LinkedList data retrieval

[Jimbot]

Hello,

I have been having a go at making a linked list. I seem to be able to add entries to the list ok but when I try to traverse the list and print its contents I get repeated data.

Here is my code:

#include <stdio.h>
#include <stdlib.h>

struct Entry
{
    char *FirstName;
    Entry *NextEntry;
};

Entry *AddEntry(Entry *ptrHead, char *FirstName);
void DisplayEntries(Entry *StartOfList);

int main()
{
	char TempString[80];
	int i;
	Entry *ptrHead = NULL;

	for (i = 0; i < 3; i++)
	{
  		printf ("Enter name: ");
  		scanf ("%s", TempString);
	
		ptrHead = AddEntry(ptrHead, TempString);
		printf("%s was added to the list at address %p with the next address at %p\n", ptrHead->FirstName, ptrHead, ptrHead->NextEntry);
	}

	DisplayEntries(ptrHead);
  	return 0;
}

Entry *AddEntry(Entry *ptrHead, char *FirstName) 
{
    Entry *NewEntry;
    
    NewEntry = new Entry;
	
    NewEntry->FirstName = FirstName;
	if(ptrHead == NULL)
	{
		//printf("First item\n");
		NewEntry->NextEntry = NULL;
	}
	else
	{
		//printf("Later item\n");
    	        NewEntry->NextEntry = ptrHead;
		//printf("Next entry has the address %p\n", ptrHead);
	}	
	ptrHead = NewEntry;

	return ptrHead;	
}

void DisplayEntries(Entry *StartOfList)
{
	Entry *TempEntry;
	int i;

	TempEntry = StartOfList;
	for(i = 0; i < 3; i++)
  	{
		if (TempEntry == NULL)
		{
			printf("End of list!\n");
		}
		else
		{
        	printf("%s is at address= %p\n", TempEntry->FirstName, TempEntry);
		TempEntry = TempEntry->NextEntry;
		}
	}
	
}

And here is my programs output:

Enter name: A
A was added to the list at address 0x804a008 with the next address at (nil)
Enter name: B
B was added to the list at address 0x804a018 with the next address at 0x804a008
Enter name: C
C was added to the list at address 0x804a028 with the next address at 0x804a018

C is at address= 0x804a028
C is at address= 0x804a018
C is at address= 0x804a008

I notice that the addresses are correct showing it is working through the list, but why is the name always the same?

Thanks for any guidance!

Jimbot

[D80DSL3A]

The problem arises from your use of a charater pointer.
In addEntry() you assign the address of TempString (which was passed from main) to all 3 nodes. The last value stored there was 'C' - so that's what is there.

Use a std::string, or at least a character array to make a copy of what is in TempString for each Entry.

You could stick with the char* if you use it to allocate memory for an array to copy TempStrings contents to.

You will also want to add a deleteList() so you can free the dynamically allocated memory for the 3 Entrys. Your program currently has a memory leak because you have calls to new but no calls to delete.

[Jimbot]

Thankyou fun2code - that was very helpful.

I will look into the delete handling as well.