Array of structure overwritten while reading from a file in C - c

Question

I am trying to build an array of structures with a string and starting address of a linked list of another structure. Several strings from each line of a file is to be filled into this data structure. But whenever I am coming back to the next line, all the variables of the array and LL that I have filled up so far is being changed to the variables in the current line. As a result all the elements of the array as well as the corresponding linked lists are giving the same result in each element of the array. Here is the code.
struct node
{
char* nodedata;
struct node* link;
};
struct motief
{
char* motiefname;
struct node* link;
};
void add_unique_nodes(struct motief*,int,char *);
int unique_motief(struct motief*,char*);
void add_unique_nodes(struct motief* motiefs,int motief_no,char * token)
{
struct node *temp,*r;
r = malloc(sizeof(struct node));
r->nodedata = token;
//for the first node
if(motiefs[motief_no].link == NULL)
{
motiefs[motief_no].link = r;
}
else
{
temp = motiefs[motief_no].link;
while(temp->link != NULL && token != temp->nodedata)
temp = temp->link;
if(token != temp->nodedata)
temp->link = r;
}
r->link = NULL;
}
void main()
{
struct motief motiefs[100];
FILE *fp, *ft;
fp = fopen("dump.txt","r");
ft = fopen("motief_nodes","w");
char line[100] ={0};
char seps[] = ",";
char* token;
int motief_no = 0;
int i,j;//loop variable
//read the database
while(!feof(fp))
{
if( fgets(line, sizeof(line), fp ))
{
if(motief_no == 1)
printf("for start of 2nd step %s\t",motiefs[0].motiefname);//????
printf("for line %d\t",motief_no);
//get the motief from each input line as a token
token = strtok (line, seps);
//store it in motief array
motiefs[motief_no].motiefname = token;
printf("%s\n",motiefs[motief_no].motiefname);
if(motief_no == 1)
printf("for zero %s\n",motiefs[0].motiefname);
motiefs[motief_no].link = NULL;
//get and store all the nodes
while (token != NULL)
{
//get the node
token = strtok (NULL, seps);
if(token != NULL)
add_unique_nodes(motiefs,motief_no,token);
}
if(motief_no == 0)
printf("for end of 1st step %s\n",motiefs[0].motiefname);
motief_no++;
if(motief_no == 2)//break at 2nd loop, at 1
break;
}
I am new to C programming. I cannot find why it is happening. Please help me to find where I am going wrong and why the file is read into the array besides the specified variable for that purpose in my code. Thanks in advance. Here are few lines from the file to be read.
000100110,1,95,89
000100111,1,95,87
000100110,1,95,74
000100110,1,95,51
I am displaying the structure with the following code
struct node* temp;
for(j=0;j<2;j++)
{
printf("turn %d\t",j);
printf("%s\t",motiefs[j].motiefname);
temp = motiefs[j].link;
printf("%s\t",temp->nodedata);
do
{
temp = temp->link;
printf("%s\t",temp->nodedata);
}while(temp->link != NULL);
printf("\n");
}
And the it shows the following overall result
for line 0 000100110
for end of 1st step 000100110
for start of 2nd step 000100111,1,95,87
for line 1 000100111
for zero 000100111
turn 0 000100111 1 95 87
turn 1 000100111 1 95 87

Answer 1

You keep changing the same memory space when you read into 'line'. you need to allocate new memory space each time you want a different array.
Picture 'line' as pointing to a specific chunk of 100 bytes in a row. You keep telling the fgets function to write to that location, and you also keep copying the address of that location into your structs when you assign the 'token' to moteifname.
Then when you change what's at that address of course it's overwriting what the struct points to as well!
You need to choose to allocate the space in each struct instead of having an internal pointer OR you need to dynamically allocate space each iteration using malloc and then free() all the pointers at the end.
https://www.codingunit.com/c-tutorial-the-functions-malloc-and-free