previous = tmp;
        network.Head = tmp;
        return;
    }

}


void DisplayWorld(World network)
{
    Individual *cur = network.Head;
    
    while(cur!=NULL)
    {
        cout<<cur->FirstName<<" "<<cur->LastName<<endl;
        cur=cur->next;
    }
    
    cout<<endl;
}

void opening (World &network )
{
    struct Individual{
    string FirstName,
    LastName,
    University;
    string Age;
    string gender;
    Friend* myFriends;
    Individual* next;
    Individual* previous;
    
};

struct World {
    Individual *Head, *Tail;
};

    
    Individual *I1 ;
    Individual *I2 ;
    I1 = new Individual;
    I2 = new Individual;
    Individual *cur;
    
//  cur = network->Head;
    
    
    
 ifstream connections;
 connections.open("conn.txt");
  while (   getline(connections, I1->FirstName,'#')  && getline(connections, I1->LastName, '#')  && getline(connections, I1->University,'#')  && getline(connections,I1->Age,'#')  && getline(connections,I1->gender,',') && getline(connections, I2->FirstName,'#')  && getline(connections, I2->LastName, '#')  && getline(connections, I2->University,'#')  && getline(connections, I2->Age,'#')  && getline(connections, I2->gender,'\n')) 
    {
   
        
        InsertInWorld(network, I1);
        InsertInWorld(network, I2);
        
    }
    
    
    
}


    
    
    int main()
    {

        World network;
        Individual *I1=new Individual;
        network.Head=NULL;
        network.Tail=NULL;
        opening(network);
        DisplayWorld(network);
        
        return 0;
    }

If anyone can help me with this compiling error . Thank you.

Answer 1

You have this one:

void opening (World &network )
{
    struct Individual{
    string FirstName,
    LastName,
    University;
    string Age;
    string gender;
    Friend* myFriends;
    Individual* next;
    Individual* previous;
    
};

and this one:

struct Individual{
    string FirstName,
    LastName,
    University;
    int Age;
    bool gender;
    Friend *myFriends;    // used as an adjacency list to enumerate all friends
    Individual *next;     // usedfor the doubly linked list denoted by World
    Individual *previous; // used for the doubly linked list denoted by World
};

The error tells you that somewhere where the first Individual type is expected, instead of that a pointer to the second Individual type is given. So you have an issue with a pointer being passed instead of a structure and you also have an issue of mixing up two different types having the same name.

Answer 2

There are two similar structs called Individual. One is at file scope, and another is inside opening(). Since they are two different types, you cannot convert pointers to them implicitly (and when you are learning, it is almost a guarantee that you are doing something wrong).

However, as @IgorTandetnik points out in the comment, the error is not about that, notice:

could not convert ... from '...Individual*' to 'Individual'
                                         ^                ^

The second type is not a pointer, so you need to dereference it:

InsertInWorld(network, *I1);

Although what you likely want to do in that case is pass a reference:

void InsertInWorld(World & network, Individual & I) {

Possibly a const one, too.

There are other issues in the code, too. I suggest you post this in the code review stack exchange site.