string:sub_string/2

截取字符串的一部分

用法：

sub_string(String, Start) -> SubString

内部实现：

-spec sub_string(String, Start) -> SubString when
      String :: string(),
      SubString :: string(),
      Start :: pos_integer().

sub_string(String, Start) -> substr(String, Start).

-spec sub_string(String, Start, Stop) -> SubString when
      String :: string(),
      SubString :: string(),
      Start :: pos_integer(),
      Stop :: pos_integer().

sub_string(String, Start, Stop) -> substr(String, Start, Stop - Start + 1).

截取从 Start 开始到字符串 String 末尾之间的子字符串

string:sub_string("abcdefg", 3)