read_json.c

char *read_file(const char *path) {
  FILE *fp;
  char *data = NULL;
  if ((fp = fopen(path, "rb")) == NULL) {
  } else if (fseek(fp, 0, SEEK_END) != 0) {
    fclose(fp);
  } else {
    size_t size = ftell(fp);
    data = (char *) malloc(size + 1);
    if (data != NULL) {
      fseek(fp, 0, SEEK_SET); /* Some platforms might not have rewind(), Oo */
      if (fread(data, 1, size, fp) != size) {
        free(data);
        return NULL;
      }
      data[size] = '\0';
    }
    fclose(fp);
  }
  return data;
}

struct config { a, b int; };

char read_json(struct config *c) {
  double dv;
  char *buf = read_file("state.json");
  int len = buf == NULL ? 0 : strlen(buf);
  if (mjson_get_number(buf, len, "$.a", &dv)) c->a = dv;
  if (mjson_get_number(buf, len, "$.b", &dv)) c->b = dv;
  free(buf);
}