C++ 11添加了一些新的字符串转换函数:
http://en.cppreference.com/w/cpp/string/basic_string/stoul
它包括stoi(string to int),stol(string to long),stoll(string to long long),stoul(string to unsigned long),stoull(string to unsigned long long).值得注意的是它是一个stou(字符串到无符号)函数.有什么理由不需要它,但所有其他的都是吗?