Inserting string at end of linked list [closed] - c++

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I am inserting a string at the end of a linked list. When I compile my file I get 2 errors:
error: ‘setData’ was not declared in this scope
setData(*string_p);
error: ‘getNext’ was not declared in this scope
newNode = getNext();
However they are defined before I use them (defined in above methods) so I do not understand the error.
#include <iostream>
#include <string>
using std::string;
using std::cout;
using std::endl;
#define SUCCESS 0
#define FAIL 1
// Represents an entry object in the linked-list
class ListEntry
{
public:
explicit ListEntry();
explicit ListEntry(const char *string_p);
~ListEntry();
string getData();
void setData(const char* string_p);
void setData(string string);
ListEntry *getNext();
ListEntry *getPrevious();
ListEntry *prev_p; // pointer to previous entry in the linked-list
ListEntry *next_p; // pointer to next entry in the linked-list
private:
string data; // entry's string
};
// Represents the linked-list object
class List
{
public:
List();
~List();
bool printForward();
bool printReverse();
bool insert(const char *string_p);
private:
int entryCount; // number of entries present in the linked-list
ListEntry *head_p; // pointer to the first entry in the list
ListEntry *tail_p; // pointer to the last entry in the list
};
// ListEntry constructor
ListEntry::ListEntry()
{
this->prev_p = NULL;
this->next_p = NULL;
return;
}
// ListEntry constructor
ListEntry::ListEntry(const char *string_p)
{
this->data = string_p;
this->prev_p = NULL;
this->next_p = NULL;
return;
}
// List entry destructor
ListEntry::~ListEntry()
{
return;
}
// Return the stored string object
string ListEntry::getData()
{
return this->data;
}
// Set the internal string data from a char*
void ListEntry::setData(const char* string_p)
{
this->data = string_p;
}
// Set the internal string data from a string
void ListEntry::setData(string string)
{
this->data = string;
}
// Returns reference to the next entry in the list
ListEntry *ListEntry::getNext()
{
return this->next_p;
}
// Returns reference to the previous entry in the list
ListEntry *ListEntry::getPrevious()
{
return this->prev_p;
}
And my Insert function (which is below the above methods in my program):
bool List::insert(const char *string_p)
{
// Please write the list insert function
//new node to be inserted
ListEntry* newNode = new ListEntry();
//List *newList = new List();
if(newNode == NULL)
{
cout << "FAILED";
}
else
{
setData(*string_p); //////ERROR HERE
if(this->head_p = NULL)
{
newNode = getNext(); //////ERROR HERE
newNode = this->head_p;
this->head_p = newNode; // newNode now points to the head node
this->entryCount++;
return SUCCESS;
}
else
{
ListEntry* temp = this->head_p;
while(temp -> next_p != NULL)
{
temp = temp -> next_p;
}
temp -> next_p = newNode;
this->entryCount++;
return SUCCESS;
}
}
}

Answer 1

You have defined the functions but you are not using them the way you have defined:
setData(*string_p); // Takes a const char*, but you have provided a char.
// *string_p dereferences the string pointer, giving the
// first char.
newNode = getNext(); // getNext is a ListEntry function, but you are trying
// to use it in the context of List. This is also true of the
// above function.

Answer 2

Your insert() method is implemented all wrong. It should look more like this instead:
int List::insert(const char *string_p)
{
//new node to be inserted
ListEntry* newNode = new ListEntry(string_p);
if (newNode == NULL)
{
cout << "FAILED";
return FAIL;
}
if (this->head_p == NULL) {
this->head_p = newNode;
}
if (this->tail_p != NULL)
{
this->tail_p->next_p = newNode;
newNode->prev_p = this->tail_p;
}
this->tail_p = newNode;
this->entryCount++;
return SUCCESS;
}

Answer 3

The functions setData and getNext are non-static member functions of the class ListEntry. So they have to be called using a member access expression.
Moreover the supplied argument of this call
setData(*string_p);
has different type than the the function expects.
You have to write at least like
newNode->setFata( string_p );
and
newNode->getNext();
though this code snippet even if the call of the function will be correct from the syntax point of view does not make sense
if(this->head_p = NULL)
{
newNode = newNode->getNext();
newNode = this->head_p;
because there is at least a memory leak.
Also this if statement
if(newNode == NULL)
will make sense if you use the following call of the new operator
ListEntry* newNode = new ( std::nothrow ) ListEntry();
The function can look the following way
bool List::insert( const char *string_p )
{
//new node to be inserted
ListEntry *newNode = new ( std::nothrow ) ListEntry( string_p );
bool success = newNode != nullptr;
if ( success )
{
if ( tail_p )
{
tail_p->next_p = newNode;
newNode->prev_p = tail_p;
}
else
{
head_p = newNode;
}
tail_p = newNode;
entryCount++;
}
return success;
}