character strings being mutated somehow - c

Question

I am working on a a small program and it has a tiny logic error which I can't seem to trace. It tracks records input of this form:
time userID weight
It searches a linked list of all previous records to find the most recent one where the userID matches the current userID. It then compares the time and weight and calculates the rate of change in the weight. If the weight has changed abruptly it print "suspicious weight change". If there is not match and the input is valid it simply adds the new record to the list.
I have it working except when the userID is added to the list it seems to overwrite all the previous userID's. So even if a new record is input which has a unique userID, it finds a match, because all the ID's a made the same.
I just need a second pair of eyes to help spot where this is happening, I am new to C so it is probably some newbie mistake. But after 8 hrs of trying to find it, I am desperate for some help!
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
#define DELIM " " /* the delimiter */
#define MAX_CHANGE (10.0/86400.0) /* 10kg/day */
/* seconds in a day is 24 hours * 60 minutes * 60 seconds */
/* return 0 if the passed strings don't math, 1 otherwise */
/* defines the structure of Node */
struct Node
{
char * id;
float weight;
int time;
struct Node * next;
} *head, *p, *t, *last;
/* Constructor which returns a pointer to a new node*/
struct Node *newNode(int *time, char * id, float *w)
{
/*note malloc returns a pointer */
struct Node *r = (struct Node *)malloc( sizeof(struct Node) );
r->time = *time;
r->id = id;
r->weight = *w;
r->next = NULL;
return r;
}
/* prints the list starting with head */
printList(struct Node * head)
{
while(head != NULL)
{
printf("%d %s %f\n",head->time,head->id,head->weight);
head = head->next;
}
}
main()
{
char line[1024];
int lasttime = 0;
int success;
int timestamp;
int duration;
char userID[1000] = "";
char *token;
char temp[1000];
float weight;
float lastweight;
float change;
float changePerTime;
head = (struct Node*)malloc(sizeof(struct Node));
head->id = "";
head->weight = 0.0;
head->time = 0;
head->next = NULL;
last = head;
/*FILE * f = fopen("C:\\Users\\Chris\\Documents\\School\\York\\Computer Science\\2031 Software Tools\\Labs\\lab3\\testcases\\06.in","r"); */
/* last points to the last node in the list
head is always the same node
p is used to travers the list
t is a pointer the most recent occurrense of a user record
*/
while (fgets(line,1024,stdin) != NULL)
{
userID[0] ='\0'; // resets userID
token = strtok(line, DELIM);
success = sscanf(token,"%d",&timestamp);
if (success < 1 || timestamp == 0)
{
printf("Invalid time\n");
continue;
}
while((token = strtok(NULL,DELIM) ) != NULL && token[0] != '.' && ! isdigit(token[0]) )
{
strcpy(temp,token); //
strcat(temp,DELIM ); // adds space between each token
strcat(userID, temp); // src temp must be a const string, not a pointer
temp[0] = '\0';
}
userID[strlen(userID)-1] = '\0'; //erases the tailing space.
if(strlen(userID) > 179 || !strlen(userID) )
{
printf("Illegal userID\n");
continue;
}
else if(token == NULL || sscanf(token,"%f", &weight) < 1 || weight < 30.0 || weight > 300.0)
{
printf("Illegal weight\n");
continue;
}
else if (lasttime >= timestamp)
{
printf("Nonmonotonic timestamps\n");
continue;
}
else
{
/* sets t to last found user record and sets "last" to the last record*/
for(p = head; p != NULL; p = p->next)
{
if(strcmp(userID,p->id) == 0)
{
t=p;
}
last = p; // set last to last p.
}
if(t == NULL)
printf("OK newuser\n");
else if(t != NULL)
{
duration = timestamp - t->time;
change = weight - t->weight;
changePerTime = change / duration;
if(changePerTime < -MAX_CHANGE || changePerTime > MAX_CHANGE)
printf("Suspiciously large weight change\n");
else
printf("OK\n");
}
/* adds node to end of list */
last->next = newNode(&timestamp,userID,&weight);
printList(head);
}
}
//fclose(f);
}

Answer 1

I can fix the over-writing by changing newNode to:
struct Node *newNode(int *time, char * id, float *w)
{ /*note malloc returns a pointer */
struct Node *r = (struct Node *)malloc( sizeof(struct Node) );
r->time = *time;
r->id = strdup(id);
r->weight = *w;
r->next = NULL;
return r;
}
Note the addition of the call to strdup.