What's gone wrong with the values in this struct?

Relatively new to C and will readily concede there are things I think I understand, but probably don’t appreciate all the nuances. This is a MWE extracted from a more involved program I wrote. It compiles and runs fine, but testing reveals that the value of ev->pin is initially correct, but is incorrect after an unrelated function call (look for ??? in the code) Looks like the memory is getting stomped on somehow, but I cannot figure out what is going on.

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

#define SCAN_EVENT_COUNT 5
#define PIN_ASSIGNMENTS {7, -1, 1, 13, 4}
#define EVENT_NAMES "first-second-third-fourth-fifth"

void init_scan_events();
int parse_string(char pInputString[],
                 char *Delimiter,
                 char *pToken[]);

struct scan_events
{
  char event_names[31];
  char *pEvent[SCAN_EVENT_COUNT];
  int pin[SCAN_EVENT_COUNT];
};

int main(void)
{
  init_scan_events();
  return (0);
}

/**
 * the following function from https://stackoverflow.com/a/2091906/633251
 * Note that `strtok` expects a `char * string` and `char * delimiter` as arguments.
 **/

int parse_string(char pInputString[],
                 char *Delimiter,
                 char *pToken[])
{
  int i = 0;
  pToken[i] = strtok(pInputString, Delimiter); // get first token
  i++;
  while ((pToken[i] = strtok(NULL, Delimiter)) != NULL) // get the rest of the tokens
  {
    i++;
  }
  return i;
}

void init_scan_events()
{
  char en[] = EVENT_NAMES;
  int en_size = strlen(en);
  int size = SCAN_EVENT_COUNT;
  int pin[] = PIN_ASSIGNMENTS;

  int token_count = 0;
  char *Delim = "-";
  int i;

  struct scan_events *ev = malloc(sizeof(struct scan_events));
  if (ev == NULL)
  {
    printf("Allocation failed\n");
  }

  for (int i = 0; i < en_size; i++) // copy EVENT_NAMES
  {
    ev->event_names[i] = en[i];
  }

  for (int i = 0; i < size; i++) // copy PIN_ASSIGNMENTS
  {
    ev->pin[i] = pin[i];
  }

  for (int i = 0; i < size; i++)
  {
    printf("% d ", ev->pin[i]); // ??? inspect pin values: correct!
  }
  printf("\n");

  token_count = parse_string(ev->event_names, Delim, ev->pEvent); // tokenize EVENT_NAMES

  for (int i = 0; i < size; i++)
  {
    printf("% d ", ev->pin[i]); // ??? check pin values: corrupted!
  }
  printf("\n");

  free(ev);
}

>Solution :

1. It’s a buffer overflow in parse_string() for the assignment pToken[5] = NULL. I suggest pass in SCAN_EVENT_COUNT and use that to limit i < 5.

2. ev->event_names may not be ‘\0’ terminated. Either run the loop to <= en_size or use strcpy().

3. sizeof EVENT_NAMES == 32 so char event_names[31] is not big enough.

4. If malloc fail you can’t use ev. It’s not unreasonable to exit(1) as you probably can’t do anything about it anyways.

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

#define DELIM "-"
#define SCAN_EVENT_COUNT 5
#define PIN_ASSIGNMENTS {7, -1, 1, 13, 4}
#define EVENT_NAMES "first-second-third-fourth-fifth"

void init_scan_events();
int parse_string(char pInputString[], const char *Delimiter, size_t n, char *pToken[]);

struct scan_events {
    char event_names[sizeof EVENT_NAMES];
    char *pEvent[SCAN_EVENT_COUNT];
    int pin[SCAN_EVENT_COUNT];
};

void init_scan_events() {
    int size = SCAN_EVENT_COUNT;
    int pin[] = PIN_ASSIGNMENTS;

    struct scan_events *ev = malloc(sizeof *ev);
    if (!ev) {
        printf("Allocation failed\n");
        exit(1);
    }

    strcpy(ev->event_names, EVENT_NAMES);

    for (int i = 0; i < size; i++) // copy PIN_ASSIGNMENTS
        ev->pin[i] = pin[i];

    for (int i = 0; i < size; i++)
        printf("% d ", ev->pin[i]); // ??? inspect pin values: correct!
    printf("\n");

    int token_count = parse_string(ev->event_names, DELIM, SCAN_EVENT_COUNT, ev->pEvent); // tokenize EVENT_NAMES
    for (int i = 0; i < size; i++)
        printf("% d ", ev->pin[i]); // ??? check pin values: corrupted!
    printf("\n");
    free(ev);
}

int parse_string(char pInputString[], const char *Delimiter, size_t n, char *pToken[]) {
    int i = 0;
    for(; i < n; i++) {
        pToken[i] = strtok(i ? NULL : pInputString, Delimiter); // get first token
        if(!pToken[i]) break;
    }
    return i;
}

int main(void) {
    init_scan_events();
}

and example run:

 7 -1  1  13  4 
 7 -1  1  13  4