如何正确打印带有人名的链表？

Question

I did a code in which I want to print a simple linked list, and the information of the list contain name of person and number phone. Unfortunately, when I print my list have only the name of the last person which I read but the phone numbers were different. I have no idea why my code didn't work.

So, here is my code

#pragma once

struct Nodd{
   int phone;
   char *name;
   Nodd *next;
};

void InsertList(Nodd *&L,int nr,char *n);
void PrintList(Nodd *&L);


#include <iostream>
#include "Header.h"
using namespace std;
void InsertList(Nodd *&L,int nr, char *n){
    Nodd *p = new Nodd;
    p->name = n;
    p->phone = nr;
    p->next = L;
    L = p;
}

void PrintList(Nodd *&L){
     Nodd *p = L;
     while(p){
       cout << p->name << " " << p-> phone << endl;
       p = p->next;
     }
}

#include <iostream>
#include "Header.h"
using namespace std;

int main(){

    Nodd *L = 0; //L = first element of the linked list
    int nr, i, t;
    char *n;
    n = new char;

    cout <<"Read number of people: ";
    cin >> t;

    for(i = 0; i < t; i++){
        cout << "Name: ";
        cin.ignore(50, '\n');
        cin.getline(n, 50);

        cout << "Phone number: ";
        cin >> nr;
        InsertList(L, nr, n);
    }

    PrintList(L);

    return 0;
}

And what I compiled was:

Read number of people: 2

Name: Elena
Phone number: 99776244

Name: Andreea 
Phone number: 98776489

............................

Andreea  98776489
Andreea  99776244

Can you help me how to fix my code?

Answer 1

You have many errors in your code:

char *n;
n = new char; // A single dynamic character

And later:

cin.getline(n, 50); UB here

as you can see assigning 50 character to a single character variable so it is an undefined behavior.

To correct it:

char* n = new char[50];

• If you pay deep look to your output what you see:

  Andreea 98776489 Andreea 99776244

The same name but the integer values are correct! So your inserting nodes function is correct but the problem is about name. Why?

In insert node you write:

p->name=n; // That is not the way you should do it.

Correct it to:

  p->name = new char[strlen(n) + 1];
  strcpy(p->name, n);

You have to allocate memory for the member name for each node not sharing the same one.

• Also when you're done with dynamic memory you must free up and clean to avoid memory leak:

   delete[] n;

• Add a function to free up memory of all nodes for the member name:

   void FreeupMemory(Nodd*& L){ Nodd* pTmp = L; while(pTmp){ delete[] pTmp->name; pTmp = pTmp->next; } }

And in main after printing the nodes data free up memory:

      FreeupMemory(L);

• What I recommend: As long as C++ offers you many powerful classes and utilities give up using dynamic arrays so here you can use class string , vector . It is really good and don't mind about memory leak.

• Believe me if your member data name was a string class object you wouldn't get stuck in such error-prone.

   struct Nodd{ int phone; std::string name; Nodd *next; }; void InsertList(Nodd *&L,int nr, std::string n){ // your code p->name = n; // ok // ... }

In main:

    std::string n;
    for(int i(0); i < t; i++){
        std::getline(std::cin, n);
    }

** Also there a bad thing:

Why you include the header in itself? "recursive inclusion"?

You can create a header file "header.h" contains only class interface and functions' prototypes and another source file "MyLinkedList.cpp" that includes the header. And main.cpp.

// header.h
#pragma once

struct Nodd{
   int phone;
   char *name;
   Nodd *next;
};

void InsertList(Nodd *&L,int nr,char *n);
void PrintList(Nodd *&L);
void FreeupMemory(Nodd*&L);


// MyLinkedList.cpp

#include "header.h"
#include <iostream>
using namespace std;


void InsertList(Nodd*& L, int nr, char* n){
    Nodd *p  = new Nodd;
    p->name  = n;
    p->phone = nr;
    p->next  = L;
    L = p;
}

void PrintList(Nodd *&L){
    Nodd* p = L;
    while(p){
        cout << p-> name << " " << p->phone << endl;
        p = p->next;
    }
}

void FreeupMemory(Nodd*& L){
    Nodd* pTmp = L;
    while(pTmp){
        delete[] pTmp->name;
            pTmp = pTmp->next;
    }
}

// main.cpp

#include <iostream>
#include "Header.h"
using namespace std;

int main(){
    Nodd* L = 0; //L = first element of the linked list
    int nr, i, t;
    char* n = new char[50];

    cout << "Read number of people: ";
    cin >> t;

    for(int i = 0; i < t; i++){
        cout << "Name: ";
        cin.ignore(1, '\n');
        cin.getline(n, 50);

        cout << "Phone number: ";
        cin >> nr;

        InsertList(L, nr ,n);
    }

    PrintList(L);
    FreeupMemory(L);
    delete[] n;

    return 0;
}

• One last thing a good linked list defines functions for adding and deleting nodes as member methods and there should be destructor to free up memory.