This is tmp code

str_tmp.cpp

void String::swap(String & rhs)
{
	char * tmp_str = str_;
	int tmp_size = size_,
  		tmp_cap = capacity_ ;

	str_ = rhs.str_;
	size_ = rhs.size_;
	capacity_ = rhs.capacity_;

	rhs.str_ = tmp_str;
	rhs.size_ = tmp_size;
	rhs.capacity_ = tmp_cap;
}

void swap(String & lhs, String & rhs)
{
	lhs.swap(rhs);
}