Assigning pointer - c++

Question

I have been working on this for a while and cannot seem to understand what is happening. I am trying to take the values in istr, put them in a linked list and sort them alphabetically. Eventually I will print them out. I am not sure where my problem is but I thought it was in the function InsertAfter. Is this not my problem and if so do you know what may be causing my linked list to not link? The last bit of code only outputs the headObj and not all of them, so I assumed that my list wasn't linking properly in nextNodePtr in each object but I am not sure. Thank you for your help!
void WordNode::InsertAfter(WordNode* nodeLoc) {
WordNode* tmpNext = 0;
tmpNext = this->nextNodePtr; // Remember next
this->nextNodePtr = nodeLoc; // this -- node -- ?
nodeLoc->nextNodePtr = tmpNext; // this -- node -- next
return;
}
wordNode.hpp
#ifndef wordNode_hpp
#define wordNode_hpp
#include <stdio.h>
#include <iostream>
#include <sstream>
#include <string>
using namespace std;
class WordNode {
public:
WordNode(string wordval = "", int count = 0, WordNode* nextLoc = 0);
void InsertAfter(WordNode* nodePtr);
WordNode* GetNext();
void PrWordNodeData();
string GetWord();
private:
string word;
WordNode* nextNodePtr;
int wordCount;
};
wordNode.cpp
#include "wordNode.hpp"
// Constructor
WordNode::WordNode(string wordval,int count, WordNode* nextLoc) {
this->word = wordval;
this->wordCount = count;
this->nextNodePtr = nextLoc;
return;
}
/* Insert node after this node.
* Before: this -- next
* After: this -- node -- next
*/
void WordNode::InsertAfter(WordNode* nodeLoc) {
WordNode* tmpNext = 0;
tmpNext = this->nextNodePtr; // Remember next
this->nextNodePtr = nodeLoc; // this -- node -- ?
nodeLoc->nextNodePtr = tmpNext; // this -- node -- next
return;
}
// Print dataVal
void WordNode::PrWordNodeData() {
cout << this->word <<": count=" <<this->wordCount << endl;
return;
}
// Grab location pointed by nextNodePtr
WordNode* WordNode::GetNext() {
return this->nextNodePtr;
}
//Returns word
string WordNode::GetWord()
{
return word;
}
main.cpp
#include <iostream>
#include <sstream>
#include <string>
#include "wordNode.hpp"
int main() {
WordNode* headObj = 0; // Create WordNode objects
WordNode* currObj = 0;
WordNode* nextObj = 0;
string istr ="555 999 777 333 111";
istringstream instring(istr);
string temp;
//Assigns first word to the head object
if (!instring.eof()){
instring >> temp;
headObj=new WordNode(temp,1);
}
currObj=headObj;
while (!instring.eof()){
instring >> temp;
nextObj=new WordNode(temp,1);
//swaps values if currObj is greater than the next word
if(currObj > nextObj) {
currObj->InsertAfter(nextObj);
}
currObj=nextObj;
}
// Print linked list
currObj = headObj;
while (currObj != 0) {
currObj->PrWordNodeData();
currObj = currObj->GetNext();
}
string i;
cin >> i;
return 0;
}

Answer 1

In the very first iteration of the loop (using the string you gave as example) you loose the reference to the head object and hence subsequent iterations will add nodes to a "headless list".
currObj=headObj;
while (!instring.eof()){
instring >> temp;
nextObj = new WordNode(temp,1);
//swaps values if currObj is greater than the next word
if(currObj->GetWord() > nextObj->GetWord()) {
currObj->InsertAfter(nextObj);
}
// And what happens if it is not greater?
currObj = nextObj; // Loose reference to head here if not greater
}
To fix your code you will either just have to add all nodes to the list and then sort it with a sorting algorithm or insert them on the fly as you intend to do now. However, to do the latter you will have to modify your insertion logic, i.e. insert node at the beginning (if new node is alphabetically lower than the first element) or at the end. I recommend reading this nice article about singly linked lists. It has examples and code for the insertions mentioned.