Append Struct object into LinkedList

I’m trying to append a struct object to a linked list. The data is read from stdin. The int attribute gets appended correctly, but all char * values previously appended keep getting replaced by the new input.

My append and getElement functions work properly for string inputs.

Here is my code:

#include "List.h"
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

typedef struct EventObj{
    char *name;
    int time;
} EventObj;
typedef EventObj* EventPtr;

void add(ListPtr a, EventObj *event);
void printTime(ListPtr a);

int main(int argc, char **argv) {
  ListPtr a1 = newList(0, NULL, NULL);
    
  char func[10], agenda[256], eventName[256], buffer[256];
  int time;

  printf("%s\n", "Begin reading inputs and appending events");
  while(fgets(buffer, 256, stdin) != NULL){
    sscanf(buffer, "%s %s %s %d", func, agenda, eventName, &time);
    EventPtr event = malloc(sizeof(*event));
    event->time = time;
    event->name = eventName;

    printf("%d ", event->time);
    printf("%s\n", event->name);
    appendList(a1, event);
  }

  printf("%s\n", "Print from the list after appending");
  printTime(a1);
  }
  


void printTime(ListPtr a){
  for (int i=0; i <length(a); i  ){
    EventPtr cur = getElement(a, i);
    printf("%d ", cur->time);
    printf("%s\n", cur->name);
  }
}

Output:


Begin reading inputs and appending events
9 event1
10 event2
12 event3
8 event4
Print from the list after appending
9 event4
10 event4
12 event4
8 event4
// this should be event1 event2 event3 event4

Append function:

bool appendList( ListPtr L, void *data ){
  if(L == NULL){
    printf("%s", "appendList: NULL List");
    return false;
  }
    NodePtr node = newNode(data);
    if(node == NULL){
    printf("%s", "appendList: NULL Node");
    return false;
  }
  node-> next = L -> head;
  L -> head = node;
  L ->length   ;
  return true;
}

getElement:

void *getElement( ListPtr L, int i){
  if(L == NULL || i > L->length){
    printf("%s", "delElement: No entry or List found\n");
    return NULL;
  }
  NodePtr tmp = L-> head;
  i = L->length - i - 1;
  while(tmp != NULL && i > 0){
    tmp = tmp -> next;
    i --;
  }
  return tmp -> data;
}

CodePudding user response：

After this statement

event->name = eventName;

in the while loop

while(fgets(buffer, 256, stdin) != NULL){

the pointer name points to the same array eventName. So the last string that was stored in the array eventName is shown for all nodes because all nodes point to this array.

You need dynamically to allocate memory for a character array in each node and copy the string stored in the array eventName in this dynamically allocated array.