注意string的insert函数的几种形式

string (1)	string& insert (size_t pos, const string& str);
substring (2)	string& insert (size_t pos, const string& str, size_t subpos, size_t sublen);
c-string (3)	string& insert (size_t pos, const char* s);
buffer (4)	string& insert (size_t pos, const char* s, size_t n);
fill (5)	string& insert (size_t pos, size_t n, char c); void insert (iterator p, size_t n, char c);
single character (6)	iterator insert (iterator p, char c);
range (7)	template <class InputIterator> void insert (iterator p, InputIterator first, InputIterator last);

另外，C++11好像还增加一个initializer_list的初始化。