C Linked List Head Pointer is changing data value [closed] - c

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I am writing a custom shell for class. I have the shell working but now I need to keep track of which commands are called by the user in a linked list, and then be able to print out these commands in a similar fashion to the history() command. The program seems to build the linked list fine however upon printing out with history(list) I begin to see errors. After several commands are entered the command and string data values for the nodes begin to change. I have checked to make sure that the addresses the pointers are pointing to stay the same, but somehow the data values are being effected.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
struct Node{
char* command;
char* string;
struct Node *next;
};
struct List{
struct Node* front;
struct Node* rear;
};
void shell_loop(void);
char *read_input(void);
char **split_input(char *input);
struct Node* createNode(char* command, char* string);
struct List* createList();
struct List* add_to_end(struct List *Q, char* command, char* string);
void history(struct List* Q);
const int TOKEN_BUFSIZE = 64;
const char* DELIMITER = " \t\r\n\a";
//#define EXIT_FAILURE
int main(int argc, char **argv)
{
shell_loop();
}
void shell_loop(void)
{
char *input;
char **arguments;
char* command;
char* string;
struct List* list = createList();
for(int i =0; i < 20; i++)
{
printf("User> ");
input = read_input();
arguments = split_input(input);
command = arguments[0];
string = arguments[1];
list = add_to_end(list, command, string);
printf("\n");
history(list);
printf("\n");
free(input);
free(arguments);
}
}
char *read_input(void)
{
char* input;
size_t bufsize = 1000;
getline(&input, &bufsize, stdin);
return input;
}
char **split_input(char *input)
{
int size_of_buffer = TOKEN_BUFSIZE, position = 0;
char **tokens = malloc(size_of_buffer * sizeof(char*));
char *token;
if(!tokens)
{
fprintf(stderr, "shell: allocation error\n");
exit(1); // fix later
}
token = strtok(input, DELIMITER);
while (token != NULL)
{
tokens[position] = token;
position ++;
if(position >= size_of_buffer)
{
size_of_buffer += TOKEN_BUFSIZE;
tokens = realloc(tokens, size_of_buffer * sizeof(char*));
if(!tokens)
{
fprintf(stderr, "shell: allocation error \n");
exit(EXIT_FAILURE); // fix later
}
}
token = strtok(NULL, DELIMITER);
}
tokens[position] = NULL;
return tokens;
}
struct Node* createNode(char* c, char* s)
{
struct Node* temp = (struct Node*)malloc(sizeof(struct Node));
temp->command = c;
temp->string = s;
temp->next = NULL;
return temp;
}
struct List* createList()
{
struct List* Q = (struct List*)malloc(sizeof(struct List));
Q->front = NULL;
Q->rear = NULL;
return Q;
}
struct List* add_to_end(struct List *Q, char* c, char* s)
{
struct Node* temp = createNode(c, s);
if(Q->front == NULL)
{
Q->front = temp;
Q->rear = temp;
temp = NULL;
return Q;
}
Q->rear->next = temp;
Q->rear = temp;
temp = NULL;
return Q;
}
void history(struct List* Q)
{
struct Node* current;
if (Q->front == NULL)
{
printf("Command List is empty!\n");
return;
}
current = Q->front;
while(current !=NULL)
{
printf("Command: %s\nString: %s\n", current->command, current->string);
current = current->next;
}
}
I have attached an output file of the history command to highlight how the first entered command eventually changes:

Answer 1

you are just shuffling pointer to stack data around, you need to copy the actual strings
command = strdup(arguments[0]);
string = strdup(arguments[1]);

Answer 2

I think you want temp->string = strdup(s) in createNode(...) instead of temp->string = s

Answer 3

Your call to getline is wrong.
If *lineptr is set to NULL and *n is set 0 before the call, then
getline() will allocate a buffer for storing the line. This buffer
should be freed by the user program. ... Alternatively, before calling getline(), *lineptr can contain a
pointer to a malloc(3)-allocated buffer *n bytes in size
Since *n is 1000 and input is uninitialized (points nowhere), getline assumes there is a buffer of 1000 chars available...which isn't.
Your call should be:
char *read_input(void)
{
char* input= 0;
size_t bufsize = 0;
getline(&input, &bufsize, stdin);
return input;
}
See the comments and other solutions for the other problems of your program.