C string splitting (explode)

explode.c

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

// return structure
struct str_explode_out {
  size_t count;
  char *strings[];
};

// destroys the input string and saves the pointer to the places that were not
// touched by the divider
struct str_explode_out *str_explode(char input[], const char divider[]) {
  // could check here if the input and divider are not null or something
  char *divtmp = strstr(input, divider);
  size_t lendiv = strlen(divider);
  size_t alloc = 8;
  // allocate memory only "once"
  struct str_explode_out *out =
      malloc(sizeof(struct str_explode_out) + sizeof(char *) * alloc);
  if (out == NULL) {
    fprintf(stderr, "out of memory on line %i", __LINE__);
    return NULL;
  }
  out->count = 0;
  // count holds the number of times the string has been split
  out->strings[0] = input;
  // strings holds the pointer to the split places
  out->count++;
  // while there are still occurences of divider on the input string
  while (divtmp != NULL) {
  	// set the places that had divider to 0, null terminating the string that was before it
    memset(divtmp, '\0', lendiv);
    // save the current location of the occurence of divider
    out->strings[out->count++] = divtmp + lendiv;
    // search for the next location of divider on what's left of the input
    divtmp = strstr(divtmp + lendiv, divider);
    // if the array is full and it's not the last element
    if (out->count == alloc && divtmp != NULL) {
      // save the pointer to the struct, so we don't leak memory in case of realloc failing
      struct str_explode_out *tmp = out;
      alloc *= 2;
      //allocate more memory for the array
      out =
          realloc(out, sizeof(struct str_explode_out) + sizeof(char *) * alloc);
      // if realloc failed
      if (out == NULL) {
        fprintf(stderr, "out of memory at line %d, returning half processed "
                        "data, good luck",
                __LINE__);
        return tmp;
      }
    }
  }
  return out;
}

int main() {
  char test_base[] = "Example, string, number, uno";
  struct str_explode_out *output_split = str_explode(test_base, ", ");
  for (int i = 0; i < output_split->count; i++) {
    printf("%s\n", output_split->strings[i]);
  }
  return 0;
}