将变量值分配给动态 c 数组

Question

Hello I want to assing my count value to this 'ob' structs 'p_id' variable. How can I do that? I read other values from file but I need an id for selection and I use count for that. But I don't know how to assing it.

My.txt file;

0 0

0 1

1 1

FILE *fp;

struct ob{ 
   int x;
   int y;
   int p_id;
};
struct ob* ptr;
int count=0;


ptr = (struct ob*)malloc(sizeof(struct ob));
while(!feof(fp))
{
  ++count;
  fscanf (fp,"%d%d%d", &ptr->x, &ptr->y, &ptr->p_id=count); /* in here I want to assing count to p_id */
  printf("%d %d %d",ptr->x, ptr->y, ptr->p_id);
  
 }
  fclose (fp);
}

Answer 1

If you're simply looking to assign a sequence number to ptr->p_id , remove it from the fscanf call and assing the value after it:

 fscanf (fp,"%d%d", &ptr->x, &ptr->y);
 ptr->p_id=count;

If you want the value to be optional, you can move the assignment before the call and let fscanf overwrite it if it's present:

 ptr->p_id=count;
 fscanf (fp,"%d%d%d", &ptr->x, &ptr->y, &ptr->p_id);

The return value of fscanf allows you to see if the value was updated or not:

RETURN VALUE
       On success, these functions return the number of input items
       successfully matched and assigned; this can be fewer than provided
       for, or even zero, in the event of an early matching failure.