// This code is licensed under CC0.
  // A copy of the license can be obtained at https://creativecommons.org/publicdomain/zero/1.0/
  // May you forever catenate in peace.
  #define strncatm(dest, sz, ...) strncat_multi((dest), (sz), __VA_ARGS__, NULL);
  char* strncat_multi(char *dest, size_t dest_sz, ...) {
    va_list srcs;
    char *dest_end;
    const char *src;
    size_t src_sz;
    size_t dest_off;
    size_t copy_sz;
    va_start(srcs, dest_sz);
    for (dest_end = dest, dest_off = 0; *dest_end && dest_off < dest_sz; dest_end++, dest_sz++);
    for (src = va_arg(srcs, const char *); src && dest_off < dest_sz; src = va_arg(srcs, const char *)) {
      src_sz = strlen(src);
      copy_sz = src_sz < (dest_sz - dest_off) ? src_sz : (dest_sz - dest_off);
      memmove(dest_end, src, copy_sz);
      dest_end += copy_sz;
      dest_off += copy_sz;
      if (dest_off < dest_sz)
      {
        *dest_end = '\0';
      }
    }
    va_end(srcs);
    return dest_end;
  }