Function string_not_empty

example/bfs_simple.cc:37–40

DEFINE_bool(part_by_in,    false,  "partition by in-degree");

bool string_not_empty(const char*, const std::string& value) {
  if (0 == value.length()) { return false; }
  return true;
}

DEFINE_validator(input, &string_not_empty);