linked list from the text file by words - c++

Question

i wanted to read the text file by words and then apply each word for the linked list
but when i apply the whole content will goes to the first node of linked list
any idea what do i have to modify in the code
updated
i wander how can i iterate the word over the linked list i know i need another loop inside the while but i do not how do to it
it is build with C++
the file is working it showing by words but what i do not understand is how to take the words to be linked to each other
code:
#include <bits/stdc++.h>
#include <iostream>
#include<string>
using namespace std;
class LinkedList{
// Struct inside the class LinkedList
// This is one node which is not needed by the caller. It is just
// for internal work.
struct Node {
string x;
Node *next;
};
// public member
public:
// constructor
LinkedList(){
head = NULL; // set head to NULL
}
// destructor
~LinkedList(){
Node *next = head;
while(next) { // iterate over all elements
Node *deleteMe = next;
next = next->next; // save pointer to the next element
delete deleteMe; // delete the current entry
}
}
// This prepends a new value at the beginning of the list
void addValue(string val){
Node *n = new Node(); // create new Node
n->x = val; // set value
n->next = head; // make the node point to the next node.
// If the list is empty, this is NULL, so the end of the list --> OK
head = n; // last but not least, make the head point at the new node.
}
// returns the first element in the list and deletes the Node.
// caution, no error-checking here!
string popValue(){
Node *n = head;
string ret = n->x;
head = head->next;
delete n;
return ret;
}
// private member
private:
Node *head; // this is the private member variable. It is just a pointer to the first Node
};
int main() { //linkedlist
LinkedList list;
//string usama="usama";
//list.addValue(usama);
//list.addValue("h");
//list.addValue("u");
//cout << list.popValue() << endl;
//cout << list.popValue() << endl;
//cout << list.popValue() << endl;
// because there is no error checking in popValue(), the following
// is undefined behavior. Probably the program will crash, because
// there are no more values in the list.
// cout << list.popValue() << endl;
//file
// filestream variable file
fstream file;
string word, t, q, filename;
// filename of the file
filename = "file.txt";
// opening file
file.open(filename.c_str());
// extracting words from the file
while (file >> word)
{
list.addValue(word);
cout<<list.popValue()<<endl;
// displaying content
//cout << word << endl;
}
return 0;
}
i know maybe something wrong with the while loop but i am stuck at it

Answer 1

You have several problems. The first is popValue() does not handle the case where head == nullptr. This will likely cause a segfault when you attempt string ret = n->x; You can add a check on head and initialize ret to avoid this issue (the empty ret will be used to terminate the iteration later)
string popValue(){
Node *n = head;
string ret {};
if (!head) /* validate head not nullptr */
return ret;
ret = n->x;
head = head->next;
delete n;
return ret;
}
Next, as addressed in the comment, you use 1 loop to addValue and popValue. That defeats the purpose of your list because every node you add is deleted when you popValue() leaving your list empty at the end of the loop. Use 2 loops, e.g.:
// extracting words from the file
while (file >> word)
list.addValue(word);
while ((t = list.popValue()).length())
cout << t << '\n';
(note: (t = list.popValue()).length() terminates the iteration when an empty-string is reached -- better to have popValue() return a node instead of string.
A short working example taking the filename to read as the first argument would be:
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
class LinkedList {
struct Node {
string x;
Node *next;
};
public:
LinkedList(){
head = NULL; // set head to NULL
}
~LinkedList(){
Node *next = head;
while(next) { // iterate over all elements
Node *deleteMe = next;
next = next->next; // save pointer to the next element
delete deleteMe; // delete the current entry
}
}
void addValue(string val){
Node *n = new Node(); // create new Node
n->x = val; // set value
n->next = head; // make the node point to the next node.
// If the list is empty, this is NULL, so the end of the list --> OK
head = n; // last but not least, make the head point at the new node.
}
string popValue(){
Node *n = head;
string ret {};
if (!head) /* validate head not nullptr */
return ret;
ret = n->x;
head = head->next;
delete n;
return ret;
}
private:
Node *head; // this is the private member variable. It is just a pointer to the first Node
};
int main (int argc, char **argv) { //linkedlist
LinkedList list;
// filestream variable file
fstream file;
string word, t, q, filename;
// opening file
if (argc < 2)
return 1;
file.open(argv[1]);
if (!file.is_open()) {
cerr << "file open failed.\n";
return 1;
}
// extracting words from the file
while (file >> word)
list.addValue(word);
while ((t = list.popValue()).length())
cout << t << '\n';
return 0;
}
Example Input File
$ cat dat/captnjack.txt
This is a tale
Of Captain Jack Sparrow
A Pirate So Brave
On the Seven Seas.
Example Use/Output
$ ./bin/llwords dat/captnjack.txt
Seas.
Seven
the
On
Brave
So
Pirate
A
Sparrow
Jack
Captain
Of
tale
a
is
This
Lastly see Why is “using namespace std;” considered bad practice? and Why should I not #include <bits/stdc++.h>?