Cannot access memory at address in C - c

Question

I've got a linked list of nodes that contain a string of characters. The program reads characters from stdin until it reaches a new line and once it has it puts this string of characters into the a new node of the list.
I've done some debugging of the different steps involved in the program and can see the list of nodes being created correctly.
However, the printf statement doesn't seem to do anything if I'm stepping through the code. If I don't step through and just run the code through I get:
Cannot access memory at address 0x2e666564
Cannot access memory at address 0x2e666564
Cannot access memory at address 0x2e666564
My source code is:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct Node {
char *string;
struct Node *next;
} List;
List *addNode(List *currentList, char *character)
{
List *tempList = calloc(1, sizeof(List));
tempList->string = strdup(character);
tempList->next = currentList;
return tempList;
}
void printList(List *currentList)
{
while (currentList != NULL)
{
printf("%s", currentList->string);
currentList = currentList->next;
}
}
int main ()
{
char currentCharacter;
char *currentString;
List *mainList = NULL;
do
{
currentCharacter = getchar();
if (currentCharacter == '\n')
{
mainList = addNode(mainList, currentString);
currentString[0] = '\0';
} else {
strcat(currentString, &currentCharacter);
}
} while (currentCharacter != '.');
mainList = addNode(mainList, currentString);
printList(mainList);
return 0;
}

Answer 1

You're calling strcat on an invalid pointer.
Something like this would work:
char currentString[128];
currentString[0] = '\0';
currentCharacter isn't null-terminated and so strcat won't work. Use strncat instead.

Answer 2

Several problems here.
The main problem is that you have not allocated space for your currentString. strcat requires that there be space in the destination array (currentString).
Also problematic: when the user enters '\n', you haven't null terminated the string you are appending, so strdup will not quite work.

Answer 3

Your main function never initializes currentString to point to allocated memory, so your call to strcat just starts adding characters to whatever '\0'-terminated string currentString happens to be pointing to.

Answer 4

You don't need strcat. You do need to assign currentString at some point. Replace:
#define BUFFER_SIZE 128
/*
shouldn't need more than 128 characters for a line of console
but you can expand it later if you want
*/
int main() {
List *mainList = NULL;
char *buffer = malloc(sizeof(char)*BUFFER_SIZE);
int currentIndex = 0;
char currentCharacter;
do {
currentCharacter = getChar();
if (currentCharacter == '\n' || currentIndex == (BUFFER_SIZE-1))
buffer[currentIndex] = 0; //the null byte needs to be added before strdup is called
mainList = addNode(mainList, buffer);
currentIndex = 0;
} else {
buffer[currentIndex++] = currentCharacter;
}
} while (currentCharacter != '.');
mainList = addNode(mainList, buffer);
return 0;
}